Semiconductor cyanide-free gold plating solution and preparation method thereof

Abstract

The application relates to the technical field of electroplating, and particularly discloses a cyanide-free electroplating gold plating solution for semiconductors and a preparation method thereof, and the cyanide-free electroplating gold plating solution for semiconductors comprises the following raw materials in parts by weight: gold-containing salt 15-30 parts, conductive salt 20-40 parts, complexing agent 10-15 parts, pH regulator 5-10 parts and plating aid 5-10 parts; the complexing agent is a mixture of 5,5-dimethylhydantoin and nicotinic acid, the mass ratio of the 5,5-dimethylhydantoin and the nicotinic acid is (2-3):1; the plating aid comprises cerium nitrate and a surfactant, and the mass ratio of the cerium nitrate and the surfactant is 1:(4-5). The cyanide-free electroplating gold plating solution for semiconductors of the application uses 5,5-dimethylhydantoin, nicotinic acid and gold ions to complex, uniformly disperses the gold ions in the plating solution, and reduces the precipitation of the gold ions in the plating solution.

Description

Technical Field

[0001] This application relates to the field of electroplating technology, specifically to a semiconductor cyanide-free electroplating gold plating solution and its preparation method. Background Technology

[0002] Gold plating is a process that uses electrolytic or chemical methods to evenly deposit gold onto the surface of a metal or other object, forming a thin layer of gold. Gold plating can be used for decoration, as well as for corrosion protection. Furthermore, taking advantage of gold's excellent electrical conductivity, it can reduce resistance and increase conductivity, thus making electroplated gold widely used in semiconductors.

[0003] Currently, gold electroplating is mainly divided into two categories: cyanide gold plating and cyanide-free gold plating. Cyanide gold plating has good chemical stability, simple and low-cost gold salt preparation, and excellent coating brightness and performance. However, cyanide gold plating contains highly toxic cyanide, which is harmful to the environment and operators, thus limiting the application of cyanide electroplating.

[0004] However, existing cyanide-free gold plating solutions often decompose after standing for a period of time, resulting in the precipitation of gold ions in the plating solution, which makes it impossible to form a stable coating during electroplating. Summary of the Invention

[0005] To improve the stability of electroplating gold solutions, this application provides a semiconductor cyanide-free electroplating gold solution and its preparation method.

[0006] In a first aspect, this application provides a cyanide-free electroplating gold plating solution for semiconductors, employing the following technical solution: A semiconductor cyanide-free electroplating gold plating solution comprises the following raw materials in parts by weight: 15-30 parts gold salt, 20-40 parts conductive salt, 10-15 parts complexing agent, 5-10 parts pH adjuster, and 5-10 parts plating flux. The ligand is a mixture of 5,5-dimethylhydantoin and nicotinic acid, wherein the mass ratio of 5,5-dimethylhydantoin to nicotinic acid is (2-3):1; the flux includes cerium nitrate and a surfactant, wherein the mass ratio of cerium nitrate to the surfactant is 1:(4-5).

[0007] By employing the above technical solution, 5,5-dimethylhydantoin and nicotinic acid are used to complex with gold ions in gold salts, reducing the precipitation of gold ions in the plating bath and improving the stability of the plating bath. Cerium nitrate and surfactants are added to the fluxing solution. The surfactants improve the wettability, dispersibility, and penetration of the plating solution, enhance the adhesion between the plating solution and the substrate, and promote a firm and uniform adhesion of the plating solution to the substrate surface, thereby improving the durability and stability of the gold plating layer. Cerium nitrate in the plating solution can refine the grains, increase the hardness of the gold plating layer, and promote excellent uniformity and leveling of the gold plating layer.

[0008] Preferably, the pH adjuster adjusts the pH of the plating solution to 4-6.

[0009] By employing the above technical solution, the pH value of the plating solution is controlled within the range of 4-6, resulting in a gold plating layer with good density and leveling properties. Simultaneously, the gold plating layer exhibits a golden color, excellent appearance and texture, and strong adhesion. When the pH value is greater than 6, the gold plating layer thickness is easily excessive, leading to poor density and weak adhesion between the plating layer and the substrate. Over time, this can cause delamination and peeling. When the pH value is too low, the gold plating layer thickness is insufficient, resulting in a discontinuous plating layer on the substrate surface and a tendency to break.

[0010] Preferably, the pH adjuster is sodium dihydrogen phosphate and disodium hydrogen phosphate.

[0011] By adopting the above technical solution, the pH value of the plating solution is adjusted by sodium dihydrogen phosphate and disodium hydrogen phosphate, and the pH value of the plating solution is controlled within a suitable range. This regulates the metal deposition rate, promotes the formation of a dense and uniform gold plating layer with small grains, and further improves the stability of the plating solution and the gold plating layer.

