Solution for plating nickel on tungsten-based ceramic and chemical plating process thereof

Abstract

The invention discloses a solution for plating nickel on tungsten-based ceramic and a chemical plating process of the solution. The chemical nickel plating solution comprises the following components of 20-50 g / L of nickel aminosulfonate, 5-50 g / L of a composite complexing agent, 1.5-15 g / L of a reducing agent, 1-5 g / L of a composite stabilizer, 0.01-1.0 g / L of a wetting agent, 0.5-5 g / L of a brightener, 0.5-5 g / L of an accelerator and the balance of DI pure water. The solution is mainly used for chemical plating deposition of a nickel-boron plating layer on tungsten-based ceramic, and the use conditions are as follows: the pH is 4.5-6.5, T is 60-80 DEG C, and t is 2-60 min. According to the chemical nickel plating solution, the stability of the plating solution is improved; and the operability in a coating production process is high. The nickel coating obtained by the coating process is firm in binding force with the tungsten substrate, high in hardness and excellent in high temperature resistance and crack resistance, and can meet various performance requirements of the HTCC ceramic.

Description

Technical Field

[0001] The invention relates to the field of material chemistry, and in particular to a solution for plating nickel on tungsten-based ceramics and a chemical plating process thereof. Background Art

[0002] Alumina high temperature co-fired ceramics are the most common type of high temperature co-fired ceramics (HTCC). They have excellent heat dissipation performance, a thermal expansion coefficient that matches the chip, low dielectric loss, and high thermal conductivity. They can meet the higher heat dissipation requirements brought about by the rapid development of electronic devices towards miniaturization, multi-functions, and high power density. In the production process of aluminum nitride HTCC, high temperature resistant tungsten (W) slurry is required, but tungsten itself is not solderable and bondable, so the tungsten conductor on the surface of the aluminum nitride HTCC substrate needs to be plated with a solderable coating. Electroplating and chemical plating are common methods for producing surface pattern solderable coatings, but electroplating requires that all patterns are electrically conductive, while chemical plating does not have this requirement and is more suitable for the production of surface solderable coatings on complex separated pattern circuits.

[0003] When the mass fraction of boron (B) is 0.23%, the melting point of nickel-boron alloy is 1450°C. When the mass fraction of B increases to 4.3%, the melting point decreases slightly, but still reaches 1350°C. Compared with the nickel-phosphorus alloy with a melting point of 890°C when the mass fraction of phosphorus (P) is 7.9%, the nickel-boron alloy has better thermal stability, and the melting point of chemically plated nickel-boron is higher than that of chemically plated nickel-phosphorus, which is more suitable for the temperature requirements of HTCC heat treatment.

[0004] Chinese patent CN 114086162 A: A production line and production process for chemical nickel-palladium-gold on tungsten-based and tungsten alloy substrates, discloses a method for chemical nickel-palladium-gold on tungsten substrates, which mainly involves the process of automated production lines, and does not explain the coating conditions of chemical nickel-palladium-gold. Patent CN116695103A: A method for chemical nickel-palladium-gold plating on alumina high-temperature co-fired ceramic substrates, introduces a method for chemical nickel-palladium-gold plating on alumina high-temperature co-fired ceramic substrates, but all the chemicals used are from the foreign brand Shangcun, and only the process parameters can be adjusted, and the core plating solution formula is not mastered. Patent CN114481102B: Plating solution for chemical nickel-boron alloy coating, its preparation method and application, discloses a plating solution formula and method for chemical nickel-boron plating, but does not mention whether this method can be normally plated on tungsten-based ceramics, and whether the bonding strength meets the requirements.

[0005] In view of the shortcomings of the above-mentioned technologies, the present invention provides a plating solution for chemically plating nickel and boron on tungsten-based ceramics, and provides a process for chemically plating nickel, palladium and gold on tungsten-based ceramics to improve the bonding strength. The obtained nickel plating layer has a strong bonding strength with the tungsten substrate, high hardness, excellent high temperature resistance and crack resistance, and can meet various performance requirements of HTCC ceramics. Summary of the invention

[0006] In order to solve the above problems, the present invention provides a solution for plating nickel on tungsten-based ceramics, which improves the stability of the plating solution and has strong operability in the film coating production process.

