JPH0444440B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a printed circuit board bonding method for electrically connecting respective bonding pattern portions of two printed circuit boards by soldering.

(Prior Art) FIG. 1 shows a bonding section of a conventional printed circuit board. This conventional example includes a flexible printed circuit board A having a structure in which a conductive pattern 2 is formed on a flexible film base 1 and the conductive pattern 2 is protected by an insulating cover film 3, and a flexible printed circuit board A made of paper epoxy, glass epoxy, etc. This figure shows the connection between a printed circuit board B having a structure in which a conductive pattern 5 is formed on a base 4 and the conductive pattern 5 is protected by a solder resist 6. That is, the bonding pattern portion 2 at the end of each conductor pattern 2, 5 of both substrates A, B
a, 5a are the bonding pattern portions 2a, 5a without covering with the cover film 3 and solder resist 6.
is exposed. Also, printed circuit board B
Preliminary solder 7 is applied on the bonding pattern portion 5a in advance. Then, as shown in FIG. 1a, the bonding pattern portions 2a and 5a of the conductor patterns 2 and 5 of both substrates A and B are faced to each other, and the bonding pattern portion 2a of the flexible printed circuit board A is connected to the printed circuit board B. They are placed so that they are in contact with the preliminary solder 7, and heat is applied with a soldering iron 8 while applying pressure to melt the preliminary solder 7 and join them.

However, in this conventional joining method, since the heating by the soldering iron 8 is indirect heating through the base film 1, it takes time for the preliminary solder 7 to melt, and the part where the preliminary solder 7 is melted is This tends to occur only in the portion that is in contact with the soldering iron 8, which causes a problem that it is difficult to perform a good solder joint. For this reason, when performing such joining, an improvement measure may be taken in which a large, special soldering iron jig is used instead of the ordinary soldering iron 8, but this poses a problem in that it becomes more labor-intensive. or,
The basic problem with the conventional method is that both joints 2
The bonding strength of the preliminary solder 7 is weak because the preliminary solder 7 is only in surface contact with a and 5a, and furthermore, in order to melt the entire preliminary solder 7, the soldering iron 8 is firmly attached to the film base 1. If crimped, the solder 7 will be pushed out to both sides, causing problems such as improper bridging with the joints 2a, 5a of the adjacent conductor patterns 2, 5.

(Object of the Invention) The present invention was made to solve the above-mentioned conventional problems, and it is an object of the present invention to provide a printed circuit board joint structure and a joining method in which the joining process is simple and the joining strength is high. With the goal.

In order to achieve the above object, the joining method of the present invention has the following features:
a first printed circuit board having a plurality of first bonding patterns; a second printed circuit board having a plurality of second bonding patterns; In addition, in the method for bonding printed circuit boards in which both bonding patterns are bonded to each other by melting preliminary solder located therebetween, the second printed circuit board is a flexible printed circuit board, and the plurality of bonding patterns in the second printed circuit board are A second bonding pattern is formed in a comb-like shape, and a length of the bonding area with at least the plurality of first bonding patterns is formed directly behind the plurality of second bonding patterns on the second printed circuit board. A plurality of heat conduction patterns having a thickness are formed to be exposed, and when the plurality of first bonding patterns and the plurality of second bonding patterns are combined, the plurality of heat conduction patterns are formed so as to be exposed. Applying direct heat to melt the preliminary solder between the two bonding patterns,
New solder is mixed and melted with the preliminary solder at the heat transfer pattern position to form the plurality of second solders.
The present invention is characterized by a method for bonding printed circuit boards in which both bonding patterns are bonded including the periphery of the comb-like protrusion at the bonding pattern position.

