JPH0215694A - Manufacture of flexible printed wiring board - Google Patents

Abstract

PURPOSE:To improve a flexible printed wiring board in high temperature resistance, continual heat resistance, an electrical property and workability by a method wherein a conductor circuit is formed directly on a polyimide film to form a wiring board, and a cover coat containing polyparabanic acid and epoxy resin is formed on the side of the conductor circuit of the board. CONSTITUTION:A conductor circuit 13 is formed directly on a polyimide film 11, and then a cover coat 15 is printed on the conductor circuit formed surface with material which contains polyparabanic acid through a printing method, which is set at a low temperature. The conductor circuit is formed directly on the polyimide film through the following methods: a method where polyimide resin is applied directly on the surface of a thin conductive material such as a copper foil, which is set through heating, and a formed copper plated board is formed into a conductor circuit through a subtractive method; a method where a circuit is formed directly on a polyimide film through an additive method. By these processes, an FPC, excellent in a high temperature resistance and continual heat resistance, can be obtained. As a pasting operation of a film can be dispensed with and a cover coat is formed through a printing, so that a printed wiring board of this design is excellent in workability and productivity and consequently a FPC of high reliability can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a flexible printed wiring board with particularly improved high-temperature heat resistance, long-term heat resistance, electrical characteristics, and workability.
Regarding the manufacturing method of FPC).

(Problems to be Solved by the Invention) With the recent development of electronic devices, printed wiring boards are being used frequently.

As shown in Figure 2, a typical example is one in which a conductive material 3 such as copper foil is bonded to a thin plastic base film l that has both insulation and flexibility using an adhesive 2, and then etched. A wiring pattern (conductor circuit) is formed, and the circuit is connected to the external environment (temperature,
A cover coat (coverlay film) 5 is provided for protection from humidity, corrosive gas, physical external forces, and the like.

For such FPCs, especially when heat resistance is required, a polyimide film is used as the base film, and a modified epoxy resin or thermosetting acrylic resin made by modifying a conductive material such as copper foil with NBR or polyamide, etc. They were attached using adhesives such as Also, the same type of adhesive was used to bond the coverlay film.

However, currently used adhesives (1) have low insulation resistance and (2) soften at high temperatures (low Tg). Therefore, the former is an important problem in FPC with fine circuits, and the current l''PC has a limit due to the insulation resistance tjC, and the latter is difficult to wire bond between bare chip and FPC in FPC. It is insufficient for applications that require heat resistance, such as high-density packaging and hair chip mounting, or applications that require high reliability.

In addition, since the work of bonding the coverlay film is done manually by humans to align it to a predetermined pattern, the alignment accuracy is poor and the workability is low. The problem with using a hot plate press, which requires a long time at high temperature and high pressure, is that the press is an expensive piece of equipment.

Furthermore, when components are mounted using soldering, which is commonly used today, in the conventional FPC, the adhesive of the copper clad board or coverlay film softens, and the moisture contained in the polyimide film rapidly expands. A blistering phenomenon occurred in the coverlay film, and there was an extremely high risk of damaging the FPC.

As a method to prevent such percentage points, a pre-baking process is required to reliably remove moisture from the polyimide film before soldering, but this process has a negative impact on work efficiency and quality during FPC mounting work. This is a major problem.

On the other hand, when forming a cover coat by a printing method, the cover coat material is required to have the electrical and chemical properties necessary for printed wiring materials, as well as heat resistance and flexibility. ing.

Printing cover coat materials for I/'r)C currently in practical use include epoxy resins with added flexibility agents such as polyols, urethane polymers, polyepoxides, NBR, polyamide resins, and polyester resins. , many of them have been given flexible properties by being modified. However, using this type of material requires sacrificing heat resistance and electrical insulation to some extent.
Moreover, it cannot be said that the moisture resistance is necessarily sufficient. Various polyimide resins have been proposed as materials with excellent properties of both heat resistance and flexibility, but after printing polyimide resin with cover coat 1, the heat treatment temperature to make the resin dense is a high temperature of approximately 400°C. Therefore, problems such as dimensional shrinkage, deformation, deterioration of the adhesive layer, oxidation of the copper foil that forms the circuit, and deterioration of physical properties due to changes in the crystal structure of the copper foil have arisen in the FPC.

