High-stability electroplating solution based on ultrapure cobaltous sulfate as well as preparation method and application of high-stability electroplating solution

Abstract

The invention discloses a high-stability electroplating solution based on ultrapure cobaltous sulfate, a preparation method and application, and the high-stability electroplating solution comprises the following raw materials: 200-300g / L of ultrapure cobaltous sulfate which meets the requirement that the total amount of impurities is less than 10ppm; 30-50 g / L of ultrapure boric acid; 5-10 g / L of a complexing agent; 0.1 g / L to 0.5 g / L of a brightening agent; and the pH is regulated to 3.5-4.5 by using a pH regulator. By optimizing the composition formula of the electroplating liquid, the technical scheme of ultralow impurity content is realized, so that the binding force, porosity and the like of a plating layer are remarkably improved, and the corrosion resistance is greatly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of electroplating, and particularly relates to a highly stable electroplating solution based on ultrapure cobalt sulfate, a preparation method and an application thereof. Background Art

[0002] Traditional cobalt sulfate electroplating solutions contain metal impurities (such as Fe, Ni, Cu), organic impurities and insoluble substances, resulting in high porosity and large internal stress of the coating, which affect the electrical conductivity and corrosion resistance of electronic components. Conventional purification processes (such as activated carbon adsorption, chemical precipitation) are difficult to increase the purity of cobalt sulfate to more than 99.99%, and are prone to introducing secondary pollution.

[0003] Therefore, in view of the above technical problems, it is necessary to provide a highly stable electroplating solution based on ultrapure cobalt sulfate, a preparation method and an application thereof.

[0004] The information disclosed in this background art section is only for enhancing the understanding of the overall background of the present invention and should not be taken as an admission or any form of suggestion that this information constitutes prior art already known to those of ordinary skill in the art. Summary of the Invention

[0005] The purpose of the present invention is to provide a highly stable electroplating solution based on ultrapure cobalt sulfate, a preparation method and an application thereof.

[0006] In order to achieve the above purpose, the technical solution provided by a specific embodiment of the present invention is as follows:

[0007] The highly stable electroplating solution based on ultrapure cobalt sulfate has the following raw material composition:

[0008] Ultrapure cobalt sulfate 200 - 300 g / L, with the total impurity content < 10 ppm;

[0009] Ultrapure boric acid 30 - 50 g / L;

[0010] Complexing agent 5 - 10 g / L;

[0011] Brightening agent 0.1 - 0.5 g / L;

[0012] And adjusted to pH 3.5 - 4.5 with a pH regulator.

[0013] In one or more embodiments of the present invention, the complexing agent is selected from: sodium citrate.

[0014] In one or more embodiments of the present invention, the brightening agent is selected from: sodium saccharin.

[0015] In one or more embodiments of the present invention, the pH regulator is selected from ultrapure sulfuric acid. Preferably, its purity ≥ 99.999%. Preferably, the purity of ultrapure boric acid ≥ 99.999%.

[0016] In one or more embodiments of the present invention, the raw materials further include rare earth elements, and the dosage thereof is 0.5 - 2 mg / L.

[0017] In one or more embodiments of the present invention, the rare earth element is selected from Y.

[0018] In one or more embodiments of the present invention, a method for preparing a highly stable electroplating solution is characterized by comprising: preparing raw materials, dissolving them in water, and then filtering to obtain the solution. The preparation of ultrapure cobalt sulfate is as follows: industrial-grade cobalt sulfate is chelated by an ion exchange resin, then subjected to gradient crystallization and vacuum sublimation. The cooling rate of the solution during the gradient crystallization is 0.3 - 0.5 °C / min.

[0019] In one or more embodiments of the present invention, the conditions for vacuum sublimation are: 10⁻³ Pa and 200 °C.

[0020] In one or more embodiments of the present invention, the filtration is carried out using a PTFE filter membrane with a pore size of 0.1 μm.

