JP3317241B2 - Pre-treatment method of stainless steel plate for photo etching - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pre-treatment method for photo-etching used in the production of precision electronic components and the like. And a pre-treatment for improving the adhesiveness.

[0002]

2. Description of the Related Art A photo-etching method is a technique for processing a metal or the like into a desired shape by corrosion using a corrosive liquid. At present, various types of precision electronic parts, printed wiring boards, shadow masks for cathode-ray tubes and ICs are used. It is an indispensable technique as a method for performing fine processing of a lead frame or the like.

[0005] The photo-etching process is generally performed in the following steps.

[0004] First, a contaminant or the like on the surface of a metal plate to be processed is removed, and a pretreatment is performed for the purpose of further improving the adhesion to a photoresist film. Thereafter, a photoresist (photosensitive resin) is applied to the surface of the metal plate, and then heated to remove the solvent of the photoresist. The photoresist film thus formed is masked with an exposure original plate and then exposed (ultraviolet radiation). Next, when this is treated with a developing solution, the photoresist in the portion not irradiated with the ultraviolet rays is dissolved and removed, and the surface of the metal plate in that portion is exposed. An exposed portion of the metal is dissolved by performing an etching process on the processed metal plate in this state by means of spraying an etching solution. Thereafter, when the remaining photoresist film is peeled off and removed, a product etched into the same pattern as the original plate for exposure is obtained.

In such an etching process, copper,
Metal plates such as steel (carbon steel, stainless steel, etc.) or iron-nickel alloy are often used as workpieces. Also,
A ferric chloride solution is most widely used as an etchant.

As described above, a number of steps must be taken before a product is obtained by etching, but a metal plate to be processed is carried out for the purpose of improving the adhesion between the photoresist film and the metal plate to be processed. Pre-treatment is also a very important step and has a significant effect on product quality.

That is, if the pre-treatment of the metal plate to be processed is inappropriate, the adhesion between the photoresist film and the metal plate becomes insufficient, and the photoresist is peeled off during the etching process, and the intention of the metal plate at that part is removed. The desired product shape cannot be obtained due to the undesired dissolution.

Further, even if the photoresist film is not peeled off, the etchant may penetrate into the interface between the photoresist film and the surface of the metal plate and crevice corrosion may occur. Progresses.
Therefore, if the adhesion between the photoresist and the metal plate is not sufficient, there are problems such as variations in product dimensions and difficulty in fine etching.

As a pretreatment method performed for the purpose of enhancing the adhesion between the photoresist film and the metal plate to be processed,
There is a method of performing degreasing treatment such as alkali degreasing, solvent degreasing and electrolytic degreasing, followed by washing and drying. However, this method alone did not provide a sufficient effect of improving the adhesion to the photoresist film, and was insufficient particularly when the processing material was an iron-based metal.

JP-A-55-122876 discloses a mixed aqueous solution of chromic acid and sulfuric acid or an alkaline oxidizing solution (a mixed aqueous solution of sodium hydroxide and sodium nitrate).
There is disclosed a method of forming an oxide film on the surface by using the method and improving the adhesion between the photoresist and the steel material.

However, even with this method, sufficient adhesion between the photoresist film and the material to be processed cannot be obtained. In particular, when a thick oxide film is present after bright annealing, the adhesion is impaired. Will be.

[0012]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a pretreatment method which enhances the adhesion between a stainless steel plate to be etched and a photoresist film and which does not cause discoloration or acid treatment unevenness on the surface of the stainless steel plate. Is to do.

[0013]

The gist of the present invention relating to a method for pretreating a stainless steel plate for photoetching is as follows.

"This is a pre-treatment method for photo-etching a stainless steel plate, in which 0.5% to less than 1% hydrofluoric acid and 2% to less than 4% by weight before applying a photoresist to the surface of the stainless steel plate. The temperature of the solution containing nitric acid is 20-35 ° C
Pre-treatment method of stainless steel plate for photo-etching processing to remove oxide film on the surface of stainless steel plate by immersion in aqueous solution for 20 to 60 seconds " It also includes the state where the aqueous solution is sprayed on the surface of the steel sheet.

The present inventor conducted various experiments and studies to develop a pretreatment method for improving the adhesion between the surface of the stainless steel plate and the photoresist, and as a result, obtained the following findings and completed the present invention.

A) The oxide film formed by the finish annealing of the stainless steel sheet has reduced adhesion, and the oxide film may be removed. However, if the oxide film is removed with a mixed acid aqueous solution of hydrofluoric acid and nitric acid instead of removal by a mechanical method such as polishing, the adhesion will be significantly improved. Disappears.

B) However, even when the mixed acid aqueous solution is used,
If the oxide film is not removed under the specified conditions,
Although the adhesion is improved, the surface of the stainless steel sheet is discolored, or the gloss peculiar to the stainless steel is lost when it is excessively pickled. In addition, when a highly corrosive acid is used, corrosion and dissolution locally occur on the steel sheet surface, resulting in color unevenness in appearance (acid treatment unevenness).

