WO2014080010A1

WO2014080010A1 - Apparatus and method for printing on a substrate

Info

Publication number: WO2014080010A1
Application number: PCT/EP2013/074606
Authority: WO
Inventors: Gianfranco Pasqualin; Marco Galiazzo; Niccolò PATRON
Original assignee: Applied Materials Italia SRL
Current assignee: Applied Materials Italia SRL
Priority date: 2012-11-26
Filing date: 2013-11-25
Publication date: 2014-05-30
Anticipated expiration: 2015-05-26
Also published as: ITUD20120199A1

Abstract

An apparatus for screen printing on a substrate (250) is provided. The apparatus includes: a substrate support (131) configured to support the substrate (250) for screen printing; and a sensor assembly (400) configured to detect a force or pressure from which a printing force on the substrate (250) can be determined, wherein the sensor assembly (400) includes at least one first sensor (325) provided at the substrate support (131), and wherein the at least one sensor (325) is adapted to detect the force or pressure during printing operations.

Description

"APPARATUS AND METHOD FOR PRINTING ON A SUBSTRATE"

FIELD OF THE INVENTION

Embodiments of the present invention relate to an apparatus for printing on a substrate. Furthermore, embodiments of the present invention relate to a method for printing on a substrate.

BACKGROUND OF THE INVENTION

Solar cells are photovoltaic (PV) devices that convert sunlight directly into electrical power. Solar cells typically have one or more p-n junctions. Each p-n junction includes two different regions within a semiconductor material where one side is denoted as the p-type region and the other as the n-type region. When the p-n junction of a solar cell is exposed to sunlight, the sunlight is directly converted to electricity through the PV effect. Solar cells generate a specific amount of electric power and are made and disposed in solar modules sized to deliver the desired amount of system power. Solar modules are joined into panels with specific frames and connectors. Solar cells are commonly formed on silicon substrates, which may be single or multicrystalline silicon substrates. A typical solar cell includes a silicon wafer, substrate, or sheet typically less than about 0.3 mm thick with a thin layer of n-type silicon on top of a p-type region formed on the substrate.

Generally, a standard silicon solar cell is fabricated on a wafer which includes a p-type base region, an n-type emitter region, and a p-n junction region disposed therebetween. An n-type region, or n-type semiconductor, is formed by doping the semiconductor with certain types of elements (e.g. phosphorous (P), arsenic (As) or antimony (Sb)), in order to increase the number of negative charge carriers, i.e. electrons. Similarly, a p-type region, or p-type semiconductor, is formed by the addition of trivalent atoms to the crystal lattice, resulting in a missing electron from one of the four covalent bonds normal for the silicon lattice. Thus the dopant atom can accept an electron from a neighboring atom's covalent bond to complete the fourth bond. The dopant atom accepts an electron, causing the loss of half of one bond from the neighboring atom and resulting in the formation of a "hole".

When light falls on the solar cell, energy from the incident photons generates electron-hole pairs on both sides of the p-n junction region. Electrons diffuse across the p-n junction to a lower energy level, and holes diffuse in the opposite direction, creating a negative charge on the emitter and a corresponding positive charge builds up in the base. When an electrical circuit is made between the emitter and the base and the p-n junction is exposed to certain wavelengths of light, a current flows. The electrical current generated by the semiconductor when illuminated flows through contacts disposed on the frontside, i.e. the light- receiving side, and the backside of the solar cell. The top contact structure is generally configured as widely-spaced thin metal lines, or fingers, that supply current to larger busbars. The back contact is generally not constrained to be formed in multiple thin metal lines, since the back contact does not prevent incident light from striking solar cell. A solar cell is generally covered with a thin layer of dielectric material, such as Si₃N₄, to act as an antireflection coating, or ARC, to minimize light reflection from the top surface of solar cell.

One major component in making commercially viable the use of solar cells to make photovoltaic devices lies in reducing the manufacturing costs required to form the solar cells by improving the device yield and increasing the substrate throughput.

Screen printing has long been used in the electronics industry for printing electrical component designs, such as electrical contacts or interconnects, on the surface of a substrate. State of the art solar cell fabrication processes also use screen printing processes. In some applications, it is desirable to screen print contact lines, such as fingers, on the solar cell substrate. The fingers are in contact with the substrate and are able to form an Ohmic connection with one or more doped regions (e.g. n-type emitter region). An Ohmic contact is a region on a semiconductor device that has been prepared so that the current- voltage (I-V) curve of the device is linear and symmetric, i.e., there is no high-resistance interface between the doped silicon region of the semiconductor device and the metal contact. Low resistance, stable contacts are critical for the performance of the solar cell and reliability of the circuits formed in the solar cell fabrication process. For this reason it is best to set the printing parameters during the printing of a pattern on the substrate appropriately.

In particular, it has been found that print tracks obtained with conventional screen-printing processes generally may have not uniform geometries and there could be inaccuracies in the depositing of the material.

There is therefore a need to improve a printing apparatus and method to overcome at least one of the drawbacks of the prior art.

SUMMARY OF THE INVENTION

According to one embodiment, an apparatus for screen printing on a substrate is provided. The apparatus includes a substrate support configured to support the substrate for screen printing and a sensor assembly configured to detect a force or pressure from which a printing force on the substrate can be determined. Typically, an apparatus for screen printing having a printing tool can be utilized.

According to a further embodiment, an apparatus for screen printing on a substrate is provided. The apparatus includes a substrate support configured to support the substrate for screen printing and a sensor assembly configured to provide at least one signal from which a printing force on the substrate can be determined.

According to yet a further embodiment, an apparatus for screen printing on a substrate is provided. The apparatus includes a substrate support configured to support the substrate for screen printing, a control unit and a sensor assembly configured to provide at least one signal to the control unit from which a printing force on the substrate can be determined.

According to yet a further embodiment, an apparatus for screen printing on a substrate is provided. The apparatus includes a substrate support configured to support the substrate for screen printing and a sensor assembly including at least one sensor at the substrate support, configured to detect a printing force on the substrate.

According to an even further embodiment, an apparatus for screen printing on a substrate is provided. The apparatus includes a printing tool, a substrate support configured to support the substrate and a sensor assembly, wherein the sensor assembly includes at least one first sensor provided at the substrate support. For example, the at least one first sensor is arranged to detect a force or pressure from which a printing force on the substrate can be determined.

According to yet a further embodiment, an apparatus for screen printing on a substrate is provided. The apparatus includes a printing tool and a sensor assembly including at least one sensor at the printing tool, configured to provide at least one signal from which a printing force on the substrate can be determined.

According to yet a further embodiment, an apparatus for screen printing on a substrate is provided. The apparatus includes a printing tool, a control unit and a sensor assembly including at least one sensor at the printing tool, configured to provide at least one signal to the control unit from which a printing force on the substrate can be determined.

According to yet a further embodiment, an apparatus for screen printing on a substrate is provided. The apparatus includes a substrate support configured to support the substrate for screen printing, a printing tool and a sensor assembly including at least one sensor at the printing tool, configured to provide at least one signal from which a printing force on the substrate can be determined.

According to yet a further embodiment, an apparatus for screen printing on a substrate is provided. The apparatus includes a substrate support configured to support the substrate for screen printing, a printing tool, a control unit and a sensor assembly including at least one sensor at the printing tool, configured to provide at least one signal to the control unit from which a printing force on the substrate can be determined.

According to yet a further embodiment, a method for screen printing on a substrate is provided. The method includes vary a force of a printing tool of a printing apparatus, wherein the force is directed towards the substrate, to compensate for variations in the force of the printing apparatus on the substrate along a printing path.

According to yet a further embodiment, an apparatus for screen printing on a substrate is provided. The apparatus includes a printing tool, a substrate support configured to support the substrate, a control unit, and a computer program memorizable in a memory readable by a computer that contains the instructions which, when carried out by the control unit, determine the execution of embodiments of a method for printing on a substrate including vary a force of the printing tool, wherein the force is directed towards the substrate, to compensate for variations in the force of the printing apparatus on the substrate along a printing path.

