JP2821070B2 - Composite printed circuit board joining method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed circuit board joining method for electrically connecting lead electrodes of two printed circuit boards by soldering.

[0002]

2. Description of the Related Art In recent years, printed wiring boards used in electronic equipment have been increased in density, multilayered, and three-dimensional due to demands for lighter, thinner, and shorter electronic devices. Particularly, in order to three-dimensionally use a limited space, a technique has been proposed which aims at higher reliability of wiring connection between a flexible substrate and a hard substrate.

For example, as shown in FIGS. 6 and 7, a solder resist film 3 is provided so as to be exposed on the surface of a through hole 2 formed in a flexible substrate 1. Similarly, a through hole 5 and a solder resist film 6 are provided on the hard substrate 4. The flexible substrate 1 and the hard substrate 4 are bonded and hardened by the adhesive layer 7.

The solder paste 8 printed on the flexible substrate 1 can be heated and melted and dropped into the through holes 5 of the hard substrate 2. Solder 9 after melting and solidification is formed, and wiring connection between flexible substrate 1 and hard substrate 2 is performed.

As another embodiment, as shown in FIG.
A flexible substrate 11 on which a plurality of lead electrodes 11a are formed;
The adhesive layer 13 is preliminarily temporarily bonded by heat and fixed to the hard substrate 12 on which a plurality of lead electrodes 12a are formed.
Thereafter, the preliminary solder 14 located between the flexible substrate 11 and the hard substrate 12 is melted by heating, so that the two lead electrodes 11a and 12a are joined together. It should be noted that the heating may be performed by any of a reflow method and a heat press method.

[0006]

In the former joining method of the prior art, air at the time of printing the solder paste 8 enters the through holes 2 and 5 to generate air bubbles at the time of heat melting, or to form a cured adhesive. If air bubbles due to the generation of gas from the layer 7 exist at the interface between the flexible substrate 1 and the hard substrate 4 at the opposing electrode portion, there is a problem such as poor conduction between the wiring connection portions of the two.

In the latter joining method, the lead electrode 1
When the facing area between 1a and 12a is small, the soldering at the joint is insufficient and there is a disadvantage that conduction failure is likely to occur. The present invention has been made in order to solve such a drawback, and a method of joining a composite printed circuit board capable of improving the electrical connection between a flexible board and a hard board, which are wired at high density, with high reliability. It is intended to provide.

[0008]

Means for achieving the above object are as follows. (1) A flexible substrate having a wiring circuit on one or both sides and a plurality of comb-shaped lead electrode portions. If, Shirubedenpa a rigid substrate having a wiring circuit on both surfaces or multilayer the joining method of the composite printed circuit board wiring connected, on both sides a plurality of comb-shaped lead electrode portion of the film base of the flexible substrate
Turns are formed, and a plurality of slits are alternately formed in the lead electrode of the comb-shaped electrode portion at both end portions of the lead electrode.
The flexible substrate and a hard substrate having a plurality of pre-soldered lead electrodes are provided so as to be disposed on the respective lead electrodes.
There is to provide a method of bonding a composite printed circuit board, characterized in that joined to face each other, and so as to hardwired melted by heating the preliminary solder.

Another means is as follows: (2) A side wall surface of a through hole is formed as the slit portion .

As another means, (3) solder plating is applied to the entire surface of the lead electrode of the flexible substrate.

[0011]

When the lead electrodes of both substrates are soldered, the heated and melted solder flows around each lead electrode and also flows into the slits, increasing the solder contact area and increasing the solder strength.

Further, when the side wall surface of the through hole is provided, the molten solder also flows into the side wall surface of the through hole, so that the solder contact area is increased and the solder strength is further increased.

Furthermore, by plating the entire surface of the lead electrode with solder, the molten solder flows over the entire periphery of each lead electrode, thereby forming a fillet portion on the entire side surface of the lead electrode, thereby further increasing the solder strength of each lead electrode. Increase.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a plan view of a main part of a lead electrode of a flexible substrate showing a first embodiment of the present invention. FIG. FIG.

