Tin deposition agent, preparation method and application

Abstract

The invention provides a tin deposition agent, a preparation method and application. The tin depositing agent comprises the following components: 12-18 g / L of tin methanesulfonate; 120 to 160 g / L of methanesulfonic acid; 30-60 g / L of a complexing agent; the compound stabilizer is prepared from 1 g / L to 5 g / L of trimethylglycine, 0.05 g / L to 1 g / L of phosphonate and 0.5 g / L to 3 g / L of sodium hydrogen sulfite; 50 to 150 mg / L of a wetting agent; and 50 to 150 mg / L of an emulsifier. The tin immersion agent is high in tin immersion rate, has excellent deoiling resistance, can effectively avoid the problems of solder mask falling, local welding refusal or bare copper exposure and the like in the tin immersion process, and can meet the requirements of industrial large-scale production.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of printed circuit board surface treatment, in particular to a tin dipping agent, a preparation method and application. BACKGROUND

[0002] Printed circuit board (PCB) as the core component of modern electronic equipment, its surface treatment process plays a crucial role in the performance and reliability of electronic equipment. Tin dipping process as a widely used PCB surface treatment technology, can form a dense tin layer on the copper surface, significantly improve the solderability and effectively protect the copper layer from oxidation. The existing tin dipping system mostly uses methyltin sulfonate as the main tin source, combined with a complexing agent containing thiourea, which can ensure the uniformity of the plating layer to a certain extent. However, the existing technology still has significant deficiencies. First, thiourea is still the most commonly used complexing agent, but thiourea has certain toxicity and environmental hazards, and is prone to decomposition to produce NH3 and H2S during the tin dipping process, which not only leads to shortening of the life of the plating solution and the need for frequent maintenance, but also attacks the solder resist ink, causing oil bleeding and soldering rejection and other quality problems. Second, some formulations use high-concentration methyltin sulfonate and multiple special additives to ensure stability, which can improve the plating solution durability to a certain extent, but the overall raw material cost is high, increasing the production burden. Third, the existing tin dipping rate is low, even if the stability is good, it is difficult to meet the efficiency requirements of large-scale horizontal production lines, limiting the process promotion. Fourth, some existing disclosed formulations are complex, such as the introduction of special amino cycloalkane carboxylic acid complexing agents or dicyanonaphthalene wetting agents, resulting in high raw material cost, difficult to prepare, and insufficient industrial adaptability. Fifth, the environmental adaptability problem is prominent, the existing tin dipping agent is prone to component imbalance or performance degradation in continuous circulation, and cannot maintain uniform tin dipping effect for a long time.

[0003] In summary, the existing tin dipping agent has technical bottlenecks in complexing agent selection, process stability, tin dipping rate, cost and environmental adaptability, and it is urgent to propose a new tin dipping agent system that can ensure the tin dipping rate while having excellent long-term stability and anti-oil bleeding performance. SUMMARY

[0004] In view of the defects in the prior art, the present application proposes a tin dipping agent, a preparation method and application. The present application coordinates tin ion stability, solution antioxidant protection and interface wetting performance, realizes high tin dipping rate, long service life of tin dipping agent, low sensitivity to solder resist oil bleeding and good solderability of the plating layer, has significant practical value and industrial promotion prospect.

[0005] The present application provides a tin dipping agent, which comprises the following components: methyltin sulfonate 12-18 g / L; methyl sulfonic acid 120-160 g / L; complexing agent 30-60 g / L; complex stabilizer comprising 1-5 g / L trimethylglycine, 0.05-1 g / L phosphonate and 0.5-3 g / L sodium bisulfite; wetting agent 50-150 mg / L; emulsifier 50-150 mg / L.

[0006] methyl sulfonic acid tin as tin ion source, providing active Sn for displacement tin plating reaction 2+ , the concentration of which is controlled within a suitable range, which is conducive to ensuring the tin plating rate and plating uniformity; methyl sulfonic acid as an acidic medium, maintaining the acidic environment of the solution, so that Sn 2+ stably exists and inhibits self-sedimentation reaction, while regulating the displacement reaction rate.

