JP7462361B1 - Surface treatment method for convex nozzle plate used in jet soldering device - Google Patents

Abstract

[Problem] To provide a jet soldering device having a convex nozzle plate with multiple nozzle holes arranged therein, capable of reducing the weight of oxidized residue. [Solution] This jet soldering device performs soldering by contacting a jet of molten solder with a board, and is equipped with a nozzle having a convex nozzle plate 14 arranged to cover the upper opening of a nozzle body 11 which is a hollow body. The convex nozzle plate 14 has multiple nozzle holes 16 arranged in a plate-like member, the nozzle holes 16 being formed inside a cylindrical flange 15 which is convex with respect to the plate-like member, and the convex nozzle plate 14 is surface-treated by electrolytic polishing. [Selected Figure] Figure 4

Description

The present invention relates to a jet soldering device that performs soldering by contacting a jet of molten solder with a substrate.

Conventionally, soldering work has been automated using a jet soldering machine. A jet soldering machine is a device that jets molten solder from a nozzle through a jet duct installed in a solder bath. Soldering is performed by bringing the solder jetted from the nozzle into contact with an object, such as a printed circuit board, being transported within the machine.

In jet soldering equipment, preventing oxidation of the molten solder is an issue, and in Patent Document 1, the solder bath body, nozzle, and pump are coated with a heat-resistant film with a low friction coefficient surface, which reduces resistance to the flow of molten solder and is therefore advantageous in preventing oxidation of the molten solder.

Japanese Utility Model Application Publication No. 61-205660

However, in the jet soldering device described in Patent Document 1, the nozzle is composed of a hollow body, the opening at the top of the body is the solder outlet, and the part of the nozzle that is to be coated is limited to the inner circumferential surface of the body. In other words, the jet soldering device described in Patent Document 1 does not have multiple nozzle holes arranged at the top of the nozzle, and the technology described in Patent Document 1 is merely a technology for reducing resistance to the flow of molten solder in the flow path up to the top of the nozzle.

In view of the above-mentioned conventional techniques, the present invention aims to provide a jet soldering device having a convex nozzle plate with multiple nozzle holes arranged thereon, which can reduce the weight of oxidized residue.

To achieve the above object, the jet soldering device of the present invention is a jet soldering device that performs soldering by contacting a jet of molten solder with a board, and is equipped with a nozzle having a convex nozzle plate arranged to cover the upper opening of the nozzle body, which is a hollow body, and the convex nozzle plate is a plate-shaped member with a plurality of nozzle holes arranged thereon, the nozzle holes being formed inside a cylindrical flange that is convex with respect to the plate-shaped member, and the convex nozzle plate is surface-treated by electrolytic polishing.

In the jet soldering device of the present invention, it is preferable that the convex nozzle plate is detachable from the nozzle body.

The jet soldering device of the present invention can achieve a significant reduction in the weight of oxidized waste compared to the comparative example in which a convex nozzle plate without electrolytic polishing is used. In addition, a preferred configuration in which the convex nozzle plate is detachable from the nozzle body makes it easy to reuse it by electrolytic polishing again.

1 is a cross-sectional view showing a main part of a jet soldering apparatus according to an embodiment of the present invention; 2 is a cross-sectional view showing a main part of the jet soldering apparatus shown in FIG. 1 in the conveying direction of the printed wiring board; FIG. 2 is a perspective view of a convex nozzle plate according to an embodiment of the present invention. FIG. 4 is a cross-sectional view of the vicinity of a convex nozzle plate in one embodiment of the present invention.

One embodiment of the present invention will now be described with reference to the drawings. FIG. 1 is a cross-sectional view showing the main parts of a jet soldering device 1 according to one embodiment of the present invention. The jet soldering device 1 is a device that performs soldering by contacting a jet of molten solder with the back surface of a printed wiring board 30, which is the object to be soldered. As multiple printed wiring boards 30 are transported one by one on a transport conveyor 31 (see FIG. 2), soldering is performed on the printed wiring boards 30 in sequence.

