JPH098450A - Soldering of printed wiring board and wave soldering tank - Google Patents

Abstract

PURPOSE: To make it possible to solder a multitude of soldering parts to a printed wiring board with good accuracy. CONSTITUTION: A method of soldering to a printed board is a method wherein the flow of a molten solder at a peel back point, at which the printed board is separated from the molten solder, which is fluidized on a rear former 7 of a secondary jet nozzle 1, is partially changed, soldering parts, between which a bridge is easy to generate, to the boad are made to melt in this changed flow and the soldering parts are soldered to the board, and for executing this method, flow conversion means 9 for changing partially the direction of fluidization of the molten solder are provided on the former 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for soldering a printed circuit board and a jet solder bath used for soldering the printed circuit board.

[0002]

2. Description of the Related Art As a method for soldering a printed circuit board, there are a reflow method, a trowel method, a dipping method and the like.

The reflow method is a method of soldering using a solder paste prepared by kneading powdered solder and a paste-like flux. In the reflow method, the solder paste is printed and applied to the soldering part of the printed circuit board by using a silk screen or a metal mask, the electronic parts are mounted on the applying part, and then heated by a heating device such as a reflow furnace. The paste is melted and the printed circuit board and electronic components are soldered.

In the reflow method, if a good solder paste is used and soldering is performed under appropriate printing conditions, a bridge that the solder is attached across adjacent leads does not occur, and therefore fine pitch electronic parts are used. Is a suitable soldering method. However, since the reflow method uses powdered solder, not only does it take a lot of time and effort to manufacture it, but also the screen and mask used for soldering, the printing device, and the jigs and devices such as the reflow furnace are expensive. Therefore, there was a problem in the cost of soldering.

The troweling method is a method of soldering a printed circuit board and an electronic component while melting wire solder with a heated soldering iron. In the trowel method, the operator performs soldering while observing the soldering condition, so even if a bridge occurs, it can be corrected immediately on the spot, or the amount of dust adhesion can be adjusted appropriately, so reliable soldering is possible. It has a feature that a mounting part can be obtained. However, this troweling method is not suitable for mass production because the soldering has to be performed at each place of the soldering portion, and thus the productivity is poor.

In the dipping method, soldering is carried out by an automatic soldering device provided with a soldering processing device such as a fluxer, a preheater, a jet solder bath, a cooler and the like.
In this dipping method, flux is applied to the printed circuit board with a fluxer, preheating is performed with a pre-heater, solder is applied in a jet solder bath, and the attached solder and the printed circuit board are cooled by a cooler, so that the printed circuit board and electronic components are processed. To solder.

This dipping method is inexpensive because it does not use a solder paste, which is time-consuming to manufacture like the reflow method, and does not use expensive jigs or devices such as a screen, a mask, a printing device, a reflow furnace, and the like. is there. Moreover, since a large number of soldering parts can be soldered in a single soldering process, they have the advantage of excellent productivity.
Therefore, the dipping method is a soldering method suitable for soldering mass-produced household electric appliances such as televisions, videos and boomboxes.

The jet solder bath used in the dipping method is provided with a primary jet nozzle and a secondary jet nozzle that gently jets solder as compared with the primary jet nozzle. The primary jet nozzle forcibly injects molten solder into the corners of electronic components and the vicinity of through holes due to rough waves, and eliminates unsoldered solder in which solder does not adhere. However, because the wave of the solder jet from the primary jet nozzle is rough, clean soldering cannot be performed, and soldering defects such as eclipse where the solder adheres to the tip of the lead in a square shape and bridges between the leads occur. I will let you. Therefore, the printed board on which the soldering failure has occurred is passed through the secondary jet nozzle, and the icicles and bridges are corrected with a jet of solder that is gentler than that of the primary jet nozzle. However, it should be noted that the secondary jet nozzle for correcting the bridge and the flutter may generate the bridge depending on the conditions.

[0009]

By the way, since recent household electric appliances tend to be light, thin, short, and small, the electronic parts used here are also becoming multifunctional, and a large number of leads are installed in one electronic part. It has a fine pitch with a narrow lead gap. For the fine pitch electronic parts, the reflow method is an effective soldering method because it does not generate a bridge relatively, but as described above, the material cost, the soldering apparatus, etc. are expensive, and thus the price reduction is required. Is not suitable for household appliances that are used. Further, the troweling method is also not suitable for mass-produced household electric appliances because soldering must be performed for each soldering portion.

