Method for electroless plating nickel-boron on a cermet high-temperature co-fired substrate tungsten metal

Abstract

The application relates to a method for electroless plating of nickel-boron on a metal ceramic high-temperature co-fired substrate tungsten metal, which comprises the following steps in sequence: alkali washing, etching, activation and electroless plating of nickel; wherein the electroless plating of nickel comprises a nickel ion source, a boron reducing agent solution, an additive solution and water. Through optimization of the whole process, high bonding force, high uniformity, excellent weldability and bondability are realized, meanwhile, sufficient nickel source supply improves the uniformity of the boron plating layer, and a simple operation process improves production efficiency.

Description

Technical Field

[0001] This invention relates to the field of semiconductor surface treatment technology, and in particular to a method for electroless nickel-boron plating on tungsten metal on a high-temperature co-fired metal-ceramic substrate. Background Technology

[0002] Currently, tungsten (W) paste is used to fill or print conductor lines in high-temperature co-fired metal ceramic substrates (HTCC), which has advantages such as high thermal conductivity, high temperature resistance, and low dielectric loss. However, the dense oxide layer on the surface of tungsten metal results in its lack of autocatalytic activity, direct solderability, and bonding capability, which cannot meet the requirements of chip bonding, brazing, and other post-assembly processes.

[0003] Electroless nickel-boron (Ni-B) plating has become the preferred option for modifying HTCC tungsten conductors due to its superior thermal stability compared to Ni-P, high hardness, adjustable solderability, low thermal resistance, and good thermal expansion matching with tungsten. However, the dense oxide film (WO3) on the tungsten surface is difficult to remove, lacks autocatalytic activity, and differs from Ni-B in lattice / thermal expansion. Direct electroless plating suffers from common bottlenecks such as difficulty in initiating plating, localized incomplete plating, weak coating adhesion, high porosity, and unstable solderability or bonding performance.

[0004] Existing technology CN115417696A discloses a surface electroplating process for tungsten layers on alumina products. This process uses electroplating instead of chemical plating, relies on conductive paths, and is prone to missed plating in complex patterns or deep holes, resulting in poor uniformity. Existing technology CN105858728A discloses a method for secondary metal chemical plating on the surface of high-temperature co-fired ceramics. This method improves adhesion by introducing a copper transition layer between tungsten and nickel. However, the copper-nickel-tungsten three-layer interface introduced by this method easily leads to stress concentration and decreased reliability, and the process is more complex and costly. Existing technology CN114086162A discloses a production line and process for chemical palladium plating on tungsten-based and tungsten alloy substrates. It adopts an automated production line design and optimizes loading and transfer, but it does not solve the fundamental problems of difficult plating initiation and weak adhesion on tungsten surfaces.

[0005] The current mainstream modification scheme is mainly electroless nickel-palladium-gold (Ni-Pd-Au) plating, which has problems such as dependence on imported plating solutions, high cost, complex process, and unresolved W-Ni interface bonding. On the other hand, electroless nickel-phosphorus (Ni-P) plating has insufficient thermal stability, is prone to embrittlement at high temperatures, and its solderability decreases significantly with increasing phosphorus content, making it difficult to adapt to the long-term high-temperature service scenarios of HTCC.

[0006] Currently available tungsten-based electroless Ni-B plating technologies are mostly general formulas and processes, without being specifically designed for the high density, patterned wiring, and ceramic-metal composite structure of tungsten metal in HTCC substrates. They generally suffer from defects such as poor pretreatment compatibility, low activation efficiency, insufficient plating solution stability, weak interfacial adhesion, and substandard solderability and bonding performance, which cannot meet the industrial requirements of high reliability, precision patterns, and mass production of HTCC substrates.

[0007] Therefore, developing a method for electroless nickel-boron plating on tungsten metal on a high-temperature co-fired metal-ceramic substrate has become an urgent problem to be solved. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention provides a method for electroless nickel-boron plating on tungsten metal on a high-temperature co-fired metal-ceramic substrate. Through full-process optimization, it achieves high adhesion, high uniformity, excellent solderability and bonding capability. At the same time, a sufficient supply of nickel source improves the uniformity of the boron plating layer. The simplified operation process also increases production efficiency.

