JPH07211996A - Flexible printed wiring board - Google Patents

Abstract

PURPOSE:To improve the elasticity of an FPC while the FPC is maintained in a highly flexible state by making the thickness of an insulating film, especially, coating film of a polyimide resin nearly equal to that of a base film only at a part requiring elasticity. CONSTITUTION:A polyimide resin resist 2 is applied to copper foil l on a base film (substrate) 3 as an insulating coating. The thickness of the resist 2 is made nearly equal to that of the base film 3 at a part requiring elasticity, namely, at such a part that the prevention of disconnection of circuits is specially required. Therefore, the elasticity of an FPC can be improved while the FPC is maintained in a highly flexible state. The above-mentioned part to be increased in thickness means the part of the FPC where the disconnection of circuits is specially required and the increased thickness of the resist 2 at the part means about 60-100-mum when the thickness of the substrate 3 is 100mum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an insulating paint, particularly a polyimide resin resist type FPC coated with a polyimide resin. More specifically, the present invention relates to an improved polyimide resin resist type FPC having both high flexibility and bending resistance with a partially increased coating thickness.

[0002]

2. Description of the Related Art Polyimide resin resist type FPCs are known from patents and the like, but none have high flexibility and bending resistance.

[0003]

In a polyimide resin resist type FPC, the thinner the resist film, the higher the flexibility, but the poorer the flex resistance, and the thicker the resist film to the same extent as the base film, the higher the flexibility. However, there is a contradictory situation such as lack of flexibility, and the conventional polyimide resin resist type FPC has the same thickness in any part, and therefore it is not possible to combine both features.

[0004]

In order to solve the above-mentioned problems, the present inventor has made the insulating coating film, particularly the polyimide resin coating film thickness to the same extent as that of the base film, only in the portion requiring bending resistance. It has been found that by increasing the thickness, it is possible to improve the flex resistance of the FPC while maintaining high flexibility, and completed the present invention.

That is, the present invention provides an FPC in which an insulating coating film is applied to a circuit formed on a plastic film substrate, in which the coating film thickness is partially increased to the same extent as the base film. Another feature is that the substrate is made of a polyimide resin, and the insulating coating film is also made of a paint mainly containing a polyimide resin.

The present invention will be described below with reference to the drawings. FIG. 1 is a schematic view showing a cross section of an FPC (an example) for explaining the features of the FPC of the present invention. A polyimide resin resist 2 is covered as a coating on the copper foil 1 on the base film (substrate) 3 as an insulating paint, but the polyimide resin resist 2 is required at a portion requiring bending resistance, that is, a portion where it is particularly desired to prevent circuit breakage. The thickness of the FPC is similar to that of the base film, so that the FPC
The bending resistance of can be improved. The part where the coating film thickness is partially increased here refers to a part of the FPC where the disconnection of the line is particularly desired to be prevented, and the partial coating film thickness is as thick as the substrate. For example, the substrate thickness is 1
When it is 00, it means that the coating film thickness is increased to about 60 to 100 μm.

The insulating paint for coating used in the present invention is not limited to the polyimide resin, but may be a polyetherimide resin, a polyamide resin, an epoxy resin or the like. In particular, when the FPC board is composed of a polyimide resin, it is preferable to use a polyimide resin as the insulating paint. As the substrate material used in the present invention,
Phenol resins, epoxy resins, polyimide resins and the like can be mentioned, but the use of polyimide resins is preferred.

[0008]

In the FPC according to the present invention, the coating film thickness is increased only in the portion where the bending resistance is required, that is, the portion where the disconnection of the circuit is particularly desired to be prevented, so that the portion where the flexibility is required is not damaged. Flex resistance can be improved. In addition, the bending resistance is improved as the coating film thickness approaches the base film thickness.

In particular, it is preferable that the base film (substrate) and the insulating coating material are made of the same material, and the one in which the base film is a polyimide resin and the insulating coating material is also mainly a polyimide resin is an FPC while maintaining high flexibility. It is more preferable from the viewpoint of improving the flex resistance of. Further, when the copper foil of the circuit is covered with substantially the same thickness on both sides, the bending resistance is best.

[0010]

The present invention will be described in detail with reference to the following examples, which do not limit the scope of the present invention. (Comparative Example 1) A base film having a thickness of 25 μm and a copper foil having a thickness of 35 μm are formed on a substrate without an adhesive, and a coverlay film of Kapton 100H (polyimide resin) / epoxy adhesive having a thickness of 125 μm is thermocompression bonded thereon. When,
A polyimide ink [manufactured by Nippon Steel Chemical Co., Ltd.] was printed, heat-cured, and a resist film thickness of 10 μm was formed on a copper foil as a prototype. -C5016 method) was performed. The results are shown in Table 1.

[0011]

[Table 1] In the case of the coverlay type, the both surfaces of the circuit are covered with the same level, so that it has excellent bending resistance. But,
It lacks thin parts and lacks flexibility. From this, as compared with the resist type FPC, the flexibility was good, but the bending resistance was at a low level of 1/4 or less.

Example 1 Next, as shown in FIG. 1, a polyimide resist type FPC prototyped in the above experiment.
Then, the polyimide resin is reprinted only on the part where the circuit breakage is particularly troublesome, and the film is thickened by heat curing (Since it is paint, it is easy to selectively increase the film thickness on the required part. ) Was prototyped.

The results of the MIT test are shown in Table 2.

[Table 2] (Use of circuit in 0.1 mm, condition; 2.0R × 500g) As a result, by increasing the resist film thickness on the copper foil to 25 μm, which is about the same as the thickness of the substrate, the bending resistance is more than 4 times. It turned out to improve. As described above, by making FPCs having different film thicknesses depending on the parts, it becomes possible to make FPCs having both high flexibility and bending resistance parts.

[0014]

As described above, the FPC of the present invention is effective when a wiring material having both a highly flexible portion and a flexible portion is required.

[Brief description of drawings]

FIG. 1 is a schematic view showing a cross section of an FPC in an example.

[Explanation of symbols]

 1 Copper foil 2 Polyimide resin resist 3 Base film

Claims (2)

[Claims] 1. In a flexible printed wiring board (hereinafter referred to as FPC) in which an insulating coating film is applied to a circuit formed on a plastic film substrate, the coating film thickness is partially increased to about the same as the base film. A flexible printed wiring board characterized by the above. 2. The flexible printed wiring board according to claim 1, wherein the substrate is made of a polyimide resin, and the insulating coating film is also made of a paint mainly containing a polyimide resin.