[0007] In the present application, trimethylglycine can enhance the solution stability of tin ions, inhibit Sn 2+ oxidation to form Sn 4 + , and prolong the service life of the tin plating agent; phosphonate can improve the tin plating efficiency by improving the activity of tin ions and the crystal nucleus formation rate; sodium bisulfite as a reducing component can consume trace amounts of oxides in the solution, inhibit the oxidation and deposition of tin ions, and ensure the tin plating rate and long-term stability.

[0008] In the present application, the wetting agent and the emulsifier can significantly improve the interfacial wettability of the tin plating solution, reduce the contact angle of the liquid droplets on the PCB surface, make the tin ions fully contact and deposit on the copper surface, thereby enhancing the adhesion of the tin layer and reducing the oil removal phenomenon of the solder resist layer or residual ink.

[0009] In some embodiments, the complex stabilizer further comprises 0.1-3 g / L 2-aminoethanesulfonic acid; 2-aminoethanesulfonic acid can enhance the compatibility of the plating layer with the solder resist ink by adjusting the surface chemical properties of the solution, significantly improving the anti-oil removal performance; by forming a weak complex with Sn 2+ ions, delaying the aging of the solution, so that the complex stabilizer plays a more significant effect in enhancing long-term stability and improving anti-oil removal performance.

[0010] In some embodiments, the complexing agent is any one of citric acid, tartaric acid or gluconic acid. The preferred complexing agent of the present application has good environmental adaptability and low toxicity, and compared with traditional complexing agents such as thiourea, it will not decompose to produce harmful gases during the tin plating process, nor will it attack the solder resist ink, thereby improving the safety and industrial applicability of the tin plating agent.

[0011] In some embodiments, the phosphonate is hydroxyethylidene diphosphonic acid or aminotri(methylene) phosphonic acid; the phosphonate can synergize with Sn2+ions and other components in the complex stabilizer to improve the uniformity and compactness of the plating layer.

[0012] and / or the wetting agent is PEG; and / or the emulsifying agent is OP-10.

[0013] In some embodiments, the tin plating agent further comprises 0.1-20 ppm of trace micro-alloying ions, the trace micro-alloying ions being Bi 3+ , Sb 3+ or Ag + ; the addition of trace micro-alloying ions can further optimize the grain structure of the plating layer and improve the compactness and solderability of the plating layer.

[0014] The application also provides a preparation method of the tin plating agent, comprising the following steps: (1) adding an acidic medium in deionized water, controlling the concentration of the acidic medium to be 120-160 g / L, and adding tin methanesulfonate and stirring until completely dissolved; (2) sequentially adding a complexing agent, a complex stabilizer, a wetting agent and an emulsifying agent, stirring and adjusting the pH to 2-3 to obtain the tin plating agent.

[0015] The application also provides a tin plating process, comprising the following steps: (1) sequentially performing oil removal, micro-etching and acid pickling pretreatment on the surface of a copper-clad plate to be treated; (2) immersing the pretreated copper-clad plate in the tin plating agent according to any one of claims 1-5 at 68-73°C for 10-20 min to form a tin plating layer.

[0016] In some embodiments, the micro-etching liquid used in step (1) is a sulfuric acid-hydrogen peroxide system, and the micro-etching depth is 0.3-0.6 μm.

[0017] In some embodiments, the thickness of the tin plating layer in step (2) is 0.5-2 μm.

[0018] The application also provides the use of the tin plating agent in forming a tin plating layer on the surface of a printed circuit board.

[0019] Compared with the prior art, the application achieves the following technical effects: (1) The tin plating agent of the present application can significantly improve the tin plating rate under the condition of ensuring the uniformity and compactness of the plating layer, greatly improve the tin plating efficiency, meet the needs of industrial large-scale production, shorten the production cycle, and improve the process productivity. Secondly, the tin plating agent of the present application has excellent anti-oil performance, which can effectively avoid the problems of solder mask layer falling off, local solder mask failure or bare copper exposure during the tin plating process, ensure the continuity and adhesion of the tin layer in the complex solder mask pattern and multi-layer board structure, and significantly improve the reliability of the finished PCB.

