Tin polishing agent for PCB (Printed Circuit Board) electrotinning and preparation method of tin polishing agent

Abstract

The invention relates to the technical field of tinning, in particular to a tinning agent for PCB electrotinning and a preparation method of the tinning agent. The tin plating solution comprises the following components: 20-40 g / L of stannous sulfate, 180-200 g / L of sulfuric acid, 4-6 g / L of 2-mercaptothiazoline, 10-30 g / L of polyethylene glycol, 2-5 g / L of methyl thiourea pyridine, 10-15 g / L of sodium hypophosphite, 5-10 g / L of polyvinylpyrrolidone, 30-50 g / L of a pH regulator, 8-12 g / L of a surfactant, 1-3 g / L of an antioxidant, 5-10 g / L of a stabilizer and 4-8 g / L of a brightener. The tinning agent prepared according to the formula and used for PCB electrotinning has good dispersity, stability, tinning quality and a bright effect.

Description

Technical Field

[0001] The present application relates to the technical field of tin plating, and more specifically, to a tin brightener for PCB electroplating tin and a preparation method thereof. Background Art

[0002] PCB electrotin plating is primarily a surface treatment process for printed circuit boards (PCBs). After PCB electrotin plating, the tin layer isolates the PCB substrate and copper foil from air, moisture, and various chemicals, preventing oxidation and corrosion of the copper foil, thereby extending the PCB's lifespan and ensuring stable performance. The tin layer also improves the PCB's surface conductivity, reduces contact resistance, and ensures stable circuit conduction.

[0003] At present, sulfate tin plating is a relatively common process method for PCB electrotin plating. Its main advantages are: easy availability of raw materials, low cost, good stability of tin brightener, and the ability to maintain relatively stable chemical properties and electroplating performance for a certain period of time, providing favorable conditions for continuous production.

[0004] However, the dispersion ability of the tin plating solution of the sulfate tin plating method is relatively poor, making it difficult to obtain a uniform coating on PCBs with complex shapes, and the problem of uneven coating thickness is prone to occur. At the same time, during the acid tin plating process, divalent tin is easily hydrolyzed, resulting in turbidity of the tin brightener, affecting the coating quality and reducing the stability and service life of the tin brightener. Summary of the Invention

[0005] In order to solve the problem that the acidic tin plating solution has poor dispersibility and divalent tin is easily hydrolyzed during the acidic tin plating process, the present application provides a tin brightener for PCB electroplating tin and a preparation method.

[0006] In a first aspect, the present application provides a tin brightener for PCB electroplating tin, which adopts the following technical solution: a tin brightener for PCB electroplating tin, using water as a solvent, comprising the following components in the following concentrations: Stannous sulfate 20-40g / L Sulfuric acid 180-200g / L 2-Mercaptothiazoline 4-6g / L Polyethylene glycol 10-30g / L Methylthiourea pyridine 2-5g / L Sodium hypophosphite 10-15g / L Polyvinylpyrrolidone 5-10g / L pH regulator 30-50g / L Surfactant 8-12g / L Antioxidants 1-3g / L Stabilizer 5-10g / L Brightener 4-8g / L.

[0007] By adopting the above technical solution, the tin brightener prepared for PCB electrotin plating effectively solves the problems of poor dispersion ability of the tin brightener and easy hydrolysis of divalent tin in the traditional sulfate tin plating method, significantly improves the stability and service life of the tin brightener, and at the same time enhances the bright effect and performance of the coating.

[0008] The ingredients added to this tin brightener, such as polyethylene glycol and polyvinyl pyrrolidone, can significantly improve the rheological and wetting properties of the tin brightener. Polyethylene glycol has good solubility and dispersibility in aqueous solution, and can form a uniform protective film in the tin brightener, reducing the surface tension of the tin brightener and making it easier for the tin brightener to spread and penetrate on the complex surface of the PCB. Polyvinyl pyrrolidone has excellent complexing and dispersing properties, and can form stable complexes with the metal ions in the tin brightener, preventing excessive aggregation of metal ions in local areas, thereby improving the adaptability and coverage of the tin brightener to complex shapes, effectively solving the problem of uneven coating thickness, and ensuring that a uniform and delicate coating can be formed even in complex areas such as tiny vias and fine circuits.