[0012] Preferably, the plating flux further includes sodium phytate and thallium sulfate, wherein the mass ratio of cerium nitrate, sodium phytate and thallium sulfate is 1:(1.2-1.5):(1.5-2).

[0013] By employing the above technical solution, sodium phytate exhibits excellent complexing properties with metal ions, which can further promote the stability of the plating solution. Simultaneously, sodium phytate possesses excellent antioxidant and color-protecting properties, enhancing the color stability of the gold plating layer. Furthermore, the addition of thallium sulfate to the plating solution accelerates gold deposition and acts as a grain refiner, resulting in a gold plating layer with good brightness.

[0014] Preferably, the plating solution further includes 1-3 parts of butynediol.

[0015] By adopting the above technical solution, adding butynediol to the plating solution can inhibit crystal growth, reduce the size of metal agglomerates, make the surface of the gold plating layer smooth and flat, and improve the flatness of the gold plating layer.

[0016] Preferably, the gold salt is sodium gold chloride.

[0017] Preferably, the conductive salt is a mixture of sodium sulfite and sodium thiosulfate.

[0018] By employing the above technical solution, a gold plating solution prepared with sodium agaride as the conductive salt and sulfite and thiosulfate as the main components allows gold ions to form a complexing effect with each component, thereby reducing the precipitation of gold ions in the plating solution. Simultaneously, the gold plating solution can form a good bond with the substrate, resulting in a better gold plating layer on the substrate surface and improving the stability of the gold plating layer.

[0019] Secondly, this application provides a method for preparing a cyanide-free electroplating gold solution for semiconductors, employing the following technical solution: A method for preparing a semiconductor cyanide-free electroplating gold plating solution includes the following specific steps: mixing gold salt, conductive salt, complexing agent, pH adjuster and plating flux and then adding the mixture to water to obtain a semiconductor cyanide-free electroplating gold plating solution.

[0020] By adopting the above technical solution, the gold plating solution prepared can coordinate with gold ions under the synergistic effect of each component to form a stable metal complex, thereby reducing the precipitation of gold ions from the plating solution and forming a bright and smooth gold plating layer.

[0021] In summary, this application has the following beneficial effects: 1. Because the plating solution formed by the combination of ligand, conductive salt and gold salt in this application combines with each other, the gold ions in the plating solution combine with each component, reducing the precipitation of gold ions in the plating solution and improving the stability of the gold plating solution.

[0022] 2. In this application, sodium phytate, butynediol and thallium sulfate are added to the gold plating solution to promote the formation of a dense, smooth and bright gold plating layer, thereby improving the smoothness and brightness of the gold plating layer. Detailed Implementation

[0023] The present application will be further described in detail below with reference to the embodiments. Example

[0024] Example 1 A cyanide-free electroplating gold plating solution for semiconductors comprises the following raw materials in parts by weight: 18 kg of gold salt, 30 kg of conductive salt, 13 kg of complexing agent, 8 kg of pH adjuster, and 8 kg of flux. The complexing agent is a mixture of 5,5-dimethylhydantoin and nicotinic acid in a mass ratio of 2.5:1; the flux is a mixture of cerium nitrate and surfactant in a mass ratio of 1:4.5; the surfactant is sodium dodecyl sulfonate; and the pH adjuster is sodium dihydrogen phosphate and disodium hydrogen phosphate.

[0025] A method for preparing a cyanide-free electroplating gold solution for semiconductors includes the following specific steps: Gold salt, conductive salt, complexing agent and plating flux are mixed and added to deionized water. The mass ratio of water to gold salt is 3:1. The mixture is stirred at 500 r / min for 15 min to form a mixed solution. Then, a pH adjuster is added to the mixed solution to adjust the pH value of the mixed solution to 5, thus obtaining a semiconductor cyanide-free electroplating gold plating solution.

[0026] Example 2-3 The difference between Examples 2-3 and Example 1 is that the content of each component in the raw material of the semiconductor cyanide-free electroplating gold plating solution is different, as shown in Table 1.

[0027] Table 1: Content of each component in Examples 1-3 Example 1 18 30 8 13 8 Example 2 15 20 5 10 10 Example 3 30 40 10 15 5 Example 4

[0028] The difference between Example 4 and Example 1 is that the ligand in the semiconductor cyanide-free electroplating gold plating solution is a mixture of 5,5-dimethylhydantoin and nicotinic acid in a mass ratio of 2:1, and the flux is a mixture of cerium nitrate and surfactant in a mass ratio of 1:5.

