JPH0415233A - Etching of polyimide film - Google Patents

Abstract

PURPOSE:To prevent a decrease in an etching speed and to reduce the cost by etching a polyimide film with an etchant comprising an aqueous solution containing an alkali, an amine compound and urea each in a specified concentration. CONSTITUTION:2.2-16wt.% alkali, 14-22wt.% amine compound and 14wt.% or above urea are dissolved in water to obtain an aqueous solution containing these components. This aqueous solution is heated to 50-70 deg.C to obtain an etchant. A polyimide film is etched with this etchant.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for processing and sowing polyimide films.

[Prior Art] Polyimide resins have been used for a variety of purposes due to their excellent heat resistance, flame resistance, dimensional stability, chemical resistance, and electrical and mechanical properties. Examples include flexible printed wiring boards and film carriers for automatic tape bonding.When used for this purpose, a substrate is created using polyimide resin in the form of a film, and a portion of the polyimide film of this substrate is used. Through-holes must be formed by etching.

By the way, methods using highly concentrated alkaline aqueous solutions and hydrazine have been attempted as methods for etching polyimide films efficiently and with high precision, but with highly concentrated alkaline aqueous solutions, sufficient etching cannot be achieved under normal conditions. However, in the method using hydrazine, there is a long time lag before etching starts, and during that time the hydrazine is exposed to the polyimide film. It is said that the metal penetrates into the inside of the hole and causes swelling, resulting in the inability to form a through hole of the desired size.

[Problems to be Solved by the Invention] In order to overcome these drawbacks, a method using a mixed solution of hydrazine and ethylenediamine has been proposed. In a mixed solution of hydrazine and ethylenediamine, swelling of the polyimide film does not occur, the amount of etching increases almost linearly with the time that the polyimide film is immersed in the etching solution, and the etching rate also increases by 24%.
It is known to be as large as about 7 min.

However, hydrazine is highly hygroscopic and absorbs moisture over time.
Hydrazine concentration decreases. As a result, the etching speed rapidly decreases, making it impossible to put it into practical use, and the etching solution must be frequently renewed, resulting in a high cost. Furthermore, the use of high concentrations of hydrazine results in the generation of white smoke, thereby deteriorating the working environment. Furthermore, hydrazine is highly toxic, and inhalation of its vapor causes inflammation of mucous membranes, making it impractical to handle in large quantities.

SUMMARY OF THE INVENTION An object of the present invention is to provide an etching method that solves the problems of the prior art, is more practical, and allows for lower costs.

[Means for Solving the Problems] As a result of various studies, the present inventor found that by using a solution with a specific composition, it is possible to obtain an etching rate that does not pose any practical problem and also to reduce costs. This led to the present invention.

That is, the etching method of the present invention that solves the above problems uses 2.2 to 16% by weight of alkali and 14 to 22% by weight.
An aqueous solution containing an amine compound of 14% by weight or more and urea of 14% by weight or more and having a liquid temperature of 50 to 70°C is used as an etching liquid.

The alkalis that can be used in the present invention are alkali metal hydroxides such as caustic soda and caustic potash, and the amine compounds include ethylenediamine, xylene diamine, trimethylene diamine, methylene diamine, propylene diamine, tetramethylene diamine, hexamethylene diamine, and pentamethylene diamine. diamines, etc.

[Operations] In the present invention, when the alkali concentration in the etching solution is low, the etching ability is extremely reduced, and when it is high, there is no resist that can be used during etching. For this reason,
The alkali concentration in the etching solution is 2.2 to 16% by weight (
Hereinafter, it is indicated as %. ). Furthermore, if the concentration of the amine compound in the etching solution is too low, the etching ability will be reduced, making it impractical; if it is too high, the etching ability will be high, but the dimensional accuracy will be deteriorated. For this reason,
It is necessary that the concentration of the amine compound be 14-22%. If the amount of urea is too small, the shape of the resulting through-hole cannot be made good, but even if more than a certain amount I is added, the shape cannot be made any better.

For this reason, it is necessary that the urea concentration be 14% or more. In the etching solution composition of the present invention, the upper limit of the solubility of urea is about 40%.

Hereinafter, the present invention will be further explained using examples and figures.

(Example) A polyimide film with a thickness of 50 μm (trade name: Kapton Toshi, DuPont) was cut into 30111111 squares and etched with a solution containing 4.8% NaOH and 19.3% ethylenediamine in a predetermined amount of urea. The polyimide film was immersed in this solution while maintaining it at a predetermined temperature, and the etching rate was measured. The relationship between the added urea concentration, temperature, and etching rate obtained from this result is
Shown in the figure. In Figure 1, A is an etching temperature of 7.
0"C1B is the result at 60℃, C is the result at 50℃, △,
The mouth and ○ indicate that the shape is good,
Mu, Kaku, and . each indicate defective items.

The present inventor investigated various conditions for practical use and found that when giving priority to dimensional accuracy, the etching speed should be 1 μm/min or more. In order to satisfy the requirements, it can be seen from FIG. 1 that the urea concentration must be 14% or higher and the etching temperature must be 50° C. or higher. The higher the etching temperature, the faster the etching rate, but since the etching solution is alkaline, it is preferable to set the etching temperature to 70''C or less in view of the working environment.

The present inventor believes that the etching mechanism that occurs in the method of the present invention is that the imide ring is fragmented by ammonia generated by the reaction between an alkali and urea, resulting in lower molecular weight, and then amidation occurs with the amine and dissolves. It is estimated that

In the practice of the present invention, the etching resist used is preferably a rubber-based resist such as bisazide-based cyclized natural rubber or cyclized butadiene rubber from the viewpoint of chemical resistance. The thickness of the resist must be 2 μm or more to prevent pinholes from forming in the formed film, and preferably 10 μm or less to avoid deteriorating pattern dimensional accuracy. .

[Example] A photoresist (product name: FSR) based on bisazide-based cyclized natural rubber was applied on the surface of a polyimide film (product name: Kapton, manufactured by DuPont) with a thickness of 50 μm.
After applying Fuji Pharmaceutical Co., Ltd.) with a whirler, 70°
C for 30 minutes to form a resist film with a true thickness of 5 to 7 μm. Then, through a predetermined mask, 110 mj
The resist was exposed to ultraviolet light. Thereafter, it was developed and post-baked at 130° C. for 30 minutes to form a pattern having a partially exposed surface of the polyimide film. Next, the etching solution of the present invention containing 13.3% NaOH, 17.7% ethylenediamine, and 24.6% urea was heated and maintained at 50°C, and the polyimide film was immersed in this etching solution. Then I did the etching. As a result, holes with approximately the same dimensions as the mask dimensions could be formed.

[Effects of the Invention] The method of the present invention does not contain hydrazine, so it is less toxic than conventional etching solutions, does not reduce the etching rate due to moisture absorption, is less expensive, and can be easily used in actual operations. It becomes like this.

[Brief explanation of drawings]

FIG. 1 shows an example of implementation of the present invention. Patent applicant: Sumitomo Metal Mining Co., Ltd.

Claims (1)

[Claims] Contains 2.2 to 16% by weight of alkali, 14 to 22% by weight of amine compound, and 14% by weight or more of urea, and has a liquid temperature of 5%.
A method for etching a polyimide film, characterized in that an aqueous solution at 0 to 70°C is used as an etching solution.