JPH0432783Y2 - - 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 resist film 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.

3 and 4 show conventional examples of this type of flexible printed wiring board, with FIG. 3 being a plan view and FIG.
The figure is a sectional view taken along the line A--A in FIG. 3.

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 and formed on the insulating film 1, and the exposed portion of the conductive pattern not covered by the resist layer 3 serves as a lead portion 2a for connection to an external terminal.

As is clear from FIG. 4, 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, the purpose of the present invention is to solve the problems of the above-mentioned conventional technology, improve the adhesion between the ends of the multilayer resist layer and the insulating film, and provide a flexible printed wiring board that is resistant to bending deformation. It is in.

[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 layers of resist films are printed and formed to cover the conductive pattern. The resist film is characterized in that the end faces of each of the resist films are formed in a wavy shape, and that the uppermost resist film is shifted in position so as to protrude from the end of the lower resist film.

[Effect]

In other words, by forming the end faces of each resist film in a wavy shape as described above, and by shifting the position of the uppermost resist film so that it protrudes from the end of the lower resist film, the bending stress acting on the end faces of the resist film is dispersed. Moreover, the flexibility at the end face is increased compared to other parts. Therefore, there is less risk that the resist film will peel off from the insulating film 1 due to bending.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a plan view of a flexible printed wiring board according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along line B-B in FIG. 1, and parts corresponding to those in FIG. There is.

This embodiment differs from the conventional example described above in the shape of the end face of the resist layer 3. That is, the resist layer 3 has a first resist film 3a, a second resist film 3b, and a third resist film 3c laminated from the bottom as in the conventional example, but the first and second resist films in the lower layer The third resist film 3c, which is the uppermost layer, partially extends from the resist films 3a and 3b. Therefore, most of the resist layer 3 has a laminated structure of the first to third resist films 3a, 3b, and 3c, but the end face is made up of only the third resist film 3c. Moreover, the end face of each layer is formed in a wave shape, and these wave-like parts 3' are formed in each resist film 3a,
This is achieved by the shape of the mask used when printing 3b and 3c.

When forming such a resist layer 3, a mask (not shown) having a corrugated end face is used on the insulating film 1 on which the conductive pattern 2 is printed, and a region of a predetermined width including the lead portion 2a is left. A resist film 3a of No. 1 is printed and baked.
Next, a second resist film 3b is printed on the first resist film 3a using the same mask as above, and this is baked. Finally, using a different mask from the above, a third resist film 3c is printed on the second resist film 3b so that its end portion protrudes from the second resist film 3b, and this is baked. Each of the resist films 3a, 3b, and 3c has a thickness of about 20 μm, and the laminated portion of the three layers has a thick film structure of about 60 μm, which enhances the waterproof effect. In addition, if the length of the extended portion consisting only of the third resist film 3c of the uppermost layer is too short, the adhesion with the insulating film 1 will be weak, and if it is too long, the waterproof effect of that portion will be weakened. , preferably 1 to 3 mm
It is best to set it to a certain degree.

In one embodiment configured as described above, the shape of the end face of the resist layer 3 is changed from the conventional straight line to a waveform, so that the stress generated when the flexible printed wiring board is bent is applied to the waveform portion 3'. As a result, the resist layer 3 is dispersed, and there is less risk that the resist layer 3 will peel off from the insulating film 1. In addition, since the portion extending to the end surface of the resist layer 3 is a part of the third resist film 3c that is printed last, the baking process that is applied to the extending portion only needs to be performed once, and the end surface However, it is possible to realize a resist layer 3 having high flexibility. Therefore, when the flexible printed wiring board is bent, the bending stress of the resist layer 3 is absorbed by the end face of the third resist film 3c coming into close contact with the insulating film 1 and being greatly deformed. Due to the synergistic effect of stress dispersion by the wavy portions 3' on the three end faces, the risk of the resist layer 3 peeling off from the insulating film 1 is extremely reduced.

In the above embodiments, the resist layer 3 has a three-layer structure.
It is also possible to have more than one layer.

[Effect of idea]

As explained above, according to the present invention, even when bending stress acts on a flexible printed wiring board, the bending stress is dispersed by the waveform shape of the end face of each resist film, and the end face of the resist layer is Since the flexibility is not impaired, it is possible to improve the adhesion between the resist layer and the insulating film, thereby providing a flexible printed wiring board with excellent waterproof effect and bending strength.

[Brief explanation of the drawing]

Figure 1 is a plan view of the main parts of a flexible printed wiring board according to an embodiment of the present invention, and Figure 2 is B of Figure 1.
3 is a plan view of a conventional flexible printed wiring board, and FIG. 4 is a sectional view taken along line A-A in FIG. 3. 1... Insulating film, 2... Conductive pattern, 2
a... Lead portion, 3... Resist layer, 3'... Wavy portion, 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 layers of resist films are printed and formed to cover the conductive pattern, the end face of each of the resist films is formed in a wave shape, and , 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.