[0029] Example 5 The difference between Example 5 and Example 1 is that the ligand in the semiconductor cyanide-free electroplating gold plating solution is a mixture of 5,5-dimethylhydantoin and nicotinic acid in a mass ratio of 3:1, and the flux is a mixture of cerium nitrate and surfactant in a mass ratio of 1:4.

[0030] Example 6 The difference between Example 6 and Example 1 is that the fluxing agent of the semiconductor cyanide-free electroplating gold plating solution also includes sodium phytate and thallium sulfate, wherein the mass ratio of cerium nitrate, sodium phytate and thallium sulfate is 1:1.3:1.8.

[0031] Example 7 The difference between Example 7 and Example 6 is that the mass ratio of cerium nitrate, sodium phytate and thallium sulfate in the flux of the semiconductor cyanide-free electroplating gold plating solution is 1:1.2:2.

[0032] Example 8 The difference between Example 8 and Example 6 is that the mass ratio of cerium nitrate, sodium phytate and thallium sulfate in the flux of the semiconductor cyanide-free electroplating gold plating solution is 1:1.5:2.

[0033] Example 9 The difference between Example 9 and Example 6 is that sodium phytate is not used in the flux of the semiconductor cyanide-free electroplating gold plating solution.

[0034] Example 10 The difference between Example 10 and Example 6 is that the semiconductor cyanide-free electroplating gold plating solution also includes 2 kg of butynediol.

[0035] The preparation method of cyanide-free electroplating gold solution for semiconductors includes the following specific steps: Gold salt, conductive salt, ligand, and flux were mixed and added to deionized water at a mass ratio of 3:1. The mixture was stirred at 500 rpm for 15 minutes to form a solution. Then, a pH adjuster was added to the solution to adjust the pH to 5. Butynediol was then added to the solution and stirred at 500 rpm for 10 minutes to obtain a cyanide-free electroplating gold plating solution for semiconductors.

[0036] Example 11 The difference between Example 11 and Example 10 is that the amount of butynediol used in the semiconductor cyanide-free electroplating gold plating solution is 1 kg.

[0037] Example 12 The difference between Example 12 and Example 10 is that the amount of butynediol used in the semiconductor cyanide-free electroplating gold plating solution is 3 kg.

[0038] Example 13 The difference between Example 13 and Example 1 is that the pH value of the semiconductor cyanide-free electroplating gold plating solution is adjusted to 7 by a pH adjuster.

[0039] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that no flux is used in the raw materials of the semiconductor cyanide-free electroplating gold plating solution.

[0040] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the flux in the semiconductor cyanide-free electroplating gold plating solution is a surfactant.

[0041] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that nicotinic acid and flux are not used in the ligand of the semiconductor cyanide-free electroplating gold plating solution.

[0042] The following performance tests were conducted on the electroplating gold plating solutions provided in Examples 1-13 and Comparative Examples 1-3 of this application, and the test results are shown in Table 2.

[0043] I. Plating solution stability The plating solution prepared in the embodiments of this application was used as a sample. 300 ml of the plating solution was placed in a beaker and left for 90 days and 180 days. The plating solution was then observed to see if any solids precipitated or the solution changed color.

[0044] II. Appearance of the gold plating layer The appearance of the gold plating layer formed by electroplating semiconductors using the gold plating solution prepared in this application was observed using a Quanta 200 scanning electron microscope.

[0045] III. Gold plating thickness The uniformity of the gold plating thickness was determined by measuring the gold plating thickness at 10 different locations on the surface of the electroplated semiconductor using XRF and calculating the average of the standard deviations of the gold plating thickness at the 10 locations.

[0046] Table 2: Performance Test Data Table Example 1 Clear and transparent with no sediment after 180 days Even and flat 4.6 Example 2 Clear and transparent with no sediment after 180 days Even and flat 4.75 Example 3 Clear and transparent with no sediment after 180 days Even and flat 4.7 Example 4 Clear and transparent with no sediment after 180 days Even and flat 4.65 Example 5 Clear and transparent with no sediment after 180 days Even and flat 4.7 Example 6 Clear and transparent with no sediment after 180 days Bright, even, and smooth 3.1 Example 7 Clear and transparent with no sediment after 180 days Bright, even, and smooth 3.2 Example 8 Clear and transparent with no sediment after 180 days Bright, even, and smooth 3.2 Example 9 Clear and transparent with no sediment after 180 days Bright, even, and smooth 3.4 Example 10 Clear and transparent with no sediment after 180 days Smooth, glossy, uniform, and flat 2.2 Example 11 Clear and transparent with no sediment after 180 days Smooth, glossy, uniform, and flat 2.3 Example 12 Clear and transparent with no sediment after 180 days Smooth, glossy, uniform, and flat 2.3 Example 13 Clear and transparent with no sediment after 180 days Uneven 5.8 Comparative Example 1 Clear and transparent with no sediment after 180 days Slightly rough and uneven. 6.3 Comparative Example 2 The solution remained clear and transparent with no sediment after 90 days; after 180 days, the plating solution became more turbid and showed a slight discoloration. Uneven 6.2 Comparative Example 3 After 90 days, the skin turned slightly yellow and produced a small amount of sediment. Rough, uneven and flat 7.1 The performance test results show that the electroplating gold solutions prepared in Examples 1-5 of this application have good stability and reduce the precipitation of gold ions from the plating solution. In Examples 1-5 of this application, under the combined action of the ligand, flux, and metal ions, stable metal complexes are formed and uniformly dispersed in the plating solution, thereby reducing the precipitation of metal ions and forming a uniform and smooth gold plating layer.