Furthermore, polyimide resins generally have low alkali resistance and tend to form a thin layer, which may pose problems in terms of reliability in cover coats.

(Means for Solving the Problems) The present invention has been made to solve the problems in the conventional techniques as described above, and the outline thereof is as follows.

In other words, as shown in Figure 1, polyimide film II
Manufacture of a flexible printed wiring board characterized in that a wiring board is made by directly forming a conductor circuit 13 thereon, and a cover coat 15 containing polyparabanic acid and epoxy resin is formed by a printing method on the conductor circuit side. It's a method.

In the present invention, as a means of directly forming a conductor circuit on a polyimide film, polyimide resin is applied directly to the surface of a thin conductive material such as copper foil, cured by heating, and the resulting copper-clad board is formed by a subcrafting method. There are two methods: a method of directly forming a circuit on a polyimide film by an additive method, and either of these methods may be used. In this way, after forming a conductor circuit directly on the polyimide film, a cover coat is formed using a printing method using a material containing polyparabanic acid and an epoxy resin on the surface on which the conductor circuit is formed, which cures at a low temperature and is heat resistant and flexible. A cover coat is applied that has both of these characteristics and also has excellent adhesiveness (adhesive strength) to the polyimide film. Unlike conventional FPCs, FPCs manufactured in this way do not contain any adhesives with low heat resistance, so they have improved reliability and productivity in terms of high-density mounting, bare chip mounting, etc. Therefore, it is possible to provide a flexible printed wiring board that is extremely advantageous in terms of cost.

The polyparabanic acid used as the cover coat of the present invention is available from Tonen Petrochemical Co., Ltd. under the trade names x'r7 and XT-8.
The epoxy resins are bisphenol A type, bisphenol F type, Talesol novolak type,
Phenol novorasoc type, polyglycol type, glycidyl ether type, cycloaliphatic type, glycidyl ether type, etc. are known, and any one of these types can be used.

In addition, by adding aliphatic amines, aromatic amines, and imidazoles as necessary, it is possible to provide Coppercoe 1 with various characteristics.

Example I Polyamic acid (N-
Methyl-2-pyrrolidone) volume/night) was applied and heated at 300°C.
After curing for 2 hours, a copper clad board was obtained. The thickness of this film was 25 μm.

Next, a parallel pattern with a circuit width and a circuit interval of 200 μm was created using the thus-obtained copper-clad plate by a subtractive method.

Next, 100 parts by weight of polyparabanic acid (Tonen Petrochemical Co., Ltd., trade name XT-8) and novolac type epoxy resin (Dow Chemical Company, trade name DE N43B) were applied to the circuit side surface.
') Cover Coat 1 containing 20 parts by weight (all solid content ratios) was coated by a printing method and heated at 180°C for 1 hour to form a cover coat layer with a thickness of 20 μm.
I) C was obtained.

Comparative Example 1 A copper film made by laminating a 25 μm thick polyimide film (Dupont East Company, trade name Kapton) and a 35 μm thick rolled copper foil with an adhesive containing epoxy resin and N)3R as main components. A parallel pattern of 200μn1 was created on the cladding board (circuit width and inter-circuit depth by the lactif method).A coverlay film made of polyimide film with a thickness of 25μi11 was placed on the circuit side surface with epoxy resin and NB.
An FPC having a coverlay film was obtained by pasting together using an adhesive containing R as a main component.

The thickness of the adhesive was 25 μm, and the coverlay films were stacked and bonded together by heating and curing at 160° C. and 50 kg/c++I.

