JPH08107281A - Multilayer flexible printed circuit board and its manufacture - Google Patents

Abstract

PURPOSE: To obtain a multilayer flexible printed circuit board, which is easy in through-hole processing, does not need a desmear treatment, is good in platability and has the high reliability of connection, by a method wherein insulating materials constituting the circuit board are all constituted of a polyimide. CONSTITUTION: Insulating materials constituting a multilayer flexible printed circuit board formed by laminating a plurality of flexible printed circuit boards are all formed of a polyimide. A polyimide adhesive film is inserted between the two-layer flexible printed circuit boards subjected to prescribed patterning and with insulating layers, which are all constituted of the polyimide and are formed on the surfaces and rears of the circuit boards, and is bonded by thermocompression to the printed circuit boards to manufacture the multilayer flexible printed circuit board. As the two-layer flexible printed circuit boards, one coated with a covering coat consisting of the polyimide is used. The polyimide adhesive film is formed, for example, by a method wherein a polyamic acid solution is applied to both surfaces of a polyimide film using a bar coater and is dried for 15 minutes at 110 deg.C or for 15 minutes at 250 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a multilayer flexible printed circuit board which has no insulating layer other than polyimide and is excellent in through hole reliability and heat resistance.

[0002]

2. Description of the Related Art A conventional multilayer flexible printed circuit board uses a base material in which a base film and a conductor layer are bonded with an adhesive or a base material in which a polyimide layer is directly formed on a conductor, and a conductor layer is not necessary. Form a plurality of conductor wiring by removing the part by etching, and make holes with a mold or a drill in the cover lay film where an acrylic or epoxy adhesive layer is formed on an insulating film such as polyimide, if necessary,
After overlapping and aligning the positions, heat and pressure are applied to make a flexible printed circuit board with a coverlay film, and acrylic or epoxy-modified polyimide-based film adhesive is inserted between multiple flexible printed circuit boards to heat it. A multilayer flexible printed circuit board was manufactured by pressure bonding.

However, according to this widely used method, various properties such as chemical resistance and heat resistance of an adhesive layer such as epoxy or acrylic used for a substrate or a coverlay, a film adhesive are used. Since it is significantly inferior to the polyimide layers used for insulating layers other than the adhesive layer, when forming a through hole, there is a problem of smear generated by heat during drilling, and swelling during desmear treatment with potassium permanganate. It had problems such as poor product yield and low reliability around through holes.

[0004]

The object of the present invention is to solve the problems caused by the above-mentioned adhesive layer made of a resin such as acryl or epoxy, in which all the insulating layers are composed of only polyimide. This is to be solved by using a flexible printed circuit board.

[0005]

According to the present invention, a so-called two-layer flexible printed circuit board in which a predetermined patterned insulating layer is entirely made of polyimide is coated with a cover coat made of polyimide as the insulating layer, and a plurality of flexible layers are further provided. A multilayer flexible printed circuit board and a method for producing the same, characterized in that the constituent insulating material is entirely made of polyimide, which is obtained by inserting a polyimide adhesive film between the printed circuit boards and performing thermocompression bonding.

As a material that can be used as a two-layer flexible printed circuit board composed only of a polyimide film layer having no adhesive layer in the present invention, a polyimide and a conductor having no ordinary acrylic or epoxy adhesive layer are used. The manufacturing method may be either a casting method or a plating method as long as it is composed of a metal foil layer. Further, either a single-sided plate or a double-sided plate can be used depending on the purpose. By subjecting this substrate to circuit processing by a usual method, a flexible printed circuit board having a pattern processed can be obtained.

As a method of applying a cover coat made of polyimide as an insulating layer to a two-layer flexible printed circuit board, a film cover lay using a polyimide adhesive on a polyimide film is thermocompression-bonded as long as it is made of only a polyimide resin. Even if the ink cover coat made of polyimide ink is applied on the two-layer flexible printed circuit board and heat-treated, the polyamic acid film is thermocompression-bonded,
It may be produced by any method such as baking and imidization.

Examples of the film adhesive used in the present invention include a single layer film of thermoplastic polyimide, and an existing polyimide film having a three-layer structure in which thermoplastic polyimide is applied as an adhesive layer on the front and back. However, as long as the material is entirely made of polyimide resin, it may be manufactured by any manufacturing method.

In the present invention, a flexible printed circuit board in which a predetermined patterned insulating layer is entirely made of polyimide is covered with a cover coat made of polyimide,
Furthermore, by inserting a polyimide adhesive film between multiple flexible printed circuit boards and thermocompression-bonding, a multilayer flexible printed circuit board in which the constituent insulating material consists entirely of polyimide can be obtained, but the method of thermocompression bonding can be a high-temperature press such as a vacuum press. It can be obtained by pressing at a temperature equal to or higher than the glass transition temperature of the film adhesive by using a material aligned by a usual method such as a pin or an eyelet using a different press. Normally, the glass transition temperature of a thermoplastic polyimide film adhesive is a high temperature of 200 ° C. or higher, but since the insulating material is entirely made of polyimide, the material does not deteriorate. On the other hand, when a normal epoxy type or acrylic type adhesive is used as the adhesive layer, the adhesive layer deteriorates, and it is impossible to press at such a high temperature.

The polyimide resin (including polyamide-imide resin) in the present invention is usually obtained by reacting a diamine with an acid anhydride and then heating or chemically imidizing the same. Is not particularly limited. Generally, diamines include phenylenediamine, diaminodiphenylmethane,
Diaminodiphenyl sulfone, diaminodiphenyl ether
Ter, etc., as the acid anhydride, trimellitic acid anhydride, pyromellitic dianhydride, biphenyl tetracarboxylic acid dianhydride, benzophenone tetracarboxylic acid dianhydride, etc. can be used, each one or Two or more kinds can be used in appropriate combination.

