JPH05198932A - Soldering method for printed board - Google Patents

Abstract

PURPOSE:To see that a lead and the through hole of a printed board can be soldered completely without causing solder inferiority between the lead and the mount of the printed board, when soldering an electronic part, where many leads are installed, to the printed board. CONSTITUTION:Solder paste 3 is applied on the mount of a printed board 1, and form solder 5 is placed thereon, and then an electronic part 6 is so mounted as to insert the leads 7 from on the form solder into through holes, and then the printed board is heated to fuse the solder paste and the form solder.

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 an electronic component, particularly an electronic component having a large number of short leads and a printed circuit board having a through hole.

[0002]

2. Description of the Related Art Generally, there are a flow method and a reflow method as a method for soldering a printed circuit board and an electronic component.

The flow method is a method in which flux is applied to the entire area of one surface of a printed circuit board on which electronic components are mounted, and then preheating is performed, and then one surface of the printed circuit board is brought into contact with the molten solder for soldering. Is.

The reflow method is to apply a solder paste to a soldering portion or to place a form solder on a soldering portion of a printed circuit board, and then mount an electronic component on the soldering portion. This is a method of soldering by heating with an irradiation device, a laser irradiation device, a hot air device, a high temperature steam device, etc. to melt the solder paste or foam solder.

Recently, electronic parts have become smaller and more multifunctional, and are highly integrated electronic parts, and a large number of leads are installed at narrow intervals. For example, PGA (Pi), which is widely used in computers and communication devices recently,
n Grid Alley) has more than 400 leads installed, and the distance between them is usually 2.54 mm.
There are narrow ones such as 1.27mm and 1.78mm. In addition to PGA, there are connector terminals and the like as parts having many leads.

When such a highly integrated electronic component is soldered by the flow method, the molten solder adhered between the leads cannot cut the solder between the leads due to surface tension and solidifies as it is to form a bridge. . Further, in the flow method, since the molten solder having a high temperature comes into direct contact with the electronic component, the function of the highly integrated electronic component, which is weak against heat, may be deteriorated due to heat shock.

In the reflow method, solder paste or foam solder is placed only on the soldering portion to gradually heat the whole, or only the soldering portion is locally heated, so that the electronic component may deteriorate in function due to heat shock. Absent.
Moreover, since a bridge is not formed if the solder paste is applied in an appropriate amount, the reflow method can be said to be the most suitable soldering method for highly integrated electronic components.

[0008]

By the way, when a highly integrated electronic component is soldered with a solder paste, a soldering failure may occur, that is, a mount of a printed circuit board and a lead may not be completely soldered. When parts were soldered with foam solder, the adhesive strength was not sufficient and the lead sometimes slipped out of the through hole.

According to the present invention, when soldering an electronic component such as a highly integrated electronic component having a large number of leads at narrow intervals to a printed circuit board, a soldering failure does not occur and the soldering strength can be sufficiently increased. To provide a soldering method.

[0010]

Means for Solving the Problems As a result of extensive studies made by the present inventors on causes of defective soldering and insufficient adhesive strength when highly integrated electronic components are soldered by a reflow method, solder paste It has been found that when used, soldering failure occurs due to insufficient solder amount.
In other words, it is only necessary to apply a large amount of solder paste in order to eliminate defective soldering, but then the coating shape collapses when heated and the solder paste comrades of adjacent soldering parts are united, As it is, it is soldered and forms a bridge. Therefore, a large amount of solder paste cannot be applied, and as a result, the amount of solder decreases and soldering failure occurs.

Further, when the foam solder is used in the reflow method, since the foam solder is simply placed on the through hole, even if the foam solder melts, it does not penetrate into the through hole and the through hole is not formed. It was also found that the adhesive strength was weakened because the leads were not soldered.

The present inventors have completed the present invention by paying attention to the fact that defective soldering and insufficient adhesive strength can be eliminated if soldering can be made to compensate for the respective drawbacks of the solder paste and the foam solder.

According to the present invention, a solder paste is applied to a soldering portion of a printed circuit board, a form solder is placed on the applying portion, and then electronic components are mounted on the solder paste applying portion and the foam solder placing portion. A soldering method for a printed circuit board, characterized in that a soldering portion is heated to melt a solder paste and a foam solder.

As the foam solder used in the present invention, a sheet-shaped foam solder in which a large number of solder washers are partially connected to form a sheet, or a single solder washer, a solder disc, a solder ball, etc. Is.

