JPH04319068A - Dispersion soldering method - Google Patents

Abstract

PURPOSE:To provide precise soldering method at a low cost. CONSTITUTION:Solder is added in liquid polybutene and stirred under inert atmosphere at a temp. <= m.p. of the solder or to obtain dispersion making the solder finely, and successively, this is brought into contact with the prescribed position in a printed wiring board. Molten solder dispersed in the polybutene is made to fine and therefore, soldering bridge at between fine wires in the fine wiring pattern can be avoided, and as the solder fine particles are not directly brought into contact with the air or the other part, oxidation and defective soldering are prevented, and the soldering can be used at lower temp., such as at 190-200 deg.C, than the temp. of prior art.

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a soldering method suitable for soldering wiring patterns on printed circuit boards, solder coating, and the like.

(Prior Art) Conventional automatic soldering techniques can be roughly divided into flow soldering and reflow soldering.

[0003] In the flow soldering method, first, adhesive is applied to a predetermined component mounting location on the top surface of a printed wiring board using an adhesive dispenser, the component is mounted using a component mounting device, and then the adhesive is dried or hardened to attach the component. After fixing,
This is a method of making solder connections between the terminals of components and predetermined conductors by turning the printed wiring board upside down and bringing so-called flow solder, which has been fluidized by heating, into contact with the printed wiring board. This method is economical since no special solder is required.

On the other hand, in the reflow soldering method, a paste or cream mixture of fine solder powder and natural resin is printed on predetermined soldering points on a printed circuit board by screen printing, components are mounted using a component mounting device, and then reflow soldering is performed. This is a method in which the solder is melted by heating in an oven to establish a connection between the component terminal and a predetermined location of the conductor. This method is suitable for soldering fine circuits because the solder is a fine powder, and the soldering temperature can be relatively low.

(Problems to be Solved by the Invention) The flow soldering method has the following drawbacks. (1) Since the solder itself is used in a fluidized manner, if the wiring pattern is a fine circuit, adjacent thin wires will be bridged by the solder and a short circuit will occur, so there is a limit to its application to fine circuits. (2) A high soldering temperature of approximately 250 to 270° C. is required, which may cause variations in the characteristics of the components and energy loss. (3) Since the surface of flow solder bulges in an arc shape due to surface tension at the point of adhesion, the amount of solder adhesion is large and it is difficult to control the film thickness. (4) Since the molten solder is in direct contact with the stirrer and tank, prolonged use can lead to solder contamination.

The reflow soldering method has the following drawbacks. (1) Printing fine circuits by screen printing is difficult;
Printing quality control is troublesome. (2) Since it is difficult to make the temperature distribution uniform in the reflow oven, there is a difference in the surface tension of the remelted solder depending on the location, which tends to cause parts to shift. (3) Although it is not as high as flow soldering, a high temperature of 210 to 240°C is required. (4) Material costs are high because a specially prepared solder paste is used. The present invention aims to solve these problems.

[0007]

SUMMARY OF THE INVENTION The present invention is not an improvement on any of the above-mentioned methods, but provides an improved soldering method based on a novel dispersion soldering principle that does not suffer from the above-mentioned disadvantages. That is, in the present invention, solder is added to liquid polybutene and mechanically stirred in an inert atmosphere at a temperature higher than the melting point of the solder to form a solder dispersion in which the solder is dispersed in fine particles. This is a soldering method characterized by bringing the solder dispersion into contact with a predetermined location on a printed circuit board. The significant difference between the present invention and the flow soldering method is that in the present invention, liquid polybutene is used as a heat medium for solder, and by stirring strongly at a temperature higher than the melting point of the solder, the solder is formed into particles with an average particle size of several microns to several tens of microns. It is at the point of atomization, which causes
It enables application to microcircuits, reduces soldering temperature, controls solder adhesion uniformly, and prevents oxidation by preventing direct contact of solder with air, baths, and stirrers. Also, the significant difference from reflow soldering is that there is no need to use expensive solder paste, there is no need for troublesome process control, and there is no problem of parts shifting due to the use of temporary fixing materials (adhesives or adhesives). There is no point.

The dispersion soldering method of the present invention includes:
It can be applied to any application that requires soldering. For example, there are various methods such as making the dispersion flow and contacting the printed circuit board as in the flow soldering method, immersing the printed circuit board in a stationary dispersion tank, forming a solder film as an external terminal of electronic components, etc. The invention is not limited to the specific applications described below.