(Example) FIGS. 2 and 3 show an example of the premise of the present invention, in which A is a flexible printed circuit board, and a circuit is mounted on an insulating film base 1 having a flexibility of 0.3 mm or less. A conductor pattern 2 is provided on which a net, lands for connecting circuit components, etc. are formed, and an insulating cover film 3 is further applied thereon to protect the conductor pattern 2. . B is constructed by similarly providing a conductive pattern 5 on an insulating base 4 made of paper epoxy material, glass epoxy material, etc., and further printing a solder resist 6 thereon. on the other hand,
At the end of the flexible printed circuit board A, the cover film 3 is cut out to expose a conductive pattern 2, and this exposed pattern 2 serves as a bonding pattern portion 2a with the printed circuit board B. or,
The conductive pattern 5 is also exposed at the end of the printed circuit board B without printing the solder resist 6.
This exposed pattern 5 is the bonding pattern portion 5a.
It is becoming. Further, preliminary solder 7 is applied on the bonding pattern portion 5a. As a characteristic feature of the present invention, the flexible printed circuit board A is provided with a dummy pattern 9 made of the same material as the conductive pattern 2a, such as copper foil, and having good thermal conductivity. As is clear from the figure, this dummy pattern 9 is provided on the film base 1 in an area directly behind the bonding pattern portion 2a.

Next, a method for joining both the substrates A and B will be described. First, the bonding pattern portions 2a and 5a of the printed circuit boards A and B are opposed to each other, and the bonding pattern portion 2a of the flexible printed circuit board A is aligned with the preliminary solder 7 of the printed circuit board B. When the soldering iron 8 is placed on the dummy pattern 9, the heat from the soldering iron 8 spreads over the entire dummy pattern 9, which has good thermal conductivity, and is transmitted to the bonding pattern portion 2a via the film base 1, and the preliminary solder is 7
Both bonding pattern parts 2a, 5a are melted in their entirety.
A strong bond can be achieved. Therefore, by providing the dummy pattern 9, the soldering iron 8
Even if the soldering iron itself is a normal soldering iron as shown in the figure, the entire preliminary solder 7 can be melted, and
Appropriate bonding can be obtained without applying particular pressure. Note that in order to prevent bridge connections between adjacent patterns due to positional deviations between the bonding pattern portions 2a and 5a, the bonding pattern portion 2a is set to be wider than the bonding pattern 5a.

Next, another example which is the premise of the present invention will be explained with reference to FIGS. 4 and 5.

Another example is the dummy pattern 9 in the above example.
This figure shows an implementation in which the conductive pattern 2 and the through hole 10 are connected, and the other configurations are the same as in the example. That is, flexible printed circuit board A
A dummy pattern 9 provided on the film base 1 is connected by a through hole 10 at a position extremely close to the bonding pattern portion 2a. Note that 10a is a land pattern for through holes. Therefore, in this embodiment, both substrates A and B
In the bonding process, the heat of the soldering iron 8 applied to the dummy pattern 9 is instantly transmitted to the bonding pattern portion 2a via the through hole 10, and the entire preliminary solder 7 can be melted in a shorter time than in the example case. can.

Next, a first embodiment of the present invention will be explained with reference to FIGS. 6 and 7.

In this first embodiment, the bonding pattern portion 2a of the flexible printed circuit board A is formed in a comb-like shape. Specifically, as shown in FIG. 7, at the bonding end of the flexible printed circuit board A, the film base 1 other than the bonding pattern portion 2a is cut out, and only the bonding pattern portion 2a is provided with comb teeth. The protrusion 12 is formed to have a shape. Note that, similarly to the above example, since the width of the bonding pattern 2a of the flexible printed circuit board A is set to be narrower than that of the bonding pattern portion 5a of the printed circuit board B, each of the protruding portions protruding in the comb shape is The width of the bonding pattern portion 5a is also narrower than the width of the bonding pattern portion 5a. Further, the dummy pattern 9 is provided on the film base 1 on the back side of the bonding pattern section 2a of the comb-like protrusion section 12. The other configurations are the same as those in the above-mentioned example, so explanations will be omitted.

Next, a method for joining both substrates A and B will be explained.