When a sheet-form foam solder is used, it is necessary to prevent a bridge from occurring at the connection between the solder washer and the solder washer.
For that purpose, it is preferable that the connecting portion is ½ or less of the diameter of the through hole and ⅕ or less of the outer diameter of the solder washer.

The solder paste may be applied by printing using a metal mask or silk screen, or may be applied by discharge with a dispenser.

When the solder paste is applied with a dispenser, the solder paste can be penetrated into the through holes by the ejection force of the dispenser. Further, even when the solder paste is applied by printing, the solder paste can be filled in the through holes by pressing at the time of printing. If the through-hole is filled with the solder paste, the through-hole and the lead can be reliably soldered.

[0018]

Next, a method of soldering an electronic component and a printed circuit board according to the present invention will be described. FIG. 1 is a perspective view illustrating a soldering method of the present invention, and FIGS. 2 to 5 are views illustrating respective steps of the soldering method of the present invention. 2 to 5 will be described below.

FIG. 2: The solder paste 3 is printed and applied on the mount 2 of the printed circuit board 1 in the same shape as the mount. The mount 2 of the printed circuit board 1 has a circular shape, and a through hole 4 is opened at the center thereof. When printing the solder paste, the solder paste is filled in the through holes by the pressing force of the squeegee.

FIG. 3: The sheet-form foam solder 5 is placed on the solder paste 3 applied. A convenient form solder for use in the present invention is one in which a large number of washer solders are partially connected and each washer solder is at the same position as the mount of the printed circuit board, as shown in FIG.

FIG. 4: After placing the sheet-shaped foam solder at a predetermined position, the leads 7 of the highly integrated electronic component 6 such as PGA are inserted into the through holes 4 of the printed board 1 through the holes of the sheet-shaped foam solder 5. To do.

FIG. 5: After mounting highly integrated electronic components on the printed circuit board, the entire printed circuit board is heated by a suitable heating device such as a reflow furnace to melt the solder paste and the foam solder. After melting and cooling, a fillet 8 of solder is formed on the mount 2 and the lead 7, and the solder also adheres to the inside of the through hole for complete soldering.

[0023]

According to the present invention, even if the amount of the solder paste applied is reduced, the foam solder compensates for it, and since the solder paste is also applied in the through holes, it is inserted into the through holes during soldering. The leads and through holes are completely soldered. Therefore, the present invention, there is no adhesion failure due to insufficient amount of solder and soldering failure due to unsoldered through holes,
It has an unprecedented excellent effect that a reliable soldered portion can be obtained.

[Brief description of drawings]

FIG. 1 is a perspective view illustrating a soldering method of the present invention.

FIG. 2 is a diagram for explaining the steps of the soldering method of the present invention in a state in which a solder paste is applied to a printed circuit board.

FIG. 3 is a view for explaining the steps of the soldering method of the present invention, showing a state in which a foam solder is placed on the solder paste application section.

FIG. 4 is a diagram for explaining the steps of the soldering method of the present invention, showing a state in which highly integrated electronic components are mounted on the foam solder.

FIG. 5 is a diagram for explaining the steps of the soldering method of the present invention, which is a state in which the solder paste and the foam solder are melted after the highly integrated electronic component is placed.

FIG. 6 is a front view of the sheet-form foam solder.

[Explanation of symbols]

 1 Printed Circuit Board 2 Mount 3 Solder Paste 4 Through Hole 5 Form Solder 6 Highly Integrated Electronic Component 7 Lead

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Osamu Munegata 405, Yatsuka-cho, Soka-shi, Saitama Senju Metal Industry Co., Ltd.

Claims (4)

[Claims] 1. A solder paste is applied to a soldering part of a printed circuit board, a form solder is placed on the applying part, electronic parts are mounted on the form solder, and then the soldering part is heated. A method for soldering a printed circuit board, which comprises melting a solder paste and a foam solder. 2. The method for soldering a printed circuit board according to claim 1, wherein the foam solder is a sheet-shaped foam solder in which a large number of solder washers are partially connected. 3. The method of soldering a printed circuit board according to claim 1, wherein the foam solder is a single foam solder such as a solder washer, a solder disk, and a solder ball. 4. The solder paste is applied in through holes of a printed circuit board.
A method for soldering a printed circuit board as described above.