[0020] (2) The tin plating agent of the present application has good long-term stability, which can maintain stable chemical activity and tin plating performance even under long-term storage and continuous cycle use conditions, avoid rapid failure or frequent replenishment of the liquid medicine, and reduce the production and maintenance cost. The raw materials are widely available, the preparation process is simple, and it is easy to directly apply in the existing production line, which has good process adaptability and industrialization popularization value. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and should not be regarded as limiting the scope. For those skilled in the art, other related drawings can also be obtained without creative labor.

[0022] Figure 1 The process flow chart of the PCB board tin plating of the present application.

[0023] Figure 2 The tin plating rate test results of test example 1 of the present application. DETAILED DESCRIPTION

[0024] In order to make the person skilled in the art better understand the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor should belong to the scope of protection of the present application.

[0025] The embodiments of the present application are not limited by the following examples, especially not limited to the types of the raw materials used in the following specific examples.

[0026] The raw materials of the examples and comparative examples are as follows: Tin methyl sulfonate: purity ≥ 99%, Wuhan Jiyesheng Technology Co., Ltd.

[0027] Methyl sulfonic acid: 471356, purity ≥ 99%, Sigma-Aldrich.

[0028] Complexing agent: citric acid, Yixuan, the same substance was used in parallel tests.

[0029] Trimethylglycine: 203-490-6, Shijiazhuang Demou Chemical Technology Co., Ltd.

[0030] Hydroxyethylidene diphosphonic acid: A00398, Wuhan Jiyesheng Technology Co., Ltd.

[0031] Sodium bisulfite: Jinan Yuanfei Chemical Industry Co., Ltd., the same substance was used in parallel tests.

[0032] Wetting agent: PRG-600, Linyi Guoli Chemical Co., Ltd.

[0033] Emulsifier: OP-10, Jinan Jirixie Chemical Co., Ltd.

[0034] 2-Aminoethanesulfonic acid: CAS No. 107-35-7, Suzhou Yakke Technology Co., Ltd.

[0035] Ag+: KR-M-004-1, average particle size: 50 nm, Anhui Kenun Nanotechnology Co., Ltd.

[0036] The preparation method of the tin deposition agent of the present application is as follows: (1) Add deionized water to the reaction kettle and start stirring (300-500 rpm, use paddle stirring or magnetic force to ensure good convection). The temperature of the reaction kettle is controlled at 20-25°C.

[0037] (2) Slowly add methyl sulfonic acid while stirring until the methyl sulfonic acid is evenly mixed with water (about 10 min).

[0038] (3) Add tin methyl sulfonic acid, add in portions and stir until completely dissolved (usually completely dissolved at room temperature for about 20 min). If a small amount of particles appear, slightly increase the stirring speed or maintain the temperature at 25-30°C to accelerate the dissolution, and ensure that there is no visible solid residue.

[0039] (4) Dissolve the complexing agent solution, the composite stabilizer solution, the wetting agent and the emulsifier separately, and slowly add them to the main kettle (Ag + Add at the same time), adjust the target pH to 2.5±0.2 using 10% NaOH.

[0040] (5) Use 0.45 µm microporous filter membrane to pressure filter the prepared solution to remove particles or insoluble residues.

[0041] The amount of the tin deposition agent of the examples and the comparative examples is shown in Tables 1-2, wherein the unit of the wetting agent and the emulsifier is mg / L, the unit of Ag+ is ppm, and the units of the rest are g / L.

[0042] Table 1 Amount of each component of the examples ;

[0043] Table 2 Amount of each component of the comparative examples

[0044] Based on the tin deposition agent formula of the above examples and the comparative examples, the PCB is tin-deposited by using the process of Figure 1 , and the steps are as follows: (1) Sample preparation: A 50 mm × 50 mm size PCB single-sided copper-clad plate (copper thickness 18 μm) is taken, the surface of which is covered with a commercial green solder resist ink and has been completely cured (UV cured).