[0007] The technical scheme of the present invention is: a solution for nickel plating on tungsten-based ceramics, wherein the chemical nickel plating solution comprises the following components in concentrations: nickel sulfamate: 20-50 g / L, a composite complexing agent: 5-50 g / L, a reducing agent: 1.5-15 g / L, a composite stabilizer: 1-5 g / L, a wetting agent: 0.01-1.0 g / L, a brightener: 0.5-5 g / L, an accelerator: 0.5-5 g / L and DI pure water: the balance.

[0008] Furthermore, the electroless nickel plating solution is used for electroless deposition of nickel-boron coating on tungsten-based ceramics, and the use conditions are: pH=4.5-6.5, T=60-80°C, t=2-60min.

[0009] Furthermore, the composite complexing agent is a composition of ethylenediamine and sodium iron ethylenediaminetetraacetate, wherein the molar ratio of ethylenediamine to Ni2+ is 4-8, and the mass ratio of ethylenediamine to sodium iron ethylenediaminetetraacetate is 10: 1. Its function is to complex the free Ni2+ in the solution and improve the stability of the plating solution.

[0010] Furthermore, the reducing agent is an aminoborane, including one or more of tri(dimethylamino)borane, monomethylamine borane, dimethylamine borane, and trimethylamine borane. During the reduction deposition process of nickel, a small amount of boron ions will co-deposit with nickel in the coating to form a nickel-boron alloy, thereby obtaining a coating with high temperature resistance and high hardness.

[0011] Furthermore, the composite stabilizer is a composition of unsaturated carboxylic acid or its salt and metal ions, wherein the unsaturated carboxylic acid or its salt is acrylic acid, sodium acrylate, methacrylic acid, sodium methacrylate, etc., with a mass concentration of 1-5 g / L, and the metal ions are provided by lead tungstate, wherein the lead ion concentration is 0.1-1.5 ppm. The combination of the two can greatly improve the stability of the plating solution and prevent the plating solution from decomposing and precipitating.

[0012] Furthermore, the wetting agent is lauroyl propyl betaine, which has good wetting and dispersing ability, can reduce the surface tension of the ceramic substrate, make Ni2+ deposit evenly on the surface of the complex substrate, and improve the throwing power.

[0013] Furthermore, the brightener is sodium dodecyl sulfate, which can refine the grains, prevent the crystal nuclei from growing too large to form nickel nodules, improve the flatness and fineness of the coating, and enhance the brightness.

[0014] Furthermore, the accelerator is 4-fluorothieno[2,3-c]pyridine-2-carboxylic acid. The fluorine in the accelerator has strong electronegativity, which can promote the hydroboration reaction and increase the deposition rate. At the same time, since it has no complexing effect on nickel ions, the reaction rate will not be reduced due to the complexing effect, and the adjustable concentration range is wider than that of traditional accelerators.