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A stainless steel plate manufactured in a normal process is subjected to finish annealing, and an oxide film is formed on the surface. In particular, in the case of photo-etching, surface gloss is important, so finish annealing of stainless steel cold-rolled steel sheet is
Since bright annealing is used, an oxide film (B
A film).

The pretreatment method of the present invention is a method for removing an oxide film on the surface of a stainless steel plate, and the conditions specified in the present invention will be described below.

1) A mixed acid aqueous solution of hydrofluoric acid and nitric acid (hereinafter,% indicates weight%) Hydrofluoric acid and nitric acid have an effect of dissolving a base material under the scale and peeling the scale. However, hydrofluoric acid is less than 0.5%,
If the amount of nitric acid is less than 2%, the effect cannot be obtained. If the scale is insufficiently removed, there arises a problem that sufficient adhesion of the photoresist film cannot be obtained, and dimensional variation is increased by etching. In an extreme case, the resist film may be peeled off during the spray etching process.

On the other hand, when the content of hydrofluoric acid exceeds 1% and the content of nitric acid exceeds 4%, discoloration occurs on the surface of the stainless steel plate or the gloss characteristic of the stainless steel is lost. If the acid becomes strong, corrosion and dissolution locally occur on the plate surface, and color unevenness (acidity unevenness) occurs on the appearance, which is not preferable in appearance. Therefore, the content of hydrofluoric acid is set to 0.5 to less than 1%, and the content of nitric acid is set to 2 to less than 4%.

2) Temperature of mixed acid aqueous solution and immersion time If the temperature of the mixed acid aqueous solution is lower than 20 ° C., it takes a long time to remove an oxide film. On the other hand, when the temperature exceeds 35 ° C., the surface of the stainless steel plate becomes rough and loses its luster. Therefore, the temperature of the mixed acid aqueous solution was set to 20 to 35 ° C.

On the other hand, if the immersion time of the stainless steel plate in the mixed acid aqueous solution is less than 20 seconds, the oxide film cannot be sufficiently removed, and sufficient adhesion of the photoresist cannot be obtained. On the other hand, if it exceeds 60 seconds, the pickling becomes excessive, and the surface of the stainless steel plate becomes rough and loses its luster. Therefore, the immersion time is 2
0 to 60 seconds.

In carrying out the pretreatment method of the present invention, first, it is preferable to perform a degreasing treatment to remove oil and contaminants adhering to the surface of the stainless steel sheet to be processed. The degreasing method may be any of solvent degreasing, alkali degreasing, electrolytic degreasing and the like.

The form of the stainless steel plate to which the pretreatment of the present invention is applied may be a sheet (cut plate) shape or a hoop (coil) shape. Further, the pretreatment method of the present invention may be applied before the etching step, but may also be applied in the final step when manufacturing a stainless steel plate. The surface of the steel sheet obtained by this pretreatment is an active surface, and when exposed to air, an oxide film called a passivation film is formed, but this film does not affect the adhesion of the photoresist.

When the pretreatment described above is performed, the oxide film on the surface of the stainless steel plate is removed and the active metal surface is exposed, so that excellent adhesion to the photoresist film is imparted. Conceivable. And, by the improvement of the adhesion of the photoresist film, the penetration of the etching solution into the interface between the stainless steel plate and the photoresist film in the spray etching process is eliminated. This minimizes variations in product dimensions for each part. Further, the progress of etching in the lateral direction (side etch) is suppressed in the spray etching process, and finer etching can be performed as compared with the case where adhesion is poor.

[0027] The pretreatment according to the present invention does not cause discoloration on the surface of the stainless steel plate, and therefore does not impair the appearance. After the pretreatment, the surface of the stainless steel plate is preferably sufficiently washed with water, dried, and then coated with a photoresist. The photoresist at this time may be any of a negative type and a positive type, and may be any of an aqueous type, a solvent type or a dry film. Thereafter, the target product can be manufactured by performing an etching process according to a normal process.

[0028]

[Example] As a steel plate to be processed, SUS having a thickness of 0.2 mm
A 304 bright annealing material was prepared. This steel sheet is manufactured in a normal rolling process, and after cold rolling, ammonia decomposition gas (hydrogen:
(Nitrogen = 1: 3) Bright annealing treatment at 1000 ° C. in an atmosphere. This was cut into a 200 mm square to obtain a pretreated test piece, which was subjected to the following pretreatment.

First, the pretreated test piece was immersed in a 10% aqueous solution of caustic soda kept at 70 ° C. for 120 seconds to degrease the surface, and then washed with water.

