JPH09302480A - Removing solution of tin or tin alloy and peeling method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a removing solution which allows peeling to be stably and safely performed without damaging a copper circuit of a substrate and a peeling method in the peeling of a metallic resist consisting of tin or a tin alloy. SOLUTION: The removing solution of tin or a tin alloy contains a base material constituted of copper or a copper alloy, and an inorganic acid or an organic acid, an oxidizing agent, an stabilizer and a heterocyclic compound having four nitrogen atoms on a heterocycle or its delivative. The method for peeling tin or a tin alloy is executed by immersing the base material constituted of copper or a copper alloy into this removing solution of tin or a tin alloy, or distributing or spraying the removing solution on the base material.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a stripping solution or stripping method for stripping tin or a tin alloy from a substrate made of copper or a copper alloy such as a printed wiring board.

[0002]

2. Description of the Related Art Copper through-hole plating is widely used to meet the demand for higher density in the production of printed wiring boards. As the method of manufacturing this through-hole plating, there are a tenting method for protecting the through-hole portion with an organic dry film or the like and a tin or tin alloy (mainly solder) stripping method. The tin or tin alloy stripping method is mainly used in. The tin or tin alloy stripping method protects the necessary circuit parts on the copper clad laminate with a metal resist made of tin or a tin alloy and removes unnecessary copper by etching. Therefore, the metal resist, which is tin or a tin alloy, is stripped.

However, it has been difficult in the past to sufficiently satisfy both the removal of tin or a tin alloy and the protection of the underlying copper circuit (prevention of dissolution, discoloration, etc.) in the stripping of the metal resist.

That is, conventionally, a copper or copper alloy is added to a stripping solution for tin or a tin alloy in order to prevent the copper material from being dissolved. For example, there are the following known technologies (patent publications).

Japanese Patent Publication No. 64-469: Thiourea Japanese Patent Publication No. 1-51548: Pyrrole, pyrazole, imidazole, triazole JP-A-2-250986: Benzotriazole JP-A-7-197279: Phthalazine JP-A-7-207465: Pyrrolidine, pyrrolidone,
Piperazine These are tin or tin alloy stripping solutions to which the above copper inhibitors have been added.

However, if these are roughly divided into two,
There were cases where the inhibitor adsorbed on copper also adsorbed on tin or a tin alloy to suppress peeling, and where the inhibitor was not suppressed but the effect of the copper inhibitor was weak.

Among the above, pyrrole, pyrazole, imidazole, triazole, phthalazine, pyrrolidine and the like have a weak anticorrosive effect on copper, while benzotriazole has a strong adsorption to the contrary, but forms a black film to be soldered. There was a problem of weakness. This is probably because the adsorption rate is slow and the copper surface is oxidized by the oxidizing agent.

Further, when nitric acid or the like is used as an etching solution, there is another problem that a yellowish brown NOx gas is generated when tin or a tin alloy is dissolved, which causes deterioration of the environment.

[0009]

An object of the present invention is to provide a stripping solution and a stripping method for stripping a metal resist made of tin or a tin alloy for stable and safe stripping without damaging the underlying copper circuit. Is to develop.

[0010]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that four nitrogen atoms on a heterocyclic ring are used as copper inhibitors in a tin or tin alloy stripping solution. It was found that it is possible to eliminate the adverse effect on the copper material while maintaining the performance as a stripping solution by adding the heterocyclic compound or its derivative. Furthermore, they have also found that it is possible to solve the problem of NOx gas generation during the dissolution of tin or tin alloy by adding acid amide, oxamide or urea as a stabilizer.

That is, the present invention is: A stripping solution for tin or a tin alloy, which comprises an inorganic or organic acid, an oxidizing agent, a stabilizer, and a heterocyclic compound having four nitrogen atoms on the heterocycle or a derivative thereof.

2. The concentration of inorganic or organic acid is 50 ~
300 g / l, the concentration of the oxidant is 0.1-200 g / l,
The concentration of the stabilizer is 0.1 to 50 g / l, and the concentration of the heterocyclic compound having four nitrogen atoms on the heterocycle or its derivative is 0.01 to 50 g / l.
The stripping solution for tin or tin alloy according to.

3. Heterocyclic compounds having 4 nitrogen atoms on the heterocycle are purine, pteridine, tetrazole,
The stripping solution for tin or tin alloy according to the above 1 or 2, which is one or more selected from hexamethylenetetramine or a derivative thereof.

4. Stabilizer is acid amide RCONH
₂ (where R is an alkyl group, an allyl group or an acyl group), oxamide NH ₂ COCONH ₂ or urea CO
The stripping solution for tin or tin alloy according to any one of 1 to 3 above, which is one or more selected from (NH ₂ ) ₂ .

