JPH05206621A - Method and apparatus for coating printed wiring board with solder - Google Patents

Abstract

PURPOSE:To provide a uniform coating method for an exposed metallic conductive part like a terminal on a printed wiring board, especially for a high-density circuit board in a continuous solder coating step. CONSTITUTION:Through a pump 6, melted solder 2 is carried from a container 7 to a container 1 so that the container 1 is filled with the melted solder 2, and the solder 2 that flows out through a hole at a wall side of the container 1 is carried back to the container 1. during that time, a printed wiring board 4 us removed from a lower part to a higher part of the solder flow against its stream, and the metallic conductive part of the printed wiring board 4 is coated with solder while the board 4 is put in contact with the solder. Moreover, a surplus of solder is blown out by a hot air from a hot air blower 5, and then a solder coating step for the metallic part of the printed wiring board is completed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and method for applying solder to a printed wiring board, which can reliably and efficiently apply the solder to a conductor portion of the printed wiring board.

[0002]

2. Description of the Related Art Conventionally, a printed wiring board is conventionally coated with an exposed metal conductor such as copper, which ensures the reliability of connection in the subsequent process of soldering electronic parts such as LSI, resistors and capacitors. It has been devised to be something. This solder application is called solder leveling, and the device is called solder leveler. As shown in FIG. 10, the solder leveler has the molten solder 20 left stationary.
FIG. 11 shows a vertical type method (see Japanese Patent Publication No. 1-15155) in which a printed wiring board 21 is vertically dipped from above and immersed therein, and solder is applied by taking it out.
As shown in the figure, while moving the printed wiring board 30 horizontally, the molten solder is supplied to the upper and lower surfaces of the printed wiring board 30,
Continuous horizontal type method of applying solder (Japanese Patent Laid-Open No. 17378/1989)
No. 1).

[0003]

By the way, the vertical solder leveler shown in FIG.
The printed wiring board 21 is immersed in 0 from above in a state of being fixed to a support, held for 1 to 10 seconds, then taken out, and hot air is blown before the solder applied to the printed wiring board 21 is cooled and solidified, The surface of the solder coating is finished uniformly, and it has been used for a long time and is widely used, but it has the following problems. (1) Work efficiency is not good because it is a lifting process for moving the printed wiring board up and down. (2) Since the surface of the molten solder is exposed to air, the oxide of the solder floats on the surface, and it is difficult to completely remove it. When this oxide adheres to the printed wiring board,
No solder is applied to that portion. (3) When the printed wiring board is dipped in the molten solder, the front end of the printed wiring board is first soldered and the rear end is dipped last. When pulling up the printed wiring board from the solder, the opposite occurs, and the front end is kept in the solder for a longer time than the rear end, which causes deterioration of the material of the printed wiring board, , The phenomenon that the soldering state is different occurs. (4) The conductors of a printed wiring board are becoming finer as the density of electronic circuits is increasing, and the spacing between conductors is becoming narrower.
In case of VLSI terminal connection, the pitch is 0.5mm
(Conductor width 0.25 mm, gap width 0.25 mm) with a pitch of 0.3 mm is planned in the future. In the vertical solder leveler, when a fine circuit is formed, defective soldering (uncoated portion, short-circuited portion, uneven distribution of solder components, difficulty in obtaining uniform thickness, etc.) increases. (5) Since the solder bath is large and a large amount of solder must be prepared at all times in order to produce molten solder, when the repetitive work is performed, the purity of the solder is greatly reduced. The thermal energy for melting is also large. (6) In order to make the temperature distribution in the solder bath constant, stirring must be performed. At this time, the oxide floating above the solder bath is caught in the solder. (7) The area of lead vapor generated is large, which is not good for health and safety. There were drawbacks such as.

The continuous horizontal solder leveler shown in FIG. 11 was developed in order to improve the drawbacks of the vertical vertical leveler. The continuous horizontal solder leveler is (1) continuous type. Therefore, it is several times more efficient than the vertical type. (2) Since it is not necessary to immerse the printed wiring board from the surface of the molten solder, a layer of antioxidant oil can be formed on the surface of the molten solder to prevent the solder from coming into contact with air. (3) The time when the printed wiring board is dipped in the solder can be made constant. (4) Since hot air blowing that makes the thickness of the solder applied to the surface of the printed wiring board uniform can be performed continuously one by one, it is easy to manage and control the condition, and Uniformity is superior to the vertical type. (5) The amount of solder used is almost the same as that of the vertical type, and it is necessary and the same problem as the vertical type remains. (6) Regarding the solder temperature, it is difficult to supply heat to the upper surface of the printed board, and a temperature difference occurs between the upper and lower sides of the printed board.
It is a new problem in the continuous horizontal solder leveler. (7) Lead vapor is easily ventilated because the whole device has a closed structure compared to the vertical type.

