阅读说明：本技术 一种铜基金属表面浸锡液及其应用 (Copper-based metal surface tin immersion liquid and application thereof ) 是由 刘江波 林章清 章晓冬 童茂军 王亚君 于 2019-11-29 设计创作，主要内容包括：本发明提供一种铜基金属表面浸锡液及其应用。所述铜基金属表面浸锡液按质量浓度计包含如下组分：锡盐10-200g/L、络合剂50-300g/L、有机酸10-400g/L、表面活性剂1-100g/L、抗氧化剂10-100g/L和贵金属1-100ppm,所述络合剂为柠檬酸、硫脲、异硫脲和硫醇的组合。本发明所述铜基金属表面浸锡液配方简单,并适用于水平或垂直生产工艺,易于控制,操作简易,得到的锡面均匀致密,并具有良好的多次可焊性。(The invention provides a copper-based metal surface tin immersion liquid and application thereof. The copper-based metal surface tin immersion liquid comprises the following components in percentage by mass: 10-200g/L of tin salt, 50-300g/L of complexing agent, 10-400g/L of organic acid, 1-100g/L of surfactant, 10-100g/L of antioxidant and 1-100ppm of noble metal, wherein the complexing agent is the combination of citric acid, thiourea, isothiourea and mercaptan. The copper-based metal surface tin immersion liquid has a simple formula, is suitable for a horizontal or vertical production process, is easy to control and operate, and has uniform and compact tin surface and good repeated weldability.)

1. The copper-based metal surface tin immersion liquid is characterized by comprising the following components in percentage by mass:

the complexing agent is a combination of citric acid, thiourea, isothiourea and mercaptan.

2. The copper-based metal surface immersion tin liquid according to claim 1, wherein the tin salt comprises any one of stannous methanesulfonate, stannous sulfamate, stannous sulfate or stannous chloride or a combination of at least two of the stannous methanesulfonate, the stannous sulfamate, the stannous sulfate or the stannous chloride, and preferably the stannous sulfamate and/or the stannous sulfate.

3. The copper-based metal surface tin immersion liquid as claimed in claim 1 or 2, wherein the mass ratio of the citric acid, the thiourea, the isothiourea and the mercaptan in the complexing agent is (0.5-1): (5-10): (4-8): (2-3).

4. Copper-based metal surface immersion tin liquid according to any one of claims 1 to 3, characterized in that the organic acid comprises any one of or a combination of at least two of methanesulfonic acid, sulfamic acid, malic acid or gluconic acid.

5. The copper-based metal surface tin immersion liquid according to any one of claims 1-4, wherein the surfactant comprises any one or a combination of at least two of fatty alcohol polyoxyethylene ether, multi-branched alkyl polyoxyethylene ether, alkylphenol polyoxyethylene ether, alkyl polyoxypropylene ether, alkylphenol polyoxypropylene ether, polyethylene glycol, polypropylene glycol or alcohol ether phosphate, preferably any one or a combination of at least two of fatty alcohol polyoxyethylene ether, multi-branched alkyl polyoxyethylene ether or alkylphenol polyoxyethylene ether;

preferably, the surfactant is a combination of fatty alcohol-polyoxyethylene ether, multi-branched alkyl polyoxyethylene ether and alkylphenol polyoxyethylene ether;

preferably, the mass ratio of the fatty alcohol-polyoxyethylene ether to the multi-branched alkyl polyoxyethylene ether to the alkylphenol polyoxyethylene ether in the surfactant is (1-5) to (2-4) to (3-5);

preferably, the EO number of the fatty alcohol-polyoxyethylene ether is 3-9;

preferably, the fatty alcohol-polyoxyethylene ether comprises any one or a combination of at least two of heterogeneous dodecyl alcohol polyoxyethylene ether, heterogeneous pentadecyl alcohol polyoxyethylene ether or lauryl alcohol polyoxyethylene ether;

preferably, the EO number of the multi-branched alkyl polyoxyethylene ether is 5 to 10;

