JPH07161774A - Circuit forming method - Google Patents

Abstract

PURPOSE:To provide the method for improvement of adhesive strength between polyimide resin and the wiring such as PWB and the like formed using a metal polyimide substrate on which a metal film is directly formed on the surface of polyimide resin. CONSTITUTION:A circuit is formed on the surface of polyimide resin by patterning the metal film directly formed on the polyimide resin surface, and the polyimide resin surface between the exposed circuits is treated by sulfuric acid solution, preferably by the sulfuric acid solution of 5vol.% or higher. As a result, the obtained PWB and the like has high adhesive strength, the decrease in adhesive strength due to deterioration is small and does not cause any practical problem. Accordingly, the adhesive strength between the circuit and the polyimide resin is high even when the PWB and the like of a very fine circuit is formed by this method, and a high reliability can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed wiring board (hereinafter referred to as "PWB") and a flexible printed circuit board (hereinafter referred to as "FPC") manufactured by using a substrate having a metal coating directly formed on a polyimide resin surface. ).), Tape automatic bonding (hereinafter referred to as "TAB"), and a method for improving the adhesion between a circuit such as a tape and a polyimide resin.

[0002]

2. Description of the Related Art Electronic components such as PWBs, FPCs, TAB tapes (hereinafter referred to as "PWBs") are manufactured by using a so-called metal polyimide substrate having a metal coating formed on a polyimide resin surface. This metal polyimide substrate is roughly classified into two types. One is manufactured by a laminating method in which a metal coating is adhered to the polyimide resin surface via an adhesive layer on the polyimide resin surface. And the other one is that the metal layer is directly provided on the surface of the polyimide resin. Such a metal-polyimide substrate is formed by providing a metal layer on the surface of the polyimide resin by using an electroless plating method, a vapor deposition method, a sputtering method, an ion plating method, or by coating a polyimide resin precursor on the surface of the metal foil. It is manufactured by curing.

When a high-density circuit is formed using a metal polyimide substrate formed by a laminating method, impurities are adsorbed by the adhesive layer in the circuit forming step, and insulation between circuits cannot be maintained. Therefore, a PWB or the like having a high-density circuit has a polyimide resin surface directly provided with a metal coating.

However, the recent demand for lighter, thinner, shorter, smaller, and more multifunctional electronic components has demanded higher density of electronic components. Those satisfying such requirements have extremely narrow circuit widths and circuit intervals.

By the way, a reduction in the circuit width means a reduction in the bonding area between the metal coating and the polyimide resin. Therefore, if the adhesion strength between the metal coating and the polyimide resin is not sufficient, the circuit obtained by processing the metal coating may be separated from the surface of the polyimide resin by a slight impact or the like. Further, in the current-art metal polyimide substrate, there is a high risk that this circuit will peel off.

In order to solve this problem, various attempts have been made to improve the adhesion strength between the metal layer and the polyimide resin. However, no valid one has been proposed yet. This is because the adhesion strength between the metal coating and the polyimide resin is affected by various effects and decreases. For example,
When a circuit is formed by patterning the metal coating, the exposed polyimide resin may be exposed to chemicals or the like used in forming the circuit, and the adhesion strength between the metal coating and the polyimide resin may be reduced.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above situation. That is, an object of the present invention is to provide a method for improving the adhesion strength between a wiring such as a PWB manufactured by using a metal polyimide substrate having a metal film directly formed on a polyimide resin surface and the polyimide resin.

[0008]

Means for Solving the Problems The inventors of the present invention used a substrate having a metal film directly formed on a polyimide resin surface, patterned the metal film to form a circuit, and then exposed the polyimide resin between the circuits. It was found that the adhesion strength of the circuit to the polyimide resin can be improved by chemically treating the resin, and the present invention has been completed.

That is, the method of the present invention for solving the above-mentioned problems is to form a circuit on the surface of a polyimide resin by patterning a metal coating formed directly on the surface of the polyimide resin to form a circuit on the surface of the polyimide resin after forming the circuit. It is treated with a sulfuric acid solution, preferably a sulfuric acid solution having a concentration of 5% by volume or more. Immersion is the simplest treatment method, but it is not limited to this.

[0010]

It is known that when a metal coating is directly formed on the surface of the polyimide resin, an altered layer of the polyimide resin exists at the interface between the polyimide resin and the metal coating regardless of the method. For example, the altered layer existing on the metal polyimide substrate obtained by the electroless plating method is formed by hydrophilically modifying the surface of the polyimide resin with alkali or the like as a pretreatment for the electroless plating.

The method of the present invention uses a metal polyimide substrate obtained by directly forming a metal coating on the surface of a polyimide resin,
After patterning the metal film to form a circuit, the polyimide resin exposed between the circuits is treated with sulfuric acid. It is considered that the reason why the circuit adhesion can be improved by the method of the present invention is that the deteriorated layer of the polyimide resin exposed between the circuits is modified by sulfuric acid to improve mechanical and chemical strength.

The sulfuric acid solution used in the present invention has a sulfuric acid concentration of 5
When it is less than the volume%, the effect of modifying the deteriorated layer is hardly obtained even if the treatment time is lengthened or the treatment temperature is raised.
Further, the treatment temperature and the treatment time are influenced by the state of the altered layer and the sulfuric acid concentration in the sulfuric acid solution used, and therefore cannot be unconditionally limited. Therefore, when applying the method of the present invention to the actual operation, it is necessary to obtain appropriate conditions in advance.

The substrate to which the present invention is applied is a substrate in which a metal coating is directly formed on the surface of a polyimide resin, and is not limited by the method of forming the metal and the kind of the metal.