Then, various pretreatment liquids shown in Table 1 were prepared, and pretreatment was performed by immersion while changing the liquid temperature and the immersion time variously as shown in Table 1. After the completion of the pretreatment, the test piece was washed with water, a photoresist was applied on the surface of the test piece in a thickness of 10 μm, and then exposed and developed in a usual process. The developed pattern had a photoresist opening width (W in FIG. 2 described below) of 100 μm. The test piece provided with the photoresist was subjected to an etching process by a spray etching method. A 47 Baume ferric chloride solution was used as an etching solution, and the solution temperature was 48 ° C.

[0031]

[Table 1]

FIG. 1 is a diagram showing a longitudinal section of an apparatus used for etching the test piece provided with a photoresist film.

This apparatus comprises an etching chamber 2 having a spray nozzle 4 for spraying an etching solution onto the surface of a test piece, and three washing chambers 3 having a washing spray 5 for washing. The test piece is conveyed into the etching chamber 2 by the conveyor 1, and is subjected to etching and then washed with water.

FIG. 2 is a cross-sectional view of a part of the processed portion after the etching process.

As shown in the figure, a photoresist film 7 is provided in close contact with the surface of the steel plate 6 to be processed. Opening 8
Is a portion from which the photoresist film has been removed by exposure and development, and the steel plate in this opening is etched into a target shape 9 by an etching solution. However, if the etching conditions are not favorable, corrosion progresses and the dotted line 10
The shape becomes larger than the target shape as shown by. If the photoresist does not adhere sufficiently to the steel sheet surface, crevice corrosion 11 occurs.

After the etching process, the photoresist film was peeled and removed, and the occurrence of crevice corrosion (width indicated by reference numeral b in FIG. 2) was observed. Further, the discoloration state was examined by comparing the surface tone of the stainless steel sheet before the pre-treatment with the color tone of the product after the etching process. Crevice corrosion and the degree of discoloration were evaluated in five stages. Table 1 shows the evaluation results. The evaluation criteria were as shown below Table 1.

As is evident from Table 1, a stainless steel sheet pretreated under the conditions specified in the present invention (treatment No. 1)
In Nos. To 8), no crevice corrosion occurred between the stainless steel plate of the test piece and the photoresist. This indicates that the adhesion between the photoresist and the stainless steel plate is sufficient. In addition, when the pretreatment method of the present invention was used, discoloration and acid unevenness of the test piece did not occur, and the appearance of the original material was maintained.

On the other hand, when a solution having a concentration lower than the concentration specified in the present invention is used (processing Nos. 9 and 10), or even when the concentration is under the conditions specified in the present invention, the pickling time is short. In the case (treatment Nos. 11 and 12), although the discoloration and acid unevenness on the material surface do not occur, the etching solution permeates the interface with the steel plate to be processed due to the poor adhesion of the photoresist film, and the test piece has Unintended dissolution occurred, resulting in impaired product shape.

Conversely, when the concentration of the solution is outside the upper limit specified in the present invention (processing Nos. 13 to 15), the adhesion of the photoresist film is improved and the penetration of the etching solution as described above is reduced. Although not observed, the surface of the material turned yellow and serious defects occurred in the surface quality of the product.

Further, even with the processing solution concentration specified in the present invention, the processing time is too long (processing No. 16, 1).
7) Or the processing temperature is too high (processing No. 18 ~
19), discoloration of the material occurs similarly, resulting in impaired appearance of the product.

Further, acids other than those specified in the present invention (treatment N
o. When the pickling treatment is performed according to 20 to 23),
Sufficient adhesion of the resist could not be obtained, and the etchant penetrated into the interface between the steel plate to be processed and the photoresist film, causing unintended dissolution of the material and failing to obtain the desired dimensions. Further, in this case, the surface of the test piece was sometimes discolored to yellow, which resulted in markedly impaired product appearance.

On the other hand, when no pickling treatment is performed (treatment N
o. No discoloration occurred in 24), but the resist film was peeled off during the etching step, and a product having the desired shape could not be obtained.

[0043]

According to the pretreatment of the present invention, the photoresist adhesion of a stainless steel plate can be remarkably improved by a relatively simple treatment, and more precise etching can be performed with high precision. Further, a useful effect such that a good product appearance can be obtained without discoloration of the material surface or acid treatment unevenness can be obtained.

[Brief description of the drawings]

FIG. 1 is a vertical sectional view of an etching apparatus.

FIG. 2 is a sectional view of a processed portion after an etching process.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Conveyor 2 Etching chamber 3 Rinse chamber 4 Etching liquid spray nozzle 5 Spray nozzle for water rinse b Crevice corrosion width W Etching width

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Claims (1)

(57) [Claims] 1. A pre-treatment method for photoetching a stainless steel plate, wherein 0.5% to less than 1% by weight of hydrofluoric acid and 2 to 4% Liquid temperature is 20-35 ° C, containing less than nitric acid
A method for pre-treating a stainless steel plate for photoetching, comprising immersing the stainless steel plate in an aqueous solution for 20 to 60 seconds to remove an oxide film on the surface of the stainless steel plate.