[0021] In one or more embodiments of the present invention, the application of the highly stable electroplating solution in the coating of precision electronic devices. The coating of precision electronic devices includes but is not limited to cobalt plating in PCB through-holes, electromagnetic shielding layers of MEMS devices, etc.

[0022] Compared with the prior art, the highly stable electroplating solution based on ultrapure cobalt sulfate, its preparation method and application of the present invention achieve a technical solution with ultra-low impurity content by optimizing the composition formula of the electroplating solution, thereby significantly improving the coating adhesion, porosity, etc., and greatly enhancing the corrosion resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments recorded in the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0024] Figure 1 It is a SEM comparison diagram of the coating before and after the introduction of Y in Example 10 of the present invention, where the left figure is before the introduction and the right figure is after the introduction;

[0025] Figure 2 It is a SEM comparison diagram of the coating before and after the introduction of Y in Example 11 of the present invention, where the left figure is before the introduction and the right figure is after the introduction;

[0026] Figure 3This is the SEM comparison diagram of the coating before and after the introduction of Y in Example 12 of the present invention. The left figure is before the introduction, and the right figure is after the introduction. Detailed implementation mode

[0027] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0028] In the high-stability electroplating solution based on ultrapure cobalt sulfate of the present invention, ultrapure cobalt sulfate is obtained as a raw material of the electrolyte through the following method. The preparation of ultrapure cobalt sulfate is as follows:

[0029] Raw material pretreatment: Industrial-grade cobalt sulfate is passed through an ion exchange resin to remove impurity ions such as Ca 2 + and Mg2+; then gradient crystallization is carried out: controlling the cooling rate (0.5 °C / min) to obtain high-purity crystals; then vacuum sublimation is carried out: further purification is carried out at 10-3 Pa and 200 °C. Preferably, the gradient crystallization temperature is 60 °C - 30 °C.

[0030] The electroplating solution is configured as follows: 200 - 300 g / L of ultrapure cobalt sulfate; 30 - 50 g / L of ultrapure boric acid; 5 - 10 g / L of complexing agent; 0.1 - 0.5 g / L of brightener; the pH regulator adjusts the solution to pH 3.5 - 4.5. The electroplated silver obtained by configuration is treated with bipolar membrane electrodialysis technology to remove Cl- impurities, so that the Cl- content < 1 ppm. Before electroplating, a dynamic filtration system (0.1 μm pore size PTFE filter membrane) can also be used to remove particulate matter in real time.

[0031] In order to improve the coating quality, rare earth elements (such as Y3+) 0.5 - 2 mg / L can also be added to the above electroplating solution to refine the coating grains and increase the coating hardness by about 20%.

[0032] The detection standard for the coating adhesion: GB / T 5270 - 2005; the detection standard for the porosity: GB / T 43102 - 2023.

[0033] Example 1:

[0034] In this example, 1 kg of industrial cobalt sulfate (purity 99%) was taken and dissolved in 5 L of ultrapure water (18.2 MΩ·cm); it was passed through a chelating resin column (DTPA type) with a flow rate of 2 BV / h, and the liquid phase was collected; then gradient crystallization was carried out, controlling the cooling rate at 0.5 °C / min to obtain high-purity crystals; then the high-purity crystals were subjected to vacuum sublimation at 10-3 Pa and 200 °C, and the sublimation product was collected to obtain ultrapure cobalt sulfate. After detection by ICP-MS, the total amount of impurities < 10 ppm.

[0035] According to the formula, 200 g / L of ultrapure cobalt sulfate; 30 g / L of ultrapure boric acid; 5 g / L of complexing agent sodium citrate; 0.1 g / L of brightening agent saccharin sodium were used to prepare the electroplating solution with deionized water as the solvent; and the pH of the electroplating solution was adjusted to pH 3.5 with ultrapure sulfuric acid. Then, a dynamic filtration system (0.1 μm pore size PTFE membrane) was used to plate on the copper substrate (current density 2 A / dm 2 , temperature 50 °C), to obtain a coating with a thickness of 5 μm and a surface roughness Ra < 0.05 μm. The coating adhesion (cross-cut method) was grade 4B; the porosity (test with potassium ferricyanide) ≤ 14 pieces / cm 2 ; there was no corrosion in an 85 °C / 85% RH environment for 800 hours.