[0009] The addition of a pH adjuster allows precise control of the pH of the tin polish, ensuring the electroplating reaction proceeds within the optimal pH range, improving plating efficiency and coating quality. The brightener, acting synergistically with the other components of the tin polish, can enhance the smoothness and brightness of the coating surface during the electroplating process. Sulfur-containing organic compounds such as 2-mercaptothiazoline can adsorb on the cathode surface, enhancing cathodic polarization, refining the coating crystals, and making the coating surface denser and smoother. Surfactants reduce the surface tension of the tin polish, improving its fluidity and wetting properties, making it easier for the tin polish to form a uniform coating on the PCB surface. Furthermore, ingredients such as polyvinylpyrrolidone also have a certain brightening effect, further enhancing the gloss and reflectivity of the coating. Through the combined action of these components, the tin polish forms a uniform, bright tin coating on the PCB surface, improving not only the PCB's appearance but also the coating's conductivity and corrosion resistance, ensuring the PCB's reliability and stability over long-term use.

[0010] The sodium hypophosphite in this tin brightener forms a stable complex with divalent tin, preventing it from oxidizing to tetravalent tin, thereby reducing the occurrence of hydrolysis. Furthermore, ingredients such as methylthiourea pyridine form stable complexes with divalent and tetravalent tin, further stabilizing the tin ions in the brightener and inhibiting the hydrolysis reaction. Furthermore, the addition of stabilizers can adjust the chemical properties of the brightener, enhancing its anti-interference ability and maintaining its stability over a longer period of time. This reduces precipitation, extends the brightener's service life, and reduces production costs.

[0011] Preferably, the surfactant is composed of sucrose fatty acid ester, stearic acid and fatty acid glyceride in a weight ratio of (4-6): (1-2): 8.

[0012] By employing this technical solution, the synergistic effect of sucrose fatty acid esters, stearic acid, and fatty acid glycerides in specific proportions can further reduce the surface tension of the tin brightener, allowing it to spread quickly and evenly across the PCB surface, covering complex areas and improving the uniformity of the coating. Furthermore, the tin brightener can quickly penetrate fine cracks on the PCB surface, ensuring its entry and deposition, thereby improving coating coverage and quality. It also effectively prevents tin brightener delamination and precipitation, ensuring uniform distribution of its components and maintaining its stability, contributing to the formation of a more detailed and uniform coating.

[0013] Preferably, the stabilizer is composed of fluoride and benzoimidazole in a weight ratio of (5-7):3.

[0014] By adopting the above technical solution, fluoride and benzoimidazole are combined in a specific ratio to work synergistically, significantly improving the stability and electroplating effect of the tin polish. Fluoride can form a stable complex with tin ions, effectively inhibiting the oxidation and hydrolysis of divalent tin, reducing the precipitation and deterioration of tin ions in the tin polish, thereby improving the stability and anti-interference ability of the tin polish, and ensuring that the tin polish remains stable for a long time under different conditions. Benzoimidazole can adsorb on the cathode surface, increasing the activation polarization during the tin plating electrodeposition process and improving the quality of the coating. The nitrogen atoms on its imidazole ring can coordinate with tin ions, further stabilizing the tin ions. The synergistic effect of the two not only improves the stability of the tin polish, but also suppresses the influence of impurity ions, preventing them from reacting with tin ions to form precipitates, avoiding tin polish turbidity and deteriorating the coating quality. In addition, this stabilizer combination can refine the crystallization of the coating, making the coating more delicate and smooth, improving the surface finish and uniformity, strengthening the adhesion of the coating to the substrate, preventing it from falling off, and improving the reliability of the coating.

[0015] Preferably, the fluoride includes at least one of sodium fluoride, potassium fluoride and stannous fluoride.

[0016] By adopting the above technical solution, the types of fluorides are optimized, the stability of the tin brightener is further improved, and the tin brightener is ensured to remain stable for a long time under different conditions.

[0017] Preferably, the brightener is composed of sulphurized castor oil, imidazole and its derivatives and sodium p-toluenesulfinate in a weight ratio of 1:(2-4):(4-6).

