JPH05167242A - Method of bonding flexible circuit board - Google Patents

Abstract

PURPOSE:To reduce as little as possible the generation of a short-circuit between bonding parts due to solder bridges, the bulge of a flexible circuit board due to the generation of gas and the positional variation of the flexible circuit board from a nonflexible circuit-board when the flexible circuit board is placed on and bonded by soldering to the nonflexible circuit board in regard to a method of bonding the flexible circuit board, in particular in regard to a method of bonding the flexible circuit board to the nonflexible circuit board. CONSTITUTION:Conductor bonding parts (copper foil bonding parts) 1a are respectively formed on both surfaces of an insulating layer 1b on a flexible circuit board 1 on one side at prescribed intervals in opposition to each other and with a through hole 1c bored in the center of each conductor bonding part 1a, a thermosetting bonding agent 3 for securing temporarily is applied to gaps between the bonding parts 1a. Conductor bonding parts (copper foil bonding parts) 2a corresponding to the conductor bonding parts on the board 1 are formed on the other nonflexible circuit board 2 and solder 4 is previously applied to the bonding parts 2a. The board 1 is placed on the board 2 and the bonding parts 1a and 2a are aligned with each other and thereafter, the solder is heated and melted and the boards 1 and 2 are bonded together.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for joining a flexible circuit board, and more particularly to a method for joining a flexible circuit board.

In recent years, with the progress of high-density mounting on circuit boards, wiring patterns for electrically connecting the boards have become finer and finer, and the pitch intervals thereof have become extremely narrow, and the number of connecting wires has increased. Is coming. In such a situation, since the flexible circuit board is flexible, when it is superposed and soldered with a non-flexible circuit board, a short circuit due to a solder bridge between the joints and swelling and position of the flexible circuit board due to gas generation There is a strong demand for minimizing the deviation.

[0003]

2. Description of the Related Art FIG. 5 is a perspective view of an essential part, and FIG.
Sectional drawing, FIG. 7 is a DD sectional view of FIG.

As shown in the respective drawings, the conventional flexible circuit board joining method is such that the conductor joint portion 12a at the end of the wiring pattern of the inflexible circuit board 12 such as a glass epoxy resin laminated substrate, that is, the copper foil joint portion is previously prepared. After applying the solder 13, the conductor joint 11a at the end of the wiring pattern of the flexible circuit board 11 to be connected, that is, the copper foil joint is overlapped,
A portion (Q) of the overlapping portion of the flexible circuit board 11 is pressed and held from above by a holding tool (not shown), and a hot ram (not shown) is joined to the copper foil joint portion of the inflexible circuit board 12
The solder 13 is applied on the surface 12a and is heated and melted to be joined.

[0005]

However, according to the above-described joining method, there is a problem that a short circuit due to a solder bridge between copper foil joints or a bulge or displacement of the flexible circuit board due to gas generation occurs. ..

In view of the above problems, the present invention swells the flexible circuit board due to a short circuit (see FIG. 7) due to a solder bridge between the joint portions and gas generation during superposition soldering and joining with an inflexible circuit board. An object of the present invention is to provide a method for joining flexible circuit boards, which can minimize positional deviation.

[0007]

In order to achieve the above object, in the method for joining a flexible circuit board according to the present invention, the flexible circuit board is electrically joined to a non-flexible circuit board. Of the flexible circuit board is formed with opposing conductor joints at predetermined intervals on both sides of the insulating layer, a through hole is bored at the center of the conductor joints, and a thermosetting property for temporarily fixing in the gap between the conductor joints. An adhesive is applied, and a conductor joint portion corresponding to the conductor joint portion of the flexible circuit board is formed on the conductor joint portion of the other inflexible circuit board, and the conductor joint portion is previously formed.
After applying solder, stacking the flexible circuit board on the inflexible circuit board and aligning the conductor joints, press a part of the overlapping part from above the flexible circuit board with a retainer. The solder is temporarily adhered and held, and the solder is heated and melted from the inflexible conductor joint portion on the side of the circuit board to be joined.

[0008]

In one flexible circuit board, conductor joints with a predetermined interval are formed on both sides of the insulating layer so as to face each other, a through hole is formed at the center of the conductor joints, and the conductor joints are temporarily fixed in the gap between the conductor joints. Apply the thermosetting adhesive of
By previously applying solder to the conductor joint portion of the other inflexible circuit board, the flexible circuit board is superposed on the inflexible circuit board so that the conductor joint portion of the other side is formed from the through hole. The conductor joints can be easily aligned with each other while visually recognizing.

Further, since a part of the overlapped portion is pressed from above the flexible circuit board with a pressing tool to be temporarily bonded and held, workability is improved and positional displacement during bonding is less likely to occur.

Further, the solder can be melted with good thermal efficiency by heating from the conductor joint portion on the side of the inflexible circuit board. In addition, since the thermosetting adhesive between the conductor joints becomes a wall and excess molten solder escapes through the through holes to the conductor joints on the opposite surface, the generated gas can also escape from the through holes. It is possible to reduce the swelling of the flexible circuit board due to the short circuit due to the bridge and the generation of gas.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The gist of the present invention will be described in detail below with reference to the embodiments shown in the drawings. Fig. 1 is a sectional view of the main part before joining
2 is a cross-sectional view taken along the line AA of FIG. 1, FIG. 3 is a cross-sectional view taken after the joining of FIG. 1, and FIG. 4 is a cross-sectional view taken along the line BB of FIG.