First, the bonding pattern portions 2a and 5a of both printed circuit boards A and B are opposed to each other, and the bonding pattern portion 2a of the flexible printed circuit board A is connected to the printed circuit board B.
Align it so that it is in contact with the preliminary solder 7. however,
In this embodiment, the tip of the bonding pattern portion 2a and the end surface of the solder resist 6 are aligned so as to leave a slight gap. Then, the soldering iron 8 is applied onto the dummy pattern 9, and the thread solder 20 is also brought into contact with the tip of the soldering iron 8 and melted. As a result, heat is spread throughout the preliminary solder 7 by the dummy pattern 9, so that the entire portion is melted, and furthermore, the melted solder thread 20 is transferred to the comb-like protrusion 12 of the flexible printed circuit board A. The bonding pattern portions 2a and 5a are completely bonded to each other, including the periphery thereof, thereby achieving extremely strong bonding between the bonding pattern portions 2a and 5a. In addition,
During this joining, it has been confirmed that under general conditions, the preliminary solder 7 and the thread solder 20 mix during the melting process.

What is distinctive about this embodiment is that whereas the above-mentioned example involves bonding by contacting both sides of the molten preliminary solder 7, this embodiment performs bonding by three-dimensional adhesion including surface contact. The reason is that it is possible to achieve a stronger and more reliable bond. In this embodiment, the molten solder 21 is also applied around the protrusion 12 having the bonding pattern 2a, especially on the side surface.
Since the width of 2 is set narrower than the width of the bonding pattern portion 5a of the printed circuit board B, there will be no possibility of incorrect bridging with the adjacent bonding pattern 2a or 5a.

Next, a second embodiment of the present invention will be described with reference to FIGS. 8 and 9.

In this second embodiment, the bonding pattern portion 2a of the flexible printed circuit board A in the other example described above is formed into a comb-like protruding portion 12, and a dummy pattern bonded by a through hole 10 is formed. Since the molten solder is also applied on the through hole 9, the film base 1 has a second through hole 10 that protects the through hole 10.
A cover film 14 is placed thereon. The other configurations are the same as those of the other examples described above, so the explanation will be omitted.

The method of joining both printed circuit boards A and B in this second embodiment is as follows with a soldering iron 8 as in the first embodiment described above.
When the dummy pattern 9 is heated, the wire solder 20 is also melted, and the entire area including the periphery of the protrusion 12 having the bonding pattern portion 2a is bonded with the molten solder 21. The fourth embodiment is characterized in that the heat of the dummy pattern 9 is quickly transferred to the bonding pattern portion 2a by the through hole 10, so that the time required for bonding is shorter than that of the structure of the first embodiment.

The feature of the embodiment described above is that the dummy pattern 9 allows both bonding pattern portions 2a, 5
The preliminary solder 7 in step (a) can be completely melted in a short time to achieve a strong bond. or,
By connecting the dummy pattern 9 and the bonding pattern portion 2a through the through hole, the bonding time can be further shortened.

Furthermore, not only the preliminary solder 7 is melted but also new solder (thread solder 2
By joining three-dimensionally using 0), a stronger and more reliable joint can be obtained.

Note that the dummy pattern 9 in the above embodiment is
In one example and the first embodiment, the pattern is an independent pattern that does not constitute a circuit network, and in the other example and the second embodiment, the through hole 10 of the bonding pattern portion 2a
For example, when the printed circuit board on which the dummy pattern 9 is provided is a double-sided board, the pattern according to the present invention may be provided as an extension pattern of the conductor pattern constituting the circuit network.

In addition, the flexible printed circuit board A was used as the printed circuit board on which the dummy pattern 9 is provided in the embodiment, because this thin flexible printed circuit board A is preferable in terms of heat conduction. In addition, in the embodiment, the length of the dummy pattern 9 was made slightly longer than the length of the bonding region in both bonding pattern portions 2a, 5a, so the dummy pattern 9
The preliminary solder 7 melts to the edge of the bonding area due to the heat conduction of the flexible printed circuit board A.
It is possible to obtain a bond that is resistant to stress caused by curvature. If there is no dummy pattern 9, the preliminary solder at the end of the bonding area may not be completely melted, resulting in the disadvantage that it may come off due to bending stress due to the curved arrangement, which is the original purpose of the flexible printed circuit board. There will be more and more.