[0015] The present invention also provides a process for solution-plating nickel-palladium-gold using nickel plating on tungsten-based ceramics. The obtained nickel plating layer has a strong bonding force with the tungsten substrate, high hardness, high temperature resistance and crack resistance, and can meet various performance requirements of HTCC ceramics. The process comprises the following steps: Step 1, degreasing: Place the tungsten-based ceramic substrate in a degreasing solution to remove oil and other impurities attached to the surface, and then wash with water before proceeding to the next process; Step 2, micro-etching: through the action of tungsten etching solution and hydrogen peroxide, a layer of tungsten and its oxide on the surface is formed into a tungstate solution, the passivation layer is removed on the surface, the roughness is increased, the bonding strength is improved, and the next process is carried out after washing; Step 3, palladium activation: a layer of palladium atoms is deposited on the surface of the tungsten substrate by palladium hydrochloride activation as the catalytic active center for subsequent nickel plating, and then the next step is carried out after water washing; Step 4: Bottom nickel electroplating: pre-electroplating a thin nickel layer of 0.5-2.0 μm thick, and then enhance the bonding strength with the bottom tungsten substrate through subsequent heat treatment, and then electroplating a nickel layer of required thickness on it to ensure that the overall bonding strength meets the requirements, and then washing and proceeding to the next process; Step 5, heat treatment: Through high-temperature heat treatment, the nickel layer will diffuse into the tungsten conductor, so that the bonding force between the nickel layer and the base metal is greatly strengthened. In view of the fact that the chemical nickel-boron plating layer is easily oxidized in an oxygen-containing atmosphere at high temperatures, a reducing gas is introduced during heat treatment or a high vacuum environment is used; Step 6, pickling and activation: After heat treatment, the nickel layer will produce a passivation effect. The nickel oxide layer is removed by pickling to improve the bonding strength and ensure the normal progress of the subsequent chemical nickel reaction. After water washing, proceed to the next process.

[0016] Step 7, chemical nickel: deposit a nickel layer of specified thickness as required, and proceed to the next process after washing.

[0017] Step 8, chemical palladium: Introducing a palladium layer between the nickel layer and the gold layer can effectively prevent the diffusion and migration of nickel and avoid corrosion of the nickel layer. It can also effectively inhibit the oxidation of the nickel layer, prevent the generation of "nickel black" defects, and improve the long-term reliability of the coating. After washing, proceed to the next process.

[0018] Step nine, chemical gold: deposit a gold plating layer according to the required thickness to ensure welding reliability and conductivity.

[0019] Furthermore, the heat treatment conditions in step five are: 300-600° C., 5-30S under nitrogen atmosphere.

[0020] Furthermore, the pickling conditions of step six are: 2-6wt% citric acid, 25-35°C, 0.5-3min.

[0021] The beneficial effects of the present invention are: 1) The composite complexing agent is used in the electroless plating solution of the present invention. By controlling the molar ratio with Ni2+, the free nickel ions in the solution can be effectively complexed to improve the stability of the plating solution, while not causing excessive complexation to inhibit the sedimentation rate and affect the normal deposition of the nickel layer.

[0022] 2) The chemical plating solution of the present invention uses a composite stabilizer. The combination of heavy metal ions and unsaturated carboxylic acids or their salts greatly improves the stability of the plating solution, prevents precipitation and decomposition, and has good economic benefits.

[0023] 3) The fluorine-containing accelerator used in the electroless plating solution of the present invention utilizes the strong electronegativity of fluorine ions to promote the hydroboration reaction, stimulates the reduction activity of amine borane, and enables it to quickly and stably reduce free nickel ions and deposit them on the target substrate. At the same time, due to its weak complexing property, it has no obvious inhibitory effect on the sedimentation rate in a wide concentration range, and has strong production operability.

[0024] 4) Compared with the traditional copper-based chemical nickel-palladium-gold process, this process adds a treatment process before chemical nickel plating. Through high-temperature treatment, nickel and tungsten are diffused to form a tightly bonded thin nickel bottom layer, which improves the bonding strength between the coating and the substrate, and lays a solid foundation for the final deposition of a nickel-palladium-gold coating that meets the requirements on tungsten-based ceramics. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0026] Figure 1 This is the macroscopic appearance image of the ceramic after nickel-palladium-gold electroplating in Example 1.

[0027] Figure 2 This is a microscopic image of the surface after nickel-palladium-gold electroplating in Example 2.

[0028] Figure 3 This is a normal microscopic lattice image of Example 3 after nickel-palladium-gold electroplating.

[0029] Figure 4 This is the surface crack image of comparative example 1 after nickel-palladium-gold electroplating and baking.

[0030] Figure 5 This is the macroscopic appearance image of Comparative Example 2 after nickel plating.