preferably, the multi-branched alkyl polyoxyethylene ether comprises any one of polyoxyethylene octyl dodecyl ether, polyoxyethylene octyl tetradecyl ether, polyoxyethylene octyl hexadecyl ether, polyoxyethylene decyl tetradecyl ether or polyoxyethylene decyl hexadecyl ether or a combination of at least two of the polyoxyethylene octyl dodecyl ether, the polyoxyethylene octyl tetradecyl ether and the polyoxyethylene decyl hexadecyl ether;

preferably, the alkylphenol ethoxylates have an EO number of 2 to 10;

preferably, the alkylphenol ethoxylate comprises any one of nonylphenol ethoxylate, octylphenol ethoxylate, dodecylphenol ethoxylate or dinonylphenol ethoxylate or a combination of at least two thereof.

6. Copper-based metal surface tin immersion liquid according to any one of claims 1 to 5, wherein the antioxidant comprises any one of or a combination of at least two of benzenediol, tert-butylhydroquinone, phosphite, ascorbic acid, dibutylhydroxytoluene or uric acid;

preferably, the noble metal comprises any one of silver, gold, iridium, rhodium, rhenium, osmium or palladium or a combination of at least two thereof.

7. Use of the copper-based metal surface immersion tin liquid according to any one of claims 1 to 6 in printed circuit board processing.

8. The use according to claim 7, wherein the method of processing the printed circuit board comprises the steps of:

(1) pretreatment: carrying out oil removal treatment and microetching treatment on the printed circuit board;

(2) pre-dipping: placing the printed circuit board pretreated in the step (1) in the copper-based metal surface tin immersion liquid, and forming a pre-immersion tin coating on the copper-based surface of the printed circuit board;

(3) tin immersion: and (3) placing the printed circuit board subjected to the pre-dipping treatment in the step (2) in the copper-based metal surface tin dipping solution again, and depositing a tin dipping tin plating layer on the copper-based surface tin dipping tin plating layer of the printed circuit board.

9. The use according to claim 7 or 8, wherein the degreasing treatment in step (1) is soaking the printed circuit board with an acidic degreasing liquid;

preferably, the acid deoiling liquid is a sulfuric acid solution;

preferably, the temperature of the oil removing treatment in the step (1) is 40-60 ℃;

preferably, the time of the oil removing treatment in the step (1) is 1-5 min;

preferably, the microetching treatment in the step (1) is to soak the printed circuit board by using microetching liquid;

preferably, the micro-etching solution comprises any one or a combination of at least two of sodium persulfate, ammonium persulfate and a sulfuric acid solution of hydrogen peroxide;

preferably, the temperature of the microetching treatment in the step (1) is 10-40 ℃;

preferably, the microetching treatment in the step (1) is carried out for 1-5 min;

preferably, the microetching amount of the microetching treatment in the step (1) is 0.5-2 μm;

preferably, the presoaking time of the step (2) is 1-5 min;

preferably, the temperature of the presoaking in the step (2) is 20-30 ℃;

preferably, the thickness of the tin prepreg layer in the step (2) is 0.1-0.3 μm;

preferably, the tin immersion time in the step (3) is 15-30 min;

preferably, the temperature of the tin immersion in the step (3) is 65-75 ℃;

preferably, the thickness of the tin-dipped tin coating in the step (3) is 0.5-1.5 μm;

preferably, step (3) is followed by step (4) of washing: washing and drying the printed circuit board obtained after the step (3) is dipped in tin;

preferably, the temperature of the water washing is 40-60 ℃;

preferably, the time of the water washing is 1-5 min;

preferably, the drying temperature is 40-80 ℃;

preferably, the drying time is 10-20 min.