5. Substrates made of copper or copper alloys on inorganic or organic acids, oxidants, stabilizers, and heterocycles
Method of stripping tin or tin alloy, characterized by immersing in a stripping solution of tin or tin alloy containing a heterocyclic compound having one nitrogen atom or a derivative thereof, or spraying or spraying the stripping solution on a substrate. .

6. The concentration of inorganic or organic acid is 50 ~
300 g / l, the concentration of the oxidant is 0.1-200 g / l,
A tin or tin alloy stripper having a stabilizer concentration of 0.1 to 50 g / l and a heterocyclic compound having four nitrogen atoms on the heterocycle or a derivative thereof of 0.01 to 50 g / l is used. 6. The method for stripping tin or tin alloy according to the above 5, which is used.

7. Heterocyclic compounds having 4 nitrogen atoms on the heterocycle are purine, pteridine, tetrazole,
7. The method for stripping tin or a tin alloy as described in 5 or 6 above, wherein a stripping solution for tin or a tin alloy, which is one or more selected from hexamethylenetetramine or a derivative thereof, is used.

[8] Stabilizer is acid amide RCONH
₂ (where R is an alkyl group, an allyl group or an acyl group), oxamide NH ₂ COCONH ₂ or urea CO
The method for stripping tin or tin alloy according to any one of 5 to 7 above, wherein a stripping solution for tin or tin alloy, which is at least one selected from (NH ₂ ) ₂ , is used.

It provides.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION In the tin or tin alloy stripping solution of the present invention, one or more inorganic acids or organic acids are used in order to enhance the solubility and stability of the stripped metal. It is possible to use various acids according to the application. For example,
Nitric acid, sulfuric acid, phosphoric acid, methanesulfonic acid, formic acid, oxalic acid, glycolic acid, citric acid, lactic acid and the like can be used, but as the inorganic acid, nitric acid which has excellent solubility and at the same time has an oxidizing property is often used. However, it is preferable to use an organic acid together in order to further increase safety. The concentration of the inorganic acid or the organic acid may be 50 to 300 g / l. 50
If it is less than g / l, the exfoliated metal is insufficiently dissolved, while if it exceeds 300 g / l, the effect of dissolving the metal is saturated and no further effect can be expected.

As the oxidizer, ferric salts such as ferric nitrate generally used for etching metals, nitric acid having an oxidizing property, hydrogen peroxide and the like can be used. A ferric salt is preferred in terms of solubility and stability. The concentration of the oxidizing agent may be 0.1 to 200 g / l. If less than 0.1 g / l, no effect is seen, while on the other hand,
Even if it exceeds 0 g / l, the effect is saturated and no further effect can be expected.

As the stabilizer used in the stripping solution of the present invention, for example, when nitric acid is used as an acid, a substance for preventing generation of NOx gas due to self-decomposition of nitric acid is added. Conventionally, as such a stabilizer, NH ₂ SO ₃ H sulfamate and the like have been used as effective, but the effect was actually small. Therefore, as a result of repeated research, acid amide RCONH ₂ (where R is an alkyl group, an allyl group, or an acyl group), oxamide NH ₂
It has been found that one or more selected from COCONH ₂ or urea CO (NH ₂ ) ₂ is most effective. Specifically, acetamide CH ₃ CONH ₂ , oxamide NH ₂ C
OCONH ₂ , propionamide C ₂ H ₅ CONH ₂ , urea CO (NH ₂ ) ₂ , butyroamide C ₃ H ₇ CONH _{2, and the} like can be used.

It is considered that the nitrite is rendered harmless by the following reaction. That is, for example, when the acid amide RCONH ₂ is used as the stabilizer, it is considered that nitrous acid is decomposed into nitrogen gas like RCONH ₂ + HNO ₂ → RCOOH + N ₂ + H ₂ O. As described above, when sulfamic acid is used as a stabilizer, sulfuric acid is generated, and lead sulfate is precipitated in the tin-lead alloy (solder) peeling, which causes a problem and results cannot be expected. In addition, the concentration of the stabilizer is 0.1 to
It may be 50 g / l.

In the development of the stripping solution of the present invention, the effect of the copper inhibitor added to the stripping solution causes deterioration of product performance when it is too strong or too weak, and when tin (or tin alloy) is dissolved. It has been found that the copper-tin alloy layer existing at the boundary between tin (or tin alloy) and the underlying copper also needs to be completely dissolved. It was also considered necessary to confirm that copper was deposited by displacement on a part of the active tin surface during dissolution and prevent this.

