A method for quickly stripping tin from PCB

Abstract

The present invention discloses a method for rapid tin stripping of printed circuit boards (PCBs). The method involves passing an etched PCB through a H2SO4-Sn(SO4)2-CH3COOH solution and adding a tin stripping accelerator. An oxidizing gas is introduced under a certain temperature and external field coupling enhancement conditions to conduct a tin stripping reaction. As the reaction proceeds, the tin coating on the PCB rapidly dissolves into the solution. This method addresses key issues such as the high environmental pollution of existing tin stripping processes and the low tin stripping efficiency of new systems. It provides a highly efficient tin stripping system and method, which is green, clean, and efficient, and is of great significance for promoting PCB production, energy conservation and consumption reduction, and environmental protection.

Description

Technical Field

[0001] The present invention specifically relates to a method for quickly stripping tin from a PCB, and belongs to the field of non-ferrous metal metallurgy. Background Art

[0002] Printed circuit boards (PCBs) are the supporting structure for electronic components. Their primary function is to connect various electronic components to form specific circuits. They are a key interconnecting element in electronic products, and any electronic product or device requires them. PCBs are of great significance to the development of our times, and their downstream industries encompass all consumer electronics, including information technology, communications, medical care, and even aerospace technology. PCBs are indispensable in various fields.

[0003] PCB production involves over 20 steps, including cutting, drilling, grinding, copper deposition, electroplating, pattern transfer, copper plating, film stripping, and etching. Tinning is essential to prevent the copper substrate pattern on the PCB from being scrapped due to corrosion or breakage during etching. The tin coating is then removed after pattern production is complete. Currently, most domestic PCB manufacturers use nitric acid or nitric acid-alkylsulfonic acid-based tin stripping solutions for tin stripping.

[0004] However, due to the inherent instability and poor selectivity of nitric acid, the properties of tin stripping water change significantly after multiple stripping cycles. The water not only contains high concentrations of tin ions (100-150 g / L), but also certain concentrations of copper and iron ions (20-30 g / L). Furthermore, heterocyclic compounds, polycyclic aromatic compounds, and other polymers gradually accumulate due to the inability to open the circuit. At this point, the tin stripping solution can no longer effectively dissolve the tin plating on the PCB board and needs to be opened and replaced. The retired tin stripping solution contains not only large amounts of valuable metals but also high concentrations of nitric acid and other organic components, making it a hazardous waste. If it is not effectively treated, it will not only result in a significant waste of resources but also pose a significant potential risk of environmental pollution. To date, the main methods for treating waste tin stripping water include precipitation, distillation, and electrolysis.

[0005] In general, there are two major problems in the current nitric acid or nitric acid-alkylsulfonic acid system tin stripping water during the tin stripping process and the treatment of tin stripping waste liquid: (1) The tin stripping process mainly uses nitric acid to dissolve tin and copper, which has the problems of heavy NOx gas pollution, large amounts of sludge and residual acid, and high costs; (2) The processes of treating tin stripping water by precipitation, electrolysis and distillation have serious problems such as large reagent consumption, low metal recovery rate, and large amount of wastewater.

[0006] In order to solve the above problems, the applicant has developed "A tin stripping water based on hydrochloric acid-tin salt system and a method for recovering tin from waste tin stripping water (application number 201410011267.0)", which provides a non-nitric acid tin stripping water based on hydrochloric acid-tin salt system. Although the results of small-scale tests show that the tin stripping water can effectively remove the tin on the tin-plated plate. However, the subsequent application of this method in the industrial practice of stripping and recycling tin on printed circuit boards has encountered serious problems such as slow tin stripping speed (more than 10 minutes) and severe corrosion of PCB copper substrates. The reason is that compared with the current nitric acid or nitric acid-alkyl sulfonic acid system tin stripping water, the tin stripping water of the hydrochloric acid-tin salt system has relatively weak oxidation performance, and its solubility performance on tin plating on PCB is even weaker, so the tin stripping speed is also slower. If you want to use this tin stripping solution to remove more tin on the PCB, you must extend the tin stripping time. However, since the corrosion of Cl- in the hydrochloric acid-tin salt system tin stripping solution on the PCB board is "pitting corrosion", it tends to form numerous small holes distributed in a dotted manner on the PCB board, resulting in a very uneven surface of the copper substrate after tin stripping, thereby affecting the subsequent electronic processing performance of the PCB.