10. Use according to any one of claims 7 to 9, characterized in that the method of processing the printed circuit board comprises in particular the steps of:

(1) pretreatment: soaking the printed circuit board with acid degreasing liquid at 40-60 deg.C for 1-5min for degreasing, soaking the printed circuit board with microetching liquid at 10-40 deg.C for 1-5min for microetching with microetching amount controlled at 0.5-2 μm;

(2) pre-dipping: placing the printed circuit board pretreated in the step (1) in the tin immersion liquid on the surface of the copper-based metal at the temperature of 20-30 ℃ for 1-5min to form a 0.1-0.3 mu m pre-immersion tin coating on the surface of the copper-based of the printed circuit board;

(3) tin immersion: placing the printed circuit board pre-soaked in the step (2) in the copper-based metal surface tin-soaking solution again for 15-30min at 65-75 ℃, and depositing a tin-soaking tin-plating layer with the thickness of 0.5-1.5 mu m on the copper-based surface pre-soaking tin-plating layer of the printed circuit board;

(4) cleaning: and (4) washing the printed circuit board obtained after the tin immersion in the step (3) for 1-5min at 40-60 ℃, and then drying for 10-20min at 40-80 ℃.

Technical Field

The invention belongs to the field of chemical tinning, and particularly relates to a copper-based metal surface tin immersion liquid and application thereof.

Background

Tin is a metal with good solderability and corrosion resistance, in the field of electricityThe application in the sub-industry is wide. With the miniaturization of electronic development, the smaller the circuit and BGA points on a Printed Circuit Board (PCB), the more solder has been widely used as a solderable plating, and the conventional hot air leveling process has failed to meet the requirements of the existing process. The chemical tin immersion process has the advantages of excellent repeated weldability, compact plating layer, simple process flow, environmental protection and the like, and is widely applied. However, since tin has a high hydrogen evolution potential and a low catalytic activity, when sodium hypophosphite, borohydride and Ti are used alone³⁺And the reducing agents can not well realize the continuous autocatalytic deposition of tin, and a thicker plating layer can not be obtained.

At present, chemical tin immersion on a copper substrate refers to that tin and copper ions are subjected to a displacement reaction, and then the tin and copper are subjected to a total reaction of two stages of tin-copper codeposition and autocatalytic deposition. The bath generally includes stannous tin as the ion source, complexing agents such as thiourea, organic acids, surfactants, brighteners, antioxidants, hypophosphite, precious metals, and the like. However, the currently available tin immersion processes have problems, such as green oil erosion, black tin surface, long tin length, and galvanic effect. Compared with galvanic phenomenon of electroless nickel-gold and electroless silver plating, chemical immersion tin has less influence on electrical performance at conventional thick lines and large pads (pads), and thus has not received sufficient attention. Nowadays, for high dielectric constant, high frequency materials or electroless tin deposition on small pad sites, such materials are required to have reduced signal transmission attenuation. At this time, the galvanic effect of the chemical immersion tin will have a certain influence on signal transmission and stability.

CN101705482A discloses an alkyl sulfonic acid chemical tin plating solution, which comprises the following components in percentage by weight: 1-40g/L of organic tin sulfonate, 5-250g/L of organic acid, 5-300g/L of complexing agent, 20-150g/L of reducing agent, 0.5-50g/L of surfactant, 0.1-25g/L of antioxidant, 1-500mg/L of noble metal salt and 0.5-3g/L of brightening agent, and a large amount of reducing agent and brightening agent are added into the alkyl sulfonic acid chemical tin plating solution, so that the prepared plating layer has high organic matter content and high brittleness, and can not meet the requirement of an electronic device on the flexibility of the plating layer, and is not suitable for chemical tin deposition on high dielectric constant, high-frequency materials or small pad positions.

CN107365986A discloses a chemical tin treatment agent and a tin plating process using the same, wherein the chemical tin treatment agent comprises the following raw materials: 100-150g/L of organic tin salt, 30-50mL/L of organic acid, 50-100g/L of complexing agent, 50-100g/L of reducing agent, 1-10g/L of chelating agent, 5-30g/L of surfactant, 1-10g/L of antioxidant, 1-10g/L of organic acid silver, 1-5g/L of gloss agent and 5-50g/L of corrosion inhibitor, wherein the chemical tin treating agent is easy to generate tin migration in a tin plating process, generates longer tin whiskers and influences the processing and use of a circuit board.

