Neutral tin plating solution and preparation method thereof

Abstract

The invention relates to a tin plating solution, in particular to a neutral tin plating solution for electroplating a terminal electrode of a micro component and a preparation method of the neutral tin plating solution. Methanesulfonic acid as a conductive salt; hydroquinone as an antioxidant; a divalent tin ion; and salts or chelates of hydroxycarboxylic acids and cyclic ester compounds thereof as complexing agents. Compared with the prior art, the method has the main advantages that the method is green and environment-friendly, the wastewater treatment process is simple, the tin plating solution has good dispersing capacity, a plating layer with the uniform thickness can be obtained on the surface of a workpiece, and the obtained plating layer is compact, uniform, small in grain size and free of pores.

Description

Technical Field

[0001] This invention relates to the field of electroplating, and more specifically to a neutral tin plating solution for electroplating the terminal electrodes of micro-components. Background Technology

[0002] Driven by emerging fields such as 5G communication, smart wearable devices, and automotive electronics, electronic components are rapidly developing towards miniaturization (01005 type and below) and high-density integration, which places higher demands on surface treatment technology. Traditional acidic tin plating systems have advantages in deposition rate, but problems such as equipment corrosion and coating performance fluctuations are becoming increasingly prominent. Especially for miniaturized components such as chip resistors and multilayer capacitors, strong acidic substances (such as sulfuric acid and hydrochloric acid) in the acidic plating solution can cause corrosion and dissolution of the components, leading to coating defects.

[0003] There are few existing neutral tin plating solutions, and most of them can only operate under weakly acidic conditions, failing to achieve a dense and uniform plating layer in a plating solution environment with a pH of 7.0±1.0. Miniature chip resistors, chip capacitors, and other components require electroplating at a pH of 7.0±1.0 to ensure normal function and a high yield rate. Therefore, developing a neutral tin plating solution is of great significance, ensuring that it does not corrode miniature components during the electroplating process while producing excellent plating results. Summary of the Invention

[0004] The purpose of this invention is to provide a neutral tin plating solution for electroplating the terminal electrodes of micro-components, which has good stability.

[0005] The objective of this invention is achieved as follows: a neutral tin plating solution for electroplating the terminal electrodes of micro-components, characterized in that: the neutral tin plating solution has a pH value of 7.0±1.0, and the neutral tin plating solution system includes: boric acid and ammonia water as buffers; methanesulfonic acid as a conductive salt; hydroquinone as an antioxidant; divalent tin ions; and hydroxycarboxylic acids and their cyclic ester salts or chelates as complexing agents, preferably gluconic acid, glucono-2-hydroxyl group, gluconolactone, gluconolactone or their salts, more preferably sodium gluconate, sodium gluconolactone, gluconolactone, or gluconolactone. Most preferably, gluconolactone.

[0006] The concentration of boric acid is 20-50 g / L.

[0007] The concentration of the ammonia solution is 70-150 mL / L.

[0008] The concentration of the methanesulfonic acid is 30-120 g / L.

[0009] The concentration of hydroquinone is 0.5-5 g / L.

[0010] The complexing agent can be used alone or in combination of two or more. In this embodiment, the concentration of the complexing agent in the neutral tin plating solution is generally 50 g / L to 250 g / L, and more preferably 80 to 150 g / L.

[0011] The concentration of divalent tin ions is 15~25 g / L.

[0012] The present invention also provides a method for preparing the above-mentioned neutral tin plating solution, comprising the following steps:

[0013] S1. Add a certain amount of deionized water to the plating tank, add methanesulfonic acid and hydroquinone under stirring, and stir evenly.

[0014] S2. Add a complexing agent to the above solution;

[0015] S3. Next, add divalent tin ions and stir until homogeneous;

[0016] S4. Finally, add boric acid and stir until homogeneous; while stirring, add ammonia to adjust the pH to 7.0±1.0.

[0017] The beneficial results of this invention are as follows:

[0018] (1) The neutral tin plating solution provided by the present invention can be completely degraded under natural conditions, is green and environmentally friendly, and has a simple wastewater treatment process, saving the cost of sewage treatment process.

[0019] (2) The neutral tin plating solution provided by the present invention has good dispersibility, which can reach 68.24%, and can obtain a uniform coating thickness on the surface of the workpiece.