[0007] To effectively increase the speed of tin stripping, the applicant also developed a "Two-Stage Tin Stripping Method for PCBs (Application No. 201811126057.0)" that provides a composite two-stage tin stripping solution with a hydrochloric acid-tin salt system in the first stage and a nitric acid-nitrate system in the second stage. This method further efficiently recovers tin online while effectively reducing the emission of ammonia nitrogen wastewater during the treatment of waste tin stripping solution. However, prominent environmental issues such as NOx gas pollution, sludge, and residual acid remain unresolved. Summary of the Invention

[0008] In response to the above-mentioned problems and shortcomings of the existing technology, the technical problem to be solved by the present invention is to provide a method for rapid PCB stripping. The method provided by the present invention can effectively shorten the stripping time, improve the stripping efficiency while avoiding the generation of NOx gas during the stripping process and the discharge of large amounts of ammonia nitrogen wastewater when treating waste stripping water. This achieves the goal of green, clean, and efficient production of PCB stripping.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] A method for rapidly stripping tin from a PCB comprises passing an etched PCB through a H2SO4-Sn(SO4)2-CH3COOH system solution and adding a tin stripping accelerator. An oxidizing gas is introduced under external field coupling enhancement conditions to carry out a tin stripping reaction. As the reaction proceeds, the tin plating on the PCB dissolves into the solution.

[0011] In the H2SO4-Sn(SO4)2-CH3COOH system solution, the H2SO4 concentration is 1-4 mol / L, the Sn(SO4)2 concentration is 100-300 g / L, and the CH3COOH concentration is 1-5 mol / L. The preferred H2SO4 concentration is 2-3 mol / L, the Sn(SO4)2 concentration is 150-250 g / L, and the CH3COOH concentration is 3-4 mol / L.

[0012] The tin stripping accelerator is a mixture of goethite and one of methanesulfonate, tartaric acid, citrate, and sulfosalicylic acid. The preferred tin stripping accelerator is a mixture of goethite and one of methanesulfonate and tartaric acid.

[0013] The concentration of the added tin stripping accelerator goethite is 1 to 10 g / L, the methane sulfonate and citrate are their metal salts, the metal is selected from at least one of sodium, potassium, and calcium, the concentration of the methane sulfonate, tartaric acid, citrate, and sulfosalicylic acid is 0.5 to 5 g / L, the preferred goethite concentration is 2 to 6 g / L, the preferred methane sulfonate and citrate are sodium methane sulfonate and sodium citrate, and the preferred concentration of methane sulfonate, tartaric acid, sodium citrate, and sulfosalicylic acid is 1 to 3 g / L.

[0014] The external field coupling enhancement condition is ultrasonic coupling shear enhancement.

[0015] The ultrasonic frequency of the ultrasonic coupling is 20-200kHz, the ultrasonic power is 10-200W, the shear rate of the shear strengthening is 2000-10000rpm, the preferred ultrasonic frequency is 50-100kHz, the ultrasonic power is 50-150W, and the preferred shear rate is 5000-8000rpm.

[0016] The oxidizing gas is one of oxygen, ozone and chlorine, and the gas flow rate is 1 to 5 L / min. The preferred oxidizing gas is oxygen, and the gas flow rate is 1.5 to 3 L / min.

[0017] The tin stripping reaction temperature is 40-80° C., and the reaction time is 10-100 seconds.

