JPH098449A - Wave soldering tank - Google Patents

Abstract

PURPOSE: To make it possible to solder efficiently a printed wiring board and in particular, to make it possible to solder a multitude of printed wiring boards with good accuracy. CONSTITUTION: A wave soldering tank has a primary nozzle and a secondary nozzle 1, a continuous rear former 7 is installed on a nozzle plate 4 on the rear side of this nozzle 1 and an oblong groove 8 is formed in this former 7.

Description

Detailed Description of the Invention

[0001]

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

[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 great deal of time to manufacture it, but the jigs and devices such as the screen, mask, printing device, reflow furnace, etc. are expensive. There was a problem with the cost.

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, even with a secondary jet nozzle for correcting bridges and fluff, bridges may occur depending on the conditions, so care must be taken.

[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.

Various factors can be considered as the cause of the occurrence of the bridge in the soldering by the secondary jet nozzle of the conventional jet solder bath. One of the factors is that the printed board is melted by the secondary jet nozzle. When the solder comes into contact with the solder, the flow velocity of the molten solder flowing on the rear former changes. In other words, the printed circuit board comes into contact with the molten solder flowing on the rear former of the secondary jet nozzle (hereinafter referred to as the rear former flowing solder),
This is because the flow velocity of the rear former fluidized solder changes when it moves away from the secondary nozzle fluidized solder.

When soldering for correcting bridges and flicker with a secondary jet nozzle, generally the same conditions as soldering in a static bath, that is, the printed circuit board is gently pulled upward from a quiet solder liquid surface. It was said that bridges would not occur if soldered in this state. If this state is reproduced by the secondary jet nozzle, the flow velocity of the rear former fluidized solder and the traveling speed of the printed circuit board are made to coincide with each other, and their relative speeds are made zero.

In a printed circuit board on which electronic components having a wide pitch of 0.8 mm or more between leads are mounted, a bridge does not occur if the relative speed is close to zero, but the distance between leads is 0.65.
On a printed circuit board that has electronic components with fine pitches of less than mm, a bridge will occur unless the relative speed approaches zero.

The reason why the secondary jet nozzle of the conventional jet solder bath cannot completely prevent the occurrence of bridging on the printed circuit board on which the fine pitch electronic parts are mounted is that the relative speed of the printed circuit board and the rear former fluidized solder is On the other hand, it is not possible to keep constant near zero. The solder jetted from the jet port flows to the front former or the rear former from a state in which it is higher than the traveling path of the printed circuit board. When the printed circuit board moves along the travel route, the solder that has risen above the travel route is pushed downward. The solder that is pushed downward flows to the front former or the rear former while increasing the flow velocity. That is, the flow velocity of the rear former fluidized solder is determined by the amount of solder that is pushed when the printed circuit board travels along the traveling path.

When the printed circuit board comes into contact with the molten solder which has become high in temperature, the resin printed circuit board is softened and a difference in thermal expansion between the front and back surfaces occurs, so that the central portion is warped downward. Even if the printed circuit boards have the same shape, the warpage is different. When the warp of the printed circuit board is large, the amount of pressing the fluidized solder is larger than that when there is no warpage, so that the flow velocity of the rear former fluidized solder is further increased. Also,
When the warpage of the printed circuit board is small, the amount of pressing the fluidized solder is smaller than that when the warpage is large, so that the flow velocity of the rear former fluidized solder is slower than the flow velocity when the warpage is large.

Therefore, for example, even if the flow speed of the rear former fluidized solder is adjusted to the traveling speed of a certain printed circuit board, the flow speed of the other printed circuit board is changed.

Since the flow velocity of the rear former fluidized solder changes for each printed circuit board in this way, even if the bridge is corrected for one printed circuit board, the flow rate of the rear former fluidized solder and the travel of the printed circuit board are different for other printed circuit boards. The speed does not match. Therefore, a bridge is generated in the printed circuit board on which the fine pitch electronic component is mounted.

When the present inventors observed the state of the molten solder flowing on the rear former of the secondary jet nozzle,
On the rear former, it was found that the molten solder had an upper layer flow and a lower layer flow, and the printed circuit board was in contact with the upper layer molten solder. Therefore, in order to completely prevent the occurrence of the bridge, the flow velocity of the upper layer flow may be matched with the traveling velocity of the printed circuit board so that the flow velocity is always constant.

[0019]

Means for Solving the Problems As a result of the inventors' earnest research on keeping the flow of the upper layer constant irrespective of the state of the printed circuit board, the flow of the upper layer accelerated by the printed circuit board on the rear former is found. It was found that when the pressure was held down, the effect propagated backward and the flow velocity of the molten solder did not change even in the part where the printed circuit board separated.

According to the present invention, in a jet solder bath in which a primary jet nozzle and a secondary jet nozzle are installed, a long rear former is installed on the exit side nozzle plate of the secondary jet nozzle. Is a jet solder bath.