Therefore, the development of a tin immersion liquid which can well realize the continuous autocatalytic deposition of tin is the focus of current research in the field.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to provide the copper-based metal surface tin immersion liquid and the application thereof.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the invention provides a copper-based metal surface tin immersion liquid, which comprises the following components by mass: 10-200g/L of tin salt, 50-300g/L of complexing agent, 10-400g/L of organic acid, 1-100g/L of surfactant, 10-100g/L of antioxidant and 1-100ppm of noble metal; the complexing agent is a combination of citric acid, thiourea, isothiourea and mercaptan.

In the present invention, the tin salt has a mass concentration of 10 to 200g/L, for example, 10g/L, 20g/L, 30g/L, 40g/L, 50g/L, 60g/L, 70g/L, 80g/L, 90g/L, 100g/L, 110g/L, 120g/L, 130g/L, 140g/L, 150g/L, 160g/L, 170g/L, 180g/L, 190g/L, 200 g/L.

In the invention, the mass concentration of the complexing agent is 50-300g/L, for example, 50g/L, 60g/L, 70g/L, 80g/L, 90g/L, 100g/L, 110g/L, 120g/L, 130g/L, 140g/L, 150g/L, 160g/L, 170g/L, 180g/L, 190g/L, 200g/L, 210g/L, 220g/L, 230g/L, 240g/L, 250g/L, 260g/L, 270g/L, 280g/L, 290g/L and 300 g/L.

In the present invention, the organic acid may have a mass concentration of 10 to 400g/L, for example, 10g/L, 20g/L, 30g/L, 40g/L, 50g/L, 60g/L, 70g/L, 80g/L, 90g/L, 100g/L, 110g/L, 120g/L, 130g/L, 140g/L, 150g/L, 160g/L, 170g/L, 180g/L, 190g/L, 200g/L, 210g/L, 220g/L, 230g/L, 240g/L, 250g/L, 260g/L, 270g/L, 280g/L, 290g/L, 300g/L, 310g/L, 320g/L, 330g/L, 340g/L, 350g/L, 360g/L, 370g/L, 380g/L, 390g/L and 400 g/L.

In the present invention, the surfactant may be present at a mass concentration of 1 to 100g/L, for example, 1g/L, 2g/L, 3g/L, 4g/L, 5g/L, 6g/L, 7g/L, 8g/L, 9g/L, 10g/L, 15g/L, 20g/L, 25g/L, 30g/L, 35g/L, 40g/L, 45g/L, 50g/L, 55g/L, 60g/L, 65g/L, 70g/L, 75g/L, 80g/L, 85g/L, 90g/L, 95g/L, or 100 g/L.

In the present invention, the antioxidant may be contained in a mass concentration of 10 to 100g/L, for example, 10g/L, 15g/L, 20g/L, 25g/L, 30g/L, 35g/L, 40g/L, 45g/L, 50g/L, 55g/L, 60g/L, 65g/L, 70g/L, 75g/L, 80g/L, 85g/L, 90g/L, 95g/L, or 100 g/L.

In the present invention, the antioxidant may be used in a mass concentration of 1 to 100ppm, for example, 1ppm, 2ppm, 3ppm, 4ppm, 5ppm, 6ppm, 7ppm, 8ppm, 9ppm, 10ppm, 12ppm, 14ppm, 16ppm, 18ppm, 20ppm, 22ppm, 24ppm, 26ppm, 28ppm, 30ppm, 32ppm, 34ppm, 36ppm, 38ppm, 40ppm, 45ppm, 50ppm, 55ppm, 60ppm, 65ppm, 70ppm, 75ppm, 80ppm, 85ppm, 90ppm, 95ppm, 100ppm of the noble metal.

In the present invention, the tin salt provides a source of tin. The complexing agent is a combination of citric acid, thiourea, isothiourea and mercaptan, and the four complexing agents are matched with each other, so that the synergistic effect is achieved, the capability of the complexing agent for complexing metal ions can be improved, and the oxidation-reduction potential of copper ions can be further reduced. The surfactant can control the galvanic effect, reduce the surface tension of the solution and improve the uniformity and compactness of the tin layer. The antioxidant prevents oxidation of stannous to stannic. The noble metal inhibits tin whisker growth.

