Chemical reduction gold working solution without additional KCN and chemical gold plating method

Abstract

The invention discloses a chemical reduction gold working solution without additionally adding KCN. The working solution does not contain potassium cyanide (KCN); the gold-potassium alloy is prepared from the following components in percentage by mass or volume: gold potassium cyanide; pure water; the complexing agent comprises 8% of anhydrous sodium acetate, 6% of sodium ethylene diamine tetracetate, 3% of sodium sulfate, 2% of glycine, 0.08% of formaldehyde, 0.0002% of lead acetate trihydrate and 80.918% of water; the stabilizer comprises 2% of ethylene diamine tetraacetic acid tetrasodium salt, 1% of potassium ferrocyanide and 97% of water; the reducing agent comprises 5% of glycine, 4% of phosphoric acid, 0.8% of formaldehyde and 90.2% of water; and a pH adjusting agent. The invention further discloses a chemical gold plating method. The working solution provided by the invention does not contain potassium cyanide (KCN), so that a non-toxic chemical plating solution is realized; and meanwhile, the consistency and high stripping degree of a gold-plated layer after gold plating can be ensured.

Description

Technical Field

[0001] This invention relates to the field of circuit board manufacturing, and more specifically, to a chemical reduction gold working solution and a chemical gold plating method that does not require the addition of KCN. Background Technology

[0002] In the fields of electronic components, semiconductor packaging, and PCB (printed circuit board) manufacturing, displacement reaction gold plating technology is a key process for ensuring the conductivity, corrosion resistance, and solderability of metal surfaces, especially those of nickel, copper, and chromium. Current chemical gold plating technologies most commonly employ cyanide (KCN) complex systems. However, cyanide (KCN) is extremely toxic, and the plating solution is difficult to handle. Existing gold plating technologies suffer from the following core drawbacks: 1. Environmental and safety issues: Poor stability of the plating solution: The plating solution is prone to self-decomposition, requiring frequent addition of stabilizers, resulting in high maintenance costs; it is also sensitive to metallic impurities, leading to a short plating solution lifespan.

[0003] 2. Insufficient coating performance: After gold plating, uneven thickness distribution occurs: the edges are too thick and the center is too thin, affecting product consistency. High porosity: the high pore density of the plating layer easily leads to corrosion. Poor adhesion: the adhesion strength between the plating layer and the substrate is low, making it prone to peeling off at high temperatures.

[0004] 3. Severe corrosion of the nickel layer: The displacement reaction leads to excessive corrosion of the nickel layer, affecting the reliability of the underlying layer. It easily forms "black pad" defects, i.e., pits in the underlying metal, thereby reducing the bonding performance between the underlying metal and the gold layer.

[0005] 4. Issues of economy and efficiency: Narrow process window: Temperature and pH fluctuations affect coating quality and increase operational difficulty. Summary of the Invention

[0006] The purpose of this invention is to provide a chemical reduction gold working solution that does not contain potassium cyanide (KCN). This working solution is used to chemically plate a gold layer on the surface of a nickel-chromium metal layer. Compared to existing technologies, this working solution does not contain potassium cyanide (KCN), thus achieving a non-toxic chemical plating solution.

[0007] The working solution does not contain potassium cyanide (KCN) and is prepared according to the following mass or volume percentage ratio, wherein the working solution comprises: 0.4-0.6g of potassium gold cyanide; 500ml of purified water; 200ml complexing agent, wherein the complexing agent comprises: 6-10% anhydrous sodium acetate, 4-8% sodium ethylenediaminetetraacetate, 2-4% sodium sulfate, 1-3% glycine, 0.05-0.1% formaldehyde, 0.001-0.003% lead acetate trihydrate, and 74.897% water; 0.2 ml of stabilizer, wherein the stabilizer comprises: 1-3% tetrasodium ethylenediaminetetraacetate, 0.5-1.5% potassium ferrous sulfate, and 95.5-97.5% water; 25ml reducing agent, wherein the reducing agent comprises: 4-6% glycine, 2-6% phosphoric acid, 0.6-1% formaldehyde, and 87-93.4% water; as well as pH adjusting agent, comprising: 25% sodium hydroxide and 75% water; The pH adjusting agent is used to adjust the pH value of the above working solution to be within the range of 5.5-6.0.

[0008] The working fluid of this invention is non-toxic, and the added stabilizer ensures that the working fluid remains stable after use, eliminating the need for frequent addition of stabilizer.

[0009] Among these processes, gold plating ensures a uniform thickness of the gold plating layer and eliminates plating pores.