The laterally elongated groove formed in the rear former according to the present invention has a semicircular section, a rectangular section, an inverted triangular section or the like. According to the results of experiments conducted by the present inventors, the cross section has a semicircular section to maintain a stable flow. The one was the best. However, in the present invention, any shape can be adopted as long as it has the effect of holding down the flow velocity of the upper layer flow when the molten solder flows into the groove.

[0022]

When the molten solder flowing on the flat rear former flows into the horizontally long groove, the flow of the lower layer flows along the bottom surface of the groove and collides with the flow of the upper layer above and in front of the groove. Therefore, when the printed circuit board comes into contact with the upper layer of the rear former fluidized solder and pushes the molten solder while the printed circuit board is running, the flow rate of the molten solder is increased for a moment, but the action of weakening the flow rate from the molten solder flowing into the groove propagates. Therefore, the flow velocity is constant throughout.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG.
2 is a perspective sectional view of a secondary jet nozzle installed in the jet solder tank of the present invention, and FIG. 2 is a view for explaining the flow of molten solder in the same front sectional view. 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 on 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 laterally long groove 8 having a semicircular cross section is formed at the tip thereof. A guide plate 9 that prevents molten solder flowing down from the rear former from splashing is installed outside the groove 8.

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

First, when a jet pump (not shown) of the secondary jet nozzle is driven, the molten solder S is blown upward from the jet port 2, partly in the front former 6 direction, and partly in the rear former 7 direction. Flow to. The rear former flowing solder flowing in the direction of the rear former 7 has different flow velocities such as the upper layer flow X and the lower layer flow Y. The lower layer flow Y flows along the rear former 7 and also inside the groove 8 along the groove. Therefore, when the lower layer flow Y reaches the end of the groove 8, the lower layer flow Y is blown upward as shown in FIG.

As shown in the figure, the upper layer flow X flows in the upper part of the secondary nozzle flowing solder and reaches the end of the groove 8,
At the end of the groove, it collides with the above-mentioned lower layer flow Y that has blown upward. Then, the upper layer flow X is prevented from flowing by the rising lower layer flow Y, and the flow velocity decreases here. If the flow of the straight upper flow is blocked midway, it is propagated backward and the flow velocity of the entire upper flow also decreases.

The printed circuit board P is caused to travel in the direction of arrow B by the transfer device (one-dot chain line) to the secondary jet nozzle in the fluidized state. The printed circuit board first comes into contact with the molten solder flowing on the front former 6, and then comes into contact with the rear former fluidized solder, and when further advanced, is separated from the rear former fluidized solder. Peel Back Point (PBP)
That is, the flow velocity of the upper layer flow in the PBP and the traveling velocity of the printed circuit board must match in order to prevent the generation of bridges in the jet solder bath.

The upper layer flow X is accelerated by the traveling printed circuit board P, but the flow velocity is not increased because the flow is blocked at the tips of the grooves 8. That is, if the flow velocity of the lower layer flow of the rear former fluidized solder is constant, the momentum of the lower layer flow being blown upward at the end of the groove 8 is also constant. Therefore, the state in which the upper layer flow is blocked at the end of the groove is always constant regardless of the flow rate of the upper layer flow, and the upper layer flow may or may not be running on the printed circuit board, and the immersion depth of the printed circuit board may be high. The flow velocity is constant even if the amount of solder pushed onto the printed circuit board changes due to a change in temperature. If the flow velocity of this upper layer flow is made to match the traveling speed of the printed circuit board, the bridge will not always be generated regardless of the state of the printed circuit board.

A printed circuit board having a large number of QFPs with a lead pitch of 0.5 mm was soldered by an automatic soldering apparatus having a jet solder bath of the present invention and a conventional automatic soldering apparatus having a jet solder bath. . In the jet solder bath of the present invention, after first searching for a condition that can completely eliminate the bridge with one printed circuit board, soldering of the same number of printed circuit boards was performed, and all the printed circuit boards had bridges. Was never generated. on the other hand,
Even with the conventional automatic soldering equipment equipped with a jet solder bath, we first searched for the condition that can eliminate the bridge with one printed circuit board, and then soldered many same printed circuit boards. Many printed circuit boards other than the board had many bridges.

[0032]

As described above, in the jet solder bath of the present invention, for a printed circuit board on which fine-pitch electronic components are mounted, if one bridge can be eliminated by one printed circuit board, After that, even if a large number of printed circuit boards are continuously soldered, it is possible to perform soldering with high reliability, which can completely prevent the generation of bridges.

[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 the jet solder bath of the present invention.

[Explanation of symbols]

 1 Secondary jet nozzle 2 Jet port 4 Exit side nozzle plate 7 Rear former 8 Groove P Printed circuit board S Molten solder PBP Peel back point

 ─────────────────────────────────────────────────── ─── 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 (1)

[Claims] 1. A jet solder bath having a primary jet nozzle and a secondary jet nozzle is provided with a long rear former on the exit side nozzle plate of the secondary jet nozzle, and the rear former is provided with a horizontally long groove. A jet solder bath characterized by being formed.