Furthermore, the dummy pattern 9 in the embodiment also has the effect of increasing the strength of the comb-like protrusions of the flexible printed circuit board A. Therefore, the accident of accidentally breaking the comb-like protrusions before joining can be prevented.

(Effects of the Invention) As described above, the present invention provides a method for connecting the first bonding pattern of the first printed circuit board and the second bonding pattern of the second printed circuit board, which is a flexible printed circuit board, between the In the method for bonding printed circuit boards in which preliminary solder is melted and bonded, the second bonding pattern on the second printed circuit board is formed into a comb-like shape, and the second bonding pattern is formed directly behind the second bonding pattern. A heat conduction pattern that is longer than the bonding area is formed, and heat is applied directly to this heat conduction pattern using a soldering iron to melt the preliminary solder between both bonding patterns, resulting in a bond using the heat conduction pattern. Due to heat conduction throughout the area, the preliminary solder can be reliably melted to the ends in a short time, and furthermore, new solder can be mixed with the preliminary solder at the position of the pattern for heat conduction and melted. Then, both bonding patterns were bonded including the periphery of the comb-like protrusion in the second bonding pattern, so 3
Dimensional joining is possible, resulting in stronger and more reliable joining.

[Brief explanation of drawings]

FIG. 1a is a sectional view of a main part showing a joint part of a conventional printed circuit board. FIG. 1b is a plan view of FIG. 1a. Second
The figure is a sectional view of a main part showing a joint part of a printed circuit board as an example of the premise of the present invention. FIG. 3 is a plan view of FIG. 2. FIG. 4 is a sectional view of a main part showing a joint part of a printed circuit board as another example on which the present invention is based. FIG. 5 is a plan view of FIG. 4. FIG. 6 is a sectional view of a main part showing a bonding part of a printed circuit board as a first embodiment of the present invention, FIG. 6a shows a state immediately before bonding, and FIG.
Figure b shows the state after bonding. FIG. 7 is a plan view of FIG. 6. FIG. 8 is a sectional view of a main part showing a bonded portion of a printed circuit board according to a second embodiment of the present invention after bonding. FIG. 9 is a plan view of FIG. 8. A... Flexible printed circuit board, B... Printed circuit board, 2, 5... Conductor pattern, 5a, 5a
...Joining pattern section, 7...Preliminary solder, 8...
Soldering iron, 9... dummy pattern, 20... thread solder.

Claims (1)

[Scope of Claims] 1. A first printed circuit board having a plurality of first bonding patterns, and a second printed circuit board having a plurality of second bonding patterns, the first printed circuit board having a plurality of second bonding patterns. In the printed circuit board bonding method of joining both bonding patterns by aligning the second bonding patterns and melting the preliminary solder located between them, the second printed circuit board is a flexible printed circuit board, and the second bonding pattern is melted. The plurality of second bonding patterns on the second printed circuit board are formed in a comb shape, and at least the plurality of first bonding patterns are formed directly behind the plurality of second bonding patterns on the second printed circuit board. A plurality of heat conduction patterns having a length of a bonding area with the pattern are formed to be exposed, and in a state where the plurality of first bonding patterns and the plurality of second bonding patterns are combined, Applying heat directly to the heat conduction pattern to melt the preliminary solder between the two bonding patterns,
New solder is mixed and melted with the preliminary solder at the heat transfer pattern position to form the plurality of second solders.
A method for bonding printed circuit boards, characterized in that both bonding patterns are bonded including the periphery of the comb-like protrusion at the bonding pattern position. 2. The method of bonding printed circuit boards according to claim 1, wherein the plurality of second bonding patterns and the plurality of heat conduction patterns are each connected by a through hole. 3. In claim 1 or 2, the plurality of second bonding patterns are formed narrower than the plurality of first bonding patterns, and the width of each of the comb-like protrusions is also narrower than the plurality of first bonding patterns. the first of the plurality
A printed circuit board bonding method characterized in that the width of the bonding pattern is narrower than that of the bonding pattern.