JPH0431199B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an apparatus for soldering printed circuit panels, i.e. printed circuit boards.

BACKGROUND OF THE INVENTION Printed circuits are manufactured having a variety of major length and width dimensions, and include one or more circuits;
The thickness of printed circuit boards can vary for many different reasons, and the thickness directly affects the flexibility of the board.

For example, printed circuits with multilayer conductor arrays use one or more bonded insulating layers to provide isolation between the layers. Holes formed through circuit boards are provided for many purposes, such as as solder terminals for attachment to another assembly, and for interconnection between multiple conductor array planes. Used as a plated through hole and as an alignment hole for instruments.

Exposed copper on the finished circuit must be covered with solder, with some exceptions. This is often referred to as presoldering. Also, it is preferable not to apply solder over all of the conductor paths, but only where it will be needed later. In order to selectively apply solder, an insulating material called a cover insulation mask or solder mask is used to cover copper parts that do not need to be covered with solder. Copper parts that need to be soldered, such as terminal pads, are left exposed and covered with solder. In other words, only the exposed copper portions on the surface of the printed circuit are solder coated.

It is also necessary to apply solder to the inner wall of the through hole that penetrates the printed circuit, and
It is necessary that these holes are not filled with solder, since if they are filled with solder when finished, it will interfere with the subsequent insertion work. The process of removing the solder that has blocked the hole from the hole is called leveling.

In particular, printed circuit boards are pre-soldered, inter alia, to facilitate soldering for subsequent operations. To be economical, such pre-solder processing must be performed as a bulk substrate coating technique. Known solder coating techniques include electrolytic plating and a technique of performing high temperature reflow after electrolytic plating. This high temperature reflow may be performed using infrared reflow techniques, high temperature liquid reflow, or high temperature vapor reflow. Another high volume solder coating technique is hot roller coating. Furthermore, techniques for performing high temperature immersion dips and high temperature leveling after high temperature immersion dips are also known. In this latter case,
Leveling can be performed by hot liquid leveling, hot steam leveling or hot gas leveling.

The last mentioned technique of immersion dip followed by high temperature leveling has been found to be most effective for many printed circuit applications.

The machines currently available for selective solder coating and hot air leveling apply the solder by vertically dipping the board into hot molten solder. Exposing the board to a hot blast of air as it is lifted from the liquid solder levels or removes excess solder and leaves all holes clean and free of solder. In these machines,
All operations must be performed manually or in conjunction with vertical and horizontal movement directing mechanisms. For this reason,
The substrates could not be fed continuously and therefore the process could not be economically effective.

Additionally, applying solder coatings in the presence of oxygen tends to be a dirty operation due to the formation of oxides. Therefore, the substrate transport mechanism has become complicated.

Another problem encountered with currently available soldering machines arises from the nature of the materials used in printed circuits, which, other than metal conductors, are sensitive to heat and thermal shock. Therefore, it is essential to accurately control time and temperature in processing operations. Furthermore, when a printed circuit board is dipped vertically into a solder bath, the area that is first dipped into the hot solder will be the last to be pulled out. In the case of thin, flexible boards often used in printed circuits, rapid immersion in hot liquid solder can cause
The board may be bent or warped, the board may be damaged, and subsequent leveling using high-temperature air may no longer be performed effectively. For these reasons, the gentle insertion of the printed circuit board into molten solder, the use of special fixtures, and the use of extensive time-temperature exposures across the printed circuit board, all of which This is not desirable.

Solder Removal technology is a technology for selectively soldering and leveling printed circuits.
Technique) is disclosed in US Pat. No. 4,315,042. The method and apparatus disclosed in that patent suffer from various drawbacks as described above. In particular, this method cannot be made continuous to be efficient and economical.

Another technique for applying solder to printed circuits is the use of so-called wave soldering equipment.
The printed circuit is passed through a wave of solder, and the solder is applied to one side of the printed circuit board. This technique has the disadvantage that many printed circuit configurations require two operations to apply solder to both sides.