BRIEF DESCRIPTION OF THE DRAWINGS So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments. The accompanying drawings relate to embodiments of the invention and are described in the following:

- Figure 1 is a schematic view of embodiments of an apparatus for printing on a substrate;

- Figure 2 is a schematic view of further embodiments of an apparatus for printing on a substrate;

- Figure 3 is a schematic view of still further embodiments of an apparatus for printing on a substrate;

- Figure 4 is a schematic view of further embodiments of an apparatus for printing on a substrate;

- Figure 5 is a schematic view of embodiments of a method for printing on a substrate;

- Figure 6 is a schematic view of further embodiments of a method for printing on a substrate;

- Figure 7 is a lateral schematic view of a printing apparatus for printing on a substrate;

- Figure 8 is a perspective view of a support structure for the substrate according to one embodiment;

- Figures 9A and 9B are a schematic representation of a printed substrate;

- Figure 10 is a schematic representation of a portion of an apparatus for printing on a substrate;

- Figure 11 is a graph showing the development of the reaction force of a printing mask due to the action of a printing tool as a function of the position;

- Figure 12 is a graph showing the development of the printing force applied by a printing tool on a printing mask as a function of the position;

- Figures 13, 14 and 15 are graphical representations of detections respectively of a reaction force of the printing mask, a printing force applied by a printing tool on the printing mask and a force acting on a substrate being printed;

- Figure 16 is an isometric schematic view of a system that can be used in connection with some embodiments of a method for printing on a substrate; - Figure 17 is a top plan schematic view of the system in Figure 16 according to one embodiment of the invention;

- Figure 18 is an isometric schematic view of another system that can be used in connection with some embodiments described herein;

- Figure 19 is a top plan schematic view of the system in Figure 18 according to one embodiment of the invention;

- Figure 20 is an isometric schematic view of another system that can be used in connection with some embodiments described herein;

- Figure 21 is a top plan schematic view of the system in Figure 20 according to one embodiment of the invention;

- Figure 22 is an isometric view of a portion of a substrate support of the screen printing system according to one embodiment described herein;

- Figure 23 is an isometric schematic view of one embodiment of a rotary actuator unit having an inspection unit positioned to inspect the front surface of the substrate.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the various embodiments of the invention, one or more examples of which are illustrated in the figures. Within the following description of the drawings, the same reference numbers refer to the same components. Generally, only the differences with respect to individual embodiments are described. Each example is provided by way of explanation of the invention and is not meant as a limitation of the invention. For example, features illustrated or described as part of one embodiment can be used on or in conjunction with other embodiments to yield yet a further embodiment. It is intended that the present invention includes such modifications and variations.

Embodiments described herein refer to a method and an apparatus for printing on a substrate, particularly for screen printing on a substrate.

It is noted here that a substrate as used within the embodiments described herein can be at least one element selected from the group consisting of: a conductive material, a conductive material with a silicon or alumina base, a plate, a wafer, a foil, a semiconductor wafer, a solar cell wafer, a Si solar cell wafer, a green-tape circuit board, and similar articles, particularly used to form photovoltaic cells or green-tape type circuits. For example, solar cell wafers or green-tape circuit boards can be provided as a substrate. Therefore, some embodiments described herein can be used for example to produce photovoltaic cells or green-tape type circuits.

Embodiments described herein provide a screen printing system, or system 110, and methods of operating thereof, for example, to achieve the metal contacts according to a desired pattern on a surface 251 of a substrate 250, e.g. of a solar cell.

Embodiments described herein, which can be combined with further embodiments described herein, may provide an apparatus 300 for screen printing on a substrate 250 as described for example with reference to Figures 1 to 4.

The apparatus 300 may include at least one printing tool 311, e.g. a squeegee 311.

Furthermore, the apparatus 300 may include a substrate support 131, e.g. a printing nest 131, configured to support a substrate 250 for screen printing.

Moreover, the apparatus 300 may include a sensor assembly 400 configured to detect at least a printing force on the substrate 250. According to different implementations of the embodiments described herein, the printing force on the substrate can be detected by one or more a load cells, one or more pressure sensors or one or more other sensors, which utilizes a strain gauge, a piezoelectric element, a piezoresistive element, a Hall-effect element, or the like. Thereby, it has to be considered that a pressure is the force exerted per unit area, such that depending on whether the one or more sensors is provided as a pressure sensor or as a force sensor or load cell, a conversion might need to be considered. It is to be understood that depending on the specific arrangement of the sensor assembly, the sensor assembly can also include at least one pressure sensor and at least one force sensor, e.g. load cell.

According to yet further embodiments, which can be combined with other embodiments described herein, the sensor assembly includes at least one sensor, such as a pressure sensor or force sensor, e.g. load cell, wherein the at least one sensor is a sensor which is independent from an actuator applying the pressure or force, i.e. the sensor does not actuate, move, or influence a printing tool or another portion of the printing apparatus.

Figures 1 to 2 are used to illustrate a plurality of embodiments in which the sensor assembly 400 can include at least one first sensor 325 provided at the substrate support 131, and/or at least one second sensor 322 provided at the printing tool 311.

Figure 3 is used to illustrate yet further embodiments, which can be combined with further embodiments described herein, in which the apparatus 300 can include a system controller 101, e.g. a control unit 101. In some implementations, the sensor assembly 400 can include at least one second sensor 322 provided at the printing tool 311, which can be for example connected to a system controller 101, e.g. a control unit 101.

As shown for example in Figures 1 to 3, a substrate support 131 is provided. The substrate support can for example be a nest or another support, on which one or more substrates 250 can rest for screen printing. Examples of a substrate support 131 are also hereinafter described with reference for instance to Figures 8 and 22. Further, a printing mask 102B, e.g. a printing screen 102B, is provided. The printing tool 311 urges material to be provided on the substrate 250 through the printing screen 102B. Typically, the substrate support 131 and the printing apparatus 300 including the printing tool 311 and the screen 102B can be moved relative to each other. Thereby, the substrate 250 can be positioned below the printing screen 102B for printing the material thereon. As shown in Figures 1 to 3, at least one sensor 322 or 325 is provided such that the force acting towards, i.e. in direction towards, the substrate, or the force acting on the substrate 250, can be detected. Typically, the force on the substrate 250 is to be understood as a force, which is perpendicular to the surface of the substrate. Thereby, other forces in the plane of the substrate might also be provided. However, the force exerted on the substrate 250 has at least one component of direction perpendicular to the substrate surface.

Embodiments of Figures 1, 2 and 3 may be combined each other to yield further embodiments. For example, further embodiments may provide that the at least one first sensor 325 can be connected to a controller 101.

As described above, embodiments described herein can include a sensor assembly 400. The sensor assembly 400 can include one, two, three, four, five or more than five sensors.

For example, the sensor assembly 400 can include one or more sensors 325 provided at the substrate support 131.

In some further examples, the sensor assembly 400 can include one or more sensors 322 provided at the printing tool 311.

For example, the sensor assembly 400 can include three sensors provided at the substrate support 131 or four sensors provided at the substrate support 131, e.g. in a quadrangular or rectangular shape, and one sensor positioned at the printing tool 311 , e.g. for detection of the force of the printing tool 311.

According to additional or alternative modifications thereof, the sensor assembly with one or more sensors can also be connected to a system controller 101, which controls the printing tool 311. The system controller 101 can, for example, also consider other information as described below for controlling the force of the printing tool 311 provided in direction towards the substrate 250.

In embodiments described for example in Figures 1 to 4 the apparatus may include a printing mask 102B e.g. a printing screen 102B.

It is noted here that a printing mask as used within the embodiments described herein can be at least one element selected from the group including: a net, a screen, a sheet, a metal sheet, a plastic sheet a stencil, a plate, a metal plate, a plastic plate, which may be, for example, provided with a plurality of distinctive features, or elements, 102C (as can bee seen for example in Figures 16, 17 and 20), such as for instance one or more element selected in a group comprising: holes, slots, trough incisions or other apertures formed therethrough. Such elements can define a pattern of screen printed material and/or placement of screen printed material (i.e., ink or paste) on a surface of a substrate. The screen printed material may for example be used for screen printing of photovoltaic cells or green-tape type circuits. For example, a printing tool, like the printing tool 311, e.g. a squeegee 311, described above, may be used to urge the screen print material through the features to form a patterned screen printed material on a surface of a substrate.

According to further embodiments, which can be combined with other embodiments described herein, the printing tool 311 can be configured to move from a first position along at least one direction of the printing mask 102B to a second position during printing, which for example defines a printing path P. Typically, the sensor assembly 400 is connected to a controller 101, and wherein the controller 101 is configured to vary the force applied by the printing tool 311 towards the substrate 250. Accordingly, the variation of the force of the printing tool 311 can be controlled such that the printing force on the substrate 250 is essentially constant when moving from the first position to the second position or can be adjusted to improve the printing characteristics and/or quality.