[0036] Example 2:

[0037] In this example, 1 kg of industrial cobalt sulfate (purity 99%) was taken and dissolved in 5 L of ultrapure water (18.2 MΩ·cm); it was passed through a chelating resin column (DTPA type) with a flow rate of 2 BV / h, and the liquid phase was collected; then gradient crystallization was carried out, controlling the cooling rate at 0.5 °C / min to obtain high-purity crystals; then the high-purity crystals were subjected to vacuum sublimation at 10-3 Pa and 200 °C, and the sublimation product was collected to obtain ultrapure cobalt sulfate. After detection by ICP-MS, the total amount of impurities < 10 ppm.

[0038] According to the formula, 250 g / L of ultrapure cobalt sulfate; 30 g / L of ultrapure boric acid; 5 g / L of complexing agent sodium citrate; 0.1 g / L of brightening agent saccharin sodium were used to prepare the electroplating solution with deionized water as the solvent; and the pH of the electroplating solution was adjusted to pH 3.5 with ultrapure sulfuric acid. Then, a dynamic filtration system (0.1 μm pore size PTFE membrane) was used to plate on the copper substrate (current density 2 A / dm 2 , temperature 50 °C), to obtain a coating with a thickness of 5 μm and a surface roughness Ra < 0.05 μm. The coating adhesion (cross-cut method) was grade 4B; the porosity (test with potassium ferricyanide) ≤ 13 pieces / cm 2 ; there was no corrosion in an 85 °C / 85% RH environment for 830 hours.

[0039] Example 3:

[0040] In this example, 1 kg of industrial cobalt sulfate (purity 99%) was taken and dissolved in 5 L of ultrapure water (18.2 MΩ·cm); it passed through a chelating resin column (DTPA type) with a flow rate of 2 BV / h, and the liquid phase was collected; then gradient crystallization was carried out, controlling the cooling rate at 0.5 °C / min to obtain high-purity crystals; then the high-purity crystals were subjected to vacuum sublimation at 10-3 Pa and 200 °C, and the sublimation product was collected to obtain ultrapure cobalt sulfate. After detection by ICP-MS, the total amount of impurities < 10 ppm.

[0041] According to the formula, 300 g / L of ultrapure cobalt sulfate; 30 g / L of ultrapure boric acid; 5 g / L of complexing agent sodium citrate; 0.1 g / L of brightening agent saccharin sodium were used to prepare the electroplating solution with deionized water as the solvent; and the pH of the electroplating solution was adjusted to pH 3.5 with ultrapure sulfuric acid. Then, a dynamic filtration system (PTFE membrane with a pore size of 0.1 μm) was used to electroplate on the copper substrate (current density 2 A / dm 2 , temperature 50 °C), and a coating with a thickness of 5 μm and a surface roughness Ra < 0.05 μm was obtained. The coating adhesion (cross-cut method) was grade 4B; the porosity (test with potassium ferricyanide) ≤ 11 per cm 2 ; there was no corrosion in an 85 °C / 85% RH environment for 840 hours.

[0042] Example 4:

[0043] In this example, 1 kg of industrial cobalt sulfate (purity 99%) was taken and dissolved in 5 L of ultrapure water (18.2 MΩ·cm); it passed through a chelating resin column (DTPA type) with a flow rate of 2 BV / h, and the liquid phase was collected; then gradient crystallization was carried out, controlling the cooling rate at 0.5 °C / min to obtain high-purity crystals; then the high-purity crystals were subjected to vacuum sublimation at 10-3 Pa and 200 °C, and the sublimation product was collected to obtain ultrapure cobalt sulfate. After detection by ICP-MS, the total amount of impurities < 10 ppm.