SUMMARY OF THE INVENTION The present invention provides an apparatus for selectively soldering and leveling printed circuit boards in a continuous manner. In particular, a roll arrangement is mounted to horizontally transport the printed circuit board across a container containing molten solder. As the printed circuit board is moved horizontally through this roll arrangement, it is immersed in the molten solder. At least one air knife located on the exit side of the roll arrangement serves to level the molten solder on the substrate as it emerges from the roll arrangement.

In one embodiment of the invention, two pairs of rolls serve to transport a printed circuit board through a solder conduit or channel formed therebetween, the solder conduit containing molten solder flowing therealong. There is. The printed circuit board is passed through a first pair of rolls that act as a barrier and boundary on one side of the solder conduit containing the solder, and then passed through the flowing solder. Furthermore, the printed circuit board
It exits the solder through a second pair of rolls that form the other boundary of the flowing solder. An air knife assembly is provided adjacent another pair of rolls that serve to transport the printed circuit board for leveling the molten solder as the printed circuit board exits the roll pair.

Each pair of rolls described above is attached so as to be pushed away from each other by a printed circuit board. With this configuration, printed circuits of various thicknesses can be passed through the roll structure.
In other words, thin flexible printed circuit boards and thicker, more rigid boards can be selectively soldered and leveled by the apparatus of the present invention.

Effect When the method and apparatus of the present invention are used, both sides of various printed circuit boards can be quickly and efficiently soldered simultaneously. If desired,
This process can be easily automated to be efficient and economical. Furthermore, by transporting the board horizontally, the parts of the board that enter the solder first come out first. It is relatively easy to control the transport speed through the solder, control the temperature of the solder, and control and eliminate the oxide contamination that naturally occurs when soldering is performed in the presence of oxygen.

EXAMPLES Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

To explain FIG. 1, the desk-shaped device 10 is
Conveniently accommodates numerous components of the present invention. The entry slot 11 for the printed circuit board to be soldered opens into horizontally arranged rolls, which are protected by removable covers, as will be described in detail below. . A cabinet 12, suitably accessible through doors, covers, etc., contains power supplies and other necessary elements for heating the solder and providing heated pressurized air for the air knife. It is accommodated. Plate 13a
The control panel 13 at the rear (FIG. 2) includes controls for controlling the solder pot temperature and the air heater temperature, an on/off motor control for the roll, a speed control for the motor, a ventilation It supports the controller and other necessary switches and gauges. Removable hood 14 and plenum 1
5 is suitably connected to an exhaust line (not shown) at outlet 16 for proper venting of the device. Outlet slot 17 leading from the horizontal roll
is provided for taking out the soldered and leveled printed circuit board.

Next, referring to FIGS. 3 and 4, a pair of rolls 20 and 21, which are shown in phantom lines in FIG. 3 for clarity, cross a container 23 filled with molten solder 24. It works to transport printed circuit boards horizontally. Suitable heaters on the walls and/or bottom of container 23 and suitable temperature sensors control solder 24 to a desired temperature, typically
Used to maintain a temperature at least about 38°C (100°C) above its melting point. Approximately 260℃ (approximately 500
It was found that the temperature of 〓) was satisfactory. If necessary, additional transport rolls or other transport means may be used to transport the printed circuit board to the introduction rolls 20 and 21.
can be sent to.

Rolls 25 and 26 receive the printed circuit boards from rolls 21 and 22 and send them to transport rolls 27 and 28, which are preferably not wetted with solder.
Although titanium rolls have been found satisfactory, ceramic rolls can also be used. Air knives 29 and 3 located near the exit of the horizontal roll arrangement
0 receives heated air via a conduit from a compressor located within the cabinet 12. The temperature, pressure and volume of air for these knives are regulated by appropriate controls on the control panel 13. If desired, additional rolls or pairs of rolls or other suitable conveyors may be used to further transport the printed circuit board after it has been selectively soldered and leveled.

A solder conduit or channel 31 is provided for applying solder to the printed circuit traveling along the path indicated by dashed line 9. Molten solder flows along this solder conduit 31 as indicated by arrow 32. solder conduit 31
are a pair of rolls 20 and 21, a pair of rolls 2
5, 26, the upper part 33 of the supply plenum chamber 34 and the upper plate 36. A support plate 37 on the inlet side of the solder conduit supports rolls 20, 21 and 25, 26 and is attached to supply plenum chamber 34. Plates 38 and 39 extend a short distance along the roll and define the beginning of the solder flow. A support plate 40 mounted at the other end of the supply plenum chamber holds the rolls 20, 21 and 25, 26 and includes slots 41 through which molten solder can be discharged from the solder conduit 31.