[0009] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for electroless nickel-boron plating on tungsten metal on a high-temperature co-fired metal-ceramic substrate, wherein the electroless nickel-boron plating method comprises the following steps in sequence: alkaline washing, etching, activation, and electroless nickel plating. The electroless nickel plating solution includes a nickel ion source, a boron reducing agent solution, an additive solution, and water.

[0010] This invention achieves surface cleanliness and activation by optimizing cleaning, etching, and activation processes, effectively reducing the difficulty of starting the plating process; it significantly improves the adhesion of the plating layer and prevents peeling by modifying the interface and controlling the deposition; it improves the continuity of the plating layer by stabilizing the plating solution system and ensuring a sufficient supply of nickel source, avoiding localized missed plating and reducing the need for continuous replenishment of the plating solution; ultimately, it enables the substrate to obtain excellent solderability, bonding capability, and mechanical properties, meeting the requirements for high-reliability packaging applications.

[0011] As a preferred technical solution of the present invention, the pH value of the electroless nickel plating solution is 3-6, for example, it can be 3, 3.5, 4, 4.5, 5, 5.5 or 6, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0012] In this invention, the pH of the electroless nickel plating solution is adjusted to 3-6 using a pH buffer solution with a concentration of 2-12 mg / L. If the pH of the electroless nickel plating solution is too low, the acidity is too strong, leading to a vigorous hydrogen evolution reaction, which easily increases the porosity of the plating layer, resulting in a loose structure, slow reaction rate, low deposition efficiency, and a long time required to reach the target thickness. This may result in a thin or uneven plating layer with high internal stress. The compressive stress accumulated inside the plating layer may weaken the bond between the plating layer and the substrate, making it prone to peeling. If the pH of the electroless nickel plating solution is too high, the deposition rate is too fast, and nickel atoms do not have enough time to arrange themselves regularly, leading to increased internal stress in the plating layer. This may cause cracks and a decrease in density. While a thicker plating layer may be obtained in a short time, the process is difficult to control, resulting in poor uniformity. Furthermore, excessively fast deposition leads to uneven plating growth, and the internal stress manifests as tensile stress, which weakens the bond strength between the plating layer and the substrate.

[0013] In this invention, the alkaline washing process includes a preparatory step, in which a cleaning solution, an etching solution, an activating solution, and a chemical nickel plating solution are prepared and placed in the cleaning tank, etching tank, activation tank, and nickel plating tank, respectively. The cleaning solution is prepared by first adding a portion of water to the cleaning tank, then adding the alkali source, and finally adding the remaining water. This order of addition prevents the alkali solution from corroding the tank. The preparation of the etching solution, activating solution, and chemical nickel plating solution is similar and will not be described in detail here.

[0014] In this invention, the electroless nickel plating process includes a post-processing step, in which the high-temperature co-fired substrate is removed from the rack, excess electroless nickel plating solution is rinsed off with water, and then air-dried.

[0015] Preferably, the nickel ion source includes a nickel sulfate solution and a nickel chloride solution.

[0016] Preferably, the concentrations of the nickel sulfate solution and the nickel chloride solution are each independently 1-10 mol / L, for example, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L, 9 mol / L or 10 mol / L, but are not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0017] Preferably, the mass ratio of the nickel sulfate solution to the nickel chloride solution is 1:(0.1-5.0), for example, it can be 1:0.1, 1:0.5, 1:1, 1:2, 1:3, 1:4 or 1:5, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0018] Preferably, the concentration of nickel ions in the electroless nickel plating solution is 9-12 mol / L, for example, it can be 9 mol / L, 10 mol / L, 11 mol / L or 12 mol / L, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0019] As a preferred technical solution of the present invention, the temperature of the electroless nickel plating is 30-90℃, for example, it can be 30℃, 40℃, 50℃, 60℃, 70℃, 80℃ or 90℃, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0020] Preferably, the electroless nickel plating time is 30-130 min, for example, it can be 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min or 130 min, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] As a preferred embodiment of the present invention, the cleaning solution used in the alkaline washing includes an alkali source and water.

[0022] Preferably, the alkali source includes sodium hydroxide solution and potassium hydroxide solution.