[0031] Figure 6This is the image of the coating peeling off after nickel-palladium-gold plating in comparative example 2. DETAILED DESCRIPTION

[0032] The technical solution of the present invention will be clearly and completely described below through specific implementation methods.

[0033] The chemical nickel plating solution of the invention comprises the following components in concentrations: nickel sulfamate: 20-50 g / L, a composite complexing agent: 5-50 g / L, a reducing agent: 1.5-15 g / L, a composite stabilizer: 1-5 g / L, a wetting agent: 0.01-1.0 g / L, a brightener: 0.5-5 g / L, an accelerator: 0.5-5 g / L and DI pure water: the balance. Example

[0034] The chemical nickel plating solution of the present embodiment includes the following components in concentrations: the following components are added to prepare a chemical nickel plating solution with the following concentrations: Nickel sulfamate: 35g / L; Ethylenediamine: 45ml / L; EDTA sodium iron: 1.2 g / L; Dimethylamine borane: 5g / L; Lead tungstate: 1.2ppm; Sodium methacrylate: 3.5g / L; Lauramidopropyl betaine: 0.5g / L; Sodium dodecyl sulfate: 2.5 g / L; 4-Fluorothieno[2,3-c]pyridine-2-carboxylic acid: 1.5 g / L.

[0035] The obtained chemical nickel plating solution was adjusted to pH=4.6 and T=75°C with citric acid and NaOH.

[0036] The process method for chemically plating nickel, palladium and gold on tungsten-based ceramics in this embodiment includes the following process steps: Step 1: Degreasing. Place the tungsten-based ceramic substrate in a degreasing solution to remove impurities such as oil stains attached to the surface. After washing, proceed to the next process.

[0037] Step 2: Micro-etching. Through the action of tungsten etching solution and hydrogen peroxide, a layer of tungsten and its oxide on the surface is formed into a tungstate solution, which removes the passivation layer on the surface, increases the roughness and improves the bonding strength. After washing, proceed to the next process.

[0038] Step 3: Palladium activation: A layer of palladium atoms is deposited on the surface of the tungsten substrate by palladium hydrochloride activation as the catalytic active center for subsequent nickel deposition. After water washing, the next step is carried out.

[0039] Step 4: Bottom nickel electroplating. A thin layer of nickel is electroplated in advance, with a thickness of 0.5 μm. The bonding strength with the bottom tungsten substrate is enhanced by subsequent heat treatment, and then a nickel layer of the required thickness is electroplated on it to ensure that the overall bonding strength meets the requirements. After water washing, proceed to the next process.

[0040] Step 5, heat treatment. Through high-temperature heat treatment, the nickel layer will diffuse into the tungsten conductor, greatly strengthening the bonding force between the nickel layer and the base metal. In view of the fact that the chemically plated nickel-boron coating is easily oxidized in an oxygen-containing atmosphere at high temperatures, a reducing gas is introduced during heat treatment or a high vacuum environment is used. Preferably, the heat treatment conditions are: 300-600°C, 5-30S in a nitrogen atmosphere.

[0041] Step 6: Pickling and activation. After heat treatment, the nickel layer will have a passivation effect. Pickling treatment removes the nickel oxide layer, improves the bonding strength, and ensures the normal progress of the subsequent chemical nickel reaction. After water washing, proceed to the next step. Preferably, the pickling conditions are: 2-6wt% citric acid, 25-35℃, 0.5-3min.

[0042] Step 7: Chemical nickel. Deposit a nickel layer of specified thickness as required. After washing, proceed to the next step.

[0043] Step 8: Chemical palladium. Introducing a palladium layer between the nickel layer and the gold layer can effectively prevent the diffusion and migration of nickel, avoid corrosion of the nickel layer, and effectively inhibit the oxidation of the nickel layer, prevent the generation of "nickel black" defects, and improve the long-term reliability of the coating. After washing, proceed to the next process.

[0044] Step 9: Chemical gold: Deposit a gold plating layer according to the required thickness to ensure welding reliability and conductivity.

