An environmentally friendly tin stripping solution for removing the copper-tin alloy layer of printed circuit boards

Abstract

The present application relates to the technical field of circuit board processing, and specifically discloses an environmentally friendly tin stripping water for stripping the copper-tin alloy layer of a printed circuit board, the tin stripping water comprising the following raw materials in weight percentage: 25-65% sulfuric acid, 2-10% hydrogen peroxide, 0.5-3% citric acid, 0.5-6% boric acid, 0.1-2% stabilizer, 0.1-2% copper protector, and the balance being deionized water; the tin stripping water provided in the present application has a scientific formula, a rigorous ratio, and is simple to prepare; the obtained tin stripping water has stable performance and can be used in a tin stripping process to achieve one-step stripping of excess tin layer and copper-tin alloy layer, with the advantages of high tin biting rate, large tin dissolving amount, low copper biting rate, fast copper-tin alloy layer stripping rate, thorough stripping without damaging the copper surface; the tin stripping water formula of the present application does not contain nitric acid with strong corrosiveness and irritation, and no strong irritating gas is generated during the production and tin stripping process; the obtained tin stripping waste liquid is convenient for recovering tin and copper, has low ammonia nitrogen and no total nitrogen, and is green and environmentally friendly.

Description

Technical Field

[0001] The present application relates to the technical field of circuit board processing, and more specifically, to an environmentally friendly tin stripping solution for stripping the copper-tin alloy layer of a printed circuit board. Background Art

[0002] In the PCB industry, the process of pattern electroplating is: first, copper is plated on the substrate, then tin is plated on the copper layer, and then the copper layer not protected by the tin layer is etched away with an etching solution, leaving the tin layer plated into a pattern and the base copper covered by it; after the etching process is completed, the excess tin layer and tin alloy layer on the copper surface need to be removed, which is the tin stripping process.

[0003] Tin stripping solution, also known as tin stripping liquid, is one of the primary chemical materials used in printed circuit board (PCB) production. It is used to remove tin plating, tin-lead alloys, copper-tin alloys, and tin solder joints. Currently, the tin stripping solution used in the PCB industry is mostly nitric acid-based, consisting primarily of nitric acid, ferric chloride, corrosion inhibitors, surfactants, nitrogen oxide inhibitors, and chelating agents. The nitric acid concentration is generally 20%-25%. Nitric acid-based tin stripping solution offers fast stripping speed and a large stripping capacity. However, the stripping process can result in the presence of significant amounts of tin, copper, and nitric acid. Nitric acid, a highly oxidizing and corrosive acid with a pungent odor, is highly irritating and corrosive to the skin and mucous membranes. Inhalation of excessive nitric acid fumes can cause acute poisoning. Furthermore, nitric acid wastewater contains nitrates, which can easily increase nitrogen pollution in water bodies. Improper handling can pose significant environmental risks.

[0004] In general, waste tin stripping liquid generated by production processes in industries such as PCBs and electroplating poses significant risks, containing high levels of tin and nitric acid and a complex system. The waste liquid contains high levels of metals, including 70-110g / L tin, 15-35g / L copper, and 30-50g / L iron. Other metals include lead, nickel, and silver. It also has a high contamination index, high free acidity (the acid equivalent concentration of nitric acid is expected to be above 4N), and a wide variety of other organic compounds (such as heterocyclic compounds, polycyclic aromatic compounds, and polymers). To date, no mature, viable industrial technology has been developed to completely address the environmental pollution caused by waste tin stripping liquid.

[0005] Therefore, it is imperative to develop a green, environmentally friendly and easy-to-handle tin stripping solution. Based on the above statement, the present application provides an environmentally friendly tin stripping solution for stripping the copper-tin alloy layer of a printed circuit board. Summary of the Invention

[0006] In order to solve the problems that existing waste tin stripping liquid poses great harm to human health and the environment and is difficult to handle, the present application provides an environmentally friendly tin stripping water for stripping the copper-tin alloy layer of a printed circuit board.

[0007] The present application provides an environmentally friendly tin stripping solution for stripping the copper-tin alloy layer of a printed circuit board, which adopts the following technical solution:

[0008] The invention discloses an environmentally friendly tin stripping solution for stripping the copper-tin alloy layer of a printed circuit board. The solution comprises the following raw materials in percentage by weight: 25-65% sulfuric acid, 2-10% hydrogen peroxide, 0.5-3% citric acid, 0.5-6% boric acid, 0.1-2% stabilizer, 0.1-2% copper protecting agent, and the balance being deionized water.