More specifically, the dispersion soldering method of the present invention preferably uses 50 vol based on polybutene in an inert atmosphere such as nitrogen or argon.
% or less of tin or tin alloy in liquid polybutene heated to a temperature of preferably 190° C. or higher, using a homogenizer preferably at 5000 revolutions/minute or higher, preferably for 1 minute or longer, and Preferably, by stirring for about 5 minutes or more, the solder is dispersed into fine particles to form a solder dispersion. This dispersion maintains a stable dispersion for about 5 minutes, so
This is guided to a predetermined soldering location on a printed wiring board, etc., and brought into contact with the soldering location on the printed wiring board, etc., while flowing or standing still.

[0010] In order to explore various heat-resistant liquid heating media suitable for dispersion soldering, the present inventor tested a large number of substances and found that they were the only heating medium that could be stably used for long periods of time at temperatures of 190°C or higher. It has been found that only polybutene (commercially available from Nippon Oil Co., Ltd.) satisfies the specified heat resistance and heat transfer requirements. Polybutene (also referred to as polybutylene) is a polymer of 1-butene and 2-butene, and its viscosity varies depending on its molecular weight, but the viscosity suitable for the present invention is about 10,000 cp at room temperature. This one is about 10c at an operating temperature of 190-200℃
It has a viscosity of ps. Furthermore, since polybutene has good heat resistance and is difficult to oxidize, it can be used repeatedly by making up for solder shortages, resulting in a significant reduction in cost. Moreover, polybutene can stably hold the solder dispersion.

During soldering, solder is added to liquid polybutene in an amount of 50 vol % or less based on the polybutene. If the amount of solder exceeds this amount, the solder will not become sufficiently fine particles. The smaller the amount of solder, the easier it is to become atomized. For example, to obtain fine solder particles with an average particle diameter of 10 μm, the amount should be about 5 vol % or less. Then, in a nitrogen gas or argon gas atmosphere, the polybutene bath is heated to 190°C or higher, preferably 190 to 200°C.
The solder is melted by increasing the temperature to , and the bath is vigorously stirred using a homogenizer. As the homogenizer, for example, an ultra-high speed homogenizer manufactured by Polytron can be used. The rotation speed of the homogenizer is 5000 times/min under the above temperature conditions.
For example, to obtain an average particle size of about 10 μm, the speed should be about 10,000 times/min or more. The stirring time is 1 minute or more, for example about 5 minutes. As a result, a dispersion of fine solder particles having an average particle diameter of several microns to several tens of microns can be obtained. If the rotation speed is lower than this, the average particle size of the fine solder powder becomes large and the particle size distribution becomes wide, making it impossible to obtain solder particles with uniform particle size.

If the solder dispersion thus formed is brought into contact with a printed wiring board, etc., the solder in the tank will gradually decrease, and the ratio of polybutene to solder will change, affecting the quality and efficiency of soldering. . Therefore, it is preferable to monitor the solder concentration in the solder-polybutene mixing tank and automatically replenish solder to maintain a predetermined solder concentration. An example of this will be shown later.

(Description of Embodiments) Preferred embodiments of the present invention will be described below. Example Solder (density: 8.42 g) was placed in a beaker with a capacity of 0.5 liters.
/cm3) 20g and heat medium polybutene (density 0
．． 87g/cm3, viscosity at room temperature approximately 10000c
ps) 200 cc (volume ratio 1.2/100) and heated to 200° C. in a nitrogen atmosphere. The viscosity at 200°C was about 10 cps. Homogenizer 10,000 times/
The molten solder was dispersed and atomized by rotary stirring for 5 minutes at a shear rate of 5 minutes to obtain a dispersion. The homogenizer was then removed, and the printed circuit board, on which many square copper-plated sections with different areas had been formed, was immersed in air while maintaining this temperature. The resulting solder adhered to each section as a constant thin layer of solder that varied depending on the immersion time. For comparison, solder was applied to a printed circuit board with the same configuration using the conventional flow soldering method. Compared to the case of the present invention, the center part of the smaller section was raised in an arc shape, and a large amount of solder adhered to the larger section. The stability of the dispersion was also examined and found to have a practical suspension time of about 5 minutes after the homogenizer was removed.

Next, process diagrams for carrying out the present invention are shown in FIGS. 2 and 3.
and 4. First, as shown in Figure 2, install a suitable dispenser 1.
A required amount of adhesive or pressure-sensitive adhesive 3 is applied to a predetermined location of the printed circuit board 2, and then, as shown in FIG. Or fix by drying etc. Finally, the board 2 is turned upside down and, as shown in FIG. 3, the solder dispersion 5 obtained by the method of the present invention is discharged from the nozzle 6 onto the printed circuit board and brought into contact with it to complete the soldering. Since the solder particles are protected by polybutene, this process can be performed in air.