It is noted that in embodiments described herein, a printing force on the substrate 250 can define an apparatus pressure, e.g. an overall pressure, on the substrate 250. For example, a printing force on the substrate 250 which is essentially constant can define an overall pressure on the substrate 250 which is essentially constant. Thereby, it should be considered that the printing force on the substrate is at least provided by the force of the printing tool 311 minus the resistance or reaction force of the printing mask 102B.

It is here noted that a force of a printing tool 311, as used within the embodiments described herein, for example with reference to Figures 1 to 6, is a force with which the printing tool 311 is commanded and may yield a pressure urging against the substrate 250 during the screen printing process along the printing path P. For example, the pressure urging against the printing mask 102B can be referred to as printing tool command pressure resulting from the printing tool force Fp applied by the printing tool 311 on the printing mask 102B, towards the substrate 250.

Figures 5 and 6 show a printing apparatus 300 having a printing tool 311, which is moved relative to the printing mask 102B along the printing path P. The sensor assembly 400, wherein in Figures 5 and 6 sensors 322 and 325 are shown, measures the printing tool force Fp, which is the force at which the printing tool 311 is moved towards the substrate. The mask 102B has a mask reaction force Fr, which depends on the position of the printing tool along path P. For example, the mask reaction force Fr in Figure 5, wherein the printing tool 311 contacts the mask 102B around a center portion of the mask 102B, can be smaller than the mask reaction force Fr in Figure 6, wherein the printing tool 311 contacts the mask 102B adjacent to an edge portion of the mask 102B. Accordingly, the resulting force Fp+Fr, which acts on the substrate 250 is not constant for a constant printing tool force Fp. Accordingly, embodiments described herein, provide apparatuses wherein assemblies to detect and vary the printing tool force Fp are provided and/or provide methods, wherein the printing tool force Fp is varied.

Embodiments described herein in combination with other embodiments described in Figures 5 and 6 may provide that the force of the printing tool 311, along said printing path P, be varied according to a mask reaction force Fr, i.e. a mask reaction pressure. For example, a mask reaction force Fr may be considered as a force exerted in turn by the printing mask 102B against the printing tool 311, at least in response to a force of the printing tool 311, urging against the printing mask 102B.

A force Fc acting on the substrate 250, i.e. an apparatus pressure or overall pressure on the substrate 250, may be considered for example as the resulting force Fp+Fr of printing tool force Fp on the printing mask 102B taking into consideration at least the mask reaction force Fr.

Embodiments described herein may provide that the at least one printing tool 311 of printing apparatus 300 can be actuated by an actuation member, for example an actuator, along a printing path P with a variable force, e.g. in direction towards the substrate, to yield a variable printing tool force Fp.

Embodiments described herein may thus provide that the apparatus 300 can be adapted to keep essentially constant, along the printing path P, an apparatus pressure, e.g. an overall pressure, that acts on the substrate 250 being processed, wherein the apparatus pressure can be for example the result of the combination of the printing tool command pressure and the mask reaction pressure.

A plurality of embodiments described for example with reference to Figure 7 can be combined with embodiments described in Figures 1 to 6 to yield yet further embodiments.

In Figure 7 a plurality of embodiments is represented in which the printing tool 311, may be actuated toward the printing mask 102B and the substrate 250, along the printing path P with said printing tool force Fp.

As shown in Figure 7, the printing tool 311 may be for example mounted in turn on a print head 301 which may for instance configured to act in a print chamber 102 of the printing apparatus 300. The print head 301 and the print chamber 102 may be for example both mounted on a support frame 302.

The support frame 302, in the embodiments shown in Figure 7, can include a vertical upright 303 which may for example be provided with a first guide 304 on which, for instance, a first support body 305 is adapted to slide in a first direction Y. A first support body 305 can be in turn provided with a second guide 306 that for example extends transversally, for example orthogonally, with respect to the first guide 304. In combination with the above-described embodiments, a second support body 307 may be adapted to slide on the second guide 306 in a second direction X.

As shown in the embodiments of Figure 7, the second support body 307 may be for example provided with a third guide 309 that for example extends parallel to the first guide 304. In combination with the above-described embodiments, a third support body 310 may be adapted to slide on the third guide 309.

Figure 7 illustrates a plurality of embodiments as described herein, in which the printing tool 311 is for example mounted on the third support body 310.

Accordingly, some embodiments, which can be provided with other embodiments described herein, include a first guide 304 and a second guide 306, wherein typically a movement in direction Y or first direction Y, e.g. perpendicular to the substrate 250, and a movement in direction X or second direction X, e.g. along printing path P can be provided. In some further embodiments, a third guide 309 can further be included, wherein a movement in direction parallel to direction Y or first direction Y, e.g. perpendicular to the substrate 250 can be provided.

Thereby, one or more of the guides 304, 306, 309 can be provided as one element selected from the group consisting of: a linear axis, a rail, a sliding glide, a guide slide bearing and sliding rail, a sliding bar, a sliding rod and a shaft guidance.

The printing tool 311 can be moved both in the first direction Y and, in some possible implementations, can be moved in the second direction X. The printing tool 311 can be moved to follow the printing path P above the substrate 250.

In some embodiments shown in Figure 7, the movement of the printing tool 311 in the first direction Y or parallel to first direction Y can be caused by the translation of the third support body 310 along the third guide 309 and/or the translation of the first support body 305 along the first guide 304.

In some embodiments shown in Figure 7, the movement of the printing tool 311 in the second direction X can be caused by the translation of the second support body 307 along the second guide 306.

In the embodiments depicted in Figure 7 by way of example, the printing tool 311 has a substantially longitudinal development and, during use, may be disposed orthogonally to the first direction Y and second direction X.

In combination with the above-described embodiments, the printing tool 311 can have for example a length at least equal to the width of the portion to be printed of the substrate 250 so that, during use, it covers the whole width of the substrate 250.

In the plurality of embodiments in Figure 7 as described in possible combination with embodiments depicted in Figures 1 to 6, the movement of the printing tool 311 may be due to the action of at least one actuation members 312A, 312B, 312C.

In some embodiments, at least one actuation member 312A may cause the sliding of the first support body 305 along the first guide 304.

In further possible embodiments, at least another actuation member 312B may cause the sliding of the second support body 307 along the second guide 306.

In still further possible embodiments, at least one further actuation member 312C may cause the sliding of the third support body 310 along the third guide 309.

According to some embodiments, which can be combined with other embodiments described herein, one or more of the guides 304, 306, 309 and one or more of the actuator members 312A, 312B, 312C can form at least one element selected from the group consisting of: a linear axis with an actuator, a linear actuator, such as a mechanical linear actuator, a hydraulic linear actuator, a piezoelectric linear actuator, or an electromechanical actuator, and a belt driven linear actuator.

Figure 7 illustrates a plurality of embodiments, which can be combined with embodiments as described herein, in which one or more position detectors 313 A, 313B, 313C may be associated respectively to one or more of the first support body 305, the second support body 307 and the third support body 310.

In some embodiments, at least one position detector 313 A may determine at least the position assumed by the third support body 310 along the first guide 304. In further embodiments, at least another position detector 313B may determine at least the position assumed by the third support body 310 along the second guide 306.

According to different embodiments, one or more position detector 313 A, 313B can be associated with a respective guide 304, 306. Accordingly, a position of the respective element as described herein along at least one of the guides 304, 306 can be measured. According to different implementations, one or more of the position detectors 313 A, 313B can be selected from the group consisting of: a mechanical position sensor, an electronic positions sensor, an electromagnetic position sensor or an optical position sensor. Position sensors which can be used are for example linear sensors. For example, the position sensor can be a capacitive transducer, an Eddy-current sensor, a Gating sensor, a Hall effect sensor, an inductive non-contact position sensor, a Laser Doppler Vibrometer, a linear variable differential transformer (LVDT), a proximity sensor or a string potentiometer.

In still further embodiments, at least one further position detector 313C may determine at least the position assumed by the third support body 310 along the third guide 309.

Figure 7 illustrates a plurality of embodiments, which may be combined with embodiments described in Figures 1 to 6, in which the printing apparatus 300 may include the printing mask 102B or screen, associated with the print chamber 102. Typically, the screen or printing mask 102B can be interposed between the printing tool 311 and a substrate support 131 for the substrate 250, which in the plurality of embodiments shown in Figure 9 can be for example a printing nest. In embodiments of Figure 7, a support element 315 may be associated to the support frame 302, for example to the first support body 305, and may also provide to support for example the printing mask 102B.

According to embodiments described herein, the printing mask 102B can have a flat or planar surface development, can be essentially quadrangular, for example rectangular, and can be attached, for example with its two opposite perimeter edges 318, to a support frame 316, that for instance may be a frame and may also, in some cases, be directly associated to the support element 315.