[0023] Preferably, the concentrations of the sodium hydroxide solution and the potassium hydroxide solution are each independently 0.1-0.15 mol / L, for example, 0.1 mol / L, 0.11 mol / L, 0.12 mol / L, 0.13 mol / L, 0.14 mol / L or 0.15 mol / L, but are not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0024] Preferably, the mass ratio of the sodium hydroxide solution to the potassium hydroxide solution is 1:(0.1-9.0), for example, it can be 1:0.1, 1:0.5, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8 or 1:9, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0025] Preferably, the total alkali concentration of the cleaning solution is 0.1-0.3 mol / L, for example, it can be 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L or 0.3 mol / L, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0026] As a preferred technical solution of the present invention, the temperature of the alkaline washing is 30-90℃, for example, it can be 30℃, 40℃, 50℃, 60℃, 70℃, 80℃ or 90℃, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0027] Preferably, the alkaline washing time is 2-15 min, for example, it can be 2 min, 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, 11 min, 12 min, 13 min, 14 min or 15 min, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0028] As a preferred embodiment of the present invention, the etching solution includes an aqueous solution of barium hydroxide.

[0029] Preferably, the concentration of barium hydroxide in the etching solution is 28-170 g / L, for example, it can be 28 g / L, 30 g / L, 40 g / L, 50 g / L, 60 g / L, 70 g / L, 80 g / L, 90 g / L, 100 g / L, 110 g / L, 120 g / L, 130 g / L, 140 g / L, 150 g / L, 160 g / L or 170 g / L, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0030] As a preferred technical solution of the present invention, the etching time is 1-9 min, for example, it can be 1 min, 2 min, 3 min, 4 min, 5 min, 6 min, 7 min, 8 min or 9 min, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0031] Preferably, the etching temperature is 30-90°C, for example, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C or 90°C, but not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0032] As a preferred embodiment of the present invention, the activation solution includes a palladium activation solution and water.

[0033] Preferably, the palladium activation solution comprises palladium chloride solution and dichlorotetraamminepalladium solution.

[0034] Preferably, the concentration of palladium ions in the activation solution is 10-30 ppm, for example, 10 ppm, 15 ppm, 20 ppm, 25 ppm or 30 ppm, but not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0035] As a preferred technical solution of the present invention, the activation temperature is 30-90℃, for example, it can be 30℃, 40℃, 50℃, 60℃, 70℃, 80℃ or 90℃, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0036] Preferably, the activation time is 1-6 min, for example, it can be 1 min, 2 min, 3 min, 4 min, 5 min or 6 min, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0037] In this invention, during alkaline washing, etching, activation, and nickel plating, the high-temperature co-fired metal-ceramic substrate is hung on a fixture, which is made of polytetrafluoroethylene (PTFE) material.

[0038] As a preferred embodiment of the present invention, the concentration of the pH buffer solution is 2-12 mg / L, for example, it can be 2 mg / L, 4 mg / L, 6 mg / L, 8 mg / L, 10 mg / L or 12 mg / L, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0039] In this invention, the pH value of the electroless nickel plating solution is adjusted to 3-6 by using a pH buffer solution. The pH value of the pH buffer solution can be 4.0 or 6.82.

[0040] In this invention, the boron reducing agent is an aminoborane, including any one or a combination of at least two of tri(dimethylamino)borane, monomethylamineborane, dimethylamineborane, and trimethylamineborane.

[0041] Preferably, the concentration of the boron reducing agent solution is 60-110 mg / L, for example, it can be 60 mg / L, 70 mg / L, 80 mg / L, 90 mg / L, 100 mg / L or 110 mg / L, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0042] In this invention, the additive includes a complexing agent and a stabilizer. The complexing agent includes ethylenediamine and / or sodium ethylenediaminetetraacetate. The stabilizer includes a composition of an unsaturated carboxylic acid or its salt with a metal ion, wherein the unsaturated carboxylic acid or its salt is any one of acrylic acid, sodium acrylate, methacrylic acid, or sodium methacrylate.