An upper solder channel 42 through which the solder flows, as indicated by arrow 43, is formed by the upper surface of plate 36. The solder flow is distributed through the dispersion wedge 4.
Controlled by 4. The solder is pumped through the opening 45 at the top end of the supply plenum chamber.
The overflowing solder flows into the solder conduit 31 and flows along the upper solder channel 42.

A solder pump 46, immersed in the molten solder and driven by a motor 47, has a pump outlet 54 connected to an inlet 55 of the supply plenum chamber. Molten solder 24 is pumped through inlet 55 and supply plenum chamber 34 through a perforated buffle formed by opening 56 in wall 57 at the end of the supply plenum chamber. This buffer is for stabilizing the flow of solder. Arrow 48 shows the solder entering the pump, and arrows 49, 50, 51 and 52 show the flow of pumped solder through the supply plenum chamber towards opening 45, which solder enters the solder conduit 31 above the supply plenum chamber. distributed, and a portion spills into the solder channel channel 42.

The inlet of tube 53 connected to pump 46 is above the molten solder level and below the oil level, as explained below.

Motor 58 drives a suitable gear arrangement mounted on drive housing 59. shaft 60
rolls 20, 21, 25 and 2 from the housing.
It extends to 6. Roll 20, 21; 25, 2
6, 27, and 28 are mounted to accept printed circuits of various thicknesses. As shown, the U-shaped slot 61 and the free drive coupling to the upper shaft 60 allow the upper rolls 20 and 25 to move freely upwardly and vertically. At the other end of the roll, a U-shaped slot 62 is journalled to the shafts of the upper rolls 20 and 25, and an opening 64 is journalled to the shaft 66 of the lower roll.

Rolls 27 and 28 are also provided with suitable drive and mounting means (not shown) to accommodate printed circuit boards of various thicknesses.

As shown, the roll structure passes the printed circuit board straight through without bending the printed circuit board. Therefore, both so-called rigid printed circuit boards and flexible printed circuit boards can be processed. of course,
In this regard, it should be understood that "rigidity" and "flexibility" are relative terms. Stiffness, i.e.
Stiffness is a function of the cross-sectional dimensions, the number of different layers included within the cross-section, and the mechanical and thermal properties of the materials used. Thick substrates generate large internal stresses when bent and also require large forces to bend. Bending thick substrates is undesirable since there is a risk of internal damage to the substrate or permanent deformation of the substrate. On the other hand, thin flexible printed circuit boards have little resistance to external forces and are generally difficult to handle. This embodiment of the invention is configured to handle both types of printed circuit boards.

For proper operation of the device, roll 2
0, 21, 25 and 26 must be wetted with molten solder. For example, rolls of nickel have been found to be satisfactorily used.

a wet roll 20 serving as a boundary for the solder conduit 31 and the upper solder channel 42;
The use of 21, 25 and 26 prevents foreign matter such as residual flux and other contaminants from adhering to the rolls. If this were to occur, there would be a constant flow of fresh solder delivered from the molten solder by the partially immersed lower rolls 21 and 26 and the solder flowing into the solder conduit 31 and solder channel 42. It can be easily washed off. Nickel or alloys with high nickel content can be used in these rolls. Pure nickel is an excellent material because it is wetted by molten solder and has low solubility in eutectic solder at 260°C (500°C).

In order to understand the soldering process performed by the apparatus of the present invention, reference will be made to FIG. 3, which shows the flow of liquid solder using the arrows mentioned above. Therefore, the pump 46
flows the solder through supply plenum chamber 34 and opening 45 . Plates 37, 38 and 39 confine the molten solder and create laminar flow in the solder conduit 31 above the supply plenum chamber and below plate 36, and rolls 20, 21 and 25, 26 Acts as a boundary. The top plate 36 of the solder conduit 31 serves the function of limiting the floating of the substrate through which the solder is passed. The overflowing solder flows along the solder channel 42. The solder within solder conduit 31 is under some pressure due to its restricted flow. The dimensions of the solder conduit 31 are as follows: rolls 25, 26 and 2.
When the printed circuit board is sent by 7 and 28,
It is made large enough so as not to impede movement of the substrate.