In embodiments described herein with reference to Figure 7, generally during use for processing substrates, the opposite perimeter edges 318 of the printing mask 102B may be disposed essentially parallel to the longitudinal extension of the printing tool 311. In this way, the action exerted by the printing tool 311 against the printing mask 102B may cause a deformation, for example an elastic or pseudo-elastic deformation, of the printing mask 102B.

The translation of the first support body 305 along the first guide 304 can cause the consequent translation of the printing mask 102B in the first direction Y in order to bring it closer to, or to distance it from, the substrate support 131. The printing tool 311 can be mounted, for example exploiting a pivoting assembly, e.g. a pin or a shaft permitting turning or oscillating, on the third support body 310 so as to rotate around an axis of rotation Z essentially parallel to the second direction X. The rotation of the printing tool 311 around the axis of rotation Z allows the printing tool 311 to adapt to any possible deviation from a flat or planar condition of the print surface.

Figure 7 illustrates a plurality of embodiments as described herein, in which the pivoting assembly can include a housing seating 317, which may be for example made in the third support body 310.

Embodiments described herein may provide that the pivoting assembly includes for example a through hole 319 made in the printing tool 311 for example with shape and sizes essentially mating with those of the housing seating 317.

The pivoting assembly can include a support pin 320 which may for example be inserted through the through hole 319 and the housing seating 317.

In a plurality of embodiments as shown for example in Figure 7 and which may be combined with embodiments described herein, the sensor assembly may include at least one sensor 322, 325 that can be associated to at least one of either the printing tool 311 or the substrate support 131 or both.

In embodiments in which for example at least one sensor 325 is associated to the substrate support 131, said at least one sensor 325 can be a sensor adapted to detect a force or a pressure indicative of at least the force or pressure acting on the substrate 250 during the printing operations.

In embodiments in which for example at least one sensor 322 is associated to the printing tool 311, said at least one sensor 322 is adapted to detect a force applied by the printing mask 102B, indicative of the mask reaction force Fr.

In embodiments in which for example a controller 101 is connected at least to said sensor 322 at the printing tool 311, data from the sensor 322 at the printing tool 311 may be exploited by the controller 101 to determine the apparatus pressure acting on the substrate 250 during the printing operations. For example, data pre-stored in a memory associated to the controller 101 and indicative of a force or pressure to be set-up for a specific screen printing process may be used by the controller 101 in combination with the indication of the mask reaction force Fr to vary the printing tool force Fp and determine the defined printing force Fc on the substrate 250.

In a plurality of embodiments as shown for example in Figure 7 and which may be combined with embodiments described herein, one or more sensors 322 can be associated in the through hole 319 of the third support body 310. Said one or more sensors 322 can be configured to detect the force acting on the support pin 320 when the printing tool 311 is in use. This force correlates to the mask reaction force Fr or the mask reaction pressure. In embodiments shown for example in Figure 7 one or more sensors 322 can be mounted directly to the support pin 320. In some implementations, one or more sensors 322 at the printing tool 311 may be configured to provide at least one signal from which a printing force on the substrate 250 can be determined. In some implementations, the signal of the one or more sensors 322 may be used by the system controller 101 to determine a printing force on the substrate 250.

In a plurality of embodiments as shown for example in Figure 7 and which may be combined with embodiments described herein, one or more sensors 325 may be mounted at the substrate support 131, to detect a force or a pressure indicative of the pressure acting on the substrate 250 due to the action of the printing tool 311. For example, one or more sensors 325 may be mounted at the substrate support 131 underneath the substrate 250.

In a plurality of embodiments as shown for example in Figure 8 and which may be combined with embodiments described herein, one or more sensors 325 may be associated directly with a support plate 138 of the substrate support 131.

As shown for example in Figure 8, a plurality of sensors 325 can be associated with the substrate support 131, each of which is adapted to detect a force or a pressure indicative of, correlating to and/or proportional to the pressure acting on the substrate 250 due to the action of the printing tool 311.

Sensors 325 may be configured to provide at least one signal from which a printing force on the substrate can be determined.

According to embodiments described herein, the sensors 322, 325, which might be force sensors, e.g. load cells, or pressure sensors as described above, can either detect a force on the substrate 250 and/or can detect a force applied by the printing tool 311. This information can, according to embodiments described herein, be utilized to adjust and/or vary the force of the printing tool 311 directed towards the substrate 250 in order to improve the printing characteristics as desired.

According to some alternative or additional implementations, as shown for example in Figure 8, four sensors 325 may be provided, mounted on the plate 138. For example, the four sensors 325 may be located in correspondence or proximity of four corners of the support plate 138, resembling a disposition at the top corners of a rectangle. In another example, the four sensors 325 may be located in an intermediate position in correspondence or proximity of four sides of the support plate 138, resembling a disposition at the sides of a rectangle.

In some embodiments the four sensors 325 may be directly associated with the support plate 138 and can detect the force or pressure acting on the support plate 138 due to the action of the printing tool 311. The force or pressure detected is in turn directly correlated to the force or pressure acting on the substrate 250.

Using a plurality of sensors 325 at the substrate support 131 allows to increase accuracy in acquiring data forces.

According to some embodiments, which can be combined with other embodiments described herein, at least three sensors 325 are provided at the substrate support 131. Thereby, pressure variations in the plane, e.g. the plane spanned by the three sensors 325, of the substrate support 131 can be detected. Accordingly, a uniform pressure along the surface of the substrate 250 or a predetermined pressure along the surface of the substrate 250 can be adjusted and/or controlled for the printing process.

It is noted here that one or more of the sensors included in the sensor assembly as used within the embodiments described herein can be at least one sensor element selected from the group comprising:

- a force sensor or transducer, such as a load cell, for example of a strain gauge load cell, a hydraulic or hydrostatic load cell, a piezoelectric load cell, a vibrating wire load cell and a capacitive load cell,

- a pressure sensor or transducer, for example of the electronic type generally used to collect a force to measure strain or deflection due to the applied force over an area, such as a piezoresistive strain gauge sensor, a capacitive sensor, an electromagnetic sensor, a piezoelectric sensor, an optical sensor or a potentiometric sensor.

In some embodiments given as a non-limiting example, the one or more sensors 325 at the support substrate 131 can be a load cell.

In some embodiments given as non-limiting example the one or more sensors 322 at the printing tool 311 can be a load cell.

Embodiments described herein, which can be combined with other embodiments described herein, may provide a method for screen printing on a substrate 250 that for instance can be performed using the printing apparatus 300. According to some embodiments described herein, the method includes:

- vary a force of a printing tool 311, of a printing apparatus 300, wherein the force is directed towards the substrate 250, to compensate for variations in the force of the printing apparatus 300 on the substrate 250 along a printing path P.

In some embodiments, the method provides that during the printing operations a substrate 250 to be printed is loaded on a support structure, for example on one of the substrate support 131, e.g. a printing nest.

The substrate support 131 can be in turn disposed in correspondence with the printing tool 311 in order to carry out the printing operations on the substrate 250.

In some embodiments, the printing tool 311 can be moved along the printing path P to print the substrate 250. Furthermore, in some embodiments the movement of the printing tool 311 towards the substrate 250 and along the printing path P may occur so as to maintain the force or pressure acting on the substrate 250 in a predetermined manner, for example essentially constant along the printing path P. Keeping essentially constant along the printing path P the force or pressure on the substrate 250 may be obtained for example by varying the printing tool force Fp applied by the printing tool 311 on the printing mask 102B so as to balance or compensate the mask reaction force Fr.

It is noted that by the term "essentially constant" force or pressure it is meant a force or pressure on the substrate 250 having a constant value or a force or pressure on the substrate 250 having variable values always included in a predefined selected range of force or pressure values, so that the development of the force or pressure on the substrate 250 is maintained in a determinate range of force or pressure tolerance of about an average value. Some exemplifying embodiments provide that the average value of force on the substrate 250 can be a value included between 30N and 80N. According to yet further examples, the force or pressure can be constant within 5 % or below, within 3 % or below, e.g. between 0.1 % and 2 %, within 1 % or below, e.g. between 0.1 % and 0.5 %.

By balancing the printing tool force Fp against the mask reaction force Fr, an essentially constant force along the printing path P may be obtained that allows to have the same printing conditions in different zones of the substrate 250, thus resulting in a homogeneous distribution of a print material M on the substrate 250.