[0018] Principles and advantages

[0019] The method of the present invention changes the original tin stripping system solution by changing the addition of CH3COOH, thereby improving the solution's solubility for metallic tin. CH3COOH is not only an environmentally friendly organic acid, but also an excellent metal ligand, which can react with tin to dissolve more tin into the solution (such as Formula 1-2). At the same time, by introducing a tin stripping promoter, the oxidizing atmosphere of the solution is improved, wherein goethite, due to its unique structure of loose porousness, can be combined with the free oxidant gas molecules in the solution, so that more oxidant gas molecules are dissolved into the solution. At this time, the oxidizing substance in the solution not only contains Sn(SO4)2 but also has a higher concentration of gaseous oxidant molecules, which accelerates the oxidation of tin and further accelerates the rate at which tin dissolves into the solution (Formula 3-5, taking oxygen as an example). What is even more surprising is that after adding ultrasonic coupled shear external field strengthening, the energy brought by the ultrasonic wave reduces the concentration polarization of the solution while exposing more tin to the solution, that is, the sulfuric acid concentration near the tin is continuously maintained at a higher concentration. On the other hand, the oxidizing gas rapidly explodes under the action of the ultrasonic wave, enhancing the oxidizing atmosphere of the solution. The addition of shear strengthening allows the solid particles in the solution to be kept at a smaller particle size and have a larger specific surface area, thereby enhancing their ability to transfer gaseous oxidants. It can also change the size of the gaseous oxidants. Similarly, smaller gas molecules have a larger specific surface area and are more oxidizing.

[0020] Sn+CH3COOH=Sn(CH3COO)2+H2 (1)

[0021] SnO+CH3COOH=Sn(CH3COO)2+H2O (2)

[0022] Sn+Sn(SO4)2+H2SO4=SnSO4+H2 (3)

[0023] Sn+O2=SnO (4)

[0024] SnO+H2SO4=SnSO4+H2O (5)

[0025] Compared with the existing nitric acid or nitric acid-alkyl sulfonic acid tin stripping system, the present invention avoids the use of nitric acid as an oxidant and solution, effectively avoiding the potential environmental risks brought about by the generation of NOx gas in the tin stripping process and the generation of a large amount of ammonia nitrogen-containing substances when treating waste tin stripping water by the existing solution system. At the same time, compared with the "a tin stripping water based on a hydrochloric acid-tin salt system and a method for recovering tin from waste tin stripping water (application number 201410011267.0)" and "a two-stage tin stripping method for PCB boards (application number 201811126057.0)" developed by the applicant, the tin stripping speed is significantly accelerated, the tin stripping efficiency is improved, and the purpose of green, clean and efficient production of PCB tin stripping is achieved. The present invention is of great significance to promoting the technological progress of PCB production, energy conservation and consumption reduction, and environmental protection in my country. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the effect of different CH3COOH concentrations on the tin stripping effect in Example 5. Specific implementation plan

[0027] The following examples are intended to further illustrate the present invention but are not intended to limit the present invention.

[0028] Example 1

[0029] A company provides tinned PCBs, which have a surface area of ​​30g per square meter.

[0030] A H2SO4-Sn(SO4)2-CH3COOH system tin stripping solution was prepared, with H2SO4 concentration of 3 mol / L, Sn(SO4)2 concentration of 150 g / L, and CH3COOH concentration of 3 mol / L. A mixture of goethite and sodium methanesulfonate was added as a tin stripping accelerator, wherein the goethite concentration was 5 g / L and the sodium methanesulfonate concentration was 3 g / L. A tin-plated PCB was added at a temperature of 60°C, an ultrasonic frequency of 100 kHz, an ultrasonic power of 100 W, and a shear rate of 8000 rpm. At the same time, oxygen gas was introduced at a gas flow rate of 2 L / min for reaction. The reaction time was 60 s. After the reaction, a tin-stripped PCB with a smooth surface was obtained. The mass of the PCB after tin stripping was weighed and reduced by 29.98 g. At the same time, the PCB after tin stripping was analyzed by chemical analysis, and it was found that the tin content on the surface of the PCB after tin stripping was basically zero. The tin stripping efficiency was calculated to be 99.93%.

[0031] Example 2

[0032] A company provides tinned PCBs, which have a surface area of ​​31g per square meter.

[0033] A H2SO4-Sn(SO4)2-CH3COOH system tin stripping solution was prepared, with H2SO4 concentration of 1 mol / L, Sn(SO4)2 concentration of 100 g / L, and CH3COOH concentration of 1 mol / L. A mixture of goethite and sodium methanesulfonate was added as a tin stripping accelerator, wherein the goethite concentration was 1 g / L and the sodium citrate concentration was 0.5 g / L. A tin-plated PCB was added at a temperature of 40°C, an ultrasonic frequency of 20 kHz, an ultrasonic power of 10 W, and a shear rate of 2000 rpm. Ozone gas was introduced at a gas flow rate of 1 L / min for reaction, and the reaction time was 90 s. After the reaction, a tin-stripped PCB with a smooth surface was obtained. The mass of the PCB after tin stripping was weighed and reduced by 30.53 g. At the same time, the PCB after tin stripping was analyzed by chemical analysis, and it was found that the tin content on the surface of the PCB after tin stripping was basically zero. The tin stripping efficiency was calculated to be 98.48%.