The above is a description of the features of the continuous horizontal solder leveler in comparison with the contents described as the defects of the vertical type.

However, the continuous horizontal solder leveler has other new problems, and the improvement thereof is urgently needed. That is, (1) The continuous horizontal solder leveler moves in a state of being sandwiched between two upper and lower combined rolls for transporting the printed wiring board. If this work is continued for a long time, the roll is contaminated with solder and solder oxide, flux, antioxidant oil, and carbides of these organic substances, and the roll must be cleaned frequently. (2) The occupied area is larger than that of the vertical type, and the equipment cost is also high. (3) The heated gas (mostly air) is blown to the solder surface immediately after applying the solder to make the solder application surface uniform, but fine particles of solder generated by blowing the gas are , In the vertical type, gravity helps, but it tends to fall down,
In the horizontal type, the particles also scatter in the traveling direction of the printed board, and fine solder particles adhere to the surface of the printed board. There were drawbacks such as.

The present invention solves the above problems and has as its object the provision of a method and apparatus for applying solder to a printed wiring board that is reliable and efficient.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above-mentioned object, a method and apparatus for applying solder to a printed wiring board according to the present invention is such that the molten solder 2 faces each other. The printed wiring board 4 is moved according to the flow of the solder flowing out, and the printed wiring board 4 is moved according to the flow of the solder flowing out. Solder is applied to the exposed metal conductor part.
The positions where the printed wiring board 4 is moved on the surfaces of the solder containers facing each other are arranged so that the molten solders 1 and 1 flowing out contact each other or form a gap of 1 mm or less, Further, the molten solder 2 that has flowed out of the solder containers 1 and 1 drops into a solder storage tank 7 provided with a heating device 9 provided in the lower portion and is stored therein, and means for difference in specific gravity, filtration, crystal crystallization, etc. Is provided with a solder storage tank 7 capable of separating impurities, and the solder container 1 and the solder storage tank 7 are connected to each other to remove the impurities in the solder storage tank 7 and the molten solder 2 is used as the solder container 1. A hot-air blowing device 5 is provided which is provided with a transfer device for sending out, and after the printed wiring board 4 has passed through the solder containers 1 and 1, heated hot air or nitrogen gas is blown from both sides of the solder-coated printed wiring board. In addition, the capacity of two more solder A mounting tool 10 holding a printed wiring board 4 is mounted between the terminals 1 and 1, and is moved upward between the solder containers 1 and 1 against the flow of the molten solder, and between the hot air blowing devices 5 and 5. It is equipped with a device that can pass through.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. 1 is a container of solder, 2 is solder in a molten state, 3 is a gap in which solder flows out of the solder container, 4 is a printed wiring board, 5 is a printed wiring board. It is a hot air blowing device that blows high-temperature gas onto the surface of a printed wiring board coated with solder.

As the solder, Japanese Industrial Standard H-63A is usually used. This is heated to 245 to 250 ° C. to be in a molten state. If the molten solder 2 is filled in the solder container 1 so that the height of the molten solder 2 is higher than the height of the solder outflow gap 3 of the solder container 1, the molten solder 2 will leave the solder outflow gap 3
It is possible to make a more continuous flow of solder that flows out in the width direction.

It is important to form and maintain this solder flow in a stable state.

Therefore, it is necessary to keep the height of the solder in the container constant and to keep the distance between the printed wiring board 4 and the solder container 1 constant. The height of the molten solder is constantly supplied by the amount of insufficient solder so that the height of the molten solder can be maintained between 5 mm and 10 mm from the gap 3 through which the solder flows out of the solder container 1.

The dimension between the solder container 1 and the printed wiring board 4 is adjusted to be equal to or less than the thickness of the solder flow. It is usually between 2 and 3 mm. If it is larger than this, a break occurs in the flow of solder. If the lower part of the gap is narrower than the upper part, a break in the solder flow is less likely to occur. Further, when the printed wiring board 4 passes, the flow of solder is temporarily blocked and the solder and the printed wiring board 4 are sufficiently brought into contact with each other. It is sufficient that the contact time between the printed wiring board 4 and the molten solder is 1 to 3 seconds. This time depends on the moving speed (pulling speed) of the printed wiring board 4 and the dimension from the gap of the solder container 1 to the lower end.