Figures 9a and 9b show possible exemplifying embodiments in which print tracks 252 are obtained on the substrate 250, exploiting screen printing with the embodiments described herein, that can have very similar properties over the whole surface extension of the surface 251 of the substrate 250.

Some embodiments provide that the printing tool 311 can be actuated, moving it in the first Y and second direction X and commanding it with a printing tool force Fp which is variable along the printing path P, so as to obtain a predetermined force or pressure, such as, an essentially constant force or pressure on the substrate 250.

Some embodiments provide that the variation in the printing tool force Fp can be obtained by commanding the actuation, by means of the controller 101, of the actuation members of the printing tool 311, for example one or more of the actuation members 312A and 312C.

Some exemplifying embodiments provide that the one or more of the actuation members 312A and 312C can be actuated by setting the electric feed current thereof.

Some embodiments provide that the movements of the printing tool 311 can also be defined according to positions detected by one or more of the position detectors 313A, 313B, 313C.

In some embodiments it can be provided that, during screen printing process, a force or pressure acting on the substrate 250 can be measured by the one or more of the one or more sensors 325 at the substrate support 131 or an indication of the force or pressure acting on the substrate 250 may be derived from signal data of the one or more sensors 322, for example processed by the controller 101.

In some embodiments, if a deviation is detected of the apparatus pressure with respect to an expected value, an intervention can be made, for example by the controller 101, on the printing tool 311 to re-establish desired conditions.

In some embodiments, interventions on the printing tool 311 to re-establish the desired conditions can be performed by the controller 101 in a feedback closed- loop control.

According to some embodiments, the printing tool force Fp can be made to vary, along the printing path P, as a function of the specific position assumed by the printing tool 311 with respect to the printing mask 102B when the printing tool 311 is moved along the printing path P during the printing operation.

In yet further embodiments, the variation in the printing tool force Fp along the printing path P can be correlated to the mask reaction force Fr that the printing mask 102B opposes against the action of the printing tool 311.

In fact, it has been found that the apparatus pressure acting on the substrate 250 can derive for example at least from the printing tool force Fp and the mask reaction force Fr. The printing tool force Fp and the mask reaction force Fr both can act in a direction essentially orthogonal to the plane of the substrate 250. In some embodiments, the printing tool force Fp and the mask reaction force Fr can have an opposite sense of action on each other, so that some of their components can cancel out each other.

In some embodiments, the apparatus pressure acting on the substrate 250 can be the resultant pressure from the combination at least of the printing tool force Fp of the printing tool 311 and the mask reaction force Fr.

The mask reaction force Fr is a parameter that can vary as a function of the properties of the printing mask 102B and in particular as a function of its sizes, the sizes of the distinctive features 102C and of the material it is made of. The mask reaction force Fr can also be a variable parameter along the printing path P. The mask reaction force Fr can be also correlated to the reciprocal connection of the printing mask 102B to the support frame 316. In particular, the mask reaction force Fr can assume for example a minimum value in correspondence with the center line of the printing mask 102B and a maximum value in correspondence with its perimeter edges 318.

According to typical embodiments, which can be combined with other embodiments described herein, the printing mask 102B can be distanced from the support plate 138 of the substrate support 131 by a determinate first distance S, also called for example "snap off. During the printing operations, the printing tool 311 can exert on the printing mask 102B a pressure correlated to the printing tool force Fp. This can consequently result in turn in a force or pressure on the substrate 250. The printing mask 102B can be thus be deformed, elastically or pseudo-elastically, and lowered by said first distance S toward the substrate 250. For example, deformation and lowering printing mask 102B can bring the substrate 250 and the printing mask 102B into contact with each other.

Figure 10 represents a plurality of embodiments that can be combined with embodiments described herein.

Embodiments of Figure 10 can provide pre-setting operations, performed for example before the actual screen printing operations are executed, to acquire data indicative of the mask reaction force Fr.

Embodiments of Figure 10 can provide that, before printing operations are performed, a development of the mask reaction force Fr or mask reaction pressure, along the printing path P is detect.

In combination with embodiments represented in Figure 10, additional embodiments may provide that, before the printing operations are carried out, printing parameters to be attributed to the printing tool 311 for the printing operations can be set, for example by the controller 101.

For instance, setting printing parameters provides at least to determine the movements to be attributed to the printing tool 311 in the first direction Y, as a function of the spatial coordinate of the second direction X, that is, along a length L of the substrate 250.

In some embodiments it is provided to calculate, for example by the controller 101, a printing tool force Fp to be variably attributed to the printing tool 311 along the printing path P, as a function of the mask reaction force Fr, with the purpose of having a defined, for example essentially constant, apparatus pressure acting on the substrate 250.

Some embodiments provide that the mask reaction force Fr can be detected, for example during setting of the printing parameters. Detection of the mask reaction force Fr can be for example performed continuously or at discrete points in different positions along the printing mask 102B, for example at discrete points included between two perimeter edges 318 of the printing mask 102B.

Figure 10 which relates to embodiments that can be combined with embodiments described herein, provides to detect a mask reaction force Fr in several positions distanced from each other along the printing path P, for example in three positions, e.g. a first position, a second position and a third position distanced each other.

It will be understood that embodiments may also provide to detect a mask reaction force Fr for example in two, four, five, six or more positions distanced from each other along the printing path P. Further, the mask reaction force Fr can be detected quasi-continuously along the printing path P or portions of the printing path P.

For the sake of comprehension and making reference to exemplifying Figures 11 and 12, a mask reaction pressure Fr is for instance detected in three positions distanced from each other along the printing path P, in which:

- in the first position the squeegee is indicated by the reference number 31 Γ, and the printing mask by the reference number 102B';

- in the second position the squeegee is indicated by the reference number 311", and the printing mask by the reference number 102B"; and

- in the third position the squeegee is indicated by the reference number 31 Γ", and the printing mask by the reference number 102B'".

In these exemplifying embodiments, during setting, which is done before the printing operation(s), it can be provided to move the printing tool 311 above the printing mask 102B in each of the above first, second and third positions.

For each position, the printing tool 311 can be moved in the first direction Y vertically against the printing mask 102B so as to move it from its non-stressed condition, shown for example by dashed line in Figure 10, to a condition where it is lowered by said first distance S. In other words, the printing tool 311 can be lowered until it touches the printing mask 102B, and further moved in the first direction Y until it deforms and lowers the printing mask 102B by said distance S.

Figure 11 and 12 show exemplifying graphical representations resembling the behavior or development of printing tool force Fp and mask reaction force Fr that can be derived by using for example embodiments as described herein. In each of the three exemplifying positions, the reaction pressure can detected by the sensors 322 at the printing tool 311, respectively a first mask reaction force Fr', a second mask reaction force Fr", and a third mask reaction force Fr'".

Some embodiments provide that the controller 101 can calculate the printing tool force Fp in the respective three positions to be attributed to the printing tool 311 in the three positions, e.g. a first printing tool force Fp', a second printing tool force Fp", and a third printing tool force Fp'".

Each of the printing tool forces Fp', Fp" and Fp'" in the three positions can be calculated by summing a constant value of force Fk to the mask reaction forces Fr', Fr" and Fr'". The constant value of force Fk can be selected to guarantee the contact of the printing mask 102B with the substrate 250 so that printing can be correctly carried out.

In some embodiments, the constant value of force Fk can be for example included between 40N and 90N.

In some embodiments, it can be provided that the calculated printing tool forces Fp', Fp" and Fp'" can be processed with respect to each other so as to define a development of the printing tool force Fp along the printing path P.

The printing path P, as e.g. shown in Figure 14, can be divided into a plurality of printing zones interposed between the positions as identified above, for example in three printing zones, e.g. a first zone 330, a second zone 331 and a third zone 332, interposed between the respective first, second and third position as identified above.

A defined value of the printing tool force Fp can be associated with each printing zone 330, 331, 332. In some embodiments, the printing tool 311 for example can exert, on the printing mask 102B, a first printing tool co force Fp' in the first zone 330, a second printing tool force Fp" in the second zone 331, and a third printing tool force Fp'" in the third zone 332. According to other implementations, the path P can be divided into three or more, e.g. 5 or more or 10 or more printing zones, wherein each zone is associated with a command pressure. Further, it is possible to adapt the command pressure or the command force quasi-continuously.

In embodiments described herein, the variation in the printing tool force Fp', Fp", Fp'" along the printing path P can be adapted to compensate for the mask reaction force Fr such that a substantially constant apparatus pressure actually acts on the substrate 250.

With the embodiments described above, it is possible to obtain print tracks with uniform and homogeneous geometric properties in the surface of the substrate 250, unlike what was possible in the state of the art, since it is possible to obtain an essentially constant apparatus pressure on the substrate.