[0018] By employing this technical solution, the synergistic effect of castor oil sulfide, imidazole and its derivatives, and sodium p-toluenesulfinate in specific proportions significantly improves the brightness and uniformity of the coating. Castor oil sulfide enhances cathodic polarization and dispersion, resulting in fine crystals and a bright surface. Imidazole and its derivatives further enhance cathodic polarization, refine crystals, and improve coating uniformity. Sodium p-toluenesulfinate complexes with tin ions, stabilizing the brightener, inhibiting hydrolysis, and preventing scorching of the coating. The synergistic effect of these three enhances the brightness and conductivity of the coating, while also improving the stability of the brightener, resulting in efficient and stable electroplating.

[0019] Preferably, the imidazole derivative includes at least one of methoxyimidazole, imidazole propionic acid, imidazole acetic acid and hydroxyimidazole.

[0020] By adopting the above technical solution and optimizing the types of imidazole derivatives, the coating crystallization can be further refined, making the coating more uniform and delicate, improving the surface finish and gloss, and making the coating denser, reducing tiny pores and defects.

[0021] Preferably, the antioxidant comprises at least one of dimercaprol, benzotriazole, hydroquinone, phytic acid and ascorbic acid.

[0022] By using these antioxidants, a protective film is formed on the surface of the coating, preventing air, moisture, and chemicals from reaching the copper foil, preventing oxidation corrosion, extending the service life of the PCB, and ensuring stable performance. At the same time, these antioxidants make the coating smoother and brighter, improving its appearance and conductivity.

[0023] Preferably, the pH adjuster is methanesulfonic acid.

[0024] Methanesulfonic acid is stable in nature and can provide a stable acidic environment for the electrotin solution, avoiding the degradation of the plating quality and the precipitation or deterioration of tin ions in the solution caused by pH fluctuations, thereby extending the service life of the tin brightener and reducing the cost and time consumption of frequent replacement of the tin brightener.

[0025] Preferably, water is used as the solvent and the following components are contained: Stannous sulfate 35g / L Sulfuric acid 200g / L 2-mercaptothiazoline 5g / L Polyethylene glycol 25g / L Methylthiourea pyridine 4g / L Sodium hypophosphite 12g / L Polyvinylpyrrolidone 9g / L pH regulator 45g / L Surfactant 11g / L Antioxidant 2g / L Stabilizer 8g / L Brightener 8g / L.

[0026] By adopting this technical solution, the concentration of each component is further limited, its dispersion ability and wettability are enhanced, and the tin brightener is evenly deposited on complex PCB surfaces, further improving the quality of the tin plating layer. It can also further enhance the stability of the tin brightener, reduce the impact of impurities, and ensure the long-term stability of the tin brightener.

[0027] In a second aspect, the present application provides a method for preparing a tin brightener for PCB electroplating tin, which adopts the following technical solution: A method for preparing a tin brightener for PCB electroplating tin comprises the following steps: First, add sulfuric acid to water and stir evenly. Then, add stannous sulfate, 2-mercaptothiazoline, polyethylene glycol, methylthiourea pyridine, sodium hypophosphite, polyvinylpyrrolidone, pH adjuster, surfactant, antioxidant, stabilizer and brightener in sequence and stir evenly to obtain a tin brightener for PCB electroplating tin.

[0028] By adopting this technical solution, the components simply need to be added sequentially and stirred evenly, eliminating the need for complex equipment or tedious steps, making it easy to operate and control. Furthermore, each component is evenly dispersed in the solution, allowing them to fully exert their effects during electroplating, synergistically improving the quality of the coating and ensuring the stability and performance consistency of the tin brightener.

[0029] In summary, this application has the following beneficial effects: 1. Significantly improve the dispersibility: By adding 2-mercaptothiazoline, polyethylene glycol, methylthiourea pyridine and other components to the sulfate tin plating system, the dispersibility of the tin brightener is effectively improved, so that the tin brightener can form a uniform coating on PCBs with complex shapes, solving the problem of uneven coating thickness caused by poor dispersibility in traditional sulfate tin plating.

[0030] 2. Effectively inhibit divalent tin hydrolysis: The synergistic effect of sodium hypophosphite and antioxidants provides a stable environment for divalent tin in an acidic tin plating environment, significantly reducing its hydrolysis probability. Simultaneously, the addition of the stabilizer can complex impurity ions in the solution, preventing them from inducing side reactions, thereby inhibiting divalent tin hydrolysis and reducing tin brightener turbidity. This ensures that the tin brightener remains in good condition over the long term, extending its service life and significantly improving the quality of the coating.

