CN101724834A - Continuously self-catalyzed deposition chemical plating solution of tin and using method thereof - Google Patents

Abstract

The invention discloses a tin continuous self-catalyzed deposition electroless plating solution and its application method, which can obtain a semi-bright, silver-white tin-copper alloy deposition layer on pure copper and copper alloy substrates. The electroless plating solution uses stannous chloride as the main salt, thiourea as the main complexing agent, trisodium citrate as the auxiliary complexing agent, sodium hypophosphite as the reducing agent, disodium edetate as the antioxidant, and hydrochloric acid as the Stabilizer, gelatin as leveling agent, benzaldehyde as auxiliary brightener. The operating conditions are: the pH value of the plating solution is 0.8~2.0, the temperature is 80~90°C, the loading volume is 0.8~1.5dm ² /L, and the mechanical stirring speed is 50~100rpm. The invention has the following advantages: semi-bright-silver-white tin-copper alloy coatings of different thicknesses can be obtained by controlling the chemical plating time, the deposition rate is fast, the crystal grains are obviously refined, the surface flatness of the coating is improved, and the stability of batch production is high ; The interface is firmly bonded, and the coating has a strong ability to resist changes after passivation treatment. It has broad application prospects in products such as deep hole parts, blind hole parts and difficult-to-handle small electronic components and PCB printed circuit boards.

Description

A kind of continuous autocatalytic deposition electroless plating solution of tin and its application method

technical field

The invention relates to the technical field of chemical plating, in particular to the continuous self-catalyzed deposition chemical tin plating technology of tin.

Background technique

Tin coating is a coating with good solderability and certain corrosion resistance, which is widely used in electronic components and printed circuit boards. At the same time, tin is stable to organic acids and tin compounds are harmless to the human body, and are also widely used in the food industry. The tin coating can be prepared by electroplating, immersion plating and electroless plating. Immersion tin plating is easy to operate and low in cost, but the thickness of the coating is limited, generally only 0.5 μm, and the plating solution is easily poisoned, which cannot meet industrial requirements. Electrolytic tin plating cannot process deep-hole parts, blind-hole parts and small electronic components that are difficult to handle; the electroless tin plating layer has uniform thickness, good dispersion ability of plating solution, high production efficiency, easy operation control, smooth and smooth surface of the coating, dense crystallization, and pores The rate is low, and the binding force is better than immersion tin and electroplating tin. It is an ideal electroless plating technology for processing complex small electronic components. However, due to the high hydrogen evolution potential and low catalytic activity of tin, if formaldehyde, sodium hypophosphite, borohydride and other reducing agents are used alone, continuous autocatalytic deposition of tin cannot be achieved, and thick coatings cannot be obtained. Electroless tin plating with strong reducing agents, such as Ti ³⁺ , V ²⁺ , and Cr ²⁺ , has not been applied industrially due to low deposition rate, poor stability, unsatisfactory repeatability, and high price. At present, the continuous autocatalytic deposition of tin is basically still in the stage of laboratory research at home and abroad.

Contents of the invention

The present invention aims at the above-mentioned deficiencies in the prior art, and provides a new electroless plating solution for continuous self-catalytic deposition of tin and its application method. The invention has the advantages of realizing continuous self-catalytic deposition of tin on the copper and copper alloy substrate, fast deposition rate, and being able to obtain a silver-white-semi-bright tin-copper alloy electroless plating layer. The formula of the plating solution is simple, easy to control, wide range of process parameters, fine crystallization of the coating, semi-bright, silvery white appearance, stable plating solution, long service life, high production stability, suitable for deep hole parts, blind hole parts and small difficult-to-handle It has a wide application prospect in electronic components and PCB printed circuit boards. It is an excellent green and environmentally friendly new technology for electronic products. It is also an ideal material coating to replace the Pb-Sn alloy coating. It meets the global lead-free trend of development.

The continuous autocatalytic deposition chemical plating solution of tin of the present invention and the feature of using method thereof are:

In the continuous autocatalytic deposition chemical plating solution of tin of the present invention, tin protochloride is used as the main salt, and the addition amount is 15 to 30 g/L, and the deposition rate and the mass percentage of tin in the coating reach the highest when 20 g/L value; using thiourea as the main complexing agent, the addition amount is 60-120g/L, the deposition rate and the mass percentage of tin in the coating reach the highest value at 90g/L; trisodium citrate is used as the auxiliary complexing agent , the addition amount is 15~30g/L; sodium hypophosphite is used as the reducing agent, the addition amount is 40~100g/L, the deposition rate and the percentage of tin in the coating reach the highest value at 90g/L.