The immersion method is the most suitable soldering method for household electric appliances in terms of cost and productivity, but it is possible to completely eliminate the bridge for fine pitch electronic parts. There was a problem that I could not. Therefore, for printed circuit boards with fine-pitch electronic components soldered in a conventional jet solder bath, an operator must perform a visual inspection of the soldered portion after soldering and correct the generated bridge with a trowel. I had to do it. An object of the present invention is to provide a jet solder bath in which a bridge does not occur on a printed circuit board on which fine-pitch electronic components are mounted.

[0011]

Various factors can be considered as the cause of the bridge formation in the soldering by the secondary jet nozzle of the conventional jet solder bath. One of the factors is the printed circuit board. There is a relationship between the flow direction of the molten solder when the secondary jet nozzle separates from the molten solder and the direction in which a large number of soldering portions are arranged in parallel.

That is, when the printed circuit board comes into contact with the molten solder (hereinafter referred to as the rear former fluidized solder) flowing on the rear former of the secondary jet nozzle and separates from the rear former fluidized solder, the juxtaposed soldering portions cause the rear former fluidization. The bridge does not occur in the direction parallel to the solder (vertical direction), but the bridge occurs in the direction perpendicular to the rear former fluidized solder (horizontal direction).

The occurrence of this bridge depends on the direction in which the surface tension of the molten solder acts. That is, the surface tension of the molten solder is always working to reduce the surface area, and the molten solder tends to be attracted to the one having a large capacity to form a spherical shape having a small area. If the soldering parts arranged side by side are in the vertical direction with respect to the rear former fluidized solder, a peel back point (hereinafter referred to as PBP) at which the printed circuit board separates from the rear former fluidized solder.
At the same time, the soldering portion at the forefront of the traveling direction is separated from the molten solder, and at the same time, the soldering portion is still immersed in the rear former fluidized solder and is attracted to the next soldering portion to which a large amount of molten solder is attached. Therefore, the molten solder between the frontmost soldering portion and the next soldering portion is not broken and does not form a bridge. This phenomenon occurs in the rear direction one after another, and the molten solder that has adhered between the soldering part in front of the final part and the soldering part in the final part is pulled by the rear former fluidized solder just after the final part, and the bridge is also formed. Do not generate. In this way, the soldered portions arranged side by side in the vertical direction have no bridges at all.

On the other hand, if the juxtaposed soldering portions are lateral to the rear former fluidized solder, the juxtaposed soldering portions of the PBP will separate from the rear former fluidized solder at one time. At this time, the molten solder that adheres between the soldering parts moves so as to reduce the surface area, but since the molten solder does not adhere to the outside of the soldering parts on both ends, the molten solder adheres. Gather in the center. The molten solder gathered in the central portion stays here because there is no molten solder behind it. Therefore, although the bridge does not occur in the soldered portion near both ends, the solder gathered from both ends remains in the vicinity of the center and becomes a bridge.

Therefore, the inventors of the present invention have noticed that bridges do not occur unless the soldering portions arranged in parallel are lateral to the rear former fluidized solder. In order to prevent a large number of soldering parts from being lateral to the rear former fluidized solder, electronic components with a large number of leads on the four sides, such as QFP, are mounted diagonally to the printed circuit board advancing direction. It was done by soldering or forcibly installing a multi-leaded connector in the same vertical direction. However,
The QFP may be inclined with respect to the printed circuit board traveling direction,
To install the connector in the same direction,
There were problems in the design of the printed circuit board and inconvenience in use. The present invention does not consider the installation direction of the electronic component or the connector at all, that is, the soldering portion on the second side of the QFP is lateral to the printed circuit board traveling direction or the connector is lateral. Even if it provides a soldering method and a jet solder bath which do not generate a bridge.

According to a first aspect of the present invention, after soldering a printed board with a primary jet nozzle, soldering defects such as bridges and flicker caused by soldering with the primary jet nozzle are corrected with a secondary jet nozzle. In the soldering method, the flow of molten solder at the peel back point where the printed circuit board separates from the molten solder flowing on the rear former of the secondary jet nozzle is partially changed, and a bridge is generated in the changed flow. It is a method of soldering a printed circuit board, characterized in that a soldering portion of the printed circuit board, which is easy to perform, is brought into contact with the printed circuit board for soldering.

