JPH07297525A - Method of processing flexible printed wiring board - Google Patents

Abstract

PURPOSE:To provide a flexible printed wiring board having good flexibility and peeling strength by a method for preventing lowering of peeling strength between a plastic film and a metallic foil which is generated as a flexible printed wiring board becomes thin. CONSTITUTION:After a metallic foil circuit is formed in a flexible printed wiring substrate and a cover-lay film is heated and compressed, a flexible printed wiring board is heated and processed at a heating temperature of 40 to 180 deg.C and a heating time of 0.1 to 20 hours with no-load (0<P<=20g/cm<2> and 0<T<=5kg/cm<2> where P is the pressure and T is the tension).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flexible printed wiring board having flexibility which is effective as a composite part having a wiring, cable or connector function for electronic equipment.

[0002]

2. Description of the Related Art In recent years, the electronic field has been remarkably developed, and especially electronic devices for communication, consumer use, etc. are becoming smaller, lighter and higher in density, and requirements for these performances are becoming more and more advanced. There is. In response to such demands, a flexible printed wiring board (hereinafter abbreviated as FPC) has flexibility and withstands repeated bending, and therefore can be mounted in a three-dimensionally high density in a narrow space. Its application is expanding as a composite part with wiring, cable, or connector function. Recently, this FPC is also frequently used for connecting a machine body such as a printer, a floppy disk drive, a hard disk drive and the like to a movable part, and accordingly, a demand for flexibility is becoming particularly strong. Therefore, as a method of improving the flexibility of FPC, the thickness of the constituent materials such as plastic film, adhesive, and metal foil should be reduced (see JP-A-63-504695), and the flexibility of the composition of the adhesive should be adjusted. Improvement (see Japanese Patent Laid-Open No. 1-170091),
It has been proposed to flatten the FPC (see Japanese Patent Laid-Open No. 4-315490). However, in many cases, the user specifies the thickness of the heat resistant film and the metal foil, and in many cases, sufficient flexibility cannot be obtained.
Regarding the above, although the flexibility is improved, the properties such as peeling strength and solder heat resistance are not improved, and there is a possibility that practical problems will occur. With respect to the above, there was a defect that the flexibility was improved but the processing was difficult and the productivity was deteriorated, and it was difficult to easily improve the flexibility.

[0003]

In general, a flexible printed wiring board comprising an insulating film, an adhesive and a metal foil is distorted due to heat and pressure during processing of each constituent material. Was there. The present inventors have found that when the FPC is bent, this strain causes bending stress to concentrate on the bent portion, resulting in poor bendability. The present invention is FPC
The present invention intends to provide a flexible printed wiring board which has excellent flexibility and is free from the distortion.

[0004]

In order to solve the above problems, the inventors of the present invention have earnestly studied a method for processing a flexible printed wiring board, and as a result, have completed the present invention. Where is, is a method of processing a flexible printed wiring board, which is characterized in that a wiring circuit is formed on the metal foil of the flexible printed wiring board, and the coverlay film is heat-pressed, and then heat-treated in an unloaded state. More specifically, in the unloaded state, the pressure P is 0 <P ≦
20 g / cm ² and a tension T of 0 <T ≦ 5 kg / cm ² , and the heat treatment is performed at a temperature of 40 to 180 ° C. and a heating time of 0.1 to 20 hours.

The present invention will be described in detail below.

According to the present invention, a wiring circuit is formed on a flexible printed wiring board in which a heat-resistant plastic film and a metal foil are laminated by heating and pressure bonding with an adhesive, and a cover lay film (adhesive layer + protective film) is heated and pressure bonded. Each component (base film, adhesive layer, metal foil circuit)
Distortion occurs due to heat and pressure, and it is built in. It was found that bending stress concentrates on this strain when the FPC is bent, which reduces the flexibility, and was developed as a processing method to remove this strain. Heating the coverlay film on the flexible printed wiring board No pressure after crimping, that is, pressure (P) is 0 <P ≦ 20g / cm ² and tension (T) is 0 <T ≦ 5kg / cm ² or less, and heating temperature is
The object was achieved by applying heat treatment at 40 to 180 ° C for 0.1 to 20 hours.

The base film for the flexible printed wiring board (constitution: base film-adhesive-metal foil) and coverlay film (constitution: base film-semi-cured adhesive) used in the present invention includes polyester, polyimide, Examples of the heat-resistant insulating film include polyparabanic acid, polyethersulfone, polyetherketone, and polyphenylene sulfide. Among them, a polyimide film is preferable when heat resistance is particularly required. The thickness is usually in the range of 12.5 to 75 μm, but an appropriate thickness is used if necessary.

The thermosetting adhesive for FPC and coverlay film used in the present invention includes nylon / epoxy type, NBR / phenol type, carboxyl group-containing NBR /
Epoxy type, polyester / epoxy type, etc.
It is selected with due consideration of the operating environment of the wiring board. The solvent used for the adhesive is an organic solvent such as methyl ethyl ketone or toluene and is not particularly limited. It is also possible to add main inorganic fillers (silica, alumina), flame retardants and the like. The thickness of the adhesive layer in the dry state is usually 5 to 30 μm for the flexible printed wiring board and 20 to 50 μm for the coverlay film, but an appropriate thickness is used as necessary. .