[0009] Preferably, the environmentally friendly tin stripping water comprises the following raw materials in weight percentage: 35-50% sulfuric acid, 4-8% hydrogen peroxide, 1-2% citric acid, 2-4% boric acid, 0.5-1.5% stabilizer, 0.5-1.5% copper protectant, and the balance is deionized water.

[0010] Preferably, the environmentally friendly tin stripping water comprises the following raw materials in percentage by weight: 35% sulfuric acid, 6% hydrogen peroxide, 2% citric acid, 2% boric acid, 1% stabilizer, 1% copper protecting agent, and the balance is deionized water.

[0011] By adopting the above technical solution, the tin stripping solution proposed in this application has a scientific formula and a rigorous ratio. It can be used in the tin stripping process to remove the excess tin layer and the copper-tin alloy layer in one step. The main reaction mechanism is as follows:

[0012] Sn+4H + +H2O2→H2SnO3↓+2H2O

[0013] Cu+H2SO4+H2O2→CuSO4+2H2O

[0014] In the above reaction, metallic tin is corroded and oxidized by the combined action of acid and hydrogen peroxide to form metastannic acid precipitate, which causes the tin to be completely eaten away; metallic copper is converted into free copper ions under the combined action of acid and hydrogen peroxide.

[0015] The sulfuric acid in the formula of the present application can provide an acidic environment and at the same time act as an oxidant to give the tin stripping water a corrosive function; hydrogen peroxide is the main component of tin biting, and the metallic tin is corroded and oxidized into divalent tin by the combined action of acid and hydrogen peroxide, so that the tin is bitten cleanly; by controlling the added concentration of hydrogen peroxide, the present application can ensure the effective removal of metallic tin while protecting the electroplated tin layer from oxidation.

[0016] In the design of this application, in order to achieve the one-step removal of excess tin layer and difficult-to-handle tin-copper alloy layer, taking into account the problems of nitric acid-type tin stripping water being highly corrosive, having a strong pungent odor, poor waste liquid recovery, and not being green and environmentally friendly, other acids are considered to replace nitric acid. Through a large number of experimental tests, the applicant found that the sulfuric acid / hydrogen peroxide combination tin stripping water can simultaneously remove excess tin layer and difficult-to-handle tin-copper alloy layer in one step, and the stripping effect is good. However, there are problems such as unstable performance of tin stripping water, easy decomposition of hydrogen peroxide, low tin dissolution rate, high copper biting rate, and damage to the copper surface.

[0017] To address the above issues, the applicant added citric acid, boric acid, stabilizers, and copper protectants to the formula. Through continuous matching tests, the formula ratio was improved, ultimately achieving stable performance of the tin stripping solution, no hydrogen peroxide cracking, high tin dissolution rate, reduced copper bite rate, and no damage to the copper surface. Among them, the co-addition of citric acid and boric acid can effectively maintain the acidity of the tin stripping solution and increase the tin bite rate; the addition of the stabilizer can stabilize the hydrogen peroxide from cracking, while further increasing the tin bite rate and reducing the copper bite rate without damaging the copper surface; the addition of the copper protector can effectively inhibit corrosion of the copper surface and reduce the copper bite rate.

[0018] The tin stripping solution formula of the present application does not contain highly corrosive and irritating nitric acid, and the production and tin stripping processes will not produce strong irritating gases. It is relatively safer than traditional nitric acid-type tin stripping solution.

[0019] After the tin stripping is completed, the tin stripping waste liquid obtained by the tin stripping water of the present application mainly contains sulfuric acid, tin, copper and a very small amount of hydrogen peroxide. It is low in ammonia nitrogen and has no total nitrogen, is green and environmentally friendly, and is convenient for recycling tin and copper. Copper can be recovered by electroplating, and the remaining sulfuric acid and tin can be recovered by conventional waste liquid treatment methods. The operation is simple and convenient.

[0020] Preferably, the stabilizer is a compound of 1.4-butanediol, sodium silicate and sodium tripolyphosphate.

[0021] Preferably, the mass ratio of the 1.4-butanediol, sodium silicate and sodium tripolyphosphate is 1-2:1:3-5.