According to a second aspect of the present invention, in a jet solder bath in which a primary jet nozzle and a secondary jet nozzle are installed, a current changing plate for partially changing the flow direction of molten solder on a rear former of the secondary jet nozzle. Is a jet solder bath.

In the jet solder bath of the present invention, if a large number of holes are formed in the rear former at appropriate places, and two pins that can be fitted into the holes are installed in the current transformer, it is possible to change the shape. By fitting the pin in the hole where you want to install the flow plate,
It can be installed in any place.

[0019]

Operation: The flow of molten solder in the PBP is partially changed, and an electronic component that easily causes a bridge at this part, such as a QFP with many soldering parts on its four sides or a connector mounted in the lateral direction, is contacted. Then, the rear former fluidized solder does not have a flow direction at a right angle with respect to the soldering portion provided in the lateral direction of the QFP or the soldering portion of the connector, but becomes an oblique direction.

When a current-changing plate is attached on the rear former of the secondary jet nozzle, the flow direction of the rear former fluidized solder passing through the current-changing plate is changed by the current-changing plate, so that the electrons are mounted laterally. It will not hit the soldered part of the component at a right angle.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a perspective sectional view of a secondary jet nozzle installed in a jet solder tank of the present invention, FIG. 2 is a front sectional view showing a soldering state of a printed circuit board, and FIG. 3 is a diagram of the jet solder tank of the present invention. It is a figure explaining the flow of the molten solder on the rear former of the next jet nozzle. For convenience of description, the description of the primary jet nozzle is omitted.

Secondary jet nozzle 1 installed in the jet solder bath
The jet port 2 is composed of an inlet side nozzle plate 3, an outlet side nozzle plate 4, and nozzle side plates 5 (one side is not shown) on both sides thereof. A front former 6 is installed above the entrance side nozzle plate 3. The front former 6 has a curved shape, and the lower end thereof is immersed in the molten solder S.

A rear former 7 is installed above the exit side nozzle plate 4 so that the angle can be adjusted as shown by an arrow A. The rear former 7 is flat and long, and a guide plate 8 that prevents the molten solder flowing down from the rear former from splashing is installed at the tip.

The rear former 7 near the exit side nozzle plate 4
Above the peel back point PBP at which the printed board P separates from the rear former fluidized solder, a plurality of flow conversion means for changing the flow direction of the molten solder, for example, a plurality of current diversion plates 9 according to one embodiment are attached. The current-changing plate 9 is a strip-shaped plate whose long side is in contact with the rear former 7, and is attached obliquely to the traveling direction B of the printed circuit board P. The current-changing plate 9 is attached at a position where the soldering portion is lateral to the traveling direction of the printed circuit board, and the connector where the soldering portion is also lateral is passed.

A large number of holes 10 are formed in the rear former 7 at the position where the current transformer 9 is attached so as not to penetrate in the thickness direction of the rear former 7, and the long side portion of the current transformer 9 that is attached to the rear former is shown. No Two pins are installed. The attachment of the current transformer plate 9 to the rear former 7 is performed by inserting and fitting the pins of the current transformer plate 9 into the holes 10 of the rear former. Since the rear former 7 has a large number of holes 10 formed therein, the current transformer plate can be mounted by inserting pins into the holes corresponding to the positions on the printed circuit board where the electronic components that easily cause bridges are mounted. It can be selected appropriately, and the current transformer plate can be accurately attached to the bridge generation point.

Next, the soldering state in the jet solder bath of the present invention having the above structure will be described.

First, the printed circuit board P is made to travel on the secondary jet nozzle 1 in the direction of the arrow B by the transfer device (dashed line). The printed circuit board P first contacts the molten solder flowing on the front former 6 and then contacts the rear former fluidized solder flowing on the rear former, and further advances to be separated from the rear former fluidized solder. This PB to leave
If the flow direction of the rear former fluidized solder at P is at right angles to the soldering portions of the electronic components arranged in parallel, a bridge will occur.

In the present invention, since the current transformer plate 9 is installed near the PBP on the rear former, when the rear former fluidized solder flows near the current transformer plate 9, the current direction is changed by the current transformer plate 9. . That is, the current transformer 9 is
The rear former fluidized solder flowing near the current-changing plate 9 is partially inclined due to the current-changing plate 9 because it is oblique to the traveling direction of the printed circuit board.

When the printed circuit board on which the electronic component having the soldering portions arranged in the lateral direction is mounted is brought into contact with the rear former fluidized solder which partially flows in the oblique direction in this way, the soldering portions arranged in parallel are contacted. No bridges will occur.