[0031] 3. Improve the stability and service life of tin brighteners: pH regulators can accurately control the pH of tin brighteners, maintain the appropriate pH range, and ensure the stable existence and synergistic effect of each component; the stabilizer effectively complexes impurity ions, further enhancing the stability of the tin brightener, reducing the cost of frequent replacement of the tin brightener, and improving production efficiency. 4. Give the coating a bright and beautiful appearance: The addition of brightener makes the coating surface bright and smooth, without the need for additional polishing, meeting the appearance requirements of electronic products. At the same time, the brightener works together with other components to further improve the quality and performance of the coating. DETAILED DESCRIPTION Example

[0032] Example 1 A tin brightener for PCB electrotin plating is prepared by the following method: First, add 180g of sulfuric acid to 1L of water and stir evenly. Then, add 20g of stannous sulfate, 4g of 2-mercaptothiazoline, 10g of polyethylene glycol, 2g of methylthiourea pyridine, 10g of sodium hypophosphite, 5g of polyvinylpyrrolidone, 30g of pH regulator, 8g of surfactant, 1g of antioxidant, 5g of stabilizer and 4g of brightener in sequence and stir evenly to obtain a tin brightener for PCB electroplating.

[0033] Among them, the concentration of stannous sulfate is 20g / L, the concentration of sulfuric acid is 180g / L, the concentration of 2-mercaptothiazoline is 4g / L, the concentration of polyethylene glycol is 10g / L, the concentration of methylthioureapyridine is 2g / L, the concentration of sodium hypophosphite is 10g / L, the concentration of polyvinylpyrrolidone is 5g / L, the concentration of pH adjuster (methylsulfonic acid) is 30g / L, the concentration of surfactant is 8g / L, the concentration of antioxidant (dimercaptopropanol) is 1g / L, the concentration of stabilizer is 5g / L, and the concentration of brightener is 4g / L.

[0034] The surfactant is composed of sucrose fatty acid ester, stearic acid and fatty acid glyceride (fatty acid monoglyceride) in a weight ratio of 4:1:8.

[0035] The stabilizer consists of fluoride (sodium fluoride) and benzoimidazole in a weight ratio of 5:3.

[0036] The brightener is composed of sulfided castor oil, imidazole and sodium p-toluenesulfinate in a weight ratio of 1:2:4.

[0037] The difference between Example 2-3 and Example 1 is that the raw material types, amounts and parameters for preparing the tin brightener for PCB electroplating are different. The specific differences are shown in Table 1: Table 1 Raw material types, dosages and parameters for preparing tin brighteners for PCB electroplating tin in Examples 1-3 In Example 2, the surfactant is composed of sucrose fatty acid ester, stearic acid and fatty acid glyceride (fatty acid diglyceride) in a weight ratio of 5:1.5:8; The stabilizer is composed of fluoride (potassium fluoride) and benzoimidazole in a weight ratio of 6:3; The brightener is composed of sulfonated castor oil, methoxyimidazole and sodium p-toluenesulfinate in a weight ratio of 1:3:5; In Example 3, the surfactant is composed of sucrose fatty acid ester, stearic acid and fatty acid glyceride (fatty acid monoglyceride) in a weight ratio of 6:2:8; The stabilizer is composed of fluoride (stannous fluoride) and benzoimidazole in a weight ratio of 7:3; The brightener is composed of sulfonated castor oil, imidazole propionic acid and sodium p-toluenesulfinate in a weight ratio of 1:4:6.

[0038] Example 4 A tin brightener for PCB electrotin plating. The difference between this embodiment and embodiment 1 is that the surfactant is sucrose fatty acid ester.

[0039] Example 5 A tin brightener for PCB electroplating tin. This embodiment differs from embodiment 1 in that the stabilizer is sodium fluoride.

[0040] Example 6 A tin brightener for PCB electrotin plating. The difference between this embodiment and embodiment 1 is that the brightener is sulfided castor oil.

