JPH06120640A - Production of flexible printed wiring board - Google Patents

Abstract

PURPOSE:To allow high density mounting of component by laminating a photosensitive resin film and filling a through hole with a photosensitive resin through exposure and developing. CONSTITUTION:The production process of flexible printed wiring board comprises a step for drilling a flexible board applied with metal foils on the opposite faces thereof and then subjecting the flexible board to metal plating, a step for filling a through hole 2 with a photosensitive resin through exposure and development, a step for roughening the surface of the photosensitive resin and then subjecting the surface to metal plating, and a step for forming an etching resist pattern, removing unnecessary metal foil layer through etching and then removing the etching resist. In such wiring board, the through hole 2 is made at a component terminal part 7 and connected with a line 8 formed on the rear. Since such wiring pattern can be formed without making any hole in the surface of the terminal 7, no solder flows out of hole at the time of solder connection thus ensuring reliability in connection. Furthermore, high density mounting is allowed by shortening the interval of terminal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a flexible printed wiring board for high density mounting.

[0002]

2. Description of the Related Art Flexible printed wiring boards are generally manufactured by the following method. That is, after punching or drilling holes on a flexible substrate, through holes are formed by electroless copper plating or electrolytic copper plating, and then an etching resist is formed on a portion to be a circuit, and an etching solution containing copper chloride / hydrochloric acid is used. Remove unnecessary copper,
Next, the etching resist is removed to manufacture a flexible printed wiring board.

[0003]

However, the wiring pattern of the flexible printed wiring board manufactured by the above manufacturing method is as shown in FIG. That is, when the wiring is pulled out from the soldering terminal 7 of the surface mount type component on the A side to the back side (B side), the line from the terminal 7 is passed through the through hole 2 and the B side line as shown in the figure. Connect with 8. Therefore, it is necessary to provide a portion where a through hole is provided between the terminals, and it is difficult to mount the parts at high density by sandwiching the Lo between the terminals.

The present invention has been made in view of the above circumstances, and provides a method for manufacturing a flexible printed wiring board in which components can be mounted at high density.

[0005]

According to the present invention, a flexible substrate having metal foils on both sides thereof is perforated, and then metal plating is performed, a photosensitive resin film is laminated and exposed.
Due to the phenomenon, the step of filling the through hole with the photosensitive resin, the step of roughening the photosensitive resin surface and metal plating, forming the resist pattern for etching, and then removing the unnecessary metal foil layer by etching, A method of manufacturing a flexible printed wiring board, comprising a step of removing a resist.

A detailed description will be given with reference to the sectional views for each step of FIG. FIG. 1A shows a flexible substrate 1 having metal foils on both sides. This substrate may be any commercially available printed wiring board substrate. For example, a polyimide film and a flexible substrate F-30VC a copper foil integrated with an adhesive ₂ RC25C21 (Nikkan Kogyo Co., Ltd., trade name) and adhesive-free, polyimide flexible substrate MCF-5510I (Hitachi Chemical Co., Ltd. Manufactured, product name, etc., and those having a small dimensional change rate are preferable.

FIG. 1B shows a state in which the through hole 2 is provided on the substrate. The method of forming the through hole is not particularly limited, and any method such as drilling, bunching, and laser drilling may be used.

Next, as shown in FIG. 1C, plated copper 3 is formed on the surface of the substrate and the inner wall of the through hole. This plating copper forming method is also not particularly limited, and commercially available electroless copper plating solutions CUST201, CUST1000 (manufactured by Hitachi Chemical Co., Ltd., trade name) and electrolytic copper plating pyrophosphate copper plating baths and copper sulfate plating baths. Etc. can be used alone or in combination.

Next, as shown in FIG. 1 (d), the photosensitive resin film 4 is attached to the substrate from one surface of the substrate by using a hot roll laminator or a vacuum hot roll laminator and the inside of the through hole. And then exposed,
Further, using trichloroethane or an alkaline aqueous solution, a phenomenon process of removing the unexposed portion is performed. As the photosensitive resin film 4, commercially available Photex SR-300
0, Photex SR-2300 (manufactured by Hitachi Chemical Co., Ltd., trade name) can be used. In addition, in order to completely fill the aqueous solution with the photosensitive resin, the substrate may be preliminarily heated as appropriate by optimizing the roll laminating conditions. When the curing is insufficient, heating or re-exposure may be performed in the developing process.

Next, the surface of the photosensitive resin is roughened to improve the adhesive force with the plated copper formed in the next step. As this roughening method, plasma treatment or chemical roughening is possible. As the chemical roughening liquid, an alkaline aqueous solution of permanganate, an acidic aqueous solution of chromic acid, or the like can be used. However, mechanical polishing such as a belt sander or a roll blanc causes contraction and expansion of the substrate, which is not preferable.