In this structure, solder conduit 31 and solder channels 42 flow when the substrate is not being processed. From here, the solder is returned to the solder container as shown in FIG. Preferably, the roll and solder conduit and solder channel are laterally offset slightly in height so that the end of the roll is higher on the solder inlet side. However, this height difference is kept small to minimize the occurrence of turbulence and thus avoid unnecessary oxide formation.

Overflowing solder pumped from the supply plenum chamber through opening 45 flows along top plate 36 and
It is directed to the roll by a dispersing wedge 44.
This further wets the roll with solder and cleans it, preventing contamination. The solder from the solder channel is then returned to the solder reservoir in container 23.

It has been found desirable to use an oil film to prevent oxygen from contacting the solder surfaces within the solder pool to minimize scum formation. The oil also combines with the oxides formed when the film breaks down. The oil, when injected into the solder stream through the fluid injector 53 of the pump 46, improves heat transfer and reduces surface tension to thoroughly wet the nickel roll and improve solderability of the printed circuit board. make it possible. The oil also increases the thermal stability of flux and other residues reaching the solder puddle, minimizing the formation of solids. Oil improves the lubricity of moving parts above and below the solder surface.
Preferably, the oil used is one that melts at high temperatures.

When a printed circuit board is to be processed, solder flux is typically applied to both sides of the board. Next, the printed circuit board is sent to the slot 11 and rolled to the roll 20.
and sent to 21. Thereafter, the printed circuit board is passed through flowing molten solder in solder conduit 31 to rolls 25 and 26, and from there to rolls 27 and 28. The printed circuit board is then exposed to heated air from air knife 29 in the case of thin flexible printed circuit boards or to both air knives 29 and 30 when processing thick rigid boards. be done.

The air knife is a small, simple design and does not include a heater in the nozzle. Such heaters increase the size of the knife and have adverse hydrodynamic effects. The size of the air knife is sufficient to effectively pass hot compressed air to create a maximum pressure drop at the exit orifice. Solder can be quickly removed by a jet of air with minimal splashing. This is in contrast to conventional air knives, which use two opposing nozzles and heat the air internally. It is difficult to achieve mechanical balance with directly opposed nozzles. Failure to achieve mechanical balance will result in more solder being deposited on one side of the circuit board than on the other. Using a single nozzle 29 as shown in FIG. 5 or staggered nozzles 29 and 30 as shown in FIG. Solder waves 29a are formed on the printed circuit board 70 immediately behind. The exit roll may be made of titanium or ceramic material that is not solder wettable, as previously described. This process effectively removes the solder from holes 71 (schematically shown) in the substrate.

Under certain conditions, the upper rolls 20 and 25
It is necessary to use a non-rotating heater located axially inside the However, if these upper rolls are set in contact with lower rolls 21 and 26 partially immersed in molten solder 24 and provided with a well-insulated hermetic mounting cover,
Heat transfer from the liquid solder alone is sufficient to maintain the upper roll at the appropriate temperature. Additionally, choosing a suitable material for the top roll, ie, a material with good thermal conductivity, low specific heat, and appropriate dimensions, will help maintain the roll at the proper temperature. However, if required for a particular application, one or both of the rolls may be conventionally heated by internal heaters.

The temperature of the air jet from the knife 29 or the knives 29 and 30 must not be such that it will completely solidify the solder immediately to the point where it contacts the substrate. Rather, the solder should be allowed to fully solidify after the surface has hardened to a naturally smooth appearance under the action of the surface tension of the solder fluid. The effects of the horizontal processing of the present invention are as follows:
This prevents so-called solder dripping. In vertical machines, the solder joints sag under the weight, but with the horizontal configuration of the present invention, this does not occur.

The location of the air heater within the cabinet 12 is determined for convenience and safety considerations. The operator is protected from injury and maintenance of the knife is such that only occasional cleaning of the orifice is required.