[0044] According to the formula, 250 g / L of ultrapure cobalt sulfate; 40 g / L of ultrapure boric acid; 8 g / L of complexing agent sodium citrate; 0.3 g / L of brightening agent saccharin sodium were used to prepare the electroplating solution with deionized water as the solvent; and the pH of the electroplating solution was adjusted to 4 with ultrapure sulfuric acid. Then, a dynamic filtration system (PTFE membrane with a pore size of 0.1 μm) was used to electroplate on the copper substrate (current density 2 A / dm 2 , temperature 50 °C), and a coating with a thickness of 5 μm and a surface roughness Ra < 0.05 μm was obtained. The coating adhesion (cross-cut method) was grade 4B; the porosity (test with potassium ferricyanide) ≤ 12 per cm 2 ; there was no corrosion in an 85 °C / 85% RH environment for 835 hours.

[0045] Example 5:

[0046] In this example, 1 kg of industrial cobalt sulfate (purity 99%) was taken and dissolved in 5 L of ultrapure water (18.2 MΩ·cm); it was passed through a chelating resin column (DTPA type) at a flow rate of 2 BV / h, and the liquid phase was collected; then gradient crystallization was carried out, controlling the cooling rate at 0.5 °C / min to obtain high-purity crystals; then the high-purity crystals were subjected to vacuum sublimation at 10-3 Pa and 200 °C, and the sublimation product was collected to obtain ultrapure cobalt sulfate. After detection by ICP-MS, the total amount of impurities was < 10 ppm.

[0047] According to the formula, 250 g / L of ultrapure cobalt sulfate; 50 g / L of ultrapure boric acid; 10 g / L of complexing agent sodium citrate; 0.5 g / L of brightening agent saccharin sodium were used to prepare the electroplating solution with deionized water as the solvent; and the pH of the electroplating solution was adjusted to 4.5 with ultrapure sulfuric acid. Then, a dynamic filtration system (0.1 μm pore size PTFE membrane) was used to plate on the copper substrate (current density 2 A / dm 2 , temperature 50 °C), and a coating with a thickness of 5 μm and a surface roughness Ra < 0.05 μm was obtained. The coating adhesion (cross-cut method) was grade 4B; the porosity (test with potassium ferricyanide) was ≤ 10 per cm 2 ; there was no corrosion in an 85 °C / 85% RH environment for 865 hours.

[0048] Example 6:

[0049] In this example, 1 kg of industrial cobalt sulfate (purity 99%) was taken and dissolved in 5 L of ultrapure water (18.2 MΩ·cm); it was passed through a chelating resin column (DTPA type) at a flow rate of 2 BV / h, and the liquid phase was collected; then gradient crystallization was carried out, controlling the cooling rate at 0.5 °C / min to obtain high-purity crystals; then the high-purity crystals were subjected to vacuum sublimation at 10-3 Pa and 200 °C, and the sublimation product was collected to obtain ultrapure cobalt sulfate. After detection by ICP-MS, the total amount of impurities was < 10 ppm.

[0050] According to the formula, 250 g / L of ultrapure cobalt sulfate; 30 g / L of ultrapure boric acid; 5 g / L of complexing agent sodium citrate; 0.1 g / L of brightening agent saccharin sodium were used to prepare the electroplating solution with deionized water as the solvent; and the pH of the electroplating solution was adjusted to 4 with ultrapure sulfuric acid. Then, a dynamic filtration system (0.1 μm pore size PTFE membrane) was used to plate on the copper substrate (current density 2 A / dm 2 , temperature 50 °C), and a coating with a thickness of 5 μm and a surface roughness Ra < 0.05 μm was obtained. The coating adhesion (cross-cut method) was grade 4B; the porosity (test with potassium ferricyanide) was ≤ 9 per cm 2 ; there was no corrosion in an 85 °C / 85% RH environment for 870 hours.

[0051] Example 7:

[0052] In this example, 1 kg of industrial cobalt sulfate (purity 99%) was taken and dissolved in 5 L of ultrapure water (18.2 MΩ·cm); it passed through a chelating resin column (DTPA type) at a flow rate of 2 BV / h, and the liquid phase was collected; then gradient crystallization was carried out, controlling the cooling rate at 0.5 °C / min to obtain high-purity crystals; then the high-purity crystals were subjected to vacuum sublimation at 10-3 Pa and 200 °C, and the sublimation product was collected to obtain ultrapure cobalt sulfate. After detection by ICP-MS, the total amount of impurities < 10 ppm.