[0014]

EXAMPLES Next, examples of the present invention will be described. (Example 1) The surface of polyimide resin film "Kapton 200 H" manufactured by Toray-Dupont Co., Ltd. was treated with an aqueous solution of 30% by volume of hydrazine monohydrate at 25 ° C. for 2 minutes,
A hydrophilic altered layer was formed on the surface of the polyimide resin. After that, it was washed with water and made by Okuno Seiyaku "OPC-80 Catalyst.
M ”was used to apply the catalyst. Then, it wash | cleaned with water and accelerated treatment was performed using "OPC-555 accelerator" by Okuno Seiyaku. After that, an electroless plating solution having the composition shown below was used to perform electroless copper plating on the surface of the polyimide resin under electroless plating conditions. Then, a uniform electroless copper plating film having a thickness of 0.2 μm was formed on the surface of the polyimide resin.

(Composition of electroless plating solution) CuSO ₄ .5H ₂ O: 10 g / l EDTA.2Na: 30 g / l 37% HCHO: 5 ml / l PEG # 1000: 0.5 g / l 2, 2'-bipyridyl: 10 mg / l

(Electroless plating conditions) Temperature: 65 ° C. Stirring: Air stirring time: 10 minutes pH: 12.5

Next, on the surface of the electroless copper plating film obtained,
Using the electrolytic copper plating solution having the composition shown below, electrolytic copper plating was performed under the electrolytic conditions shown below. Then, a copper coating having a thickness of 35 μm was formed on the surface of the polyimide resin.

(Composition of plating solution) CuSO ₄ .5H ₂ O: 80 g / l H ₂ SO ₄ : 180 g / l

(Plating conditions) Temperature: 23 ° C. Positive electrode: Phosphorus-containing copper Cathode current density: 3 A / dm ² Stirring: Air and cathode rocker time: 1 hour

Next, a substrate having a circuit with a width of 35 μm and an interval of 35 μm was prepared from the obtained copper plating film by a photolithography technique. Then, the adhesion strength of the circuit to the polyimide resin on this substrate was measured by a conventional method. The obtained adhesion strength was 1.0 Kgf / cm.

Thereafter, this substrate was immersed in a sulfuric acid solution having a concentration of 20% by volume at 25 ° C. for 1 hour. Then, it was washed with water and dried in air, and the adhesion strength of the circuit to the polyimide resin was measured in the same manner as above. The obtained adhesion strength is 1.2 Kgf /
It was cm.

Next, this substrate was placed at a concentration of 20% by weight at 25 ° C.
The sample was immersed in the hydrochloric acid solution (1) for 1 hour to perform a deterioration test. Then, the adhesion strength between the circuit and the polyimide resin was measured. The obtained adhesion strength was 1.0 Kgf / cm. It can be said that this substrate is practical and has high reliability.

Example 2 The concentration of the sulfuric acid solution used for the treatment was 5% by volume, the treatment temperature was 50 ° C., and the treatment time was 1
A circuit was formed in the same manner as in Example 1 except that the time was set.

The adhesion strength between the circuit and the polyimide resin was measured in the same manner as in Example 1. The obtained adhesion strength is 1.1.
It was Kgf / cm.

Next, a deterioration test was conducted in the same manner as in Example 1. Then, the adhesion strength between the circuit and the polyimide resin was measured. The obtained adhesion strength was 1.0 Kgf / cm. It can be said that this substrate is practical and has high reliability.

Example 3 A substrate having a copper film formed on the surface of a polyimide resin by a vapor deposition method (“Nova manufactured by Sherdal Co.”)
A circuit was formed in the same manner as in Example 1 except that "clad") was used.

Then, the adhesion strength of the circuit to the polyimide resin on this substrate was measured in the same manner as in Example 1. The obtained adhesion strength was 1.0 Kgf / cm.

Thereafter, this substrate was immersed in a sulfuric acid solution having a concentration of 20% by volume at 25 ° C. for 1 hour. Then, it was washed with water and dried in air, and the adhesion strength of the circuit to the polyimide resin was measured in the same manner as above. The obtained adhesion strength is 1.1 Kgf /
It was cm.

Then, a deterioration test was conducted in the same manner as in Example 1. Then, the adhesion strength between the circuit and the polyimide resin was measured. The obtained adhesion strength was 1.0 Kgf / cm. It can be said that this substrate is practical and has high reliability.

(Comparative Example 1) The concentration of the sulfuric acid solution used for the treatment was 4% by volume, the treatment temperature was 60 ° C., and the treatment time was 2
A circuit was formed in the same manner as in Example 1 except that the time was set.

The adhesion strength between the circuit and the polyimide resin was measured in the same manner as in Example 1. The obtained adhesion strength is 1.1.
It was Kgf / cm.

Then, a deterioration test was conducted in the same manner as in Example 1. Then, the adhesion strength between the circuit and the polyimide resin was measured. The obtained adhesion strength was 0.6 Kgf / cm, and a remarkable decrease was observed. This substrate is unreliable.

[0033]

EFFECTS OF THE INVENTION PWBs produced by the method of the present invention have a high adhesion strength, and the deterioration of the adhesion strength due to deterioration is slight, which is not a practical problem.

Therefore, even when a PWB or the like having an extremely fine circuit is produced by the method of the present invention, the adhesion strength between the circuit and the polyimide resin is high and the reliability is sufficiently high.

Claims (2)

[Claims] 1. A method for forming a circuit on a surface of a polyimide resin by patterning a metal coating formed directly on the surface of the polyimide resin, wherein the exposed surface of the polyimide resin is treated with a sulfuric acid solution after the circuit is formed. Circuit formation method. 2. The circuit forming method according to claim 1, wherein the sulfuric acid concentration in the sulfuric acid solution is 5% by volume or more.