[0043] Preferably, the concentration of the additive solution is 2-18 mg / L, for example, it can be 2 mg / L, 4 mg / L, 6 mg / L, 8 mg / L, 10 mg / L, 12 mg / L, 14 mg / L, 16 mg / L or 18 mg / L, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0044] Compared with the prior art, the present invention has at least the following beneficial effects: This invention relates to a method for electroless nickel-boron plating on tungsten metal on a high-temperature co-fired metal-ceramic substrate. By improving the entire process, optimizing the cleaning, etching, and activation processes, surface cleanliness and activation are achieved, effectively reducing the difficulty of starting the plating process. Through interface modification and deposition control, the adhesion of the plating layer is significantly improved, preventing peeling and flaking. By stabilizing the plating solution system and ensuring a sufficient supply of nickel source, the continuity of the plating layer is improved, avoiding localized missed plating and reducing the need for continuous replenishment of the plating solution. Ultimately, the substrate achieves excellent solderability, bonding capability, and mechanical properties, meeting the requirements for high-reliability packaging. The density of the plating layer is ≥92%, and under preferred conditions, the density is ≥97%. Attached Figure Description

[0045] Figure 1 This is a process flow diagram of the electroless nickel-boron plating process on tungsten metal on a high-temperature co-fired metal-ceramic substrate according to the present invention. Detailed Implementation

[0046] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0047] Example 1 This embodiment provides a method for electroless nickel-boron plating on tungsten metal on a high-temperature co-fired metal-ceramic substrate, the method comprising the following steps: (1) Preparation: Prepare cleaning solution, etching solution, activation solution and electroless nickel plating solution, and place them in the cleaning tank, etching tank, activation tank and nickel plating tank respectively; The cleaning solution includes an alkali source and water. The alkali source includes a mixed solution of 0.12 mol / L sodium hydroxide solution and 0.12 mol / L potassium hydroxide solution, wherein the mass ratio of the sodium hydroxide solution to the potassium hydroxide solution is 1:5, and the total alkali concentration of the cleaning solution is 0.20 mol / L. The etching solution includes an aqueous solution of barium hydroxide, and the concentration of barium hydroxide in the etching solution is 100 g / L; The activation solution includes a palladium activation solution and water, wherein the palladium activation solution includes a palladium chloride solution and a dichlorotetraamminepalladium solution, and the concentration of palladium ions in the activation solution is 15 ppm; The electroless nickel plating solution comprises a nickel ion source, a pH buffer solution, a boron reducing agent solution, an additive solution, and water. The pH value of the electroless nickel plating solution is 5. The nickel ion source is a 1 mol / L nickel sulfate solution and a 10 mol / L nickel chloride solution, with a mass ratio of 1:3. The concentration of nickel ions in the electroless nickel plating solution is 12 mol / L. The boron reducing agent solution is monomethylamine borane with a concentration of 90 mg / L. The additive solution is a combination of sodium ethylenediaminetetraacetate and acrylic acid, with each component having a concentration of 10 mg / L. (2) Hanging: Hang the high-temperature co-fired metal ceramic substrate to be plated on the hanger; (3) Alkaline washing: Hang the hanger on the rocker arm of the cleaning tank and suspend it in the cleaning solution. Clean at 60°C for 10 minutes, then rinse with pure water for 1 minute and remove the hanger. (4) Etching: Hang the fixture on the rocker arm of the etching tank and suspend it in the etching solution. Etch at 60°C for 5 minutes, then remove the fixture. (5) Activation: Hang the fixture on the rocker arm of the activation tank and suspend it in the activation liquid. Activate at 60°C for 4 minutes, then remove the fixture. (6) Chemical nickel plating: Hang the rack on the rocker arm of the nickel plating tank and suspend it in the nickel plating solution. Plating nickel at 60°C for 80 minutes, then remove the rack. (7) Post-processing: Remove the nickel-boron plated metal-ceramic high-temperature co-fired substrate from the rack, rinse off the excess nickel liquid with pure water, and air dry.