[0022] By adopting the above technical solution, the stabilizer added to the tin stripping water formula of the present application is a compound of 1.4-butanediol, sodium silicate and sodium tripolyphosphate, which can effectively stabilize the hydrogen peroxide and prevent it from cracking, thereby increasing the tin biting rate while reducing the copper biting rate without damaging the copper surface; by controlling the mass ratio of 1.4-butanediol, sodium silicate and sodium tripolyphosphate to 1-2:1:3-5, especially 2:1:4, the stability of the hydrogen peroxide can be further improved, so that the hydrogen peroxide in the formula does not crack during storage, transportation and use; the tin biting rate is further increased, while reducing the copper biting rate without damaging the copper surface.

[0023] Preferably, the mass ratio of the hydrogen peroxide to the stabilizer is 5-20:1.

[0024] By adopting the above technical solution, the mass ratio of hydrogen peroxide to stabilizer in the formula is controlled to 5-20:1, especially 6:1, which can further stabilize the performance of hydrogen peroxide, thereby ensuring effective removal of metallic tin while protecting the electroplated tin layer from oxidation.

[0025] Preferably, the copper protecting agent is one or more of benzotriazole, N,N-dimethylacetamide, and methylbenzotriazole.

[0026] Preferably, the copper protecting agent is a compound of benzotriazole and N,N-dimethylacetamide in a mass ratio of 1:1-1.5.

[0027] By adopting the above technical solution, the copper protecting agent added to the tin stripping water formula of the present application is a compound of benzotriazole and N,N-dimethylacetamide. By controlling the mass ratio of benzotriazole and N,N-dimethylacetamide to 1:1-1.5, especially 1:1.5, the corrosion of the copper surface can be further inhibited, the copper biting rate can be reduced, and the copper surface can be protected.

[0028] Preferably, the preparation method of the environmentally friendly tin stripping water is: according to the above ratio, the raw materials are mixed, dissolved and dispersed to prepare the required tin stripping water.

[0029] By adopting the above technical solution, the preparation method of the tin stripping water proposed in this application is simple, and no strong irritating gas is generated during the preparation and use process, which is green and environmentally friendly.

[0030] In summary, this application has the following beneficial effects:

[0031] The tin stripping water provided in this application has a scientific formula, a strict ratio, and is simple to prepare. The resulting tin stripping water has stable performance and can be used in a tin stripping process to remove excess tin and copper-tin alloy layers in one step. It has the advantages of a high tin biting rate, a large amount of tin dissolved, a low copper biting rate, a fast copper-tin alloy layer stripping rate, and a thorough stripping without damaging the copper surface.

[0032] The tin stripping water formula of the present application does not contain nitric acid, which is highly corrosive and irritating. The production and tin stripping processes will not produce strong irritating gases. It is relatively safer than traditional nitric acid-type tin stripping water. The resulting tin stripping waste liquid is convenient for recycling tin and copper, has low ammonia nitrogen and no total nitrogen, and is green and environmentally friendly. DETAILED DESCRIPTION

[0033] The present application is further described in detail below with reference to the embodiments.

[0034] Example

[0035] Example 1

[0036] An environmentally friendly tin stripping solution for stripping the copper-tin alloy layer of a printed circuit board comprises the following raw materials in weight percentage: 25% sulfuric acid (50% by mass), 2% hydrogen peroxide (30% by mass), 0.5% citric acid, 0.5% boric acid, 0.1% stabilizer, 0.1% copper protectant, and the balance being deionized water;

[0037] The stabilizer is a compound of 1.4-butanediol, sodium silicate and sodium tripolyphosphate in a mass ratio of 1:1:3;

[0038] The copper protecting agent is a compound of benzotriazole and N,N-dimethylacetamide in a mass ratio of 1:1.

[0039] Example 2

[0040] An environmentally friendly tin stripping solution for stripping the copper-tin alloy layer of a printed circuit board comprises the following raw materials in percentage by weight: 35% sulfuric acid (50% by mass), 4% hydrogen peroxide (30% by mass), 1% citric acid, 2% boric acid, 0.5% stabilizer, 0.5% copper protectant, and the balance deionized water;

[0041] The stabilizer is a compound of 1.4-butanediol, sodium silicate and sodium tripolyphosphate in a mass ratio of 2:1:3;

[0042] The copper protecting agent is a compound of benzotriazole and N,N-dimethylacetamide in a mass ratio of 1:1.2.