[0045] Among them, the medicines used in steps 1 to 3, and steps 8 to 9 are all purchased from Zhuhai Chuangzhi Chenggong Technology Co., Ltd. Specifically: Oil removal, CG1551 series: CG1551-3: 60-100ml / l, 25-35℃, 3-5min.

[0046] Micro-etching, CG702 series: CG702B: 450-550ml / L, H2O2: 140-200g / L, pH=6.0-7.0, 60-70℃, 10-90S.

[0047] Palladium activation, CG1563 series: CG1563A: 20-30ml / L, CG1563B: 80-120ml / L, HCl: 15-25ml / L, 25-30℃, 0.5-3min.

[0048] Chemical palladium, CG1557 series: CG1557-1: 100-140ml / L, CG1557B: 8-12ml / L, CG1557C: 120-140ml / L, CG1557A: 80-120ml / L. pH=7.0-7.5, 50-58℃, 20-60min.

[0049] Chemical gold, CG1558 series: CG1558-8M: 400-600ml / L, CG1558-8A: 15-25ml / L, Au: 0.5-1.0g / L, pH=5.0-6.0, 75-85℃, 20-60min. Example

[0050] Add the following components to prepare a chemical nickel plating solution of the following concentrations: Nickel sulfamate: 30g / L; Ethylenediamine: 55ml / L; EDTA sodium iron: 0.8 g / L; Dimethylamine borane: 10 g / L; Lead tungstate: 1.2ppm; Sodium methacrylate: 3.5g / L; Lauramidopropyl betaine: 0.5g / L; Sodium dodecyl sulfate: 3.5 g / L; 4-Fluorothieno[2,3-c]pyridine-2-carboxylic acid: 1.2 g / L.

[0051] The obtained chemical nickel plating solution was adjusted to pH=5.8 and T=70°C with citric acid and NaOH.

[0052] In this embodiment, the steps of completing the tungsten-based ceramic according to the process flow are similar to those of Embodiment 1, wherein in step 4, the bottom nickel electroless plating thickness is 1.0 μm, and the other steps are performed according to the median values ​​of the given conditions. Example

[0053] 1. Add the following components to prepare a chemical nickel plating solution with the following concentrations: Nickel sulfamate: 30g / L; Ethylenediamine: 50ml / L; EDTA sodium iron: 1.5 g / L; Trimethylamine borane: 15g / L; Lead tungstate: 1.5ppm; Sodium methacrylate: 2.8g / L; Lauramidopropyl betaine: 0.8g / L; Sodium dodecyl sulfate: 4.5 g / L; 4-Fluorothieno[2,3-c]pyridine-2-carboxylic acid: 1.5 g / L.

[0054] The obtained chemical nickel plating solution was adjusted to pH=6.5 and T=65°C with citric acid and NaOH.

[0055] In this embodiment, the steps of completing the tungsten-based ceramic according to the process flow are similar to those of Embodiment 1, wherein in step 4, the bottom nickel electroless plating thickness is 1.8 μm, and the other steps are performed according to the median values ​​of the given conditions.

[0056] Comparative Example 1 Add the following components to prepare a chemical nickel plating solution of the following concentrations: Nickel sulfamate: 30g / L; Ethylenediamine: 50ml / L; EDTA sodium iron: 1.5 g / L; Trimethylamine borane: 15g / L; Lead tungstate: 1.5ppm; Sodium methacrylate: 2.8g / L; Lauramidopropyl betaine: 0.6g / L; Sodium dodecyl sulfate: 0g / L; 4-Fluorothieno[2,3-c]pyridine-2-carboxylic acid: 0.5 g / L.

[0057] The obtained chemical nickel plating solution was adjusted to pH=6.5 and T=65°C with citric acid and NaOH.

[0058] The tungsten-based ceramics complete the chemical nickel-palladium-gold process from step one to step nine according to the process flow, wherein in step four, the bottom nickel electroless plating thickness is 1.5 μm, and the other steps are performed according to the median value of the given conditions.