[0053] According to the formula, 250 g / L of ultrapure cobalt sulfate; 30 g / L of ultrapure boric acid; 5 g / L of complexing agent sodium citrate; 0.1 g / L of brightening agent saccharin sodium were used to prepare the electroplating solution with deionized water as the solvent; and the pH of the electroplating solution was adjusted to 4.5 with ultrapure sulfuric acid. Then, a dynamic filtration system (0.1 μm pore size PTFE membrane) was used to electroplate on the copper substrate (current density 2 A / dm 2 , temperature 50 °C), and a coating with a thickness of 5 μm and a surface roughness Ra < 0.05 μm was obtained. The coating adhesion (cross-cut method) was grade 4B; the porosity (test with potassium ferricyanide) ≤ 8 per cm 2 ; there was no corrosion in an 85 °C / 85% RH environment for 880 hours.

[0054] Example 8:

[0055] In this example, 1 kg of industrial cobalt sulfate (purity 99%) was taken and dissolved in 5 L of ultrapure water (18.2 MΩ·cm); it passed through a chelating resin column (DTPA type) at a flow rate of 2 BV / h, and the liquid phase was collected; then gradient crystallization was carried out, controlling the cooling rate at 0.3 °C / min to obtain high-purity crystals; then the high-purity crystals were subjected to vacuum sublimation at 10-3 Pa and 200 °C, and the sublimation product was collected to obtain ultrapure cobalt sulfate. After detection by ICP-MS, the total amount of impurities < 10 ppm.

[0056] According to the formula, 250 g / L of ultrapure cobalt sulfate; 30 g / L of ultrapure boric acid; 5 g / L of complexing agent sodium citrate; 0.1 g / L of brightening agent saccharin sodium were used to prepare the electroplating solution with deionized water as the solvent; and the pH of the electroplating solution was adjusted to pH 3.5 with ultrapure sulfuric acid. Then, a dynamic filtration system (0.1 μm pore size PTFE membrane) was used to electroplate on the copper substrate (current density 2 A / dm 2 , temperature 50 °C), and a coating with a thickness of 5 μm and a surface roughness Ra < 0.05 μm was obtained. The coating adhesion (cross-cut method) was grade 4B; the porosity (test with potassium ferricyanide) ≤ 7 per cm 2 ; there was no corrosion in an 85 °C / 85% RH environment for 900 hours.

[0057] Example 9:

[0058] In this example, 1 kg of industrial cobalt sulfate (purity 99%) was taken and dissolved in 5 L of ultrapure water (18.2 MΩ·cm); it was passed through a chelating resin column (DTPA type) with a flow rate of 2 BV / h, and the liquid phase was collected; then gradient crystallization was carried out, controlling the cooling rate at 0.4 °C / min to obtain high-purity crystals; then the high-purity crystals were subjected to vacuum sublimation at 10-3 Pa and 200 °C, and the sublimation product was collected to obtain ultrapure cobalt sulfate. After detection by ICP-MS, the total amount of impurities < 10 ppm.

[0059] According to the formula, 250 g / L of ultrapure cobalt sulfate; 30 g / L of ultrapure boric acid; 5 g / L of complexing agent sodium citrate; 0.1 g / L of brightening agent saccharin sodium were used to prepare the electroplating solution with deionized water as the solvent; and the pH of the electroplating solution was adjusted to pH 3.5 with ultrapure sulfuric acid. Then, a dynamic filtration system (0.1 μm pore size PTFE membrane) was used to apply the plating on the copper substrate (current density 2 A / dm 2 , temperature 50 °C), and a coating with a thickness of 5 μm and a surface roughness Ra < 0.05 μm was obtained. The coating adhesion (cross-cut method) was grade 4B; the porosity (test with potassium ferricyanide) ≤ 6 per cm 2 ; there was no corrosion in an 85 °C / 85% RH environment for 930 hours.