Next, as shown in FIG. 1E, plated copper 3'is formed on the surface of the substrate by the same method as described above. Furthermore,
After forming an etching resist pattern on this surface, the unnecessary metal copper is removed by etching, and then the etching resist is removed.
The flexible printed wiring board shown in can be manufactured. As the etching resist, a commercially available product can be used.
2 (manufactured by Hitachi Chemical Co., Ltd., trade name), solvent development type Liston T-1206 (manufactured by DuPont, trade name), and the like can be used.

[0012]

In the flexible printed wiring board according to the present invention, as shown in FIG.
Can be connected to the line 8 on the back surface. Even if such a wiring pattern is formed, the surface of the terminal 7 has no holes and is flat, so that solder does not flow out from the holes even when solder connection is made, and solder connection reliability can be secured. Further, since the terminal interval can be reduced from the conventional L ₀ to L ₁ , components can be mounted at high density.

[0013]

[Examples] 1) A polyimide adhesive-free flexible substrate MCF-5510I (manufactured by Hitachi Chemical Co., Ltd.) was drilled (minimum diameter φ0.2 mm), and then a catalyst solution HS-101B for electroless copper plating (Hitachi Chemical Co., Ltd.) Made in the company, product name), soaked in water, washed with water, electroless copper plating solution CUST-20
1 (manufactured by Hitachi Chemical Co., Ltd., trade name) is immersed at room temperature for 20 minutes to form a plated copper film having a thickness of about 0.3 μm. Furthermore, it is immersed in a copper sulfate plating solution to obtain a current density of 3 A / d.
m ² and a plating time of 30 minutes formed plated copper having a thickness of 15 to 20 μm. 2) Next, photosensitive resin film, Fotec SR-3000
(Hitachi Chemical Co., Ltd., trade name) with a thickness of 70 μm was hot-roll laminated on the B side from the side on which the terminals were not formed. The conditions are a roll temperature of 130 ° C., a pressure of 40 psi, and a feed rate of 0.3 m / min. 3) Photomasks were overlaid, exposed under the condition of 130 mJ / cm ² , and then trichloroethane (18 ° C., spray pressure 1.
Develop at 6 kg / cm ² ) for 90 seconds. Next is 1.0 J /
After exposing again at cm ^2, it was heated at 150 ° C. for 40 minutes. 4) Next, in order to roughen the surface of the photosensitive resin, an aqueous alkaline permanganate solution (NaOH 26 g / l, KMn) is used.
After dipping in O ₄ 60 g / l, temperature 50 ° C.) for 15 minutes, plated copper was formed by the same method as in 1) above. 5) Next, as an etching resist, Photec 87
2 (thickness 25 μm) was formed on both sides by a hot roll laminator. This condition is roll temperature 110 ℃, pressure 30
psi, feed rate 1.1 m / min. 6) A photomask was overlaid, exposed under conditions of 65 mJ / cm ² , and developed for 60 seconds with a 3% NaOH aqueous solution (40 ° C.), and then unnecessary copper was removed with a copper chloride-based etching solution. Next, the etching resist was removed by immersing it in a 10% NaOH aqueous solution (45 ° C.) for 90 seconds.

COMPARATIVE EXAMPLE A flexible printed wiring board was manufactured except for the steps 2), 3) and 4) in the steps of the example of Comparative Example 1). However, the drilling data and photomask pattern used are different from those in the example.

[0015]

In the flexible printed wiring board according to the present invention, the surface mounting resistors and capacitors can be mounted at a high density, so that the substrate size can be reduced by about 20% as compared with the comparative example. Further, since the hot roll lasing machine with a small stress applied to the substrate for filling the photosensitive resin into the through holes was used, the dimensional change rate was almost the same as that of the comparative example, and there was no problem in manufacturing stability.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of each manufacturing process showing an embodiment of the present invention.

FIG. 2 is a top view showing a wiring pattern of a conventional example.

FIG. 3 is a top view showing a wiring pattern according to an embodiment of the present invention.

[Explanation of symbols]

 1. Flexible substrate 2. Through hole 3,3 '. Plated copper 4. Photosensitive resin 5. Flat terminal 6. Line 7. A side terminal 8. Line on side B

Claims (1)

[Claims] 1. A method for manufacturing a flexible printed wiring board, which comprises the following steps. (A) A step of metal-plating after perforating a flexible substrate having metal foils on both sides. (B) A step of laminating a photosensitive resin film, and filling the photosensitive resin in the through holes by exposure and a phenomenon. (C) A step of roughening the surface of the photosensitive resin and performing metal plating. (D) A step of removing an unnecessary metal foil by etching after forming a resist pattern for etching, and then removing the etching resist.