The dimension from the gap where the solder flows out of the solder container 1 to the lower end of the solder container 1 may be 30 to 50 cm. The moving speed of the printed wiring board 4 is between 1 and 3 during this period.
Try to pass in seconds. Converted to speed, about 10m /
Minutes are good.

The containers 1 face each other so as to face each other, and the molten solder may always flow, or may flow only when the printed wiring board 4 passes. The printed wiring board 4 is designed to move together with a carrier having both ends fixed, that is, the fixture 10, so that nothing comes into contact with the circuit surface of the printed wiring board 4.

Printed wiring board 4 which has passed through the flow of solder
Uses a hot air blowing device 5 having the same operation principle as that used in a normal solder leveler (vertical type and continuous horizontal type) to blow off excess solder to form a uniform solder application surface.

According to the present invention, all the troubles of the continuous horizontal solder leveler caused by the transport rolls are eliminated. Also, unlike the continuous horizontal type, the defect due to the antioxidant oil is not used near the printed wiring board 4, and fresh solder can always be supplied to the printed wiring board 4. Therefore, this point can be improved. it can. The machine can also have a compact structure, which is a feature of the vertical solder leveler. The disadvantage of the continuous horizontal solder leveler is that the solder fine particles adhere to the vertical type, which is an advantage of the vertical type.The gravity of the solder fine particles makes it easier to drop down. Since it is not pressed into the plate, the number is very small.

As for the gap 3 of the solder container 1 from which the molten solder 2 flows out, the side face of the solder container 1 is simply opened as shown in FIG. 1, and the gap is used.
As shown in FIG. 2, the solder flowing out of the solder flowing out gap 3 of the solder container 1 flows on the slope, and the solder flowing with drop energy passes through the printed wiring board. Can be devised for the purpose of obtaining In many cases, a space is created between the free surface of the molten solder 2 flowing out from the gap 3 from which the solder flows out inside the solder container 1 and the upper surface of the solder container 1. This space is filled with an inert gas such as nitrogen gas, and the size of the space is kept as small as possible so that the molten solder is not exposed to air for a long time. The static solder surface is
An oxide film is easily formed, but if it is in a fluid state, oxidation hardly occurs.

Further, as shown in FIG. 3, it is possible to float an inorganic shielding plate 12 on the solder surface so that there is no space above the solder.

Also, as shown in FIG. 4, even when the upper portion of the solder container 1 is in an open state, the upper free surface 13 of the molten solder is placed above the gap 3 through which the solder flows out. It is possible to prevent the oxide film formed on the solder surface from flowing out to the printed wiring board 4. By opening the upper part of the container 1 in this way, oxides and the like can be removed automatically or periodically by hand.

In FIGS. 5 and 7, after the molten solder 2 flowing out from the solder container 1 comes into contact with the printed wiring board 4,
It is shown that the solder drops into the solder storage tank 7 and returns to the solder container 1 again by the pump 6.

Reference numeral 9 denotes a heating device such as an electric heater for heating the solder 2 in a molten state. Although not shown, in order to keep the temperature of the solder 2 in a molten state constant, the inside and outside of the solder container 1 and a pump It is also possible to heat various parts such as the periphery of 6 and piping. When the molten solder 2 is solidified, the equipment is damaged. Therefore, at the end of the work, the solder discharge bubble 8 is opened.
The solder shall be discharged as much as possible.

When the oxide of solder touches air at high temperature,
The solder is accumulated on the solder storage tank 7 so that it can be removed. The solder storage tank 7 can also be used for removing metals such as copper by the crystal protrusion method.

In the solder coating of the conductor portion of the printed wiring board 4 of the present invention, the apparatus of FIG. 5 is arranged so that they face each other as shown in FIG. 7, and the solder flows out from the solder container 1. Then, the printed wiring board 4 is moved. As shown in FIG. 6, the printed wiring board 4 is clamped at its end with a fixture 10 which is a non-solder coating heat-resistant material (metal, polyimide, etc.), and the fixture 10 is fixed to a transfer tool such as a chain. To pass between the solder containers 1 and 1.