[0041] Example 7 A tin brightener for PCB electrotin plating. This embodiment differs from Example 1 in that it comprises 35 g / L stannous sulfate, 200 g / L sulfuric acid, 5 g / L 2-mercaptothiazoline, 25 g / L polyethylene glycol, 4 g / L methylthiourea pyridine, 12 g / L sodium hypophosphite, 9 g / L polyvinylpyrrolidone, 45 g / L pH regulator, 11 g / L surfactant, 2 g / L antioxidant, 8 g / L stabilizer, and 8 g / L brightener.

[0042] Comparative Example Comparative Example 1 A tin brightener for PCB electrotin plating. This comparative example differs from Example 1 in that zinc dithiophosphate is used instead of 2-mercaptothiazoline.

[0043] Comparative Example 2 A tin brightener for PCB electrotin plating. The difference between this comparative example and Example 1 is that sodium sulfite is used instead of sodium hypophosphite.

[0044] Comparative Example 3 A tin brightener for PCB electrotin plating. The difference between this comparative example and Example 1 is that polyvinyl pyrrolidone is not added.

[0045] Comparative Example 4 A tin brightener for PCB electrotin plating. This comparative example differs from Example 1 in that methanesulfonic acid is not added.

[0046] Comparative Example 5 A tin brightener for PCB electrotin plating. The difference between this comparative example and Example 1 is that the concentration of methylthiourea pyridine is 10 g / L.

[0047] Comparative Example 6 A tin brightener for PCB electrotin plating. The difference between this comparative example and Example 1 is that the concentration of the surfactant is 5 g / L.

[0048] Comparative Example 7 A tin brightener for PCB electroplating tin. The difference between this comparative example and Example 1 is that the concentration of the pH regulator (methanesulfonic acid) is 20 g / L.

[0049] Comparative Example 8 A tin brightener for PCB electroplating tin. The difference between this comparative example and Example 1 is that the concentration of the stabilizer is 2 g / L.

[0050] Comparative Example 9 A tin brightener for PCB electrotin plating. The difference between this comparative example and Example 1 is that no surfactant is added.

[0051] Test method / test method: A PCB with a size of 100 mm × 100 mm, including 5 blind holes (aperture 0.3 mm, depth 2 mm), 10 narrow gaps (width 0.2 mm, length 5 mm) and multiple pads, was selected and electroplated using the tin brighteners of Examples 1-7 and Comparative Examples 1-9. The electroplating parameters were: current density 1.5 A / dm 2 After electroplating, the tinning process was performed at 35°C for 30 minutes. A contact profilometer was used to measure the plating thickness at the bottom of the blind hole, on both sides of the narrow gap, and on the flat area of ​​the PCB board. Three measurements were taken for each area, and the average value was taken to calculate the standard deviation of the thickness at each location.

[0052] Coating quality: 1. Adhesion test: Use the tape sticking method to process the PCB coating after tinning and calculate the proportion of the falling area.

[0053] 2. Using a wear tester, apply the same load (500g) and friction number (1000 times) to the two coatings, and observe the wear marks of the coatings.

[0054] Brightness test: The glossiness of the two coatings was measured using a gloss meter, with five measurements taken on each test piece and the average taken. The average glossiness of the coating in the experimental group was 85%, while that in the control group was 60%, indicating that the tin brightener in this application imparts a better gloss and aesthetic appearance to the coating.

[0055] Stability: 1 L of tin polish from Examples 1-7 and Comparative Examples 1-9 was stored under the same environmental conditions (temperature 25°C, humidity 50%). Changes in the appearance of the polish were observed and recorded daily. Observation was continued for 7 days to see if any turbidity developed. The test data is shown in Table 2: Table 2 Test data of Examples 1-7 and Comparative Examples 1-9 It can be seen from the experimental data of Example 1 and Comparative Examples 1-9 that the tin brightener for PCB electroplating provided by the present application performs well in terms of dispersibility, bonding strength, wear resistance, brightness and stability.