[0059] Comparative Example 2 Add the following components to prepare a chemical nickel plating solution of the following concentrations: Nickel sulfamate: 30g / L; Ethylenediamine: 50ml / L; EDTA sodium iron: 1.5 g / L; Trimethylamine borane: 15g / L; Lead tungstate: 1.5ppm; Sodium methacrylate: 2.8g / L; Lauramidopropyl betaine: 0.8g / L; Sodium dodecyl sulfate: 4.5 g / L; 4-Fluorothieno[2,3-c]pyridine-2-carboxylic acid: 1.5 g / L.

[0060] 2. The obtained chemical nickel plating solution was adjusted to pH=6.5 and T=65°C with citric acid and NaOH.

[0061] 3. The tungsten-based ceramics are processed through the chemical nickel-palladium-gold process of steps 1 to 9 according to the process flow, wherein steps 4 to 6 are omitted, i.e., the bottomless nickel electroless plating, high temperature treatment, and acid pickling activation process are performed, and nickel-palladium-gold is directly electrolessly plated after palladium activation.

[0062] Table 1 Coating performance test table Chemical Plating Example Nickel layer hardness / HV Microcrystalline Cracks after high temperature baking Gold wire bonding tensile strength / N SnPb welding tensile strength value / N Example 1 678.5 Smaller grains none 0.1168 53.5 Example 2 659.7 Smaller grains none 0.1095 48.7 Example 3 712.3 Smaller grains none 0.1147 39.6 Comparative Example 1 598.4 Larger grains There are 2-3 lines under 250X field of view 0.0954 49.3 Comparative Example 2 643.6 Larger grains none 0.0453 12.5 It can be seen from the above examples and comparative examples that after the nickel-boron coating is plated with the plating solution of the present invention in Example 1 to Example 3, the hardness of the nickel layer is above 650HV, the grains are small, the surface is bright, and the coating has no cracks after high-temperature baking. The gold wire bonding tensile force values ​​are all greater than 0.0735N, and the SnPb welding tensile force values ​​are all greater than 2Kg. Referring to GJB548B-2005 "Microelectronic Device Test Methods and Procedures Bonding Strength (Destructive Bonding Tensile Test)", the strength bonding index is met, and the surface modification assembly process requirements of ceramic products can be met. In Comparative Example 1, no brightener is added to the nickel solution, the resulting coating has large grains, and the internal stress is also large. After high-temperature baking, obvious cracks appear in the coating. In Comparative Example 2, the bottom nickel high-temperature treatment plating process of step 4 to step 6 is not adopted. After the thick nickel layer is plated, the surface is abnormally bubbling, and after the nickel palladium gold is plated, the surface peels off, that is, the bonding force is poor, and the coating deposited on the tungsten-based ceramic does not meet the bonding force requirements.

[0063] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art may make various modifications or equivalent substitutions to the present invention within the essence and protection scope of the present invention, and such modifications or equivalent substitutions should also be deemed to fall within the protection scope of the technical solution of the present invention.

Claims

1. A solution for plating nickel on tungsten-based ceramics, characterized in that: The chemical nickel plating solution includes components with the following concentrations: nickel sulfamate: 20-50 g / L, composite complexing agent: 5-50 g / L, reducing agent: 1.5-15 g / L, composite stabilizer: 1-5 g / L, wetting agent: 0.01-1.0 g / L, brightener: 0.5-5 g / L, accelerator: 0.5-5 g / L and DI pure water: balance.

2. The solution for plating nickel on tungsten-based ceramics according to claim 1, characterized in that: The electroless nickel plating solution is used for the electroless deposition of nickel-boron coating on tungsten-based ceramics. The use conditions are: pH=4.5-6.5, T=60-80℃, t=2-60min.