In FIG. 1, the printed wiring board 30 is transported from the back side of the paper to the front side of the paper. FIG. 2 is a cross-sectional view showing the main parts of the jet soldering device 1 in the transport direction of the printed wiring board 30. In FIG. 2, for convenience of illustration, the transport conveyor 31 is simplified and illustrated by a single two-dot chain line. The transport conveyor 31 is inclined, with the downstream side lower and the upstream side higher. The printed wiring board 30 is transported from the downstream side to the upstream side (in the direction of arrow a).

The structure of the jet soldering device 1 will be described below with reference to Figures 1 and 2. In Figure 1, a first duct 3 is disposed inside a solder bath 2, and a primary nozzle 10 is disposed above the first duct 3. In Figure 2, the primary nozzle 10 is mainly composed of a nozzle body 11, which is a hollow body, and a convex nozzle plate 14 disposed so as to cover the opening at the top of the nozzle body 11. Details of the convex nozzle plate 14 will be described later.

In FIG. 1, an impeller 5 is disposed at the end of the first duct 3. The impeller 5 rotates integrally with a rotating shaft 7, which rotates as a result of the rotation of a pulley 6. The pulley 6 rotates when a belt (not shown) that is wrapped around the pulley 6 is driven by a motor (not shown).

As the impeller 5 rotates, the molten solder in the first duct 3 is sent to the nozzle body 11 of the primary nozzle 10, as shown by the arrow in Figure 1, and the molten solder rises within the nozzle body 11. The rising molten solder jets out from the holes in the convex nozzle plate 14 and comes into contact with the printed wiring board 30.

As shown in FIG. 2, in the transport direction (direction of arrow a) of the printed wiring board 30, the secondary nozzle 20 is disposed upstream of the primary nozzle 10. A front plate 12 and a back plate 13 are fixed to the nozzle body 11 of the primary nozzle 10, and a convex nozzle plate 14 is disposed so as to span both plates 12, 13.

The secondary nozzle 20 is mainly made up of a front wave guide 22 fixed to the downstream side of the nozzle body 21, which is a hollow body, and a center plate 23 and a back plate 24 fixed to the upstream side of the nozzle body 21. The upper part of the secondary nozzle 20 has a wall formed by a side plate 25.

In the state shown in FIG. 2, the printed wiring board 30 is located above the primary nozzle 10, and soldering is performed by a jet of molten solder from the convex nozzle plate 14. The molten solder that comes into contact with the printed wiring board 30 flows back into the solder bath 2 along the front plate 12 and back plate 13.

When the printed wiring board 30 above the primary nozzle 10 is transported upstream (in the direction of arrow a), a second soldering is performed by a jet of solder from the secondary nozzle 20. The molten solder that comes into contact with the printed wiring board 30 flows back into the solder bath 2 along the front wave guide 22, center plate 23, and back plate 24.

The supply of molten solder to the secondary nozzle 20 is the same as that on the primary nozzle 10 side. The secondary nozzle 20 side is also provided with a dedicated impeller 5 and a mechanism similar to the impeller 5 rotation mechanism provided on the primary nozzle 10 side. The impeller 5 is arranged in the second duct 8 below the secondary nozzle 20, similar to the first duct 3 shown in FIG. 1, and the rotation of the impeller 5 sends the molten solder in the second duct 8 to the nozzle body 21 of the secondary nozzle 20. The impeller 5 rotation mechanism is also the same as that on the first duct 10 side.

Figure 3 shows a perspective view of the convex nozzle plate 14. Figure 4 shows a cross-sectional view of the vicinity of the convex nozzle plate 14. In Figure 3, the convex nozzle plate 14 is a plate-shaped member with a plurality of ejection holes 16 arranged at a predetermined pitch. The ejection holes 16 are formed on the inside of a cylindrical flange 15 that is convex with respect to the plate-shaped member. There are no particular limitations on the method of forming the cylindrical flange 15, and it may be formed by burring or cutting.