Preferably, the tin salt comprises any one of stannous methanesulfonate, stannous sulfamate, stannous sulfate or stannous chloride or a combination of at least two of them, preferably stannous sulfamate and/or stannous sulfate.

Preferably, the mass ratio of the citric acid, the thiourea, the isothiourea and the thiol in the complexing agent is (0.5-1): 5-10): 4-8): 2-3, and may be, for example, 0.5:5:4:2, 0.5:6:4:2, 0.5:8:4:2, 0.5:10:4:2, 1:5:4:2, 1:6:4:2, 1:7:4:2, 1:8:4:2, 1:9:4:2, 1:10:4:2, 1:5:5:2, 1:6:5:2, 1:7:5:2, 1:8:7:2, 1:9:7:2, 1:10:7:2, 1:5:4:3, 1:6:4:3, 1:7:4:3, 1:8:4:3, 1:9:4:3, 1:3: 4: 3.

Preferably, the organic acid comprises any one of or a combination of at least two of methanesulfonic acid, sulfamic acid, malic acid or gluconic acid.

Preferably, the surfactant comprises any one or a combination of at least two of fatty alcohol polyoxyethylene ether, multi-branched alkyl polyoxyethylene ether, alkylphenol polyoxyethylene ether, alkyl polyoxypropylene ether, alkylphenol polyoxypropylene ether, polyethylene glycol, polypropylene glycol or alcohol ether phosphate, preferably any one or a combination of at least two of fatty alcohol polyoxyethylene ether, multi-branched alkyl polyoxyethylene ether or alkylphenol polyoxyethylene ether.

The galvanic effect usually occurs under the crack between the solder resist and the copper face. In the tin deposition process, when the gap of the crack is very small, the tin deposition liquid is limited to supply tin ions to the copper deposition liquid, but the copper can be corroded to copper ions, and then tin deposition reaction occurs on the copper surface outside the crack. The surfactant disclosed by the invention can control the galvanic effect in the tinning process, reduce the surface tension of the solution and improve the uniformity and compactness of a tin layer.

In the present invention, the multi-branched alkyl polyoxyethylene ether is a polyoxyethylene ether containing at least one branched alkyl group. The branched chain may be, for example, ethylhexyl, isodecyl, butyldodecyl, heptylundecyl, isoheptylundecyl, isoheptylisoundecyl, dodecylhexyl, octyldodecyl or the like.

As a preferred technical scheme of the invention, the surfactant is a combination of fatty alcohol-polyoxyethylene ether, multi-branched alkyl polyoxyethylene ether and alkylphenol polyoxyethylene ether. The three surfactants are matched with each other to have a synergistic effect, the galvanic effect can be further inhibited, the surface tension of the solution is reduced, hydrogen bubbles are more difficult to stay on the surface of a cathode, and dents and pinholes on a plating layer are well avoided, so that the dispersing capacity, the anti-foaming capacity and the displacement performance of the plating solution are further improved.

Preferably, the mass ratio of the fatty alcohol-polyoxyethylene ether to the multi-branched alkyl-polyoxyethylene ether to the alkylphenol polyoxyethylene ether in the surfactant is (1-5) to (2-4) to (3-5), and may be, for example, 1:2:3, 1:3:3, 1:4:3, 2:2:3, 2:3:3, 2:4:3, 3:2:3, 4:3:3, 4:4:3, 5:2:4, 5:2:5, 5:3:3, 5:3:4, and 5:3: 5.

Preferably, the fatty alcohol polyoxyethylene ether has an EO number of 3 to 9, and may be, for example, 3, 4, 5, 6, 7, 8 or 9.

Preferably, the fatty alcohol-polyoxyethylene ether comprises any one of isomeric dodecyl alcohol polyoxyethylene ether, isomeric pentadecyl alcohol polyoxyethylene ether or lauryl alcohol polyoxyethylene ether or a combination of at least two of isomeric dodecyl alcohol polyoxyethylene ether and lauryl alcohol polyoxyethylene ether.

