JPH04206590A - Manufacture of flexible printed circuit board - Google Patents

Abstract

PURPOSE:To enable a two-layered flexible printed circuit board provided with no adhesive layer subjected to a boring process to be easily formed excellent in quality without deteriorating it in intrinsic characteristics by a method wherein a film of specific material is formed on a conductive foil, a prescribed hole is bored in it, and then the film is made to turn fully into imide. CONSTITUTION:When a semi-cured polyamic acid film is formed on a conductive foil, a prescribed hole can be easily, quickly, and surely provided to the foil provided with the film through etching resist application, development, and light exposure using a polyimide etching solution. Thereafter, the film concerned is made to turn fully into imide, whereby a flexible printed circuit board provided with a support film subjected to a hole boring process can be obtained without deteriorating in properties such as alkali resistance, solvent resistance, heat resistance, and electrical properties that a two-layered flexible printed circuit board with no adhesive layer intrinsically has.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is for producing a flexible printed circuit board having a perforated support film layer in a two-layer flexible printed circuit board without an adhesive layer. It is about the method.

[Conventional technology] As electronic equipment becomes smaller and lighter, the uses of conventional flexible printed circuit boards are expanding, and recently they have been used not only as conventional wiring boards, but also as TAB carrier tapes. There is also an increasing use of perforated substrates in support films such as the following.

As a manufacturing method of such a flexible printed circuit board having holes formed in the support film layer and conductor wiring, holes are formed in the support film layer in advance by punching, etc., and the conductor layer is attached using an adhesive. After lamination, there is a method to form a wiring circuit, a method of directly applying a polyamic acid solution to the conductor layer, drying and imidization, or a method of forming a conductor layer on the support film layer by vapor deposition or sputtering method, and then laser treatment. Alternatively, a method is used in which holes are formed in the support film layer using a strong alkaline solution and then a wiring circuit is formed.

However, in these conventionally used methods,
Each has drawbacks in heat resistance, adhesion, processability, and chemical resistance. First, in a three-layer flexible printed circuit board that has an adhesive layer, the heat resistance of the adhesive layer is low, so even if polyimide is used for the support film, the heat resistance of the adhesive layer is limited. It has the disadvantage of being determined by gender. When the conductor layer is formed by vapor deposition or sputtering, there are disadvantages such as low adhesion between the support film layer and the conductor layer, or the disadvantage that the thickness and density become uneven when the conductor layer is thickened. are doing. If a polyamic acid solution is directly applied to the conductor layer, dried, and imidized, then hole processing is performed, the laser used for processing is extremely expensive, or polyimide with a molecular structure that can be etched with alkali after imidization is It has the disadvantage that its solvent resistance is slightly lowered, and that it is highly dangerous because it uses a strong alkaline solution as an etching solution, and that it cannot be easily disposed of as a waste solution.

[Problems to be Solved by the Invention] The purpose of the present invention is to solve the problem without reducing the alkali resistance, solvent resistance, heat resistance, and electrical properties of a two-layer flexible printed circuit board without an adhesive layer. The present invention provides a method for manufacturing a flexible printed circuit board having a perforated support film.

[Means for Solving the Problems] The present invention is characterized in that a semi-cured polyamic acid film is formed on a conductive foil, and then, after predetermined openings are provided in the film, imidization is completed. This is a method for manufacturing a flexible printed circuit board.

That is, a polyamic acid solution is directly applied to the conductor layer and dried until it becomes tack-free to form a polyamic acid film. Next, an etching resist is applied thereon and dried, developed and exposed so that only the areas where holes are required are removed, and the exposed polyamic acid film is removed with a polyimide etching solution. After the removal is completed, the etching resist is peeled off, imidized sufficiently, and a flexible printed circuit board with holes provided at predetermined positions is manufactured.

In the present invention, the appropriate conditions for drying the bonoamic acid solution to form a semi-cured polyamic acid film are 80 to 250°C for 10 to 30 minutes; if the temperature is lower than this and the time is shorter, , a sharp line cannot be obtained at the etched boundary, and over-etching occurs to the lower part of the etching resist. On the other hand, if the temperature is higher than this and the time is longer, etching takes longer time, the etching resist is attacked by the etching solution, and sharp lines cannot be obtained at the edge portions. Furthermore, by adjusting the drying temperature and time, it becomes possible to freely adjust the etching rate. As the polyimide etching solution, a solution such as hydrazine or ethylenediamine diluted to 5 to 30% by weight can be used. When an alkaline solution such as KOH or NaOH is used, etching can be performed at low temperature and in a short time. can.

Moreover, the polyamic acid in the present invention is usually obtained by reacting a diamine and an acid anhydride. Examples of diamines include ■-phenylene diamine, diaminodiphenylmethane, diaminodiphenylsulfone, diaminodiphenyl ether, etc., and examples of acid anhydrides include trimellitic anhydride, pyromellitic dianhydride, benzenetetracarboxylic dianhydride, benzophenone. Tetracarboxylic dianhydride and the like can be used, and each can be used alone or in an appropriate combination of two or more. The imidization rate in the state of polyamic acid film is 10-5
0%, preferably 20-40%.

Examples of materials that can be used as the conductor layer include metal foils such as copper, aluminum, constantan, and nickel.

[Function] The present invention can be applied by directly applying a polyamic acid solution onto a conductor layer.
By drying and etching the polyamic acid in a semi-hardened state, then completing imidization and forming conductor wiring, it is possible to easily and inexpensively create two-layer flexible printed circuits with holes in the supporting film layer. A substrate can be obtained.

[Example] A polyamic acid solution was applied onto a commercially available copper foil using a spinner, and dried at 150°C for 15 minutes to obtain a polyamic acid film. After applying a commercially available etching resist to the entire surface and drying it, the areas to be etched are exposed and developed, and the exposed polyamic acid film is
When the film was immersed in a 25% KOHOH solution heated to 0°C, the exposed portion of the film was dissolved in about 2 minutes, exposing the copper foil surface. After that, the etching resist was peeled off and 38
Heating was performed at 0°C for 1 hour to complete imidization. The properties of the obtained two-layer flexible printed circuit board were similar to those produced by directly coating, drying, and imidizing copper foil on a copper foil using a conventional method. Table 1 shows the characteristics of both. The ease of hole machining is also described.

Table 1 [Effects of the Invention] According to the present invention, it is possible to easily etch the Voimide support film in a very short time, and there is no change in the properties after the completion of imidization. This method is suitable as a method for manufacturing a flexible printed circuit board having holes processed therein.

Claims (1)

[Claims] (1) A method for manufacturing a flexible printed circuit board, which comprises forming a semi-cured polyamic acid film on a conductive foil, then forming predetermined openings in the film, and then completing imidization. .