[0056] The standard deviations of Examples 1 to 7 are all lower than 0.15 μm, and the standard deviations of Comparative Examples 1 to 9 are all higher than 0.15 μm, indicating that the tin brightener for PCB electroplating prepared by the formulation in this application has good dispersibility; The shedding areas of Examples 1 to 7 are all less than 0.15%, and the shedding areas of Comparative Examples 1 to 9 are generally higher, indicating that the tin brightener for PCB electroplating prepared by the formulation in this application has good coating adhesion; Examples 1 to 7 all showed no obvious wear and bottom exposure, while some comparative examples showed slight or obvious wear marks, such as comparative examples 3, 4, and 9, indicating that the tin brightener for PCB electroplating tin prepared by the formulation of this application has good wear resistance; From the experimental results of bonding strength and wear resistance, the formulation in this application can greatly improve the quality of the tin plating layer of the tin brightener used for PCB electroplating tin; The brightness of the comparative examples is generally lower than that of the examples, mostly between 74GU and 81GU, indicating that the brightness effect is not as good as that of the examples, indicating that the tin brightener for PCB electroplating tin prepared by the formula of this application has a good brightness effect; Examples 1 to 7 are all clear, indicating that the tin brightener remains in good condition during storage. The stability of the comparative examples is poor, and most of them become turbid during storage, indicating that the tin brightener for PCB electroplating prepared by the formulation of this application has good stability.

[0057] It can be seen from the experimental data of Example 1 and Examples 4-6 that by optimizing the type and amount of stabilizer, the type and amount of surfactant, and the type and amount of brightener, the dispersibility of the tin brightener used for PCB electrotin plating, the quality of the tin plating layer, and the brightening effect can be improved.

[0058] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A tin brightener for PCB electroplating, characterized in that: Using water as solvent, it contains the following components in the following concentrations: Stannous sulfate 20-40g / L Sulfuric acid 180-200g / L 2-Mercaptothiazoline 4-6g / L Polyethylene glycol 10-30g / L Methylthiourea pyridine 2-5g / L Sodium hypophosphite 10-15g / L Polyvinylpyrrolidone 5-10g / L pH regulator 30-50g / L Surfactant 8-12g / L Antioxidants 1-3g / L Stabilizer 5-10g / L Brightener 4-8g / L.

2. The tin brightener for PCB electrotin plating according to claim 1, characterized in that: The surfactant is composed of sucrose fatty acid ester, stearic acid and fatty acid glyceride in a weight ratio of (4-6): (1-2):

8.

3. The tin brightener for PCB electrotin plating according to claim 1, characterized in that: The stabilizer is composed of fluoride and benzoimidazole in a weight ratio of (5-7):

3.

4. The tin brightener for PCB electrotin plating according to claim 3, characterized in that: The fluoride includes at least one of sodium fluoride, potassium fluoride and stannous fluoride.

5. The tin brightener for PCB electrotin plating according to claim 1, characterized in that: The brightener is composed of sulfonated castor oil, imidazole and its derivatives and sodium p-toluenesulfinate in a weight ratio of 1: (2-4): (4-6).

6. The tin brightener for PCB electrotin plating according to claim 5, characterized in that: The imidazole derivative includes at least one of methoxyimidazole, imidazole propionic acid, imidazole acetic acid and hydroxyimidazole.

7. The tin brightener for PCB electrotin plating according to claim 1, characterized in that: The antioxidant includes at least one of dimercaprol, benzotriazole, hydroquinone, phytic acid and ascorbic acid.

8. The tin brightener for PCB electrotin plating according to claim 1, characterized in that: The pH adjuster is methanesulfonic acid.

9. The tin brightener for PCB electrotin plating according to claim 1, characterized in that: Using water as solvent, it contains the following components in the following concentrations: Stannous sulfate 35g / L Sulfuric acid 200g / L 2-Mercaptothiazoline 5g / L Polyethylene glycol 25g / L Methylthiourea pyridine 4g / L Sodium hypophosphite 12g / L Polyvinylpyrrolidone 9g / L pH regulator 45g / L Surfactant 11g / L Antioxidant 2g / L Stabilizer 8g / L Brightener 8g / L.

10. A method for preparing a tin brightener for PCB electroplating tin according to any one of claims 1 to 9, characterized in that: The following steps are involved: First, add sulfuric acid to water and stir evenly. Then, add stannous sulfate, 2-mercaptothiazoline, polyethylene glycol, methylthiourea pyridine, sodium hypophosphite, polyvinylpyrrolidone, pH adjuster, surfactant, antioxidant, stabilizer and brightener in sequence and stir evenly to obtain a tin brightener for PCB electroplating tin.

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