The plurality of lead electrodes 21a provided on the flexible substrate 21 are formed in a comb shape.
a is provided with a plurality of slits 21b. Specifically, the film base 22 other than the area of the lead electrode 21a is cut off at the joint side end of the flexible substrate 21,
Only the area of the lead electrode 21a is a comb-shaped projection 23.
It is formed so that it becomes.

On the other hand, a plurality of lead electrodes 2
4a are formed, and preliminary solder 25 is applied on each lead electrode 24a.

Next, a method of joining the two substrates 21 and 24 will be described. First, the lead electrodes 21a and 24a of the substrates 21 and 24 are opposed to each other, and the lead electrodes 21a of the flexible substrate 21 are aligned so as to be in contact with the preliminary solder 25 of the hard substrate 24. Then, the adhesive layer 26 is temporarily bonded in advance by heat, and the flexible substrate 21 and the hard substrate 24 are fixed. Then, the lead electrodes 21a and 24a are joined by heating the preliminary solder 25 with a soldering iron (not shown) to re-melt the solder.

The width of the lead electrode 21a is set to be narrower than that of the lead electrode 24a in order to prevent a bridge connection with an adjacent electrode due to a displacement of each of the lead electrodes 21a and 24a.

Good bonding can be obtained by any of the reflow method and the heat press method.

As described above, the lead electrodes 21 of both substrates
When the solders a and 24a are soldered, the melted solder flows around each lead electrode 21a and also flows into the slit 21b provided in the lead electrode 21a, so that the contact area of the solder increases.

FIG. 3 is a plan view of a main part of a second embodiment of the present invention in which a flexible substrate and a hard substrate are connected by wiring, and FIG. 4 is a cross-sectional view of the main part of FIG. ) Is the arrow AA in FIG.
FIG. 4B is a cross-sectional view of FIG. 3B, and FIG. 4C is a cross-sectional view of FIG.

The flexible substrate 31 has conductor patterns 33 formed on both sides of a film base 32.
Are connected by a plurality of through-hole side wall surfaces 33a, 33a.

On the other hand, the hard substrate 35 is
And a plurality of lead electrodes 37, 37.

When the two substrates 31 and 35 are connected by wiring, the lead electrodes 34 and 37 of the two substrates 31 and 35 are opposed to each other, and the lead electrodes 34 of the flexible substrate 31 are connected to the hard substrate 3.
The lead electrode 37 having the 5 preliminary solders 36 is combined. Then, the bonding layer 38 is temporarily bonded in advance by heat, and the substrates 31 and 35 are fixed. Then, the lead electrodes 34 and 37 are joined by heating the preliminary solder 36 with a soldering iron (not shown) to re-melt the solder.

In this case, the molten solder also flows into the side wall surfaces 33a, 33a of the through holes, and a fillet portion 39 is formed on the side wall portion, so that the solder strength of each of the lead electrodes 34 and 37 is increased.

FIG. 5 is a sectional view of a main part of a third embodiment of the present invention in which a flexible substrate and a hard substrate are connected by wiring. The plan view of the main part is the same as that of the second embodiment shown in FIG. 5A is a cross-sectional view corresponding to an arrow AA in FIG. 3, and FIG. 5B is a cross-sectional view corresponding to an arrow BB in FIG.

The flexible substrate 41 has a conductor pattern 43 formed on the entire surface of the film base 42.
Are provided with a plurality of lead electrodes 45, 45 each having a solder plating layer 44 formed on the entire surface thereof. Note that the lead electrode 45 may have the slit 21b or the through-hole side wall surface 33a.

On the other hand, the hard substrate 46 is
And a plurality of lead electrodes 48, 48.