In the continuous autocatalytic deposition chemical plating solution of tin of the present invention, disodium edetate is adopted as the Sn ²⁺ antioxidant in the plating solution, and the addition amount is 3～5g/L, and the deposition rate and the quality of tin in the plating layer The content reaches the highest value at 3g/L; hydrochloric acid is used as a stabilizer to prevent the oxidation of Sn ²⁺ in the plating solution, and the addition amount is 35-65ml/L;

In the continuous autocatalytic deposition chemical plating solution of tin of the present invention, gelatin is adopted as a leveling agent, which can play an obvious leveling effect after adding gelatin, and the addition amount of gelatin is 0.2～1.0g/L; The addition of benzaldehyde can expand the scope of the bright area of the coating, and the effect of grain refinement is obvious. Toughness and brazeability of the coating.

The continuous autocatalytic deposition electroless tin plating solution of the present invention is characterized in that: the prepared electroless tin plating solution can precipitate white flocculent substances at room temperature. After the temperature of the plating solution rises to 65°C, the white flocculent substance redissolves, allowing repeated electroless tin plating.

In the method for using the electroless plating solution for continuous self-catalytic deposition of tin of the present invention, the pH value of the plating solution is controlled at 0.8-2.0. When the pH value is low, the surface of the coating is rough and black, and the surface quality is poor. When the pH value is high, the hydrolysis of Sn ²⁺ is intensified, and Sn(OH) ₂ colloids are produced in the plating solution, and the stability is reduced.

In the method for using the electroless plating solution for continuous self-catalytic deposition of tin of the present invention, the temperature of the plating solution is constantly controlled at 80-90°C. The bath temperature is too low and the deposition rate is slow. The temperature of the plating solution is too high, and the evaporation of the plating solution is large.

In the use method of the continuous self-catalytic deposition chemical plating solution of tin of the present invention, it is characterized in that: the plating solution is suitable for carrying out chemical tin plating on the surface of pure copper and copper alloy substrates, can successfully realize the continuous self-catalytic deposition of tin, and obtain different Thick silver-white-semi-bright tin-copper alloy plating.

In the use method of the continuous self-catalytic deposition chemical plating solution of tin of the present invention, it is characterized in that: the electroless tin plating on the copper substrate is divided into three stages of copper-tin replacement reaction period, copper-tin co-deposition period and tin self-catalytic deposition period , the entire plating process realizes the self-catalytic deposition of tin, and the thickness of the coating is controlled by changing the electroless plating time.

The preparation method of the continuous self-catalytic deposition electroless plating solution of a kind of tin of the present invention is: 1. ethylenediaminetetraacetic acid disodium is dissolved with distilled water, forms A liquid; 2. add stannous chloride in hydrochloric acid, stir to make 3. Add liquid B to liquid A under stirring to form liquid C; 4. Dissolve thiourea with distilled water and add it to liquid C while stirring to form liquid D; 5. Dissolve citric acid with distilled water Add trisodium to liquid D under stirring to form liquid E; 6. Dissolve gelatin with distilled water to a transparent solution, filter and add to liquid E; 7). Add benzaldehyde to liquid E; 8. Adjust E with hydrochloric acid or ammonia water The pH value of the solution was fixed to volume and filtered to obtain the electroless tin plating solution.

Compared with prior art, the present invention has following advantage or positive effect:

1. The continuous self-catalytic deposition of tin is realized on the copper base, the deposition speed is fast, and silver-white-semi-bright tin-copper alloy electroless coatings with different thicknesses can be obtained;

2. The addition of gelatin and benzaldehyde in the electroless plating solution can significantly refine the grains, improve the surface flatness of the coating, and reduce the porosity;

3. The formula of the plating solution is simple, easy to control, and the range of process parameters is wide;

4. The bath is stable, the service life is long, and the stability of batch production is high. Based on the deposition thickness of 3~5μm, the plating area of 1L electroless tin plating solution is 12~13dm ² ;

5. The electroless coating is semi-bright and silvery white, and when the thickness is 5~7μm, it can meet the brazing requirements;

6. The chemical plating layer and the copper substrate are firmly combined without peeling, peeling and peeling;

7. After passivation treatment, the electroless coating has strong resistance to change;

8. The plating solution has strong throwing and deep plating capabilities, and has a broad application prospect in the surface strengthening treatment of deep-hole parts, blind-hole parts, and some difficult-to-handle small electronic components and PCB printed circuit boards.