Comparative Example 2 A polyimide film with a thickness of 25 μm (Dupont Toshi, trade name: Kapton) and a rolled copper foil with a thickness of 35 μm were
A bonded copper clad board was obtained using an adhesive mainly composed of epoxy resin and NBR, and a parallel pattern with a circuit width and a circuit interval of 200 μm was created using the subtractive method. A solder resist containing liquid epoxy resin as the main component was applied to the circuit surface by a printing method, and then heated at 150°C for 30 minutes.
F with a resist layer of about 20 μm thick after heating for 0 minutes.
I got a PC.

Comparative Example 3 Polyamide fjlcN obtained from bilomelic anhydride 1-acid and diaminodiphenyl ether on rolled copper foil with a thickness of 35 μm
-Methyl-2-pyrrolidone solution) and heated to 300°C.
After curing for 2 hours, a copper clad board was obtained. The thickness of the film is 25
It was μm. A parallel pattern with a circuit width and a circuit interval of 200 μm was formed from the copper-clad plate using the subtractive method. Then, on the circuit side surface) 25 μm thick polyimide film is coated with 25 μm thick epoxy resin and NBR.
160℃, 50K via an adhesive layer mainly composed of
An FPC having a coverlay film was obtained by bonding under the conditions of g/cJ.

Comparative Example 4 A polyamic acid (N-methyl-2-pyrrolidone solution) obtained from pyromellitic anhydride and diaminodiphenyl ether was applied to a rolled copper foil with a thickness of 35 μm and cured at 300° C. for 2 hours to obtain a copper-clad board. Ta. The thickness of this film is 25μm
Met. A parallel pattern with a circuit width and a circuit interval of 200 μm was formed from the copper-clad plate using the subtractive method. Next, a solder resist mainly composed of liquid epoxy resin was applied to the circuit side surface by a printing method, and
Heating at °C for 30 minutes yielded an FPC with a resist I-layer approximately 20 μm thick.

Comparative Example 5 Polyamic acid (N-
Methyl-2-pyrrolidone? 30
It was cured at 0° C. for 2 hours to obtain a copper clad board.

The thickness of this film was 25 μm and -2.

The circuit width,
A parallel pattern with a circuit interval of 200 μm was created. Next, a cover coat containing the polyamic acid as a main component was applied to the circuit side surface by the 1-drawing 111 method, and heated at 300° C. for 30 minutes to obtain an FPC having a resist layer with a thickness of about 20 μm.

Table 1 shows the results of a comparative evaluation of the FPCs obtained in the above Examples and Comparative Examples in terms of copper foil tensile strength, insulation resistance between circuits, soldering heat resistance, bending resistance, and appearance. It is. According to this, there is no significant difference in the peel strength of the copper foil and the insulation resistance between the circuits, but in terms of solder heat resistance, Comparative Examples 1 to 3 have poor blistering, and the bending resistance is lower in Comparative Examples 2 and 4. Comparative Example 5 had defects in appearance, such as severe curling, while Example 1 according to the present invention was satisfactory in all properties.

(Effects of the Invention) Since the present invention is a method for manufacturing an FPC board without using an adhesive, it is possible to obtain an FPC with excellent high-temperature heat resistance and long-term heat resistance. Since there is no work required and the cover coat is also generated by printing, workability and productivity are good, and each plastic material is flexible and has rich electrical properties, making it a reliable FPC.
can be easily obtained.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of an FPC obtained by the present invention, and FIG. 2 is a sectional view showing an example of an FPC obtained by a conventional method. DESCRIPTION OF SYMBOLS 1... Plastic base film, 2... Adhesive, 3... Conductive material, 4... Adhesive, 5... Cover coat, 11... Polyimide film, 13...
Conductor circuit, 15...cover coat

Claims (1)

[Claims] A method for producing a flexible printed wiring board, comprising forming a conductor circuit directly on a polyimide film, and then forming a cover coat containing polyparabanic acid and an epoxy resin on the surface containing the conductor circuit by a printing method.