On the contrary, if the printing tool is commanded with a constant pressure but without taking into account the reaction of the printing mask, it has been found that the print tracks generally may have not uniform geometries at least at the start and end of printing path, where the influence of the reaction of the printing mask can be more evident. In the same way, even if a fixed vertical position is set for the squeegee with respect to the substrate, in any case there could be inaccuracies in the depositing of the material. It was considered that these printing modes with a set position can be in fact influenced by dimensional tolerances of the printing apparatus, variations in the thickness of each substrate and possible wear on mobile parts of the squeegee.

It has been found that, on the contrary, embodiments of the apparatus and method for printing a substrate described herein allow for taking into proper consideration the reaction of the printing mask so that the apparatus pressure on the substrate is effectively kept constant or with predetermine characteristics, which is different from the apparatus pressure on the substrate for a constant command pressure. With embodiments of the method and apparatus for printing a substrate described herein the print tracks may have uniform geometries and the print quality of the substrates can be increased.

Experimental tests Figures 13, 14 and 15 are graphs that show respectively the development detected of the mask reaction force Fr, i.e. the mask reaction pressure, the printing tool force Fp, i.e. the printing tool command pressure and the printing force Fc on the substrate 250, i.e. the apparatus pressure acting on the substrate 250, detected along the printing path P.

The values were acquired by setting the first distance S at 2300 m, a printing speed of 160 mm/s and a printing force of 90N.

As can be seen by comparing Figures 13 and 14, the development of the mask reaction force Fr and that of the printing tool force Fp are substantially analogous, except for their intensity.

Figure 15 shows the development of the printing force Fc on the substrate 250 detected by the pressure sensors 325 along the printing path P. As can be seen from this graph, a substantially constant printing force Fc acts on the substrate 250.

With reference to Figures 9 A and 9B, detections were made on a sample of ten substrates printed using a known method and with the method according to one of the embodiments described above.

In particular, for each sample the consumption of print material M, and the width and height of the print tracks 252 made on the substrate 250 were assessed. More specifically, on the substrate 250 (Figures 9A and 9B) print tracks 252 were made including fingers 334 and busbars 335.

With reference to Figure 9A the width of the fingers 334 was detected and compared in four zones, respectively a first zone Zl, a second zone Z2, a third zone Z3 and a fourth zone Z4.

With reference to Figure 9B the height of the fingers 334 and busbars 335 was detected and compared in three zones, respectively a first zone Al, a second zone

A2 and a third zone A3. The comparisons are shown in Table 1.

Table 1

Known New printing method method

Consumption of print material [g] 182 172

Width of fingers in Zl [ m] 79 80.7 Width of fingers in Z2 [ m] 81.2 81

Width of fingers in Z3 [ m] 82.9 82

Width of fingers in Z4 [ m] 83.9 82

Comparison of width of fingers in detection

zones

Zl - Z2 [ m] 2.2 0.3

Zl - Z3 [ m] 3.9 1.3

Z4 - Z2 [ m] 2.7 1

Z4 - Z3 [ m] 1 0

Height of busbars in Al [ m] 25.7 22.7

Height of busbars in A2[ m] 22.9 22.2

Height of busbars in A3[ m] 24.7 22

Al - A2 [ m] 2.8 0.5

A3 - A2 [ m] 1.8 0.7

Height of fingers in Al [ m] 24.7 22.3

Height of fingers in A2 [ m] 22.4 21.8

Height of fingers in A3 [ m] 23.9 21.4

Al - A2 [ m] 2.3 0.5

A3 - A2 [ m] 1.5 0.9

From the comparison of the data shown above, it is believed that with embodiments of the method and apparatus described herein it is possible to obtain a reduction in the consumption of print material M used for making the print tracks 252.

Furthermore, it is believed that, along the printing path P, print tracks 252 are obtained that have improved uniformity of sizes, with the advantage of better electrical characteristics for the print tracks 252 obtained.

According to different embodiments, which can be combined with other embodiments described herein, one printing apparatus (see for example Figures 16, 17, 20 and 21), two printing apparatuses (see for example Figures 18 and 19), three printing apparatuses or even more printing apparatus can be provided. Typically, each printing apparatus can be a screen printing apparatus, wherein material to be printed onto a substrate 250, for example, a conductive paste, is urged through a printing mask 102B, i.e. a screen or the like. According to typical implementations, a printing tool 311, which can also be referred to as a squeegee 311, can be provided to urge the material to be printed onto the substrate 250, for example according to a predefined pattern.

According to yet further embodiments, which can be combined with other embodiments described herein, one or more substrate supports 131 are provided. The substrate supports 131 support the substrate during printing and/or during transport of the substrate 250. According to some implementations, at least two substrate supports 131 are provided for each printing apparatus. Thereby, throughput might be increased as one substrate support 131 is available in the event of failure of one of the two substrate supports 131 and/or one substrate support 131 can receive a substrate 250 while another substrate 250 is printed on another substrate support 131.

The examples shown in Figures 16 and 17 includes, for example, four substrate supports 131 for one printing apparatus. The substrate support can be a flat plate, a portion of a transport system, a substrate holder, a pedestal or other support for supporting the substrate. Typically, a printing nest 131 as described in Figure 21 below can be used as a substrate support 131. The printing nest thereby, includes at least one of: a transfer mechanism, a disposable substrate receiving surface, a substrate receiving surface feeding mechanism, a driving mechanism, an optical transparent substrate receiving surface, a substrate fixation, e.g. a clamp, a vacuum suctions means or the like.

Figure 16 is an isometric schematic view of a possible implementation of a screen printing system 110 including a conveyor 111, or incoming conveyer 111, a printing apparatus, which can for example include a rotary actuator assembly 130 and a screen print chamber 102, and a conveyor 112, or output conveyor 112. Embodiments of the printing apparatus 300 as described herein can be used in the screen printing system 110 of Figure 16.

The conveyor 111 may be configured to receive the substrate 250 from an input device, such as an input conveyor 113 (i.e., path "A" in Figures 16 and 17). The conveyor 111 can transfer the substrate 250 to a substrate support 131, e.g. a printing nest 131. The substrate support or printing nest 131 can be provided at a print table, in a print chamber 102 or the like. For example, the print table can be provided as a rotary actuator assembly 130. The conveyor 112 may be configured to receive a processed substrate 250 from a substrate support 131. The substrate support 131 can be coupled to a rotary actuator assembly 130. The conveyor 112 can transfer the substrate 250 to a substrate removal device, such as an exit conveyor 114 (i.e., path "E" in Figures 16 and 17). The input conveyor 113 and the exit conveyor 114 may be automated substrate handling devices that are part of a larger production line.

In general, a substrate 250 to be screen printed with embodiments described herein can be loaded on the printing apparatus, for example on the substrate support 131.

In some exemplifying embodiments, the substrate support 131 and printing apparatus 300 can move relative to each other in order to align the substrate 250 to the screen printed pattern that is to be deposited on the surface of a substrate 250.

For example, the screen printed pattern that is to be deposited can be aligned to the substrate 250 in an automated fashion by orienting the screen printing mask 102B in a desired position over the substrate surface using actuators 102 A and information received by the system controller 101 from an inspection assembly 200. An inspection assembly 200 can include one or more optical inspection devices or video inspection devices. In some embodiments, a camera is provided as an example of optical inspection device or video inspection device.

In some exemplifying embodiments, a screen print chamber 102 can be adapted to deposit a metal containing or dielectric containing material on a solar cell substrate having a width between about 125 mm and 156 mm and a length between about 70 mm and 156 mm.

In some exemplifying embodiments, the screen print chamber 102 can be adapted to deposit a metal containing paste on the surface of the substrate to form the metal contact structure on a surface of a substrate.

According to some exemplifying embodiments, which can be combined with other embodiments described herein, the rotary actuator assembly 130 may be rotated and angularly positioned about the "F" axis (Figure 16), for example by a rotary actuator (not shown). Typically the rotary actuator can be provided below the support. In some possible implementations, for example a system controller 101 may further be used for rotating and angular positioning the rotary actuator assembly 130.

According to some embodiments, which can be combined with other embodiments described herein, the substrate supports 131 may be selectively angularly positioned within the screen printing system 110 (i.e., paths "Dl" and "D2" in Figure 17). The rotary actuator assembly 130 may also have one or more supporting components to facilitate the control of the printing nests 131 or other automated devices used to perform a substrate processing sequence in the screen printing system 110.