[0011]

According to the present invention, since the constituent material is entirely made of polyimide, it is modified with an epoxy resin or the like which requires thermocompression bonding at a high temperature of 200 ° C. or higher, which could not be used due to the heat resistance of the material. It is possible to use a pure thermoplastic polyimide adhesive film which is not used, and it is possible to easily obtain a multilayer flexible printed circuit board in which the insulating layer is entirely made of polyimide, which is excellent in productivity, yield, and characteristics.

[0012]

【Example】

[Example 1] 20.53 g of 2,2-bis [4- (4-aminophenoxy) phenyl] propane in a 4-neck separable flask equipped with a thermometer, a stirrer, a reflux condenser and a dry nitrogen gas inlet. Taking 14.62 g of 1,3-bis (3-aminophenoxy) benzene, 90% by weight of anhydrous N-methyl-2-pyrrolidone and 10 parts of toluene were added.
The mixed solvent of weight% is used, and the solid content ratio in all the raw materials is 20.
It was dissolved by adding an amount enough to make it wt%. Dry nitrogen gas was allowed to flow throughout the entire process from the preparation of the reaction to the removal of the product. Next, 20.60 g of purified 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride and 9.76 g of benzophenonetetracarboxylic dianhydride were added little by little with stirring, but the reaction was exothermic, so external This was cooled by circulating cold water of about 15 ° C. in the water tank. After the addition, the internal temperature was set to 20 ° C., the reaction was terminated by stirring for 5 hours to obtain a polyamic acid solution, and the glass transition temperature after imidization of the obtained resin was 229 ° C.

A commercially available polyimide film (manufactured by DuPont: Kapton 1) was prepared from this polyamic acid solution using a bar coater.
00H) has a thickness of 2 after imidization with a bar coater on one side.
Apply so that it becomes 0 μm, and at 110 ℃ for 15 minutes, 250
It was dried at ℃ for 15 minutes to obtain a cover lay film having thermoplastic polyimide on one surface.

Similarly, this polyamic acid solution was applied by a bar coater to both sides of a commercially available polyimide film (manufactured by DuPont: Kapton 100H) so that the thickness after imidization was 20 μm by a bar coater, and at 110 ° C. for 15 minutes. ,
It was dried at 250 ° C. for 15 minutes to obtain a polyimide adhesive film having thermoplastic polyimide on both sides.

A double-sided two-layer flexible printed circuit board was obtained by subjecting a copper foil surface of a commercially available double-sided two-layer flexible printed circuit board Espanex (manufactured by Nippon Steel Chemical Co., Ltd.) to a predetermined circuit processing. A coverlay film is placed on both sides of the obtained double-sided two-layer flexible printed circuit board so that the thermoplastic polyimide side faces the circuit board side.
By heating and pressure bonding at 80 ° C., 40 kg / cm ² for 15 minutes, a double-sided flexible printed circuit board with a cover lay film in which the insulating layer was made of only polyimide was obtained.

A copper foil surface of a polyimide adhesive film on both sides of a double-sided flexible printed circuit board with a coverlay film and a double-sided flexible printed circuit board (Espanex: Nippon Steel Chemical Co., Ltd.) faces outward. 280 ℃, using a vacuum press
40 kg / cm ² , heating and pressure bonding for 15 minutes were performed to laminate. Furthermore, the cover lay obtained by drilling, through-hole plating, and patterning this laminated plate, and then performing the predetermined hole drilling was performed under the same conditions as described above (cover lay so that the thermoplastic polyimide surface faces the circuit board side). Place the film, heat and press it at 280 ° C, 40 kg / cm ² , 15 minutes) using a vacuum press, and then perform external shape processing and the insulating layer will consist of only polyimide 4
A layer flexible printed circuit board was obtained.

According to this method, no desmear treatment is required because the finished state is good and almost no smear occurs because no adhesive such as epoxy or acrylic is used even when drilling for the through hole. It was Moreover, even if desmearing is performed by the potassium permanganate treatment, the insulating layer does not elute because it has extremely excellent chemical resistance. The multi-layer flexible printed circuit board thus obtained exhibits excellent heat resistance (solder heat resistance 300 ° C./30 seconds float: OK) because the insulating layer is entirely made of polyimide, and various treatments (JIS C 5012
It also showed extremely excellent characteristics against 9.3 thermal shock cycles (OK).

[0018]

According to the manufacturing method of the present invention, it is possible to obtain a multilayer flexible printed circuit board in which all insulating materials are made of polyimide by the same process as the conventional one, and the obtained multilayer flexible printed circuit board is not through-hole processed. It is an excellent circuit board that is easy to use, does not require desmear, has good plating properties, and has high connection reliability.

Claims (3)

[Claims] 1. A multilayer flexible printed circuit board comprising a plurality of flexible printed circuit boards laminated together,
A multi-layer flexible printed circuit board characterized in that all the insulating materials that it comprises are made of polyimide. 2. A multilayer flexible printed circuit board, characterized in that a polyimide adhesive film is inserted and thermocompression-bonded between a plurality of so-called two-layer flexible printed circuit boards, each of which has a predetermined pattern and whose insulating layer is entirely made of polyimide. Manufacturing method. 3. The method of manufacturing a multilayer flexible printed circuit board according to claim 2, wherein the two-layer flexible printed circuit board is a cover-coated two-layer flexible printed circuit board made of polyimide.