JPS61245872A - Manufacture of heat resistant substrate - Google Patents

Abstract

PURPOSE:To prevent the deterioration of the polyimide on a substrate, by using aluminum as a metal base material and directly forming a polyimide layer to the surface thereof. CONSTITUTION:In manufacturing a heat resistant substrate used in a printed wiring board, an aluminum base material or a base material of which the surface is covered with metal aluminum is used as a metal base material. Polyamide acid or polyimide varnish is directly applied to the surface of the metal base material and dried and cured to make it possible to directly form the polyimide layer on the metal base material. Because the deteroration of the polyimide layer is generated by the reaction of the copper (II) ion occurring from a copper base material and polyimide in the presence of oxygen, said deterioration is suppressed to a large extent when aluminum is used.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a heat-resistant substrate used for printed wiring boards.

[Conventional technology]

Printed wiring board substrates with conductor circuits formed on the surface of an insulating base material are those made by impregnating and hardening a cellulose base material or glass cloth with phenol resin or ebony resin and pasting copper foil on the surface of the insulating base material. Alternatively, there is a flexible printed circuit board in which copper foil is adhered to a film such as polyimide.

Among these, flexible printed circuit boards have recently been increasingly used as a means to achieve smaller size, higher density, and thinner electronic equipment. Conventional flexible printed circuit boards are manufactured by bonding polyimide film and steel foil with adhesive, so their properties such as heat resistance, chemical resistance, flame retardance, electrical properties, and adhesion are The excellent adhesive properties of polyimide could not be fully utilized because the adhesive used was the one controlling the problem.

As a way to solve this problem, polyamic acid (
A method has been proposed in which a polyimide precursor (polyimide precursor) or a polyimide solution is directly cast-coated, solvent removed, and cured (hereinafter abbreviated as direct coating method).

[Problem that the invention seeks to solve]

This method not only solves the above-mentioned deterioration in properties caused by the adhesive, but also enables a significant simplification of the manufacturing process.

However, if this method is performed in the atmosphere.

Another problem is that the properties of the polyimide layer itself of the resulting printed circuit board are significantly lower than those made from a film alone. The present invention aims to provide a heat-resistant substrate using a direct coating method that does not have such drawbacks.

[Means for solving problems]

The present inventors conducted intensive research on the deterioration mechanism of the polyimide layer of printed circuit boards obtained by the above-mentioned direct coating method.
t) It was determined that this was caused by a reaction between ions and polyimide.

Therefore, the inventors have discovered that the use of aluminum as the metal base material significantly improves the deterioration of the polyimide layer compared to the case of copper, leading to the present invention.

That is, the present invention involves directly applying polyamic acid or polyimide varnish to the surface of an aluminum base material or a metal base material whose surface is covered with metal aluminum, and drying and curing to form a polyimide layer directly on the metal base material. It is characterized by:

Here, the aluminum base material includes aluminum foil or aluminum thin plate, and the metal base material whose surface is covered with metal aluminum refers to copper foil that is bonded by pressure bonding (cladding), plating, sputtering, or ion beam method. A layer of metallic aluminum is formed on the surface of a metal such as, and then a composite material is included.

Moreover, the type of polyamic acid varnish or polyimide varnish used in the present invention is not particularly limited as long as it is obtained by reacting an aromatic polycarboxylic acid with an aromatic diamine.

The structure of the substrate obtained by the present invention includes aluminum foil alone or composite foil coated with polyimide on one or both sides, a polyimide layer inside and metal foil arranged on both sides of the polyimide layer, and foil. It is possible to use a board instead.

As a method for applying the polyamic acid varnish or polyimide varnish, a commonly used method such as a casting method can be applied. The coated material is then dried to remove the solvent in a dryer at a low temperature and then passed through a curing oven at a high temperature to form a film.

The present invention will be further explained below using examples.

Example 1 p-phenylenediamine as the diamine component and s,5',4,4'-biphenyltetracarboxylic dianhydride as the acid anhydride iN-Methylpyrrolidone After reaction in a solvent, the viscosity was adjusted and rotational viscosity was determined. A viscous polyamic acid varnish with a void of 1.000 was used.

This varnish was cast onto a 75 μm thick aluminum foil, dried at 50°C to 100°C to remove the solvent, and then heated at 400°C for 10 minutes to convert the polyamic acid into polyimide through a ring-closing reaction to form a flexible printed circuit board. Created.

Comparative Example 1 A flexible printed circuit board was produced in the same manner as in Example 1 using electrolytic steel foil with a thickness of 35 μm as the metal foil.Example 2 A cladding of copper foil (9μ) and aluminum foil (75μ) as the metal foil A flexible printed circuit board was produced in the same manner as in Example 1 using irises.

Comparative Example 2 A flexible printed circuit board was produced by the method of Example 1 using oxygen-free steel foil plated with chrome to a thickness of 35 μm as the metal foil.

Example 5 As a metal foil, a pure aluminum film was applied to the copper foil of Comparative Example 2 to a thickness of 1,000 mm by sputtering.
The polyamic acid varnish of Example 1 was applied with an applicator, the solvent was removed at 50°C to 100°C, and then the varnish was applied at 400°C for 10
A substrate was obtained by heating and curing for a minute.

Comparative Example & A substrate was obtained in the same manner as in Example 3 using a 35 μm thick copper foil plated with nickel as the metal foil.

Example 4゜4.4'-diaminodiphenyl ether and 3.3',
4.

4'-biphenyltetracarboxylic dianhydride was subjected to an IHrl condensation reaction in p-chlorophenol at 170°C to obtain a polyimide varnish having a rotational viscosity of 1700 poise. The polyimide in the solution was 5wt.

%. This polyimide varnish was cast on a 75 μn aluminum foil,
A flexible printed circuit board was obtained by IHr heating at 300°C.

Comparative Example 4 A 7-lexiple printed circuit board was obtained in the same manner as in Example 4 except that a double-sided roughened copper foil having a thickness of 358°C was used.

The metal foil of the substrates prepared in Examples 1 to 4 and Comparative Examples 1 to 4 was completely removed by etching to obtain a film having only a polyimide layer, and the tensile strength and elongation at break were measured.

Further, a tensile test of the polyimide film used in Example 1, which was prepared by coating a glass plate with the polyamic acid varnish, was used as a blank. The measurement results are shown in Table 1.

Table 1 As is clear from Table 1, when the metal in contact with the polyimide is aluminum, the deterioration of the polyimide falls within a range that poses no practical problems.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to manufacture a heat-resistant substrate without deterioration of polyimide by a direct coating method,
t.

Claims (1)

[Claims] 1. Production of a heat-resistant substrate characterized by applying polyamic acid or polyimide varnish directly to the surface of an aluminum base material or a metal base material whose surface is covered with metal aluminum, and drying and curing it. Law. 2. The method for producing a heat-resistant substrate according to claim 1, wherein the aluminum base material is aluminum foil. 3. The method for manufacturing a heat-resistant substrate according to claim 1, wherein the metal base material is copper foil.