According to a plurality of embodiments described with respect to Figures 16 and 17, which can be combined with other embodiments described herein, the rotary actuator assembly 130 can include a plurality of substrate supports 131, e.g. printing nests 131, that are each adapted to support a substrate 250 during the screen printing process performed within the screen print chamber 102. For example, the rotary actuator assembly 130 can include four substrate supports 131.

Figure 17 schematically illustrates some possible implementations of the position of the rotary actuator assembly 130 in which one substrate support 131 is in position "1" to receive a substrate 250 from the conveyor 111, another substrate support 131 is in position "2" within the screen print chamber 102 so that another substrate 250 can receive a screen printed pattern on a surface 251 thereof, another substrate support 131 is in position "3" for transferring a processed substrate 250 to the conveyor 112, and another substrate support 131 is in position "4", which is an intermediate stage between position "3" and position

Figure 18 is an isometric view and Figure 19 is a top plan schematic view of a printing system 110 according to a plurality of embodiments, which can be combined with other embodiments described herein that can be used to form for example the metal contacts according to a desired pattern on a surface 251 of a solar cell substrate 250.

Embodiments of the screen printing system 110 in Figures 18 and 19 generally can include two conveyors 111 or incoming conveyors 111 and a printing apparatus, which can for example include an actuator assembly 130. The actuator assembly can be for instance configured as a rotary table or rotary actuator. The printing apparatus of screen printing system 110 in Figures 18 and 19 can also include a plurality of screen print chambers 102. The conveyors 111 can transfer substrates 250 to a plurality of substrate supports 131, e.g. printing nests 131. The printing apparatus of system 110 in Figures 18 and 19 can also include two conveyors 112, or outgoing conveyors 112. The printing apparatus of system 110 in Figures 18 and 19 can also include a system controller 101. The conveyors 111 may be configured in a parallel processing configuration so that each can receive unprocessed substrates 250 from an input device, such as an input conveyor 113. The conveyors 111 can further transfer each unprocessed substrate 250 to a substrate support 131, which may for example be coupled to the actuator assembly 130. In addition, the conveyors 112 may be configured parallel so that each can receive a processed substrate 250 from a substrate support 131, and for example transfer each processed substrate 250 to a substrate removal device, such as an exit conveyor 114.

In some embodiments, which can be combined with other embodiments described herein, the screen printing system 110 in Figures 18 and 19 may have two substrate supports 131 (in positions "1" and "3" in Figure 19) each positioned both to transfer a processed substrate 250 to the conveyor 112 and also to receive a non-processed substrate 250 from the incoming conveyor 111.

Thus, in the screen printing system 110, the movement of the substrate generally follows the path "A" (Figure 19). In this possible implementation, each of the two other printing nests 131 (in positions "2" and "4") is positioned under the screen print chamber 102, so that screen printing can be carried out on the non-processed substrates 250 located on the respective printing nests 131.

Parallel processing configuration may allow increasing productive capacity with a minimum bulk of the processing system. Although the system 110 is illustrated in Figures 18 and 19 with two screen print chambers 102 and four substrate support 131, e.g. printing nests 131, the system 110 can include additional screen print chambers 102 and/or substrate support 131.

Figure 20 is an isometric view and Figure 21 is a top plan schematic view of embodiments of the screen printing system 110 which can be combined with other embodiments described herein and which can be used to form for example the metal contacts in a desired pattern on a surface 251 of a solar cell substrate 250.

In the examples of Figures 20 and 21, the screen printing system 110 can include a conveyor 111, or incoming conveyor 111, a printing apparatus, which can include an actuator unit 230, which in some embodiments can be configured for example as a linear movement unit and a screen print chamber 102, a conveyor 112, or outgoing conveyor 112, and a system controller 101. The conveyor 111 can be configured to receive a substrate 250 from an input device, such as an input conveyor 113 (i.e., path "A" in Figures 20 and 21). The conveyor 111 can also transfer the substrate 250 to a substrate support 131 that can be for example coupled at inlet to the actuator unit 230. The conveyor 112 can be configured to receive a processed substrate 250 from a substrate support 131 that can be coupled at exit to the actuator unit 230. The conveyor 112 can also transfer the substrate 250 to a substrate removal device, such as an exit conveyor 114 (i.e., path "E" in Figures 20 and 21). The input conveyor 113 and the exit conveyor 114 may be for example automated substrate handling devices that are part of a larger production line.

In the examples of Figures 20 and 21 the conveyor 111 can transport the substrates 250 from: (i) a first position "1" as shown in Figure 21 in which the substrate 250 is introduced into the screen print chamber 102; (ii) a second position "2" inside the screen print chamber 102; and (iii) a third position "3" in which the processed substrate 250 is discharged from the screen print chamber 102 and conveyed to other operating stations.

For example, in the case of a double or multiple print, the substrate 250 can be again introduced into the screen print chamber 102 in position "2" to carry out a second or further printing step and can be then discharged again from the screen print chamber 102 passing to position "3". This alternate movement can be repeated a number of times coordinated with the number of layers to be printed, until the final product is definitively discharged.

Embodiments of a substrate support 131, e.g. printing nest 131, which can be combined with other embodiments described herein, are described with reference to Figure 22. The substrate support 131 can be configured to support a substrate 250 for screen printing. In the example of Figure 22 a substrate support 131 generally can include a conveyor assembly 139. For example, the conveyor assembly 139 can include at least one or more elements selected in a group comprising: a feed spool 135, a take-up spool 136, rollers 140 and one or more actuators 148. The one or more actuators 148 can be coupled to the feed spool 135 and/or take-up spool 136. The one or more actuators 148 are adapted to feed and retain a supporting material 137 positioned across a support plate 138. In some possible implementations, the support plate 138 generally can have a substrate supporting surface on which the substrate 250 and supporting material 137 can be positioned during the screen printing process performed in the screen print chamber 102.

In embodiments described herein, which can be combined with further embodiments described herein, the supporting material 137 can be for example a porous material that allows a substrate 250, which is disposed on one side of the supporting material 137, to be retained on the plate 138 by a vacuum applied to the opposing side of the supporting material 137 by a conventional vacuum generating device (e.g., vacuum pump, vacuum ejector).

In the examples of Figure 22 a vacuum, or underpressure, can be for example applied to vacuum ports (not shown) formed in the substrate supporting surface of the plate 138 so that the substrate can be "chucked" to the substrate supporting surface of the plate 138.

In embodiments described herein, which can be combined with other embodiments described herein, the supporting material 137 can be a porous material, e.g. permeable to air, that may consist, for instance, of a porous paper, or another analogous material, for instance a plastic or textile material that performs the same, similar or equivalent function.

In the examples of Figure 22, the actuators 148 can be for example coupled to, or adapted to engage with, one or more of the feed spool 135 and the take-up spool 136 so that the movement of a substrate 250 positioned on the supporting material 137 can be accurately controlled within the substrate support 131. According to some exemplifying implementations, feed spool 135 and take-up spool 136 may each be adapted to receive opposing ends of a length of the supporting material 137. In some exemplifying embodiments, the actuators 148 each can contain one or more drive wheels 147 that are coupled to, or in contact with, the surface of the supporting material 137 positioned on the feed spool 135 and/or the take-up spool 136, to control the motion and position of the supporting material 137 across the support plate 138.

One or more of the screen print chambers 102 described with the screen print systems 110 may be adapted to deposit material in a desired pattern on the surface of a substrate 250 positioned on the substrate support 131, in position "2" during the screen printing process.

In some possible implementations, the screen print chamber 102 can include a plurality of actuators, for example, actuators 102A (e.g., stepper motors or servomotors) that are in communication with the system controller 101. The actuators 102 A can be used to adjust the position and/or angular orientation of the screen printing mask 102B (Figures 16 and 21) disposed within the screen print chamber 102 with respect to the substrate 250 being printed.

According to some embodiments, which can be combined with embodiments described herein, an inspection assembly 200 can be associated with each of the screen print systems 110 shown in Figures 16-21, and can be adapted to inspect a substrate 250 disposed on the substrate support 131, on which the desired pattern is screen printed.

With reference to Figure 23 embodiments of an inspection assembly 200 are described which can be adapted to identify and inspect the substrates 250 before and after printing.