[0045] (2) Oil removal treatment: The PCB is immersed in a 5% NaOH solution, the temperature of which is controlled at 40±2℃, and is gently stirred on a magnetic stirrer for 3 min. After being taken out, it is rinsed with a large amount of deionized water for 30 s, and is dried by using nitrogen, so as to remove the oil and dirt on the surface of the PCB and ensure uniform tin deposition.

[0046] (3) Micro-etching treatment: The PCB after oil removal is immersed in a sulfuric acid-hydrogen peroxide micro-etching solution (H2SO4 50 g / L + H2O2 20 mL / L), the temperature of which is 25±2℃, and is stirred for 2 min, and the micro-etching depth is controlled at 0.6 μm. After micro-etching, it is immediately rinsed with a large amount of deionized water and dried. The micro-etching can remove the copper surface oxide film and increase the surface roughness, so as to facilitate the tin deposition adhesion.

[0047] (4) Pickling treatment: The PCB after micro-etching is immersed in a 10% methylsulfonic acid solution, the temperature of which is 25±2℃, and is soaked for 2 min to remove the surface residual oxide and alkaline micro-etching residue. After being taken out, it is rinsed with a large amount of deionized water and dried.

[0048] (5) Tin deposition treatment: The pretreated PCB is immersed in the tin deposition agent prepared by the examples and the comparative examples, respectively, the temperature of which is controlled at 70±2℃, and is soaked for different times. In the soaking process, a magnetic stirrer is used to gently stir the liquid to ensure uniform flow of the liquid and avoid local deposition unevenness. No obvious bubbles or precipitates are generated in the tin deposition process.

[0049] (6) Post-tinning cleaning and drying: After the completion of the tinning, the PCB board is taken out and immediately rinsed with a large amount of deionized water for 30 s, and then dried with nitrogen to ensure that the surface is free of residual tinning agent.

[0050] [TEST EXAMPLES] Test Example 1: PCB board tinning rate test In step (5) of the above tinning process, PCB board samples were taken out at different time points (2 min, 5 min, 10 min and 15 min), and each time the sample was rinsed with deionized water for 30 s and dried, fixed on an X-ray thickness gauge (Seifert X-ray Analyzer), and 5 points were selected for each board to ensure the uniformity of the tin layer thickness evaluation.

[0051] Among them, the X-ray tube voltage is set at 40 kV, and the tube current is set at 0.2 mA.

[0052] The tinning rate (μm / min) is calculated according to the following formula: Tinning rate = tin layer thickness (μm) / tinning time (min).

[0053] The test results are as follows: Table 3 Tinning rate test results

[0054] From Table 3 and Figure 2 The results show that the tin layer thickness of Examples 1-7 can reach 1.26-1.38 μm at 10 min, and the average tinning rate is between 0.126 and 0.138 μm / min. The present application achieves the effect of efficient tinning through the synergistic effect of the components. In contrast, Comparative Example 1 does not add trimethylglycine, resulting in insufficient stability of tin ions and reduced tinning rate; Comparative Example 2 does not add phosphonate, affecting the activity of tin ions and the formation of crystal nuclei, resulting in the slowest tinning rate; Comparative Example 3 does not add sodium bisulfite, the reducing property of the solution is insufficient, the tin ions are easily oxidized, and the uniformity and thickness of the plating layer decrease; Comparative Example 4 has too much trimethylglycine, the tin ions are excessively complexed, the free tin concentration is reduced, and the tinning rate is slowed down; Comparative Example 5 has too much trimethylglycine, but the tinning rate is not significantly improved compared to Example 1, and instead increases the use cost of raw materials; Comparative Example 6 has too much sodium bisulfite, the reducing property is too strong, resulting in uneven local deposition and decreased plating layer quality; Comparative Example 7 does not contain wetting agent and emulsifier, the solution has poor wetting property, the tin ions are unevenly distributed on the surface of the PCB, and the tinning rate is reduced. In summary, the tinning performance of each comparative example is insufficient, mainly due to the absence of key components or unreasonable ratio, which cannot achieve the efficient, uniform and stable tinning effect of the tinning agent of the examples.