[0034] Example 3

[0035] A company provides tinned PCBs, which have a surface area of ​​31g per square meter.

[0036] A H2SO4-Sn(SO4)2-CH3COOH system tin stripping solution was prepared, with H2SO4 concentration of 4 mol / L, Sn(SO4)2 concentration of 300 g / L, and CH3COOH concentration of 5 mol / L. A mixture of goethite and sodium methanesulfonate was added as a tin stripping accelerator, wherein the goethite concentration was 10 g / L and the tartaric acid concentration was 5 g / L. A tin-plated PCB was added at a temperature of 80°C, an ultrasonic frequency of 200 kHz, an ultrasonic power of 200 W, and a shear rate of 10,000 rpm. Oxygen was introduced at a gas flow rate of 5 L / min for reaction. The reaction time was 31 s. After the reaction, a tin-stripped PCB with a smooth surface was obtained. The mass of the PCB after tin stripping was weighed and reduced by 31 g. At the same time, the PCB after tin stripping was analyzed by chemical analysis, and it was found that the tin content on the surface of the PCB after tin stripping was basically zero. The tin stripping efficiency was calculated to be 100%.

[0037] Example 4

[0038] A company provides tinned PCBs, which have a surface area of ​​30g per square meter.

[0039] A H2SO4-Sn(SO4)2-CH3COOH system tin stripping solution was prepared, with H2SO4 concentration of 3 mol / L, Sn(SO4)2 concentration of 250 g / L, and CH3COOH concentration of 4 mol / L. A mixture of goethite and sodium methanesulfonate was added as a tin stripping accelerator, wherein the goethite concentration was 6 g / L and the sulfosalicylic acid concentration was 2 g / L. A tin-plated PCB was added at a temperature of 70°C, an ultrasonic frequency of 40 kHz, an ultrasonic power of 100 W, and a shear rate of 5000 rpm. Chlorine gas was introduced at a gas flow rate of 3 L / min for reaction, and the reaction time was 60 s. After the reaction, a tin-stripped PCB with a smooth surface was obtained. The mass of the PCB after tin stripping was weighed and reduced by 29.79 g. At the same time, the PCB after tin stripping was analyzed by chemical analysis, and it was found that the tin content on the surface of the PCB after tin stripping was basically zero. The tin stripping efficiency was calculated to be 99.30%.

[0040] Example 5

[0041] The other conditions were the same as those in Example 1, except that the concentrations of CH3COOH were 0, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, and 5 mol / L. The six groups of experiments were finally used to calculate the tin stripping efficiency by chemical analysis. Figure 1 shown.

[0042] Comparative Example 1 (Stripping Solvent Configured Under Parameters Not in the Present Invention)

[0043] A company provides tinned PCBs, which have a surface area of ​​30g per square meter.

[0044] A H2SO4-Sn(SO4)2 system tin stripping solution was prepared with an H2SO4 concentration of 3 mol / L and a Sn(SO4)2 concentration of 250 g / L. A mixture of goethite and sodium methanesulfonate was added as a tin stripping accelerator, wherein the goethite concentration was 6 g / L and the sulfosalicylic acid concentration was 2 g / L. A tin-plated PCB was added at a temperature of 70°C, an ultrasonic frequency of 40 kHz, an ultrasonic power of 100 W, and a shear rate of 5000 rpm. Chlorine gas was introduced at a gas flow rate of 3 L / min for reaction. The reaction time was 120 s. After the reaction, a tin-stripped PCB with obvious silver-white metal on the surface was obtained. The mass of the PCB after tin stripping was weighed and reduced by 27.79 g. At the same time, the PCB after tin stripping was analyzed by chemical analysis, and it was found that the tin-plated layer on the surface of the PCB after tin stripping was difficult to completely remove. The tin stripping efficiency was calculated to be 92.63%, and 7.37% of tin still remained on the PCB.