[0020] (3) The neutral tin plating solution provided by the present invention can obtain a dense and uniform plating layer with small grains and no pores. Attached Figure Description

[0021] To further explain the beneficial effects of the neutral tin plating solution provided in this invention, corresponding drawings are provided.

[0022] Figure 1 The electroplating effect produced by the tin plating solution in Example 1 of this application is shown in the figure. The solution temperature is 20°C and the current density is 0.2 A / dm³. 2 The electroplating time was 5 minutes. The image is an SEM image of the upper surface of the coating, which shows the crystalline state of the coating. The grains are small, and the crystals are squeezed together with the boundaries tightly connected.

[0023] Figure 2 To illustrate the electroplating effect of the tin plating solution in Example 2 of this application, the solution temperature was 20°C and the current density was 0.2 A / dm³. 2The electroplating time was 5 minutes. The image is a SEM image of the upper surface of the coating, which shows the crystalline state of the coating. The grains are small and dense, with certain micro-undulation areas and no pores on the surface.

[0024] Figure 3 The electroplating effect produced by the tin plating solution in Example 3 of this application is shown in the figure. The solution temperature is 20°C and the current density is 0.2 A / dm³. 2 The electroplating time was 5 minutes. The image is an SEM image of the upper surface of the coating, which shows the crystalline state of the coating. The grains are small, and the crystals are uniformly blocky with dense and fine grains.

[0025] Figure 4 To demonstrate the electroplating effect of the tin plating solution in Comparative Example 1 of this application, the solution temperature was 20°C and the current density was 0.2 A / dm³. 2 The electroplating time was 5 minutes. The image is an SEM image of the upper surface of the coating, which shows the crystalline state of the coating. The grain size is irregular, and there are many gaps and pores between the crystals.

[0026] Figure 5 To demonstrate the electroplating effect of the tin plating solution in Comparative Example 2 of this application, the solution temperature was 20°C and the current density was 0.2 A / dm³. 2 The electroplating time was 5 minutes. The image is an SEM image of the upper surface of the coating, which shows the crystalline state of the coating. The grains exhibit a laterally growing network, with gaps between the crystals and numerous pores. Detailed Implementation

[0027] This invention relates to a neutral tin plating solution for electroplating the terminal electrodes of micro-components. The neutral tin plating solution has a pH value of 7.0 ± 1.0. This neutral tin plating solution system comprises:

[0028] Boric acid, used as a buffer solution, is preferably at a concentration of 20-50 g / L, and ammonia water is preferably at a concentration of 70-150 mL / L. Methylsulfonic acid, used as a conductive salt, is preferably at a concentration of 30-120 g / L. Hydroquinone, used as an antioxidant, is preferably at a concentration of 0.5-5 g / L. At least one of HEDP, tetrasodium EDTA, sodium citrate, gluconolactone, and sodium gluconate, used as a complexing agent, is a green complexing agent with low environmental pollution and low irritation to the human body; its preferred concentration is 70-150 g / L. Divalent tin ions, used as the main salt, are added via a 70% stannous methanesulfonate solution; the preferred concentration is 15-25 g / L. The preparation method steps are as follows:

[0029] S1. Add a certain amount of deionized water to the plating tank, add methanesulfonic acid and hydroquinone under stirring, and stir evenly.

[0030] S2. Add a complexing agent to the above solution;

[0031] S3. Next, add divalent tin ions and stir until homogeneous;

[0032] S4. Finally, add boric acid and stir until homogeneous; while stirring, add ammonia to adjust the pH to 7.0±1.0.

[0033] Example 1

[0034] Prepare a 1L neutral tin plating solution by mixing 20g boric acid, 70g methanesulfonic acid, 5g hydroquinone, 90g sodium gluconate, 15g divalent tin ions, and the remainder being water. Adjust the pH to 6 with ammonia.

[0035] Example 2

[0036] Prepare a 1L neutral tin plating solution by mixing 30g boric acid, 50g methanesulfonic acid, 0.5g hydroquinone, 80g gluconic acid, 22g divalent tin ions, and the remainder being water. Adjust the pH to 7 with ammonia.