As shown in the drawings, the method of electrically bonding a flexible circuit board to a non-flexible circuit board is such that one tape-shaped flexible circuit board 1 is provided on both sides of the insulating layer 1b at predetermined intervals. Conductor joints with a predetermined line width arranged
1a, that is, the copper foil joints are formed to face each other. The copper foil joint portion 1a-1 on the joint surface side is formed by peeling off the insulating layer 1b-1 on one side (lower side) of the copper foil joint portion 1a-1 to expose the end itself of a wiring pattern (not shown). These wiring patterns and copper foil joints 1a are insulating layers.
A solder resist (not shown) is applied to 1b in advance by pattern etching processing of the deposited copper foil, and except for the copper foil bonding portion 1a to be soldered.

Further, a through hole having a diameter smaller than the line width of the copper foil joint 1a is formed at the center of the copper foil joint 1a on both sides thereof.
1c is perforated by punching. It is desirable to punch the through hole 1c before the pattern etching of the copper foil in order to reduce distortion. Also, the through hole plating on the inner wall surface of the through hole 1c is the thickness of the insulating layer 1b of the flexible circuit board 1. Since it is thin, it may be omitted. Next, a thermosetting adhesive 3 for temporarily adhering to the gap between the copper foil joints 1a-1 on the joint surface is applied by screen printing.

On the other hand, the other inflexible circuit board 2, for example, a glass epoxy resin laminated board, is formed by pattern etching the conductor joint portion 2a corresponding to the copper foil joint portion 1a of the flexible circuit board 1, that is, the copper foil joint portion. Formed, and the creamy solder 4 is applied to the copper foil joint 2a in advance.

Next, the flexible circuit board 1 is overlaid on the inflexible circuit board 2, the copper foil joints 2a, 1a-1 are aligned with each other, and a part P of the overlapped portion is covered by the flexible circuit board 1. From above, hold it with a pressing tool (not shown) and temporarily hold it with a thermosetting adhesive 3 applied beforehand, and apply a hot ram (not shown) to the copper foil joint 2a on the inflexible circuit board 2 side for soldering. 4 is melted by heating and joined.

As described above, in one flexible circuit board, conductor joints are formed on both surfaces of the insulating layer so as to face each other, through holes are formed in the conductor joints, and a thermosetting adhesive is provided in the gap between the conductor joints. It is possible to visually confirm that the conductor joints on the other side can be seen evenly from the through holes by applying the solder and applying solder to the conductor joints on the other inflexible circuit board in advance. However, since the conductor joints are aligned with each other, the positioning can be facilitated.

Further, since the flexible circuit board can be pressed from above to be temporarily adhered and held, workability is improved and positional displacement during bonding is less likely to occur. Furthermore, since the thermosetting adhesive between the conductor joints becomes a wall, excess molten solder escapes through the through holes to the conductor joints on the opposite side, and the generated gas also escapes from the through holes. Swelling of the flexible circuit board due to short circuit and gas generation can be reduced. At that time, the thermosetting adhesive can be cured after bonding to further enhance the mechanical bonding strength.

It should be noted that although the above-mentioned joining portions are the respective edge portions of the circuit board, it goes without saying that they can be joined by the same method even inside the circuit board.

[0019]

As described above in detail, according to the present invention,
When joining a flexible circuit board to a non-flexible circuit board, it is possible to reduce short-circuits due to solder bridges between joints and swelling and displacement of the flexible circuit board due to gas generation, thus improving work efficiency. The yield is improved, and a highly reliable high-density packaging circuit board can be manufactured at low cost, which is extremely useful in the industry.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a main part before joining according to an embodiment of the present invention.

2 is a sectional view taken along line AA of FIG.

FIG. 3 is a sectional view after joining in FIG.

FIG. 4 is a sectional view taken along line BB of FIG.

FIG. 5 is a perspective view of a main part according to a conventional technique.

FIG. 6 is a sectional view taken along line CC of FIG.

7 is a sectional view taken along line DD of FIG.

[Explanation of symbols]

 1 is a flexible circuit board 1a, 1a-1, 2a is a conductor joint (copper foil joint) 1b, 1b-1 is an insulating layer 1c is a through hole 2 is a non-flexible circuit board 3 is a thermosetting adhesive 4 is solder

Claims (1)

[Claims] 1. A method of electrically joining a flexible circuit board to a non-flexible circuit board, wherein one flexible circuit board (1) has conductor joining portions at predetermined intervals on both surfaces of its insulating layer (1b). (1a) are formed to face each other, and a through hole (1c) is formed at the center of the conductor joint portion (1a), and the conductor joint portion is formed.
Of the (1a), a thermosetting adhesive (3) for temporary fixing is applied in the gap between the conductor joints (1a-1) on the joint surface side, and the other inflexible circuit board (2) is the conductor joint (2) corresponding to the conductor joint (1a) of the flexible circuit board (1).
a) is formed, solder (4) is applied in advance on the conductor joint (2a), and the flexible circuit board (2) is applied to the inflexible circuit board (2).
After aligning (1) and aligning the conductor joints (2a, 1a-1) with each other, part of the overlapped parts is placed on the flexible circuit board.
(1) Hold the temporary adhesive by pressing it with a presser from the top, and from the inflexible circuit board (2) side conductor joint (2a) to the solder
(4) A method for joining a flexible circuit board, which comprises heating and melting and joining.