JPH0432782Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a flexible printed wiring board, and particularly to a laminated structure of a resist layer deposited on a conductive pattern made of silver, carbon, or the like.

[Conventional technology]

2. Description of the Related Art Flexible printed wiring boards are known and used in various electronic devices mainly for connecting circuit components.

Figures 2 and 3 show conventional examples of this type of flexible printed wiring board, with Figure 2 being a plan view and Figure 3 being a plan view.
The figure is a sectional view taken along the line A--A in FIG. 2.

In these figures, 1 is a flexible insulating film such as polyester, 2 is a conductive pattern made of silver or carbon printed on the insulating film 1, and 3 is a conductive pattern excluding a part of the conductive pattern 2. This is a resist layer printed on an insulating film 1, and the exposed portion of the conductive pattern 2 not covered by the resist layer 3 serves as a lead portion 2a for connection to an external terminal.

As is clear from FIG. 3, the resist layer 3
are the first to third resist films 3a, 3b, 3c
These have a three-layer structure consisting of a first resist film 3a printed and baked on the insulating film 1, and then a second resist film 3b printed and baked on the first resist film 3a, Further, a third resist film 3c is formed on the second resist film 3b by printing and baking. Each resist film 3a,
3b and 3c are patterned into the same shape using the same mask, and the film thickness per layer is, for example, about 20 μm, thereby achieving a highly insulating resist layer 3 with a total thickness of about 60 μm. There is.

[Problem that the invention attempts to solve]

In the conventional flexible printed wiring board configured in this way, the film thickness of the resist layer 3 can be increased to a degree that cannot be obtained with a single layer structure. When used in equipment that is frequently immersed, the thick resist layer 3 has the advantage that the waterproofing effect is enhanced.

However, when the resist layer 3 has a laminated structure, the number of firings increases accordingly, and the rigidity of the resist layer 3 increases due to repeated hardening during firing, and for example, the flexible printed wiring board may be bent during wiring work. However, there was a drawback that the resist layer 3, which has poor flexibility, could not follow the bending of the highly flexible insulating film 1, and the resist layer 3 would peel off from the insulating film 1. In particular, when the resist layer 3 is peeled off from the insulating film 1,
When the conductive pattern 2 formed on the insulating film 1 adheres to the resist layer 3 side, not only the original resist function is impaired, but also a serious defect occurs in that the conductive pattern 2 breaks near the lead portion 2a.

Therefore, an object of the present invention is to solve the problems of the prior art described above, to provide a flexible printed wiring board that ensures flexibility at the end of a multilayer resist layer and is resistant to bending deformation.

[Means for solving problems]

In order to achieve the above object, the present invention provides a flexible printed wiring board in which a conductive pattern is provided on a flexible insulating film, and a plurality of resist layers are provided covering the conductive pattern. Among the resist films constituting the resist layer, the uppermost resist film is dislocated in a protruding state from the end of the lower resist film.

[Effect]

In a resist layer having a multilayer structure, the uppermost resist film is shifted from the edge of the lower resist film in a protruding state, so that the flexibility at the end face is increased compared to other parts. Therefore, even if the flexible printed wiring board is bent, the bending stress of the resist layer is absorbed by the deformation of the end face, and the risk of the resist layer peeling off from the insulating film is reduced.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail using the drawings.

FIG. 1 is a sectional view of main parts of a flexible printed wiring board according to an embodiment of the present invention, and in FIG. 3, corresponding parts are given the same reference numerals.

This embodiment differs from the conventional example described above in the laminated structure of the resist layer 3. That is, the resist layer 3 includes, in order from the bottom, the first resist film 3a,
It consists of a second resist film 3b and a third resist film 3c, and the third resist film 3c, which is the uppermost layer, extends from the end surfaces of the first and second resist films 3a and 3b, which are the lower layers. Therefore, most of the resist layer 3 consists of the first to third resist films 3a, 3b,
3c, but the end face is a single layer portion 3' consisting only of the third resist film 3c.

In forming such a resist layer 3, a first resist film 3a is printed on the insulating film 1 on which the conductive pattern 2 has been printed, leaving an area of a predetermined width including the lead portion 2a, and then baked.
Next, a second resist film 3b is printed on the first resist film 3a using the same mask, and then baked. Finally, using a different mask from the above, a third resist film 3c is formed on the second resist film 3b so that the cut portion protrudes from the second resist film 3b.
Print it and fire it. Each resist film 3a,
The film thickness of each of 3b and 3c is about 20 μm,
The laminated portion of the three layers has a resist layer 3 with a thick film structure of approximately 60 μm, which enhances the waterproof effect. In addition, if the length of the single layer portion 3' is too short, the adhesion with the insulating film 1 will be weak, and if it is too long, the waterproof effect of that part will be weakened, so it is preferably set to about 1 to 3 mm. good.

In one embodiment configured in this way, the single layer portion 3' extending to the end surface of the resist layer 3 is a part of the third resist film 3c to be printed last, so that the The firing process performed on the single layer portion 3' can be performed only once, and the single layer portion 3' with excellent flexibility can be realized. Therefore, when the flexible printed wiring board is bent, the single-layer portion 3' of the resist layer 3 closely adheres to the insulating film 1 and deforms greatly, absorbing the bending stress and causing the resist layer 3 to peel off from the insulating film 1. There is less chance of it happening.

It should be noted that the resist layer 3 is not limited to the three-layer structure of the above-mentioned embodiments, but can be made of two or four or more layers depending on changes in the film thickness per layer, waterproof conditions, etc., and further, The protruding portion at the end does not necessarily have to be one layer; the point is that at least the uppermost resist film out of all the layers of the resist film is shifted and protrudes from the end of the lower resist film. A similar effect can be achieved.

[Effect of idea]

As explained above, according to the present invention, even when the resist layer has a multilayer structure, the flexibility of the end face is not impaired, so even when bending stress is applied to the flexible printed wiring board, the resist layer It is possible to improve the adhesion between the film and the insulating film, thereby providing a flexible printed wiring board that has excellent waterproof effects and is resistant to bending.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of the main parts of a flexible printed wiring board according to an embodiment of the present invention, Fig. 2 is a plan view of a conventional flexible printed wiring board, and Fig. 3 is taken along line A-A in Fig. 2. FIG. 1... Insulating film, 2... Conductive pattern, 2
a... Lead part, 3... Resist layer, 3'... Single layer part, 3a... First resist film, 3b... Second
resist film, 3c... third resist film.

Claims (1)

[Scope of utility model registration request] In a flexible printed wiring board in which a conductive pattern is provided on a flexible insulating film, and a plurality of resist layers are printed and formed to cover the conductive pattern, among the resist films constituting the resist layer, A flexible printed wiring board characterized in that the uppermost resist film is displaced from the edge of the lower resist film in a protruding state.