In FIG. 4, the convex nozzle plate 14 is shown in a cross-sectional view taken along line AA in FIG. 3. As shown by the arrow in FIG. 4, the molten solder that rises inside the nozzle body 11 ejects as a jet from the ejection hole 16 of the convex nozzle plate 14.

In jet soldering equipment, oxide scum, which is a black powdery oxide, is generated. Because oxide scum does not contribute to soldering, when oxide scum is generated, the amount of solder that can be used for soldering is reduced by its amount. For this reason, it is not possible to use all of the solder put into the solder bath 2 for soldering, and the amount of oxide scum generated is lost. Therefore, if a large amount of oxide scum is generated, the amount of solder lost also increases, and in addition, the burden of the removal work also increases.

Furthermore, if a large amount of oxidized residue is generated, soldering defects are more likely to occur. One of the reasons for this is that oxidized residue adheres to the holes in the convex nozzle plate 14, obstructing the flow of the solder jet.

The inventors of the present application have been working on reducing oxidized waste and have conducted various tests, and as a result have found that electrolytic polishing of the convex nozzle plate 14 has an advantageous effect on reducing oxidized waste. The test process is described below.

Comparative examples and examples are shown in Table 1. The basic configurations of the comparative examples and examples are the same as the jet soldering apparatus 1 shown in Figures 1 and 2. The jet soldering apparatuses 1 according to the comparative examples and examples are the same model, and the structures of the primary nozzle 10 and secondary nozzle 20 are the same, except for the presence or absence of electrolytic polishing of the convex nozzle plate 14.

In the example, the convex nozzle plate 14 of the primary nozzle 10 (made of stainless steel: SUS316L) is surface-treated by electrolytic polishing, while the other components of the primary nozzle 10 are not surface-treated. Electrolytic polishing is a surface treatment in which the object to be polished is treated as the positive side and a direct current is passed between the object and a negative side counter electrode via an electrolyte to dissolve and polish the surface of the object to be polished. In the comparative example, the structure and material of the convex nozzle plate 14 are the same, but electrolytic polishing is not performed. Additionally, in both the example and comparative example, the components of the secondary nozzle 20 are not surface-treated.

For convenience, the comparative example will be referred to as Comparative Example 1, and the examples will be referred to as Examples 1 and 2 due to the difference in test conditions. Table 2 below shows the test results when Example 1 and Comparative Example 1 were operated for 8 hours. The jet rotation speed is the frequency of the motor (not shown) that drives the impeller 5 (FIG. 1). The solder temperature was 255° C. (the same for Example 2 described below), and in order to standardize the test conditions, the wave height of Example 1 and Comparative Example 1 was the same 10 mm on both the primary nozzle 10 side and the secondary nozzle 20 side.

As shown in Table 2, in Comparative Example 1, the weight of the oxidized waste was 3.30 kg/8 hours, whereas in Example 1, it was reduced to 1.70 kg/8 hours. In this case, the reduction in Example 1 compared to Comparative Example 1 was 1.6 kg, and the reduction rate was 48.5%, meaning that Example 1 achieved a significant reduction in the weight of the oxidized waste compared to Comparative Example 1.

Table 3 adds Example 2 to Comparative Example 1 and Example 1 shown in Table 2. Example 1 and Comparative Example 1 have the same wave height of 10 mm, but Example 2 has the same jet rotation speed of 40.00 Hz as Comparative Example 1.

In Table 3, comparing Comparative Example 1 and Example 2, the jet rotation speed is the same for both, but the wave height is higher in Example 2 than in Comparative Example 1. In other words, to achieve the same wave height in Example 2 as in Comparative Example 1, the jet rotation speed can be reduced. More specifically, while Example 1 has the same wave height as Comparative Example 1, the jet rotation speed in Example 1 is lower than that in Comparative Example 1.

Therefore, by using a convex nozzle plate 14 with electrolytic polishing, the required wave height can be secured by lowering the jet rotation speed. It is known that lowering the jet rotation speed reduces the weight of oxidized residue. For this reason, being able to secure the required wave height by lowering the jet rotation speed is one of the reasons why, in Table 2, Example 1 has a lower weight of oxidized residue than Comparative Example 1. In addition, since lowering the jet rotation speed stabilizes the solder discharge shape, being able to secure the required wave height by lowering the jet rotation speed is also advantageous in terms of soldering quality.