In order to solve such problems, it was found that any of the above problems can be solved by adding a heterocyclic compound having four nitrogen atoms on the heterocycle or a derivative thereof as a copper inhibitor. It was Specifically, one or more selected from purine, pteridine, tetrazole, hexamethylenetetramine, or derivatives thereof are used.

These copper inhibitors not only prevent the dissolution of the underlying copper, but also dissolve the plating films having different thicknesses, especially the leveler film having large variations.
It is characterized in that when the copper-tin alloy layer is completely dissolved, the underlying pure copper layer is not dissolved and remains uniformly. this is,
As the adsorption characteristics of the copper inhibitor of the present invention, it means that the adsorption to the pure copper layer is different from the adsorption to other tin or copper-tin alloy layer. This is considered to be an important characteristic in actual operation.

The concentration of these copper inhibitors is 0.0
It may be 1 to 50 g / l. If it is less than 0.01 g / l, no copper inhibitor effect is observed, while if it exceeds 50 g / l, no further effect can be expected.

In order to enhance the stability of the stripping solution, pH
Adding a buffer is also effective. For example, ammonium salt such as ammonium nitrate may be added.

Chloride ions weaken the anticorrosive effect of copper,
Although it usually causes corrosion, it should be avoided. On the other hand, it also has the function of increasing the solubility of solder, so refusing the addition of chlorine when considering such characteristics and covering the defects. Not a thing.

Furthermore, the copper inhibitor of the present invention can be used in combination with other copper inhibitors such as benzotriazole which have been generally used conventionally. And, such additives or auxiliary agents are included in the present invention as long as they do not depart from the scope of the present invention.

The stripping target of the stripping solution of the present invention is tin or a tin alloy. As a tin alloy, a tin-lead alloy (solder),
Examples thereof include a tin-zinc alloy and a tin-nickel alloy.

In the present invention, the base material capable of suppressing dissolution / erosion is copper or copper alloy.
When actually peeling off tin or a tin alloy, the peeling is carried out by immersing a base material made of copper or a copper alloy in the above-mentioned peeling liquid, or by spraying or spraying the peeling liquid on the base material. Although the peeling rate is increased by increasing the treatment temperature, the corrosiveness with respect to the base material is also increased at the same time, and therefore it is generally preferable to perform the peeling at 15 to 35 ° C.

The present invention will be described below based on examples, but the present invention is not limited to these examples.

[0034]

Example The following composition liquid was prepared as the basic composition of the stripping solution.

Inorganic acid: Nitric acid (62%) 300 ml / l Oxidizing agent: Ferric nitrate hexahydrate 100 g / l Organic acid: Glycolic acid 50 g / l Stabilizers such as acetamide, oxamide and urea in this basic solution A stripping solution was prepared by adding 2 g / l, and 2 g / l of a heterocyclic compound having 4 nitrogen atoms on the heterocycle shown in Table 1 or a derivative thereof as a copper inhibitor, respectively. The temperature of the solution was set to 25 ° C., and the stripping solution was dipped in a substrate in which solder of 60% tin 40% lead composition of about 5 μm was dipped on both surfaces of the copper clad laminate to completely dissolve the solder plating film.
Peeling was performed until the copper surface of the base material was exposed. Solder solubility was visually evaluated from the time required for peeling, and the appearance (color) of the substrate after peeling was visually evaluated. Furthermore, the solder wettability of the substrate after peeling the solder was evaluated visually.

On the other hand, in order to investigate the effect of suppressing copper dissolution, a substrate not subjected to solder plating was immersed in a stripping solution and the amount of copper dissolved was measured. Table 1 shows the results. The solder solubility (in all test results, the time required to dissolve 5 μm solder was within 30 seconds), the appearance of the substrate, and the solder wettability after peeling were good in all cases. Further, the amount of copper dissolved is 0.
It was sufficiently small as less than 1 μm / min, and was excellent in the copper dissolution inhibiting effect. In addition, generation of NOx gas during stripping was not detected. Further, when two or more kinds of heterocyclic compounds having four nitrogen atoms on the heterocycle are added (Examples 10 and 11), not only copper dissolution suppressing effect and appearance but also solder or tin dissolution There is also an increase in the limit concentration. It is considered that this is because by adding two or more kinds having different molecular size, shape and other properties, the adsorption property on the copper surface and the solubility of the metal were improved, and the liquid stabilizing effect could be maintained. . (Comparative Example) Similar to the example, as the basic composition of the stripping solution,
The following composition liquid was prepared.

Inorganic acid: Nitric acid (62%) 300 ml / l Oxidizing agent: Ferric nitrate hexahydrate 100 g / l Organic acid: Glycolic acid 50 g / l Stabilizers such as acetamide, oxamide and urea in this basic solution A stripping solution containing 2 g / l and a conventionally known copper inhibitor was prepared. Using this stripping solution, the same evaluation test as in the example was conducted.