When the two substrates 41 and 46 are connected by wiring, the lead electrodes 45 and 48 of the two substrates 41 and 46 are opposed to each other, and the lead electrodes 45 of the flexible substrate 41 are connected to the hard substrate 4.
6 and the lead electrode 48 having the preliminary solder 47. Then, an adhesive layer (not shown) provided in advance is temporarily bonded by heat, and the substrates 41 and 46 are fixed. After that, the pre-solder 47 is heated again by a soldering iron (not shown) to be re-melted, so that the lead electrodes 45 and 48 are joined.

In this case, the molten solder flows into each side surface portion 45a of the lead electrode, and a fillet portion 49 is formed on the side surface portion 45a, so that the solder strength of each of the lead electrodes 45 and 48 is increased.

[0031]

Since the present invention has the above-described structure, the following effects can be obtained. The pre-solder of the bonding lead electrode of the hard board is melted and the lead electrodes of both boards are soldered. However, since the lead electrodes of the flexible board have slits, the molten solder may also flow into the slits. Therefore, the solder contact area increases, and a stronger and more reliable bonding can be obtained.

Further, by forming the side wall surface of the through hole on the lead electrode, the solder flows into the side wall surface of the through hole, and a fillet portion is formed, so that the solder strength is further increased.

Further, by forming a solder plating layer on the entire surface of the lead electrode, the solder flows into the entire area of the side wall surface of the lead electrode, and a fillet portion is formed, thereby further increasing the solder strength.

[Brief description of the drawings]

FIG. 1 is a plan view of a main part of a lead electrode of a flexible substrate according to the present invention.

FIG. 2 is a plan view of a main part showing a connection between a flexible substrate and a hard substrate according to the first embodiment of the present invention.

FIG. 3 is a plan view of a main part showing a connection between a flexible substrate and a hard substrate according to a second embodiment of the present invention.

4 is a cross-sectional view of a main part of FIG. 3; FIG.
A sectional view, (b) is an arrow BB sectional view, (c) is an arrow C
It is -C sectional drawing.

5 (a) and 5 (b) are main part views showing a connection between a flexible substrate and a hard substrate according to a third embodiment of the present invention, wherein FIG. 5 (a) is a cross-sectional view corresponding to arrow AA in FIG. 3, and FIG. FIG. 4 is a sectional view corresponding to an arrow BB in FIG. 3.

FIG. 6 is a cross-sectional view of a through-hole after a solder paste printing step, showing a bonding between a flexible substrate and a hard substrate according to the related art.

FIG. 7 is a cross-sectional view of a through hole in which wiring is connected by a heating and melting step of the solder paste.

FIG. 8 is a plan view of a main part showing a connection between a flexible substrate and a hard substrate according to another embodiment of the prior art.

[Explanation of symbols]

21, 31, 41 Flexible substrate 21a, 24a, 34, 37, 45, 48 Lead electrode 21b Slit 24, 35, 46 Hard substrate 33a Through hole side wall surface 39, 49 Fillet portion 44 Solder plating layer

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H05K 3/36 H05K 1/14 H05K 1/11

Claims (3)

(57) [Claims] [Claim 1 further comprising a printed circuit on one or both sides, a flexible substrate having a plurality of comb-shaped lead electrode portion, a composite printed circuit board wiring connecting the rigid substrate having a wiring circuit on both surfaces or multilayer In the bonding method, the plurality of comb-shaped lead electrode portions of the flexible substrate are provided on both sides of a film base.
A plurality of slits are formed in a lead electrode of the comb-shaped electrode portion on both side ends of the lead electrode.
The flexible substrate and a hard substrate having a plurality of pre-soldered lead electrodes are joined so that each lead electrode faces each other, and the pre-solder is heated and melted. A method of joining a composite printed circuit board, wherein the connection is made by wiring. 2. The method according to claim 1, wherein a side wall surface of a through hole is formed as the slit . 3. The method according to claim 1, wherein the entire surface of the lead electrode of the flexible substrate is plated with solder.