[0043] Example 3

[0044] An environmentally friendly tin stripping solution for stripping the copper-tin alloy layer of a printed circuit board comprises the following raw materials in percentage by weight: 35% sulfuric acid (50% by mass), 6% hydrogen peroxide (30% by mass), 2% citric acid, 2% boric acid, 1% stabilizer, 1% copper protecting agent, and the balance being deionized water;

[0045] The stabilizer is a compound of 1.4-butanediol, sodium silicate and sodium tripolyphosphate in a mass ratio of 2:1:4;

[0046] The copper protecting agent is a compound of benzotriazole and N,N-dimethylacetamide in a mass ratio of 1:1.5.

[0047] Example 4

[0048] An environmentally friendly tin stripping solution for stripping the copper-tin alloy layer of a printed circuit board comprises the following raw materials in weight percentage: 50% sulfuric acid (50% by mass), 8% hydrogen peroxide (30% by mass), 2% citric acid, 4% boric acid, 1.5% stabilizer, 1.5% copper protectant, and the balance deionized water;

[0049] The stabilizer is a compound of 1.4-butanediol, sodium silicate and sodium tripolyphosphate in a mass ratio of 1:1:5;

[0050] The copper protecting agent is a compound of benzotriazole and N,N-dimethylacetamide in a mass ratio of 1:1.5.

[0051] Example 5

[0052] An environmentally friendly tin stripping solution for stripping the copper-tin alloy layer of a printed circuit board comprises the following raw materials in percentage by weight: 65% sulfuric acid (50% by mass), 10% hydrogen peroxide (30% by mass), 3% citric acid, 6% boric acid, 2% stabilizer, 2% copper protecting agent, and the balance being deionized water;

[0053] The stabilizer is a compound of 1.4-butanediol, sodium silicate and sodium tripolyphosphate in a mass ratio of 2:1:5;

[0054] The copper protecting agent is a compound of benzotriazole and N,N-dimethylacetamide in a mass ratio of 1:1.5.

[0055] Example 6

[0056] Example 6 is the same as Example 3, except that the stabilizer is a compound of 1.4-butanediol, sodium silicate and sodium tripolyphosphate in a mass ratio of 1:1:1.

[0057] Example 7

[0058] Example 7 is the same as Example 3, except that the stabilizer is a compound of 1.4-butanediol and sodium silicate in a mass ratio of 2:1.

[0059] Example 8

[0060] Example 8 is the same as Example 3, except that the stabilizer is a compound of 1.4-butanediol and sodium tripolyphosphate in a mass ratio of 1:2.

[0061] Example 9

[0062] Example 9 is the same as Example 3, except that the stabilizer is sodium silicate.

[0063] Example 10

[0064] Example 10 is the same as Example 3, except that the stabilizer is sodium tripolyphosphate.

[0065] Example 11

[0066] Example 11 is the same as Example 3, except that the copper protecting agent is a compound of benzotriazole and N,N-dimethylacetamide in a mass ratio of 1.5:1.

[0067] Example 12

[0068] Example 12 is the same as Example 3, except that the copper protecting agent is benzotriazole.

[0069] Example 13

[0070] Example 13 is the same as Example 3, except that the copper protecting agent is N,N-dimethylacetamide.

[0071] Example 14

[0072] Example 14 is the same as Example 3, except that the copper protecting agent is methylbenzimidazole.

[0073] The preparation method of the environmentally friendly tin stripping water in the above embodiments 1-14 is: according to the above ratio, the raw materials are mixed, dissolved and dispersed to prepare the required tin stripping water.

[0074] Tin stripping water performance test

[0075] The tin plate, copper plate and copper-tin alloy layer plate (specifically, the surface of the copper substrate is covered with a copper-tin alloy layer with a thickness of 5um) were cut into 50mm×50mm areas as test substrates, and the tin stripping rate, copper stripping rate and copper-tin alloy layer stripping ability were tested using the tin stripping water in the above Examples 1-14 (the temperature was stabilized at 30°C).

[0076] Among them, the tin bite rate (μm / min) = [the weight of the tin plate before treatment (g) and the weight of the tin plate after treatment (g)] ÷ the substrate area (m 2 )÷7.28(g / cm 3 )÷processing time (min);

[0077] Copper bite rate (μm / min) = [weight of copper plate before treatment (g) weight of copper plate after treatment (g)] ÷ substrate area (m 2 )÷8.92(g / cm 3 )÷processing time (min);

[0078] Ability to bite the copper-tin alloy layer: the time required to completely remove the copper-tin alloy layer;

[0079] The test results are shown in Table 1 below:

[0080] Table 1:

[0081]

[0082] It can be seen from the results shown in Table 1 above that the environmentally friendly tin stripping water in Examples 1-5 of the present application has a fast tin biting rate, a low copper biting rate, a fast copper-tin alloy layer biting rate, and excellent comprehensive performance. In particular, the environmentally friendly tin stripping water in Example 3 can achieve a low copper biting rate while maintaining a high tin biting rate, and has a strong ability to bite the copper-tin alloy layer.