Based on the above, the inventors of the present application have achieved a significant reduction in the weight of oxidized residue by using a convex nozzle plate 14 that has been surface-treated by electrolytic polishing in a jet-type soldering device 1. The reason for this effect is not entirely clear, but it is speculated that one of the reasons is that electrolytic polishing is a surface treatment that reduces surface roughness, and electrolytic polishing is limited to the convex nozzle plate 14 rather than the entire solder flow path, which reduces the surface roughness near the nozzle hole 16.

Specifically, since the nozzle hole 16 is the part where the cross-sectional area of the solder flow is small and resistance to the flow is generated, it is presumed that reducing the surface roughness of this part directly contributes to stabilizing the solder flow and also contributes to reducing the weight of oxidized residue. This can also be presumed from the fact that, in Table 3, Example 2 has a higher wave height than Comparative Example 1, even though the jet rotation speed is the same for Example 2 and Comparative Example 1.

As shown in Figures 3 and 4, an end face 17 is formed on the upper part of the cylindrical flange 15. The surface roughness of the end face 17 is also reduced by electrolytic polishing, so that oxidized scum is less likely to adhere to the end face 17. In this case, the ejection hole 16 is less likely to be blocked by oxidized scum, and a stable flow of solder is maintained in the ejection hole 16. This is also presumably a factor in reducing the weight of oxidized scum.

On the other hand, if the surface roughness of the convex nozzle plate 14 is merely to be reduced, this can be achieved by physical polishing or coating, but these require extensive processing and construction, and maintenance is not easy. In particular, polishing the inner and outer surfaces of the cylindrical flange 15 by physical polishing is a significant workload. With electrolytic polishing as in the present invention, processing is easy, and reuse in the event of deterioration is possible. More specifically, reuse is possible by simply subjecting the convex nozzle plate 14 to electrolytic polishing again. In this case, if the convex nozzle plate 14 is configured to be detachable from the primary nozzle body 11 in FIG. 4, it is sufficient to subject the removed convex nozzle plate 14 to electrolytic polishing, making reuse easy.

In addition, in Example 1, although electrolytic polishing was performed only on the convex nozzle plate 14 and not on the entire solder flow path, as described above, Example 1 achieved a significant reduction in the weight of oxidized residue. Therefore, by performing electrolytic polishing on the components that make up the solder flow path, such as the duct 3 and nozzle body 11 shown in Figure 3, it is expected that the weight of oxidized residue will be further reduced.

Although one embodiment of the present invention has been described above, the embodiment is merely an example and may be modified as appropriate. For example, in Figures 3 and 4, the convex nozzle plate 14 is a separate part from the primary nozzle body 11, but it may be molded integrally with the primary nozzle body 11.

REFERENCE SIGNS LIST 1 Jet soldering device 2 Solder bath 3 First duct 8 Second duct 10 Primary nozzle 11 Primary nozzle body 14 Convex nozzle plate 15 Cylindrical flange 16 Jet hole 20 Secondary nozzle 21 Secondary nozzle body 30 Printed wiring board

Claims (2)

A surface treatment method for a convex nozzle plate used in a jet soldering apparatus that performs soldering by contacting a jet of molten solder with a substrate, comprising the steps of:
The convex nozzle plate has a convex nozzle plate arranged so as to cover an opening at an upper part of a nozzle body which is a hollow body, and a plurality of ejection holes are arranged in the plate-shaped member ,
The ejection hole is formed on the inside of a cylindrical flange that is convex with respect to the plate-like member,
A surface treatment method for a convex nozzle plate used in a jet soldering apparatus, comprising the steps of: subjecting the convex nozzle plate to surface treatment by electrolytic polishing without physical polishing. 2. The method for surface treatment of a convex nozzle plate used in a jet soldering apparatus according to claim 1, wherein the convex nozzle plate is detachable from the nozzle body.

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