Reference numeral 11 is a rectifying plate that guides the flow of the falling solder to a predetermined solder storage tank 7 so that the angle can be changed while the printed wiring board 4 is passing or not. There is. This prevents the printed wiring board 4 on standby from being contaminated during standby. In this case, it is also possible to control the flow of solder from the gap 3 through which the solder flows.

Further, as shown in FIG. 9, the printed wiring board 4
The movement of is not limited to the vertical direction, but has a climbing angle in the horizontal direction as well as in the horizontal direction, and it is also possible to bring the solder close to horizontal until the solder flowing out stops flowing in the horizontal direction of the printed wiring board 4. Is. Further, the solder containers 1 are arranged so that the printed wiring board 4 can be moved in the horizontal direction, and the solder flowing down in the traveling direction of the printed wiring board 4 has a solder container 1 below.
The guide groove is provided as it is and allowed to flow out to the solder holder, and the upper container can be continuously applied to the solder by collecting it in a predetermined container by vacuum suction or air blowing to the outlet of the container.

The printed wiring board 4 to which the solder is applied has a circuit-processed copper-clad laminate in which a glass foil reinforced Epokin laminate (FR-4) is pasted with a copper foil having a thickness of about 35 micrometers. To use. The thickness is 1.6 mm, the size is 500 mm × 600 mm, and the circuit has 0.5 mm pitch terminals (terminal width 0.25 mm, terminal spacing 0.25 m).
The present invention includes 30 four-layer circuit boards for a small TV including a terminal group for a surface-mount type LSI having m). One circuit board is 90mm x 90mm, 500mm x 600
The circuit processed product having a size of 5 mm is divided into 5 pieces vertically and 6 pieces horizontally. The surface of the circuit is protected by coating with an exothermic paint using an Epokin resin as a binder, leaving a conductor portion for soldering an electronic component in a later step.

The printed wiring board 4 is completed by applying solder to the exposed terminal portions of the conductor metal and cutting it one by one to finish.

In the exposed metal portion to which the solder is applied, the copper surface may be contaminated during storage or undergo surface oxidation. Therefore, pretreatment is performed prior to applying the solder. This process starts by first immersing in an inorganic acid and then washing with water, draining and drying this, and immediately applying solder. As the inorganic acid, a mixed solution of sulfuric acid and hydrogen peroxide is widely used. Flux (HF-805 manufactured by Hitachi Chemical Co., Ltd.) was applied to the pre-processed printed wiring board 4 to a thickness of 3 μm, and as shown in FIG. The four sides are fixed by a fixture 10 in which a thin plate is formed in a U shape. The fixture 10 at the end of the printed wiring board 4 having a length of 600 mm has a protrusion, and by utilizing this protrusion, the two solder containers 1 and 1 facing each other as shown in FIG. At a predetermined position (between the solder storage tank 7 and the rectifying plate 11), the wire is attached to the transfer wire and kept waiting. During this time, the outflow amount of the solder from the rectifying plate 11 and the gap 3 is reduced so that the solder does not adhere to the printed wiring board 4. It is preferable to reduce the waiting time as much as possible, and when continuously performing the work, since it is attached to the transfer tool while keeping a space of 200 to 800 mm from the preceding solder coating of the printed wiring board 4, the time is kept. Automating the time to fix to the transfer tool to be 1-2 seconds. This is done by engaging the transfer wire with the key of the fixture 10 of the printed wiring board 4. The printed wiring board 4 is pulled upward by a transfer wire depending on the flow of solder flowing out of the solder container 1 during the solder application process.
At this time, the fixture 10 of the printed wiring board 4 also serves to maintain a distance such that the solder container 1 and the printed wiring board 4 do not come into contact with each other. When the printed wiring board 4 reaches the lower end of the solder container 1, the amount of the solder (H63A) flowing from the gap 3 is reduced so that the molten solder is filled between the printed wiring board 4 and the solder container 1. The distance between the solder container 1 and the printed wiring board 4 is about 5 mm in the upper part and 0.5 in the lower part.
When the thickness is set to about 1 mm, the molten solder is temporarily blocked between the solder container 1 and the printed wiring board 4, and a sufficient contact time with the conductive metal to be soldered is obtained. This time may be 1.5 to 3 seconds when the temperature of the molten solder is 245 ° C. The contact time of the printed wiring board 4 with the solder depends on the distance from the gap 3 of the solder container 1 to the lower end of the container and the lifting speed. When this distance is 300 mm, the lifting speed is 10
If 0 mm / sec, the solder and the conductor metal are in contact with each other for 3 seconds. The printed wiring board 4 receives hot air from the hot air outlet of the hot air blowing device 5 immediately after passing through the solder flow. The hot air is heated at a temperature of 230 ° C. to 250 ° C., a pressure of 1.5 kilograms / Heihou centimeter, and the air outlet spacing is 0.5 mm, the angle is 100 ° C., and the hot air is blown slightly downward. After the hot air is blown, the printed wiring board 4 is cooled in the air and the solder application process is completed.