Preferably, the multi-branched alkyl polyoxyethylene ether has an EO number of 5 to 10, and may be, for example, 5, 6, 7, 8, 9 or 10.

Preferably, the multi-branched alkyl polyoxyethylene ether comprises any one of polyoxyethylene octyl dodecyl ether, polyoxyethylene octyl tetradecyl ether, polyoxyethylene octyl hexadecyl ether, polyoxyethylene decyl tetradecyl ether or polyoxyethylene decyl hexadecyl ether or a combination of at least two of them.

Preferably, the alkylphenol ethoxylates have an EO number of 2 to 10, which may be, for example, 2, 3, 4, 5, 6, 7, 8, 9, 10.

Preferably, the alkylphenol ethoxylate comprises any one of nonylphenol ethoxylate, octylphenol ethoxylate, dodecylphenol ethoxylate or dinonylphenol ethoxylate or a combination of at least two thereof.

Preferably, the antioxidant comprises any one of or a combination of at least two of benzenediol, tert-butylhydroquinone, phosphite, ascorbic acid, dibutylhydroxytoluene, or uric acid.

Preferably, the noble metal comprises any one of silver, gold, iridium, rhodium, rhenium, osmium or palladium or a combination of at least two thereof.

In a second aspect, the invention provides a use of the copper-based metal surface immersion tin liquid in processing of printed circuit boards.

Preferably, the processing method of the printed circuit board specifically includes the following steps:

(1) pretreatment: carrying out oil removal treatment and microetching treatment on the printed circuit board;

(2) pre-dipping: placing the printed circuit board pretreated in the step (1) in the copper-based metal surface tin-dipping solution of the first aspect, and forming a tin-pre-dipping layer on the copper-based surface of the printed circuit board;

(3) tin immersion: and (3) placing the printed circuit board subjected to the pre-dipping treatment in the step (2) in the copper-based metal surface tin-dipping solution of the first aspect again, and depositing a tin-dipping tin-plating layer on the copper-based surface tin-dipping layer of the printed circuit board.

Preferably, the degreasing treatment in the step (1) is to soak the printed circuit board with an acidic degreasing liquid.

Preferably, the acidic deoiling liquid is a sulfuric acid solution.

Preferably, the temperature of the degreasing treatment in step (1) is 40-60 ℃, for example, 40 ℃, 42 ℃, 44 ℃, 46 ℃, 48 ℃, 50 ℃, 52 ℃, 54 ℃, 56 ℃, 58 ℃ and 60 ℃.

Preferably, the time of the degreasing treatment in the step (1) is 1-5min, for example, 1min, 2min, 3min, 4min, 5 min.

Preferably, the microetching treatment in the step (1) is to soak the printed circuit board by using a microetching solution.

Preferably, the microetching solution comprises any one or a combination of at least two of sodium persulfate, ammonium persulfate or a sulfuric acid solution of hydrogen peroxide.

Preferably, the microetching treatment in step (1) is performed at a temperature of 10-40 deg.C, for example, 10 deg.C, 12 deg.C, 14 deg.C, 16 deg.C, 18 deg.C, 20 deg.C, 22 deg.C, 24 deg.C, 26 deg.C, 28 deg.C, 30 deg.C, 32 deg.C, 34 deg.C, 36 deg.C, 38 deg.C, 40.

Preferably, the microetching treatment in step (1) is carried out for 1-5min, such as 1min, 2min, 3min, 4min and 5 min.

Preferably, the microetching treatment in the step (1) has a microetching amount of 0.5 to 2 μm, and may be, for example, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm.

Preferably, the presoaking time in step (2) is 1-5min, such as 1min, 2min, 3min, 4min, 5 min.

Preferably, the temperature of the pre-dipping in the step (2) is 20 to 30 ℃, for example, 20 ℃, 22 ℃, 24 ℃, 26 ℃, 28 ℃ and 30 ℃.