[0037] Example 3

[0038] Prepare a 1L neutral tin plating solution by mixing 36g boric acid, 90g methanesulfonic acid, 2g hydroquinone, 100g gluconolactone, 20g divalent tin ions, and the remainder being water. Adjust the pH to 6.5 with ammonia.

[0039] Comparative Example 1

[0040] Prepare a 1L neutral tin plating solution by mixing 36g boric acid, 90g methanesulfonic acid, 2g hydroquinone, 90g citric acid, 20g divalent tin ions, and the remainder being water. Adjust the pH to 6.5 with ammonia.

[0041] Comparative Example 2

[0042] Prepare a 1L neutral tin plating solution by mixing 36g boric acid, 90g methanesulfonic acid, 2g hydroquinone, 90g hydroxyethylidene diphosphonic acid, 20g divalent tin ions, and the remainder being water. Adjust the pH to 6.5 with ammonia.

[0043] The dispersing ability of a plating solution refers to its ability to uniformly distribute the plating thickness on the workpiece surface. To evaluate the dispersing performance of the plating solution described in this invention, the near-far cathode method is used for testing. This method effectively reflects the ability of the plating solution to form a uniform plating layer on the electrode surface at different locations. Two identical brass sheets are placed in a Haring tank as cathodes, designated as the near-cathode and the far-cathode. The distance between the near-cathode and the anode is L, and the distance between the far-cathode and the anode is 2L, i.e., the electrode spacing ratio K=2. During the test, a constant current of 0.5 A / dm is applied under normal temperature conditions. 2Electroplating was performed for 5 minutes. After electroplating, the cathode sample was removed and dried, and the deposition mass M1 in the near-cathode region and the deposition mass M2 in the far-cathode region were weighed. The dispersion coefficient T of the plating solution was calculated according to the following formula (1):

[0044] (1)

[0045] Where T represents the dispersion coefficient, K represents the ratio of the distance between the near and far cathodes and the anode (K=2), M1 is the deposition mass near the cathode, and M2 is the deposition mass far from the cathode. The closer the dispersion coefficient T is to 100%, the better the dispersion performance of the plating solution, and the more uniform the thickness of the coating can be obtained at different positions of the cathode.

[0046] Table 1. Examples and Plating Solution Performance Test Results serial number Dispersion capability Example 1 64.38% Example 2 61.78% Example 3 68.24% Comparative Example 1 42.85% Comparative Example 2 52.95%

Claims

1. A neutral tin plating solution for electroplating terminal electrodes of micro-components, characterized in that: The neutral tin plating solution has a pH of 7.0±1.0 and includes: boric acid and ammonia as buffers; methanesulfonic acid as a conductive salt; hydroquinone as an antioxidant; divalent tin ions; and salts or chelates of hydroxycarboxylic acids and their cyclic ester compounds as complexing agents.

2. The neutral tin plating solution for electroplating terminal electrodes of micro-components according to claim 1, characterized in that: The concentration of boric acid is 20-50 g / L.

3. The neutral tin plating solution for electroplating terminal electrodes of micro-components according to claim 1, characterized in that: The concentration of the methanesulfonic acid is 30-120 g / L.

4. The neutral tin plating solution for electroplating terminal electrodes of micro-components according to claim 1, characterized in that: The concentration of hydroquinone is 0.5-5 g / L.

5. The neutral tin plating solution for electroplating terminal electrodes of micro-components according to claim 1, characterized in that: The concentration of divalent tin ions is 15-25 g / L.

6. The neutral tin plating solution for electroplating terminal electrodes of micro-components according to claim 1, characterized in that: The complexing agent includes at least one of sodium gluconate, sodium gluconate, gluconolactone, or gluconolactone.

7. The neutral tin plating solution for electroplating terminal electrodes of micro-components according to claim 6, characterized in that: The concentration of the complexing agent is 80~150g / L.

8. A method for preparing a neutral tin plating solution for electroplating terminal electrodes of micro-components as described in any one of claims 1-7, characterized in that, Includes the following steps: S1. Add a certain amount of deionized water to the plating tank, add methanesulfonic acid and hydroquinone under stirring, and stir evenly. S2. Add a complexing agent to the above solution; S3. Next, add divalent tin ions and stir until homogeneous; S4. Finally, add boric acid and stir until homogeneous; while stirring, add ammonia to adjust the pH to 7.0±1.0.

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