[0060] Example 10:

[0061] In this example, 1 kg of industrial cobalt sulfate (purity 99%) was taken and dissolved in 5 L of ultrapure water (18.2 MΩ·cm); it was passed through a chelating resin column (DTPA type) with a flow rate of 2 BV / h, and the liquid phase was collected; then gradient crystallization was carried out, controlling the cooling rate at 0.5 °C / min to obtain high-purity crystals; then the high-purity crystals were subjected to vacuum sublimation at 10-3 Pa and 200 °C, and the sublimation product was collected to obtain ultrapure cobalt sulfate. After detection by ICP-MS, the total amount of impurities < 10 ppm.

[0062] According to the formula, 250 g / L of ultrapure cobalt sulfate; 30 g / L of ultrapure boric acid; 5 g / L of complexing agent sodium citrate; 0.1 g / L of brightening agent saccharin sodium; yttrium salt at 0.5 mg / L with Y 3+ recorded were used to prepare the electroplating solution with deionized water as the solvent; and the pH of the electroplating solution was adjusted to pH 3.5 with ultrapure sulfuric acid. Then, a dynamic filtration system (0.1 μm pore size PTFE membrane) was used to apply the plating on the copper substrate (current density 2 A / dm 2 , temperature 50 °C), and a coating with a thickness of 5 μm and a surface roughness Ra < 0.05 μm was obtained. The coating adhesion (cross-cut method) was grade 4B; the porosity (test with potassium ferricyanide) ≤ 5 per cm 2 ; there was no corrosion in an 85 °C / 85% RH environment for 950 hours, as Figure 1 shown.

[0063] Example 11:

[0064] In this example, 1 kg of industrial cobalt sulfate (purity 99%) was taken and dissolved in 5 L of ultrapure water (18.2 MΩ·cm); it passed through a chelating resin column (DTPA type) with a flow rate of 2 BV / h, and the liquid phase was collected; then gradient crystallization was carried out, controlling the cooling rate at 0.5 °C / min to obtain high-purity crystals; then the high-purity crystals were subjected to vacuum sublimation at 10-3 Pa and 200 °C, and the sublimation product was collected to obtain ultrapure cobalt sulfate. After detection by ICP-MS, the total amount of impurities < 10 ppm.

[0065] According to the formula, ultrapure cobalt sulfate is 250 g / L; ultrapure boric acid is 30 g / L; the complexing agent sodium citrate is 5 g / L; the brightening agent saccharin sodium is 0.1 g / L; the yttrium salt is in the form of Y 3+ Record 1.2 mg / L and prepare the electroplating solution with deionized water as the solvent; and adjust the pH of the electroplating solution to pH 3.5 with ultrapure sulfuric acid. Then use a dynamic filtration system (0.1 μm pore size PTFE membrane) to plate on the copper substrate (current density 2 A / dm 2 , temperature 50 °C), to obtain a coating with a thickness of 5 μm and a surface roughness Ra < 0.05 μm. The coating adhesion (cross-cut method) is grade 4B; the porosity (test with potassium ferricyanide) ≤ 4 per cm 2 ; there is no corrosion in an 85 °C / 85% RH environment for 985 hours, as Figure 2 shown.

[0066] Example 12:

[0067] In this example, 1 kg of industrial cobalt sulfate (purity 99%) was taken and dissolved in 5 L of ultrapure water (18.2 MΩ·cm); it passed through a chelating resin column (DTPA type) with a flow rate of 2 BV / h, and the liquid phase was collected; then gradient crystallization was carried out, controlling the cooling rate at 0.5 °C / min to obtain high-purity crystals; then the high-purity crystals were subjected to vacuum sublimation at 10-3 Pa and 200 °C, and the sublimation product was collected to obtain ultrapure cobalt sulfate. After detection by ICP-MS, the total amount of impurities < 10 ppm.