An inspection assembly 200 as used herein in combination with embodiments described herein may include one or more cameras 121 (e.g., a camera having an electronic image sensor, such as a CCD image sensor, a CCD camera, or a camera having an electronic image sensor, such as a CMOS image sensor). It is possible to provide embodiments in which the inspection assembly 200 includes two, three, four, five or even more cameras 121. Moreover, an inspection assembly 200 can also include for example electronic components capable of inspecting and communicating the inspection results to the system controller 101 used to analyze the orientation and position of the substrate 250 on the substrate support 131. In some implementations, the camera 121 is for example positioned over the surface 251 of the substrate 250 so that a viewing area 122 of the camera 121 can inspect at least one part or region of the surface 251. As described above in connection with possible embodiments, the information received by the camera 121 can be used to perform at least one or more of the following operations: to align the screen printing mask 102B and thus the subsequently deposited material, and to acquire an image of the layer deposited on the substrate 250.

According to some examples of camera 121, the camera 121 can be an InGaAs type camera that has for example a cooled CCD array to enhance the signal-to- noise ratio of the detect signal. In some possible implementations, the inspection assembly 200 can be isolated from ambient light by enclosing or shielding the areas between the surface 251 of the substrate 250 and the camera 121.

In some possible embodiments which can be combined with embodiments described herein, the inspection assembly 200 can also include one or more optical filters (not shown) that are disposed between the camera 121 and the surface of the substrate 250. For example, the optical filter(s) can be selected to allow only certain desired wavelengths to pass to the camera 121 to reduce the amount of unwanted energy being received by the camera 121 to improve the signal-to-noise ratio of the detected radiation. Example of optical filter(s) can be for example one or more filter selected in a group comprising: a bandpass filter, a narrowband filter, an optical edge filter, a notch filter, or a wideband filter purchased from, for example, Barr Associates, Inc. or from Andover Corporation.

Possible embodiments of the system controller 101, e.g. control unit 101, can be used to facilitate the control and automation of the overall screen printing system 110 and may include at least one of the elements selected in a group including: a central processing unit (CPU) (not shown), memory (not shown), and support circuits (or I/O) (not shown). For example, the CPU may be one of any form of computer processors that can be used in industrial settings for controlling various chamber processes and hardware (e.g., conveyors, optical inspection assemblies, motors, fluid delivery hardware, etc.) and monitor the system and chamber processes (e.g., substrate position, process time, detector signal, etc.). The memory can be connected to the CPU, and may be one or more of a readily available memory, such as random access memory (RAM), read only memory (ROM), floppy disk, hard disk, mass memory or any other form of digital storage, local or remote. Software instructions and data can be for example coded and stored within the memory for instructing the CPU. The support circuits can be also connected to the CPU for supporting the processor in a conventional manner. The support circuits may include for example at least one of: cache, power supplies, clock circuits, input/output circuitry, subsystems, and the like. A program (or computer instructions) readable by the system controller 101 can determine which tasks are performable on a substrate. In some embodiments, the program is software readable by the system controller 101. The controller 101 includes code to generate and store at least substrate positional information, the sequence of movement of the various controlled components, substrate optical inspection system information, and any other corresponding combination.

Embodiments of the method for printing on a substrate as described herein can be included in a computer program memorizable in a mean readable by a computer that contains the instructions which, when carried out by the controller 101, determine the execution of the printing method by means of a screen printing system 110.

According to one aspect, an apparatus for screen printing on a substrate, the apparatus includes a substrate support configured to support the substrate for screen printing, and a sensor assembly configured to detect a force or pressure from which a printing force on the substrate can be determined.

The sensor assembly may include at least one first sensor provided at the substrate support.

The apparatus may further include a printing tool, wherein the sensor assembly includes at least one second sensor provided at the printing tool.

The sensor assembly may further include at least one third sensor provided at the substrate support, particularly at least one third sensor, one fourth sensor and one fifth sensor provided at the substrate support.

The apparatus may further includes a printing mask and a printing tool, wherein the printing tool may be configured to move along at least one direction on the printing mask during printing, wherein the sensor assembly may be connected to a control unit, and wherein the control unit may be configured to vary the force applied by the printing tool towards the substrate such that the printing force on the substrate is adjusted, particularly to be essentially constant, when moving along said least one direction.

The apparatus may further include at least one actuation member controlled by the control unit to actuate said printing tool with a force that varies along said at least one direction.

The control unit may be configured to vary said force of the printing tool according to a signal of the sensor assembly, particularly wherein a reaction force of said printing mask is taken into account.

According to another aspect, a method for screen printing on a substrate includes varying a force of a printing tool of a printing apparatus, wherein the force is directed towards the substrate, to compensate for variations in the force of the printing apparatus on the substrate along a printing path.

The method may include actuating the printing tool to vary the force along said printing path.

Said force may be varied along the printing path as a function of the position of said printing tool with respect to a printing mask of said printing apparatus.

Said force may be varied along said printing path according to a reaction force of said printing mask and/or a signal of a sensor assembly.

The method may include detecting the reaction force of said printing mask before, or during, one or more printing operations.

The detecting the reaction force may provide to move the printing tool toward said printing mask in order to deform and lower said printing mask by a first distance with respect to a non-stressed condition of said printing mask.

The method may include the calculation of the force of the printing tool, correlated to said reaction force.

The method may include modifying said force of the printing tool if a deviation in the force of the printing apparatus on the substrate is detected.

While the foregoing is directed to embodiments described herein, other and further embodiments may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

1. An apparatus for screen printing on a substrate (250), the apparatus includes: a substrate support (131) configured to support the substrate (250) for screen printing; and

a sensor assembly (400) configured to detect a force or pressure from which a printing force on the substrate (250) can be determined,

wherein the sensor assembly (400) includes at least one first sensor (325) provided at the substrate support (131), and wherein the at least one sensor (325) is adapted to detect the force or pressure during printing operations.

2. The apparatus in accordance with claim 1, further including:

a printing tool (311), wherein the sensor assembly includes at least one second sensor (322) provided at the printing tool (311).

3. The apparatus in accordance with any of claims 2 or 3, wherein the sensor assembly (400) further includes at least one third sensor (325) provided at the substrate support (131), particularly at least one third sensor (325), one fourth sensor (325) and one fifth sensor (325) provided at the substrate support (131).

4. The apparatus in accordance with claim 1, further including:

a printing mask (102B);

a printing tool (131);

wherein the printing tool (311) is configured to move along at least one direction on the printing mask (102B) during printing, wherein the sensor assembly (400) is connected to a control unit (101), and wherein the control unit (101) is configured to vary the force applied by the printing tool (311) towards the substrate (250) such that the printing force on the substrate (250) is adjusted, particularly to be essentially constant, when moving along said least one direction.

5. The apparatus in accordance with claim 4, further including:

- at least one actuation member (312 A, 312B, 312C) controlled by the control unit (101) to actuate said printing tool (311) with a force that varies along said at least one direction.

6. The apparatus in accordance with claims 4 or 5, wherein the control unit (101) is configured to vary said force of the printing tool (311) according to a signal of the sensor assembly (400), particularly wherein a reaction force (Fr) of said printing mask (102B) is taken into account.

7. A method for screen printing on a substrate (250), the method includes:

- vary a force of a printing tool (311) of a printing apparatus (300), wherein the force is directed towards the substrate (250), to compensate for variations in the force of the printing apparatus (300) on the substrate (250) along a printing path (P), wherein the force is detected during printing operations by at least one sensor (325) provided at a substrate support (131).

8. The method in accordance with claim 7, including actuating the printing tool (311) to vary the force along said printing path (P).

9. The method in accordance with claim 8, wherein said force is varied along the printing path (P) as a function of the position of said printing tool (311) with respect to a printing mask (102B) of said printing apparatus (300).

10. The method in accordance with claim 9, wherein said force is varied along said printing path (P) according to a reaction force (Fr) of said printing mask (102B) and/or a signal of a sensor assembly (400).

11. The method in accordance with claim 10, including detecting the reaction force (Fr) of said printing mask (102B) before, or during, one or more printing operations.

12. The method in accordance with claim 11, wherein detecting the reaction force (Fr) provides to move the printing tool (311) toward said printing mask (102B) in order to deform and lower said printing mask (102B) by a first distance (S) with respect to a non-stressed condition of said printing mask (102B).

13. The method in accordance with claim 11 or 12, including the calculation of the force of the printing tool (311), correlated to said reaction force (Fr).

14. The method in accordance with any of claims from 7 to 13, including modifying said force of the printing tool (311) if a deviation in the force of the printing apparatus (300) on the substrate (250) is detected.

15. A method for printing a paste on a substrate using a screen, the method comprising:

moving a printing tool over the screen at a screen force for coating the substrate with a paste;

measuring the substrate force the printing tool is exerting on the substrate; and changing the screen force depending on the measured substrate force.