[0048] Example 2 This embodiment provides a method for electroless nickel-boron plating on tungsten metal on a high-temperature co-fired metal-ceramic substrate, the method comprising the following steps: (1) Preparation: Prepare cleaning solution, etching solution, activation solution and electroless nickel plating solution, and place them in the cleaning tank, etching tank, activation tank and nickel plating tank respectively; The cleaning solution includes an alkali source and water. The alkali source includes a mixed solution of 0.1 mol / L sodium hydroxide solution and 0.15 mol / L potassium hydroxide solution, wherein the mass ratio of the sodium hydroxide solution to the potassium hydroxide solution is 1:0.1, and the total alkali concentration of the cleaning solution is 0.24 mol / L. The etching solution includes an aqueous solution of barium hydroxide, and the concentration of barium hydroxide in the etching solution is 130 g / L. The activation solution includes a palladium activation solution and water. The palladium activation solution includes a palladium chloride solution and a dichlorotetraamminepalladium solution. The concentration of palladium ions in the activation solution is 20 ppm. The electroless nickel plating solution comprises a nickel ion source, a pH buffer solution, a boron reducing agent solution, an additive solution, and water. The pH value of the electroless nickel plating solution is 6. The nickel ion source consists of a 2 mol / L nickel sulfate solution and a 9 mol / L nickel chloride solution, with a mass ratio of 1:0.1. The concentration of nickel ions in the electroless nickel plating solution is 2 mol / L. The boron reducing agent solution is dimethylamine borane with a concentration of 60 mg / L. The additive solution consists of ethylenediamine and sodium acrylate, each with a concentration of 18 mg / L. (2) Hanging: Hang the high-temperature co-fired metal ceramic substrate to be plated on the hanger; (3) Alkaline washing: Hang the hanger on the rocker arm of the cleaning tank and suspend it in the cleaning solution. Clean at 30°C for 15 minutes, then rinse with pure water for 1 minute and remove the hanger. (4) Etching: Hang the fixture on the rocker arm of the etching tank and suspend it in the etching solution. Etch at 90°C for 1 minute and then remove the fixture. (5) Activation: Hang the fixture on the rocker arm of the activation tank and suspend it in the activation liquid. Activate at 30°C for 6 minutes and then remove the fixture. (6) Chemical nickel plating: Hang the rack on the rocker arm of the nickel plating tank and suspend it in the nickel plating solution. Plating nickel at 90°C for 30 minutes, then remove the rack. (7) Post-processing: Remove the nickel-boron plated metal-ceramic high-temperature co-fired substrate from the rack, rinse off the excess nickel liquid with pure water, and air dry.

[0049] Example 3 This embodiment provides a method for electroless nickel-boron plating on tungsten metal on a high-temperature co-fired metal-ceramic substrate, the method comprising the following steps: (1) Preparation: Prepare cleaning solution, etching solution, activation solution and electroless nickel plating solution, and place them in the cleaning tank, etching tank, activation tank and nickel plating tank respectively; The cleaning solution includes an alkali source and water. The alkali source includes a mixed solution of 0.15 mol / L sodium hydroxide solution and 0.15 mol / L potassium hydroxide solution, wherein the mass ratio of sodium hydroxide solution to potassium hydroxide solution is 1:9, and the total alkali concentration of the cleaning solution is 0.26 mol / L. The etching solution includes an aqueous solution of barium hydroxide, and the concentration of barium hydroxide in the etching solution is 150 g / L. The activation solution includes a palladium activation solution and water. The palladium activation solution includes a palladium chloride solution and a dichlorotetraamminepalladium solution. The concentration of palladium ions in the activation solution is 25 ppm. The electroless nickel plating solution comprises a nickel ion source, a pH buffer solution, a boron reducing agent solution, an additive solution, and water. The pH value of the electroless nickel plating solution is 3. The nickel ion source consists of a 3 mol / L nickel sulfate solution and an 8 mol / L nickel chloride solution, with a mass ratio of 1:5.0. The concentration of nickel ions in the electroless nickel plating solution is 12 mol / L. The boron reducing agent solution is trimethylamine borane with a concentration of 110 mg / L. The additive solution consists of ethylenediamine and sodium methacrylate, each with a concentration of 2 mg / L. (2) Hanging: Hang the high-temperature co-fired metal ceramic substrate to be plated on the hanger; (3) Alkaline washing: Hang the hanger on the rocker arm of the cleaning tank and suspend it in the cleaning solution. Clean at 90°C for 2 minutes, then rinse with pure water for 1 minute and remove the hanger. (4) Etching: Hang the fixture on the rocker arm of the etching tank and suspend it in the etching solution. Etch at 30°C for 9 minutes, then remove the fixture; (5) Activation: Hang the fixture on the rocker arm of the activation tank and suspend it in the activation liquid. Activate at 90°C for 1 minute and then remove the fixture. (6) Chemical nickel plating: Hang the rack on the rocker arm of the nickel plating tank and suspend it in the nickel plating solution. Plating nickel at 30°C for 130 minutes, then remove the rack. (7) Post-processing: Remove the nickel-boron plated metal-ceramic high-temperature co-fired substrate from the rack, rinse off the excess nickel liquid with pure water, and air dry.