[0068] According to the formula, ultrapure cobalt sulfate is 250 g / L; ultrapure boric acid is 30 g / L; the complexing agent sodium citrate is 5 g / L; the brightening agent saccharin sodium is 0.1 g / L; the yttrium salt is in the form of Y 3+ Record 2 mg / L and prepare the electroplating solution with deionized water as the solvent; and adjust the pH of the electroplating solution to pH 3.5 with ultrapure sulfuric acid. Then use a dynamic filtration system (0.1 μm pore size PTFE membrane) to plate on the copper substrate (current density 2 A / dm 2 , temperature 50 °C), to obtain a coating with a thickness of 5 μm and a surface roughness Ra < 0.05 μm. The coating adhesion (cross-cut method) is grade 4B; the porosity (test with potassium ferricyanide) ≤ 3 per cm 2; No corrosion after 1000 hours in an environment of 85°C / 85% RH, as Figure 3 shown.

[0069] Comparative Example 1

[0070] The difference between this comparative example and Example 2 is only that: the ultrapure cobalt sulfate in the formula is replaced with industrial-grade cobalt sulfate of the same mass. The coating adhesion (cross-cut method) is Grade 1B; the porosity (test with potassium ferricyanide) ≤ 16 pieces / cm 2 ; No corrosion after 730 hours in an environment of 85°C / 85% RH.

[0071] Comparative Example 2

[0072] The difference between this comparative example and Example 2 is only that: the ultrapure boric acid in the formula is replaced with industrial-grade boric acid of the same mass. The coating adhesion (cross-cut method) is Grade 2B; the porosity (test with potassium ferricyanide) ≤ 15 pieces / cm 2 ; No corrosion after 745 hours in an environment of 85°C / 85% RH.

[0073] Comparative Example 3

[0074] The difference between this comparative example and Example 2 is only that: the ultrapure sulfuric acid in the formula is replaced with industrial-grade sulfuric acid of the same mass. The coating adhesion (cross-cut method) is Grade 3B; the porosity (test with potassium ferricyanide) ≤ 15 pieces / cm 2 ; No corrosion after 750 hours in an environment of 85°C / 85% RH.

[0075] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention.

[0076] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A highly stable electroplating solution based on ultra-pure cobalt sulfate, the raw material composition of which includes: Ultra-pure cobalt sulfate 200 - 300 g / L, with the total impurity content < 10 ppm; Ultra-pure boric acid 30 - 50 g / L; Complexing agent 5 - 10 g / L; Brightening agent 0.1 - 0.5 g / L; And adjusted to pH 3.5 - 4.5 with a pH regulator.

2. The highly stable electroplating solution according to claim 1, wherein The complexing agent is selected from: sodium citrate.

3. The highly stable electroplating solution according to claim 1, wherein The brightening agent is selected from: sodium saccharin.

4. The highly stable electroplating solution according to claim 1, wherein, The pH regulator is selected from ultra-pure sulfuric acid.

5. The highly stable electroplating solution according to any one of claims 1-4, characterized in that, The raw materials also include rare earth elements, and the dosage is 0.5 - 2 mg / L.

6. The highly stable electroplating solution according to claim 5, wherein The rare earth element is selected from Y.

7. The preparation method of the highly stable electroplating solution according to any one of claims 1-6, characterized in that, Including: Prepared by preparing the raw materials, dissolving them in water and then filtering. The preparation of ultra-pure cobalt sulfate is: chelating industrial-grade cobalt sulfate with an ion exchange resin, followed by gradient crystallization and vacuum sublimation. The cooling rate of the solution during the gradient crystallization is 0.3 - 0.5 °C / min.

8. The preparation method of the highly stable electroplating solution according to claim 7, wherein, The conditions for the vacuum sublimation are: 10-3 Pa, 200 °C.

9. The preparation method of the highly stable electroplating solution according to claim 7, wherein, The filtration is through a PTFE filter membrane with a pore size of 0.1 μm.

10. Use of the highly stable electroplating solution according to any one of claims 1 - 6 in the coating of precision electronic devices.

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