The results are shown in Table 2. When benzothiazole and thiobarbituric acid were added, it took 2 minutes or more to dissolve the solder of 5 μm, and the dissolution of the solder was poor. When pyrrolidine, phthalazine, imidazole, triazole, and benzotriazole were used, the solder solubility was good within 30 seconds for dissolving 5 μm solder, but the base material after peeling turned reddish black. However, the solder wettability after that was also poor. The reddish black color is considered to be due to the slow adsorption of the inhibitor and the oxidation of the copper surface. Further, the amount of copper dissolved was larger than in the case of the examples, and particularly in the case of pyrrolidine, phthalazine and imidazole, the effect of suppressing copper dissolution was insufficient.

When acetamide, oxamide, urea, propionamide or butyroamide is used as a stabilizer, carboxylic acid is produced and nitrogen gas is emitted.
NOx gas was not detected. However, when conventional sulfamic acid was used as the stabilizer, generation of NOx gas was detected, and precipitation of lead sulfate was observed in the stripping solution.

[0040]

[Table 1]

[0041]

[Table 2]

[0042]

EFFECT OF THE INVENTION The tin or tin alloy stripper of the present invention has a low solubility of a copper base material and an excellent solubility of tin or a tin alloy,
No discoloration of the substrate after peeling is observed, and the solder wettability after that is excellent. Further, even when nitric acid is used, generation of harmful nitrous acid gas does not occur. Therefore, in stripping a metal resist made of tin or a tin alloy for performing copper through-hole plating, it is extremely useful as a stripping solution for performing stable and safe stripping without damaging the underlying copper circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Sho Okada 3-2-1 Tsujiko, Takatsuki City, Osaka Prefecture Nikko Metal Plating Co., Ltd. (72) Inventor Yasuo Mori 3-2-1 Tsujiko, Takatsuki City, Osaka Prefecture No. Nikko Metal Plating Co., Ltd.

Claims (8)

[Claims] 1. An inorganic or organic acid, an oxidizing agent, a stabilizer,
And a stripping solution for tin or a tin alloy, which contains a heterocyclic compound having four nitrogen atoms on the heterocycle or a derivative thereof. 2. The concentration of the inorganic or organic acid is 50 to 30.
0 g / l, the concentration of the oxidant is 0.1 to 200 g / l, the concentration of the stabilizer is 0.1 to 50 g / l, and the concentration of the heterocyclic compound having four nitrogen atoms on the heterocycle or its derivative is It is 0.01-50g / l, It is characterized by the above-mentioned.
The stripping solution for tin or tin alloy according to. 3. The heterocyclic compound having 4 nitrogen atoms on the heterocycle is one or more selected from purine, pteridine, tetrazole, hexamethylenetetramine, or derivatives thereof. The stripping solution for tin or tin alloy according to claim 1 or 2. 4. The stabilizer is one or more selected from acid amide RCONH ₂ (where R is an alkyl group, an allyl group or an acyl group), oxamide NH ₂ COCONH ₂ or urea CO (NH ₂ ) _2. Claims 1 to 1 characterized in that
The tin or tin alloy stripping solution according to item 3. 5. Tin or tin containing a base material made of copper or a copper alloy containing an inorganic or organic acid, an oxidizing agent, a stabilizer, and a heterocyclic compound having four nitrogen atoms on the heterocycle or a derivative thereof. A method for stripping tin or tin alloy, which comprises immersing in a stripping solution for alloy or spraying or spraying the stripping solution on a substrate. 6. The concentration of an inorganic acid or an organic acid is 50 to 30.
0 g / l, the concentration of the oxidant is 0.1 to 200 g / l, the concentration of the stabilizer is 0.1 to 50 g / l, and the concentration of the heterocyclic compound having four nitrogen atoms on the heterocycle or its derivative is The tin or tin alloy stripping method according to claim 5, wherein a tin or tin alloy stripping solution of 0.01 to 50 g / l is used. 7. The exfoliation of tin or a tin alloy, wherein the heterocyclic compound having four nitrogen atoms on the heterocycle is at least one selected from purine, pteridine, tetrazole, hexamethylenetetramine, or derivatives thereof. A method of stripping tin or a tin alloy according to claim 5, wherein a liquid is used. 8. The stabilizer is one or more selected from acid amide RCONH ₂ (where R is an alkyl group, an allyl group or an acyl group), oxamide NH ₂ COCONH ₂ or urea CO (NH ₂ ) _2. The method for stripping tin or a tin alloy according to claim 5, wherein a stripping solution for tin or a tin alloy is used.