An important advantage provided by this embodiment of the invention is that only the exposed copper parts on both sides of the printed circuit board are soldered, while the entire circuit board is exposed to high soldering temperatures for a very short time. That's true. Further advantages include improved control of the soldering and leveling process, the device can be easily integrated into fully automated equipment, no special mounting equipment is required for processing printed circuit boards, and Space and energy efficiency is considerably improved compared to known soldering and leveling processes.

The apparatus described with respect to FIGS. 1-5 can be used to process both rigid and flexible printed circuit boards.

The processing apparatus shown in FIGS. 1-5 naturally causes the portion of the substrate that first enters the liquid solder to be the first to be removed from the solder. Furthermore,
The speed of the rolls can be adjusted over a wide range, and the volume of the solder container and the energy required to heat the solder are low relative to the processing capacity of the equipment. Additionally, contamination of the solder by the copper being processed is reduced by the short time the board is immersed in the solder. Therefore, the frequency with which the solder has to be replaced is considerably lower than with known methods.

The collected oxides can also be removed by applying a salt to the roll that converts the oxides to sludge. This salt can also be used as a roll cleaning flux. The last roll, if made of titanium, can be cleaned with water if a water-soluble flux is used, or with a solvent if a solvent-soluble flux is used for the printed circuit board.

Although the apparatus of the invention has been described in terms of specific embodiments, it will be understood that various modifications will be apparent to those skilled in the art, and that the invention is defined only by the scope of the claims.

[Brief explanation of drawings]

FIG. 1 is a front perspective view of an apparatus of the present invention for soldering and leveling printed circuit boards, and FIG.
A perspective view from the rear of the device shown in FIG.
1 is a perspective view of the apparatus of the invention shown in FIG. 1, with the cabinet cover removed and partially disassembled to clearly illustrate the invention; FIG. , a schematic end view of a portion of the apparatus of FIG. 3, and FIG.
FIG. 2 is an enlarged perspective view showing one in detail. 10... Desk device, 11... Entrance slot,
12...cabinet, 13...control panel, 14...
...Hood, 15...Plenum, 16...Exit, 1
7...Exit slot, 20, 21, 25, 26,
27, 28...roll, 23...container, 24...
Melted solder, 29, 30... Air knife, 31...
Solder conduit, 34... Supply plenum room, 36
... Upper plate, 37, 40 ... Support plate, 38, 39 ... Plate, 41 ... Slot, 42 ... Solder channel, 44 ... Dispersion wedge, 45 ... Opening, 46 ... Pump, 47 ...
Motor, 53...Tube, 58...Motor, 5
3... Drive housing, 60... Shaft, 6
1,62...U-shaped slot.

Claims (1)

[Scope of Claims] 1. A container for molten solder, and means for supplying heat to the container to maintain the molten solder at a desired temperature;
a plurality of pairs of rolls mounted in a horizontal configuration to transport printed circuit boards horizontally across the container; two of the plurality of roll pairs; means for attaching the second part so as to be located above the second
and a solder conduit forming means for forming a solder conduit between the two roll pairs, the solder conduit forming means including an upper plate and a lower plate extending horizontally between the two roll pairs. , the upper plate and the lower plate are arranged substantially parallel to each other with a predetermined space therebetween; Solder is pumped into the space between the plates so that the molten solder flows horizontally across the top surface of the bottom plate toward the other ends of the top and bottom plates, where it flows between the plates. and means for pumping the printed circuit board back from the space into the container, the printed circuit board being conveyed through the pair of rolls in the horizontal configuration being conveyed through a horizontal flow of molten solder formed on the upper surface of the lower plate. A soldering processing apparatus for a printed circuit board, characterized in that floating of the printed circuit board due to the molten solder is limited by the lower surface of the upper plate. 2. The pressure feeding means pumps the solder from the container to the upper surface of the upper plate at one end of the upper plate and the lower plate, so that the molten solder horizontally covers the upper surface of the lower plate and the upper surface of the upper plate. 1 . The flow also flows towards the other end of the upper plate and the lower plate and returns to the container at the other end from the space between the plates and the upper surface of the upper plate. The soldering processing device for printed circuit boards described above.