[0055] Test Example 2: Anti-de-rosin performance test of the tin immersion agent By adjusting the tin immersion time, the thickness of the tin layer was controlled to be consistent, and the following tests were carried out.

[0056] (1) Contact angle measurement: five evenly distributed measurement points were selected on the surface of the PCB board after tin immersion, 20 μL of deionized water was added using a contact angle meter (Kruss DSA100 type), after the liquid drop was added, the liquid drop was naturally settled and stabilized for 5 s, and then the static contact angle was photographed. Each measurement point was recorded for 3 seconds, and the instrument automatically calculated the average contact angle value. After completing the measurement of the five measurement points, the average value was taken as the contact angle index of the PCB board.

[0057] (2) The PCB board after tin immersion and cleaning and drying was taken out, and a clean brush was used to evenly coat a halogen-free rosin-based flux (in line with J-STD-004 standard) on the tin plated area of the board surface, and the thickness meter confirmed that the thickness was about 10 μL, ensuring that the tin layer was covered but not accumulated. After coating, stand for 1 min to let the flux dry naturally and adhere to the surface of the tin layer. Then, a manual soldering was used to test the solderability on the tin plated area: the soldering iron temperature was controlled at 350±10℃, and a tin wire (about 1 mm in diameter) was used to individually solder at each tin plated measurement point, with a contact time of 2-3 seconds with the PCB surface, forming a small solder joint of about 2 mm. After soldering, naturally cool for 30 seconds. Use an optical microscope (50x magnification) to observe the solder joint and the surrounding tin plated layer, check whether the tin layer continuously covers the solder mask area, whether there is bare copper, tin layer peeling or soldering rejection spots. Use ImageJ image analysis software to calculate the area percentage (%) of bare copper or soldering rejection.

[0058] The tin layer thickness measurement results of the PCB board used in Test Example 2 are as follows: Table 4 Tin layer thickness measurement results (unit: μm) ;

[0059] From the results in Table 4, it can be seen that the tin immersion layer of the PCB board obtained by the tin immersion process of the present application is uniform in thickness, and the total thickness of the tin immersion layer is about 1.2000±0.03 μm.

[0060] The performance test results of Test Example 2 are shown in Table 5: Table 5 Anti-de-rosin performance test results of the tin immersion agent

[0061] From the results of Table 5, the PCB surface contact angles of Examples 1-7 of the present application are all between 36° and 44°, indicating that the tin plated layer surface is good hydrophilic, the solution wettability is excellent, and there is no obvious oily residue on the surface of the solder resist layer and tin layer during the tin plating process. In contrast, the contact angles of the comparative examples are significantly higher, especially Comparative Examples 2 and 7, indicating poor surface wettability, oily residue or interface contamination, thereby affecting the tin plating quality. In addition, the bare copper / reflow soldering area of the example group after soldering is very low, among which Example 1 is the best, indicating that the interface wettability and adhesion of the tin plated layer with the solder resist layer and solder tin are the best. In summary, the tin plating agent of the present application can effectively improve the wettability of the plated layer, improve the interface bonding performance of the plated layer with the solder resist / solder tin, reduce the risk of oil removal and soldering resistance, and thereby improve the reliability and solderability of the PCB.

[0062] Test Example 3: Long-term stability test of tin plating agent: The prepared tin plating agent was stored in a glass container according to the conventional formula, the container was sealed to avoid light and evaporation. The tin plating agent sample was divided into multiple storage period groups, respectively 0 days (newly prepared), 15 days, 30 days, 90 days, 180 days, and part of the tin plating agent was taken out for performance test at each time point. The storage temperature was controlled at room temperature 23±2℃, and the relative humidity was 50±5%. Including anti-oil removal test and solderability test.