[0083] It can be seen from Examples 3 and 6-10 that using a compound of 1.4-butanediol, sodium silicate and sodium tripolyphosphate as a stabilizer can effectively stabilize hydrogen peroxide from decomposing, while increasing the tin biting rate and reducing the copper biting rate without damaging the copper surface.

[0084] It can be seen from Examples 3 and 11-14 that the copper protecting agent using a compound of benzotriazole and N,N-dimethylacetamide can further inhibit the corrosion of the copper surface, reduce the copper biting rate, and protect the copper surface.

[0085] The applicant used Example 3 as a control example and obtained Verification Examples 1-10 by changing the formulation ratio. The specific formulation ratios are shown in Table 2 below:

[0086] Table 2:

[0087]

[0088]

[0089] According to the tin stripping water performance test method in the above examples 1-14, the tin stripping water performance in the verification examples 1-25 was tested and the results shown in Table 3 below were obtained:

[0090] Table 3:

[0091]

[0092]

[0093] From the results shown in Table 3 above, it can be seen that the environmentally friendly tin stripping water proposed in this application requires a specific raw material ratio to achieve the best comprehensive performance. Lowering the sulfuric acid concentration will result in incomplete tin stripping or incomplete stripping, while too high a sulfuric acid concentration will increase the copper bite rate and cause discoloration on the copper surface; lowering the hydrogen peroxide content will also result in incomplete tin stripping, and too high a hydrogen peroxide concentration will increase the copper bite rate and cause discoloration on the copper surface; if the amount of stabilizer added is too low, the hydrogen peroxide will become unstable and easy to decompose; if the amount of copper protectant added is too low, the copper bite rate will be too high and the copper surface will be discolored.

[0094] The specific embodiments are merely explanations of the present application and are not limitations of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the embodiments as needed, but as long as they are within the scope of the claims of the present application, they are protected by patent law.

Claims

1. An environmentally friendly tin stripping solution for removing the copper-tin alloy layer of a printed circuit board, characterized in that: The invention comprises the following raw materials in weight percentage: 25-65% sulfuric acid, 2-10% hydrogen peroxide, 0.5-3% citric acid, 0.5-6% boric acid, 0.1-2% stabilizer, 0.1-2% copper protector, and the balance is deionized water; the copper protector is a compound of benzotriazole and N,N-dimethylacetamide in a mass ratio of 1:1-1.5; the stabilizer is a compound of 1,4-butanediol, sodium silicate, and sodium tripolyphosphate; The mass ratio of 1.4-butanediol, sodium silicate and sodium tripolyphosphate is 1-2:1:3-5.

2. The environmentally friendly tin stripping solution for removing the copper-tin alloy layer of a printed circuit board according to claim 1, characterized in that: The method comprises the following raw materials in weight percentage: 35-50% sulfuric acid, 4-8% hydrogen peroxide, 1-2% citric acid, 2-4% boric acid, 0.5-1.5% stabilizer, 0.5-1.5% copper protecting agent, and the balance is deionized water.

3. The environmentally friendly tin stripping solution for removing the copper-tin alloy layer of a printed circuit board according to claim 1, characterized in that: The method comprises the following raw materials in percentage by weight: 35% sulfuric acid, 6% hydrogen peroxide, 2% citric acid, 2% boric acid, 1% stabilizer, 1% copper protecting agent, and the balance being deionized water.

4. The environmentally friendly tin stripping solution for removing the copper-tin alloy layer of a printed circuit board according to claim 3, characterized in that: The mass ratio of the hydrogen peroxide to the stabilizer is 5-20:

1.

5. The environmentally friendly tin stripping solution for removing the copper-tin alloy layer of a printed circuit board according to any one of claims 1 to 4, characterized in that: The preparation method of the environmentally friendly tin stripping water is as follows: the raw materials are mixed, dissolved and dispersed according to the above ratio to prepare the required tin stripping water.

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