3. The solution for plating nickel on tungsten-based ceramics according to claim 1, characterized in that: The composite complexing agent is a composition of ethylenediamine and sodium iron ethylenediaminetetraacetate, wherein the molar ratio of ethylenediamine to Ni2+ is 4-8, and the mass ratio of ethylenediamine to sodium iron ethylenediaminetetraacetate is 10:

1.

4. The solution for plating nickel on tungsten-based ceramics according to claim 1, characterized in that: The reducing agent is an aminoborane, including one or more of tri(dimethylamino)borane, monomethylamine borane, dimethylamine borane and trimethylamine borane.

5. The solution for plating nickel on tungsten-based ceramics according to claim 1, characterized in that: The composite stabilizer is a composition of unsaturated carboxylic acid or its salt and metal ions, wherein the unsaturated carboxylic acid or its salt is acrylic acid, sodium acrylate, methacrylic acid, sodium methacrylate, etc., with a mass concentration of 1-5g / L, and the metal ions are provided by lead tungstate, wherein the lead ion concentration is 0.1-1.5ppm.

6. The solution for plating nickel on tungsten-based ceramics according to claim 1, characterized in that: The wetting agent is lauryl amide propyl betaine.

7. The solution for plating nickel on tungsten-based ceramics according to claim 1, characterized in that: The brightener is sodium lauryl sulfate.

8. The solution for plating nickel on tungsten-based ceramics according to claim 1, characterized in that: The accelerator is 4-fluorothieno[2,3-c]pyridine-2-carboxylic acid.

9. The process of solution-based nickel-palladium-gold plating on tungsten-based ceramics according to claim 1 is characterized in that: The steps include: Step 1, degreasing: Place the tungsten-based ceramic substrate in a degreasing solution to remove oil and other impurities attached to the surface, and then wash with water before proceeding to the next process; Step 2, micro-etching: through the action of tungsten etching solution and hydrogen peroxide, a layer of tungsten and its oxide on the surface is formed into a tungstate solution, the passivation layer is removed on the surface, the roughness is increased, the bonding strength is improved, and the next process is carried out after washing; Step 3, palladium activation: a layer of palladium atoms is deposited on the surface of the tungsten substrate by palladium hydrochloride activation as the catalytic active center for subsequent nickel plating, and then the next process is carried out after water washing; Step 4: Bottom nickel electroplating: pre-electroplating a thin nickel layer of 0.5-2.0 μm thick, and then enhance the bonding strength with the bottom tungsten substrate through subsequent heat treatment, and then electroplating a nickel layer of required thickness on it to ensure that the overall bonding strength meets the requirements, and then washing and proceeding to the next process; Step 5, heat treatment: Through high-temperature heat treatment, the nickel layer will diffuse into the tungsten conductor, so that the bonding force between the nickel layer and the base metal is greatly strengthened. In view of the fact that the chemical nickel-boron plating layer is easily oxidized in an oxygen-containing atmosphere at high temperatures, a reducing gas is introduced during heat treatment or a high vacuum environment is used; Step 6, pickling and activation: After heat treatment, the nickel layer will produce a passivation effect. The nickel oxide layer is removed by pickling to improve the bonding strength and ensure the normal progress of the subsequent chemical nickel reaction. After water washing, the next process is carried out; Step 7, chemical nickel: deposit a nickel layer of specified thickness as required, and proceed to the next process after washing; Step 8, chemical palladium: Introducing a palladium layer between the nickel layer and the gold layer can effectively prevent the diffusion and migration of nickel, avoid corrosion of the nickel layer, and effectively inhibit the oxidation of the nickel layer, prevent the generation of "nickel black" defects, and improve the long-term reliability of the coating. After washing, proceed to the next process; Step nine, chemical gold: deposit a gold plating layer according to the required thickness to ensure welding reliability and conductivity.

10. The process for chemically plating nickel-palladium-gold according to claim 8, characterized in that: The heat treatment conditions of step 5 are: 300-600°C, 5-30S under nitrogen atmosphere; the pickling conditions of step 6 are: 2-6wt% citric acid, 25-35°C, 0.5-3min.

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