[0050] Example 4 This embodiment provides a method for electroless nickel-boron plating on tungsten metal on a high-temperature co-fired metal-ceramic substrate. The only difference from Embodiment 1 is that the total alkali concentration of the cleaning solution is 0.05 mol / L, while the rest are the same as in Embodiment 1.

[0051] Example 5 This embodiment provides a method for electroless nickel-boron plating on tungsten metal on a high-temperature co-fired metal-ceramic substrate. The only difference from Embodiment 1 is that the total alkali concentration of the cleaning solution is 0.35 mol / L, while the rest is the same as in Embodiment 1.

[0052] Example 6 This embodiment provides a method for electroless nickel-boron plating on tungsten metal on a high-temperature co-fired metal-ceramic substrate. The only difference from Embodiment 1 is that the nickel ion source is a single nickel source, which is a nickel sulfate solution, and the concentration of nickel ions remains unchanged.

[0053] Example 7 This embodiment provides a method for electroless nickel-boron plating on tungsten metal on a high-temperature co-fired metal-ceramic substrate. The only difference from Embodiment 1 is that the pH value of the electroless nickel plating solution is 2, while the rest are the same as in Embodiment 1.

[0054] Example 8 This embodiment provides a method for electroless nickel-boron plating on tungsten metal on a high-temperature co-fired metal-ceramic substrate. The only difference from Embodiment 1 is that the pH value of the electroless nickel plating solution is 7, while the rest are the same as in Embodiment 1.

[0055] Comparative Example 1 This comparative example provides a method for electroless nickel-boron plating on tungsten metal on a high-temperature co-fired metal-ceramic substrate. The difference from Example 1 is that step (3) alkaline washing is omitted, while the rest is the same as Example 1.

[0056] Comparative Example 2 This comparative example provides a method for electroless nickel-boron plating on tungsten metal on a high-temperature co-fired metal-ceramic substrate. The difference from Example 1 is that step (4) etching is omitted, while the rest are the same as in Example 1.

[0057] Comparative Example 3 This comparative example provides a method for electroless nickel-boron plating on tungsten metal on a high-temperature co-fired metal-ceramic substrate. The difference from Example 1 is that step (5) activation is omitted, while the rest is the same as Example 1.

[0058] Performance Testing: The density, thickness, and tensile strength of the coatings prepared in Examples 1-8 and Comparative Examples 1-3 were tested. Density Testing: Using the Archimedes displacement method, the dry weight M1 of the nickel-plated part was weighed, placed in a vacuum drying oven, and the vacuum was evacuated to 0.095 MPa for 15 minutes. The vacuum valve was then closed, the stop clamp was opened, and pure water was allowed to submerge the sample for 30 minutes. The suspended weight M2 was then weighed. The density was calculated using the formula K = [M1...] ρ 水 / (M1-M2) ρ 理论 ] 100%; Thickness: Tested using a film thickness gauge, test time 60s; Tensile test: Weld a terminal to the nickel-plated end, use a press to fix the sample on a tensile testing machine, hook the welded terminal with the hook of the tensile testing machine, and pull upward at a rate of 0.5N / min until it breaks. The force at this time is the tensile force of the sample.

[0059] The test results are shown in Table 1.

[0060] Table 1 The test results show that: (1) As can be seen from Examples 1 to 3, the present invention achieves high bonding strength, high uniformity, excellent solderability and bonding ability by optimizing the entire process of alkaline washing, etching, activation and electroless nickel plating. At the same time, the sufficient supply of nickel source improves the uniformity of boron plating layer, makes the plating structure more compact, reduces the porosity of plating layer, and improves the plating effect and quality.

[0061] (2) As can be seen from the combined examples 1 and 4 and 5, the present invention further limits the concentration of the cleaning solution, so that the cleaning is more thorough and will not be over-cleaned, thus avoiding damage to the metal-ceramic high-temperature co-fired substrate.