[0045] Comparative Example 2 (without adding tin stripping accelerator)

[0046] A company provides tinned PCBs, which have a surface area of ​​30g per square meter.

[0047] A solution was prepared as described in Example 1, except that no tin stripping accelerator was added. Tin stripping was also carried out for 60 seconds at the temperature, oxidizing gas type, gas flow rate, ultrasonic frequency, ultrasonic power, and shear rate described in Example 1. After the reaction, a tin-stripped PCB with obvious silvery-white metal on the surface was obtained. The mass of the tin-stripped PCB was weighed and found to be 27.52 g lighter. Chemical analysis of the tin-stripped PCB revealed that the tin layer on the surface of the PCB was difficult to completely remove after the tin stripping. Calculation showed that the tin stripping efficiency was 91.73%, with 8.27% of tin remaining on the PCB.

[0048] Comparative Example 3 (without addition of oxidizing gas)

[0049] A company provides tinned PCBs, which have a surface area of ​​30g per square meter.

[0050] A solution was prepared as described in Example 1, except that no oxidizing gas was added. Tin stripping was also carried out for 60 seconds at the temperature, type of tin stripping accelerator, concentration of tin stripping accelerator, ultrasonic frequency, ultrasonic power, and shear rate described in Example 1. After the reaction, a tin-stripped PCB with obvious silvery-white metal on the surface was obtained. The mass of the tin-stripped PCB was weighed and found to be 26.94 g lighter. Chemical analysis of the tin-stripped PCB revealed that the tin plating on the surface of the PCB was difficult to completely remove. Calculation showed that the tin stripping efficiency was 89.80%, with 10.20% of tin remaining on the PCB.

[0051] Comparative Example 4 (no ultrasonic coupling shear external field enhancement)

[0052] A company provides tinned PCBs, which have a surface area of ​​30g per square meter.

[0053] A solution was prepared as described in Example 1, except that ultrasonic coupled shear external field enhancement was not applied. Tin stripping was also carried out for 60 seconds at the temperature, type of tin stripping accelerator, concentration of tin stripping accelerator, type of oxidizing gas, and gas flow rate described in Example 1. After the reaction, a tin-stripped PCB with obvious silver-white metal on the surface was obtained. The mass of the tin-stripped PCB was weighed and found to be 26.86 g lighter. At the same time, chemical analysis was used to analyze the tin-stripped PCB, and it was found that the tin plating layer on the surface of the PCB was difficult to completely remove after the tin stripping. The calculation showed that the tin stripping efficiency was 89.53%, and 10.47% of tin still remained on the PCB.

Claims

1. A method for rapid tin stripping of PCB, characterized by: The etched PCB is passed through a H2SO4-Sn(SO4)2-CH3COOH system solution and a tin stripping accelerator is added. An oxidizing gas is introduced under external field coupling enhancement conditions to carry out a tin stripping reaction. As the reaction proceeds, the tin plating on the PCB dissolves into the solution. The tin stripping accelerator is a mixture of goethite and one of methanesulfonate, tartaric acid, citrate, and sulfosalicylic acid. The external field coupling enhancement conditions are ultrasonic coupled shear enhancement.

2. The method according to claim 1, wherein: In the H2SO4-Sn(SO4)2-CH3COOH system solution, the H2SO4 concentration is 1~4 mol / L, the Sn(SO4)2 concentration is 100~300 g / L, and the CH3COOH concentration is 1~5 mol / L.

3. The method according to claim 1, wherein: The concentration of the goethite is 1-10 g / L, the methanesulfonate and citrate are metal salts thereof, the metal is selected from at least one of sodium, potassium, and calcium, and the concentration of the methanesulfonate, tartaric acid, citrate, and sulfosalicylic acid is 0.5-5 g / L.

4. The method according to claim 1, wherein: The ultrasonic frequency of the ultrasound is 20-200 kHz, and the ultrasonic power is 10-200 W.

5. The method according to claim 1, wherein: The oxidizing gas is one of oxygen, ozone, and chlorine, and the gas flow rate is 1-5 L / min.

6. The method according to claim 1, wherein: The tin stripping reaction temperature is 40-80°C, and the reaction time is 10-100 s.

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