[0047] In Examples 6-8 of this application, different amounts of sodium phytate and thallium sulfate were added to the plating bath. Performance testing results showed that the combination of sodium phytate and metal ions further improved the stability of the plating bath. Simultaneously, thallium sulfate made the gold plating layer finer and more lustrous, improving its brightness. In Example 9, sodium phytate was not used in the plating bath. Performance testing results showed that the overall performance of the plating bath decreased slightly. This is because the complexation of sodium phytate with metal ions promotes a more uniform distribution of metal ions in the plating bath. Sodium phytate also has a certain color-protecting ability, protecting the gloss and durability of the gold plating layer.

[0048] In Examples 10-12 of this application, different amounts of butynediol were added to the plating solution. As can be seen from the performance test results, the appearance and texture of the gold plating layer were improved, the surface of the gold plating layer was smoother and flatter, and it also had excellent gloss.

[0049] In Example 13 of this application, the pH value of the plating solution was increased. As can be seen from the performance test results, although the plating solution still has a certain stability, the density of the gold plating layer formed during electroplating is poor and the gold plating layer is uneven. This may be because the pH value of the plating solution is too high, the gold deposition rate in the plating solution is too fast, and the gold plating layer formed is prone to unevenness.

[0050] A comparison of the performance test results of Comparative Examples 1, 2, 3 and Example 1 shows that in Comparative Example 2, without the use of cerium nitrate, the surface of the gold plating layer exhibits significant and uneven particle formation. In Comparative Example 1, no flux was used, and in Comparative Example 3, neither flux nor nicotinic acid was used. Performance test results indicate that gold ion precipitation occurred in the plating solution, and the surface of the gold plating layer showed significant particle formation and decreased smoothness. This further demonstrates that the synergistic effect of the various components in this application is necessary to achieve good stability in the plating solution and to ensure the formation of a gold plating layer with excellent gloss and smoothness.

[0051] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A semiconductor cyanide-free electroplating gold plating solution, characterized in that, The raw materials include the following parts by weight: 15-30 parts gold salt, 20-40 parts conductive salt, 10-15 parts complexing agent, 5-10 parts pH adjuster, and 5-10 parts plating flux. The ligand is a mixture of 5,5-dimethylhydantoin and nicotinic acid, wherein the mass ratio of 5,5-dimethylhydantoin to nicotinic acid is (2-3):1; the fluxing agent includes cerium nitrate, surfactant, sodium phytate and thallium sulfate, wherein the mass ratio of cerium nitrate to surfactant is 1:(4-5), and the mass ratio of cerium nitrate, sodium phytate and thallium sulfate is 1:(1.2-1.5):(1.5-2).

2. The semiconductor cyanide-free electroplating gold plating solution according to claim 1, characterized in that: The pH adjuster adjusts the pH of the plating solution to 4-6.

3. The semiconductor cyanide-free electroplating gold plating solution according to claim 2, characterized in that: The pH adjuster is sodium dihydrogen phosphate and disodium hydrogen phosphate.

4. The semiconductor cyanide-free electroplating gold plating solution according to claim 1, characterized in that: The plating solution also includes 1-3 parts of butynediol.

5. The semiconductor cyanide-free electroplating gold plating solution according to claim 1, characterized in that: The gold salt is sodium gold chloride.

6. The semiconductor cyanide-free electroplating gold plating solution according to claim 1, characterized in that: The conductive salt is a mixture of sodium sulfite and sodium thiosulfate.

7. A method for preparing a semiconductor cyanide-free electroplating gold plating solution as described in any one of claims 1-6, characterized in that: The specific steps include: mixing gold salt, conductive salt, complexing agent, pH adjuster and plating flux and then adding it to water to prepare a semiconductor cyanide-free electroplating gold plating solution.