[0063] Table 6 Average contact angle (°)

[0064] Table 7 Bare copper or soldering resistance area (%)

[0065] The test results of Tables 6-7 show that Examples 1-7 of the present application maintain a low contact angle and a small bare copper / soldering resistance area throughout the storage period. Even after 180 days of storage, the contact angle of Example 1 is only 39.0°, and the bare copper / soldering resistance area is 1.80%, indicating that the tin plating agent of the present application can still maintain excellent anti-oil removal performance and solderability during a storage period of up to 6 months. The long-term stability and anti-oil removal performance of the tin plating agent of the present application are mainly due to the synergistic effect of the specific composite stabilizer design and the auxiliary agent, so that the tin ions remain active during storage, and the plating solution is not easy to age or fail, thereby meeting the needs of printed circuit board production for long-term storage and stability of the tin plating solution. In contrast, the long-term stability of Comparative Examples 1-7 significantly decreases. The contact angles of Comparative Examples 1, 3 and 7 all exceed 65° after 90 days, and the bare copper / soldering resistance area exceeds 9%, showing local soldering resistance or poor tin layer adhesion during soldering. Among them, the contact angle of Comparative Example 1 reaches 85.1° at 90 days, and the bare copper / soldering resistance area is 25.41%, which is obviously failed.

[0066] In summary, the tin remelting agent of the present application can still maintain good anti-oil separation performance and weldability in long-term storage, while the comparative examples are obviously insufficient in long-term stability due to the absence or unreasonable ratio, highlighting the advantages and reliability of the formula of the present application in practical application.

[0067] The above merely describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A tin deposition agent characterized by comprising: The stannum sinking agent comprises the following components: stannous methanesulfonate 12~18 g / L; methanesulfonic acid 120~160 g / L; complexing agent 30~60 g / L; composite stabilizer comprising 1~5 g / L trimethylglycine, 0.05~1 g / L phosphonate and 0.5~3 g / L sodium bisulfite; wetting agent 50~150 mg / L; emulsifier 50~150 mg / L.

2. The tinning agent of claim 1, wherein The composite stabilizer further comprises 0.1~3 g / L 2-aminoethanesulfonic acid.

3. The tinning agent of claim 1, wherein The complexing agent is any one of citric acid, tartaric acid or gluconic acid.

4. The tinning agent of claim 1, wherein The phosphonate is hydroxyethylidene diphosphonic acid or aminotri(methylene) phosphonic acid; and / or the wetting agent is PEG; and / or the emulsifier is OP-10.

5. The tinning agent of claim 1, wherein The tinning agent also includes 0.1 to 20 ppm of trace microalloying ions, the trace microalloying ions being Bi 3+ , Sb 3+ , or Ag + .

6. The method of producing a tin deposition agent according to any one of claims 1 to 5, characterized by, The method comprises the following steps: (1) adding an acidic medium in deionized water, controlling the concentration of the acidic medium to be 120~160 g / L, adding stannous methanesulfonate and stirring until completely dissolved; (2) sequentially adding a complexing agent, a composite stabilizer, a wetting agent and an emulsifier, stirring and adjusting the pH to 2~3 to obtain the stannum sinking agent.

7. A tin dipping process characterized by, The method comprises the following steps: (1) sequentially performing oil removal, micro-etching and acid pickling pretreatment on the surface of the copper-clad plate to be treated; (2) immersing the pretreated copper-clad plate in the stannum sinking agent of any one of claims 1~5 at 68~73℃ for 10~20 min to form a tin plating layer.

8. The tinning process of claim 7, wherein, The micro-etching liquid used in step (1) is a sulfuric acid-hydrogen peroxide system and the micro-etching depth is 0.3~0.6 μm.

9. The tinning process of claim 7, wherein, The thickness of the tin plating layer in step (2) is 0.5~2 μm.

10. Use of the stannum sinking agent of any one of claims 1~5 in forming a tin plating layer on the surface of a printed circuit board.

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