[0010] This invention also discloses a gold plating method for forming a gold plating layer using the above-mentioned working solution chemical plating layer, the method comprising: Step S1: After cleaning, micro-etching, acid washing and rinsing on the copper substrate, electroless nickel plating is performed. Step S2: Wash the nickel-plated substrate with water, and then plate a palladium layer; Step S3: After washing the palladium-plated substrate with water, gold is then plated using the working solution as described in claim 2, followed by washing with water again. During the gold plating process, the temperature of the gold plating solution is between 80-87℃, and the gold plating time is 10-15 minutes. Attached Figure Description

[0011] Figures 1 to 3 This is a magnified microscopic image of the surface of the gold plating layer after chemical gold plating with the working solution of this invention. Detailed Implementation

[0012] The present invention will be further described and illustrated below with reference to specific embodiments and the accompanying drawings: This invention discloses a chemically reduced gold working solution without the addition of potassium cyanide (KCN), wherein the working solution does not contain potassium cyanide (KCN); and is prepared according to the following mass or volume percentage ratio, wherein the working solution comprises: 0.4-0.6g of potassium gold cyanide; 500ml of purified water; 200ml complexing agent, wherein the complexing agent comprises: 6-10% anhydrous sodium acetate, 4-8% sodium ethylenediaminetetraacetate, 2-4% sodium sulfate, 1-3% glycine, 0.05-0.1% formaldehyde, 0.001-0.003% lead acetate trihydrate, and 74.897% water; 0.2 ml of stabilizer, wherein the stabilizer comprises: 1-3% tetrasodium ethylenediaminetetraacetate, 0.5-1.5% potassium ferrous sulfate, and 95.5-97.5% water; 25ml reducing agent, wherein the reducing agent comprises: 4-6% glycine, 2-6% phosphoric acid, 0.6-1% formaldehyde, and 87-93.4% water; pH adjusting agent, comprising: 25% sodium hydroxide and 75% water; The pH adjusting agent is used to adjust the pH value of the above working solution to be within the range of 5.5-6.0.

[0013] One optimal implementation method is to prepare the working solution according to the following proportions: 0.5g potassium gold cyanide; 500ml pure water; 200ml complexing agent, comprising: 8% anhydrous sodium acetate, 6% sodium ethylenediaminetetraacetate, 3% sodium sulfate, 2% glycine, 0.08% formaldehyde, 0.0002% lead acetate trihydrate, and 80.918% water; 0.2ml stabilizer, comprising: 2% tetrasodium ethylenediaminetetraacetate, 1% potassium ferrous sulfate, and 97% water; 25ml reducing agent, comprising: 5% glycine, 4% phosphoric acid, 0.8% formaldehyde, and 90.2% water; and pH adjuster, comprising: 25% sodium hydroxide and 75% water.

[0014] The applicant used the above-mentioned optimal working solution ratio to plate gold on the copper layer and tested the plating according to the following testing standards.

[0015] 1. Comparative analysis of deposition rate and coating thickness It can be seen that the thickness distribution coefficient (CV) of the gold plating layer is less than 8.5%, and the uniformity meets the qualified standard.

[0016] 2. Comparative analysis of bonding strength, corrosion resistance, weldability, and bond strength tests: Based on the testing methods listed in the table above, the conclusion is that the gold layer after gold plating with the working solution meets the testing standards and is qualified.

[0017] In this invention, the working fluid is prepared by the following steps: a. Add 500ml of pure water to the beaker; b. Add 200ml of complexing agent to the beaker and stir well; c. Add 25m of reducing agent to the beaker and stir well; d. Add 0.73g of the main salt to the beaker and stir well; e. Adjust the pH of the liquid in the beaker to the range of 5.6-6.0, add pH adjuster, and stir well; f. Add 0.2 ml of stabilizer to a beaker and stir well. Then add pure water to make up to 1 L to prepare the working solution.

[0018] Steps e and f include: placing the solution in a beaker into a thermostatic magnetic stirrer, stirring at a temperature of 83°C to 87°C for 10 minutes until the solution is homogeneous.

[0019] In this invention, the working fluid has good stability and does not require frequent addition of stabilizers, which helps to reduce maintenance costs; it is not sensitive to the deposition of metal impurities, has a long working fluid life, and can maintain the acidity or alkalinity of the solution for a long time.