As the metal foil used in the present invention, electrolytic copper foil, rolled copper foil, aluminum foil, tungsten foil, nickel foil, etc. which have been conventionally used or proposed to be used can be arbitrarily selected. it can. Generally, electrolytic copper foil and rolled copper foil are used, but rolled copper foil is preferably used when flexibility and folding resistance are particularly required. A metal foil having a thickness of 18 to 35 μm is usually used, but a metal foil having an appropriate thickness is used if necessary.
When a rolled copper foil is used, the copper foil is usually heat-treated in order to improve the flexibility of the copper foil itself. 140 to 180 ℃, 0.5 to 24 for film and metal foil
It is common to perform heat treatment for a period of time.

Flexible printed wiring board and FPC
A method of processing (flexible printed wiring board) will be described. The adhesive composition solution prepared in advance is applied to the insulating film in a dry state to a thickness of 5 to 30 μm using a reverse roll coater, a comma coater, etc., and heated and dried at 80 to 140 ° C. with an in-line dryer. The solvent is evaporated to bring the adhesive into a semi-cured state. A metal foil is superposed on the adhesive surface of the electrically insulating film with the adhesive, heat-pressed by a roll laminator, and after-cured if necessary, to obtain a substrate for flexible printed wiring. As the pressure bonding condition, a temperature of 80 to
It is preferable that the temperature is 140 ° C., the linear pressure is 10 to 30 kg / cm 2, and the speed is 1 to 10 m / min. A pattern is formed on the metal foil by screen printing or a photosensitive film on the flexible printed wiring board. Further, through an etching step, a metal foil circuit is produced, and a cover lay film, which is a protective film with an adhesive, is heated and pressure-bonded thereto to obtain an FPC. The conditions for thermocompression bonding are usually a temperature of 120 to 180 ° C and a pressure of 10
~ 50kg / cm ² , 0.5 ~ 2.0 hours.

In order to remove the distortion of the FPC which is a feature of the present invention, the FPC is 0.1 to 0.1 at 40 to 180 ° C. under no load.
20 hours is preferred, more preferably 80-160 ° C, 0.5-
It is necessary to perform heat treatment for 15 hours. When the heating temperature is lower than 40 ° C., the strain between the flexible printed wiring board and the coverlay film is not sufficiently removed, and the flexibility is lowered. When the temperature exceeds 180 ° C, the adhesive used for the flexible printed wiring board is deteriorated and the wiring board is deformed by heat, which is not preferable. The heating time is determined in consideration of the heating temperature, but it is preferably shorter in consideration of work efficiency and the like. Incidentally, the no-load state at this time means a state in which the FPC is not deformed by pressure, tension, etc. Specifically, 0 <P ≦ 20 g / cm ² at pressure (P) and 0 <T at tension (T). ≦ 5 kg / cm ² is preferable, more preferably 0 <P
≦ 10 g / cm ² , 0 <T ≦ 1 kg / cm ² . Pressure is 20g / cm ²
When the tension exceeds 5 kg / cm ² , the FPC is distorted, the flexibility is lowered and the FPC is deformed, which is not preferable.

[0011]

EXAMPLES The embodiments of the present invention will be specifically described below with reference to examples, but the present invention is not limited thereto. (Examples 1 to 4, Comparative Examples 1 to 4) Polyimide film
Apply epoxy adhesive to 25μm of Kapton 100H (trade name of DuPont) so that the thickness after curing is 10μm,
Heated and semi-cured, heat-pressed a rolled copper foil (thickness 35 μm), after-cured at 180 ° C for 3 hours to produce a flexible printed wiring board GAS33S42 (Shin-Etsu Chemical Co., Ltd. product name) The circuit shown in Fig. 1 is formed, and a polyimide film Kapton 100H (trade name, manufactured by DuPont, thickness: 25 μm) is used.
A cover lay film CA333 (trade name, manufactured by Shin-Etsu Chemical Co., Ltd.) having m was thermocompression bonded at 150 ° C., 30 kg / cm ² , 60 minutes to obtain a flexible printed wiring board. This wiring board was subjected to heat treatment under the conditions shown in Table 1 under no load to remove distortion, and Table 1 shows the physical properties of the flexible printed wiring board.

(Physical property evaluation method) (1) Flexibility: Measured according to IPC FC 241. Using a high-speed bending tester SEK-31B4S (trade name of Shin-Etsu Engineering Co., Ltd.), the resistance value of the circuit shown in FIG.
0.4 Ω), and measure the number of bends when it exceeds 10%. Set the stroke to 20 mm, the bending radius to 2.0 mm, and the rotation speed to 3000 rpm. (2) Appearance: The presence or absence of discoloration and deformation is visually determined. ◯: good, Δ: acceptable, ×: not acceptable.

[0013]

[Table 1]

[0014]

According to the present invention, it is possible to provide a flexible printed wiring board having excellent flexibility by removing distortion by heating the flexible printed wiring board in a non-loaded state. The utility value is extremely high.

[Brief description of drawings]

FIG. 1 is a plan view showing a test piece for bending test of a flexible printed wiring board according to the present invention.

Claims (2)

[Claims] 1. A method for processing a flexible printed wiring board, which comprises forming a wiring circuit on a metal foil of a substrate for flexible printed wiring, heating and press-bonding a coverlay film, and then performing heat treatment in an unloaded state. 2. The unloaded state according to claim 1, wherein the pressure P is 0 <
A method for processing a flexible printed wiring board in which P ≦ 20 g / cm ² and tension T are 0 <T ≦ 5 kg / cm ² , and the heat treatment is performed at a temperature of 40 to 180 ° C. and a heating time of 0.1 to 20 hours.