Detailed ways

The present invention will be further described below with embodiment. But they do not constitute a limitation of the present invention.

Example 1:

The formula of electroless tin plating solution is:

Stannous chloride 30g/L

Hydrochloric acid 40ml/L

Disodium EDTA 5g/L

Thiourea 120g/L

Trisodium citrate 30g/L

Sodium hypophosphite 100g/L

Gelatin 0.5g/L

Benzaldehyde 1.0ml/L

The technological conditions of the electroless tin plating solution are: the temperature of the plating solution is 88±2°C, the pH value is 2.0, the electroless plating time is 3 hours, and the loading amount of the plating solution is 1.2dm ² /L.

The electroless plating layer obtained in Example 1 has a thickness of 31.4 μm, a silvery-white-semi-bright appearance, a tin content of 95.8 wt%, and a porosity of less than 4 pieces/6cm ² . In a tin-lead alloy in which the flux is 25% rosin isopropanol and the solder is 60% tin + 40% lead, the wetting time is less than 2s, and the solderability is good. After passivation treatment, the appearance and color of the coating will not change after being placed in the air for 3 months. The passivation process is: K ₂ Cr ₂ O ₇ 2H ₂ O: 15g/L, KOH: 5~8g/L, (NH ₄ ) ₆ Mo ₇ O ₂₄ 4H ₂ O: 15~18g/L, T: Room temperature, time: 10-15 minutes.

Example 2:

The formula of electroless tin plating solution is:

Stannous chloride 20g/L

Hydrochloric acid 50ml/L

Disodium EDTA 3g/L

Thiourea 100g/L

Citric acid 20g/L

Trisodium hypophosphite 80g/L

Gelatin 0.3g/L

Benzaldehyde 1.0ml/L

The technological conditions of the electroless tin plating solution are: the temperature of the plating solution is 88±2°C, the pH value is 1.5, the electroless plating time is 3 hours, and the loading amount of the plating solution is 1.2dm ² /L.

The thickness of the electroless plating layer obtained in Example 2 is 25.5 μm, the appearance is silver-white-semi-bright, the tin content is 93.6 wt%, and the porosity is lower than 4/6cm ² . In a tin-lead alloy in which the flux is 25% rosin isopropanol and the solder is 60% tin + 40% lead, the wetting time is less than 2s, and the solderability is good. After passivation treatment, the appearance and color of the coating remain unchanged after being placed in the air for 3 months.

Example 3:

The formula of electroless tin plating solution is:

Stannous chloride 15g/L

Hydrochloric acid 60ml/L

Disodium EDTA 3g/L

Thiourea 80g/L

Citric acid 15g/L

Trisodium hypophosphite 80g/L

Gelatin 0.3g/L

Benzaldehyde 0.5ml/L

The technological conditions of the electroless tin plating solution are: the temperature of the plating solution is 88±2°C, the pH value is 1.0, the electroless plating time is 3 hours, and the loading amount of the plating solution is 1.2dm ² /L.

The electroless coating obtained in Example 3 has a thickness of 21.2 μm, a silvery white appearance, a tin content of 92.8 wt%, and a porosity of less than 4 pieces/6cm ² . In a tin-lead alloy in which the flux is 25% rosin isopropanol and the solder is 60% tin + 40% lead, the wetting time is less than 2s, and the solderability is good. After passivation treatment, after 3 months in the air, the appearance and color of the electroless tin plating layer have no change.

Example 4:

The formulation of the electroless tin plating solution is the same as that of Example 1, and the process conditions are basically the same as that of Example 1, except that the loading of the electroless plating solution is 1.5 dm ² /L. The thickness of the obtained electroless plating layer was 26.9 μm, and other properties were basically the same as those in Example 1.