[0020] like Figures 1 to 3 , Figures 1 to 3 These are magnified microscopic images of the gold plating layer surface after chemical gold plating using the working solution of this application, at 1K, 3K, and 5K magnifications. In this invention, the working solution ensures uniform gold plating layer thickness distribution after plating, with consistent thickness at the edges and center, and low variation. Furthermore, it essentially eliminates surface porosity in the gold plating layer. The gold plating layer exhibits strong adhesion and is not easily peeled off.

[0021] The working fluid of this application will not form pits on the surface of the gold plating layer, nor will it reduce the bonding performance between the underlying nickel-chromium metal and the gold layer.

[0022] The working solution of this application is less affected by temperature and pH fluctuations, ensuring the thickness and density of the coating and improving the consistency of the gold plating layer.

[0023] This invention also discloses a gold plating method using a chemically reduced gold working solution without the addition of KCN. The method is used to obtain a nickel-palladium-gold plating layer on a copper substrate, and includes the following steps: Step S1: After cleaning, micro-etching, acid washing and rinsing on the copper substrate, electroless nickel plating is performed. Step S2: Wash the nickel-plated substrate with water, and then plate a palladium layer; Step S3: After washing the palladium-plated substrate with water, gold is then plated using the working solution as described in claim 2, followed by washing with water again. During the gold plating process, the temperature of the gold plating solution is between 80-87℃, and the gold plating time is 10-15 minutes.

[0024] In this process, copper is cleaned, soaked, and activated in an acidic environment to remove surface copper oxide, making it easier to etch and chemically plate the copper surface. The activation process causes the copper surface to adsorb activated ions.

[0025] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A chemical reducing gold working solution without additional KCN, characterized in that, The working solution does not contain potassium cyanide (KCN); and is prepared according to the following mass or volume percentage ratio, wherein the working solution comprises: 0.4-0.6g of potassium dicyanoaurate; 500ml of pure water; 200ml of complexing agent, the complexing agent comprising: 6-10% of anhydrous sodium acetate, 4-8% of sodium ethylenediaminetetraacetate, 2-4% of sodium sulfate, 1-3% of glycine, 0.05-0.1% of formaldehyde, 0.001-0.003% of lead acetate trihydrate, and 74.897% of water; 0.2ml of stabilizer, the stabilizer comprising: 1-3% of ethylenediaminetetraacetic acid tetrasodium, 0.5-1.5% of potassium ferrocyanide, and 95.5-97.5% of water; 25ml of reducing agent, the reducing agent comprising: 4-6% of glycine, 2-6% of phosphoric acid, 0.6-1% of formaldehyde, and 87-93.4% of water; and A PH adjusting agent, the adjusting agent comprising: 25% of sodium hydroxide and 75% of water; Wherein, the PH adjusting agent is used to adjust the PH value of the above-mentioned working solution to be in the range of 5.5-6.

0. The working solution is prepared by the following steps:

2. The chemical reducing gold working solution without additional KCN according to claim 1, characterized in that, a. Add 500ml of pure water in a beaker; b. Add 200ml of complexing agent in the beaker and stir uniformly; c. Add 25ml of reducing agent in the beaker and stir uniformly; d. Add 0.5g of main salt in the beaker and stir uniformly; e. Adjust the pH of the liquid in the beaker to be in the range of 5.6-6.0, add the pH adjusting agent, and stir uniformly; f. Add 0.2ml of stabilizer in the beaker and stir uniformly, and supplement with pure water to 1L to obtain the working solution. Wherein, 3. The chemical reducing gold working solution without additional KCN according to claim 2, characterized in that, The steps e, f comprise: placing the solution in the beaker into a heat-collecting constant-temperature magnetic stirrer, stirring at a temperature of 83-87℃, and stirring for 10 minutes to 1 hour until the solution is uniform.

4. A gold plating method using the chemical reducing gold working solution without additional KCN, characterized in that the method is used to electroplate a nickel-palladium-gold plating layer on a copper substrate, and the method comprises the following steps: Step S1: after cleaning, micro-etching, acid washing, and water washing on the copper substrate, chemical nickel plating is performed; Step S2: water washing is performed on the nickel-plated substrate, and then a palladium layer is plated; Step S3: after water washing on the palladium-plated substrate, gold plating is performed using the working solution according to claim 2, and then water washing is performed again; Wherein, during gold plating, the temperature of the gold plating working solution is between 80-87℃, and the gold plating time is 10-15 minutes. The copper is cleaned, soaked, and activated in an acidic environment to remove surface copper oxide, so as to facilitate the erosion and chemical plating treatment of the copper surface, and the activation treatment enables the copper surface to adsorb activation ions.

5. The gold plating method of claim 4, wherein the chemical reducing gold working solution does not contain KCN. ​

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