When applying solder in this way,
It was possible to apply 100% of non-coated parts uniformly to all 0.5 mm pitch LSI terminals, and to perform continuous work for about 8 hours. If the stains on the roll, etc. were not cleaned, the solder powder application part occurred.

[0031]

The present invention is constructed as described above and has the following effects.

1. According to this invention, the molten solder is
The solder flows out from the gap 3 and the printed wiring board 4
It comes in contact with the surface of. The solder 2 flowing out from the gap 3 from which the solder flows out is in a state where it is not in contact with air and does not contain an oxide. The distance from the gap 3 from which the solder flows out to the printed wiring board 4 is also 5 mm or less. During this time, air is contacted, but since it is a short time of about 0.5 seconds, no trouble occurs due to the formation of oxides. For completeness, this area can be filled with an inert gas. Since organic substances such as antioxidant oil are a mechanism that does not need to be used at all, there is no risk of contamination due to them. The antioxidant is applied to the printed wiring board 4 in advance. However, the excess of the antioxidant drops into the solder storage tank 7 due to the flow of solder and floats because its specific gravity is light on the surface, and is completely separated from the solder. Therefore, there is no chance that the printed wiring board 4 is contaminated by reaching the surface of the printed wiring board 4 from the solder container 1 through the gap 3 again through the pump 6.

2. The production efficiency is better than the vertical type conventional method because it is a continuous operation rather than a lifting process. Further, since parts such as rolls that cause contamination in a continuous horizontal type are not used, it is not necessary to frequently clean the roll, which is essential for the conventional continuous horizontal type method, and high efficiency is achieved.

3. In the vertical type conventional method, the solder dipping time was extremely long at the front end of the printed wiring board 4, but in the present invention, a uniform time from the front end to the rear end of the printed wiring board 4 is achieved. This is an action because it is designed to enter the solder from the tip and exit from the tip when exiting.

4. With the progress of higher densities, vertical solder levelers have become difficult to apply solder to fine circuits. As a solution to this, a continuous horizontal solder leveler was born. In the solder leveler of the present invention, continuous solder application is possible, so that in principle the condition control is easy as in the continuous horizontal type, and the surface of the high-definition printed wiring board 4 can be evenly applied. In addition, the aforementioned oxides and antioxidant oils,
Since there is no carbonized tar-like impurity of organic matter such as flux, it is possible to obtain a solder-coated printed wiring board 4 having a more stable quality than the continuous horizontal solder leveler.

5. The amount of solder used in the solder leveler according to the present invention is the solder container 1, the solder reservoir 7, the solder flow from the gap 3, and the solder in the pump 6 and the pipe. This amount of solder is about one-tenth of the amount of continuous horizontal and vertical solder levelers. this is,
This is because the printed wiring board 4 can be applied with solder in a solder flow of about 10 mm × 500 mm × 600 mm at maximum. In the two conventional methods, the container of the applied solder is
Usually, it is 700 mm × 700 mm × 700 mm, which is about 70 times that of the solder leveler of the present invention.

6. In the case of the present invention, since the temperature distribution is performed in the solder flow sandwiched between the solder containers 1, a constant value can be secured by the heat retaining effect of the solder container 1. There are very few parts such as air that cause temperature drop.

7. The generation of lead vapor occurs in the space between the two solder containers 1 and 1 and the surface of the solder storage tank 7 with less exposed area than in the conventional method, and it is easy to form a sealable structure. It makes it easier to manage safety and health by sucking in the generated steam.

8. The occupying area of the machine is about the same as that of the conventional vertical solder leveler, which is about 1/5 of the continuous horizontal solder leveler.

9. The solder fine particles adhering to the surface of the printed wiring board 4 were often found in the continuous horizontal type. However, the solder leveler of the present invention has a vertical type structure like the conventional vertical type solder leveler. Since the generated solder fine particles fall downward due to gravity, the amount becomes small.