Next, an example of an apparatus for carrying out the method of the present invention will be shown with reference to FIG. Note that in this example, the solder bath for performing soldering is sealed and filled with an inert atmosphere, but even if only this part is exposed to the air, the polybutene effectively blocks the solder from the air, so the solder does not melt. Prevents oxidation and does not cause much trouble. Now, in FIG. 1, a homogenization tank 10 contains a solder/polybutene mixture. The inside of the homogenizer tank 10 is maintained at a temperature that keeps the solder in a molten state by a heater (not shown). A homogenizer 11 is attached to the tank 10, and its blades 12 intensively disperse the solder and polybutene to form a dispersion D in which finely divided solder is dispersed in the polybutene. Nitrogen gas is introduced into tank 10 from nitrogen tank 13 to prevent solder from oxidizing. The thus formed dispersion is guided by a heat-resistant pump 14 to a solder bath 17 via conduits 15 and 16, and is sprayed from a nozzle 18 onto a printed wiring board PCB. Nitrogen gas is preferably introduced into the solder bath 17 from a nitrogen tank 24 to prevent oxidation of the solder. The remaining dispersion returns to the bottom of the homogenization tank 10 via a return line 19. Note that the pipe through which dispersion D flows is kept warm or heated. Also, tanks, baths,
It is advisable to take measures such as lining the pipes and nozzles with stainless steel. In addition, there are two ways to apply the dispersion to the substrate PCB:
You can apply it from above, or you can apply it to both sides (if soldering is required on both sides) as a double flow. Note that since the thickness of solder adhesion on the printed circuit board is a function of the solder concentration, flow rate, and contact time of the dispersion, a predetermined relationship may be appropriately selected.

The conduit 15 is provided with a solder concentration meter 20 that uses, for example, light transmission, and monitors the concentration every moment. The obtained concentration is converted into an electric signal and compared with a limit concentration in a comparator 21. When solder shortage occurs, the control valve 23 of the solder tank 22 is opened to replenish solder.

(Effects of the Invention) As described above, according to the present invention, (1) The molten solder dispersed in polybutene has an average particle diameter of several microns to several tens of microns, for example, about 10 microns, and the solder/ Since the polybutene ratio is low, the solder film thickness can be freely controlled in a state similar to electroplating. Therefore, even if the wiring pattern is a fine circuit, solder bridges between fine lines can be avoided. (2) Since the solder is dispersed in polybutene, it does not come into direct contact with the atmosphere or other parts, so oxidation is prevented and solder defects do not occur. (3) Since polybutene is used as a heat medium, a soldering temperature of 190 to 200° C. can be used, which is lower than conventional soldering temperatures. The above are the main effects, but (4) In the case of flow soldering, the decrease in efficiency due to the lower solder/polybutene ratio compared to flow soldering can be easily compensated for by controlling the flow rate of the dispersion. . (5) Polybutene is heat resistant and does not easily deteriorate, so it can be used permanently while replenishing solder. (6) There are no problems caused by screen printing such as reflow soldering, or problems such as uneven temperature distribution on the board.
The cost is also low.

[Brief explanation of drawings]

FIG. 1 shows an example of a device implementing the method of the invention.

FIG. 2 shows the adhesive application process during printed circuit board mounting using the method of the present invention.

FIG. 3 shows a component mounting process when mounting a printed circuit board using the method of the present invention.

FIG. 4 shows a soldering process when mounting a printed circuit board using the method of the present invention.

[Explanation of symbols] 10: Homogenization tank, 11: Homogenizer, 12: Vane 13: Nitrogen tank, 14: Heat resistant pump, 15, 16:
Pipe 17: Solder bath, 18: Nozzle, 19: Return pipe, 20:
Solder concentration meter 21: Comparator, 22: Solder tank, 23: Control valve, 24
:Nitrogen tank

Claims (6)

[Claims] Claim 1: Solder is added to liquid polybutene and mechanically stirred in an inert atmosphere at a temperature above the melting point of the solder to form a solder dispersion in which the solder is dispersed in fine particles. A soldering method characterized by bringing the solder dispersion into contact with a predetermined location that requires soldering. [Claim 2] The solder is 50V based on polybutene.
The soldering method according to claim 1, wherein the soldering method is used in an amount of ol% or less. 3. The soldering method according to claim 1, wherein the temperature above the melting point of the solder is 183° C. or above. 4. The soldering method according to claim 1, wherein the dispersion is formed by stirring the solder and polybutene with a homogenizer at 5,000 revolutions per minute or more for one minute or more. 5. The soldering method according to claim 1, wherein the printed circuit board is brought into contact with the printed circuit board by dipping the printed circuit board in a solder dispersion or by flowing the solder dispersion into contact with the printed circuit board. 6. The soldering method according to claim 1, wherein the solder concentration is monitored and solder is replenished when the solder concentration falls below a predetermined value.