This will be described with reference to FIG. 3, which illustrates an example in which the current-changing plates 9 are arranged at two positions for the convenience of understanding. In FIG. 3, assuming that the printed circuit board is transparent, such as glass, so that the flow of the rear former fluidized solder can be seen, on the back side of the printed circuit board made of glass, a large number of soldering parts L ... A large number of soldering portions K of ... Can be seen. The printed circuit board P runs in the direction of arrow B,
The rear former fluidized solder S also flows in the direction of arrow C, which is the same direction as the printed circuit board. In the rear former fluidized solder S, current transformer plates 9 and 9 shown by chain lines are obliquely attached. The rear former fluidized solder S originally flows in parallel to the traveling direction of the printed circuit board, but since the current transformer plate 9 is obliquely attached on the rear former, as shown in FIG. In, the flow direction is diagonal.

When the printed circuit board having the QFP or the connector passes through the place where the rear former fluidized solder flows obliquely in the vicinity of the current transformer plate 9 as described above, a large number of the printed circuit boards arranged side by side in the running direction of the printed circuit board. In the PBP, since the soldering portion of (1) is separated from the rear side in the flow direction of the rear former fluidized solder, the soldering portion becomes like the above-mentioned vertical parallel soldering portion, and the bridge does not occur. Needless to say, the shape of the current-changing plate 9 and the arrangement location and the number of arrangements are not limited to this example, and can be appropriately selected.

[0032]

As described above, according to the present invention, Q
Even if the mounting direction of electronic components such as FPs and connectors in which many soldering parts are arranged side by side is such that bridges are likely to occur, they are arranged side by side by partially changing the flowing direction of the rear former flowing solder. Since a large number of soldering portions are soldered by flowing in an oblique direction, it is possible to suppress the occurrence of bridges. Therefore, the design of the printed circuit board has a number of Q
This is an unprecedented excellent effect that it is possible to obtain a reliable soldered portion that can be freely performed without being restricted by the mounting direction or mounting position of the FP, the connector, and the like, and that does not cause soldering failure.

[Brief description of drawings]

FIG. 1 is a perspective sectional view of a secondary jet nozzle installed in a jet solder bath of the present invention.

FIG. 2 is a front sectional view of a secondary jet nozzle installed in a jet solder tank of the present invention, illustrating a soldering process for a printed circuit board.

FIG. 3 is a diagram illustrating a soldering method of the present invention.

[Explanation of symbols]

 1 Secondary Jet Nozzle 2 Jet Port 3 Entry Side Nozzle Plate 4 Exit Side Nozzle Plate 7 Rear Former 9 Current Change Plate 10 Hole P Printed Circuit Board PBP Peel Back Point S Molten Solder

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Hideaki Fukuda 1-2-11 Ikenohata, Taito-ku, Tokyo Aiwa Co., Ltd. (72) Inventor Zen Mitsuo, 23, Senju-Hashidocho, Adachi-ku, Tokyo Senju Metal Industry Co., Ltd. (72) Inventor Yasuhiro Watanabe 23, Senju-Hashidocho, Adachi-ku, Tokyo Senju Metal Industry Co., Ltd.

Claims (4)

[Claims] 1. A method of soldering a printed circuit board with a primary jet nozzle, and then correcting a soldering defect such as a bridge or icicle caused by soldering with the primary jet nozzle with a secondary jet nozzle to perform soldering. Part of the flow of the molten solder at the peel back point where the printed circuit board separates from the molten solder flowing on the rear former of the secondary jet nozzle, and a bridge is easily generated in the changed flow. A soldering method for a printed circuit board, which is characterized in that the soldering portions are brought into contact with each other for soldering. 2. In a jet solder bath in which a primary jet nozzle and a secondary jet nozzle are installed, flow conversion means for partially changing the flow direction of the molten solder is provided on a rear former of the secondary jet nozzle. A jet solder bath characterized by that. 3. The jet solder bath according to claim 2, wherein the flow conversion means includes a current transformer plate detachably attached to the rear former. 4. The rear former is provided with a large number of holes, and the current transformer plate is provided with pins that can be fitted into the holes of the rear former, and the pins of the current transformer plate are provided at appropriate positions on the rear former. By inserting and fitting into the hole of
The jet solder bath according to claim 3, wherein the current-changing plate is attached at a desired position.