JPH0338090A - Screen-printing of pasty substance - Google Patents

Abstract

PURPOSE:To shorten the setting time of printing items and improve the printing quality by previously preparing a current-viscosity collation chart according to desirably-set various printing items and driving a squeezee in accordance with the printing items, and then, discriminating the viscosity of a pasty substance. CONSTITUTION:A current-viscosity collation chart 25 between the input current of a DC motor 20 for driving a squeezee 15 and the viscosity of a pasty substance 5 which is used as a printing medium is previously prepared under such desirably set printing items as squeezee pressing force and squeezee running speed. Then, when screen printing is performed on a circuit substrate 1, a blind patch of the same material as that of a screen 10 is used and the input current of the motor 20 is measured by driving the squeezee 15 under the printing items used for preparing the chart 25 so as to confirm the optimum printing items corresponding to the viscosity obtained from the chart 25. Then the confirmed items are adopted to the used screen 10 so that the screen printing can be performed under the optimum printing items. Therefore, screen printing which is reduced in printing item setting time and stabilized in quality can be realized.

Description

[Detailed Description of the Invention] [Summary] This invention relates to a screen printing method, especially a screen printing method for a paste-like substance with a large change in viscosity, and the present invention relates to a screen-printing method for a paste-like substance that takes a short time to set printing specifications and has stable quality. The purpose of this method is to provide a method for pressing a squeegee that is set as desired based on the printing specifications of force and squeegee running speed, the input current of the DC motor that drives the squeegee, and the viscosity of the paste-like substance that becomes the printing medium. of,
A current/viscosity comparison chart is created in advance, and when screen printing a circuit board using the paste-like substance, the squeegee is driven with the printing specifications and the input current of the DC motor is measured. The viscosity of the pasty substance at the time of printing is determined, and printing is started using the optimum printing specifications corresponding to the determined viscosity.

[Industrial application field]

The present invention relates to a screen printing method, and particularly to a screen printing method for a paste-like material whose viscosity changes greatly.

To surface-mount chip components on a circuit board, screen print cream solder to form a pattern with the desired shape and desired thickness at a predetermined location on the circuit board, and position the electrodes of the chip component on that pattern. It is common to perform reflow soldering after aligning and temporarily bonding.

[Conventional technology]

FIG. 2 is a sectional view showing the main parts of the screen printing machine.

In FIG. 2, reference numeral 1 denotes a circuit board on which chip components are mounted, and is placed at a predetermined position on a base 2 of a screen printing machine.

Reference numeral 5 denotes a printing medium, which is, for example, a paste-like substance such as cream solder. 6 is a pattern of a desired shape obtained on the surface of the circuit board 1 by screen printing the paste material 5.

Reference numeral 10 denotes a screen made of a thin stainless steel plate or the like, with mask holes 11 provided at locations corresponding to the patterns 6.

A squeegee 15 is made of, for example, urethane rubber, and its upper end is held by a squeegee holder 16.

By fixing the squeegee holder 16 to the lower end of the air cylinder 17, the squeegee pressing force (the force with which the squeegee 15 presses the screen 10) can be adjusted as desired.

Reference numeral 19 denotes a drive screw that imparts running and reciprocating motion to the squeegee 15. Reference numeral 18 denotes a female screw member that is screwed into the drive screw 19, and the air cylinder 17 is fixed to the female screw member 18.

Further, the female threaded member 18 is provided with a guide hole parallel to the screw hole, and a guide bar (not shown) parallel to the drive screw 19 is inserted into this Gantt hole.

Therefore, the DC motor (DC motor 20 in FIG.
) when the drive screw 19 is rotated, the rotational motion of the motor is converted into linear motion, and the internally threaded member 18. That is, the air cylinder 17 moves in a straight line, and the squeegee 15 moves toward the screen 10.
Slide on the top.

In this case, it goes without saying that the squeegee running speed is determined by the rotational speed of the DC motor.

In addition, by using the drive screw 19 as a ball screw and screwing it into the female screw member 18 via a ball, a highly efficient screw mechanism can be achieved.

In the above-mentioned configuration, the screen 10 is set on the surface of the circuit board l, and the paste-like substance 5 is put on the upper surface of the screen lO, and then the squeegee 15 is run to spread the paste-like substance 5 onto the surface of the screen lO. A pattern 6 made of the paste-like material 5 is formed on the surface of the circuit board 1 by applying the paste-like material 5 so as to press it against the surface of the circuit board 1 and transferring the paste-like material 5 from the mask hole 11 onto the surface of the circuit board 1.