That is, according to the apparatus of the present invention, when the conductor portion of the printed wiring board 4 is applied with the solder, the solder is always high in purity and can be supplied at a constant temperature. Is less likely to occur. Furthermore, continuous work is possible and efficient. Moreover, since the device is simple, the installation area is small, and the generation of lead vapor is locally suppressed as a closed structure,
It is safe to collect exhaust gas. Further, it is easy to maintain and manage the device and maintain and manage the solder. In addition, the amount of solder used is small, and the thermal energy required for melting can be small.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a main part of a first embodiment.

FIG. 2 is a vertical sectional view of a main part of the second embodiment.

FIG. 3 is a vertical cross-sectional view of the main part of the third embodiment.

FIG. 4 is a vertical sectional view of a main part of a fourth embodiment.

FIG. 5 is an explanatory diagram showing a circulating state of the entire flow of solder.

FIG. 6 is a schematic explanatory view showing a situation where the printed wiring board 4 is fixed to a fixture.

FIG. 7 is an explanatory diagram showing the whole of the first embodiment.

FIG. 8 is a partially enlarged sectional view of a fifth embodiment.

FIG. 9 is a vertical cross-sectional view of the main parts of the sixth embodiment.

[Name of code]

 1 Solder Container 2 Molten Solder 3 Solder Gap 4 Printed Wiring Board 5 Hot Air Blowing Device 6 Pump 7 Solder Reservoir 8 Solder Discharge Bubble 9 Heating Device 10 Fixture 11 Rectifier 12 Shield 13 Upper Free Surface

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[Procedure amendment]

[Submission date] December 24, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a main part of a first embodiment.

FIG. 2 is a vertical sectional view of a main part of the second embodiment.

FIG. 3 is a vertical cross-sectional view of the main part of the third embodiment.

FIG. 4 is a vertical sectional view of a main part of a fourth embodiment.

FIG. 5 is an explanatory diagram showing a circulating state of the entire flow of solder.

FIG. 6 is a schematic explanatory view showing a situation where the printed wiring board 4 is fixed to a fixture.

FIG. 7 is an explanatory diagram showing the whole of the first embodiment.

FIG. 8 is a partially enlarged sectional view of a fifth embodiment.

FIG. 9 is a vertical cross-sectional view of the main parts of the sixth embodiment.

10 to 11 are explanatory views of a conventional example.

[Name of code] 1 Solder container 2 Solder in molten state 3 Gap in which solder flows out 4 Printed wiring board 5 Hot air blower 6 Pump 7 Solder reservoir 8 Solder discharge bubble 9 Heating device 10 Fixture 11 Rectifier 12 Shield 13 Upper free surface

Claims (6)

[Claims] 1. A molten solder (2) is caused to flow out from solder flow gaps (3, 3) provided on the side surfaces of two solder containers (1, 1) facing each other. Then, the printed wiring board 4 is moved and solder is applied to the exposed metal conductor portion of the printed wiring board 4, and the solder of the printed wiring board is applied. 2. The space where the printed wiring board 4 is moved on the surfaces of the two solder containers facing each other is such that the melted solders 1, 1 flowing out contact each other or form a gap of 1 mm or less. The device for applying solder to a printed wiring board according to claim 1, wherein 3. The molten solder 2 flowing out from the solder containers 1 and 1 drops and is stored in a solder storage tank 7 provided with a heating device 9 provided at a lower portion, and the difference in specific gravity, filtration, and crystallization. 3. The solder coating apparatus according to claim 1, further comprising a solder storage tank 7 capable of separating impurities by means such as folding. 4. A transfer device for connecting the solder container 1 and the solder storage tank 7 and sending out the molten solder 2 from which impurities in the solder storage tank 7 have been removed to the solder container 1 are provided. An apparatus for applying solder to the printed wiring board according to claim 1. 5. A hot air blower (5) for blowing heated hot air or nitrogen gas from both sides of the printed wiring board (4) coated with solder after the printed wiring board (4) has passed through the solder containers (1, 1). An apparatus for applying solder to a printed wiring board, which is characterized in that 6. A fixture 10 holding a printed wiring board 4 is mounted between two solder containers 1 and 1, and the solder containers 1 and 1 are upwardly moved against the flow of molten solder. A device for applying solder to a printed wiring board, which is provided with a device that can move and pass between the hot air blowing devices 5 and 5.