Preferably, the thickness of the tin prepreg layer in the step (2) is 0.1 to 0.3. mu.m, and may be, for example, 0.1. mu.m, 0.12. mu.m, 0.14. mu.m, 0.16. mu.m, 0.18. mu.m, 0.2. mu.m, 0.22. mu.m, 0.24. mu.m, 0.26. mu.m, 0.28. mu.m, or 0.3. mu.m.

Preferably, the time for dipping tin in step (3) is 15-30min, such as 15min, 16min, 18min, 20min, 22min, 24min, 26min, 28min, and 30 min.

Preferably, the tin immersion temperature in step (3) is 65-75 deg.C, such as 65 deg.C, 66 deg.C, 67 deg.C, 68 deg.C, 69 deg.C, 70 deg.C, 71 deg.C, 72 deg.C, 73 deg.C, 74 deg.C, 75 deg.C.

Preferably, the thickness of the tin-dipped tin coating in the step (3) is 0.5-1.5 μm, and may be, for example, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm.

Preferably, step (3) is followed by step (4) of washing: and (4) washing and drying the printed circuit board obtained after the step (3) is subjected to tin immersion.

Preferably, the temperature of the water washing is 40-60 ℃, for example, 40 ℃, 42 ℃, 44 ℃, 46 ℃, 48 ℃, 50 ℃, 52 ℃, 54 ℃, 56 ℃, 58 ℃, 60 ℃.

Preferably, the time of the water washing is 1-5min, for example, 1min, 2min, 3min, 4min, 5 min.

Preferably, the temperature of the drying is 40-80 deg.C, such as 40 deg.C, 45 deg.C, 50 deg.C, 55 deg.C, 60 deg.C, 65 deg.C, 70 deg.C, 75 deg.C, 80 deg.C.

Preferably, the drying time is 10-20min, such as 10min, 12min, 14min, 16min, 18min, 20 min.

Preferably, the processing method of the printed circuit board specifically comprises the following steps:

(1) pretreatment: soaking the printed circuit board with acid degreasing liquid at 40-60 deg.C for 1-5min for degreasing, soaking the printed circuit board with microetching liquid at 10-40 deg.C for 1-5min for microetching with microetching amount controlled at 0.5-2 μm;

(2) pre-dipping: placing the printed circuit board pretreated in the step (1) in the tin immersion liquid on the surface of the copper-based metal at the temperature of 20-30 ℃ for 1-5min to form a 0.1-0.3 mu m pre-immersion tin coating on the surface of the copper-based of the printed circuit board;

(3) tin immersion: placing the printed circuit board pre-soaked in the step (2) in the copper-based metal surface tin-soaking solution again for 15-30min at 65-75 ℃, and depositing a tin-soaking tin-plating layer with the thickness of 0.5-1.5 mu m on the copper-based surface pre-soaking tin-plating layer of the printed circuit board;

(4) cleaning: washing the printed circuit board obtained after the tin immersion in the step (3) for 1-5min at 40-60 ℃, and drying for 10-20min at 40-80 DEG C

Compared with the prior art, the invention has the following beneficial effects:

(1) the copper-based metal surface tin immersion liquid can effectively improve the activity and stability of the plating liquid, and simultaneously can ensure the long-time stability of the plating liquid, so that the plating speed is improved in the subsequent chemical plating, the formed chemical tin plating layer has high compactness and bright surface layer, and the problems of slow plating speed, loose plating layer and easiness in darkening of the existing chemical tin plating liquid are solved.

(2) The copper-based metal surface tin immersion liquid disclosed by the invention is simple in formula and easy to control, the thickness of a tin layer obtained by tin immersion is more than 1 mu m, the Javanni effect of a hole ring and a side etching position of a circuit board covered by green oil is less than 3 mu m, good weldability is kept after three times of reflow soldering, and the tin surface is not yellow.

Drawings

FIG. 1 is a scanning electron microscope spectrum of a tin-plated layer of a printed circuit board processed in example 1.

FIG. 2 is a spectrum of elemental analysis of a tin-plated layer of a printed circuit board processed in example 1.

Detailed Description

The technical solution of the present invention is further explained by the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.