On the other hand, the print quality of screen printing is influenced by printing specifications (squeegee running speed and squeegee pressing force), and the printing specifications are mainly determined by the viscosity of the paste material 5.

Therefore, conventionally, each time screen printing is started, the viscosity of the paste substance 5 at that point is measured, the optimum printing specifications are set, and based on the printing specifications,
Screen printing is performed.

For example, when the viscosity of the paste-like substance 5 is high, printing quality is improved by increasing the squeegee pressing force and slowing down the squeegee running speed.

[Problem to be solved by the invention]

However, when the paste-like substance is cream solder, its viscosity not only differs depending on the composition of the cream solder, but also changes depending on the length of time it is left in the air, such that the viscosity increases as the time it is left in the air is longer.

On the other hand, when the viscosity of cream solder is measured using a viscometer, a normal viscometer has a large variation and a measurement error of about ±30%.

Therefore, conventionally, each time you start screen printing,
The cream solder is placed in a container, the worker stirs the cream solder, and the viscosity is estimated by the feel of the stirring. Next, print specifications that are considered appropriate for the viscosity (squeegee running speed,
Printing is performed using the circuit board that becomes the product by pressing the squeegee (force). Then, the printing quality is checked, the printing specifications are corrected, and the next new circuit board is printed.

That is, the conventional screen printing method has problems in that it takes a lot of time to set printing specifications and in that the print quality at the initial stage of printing is poor.

The present invention was created in view of these points, and an object of the present invention is to provide a screen printing method for paste-like materials that requires a short time to set printing specifications and has stable quality.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a direct current motor 20 that drives the squeegee 15 under the printing specifications of the desired squeegee pressing force and squeegee running speed, as illustrated in FIG. A current/viscosity comparison chart 25 between the input current and the viscosity of the paste-like substance 5 serving as the printing medium is created in advance.

When screen printing the paste-like substance 5 on the circuit board l, the squeegee 15 is driven according to the printing specifications and the input current of the DC motor 20 is measured, so that the paste-like substance 5 can be printed at that point. The viscosity is determined, and screen printing is started using the optimal printing specifications corresponding to the determined viscosity.

[Effect]

The optimum printing specifications for the viscosity of pasty substances can be found in the materials provided by the manufacturer of the screen printing machine.

It is known from past experimental data.

Furthermore, when the squeegee pressing force and squeegee running speed are constant, as the viscosity of the paste substance increases, a proportionately larger squeegee driving force is required.

On the other hand, when the rotational speed is constant (that is, the squeegee running speed is constant), the input current and rotational torque of the DC motor that drives the squeegee are proportional.

That is, when printing is performed under the printing specifications of the desired squeegee pressing force and squeegee running speed, the input current of the DC motor is proportional to the viscosity of the paste-like substance.

Therefore, as in the method of the present invention, a current/viscosity contrast chart of the input current of the DC motor and the viscosity of the paste-like material is created in advance, and when starting screen printing using the paste-like material, By driving the squeegee with the above specifications and measuring the input current of the DC motor, the viscosity at that point can be determined.

Therefore, it is possible to select the optimum printing specifications for the viscosity of the paste material at that time. That is, the time required to set printing specifications is significantly reduced.

On the other hand, the screen used in the viscosity measurement according to the method of the present invention may be a simple blind plate made of the same material as the screen and without mask holes, without using a screen provided with mask holes. Therefore, since the first set circuit board is not subjected to trial printing, high-quality printed circuit boards can be obtained from the beginning of printing.

〔Example〕

The present invention will be specifically described below with reference to the drawings. Note that the same reference numerals indicate the same objects throughout the figures.

FIG. 1 is a block diagram showing the method of the present invention, in which a circuit board 1 to be printed is placed at a predetermined position on a base 2 of a screen printing machine.

On the other hand, a screen 10 provided with mask holes 11 at locations corresponding to patterns 6 to be printed is set so as to be adhered to the surface of the circuit board l.

The squeegee 15, whose lower edge presses the surface of the screen 10 and performs a sliding movement, is held at its upper end by a squeegee holder 16, which is fixed to the lower end of the air cylinder 17.

A female screw member 18 is fixed to the air cylinder 17, and the female screw member 18 is screwed into a drive screw 19 parallel to the circuit board l. The drive screw 19 is connected to a DC motor 20, and an ammeter 22 is set in a power supply circuit 21 of the DC motor 20.

As configured as described above, when the DC motor 20 is driven, the drive screw 19 rotates, the rotational motion is converted into linear motion via the female threaded member 18, and the air cylinder 17, that is, the squeegee 15 is linearly interlocked. and slides on the screen IO.