Example 5:

The formulation of the electroless tin plating solution is the same as that of Example 2, and the process conditions are basically the same as that of Example 2, except that the loading of the electroless tin plating solution is 0.8dm ² /L. The thickness of the obtained electroless plating layer was 30.8 μm, and other properties were basically the same as those in Example 2.

Claims (6)

1. a continuous self-catalytic deposition chemical plating solution of tin, is characterized in that: chemical plating solution is the self-catalytic deposition system of acidic chloride electroless tin plating, takes tin protochloride as main salt, and addition is 15～30g/ L; use thiourea as the main complexing agent, the addition amount is 60~120g/L; use trisodium citrate as the auxiliary complexing agent, the addition amount is 15~30g/L; use sodium hypophosphite as the reducing agent, the addition amount 40~100g/L; disodium ethylenediaminetetraacetic acid is used as an antioxidant, and the addition amount is 0.2~1.0g/L; hydrochloric acid is used as a stabilizer, and the addition amount is 35~65ml/L; gelatin is added to the chemical plating solution , the addition amount is 0.2~1.0g/L; benzaldehyde is used as the auxiliary brightener, the addition amount is 0.5~2.0mL/L; hydrochloric acid or ammonia water is used as the pH value regulator of the plating solution. 2. a kind of preparation method of the continuous self-catalytic deposition electroless plating solution of tin, it is characterized in that containing following steps: (1) disodium edetate is dissolved with distilled water, forms A liquid; (2) in hydrochloric acid, add Stin protochloride, stir to make it dissolve and form B liquid; (3) add B liquid in A liquid under stirring, form C liquid; (4) dissolve thiourea with distilled water, add in C liquid under stirring, form D (5) Dissolve trisodium citrate with distilled water, and add it to liquid D under stirring to form liquid E; (6) Dissolve gelatin in distilled water to a transparent solution, filter and add to liquid E; (7) Add benzaldehyde to In liquid E; (8) adjust the pH value of liquid E with hydrochloric acid or ammonia water, constant volume, and filter to obtain an electroless tin plating liquid. 3. the preparation method of the continuous autocatalytic deposition electroless plating solution of a kind of tin according to claim 2, is characterized in that: the addition of described stannous chloride is 15～30g/L, the addition of thiourea The added amount of trisodium citrate is 15~30g/L, the added amount of sodium hypophosphite is 40~100g/L, and the added amount of disodium edetate is 3~5g/L L, the added amount of hydrochloric acid is 35~65ml/L, the added amount of gelatin is 0.2~1.0g/L, and the added amount of benzaldehyde is 0.5~2.0mL/L. 4. a kind of continuous self-catalyzed deposition electroless plating method of tin, it is characterized in that: electroless plating solution is the self-catalyzed deposition system of acidic chloride electroless tin plating, with tin protochloride as main salt, addition is 15 ~30g/L; with thiourea as the main complexing agent, the addition amount is 60~120g/L; with trisodium citrate as the auxiliary complexing agent, the addition amount is 15~30g/L; with sodium hypophosphite as the reducing agent , the addition amount is 40~100g/L; disodium edetate is used as antioxidant, the addition amount is 0.2~1.0g/L; hydrochloric acid is used as stabilizer, the addition amount is 35~65ml/L; chemical plating solution Add gelatin in the medium, the addition amount is 0.2~1.0g/L; use benzaldehyde as the auxiliary brightener, the addition amount is 0.5~2.0mL/L; use hydrochloric acid or ammonia water as the pH value regulator of the plating solution, the operating conditions are: plating solution The pH value is 0.8~2.0, the temperature is 80~90°C, the loading volume is 0.8~1.5dm ² /L, and the mechanical stirring speed is 50~100rpm. 5. the using method of the continuous self-catalytic deposition electroless plating solution of a kind of tin according to claim 4, is characterized in that: the electroless tin plating solution of preparation can separate out white flocculent substance at room temperature, when plating solution in production process After the temperature rises to 65°C, the white flocculent substance redissolves, and the electroless tin plating process can be repeated. 6. the using method of the continuous autocatalytic deposition electroless plating solution of a kind of tin according to claim 4, is characterized in that: at pure copper and copper alloy substrate surface electroless tin plating, obtains the semi-bright-silver white of different thicknesses Tin-copper alloy plating.