Note that by adjusting the rotation speed of the DC motor 20, a desired squeegee running speed can be obtained.

Further, by adjusting the air pressure that drives the air cylinder 17, the force of pressing the squeegee can be adjusted as desired.

In the method of the present invention, a current/viscosity contrast chart 25 is prepared in advance in the following manner using a screen printing machine configured as described above.

Paste-like substance (cream solder) 5 on the screen IO
is applied, and the printing specifications set as desired, that is, the predetermined squeegee pressing force (e.g. 2 kg) and the predetermined squeegee running speed (e.g. 20 m/s) are applied, and the input current at that time and the paste form are determined. Record the viscosity of material '15.

Next, by changing the viscosity of the paste substance 5, the DC motor 2
0, and the input current at that time and the paste-like substance 5
Record the viscosity.

Repeat the above to create a current/viscosity comparison chart. In the method of the present invention, as shown in FIG. 1, the scale board for displaying the current value of the ammeter 22 is accompanied by the viscosity value to form a current/viscosity contrast chart 25.

The viscosity of the paste-like substance entered in this current/viscosity comparison chart 25 is measured by repeatedly measuring the same sample several times using the viscometer described in the materials provided by the manufacturer of the screen printing machine, and using the average value. Of course, it is necessary to eliminate errors.

Note that the current/viscosity comparison chart may be created as follows.

That is, without measuring the viscosity of the paste substance 5 using a commercially available viscometer, first print the paste substance 5 of any viscosity whose display value on the viscometer is unknown using the printing specifications described above. Measure the input current.

Subsequently, screen printing is actually performed using a paste-like substance of that viscosity, and the optimum printing specifications for that viscosity are experimentally determined.

Next, change the viscosity and repeat the above to find the input current and optimal printing specifications.

Repeat the above to create a comparison chart of different input currents and the optimum printing specifications at those current values.

Therefore, the viscosity described in the current/viscosity comparison chart in this case is not the viscosity shown on the viscometer, but a mere symbol (a symbol in place of the printed specifications).

The current/viscosity comparison chart 25 as described above is created at the time of purchase of the screen printing machine.

When actually screen printing the circuit board l using the paste material 5, a simple blind plate without mask holes made of the same material as the screen is used, and the squeegee 15 is moved to meet the printing specifications (current, viscosity, etc.). The input current of the DC motor 20 is measured.

Then, confirm the optimal printing specifications corresponding to the viscosity obtained from the current/viscosity comparison chart 25, replace the blind screen plate used for viscosity measurement with the screen printing to be used, and screen with the optimal printing specifications. Perform printing.

Since the above-described screen printing method is used, the time required to set the printing specifications is almost the same as the time required for one screen printing, and is therefore short.

Furthermore, since there is no need to use a screen with mask holes for the screen used for viscosity measurement, the printing quality is high and stable from the first circuit board set.

It goes without saying that the paste-like substance of the present invention is effective when applied not only to cream solder but also to other paste-like substances whose viscosity easily changes.

〔Effect of the invention〕

As explained above, in the present invention, a current/viscosity contrast chart is created in advance under desired printing specifications, and a squeegee is driven using the printing specifications during screen printing to form a paste at that point. This is a printing method for determining the viscosity of a substance, and has excellent practical effects in that it takes a short time to set printing parameters and the printing quality is high and stable.

[Brief explanation of drawings]

FIG. 1 is a component diagram showing the method of the present invention, and FIG. 2 is a sectional view showing the main parts of a screen printing machine. In the figure, l is a circuit board, 2 is a base, 5 is a paste-like substance, 6 is a pattern, IO is a screen,
11 is a mask hole, 15 is a squeegee, 1
6 is a squeegee holder, 17 is an air cylinder, 1
8 is a female screw member, 19 is a drive screw, 20 is a DC motor 22 is an ammeter, and 25 is a current/viscosity comparison chart.

Claims (1)

[Claims] Under the printing specifications of the squeegee pressing force and squeegee running speed set as desired, the input current of the DC motor (20) that drives the squeegee (15) and the paste-like material ( Current/viscosity comparison chart (25) with the viscosity of 5)
is prepared in advance, and when screen printing the circuit board (1) using the paste-like substance (5), the input current of the DC motor (20) is controlled by driving the squeegee (15) according to the printing specifications. The viscosity of the paste-like substance (5) at the time of printing is determined by measuring the viscosity of the paste-like substance (5), and printing is started with the optimum printing specifications corresponding to the determined viscosity. Screen printing method.