[0062] (3) As can be seen from the combined examples 1 and 6, the present invention provides a mixed nickel solution composed of nickel sulfate and nickel chloride, which ensures that the nickel solution can provide sufficient nickel ions, promotes the redox reaction in the forward direction without replenishing the nickel solution, improves the uniformity of the coating, and ensures the continuity of the nickel plating process. However, when the nickel ion source is a single nickel source nickel sulfate solution, the nickel source is unstable, the coating thickness is uneven, which in turn affects the low density and low tensile strength, which does not meet the requirements. It is necessary to replenish the nickel solution from time to time, and the required nickel plating time is long, which reduces the production efficiency.

[0063] (4) As can be seen from Examples 1 and 7 and 8, when the pH value of the electroless nickel plating solution is too low, the acidity is too strong, the hydrogen evolution reaction is violent, which easily leads to an increase in the porosity of the coating, a loose structure, a slow reaction rate, low deposition efficiency, and a long time required to reach the target thickness. This may result in a thin or uneven coating, high internal stress, and the compressive stress accumulated inside the coating may lead to a poor bond between the coating and the substrate, making it easy to peel off. When the pH value of the electroless nickel plating solution is too high, the deposition rate is too fast, and the nickel atoms do not have time to arrange themselves regularly, which leads to an increase in the internal stress of the coating, which may cause cracks and a decrease in density. A thicker coating may be obtained in a short time, but the process is not easy to control and the uniformity is poor. In addition, if the deposition rate is too fast, the coating growth is uneven, and the internal stress is manifested as tensile stress, which will weaken its bonding strength with the substrate. Therefore, the present invention limits the pH value of the electroless nickel plating solution to 3-6.

[0064] (5) As can be seen from Example 1 and Comparative Example 1, when the alkaline washing step is missing, the oil stains, fingerprints and other contaminants on the substrate surface are not removed, forming a physical barrier that hinders the effective contact of the plating solution, resulting in the coating not being deposited evenly, the coating adhesion (tension) is severely reduced, and problems such as peeling, blistering and missed plating may occur.

[0065] (6) As can be seen from Example 1 and Comparative Example 2, when the etching step is missing, the smooth surface will weaken this effect, directly affecting the bonding force, and the adhesion (tension) between the coating and the substrate will be significantly reduced.

[0066] (7) As can be seen from Example 1 and Comparative Example 3, activation is usually used to adsorb a layer of noble metal with catalytic activity (such as palladium) on a non-catalytic surface (such as ceramics), or to remove the passivation film on the metal surface to expose the active surface, thereby initiating an electroplating reaction. If activation is omitted, the reaction will be difficult to start spontaneously.

[0067] In summary, this invention optimizes the entire process of electroless nickel-boron plating on tungsten metal on a high-temperature co-fired metal-ceramic substrate, achieving high adhesion, high uniformity, excellent solderability and bonding properties. At the same time, a sufficient supply of nickel source improves the uniformity of the boron plating layer, simplifies the operation process, and increases production efficiency.

[0068] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for electroless plating of nickel and boron onto tungsten metal on a high-temperature co-fired metal-ceramic substrate, characterized in that, The method for electroless nickel-boron plating includes the following steps in sequence: alkaline washing, etching, activation, and electroless nickel plating; The electroless nickel plating solution includes a nickel ion source, a boron reducing agent solution, an additive solution, and water.

2. The method according to claim 1, characterized in that, The pH value of the electroless nickel plating solution is 3-6; Preferably, the nickel ion source includes a nickel sulfate solution and a nickel chloride solution; Preferably, the concentrations of the nickel sulfate solution and the nickel chloride solution are each independently 1-10 mol / L; Preferably, the mass ratio of the nickel sulfate solution to the nickel chloride solution is 1:(0.1-5.0); Preferably, the concentration of nickel ions in the electroless nickel plating solution is 9-12 mol / L.

3. The method according to claim 1 or 2, characterized in that, The temperature for the electroless nickel plating is 30-90℃; Preferably, the electroless nickel plating time is 30-130 minutes.

4. The method according to any one of claims 1-3, characterized in that, The cleaning solution used in the alkaline washing includes an alkali source and water; Preferably, the alkali source includes sodium hydroxide solution and potassium hydroxide solution; Preferably, the concentrations of the sodium hydroxide solution and the potassium hydroxide solution are each independently 0.1-0.15 mol / L; Preferably, the mass ratio of the sodium hydroxide solution to the potassium hydroxide solution is 1:(0.1-9.0); Preferably, the total alkali concentration of the cleaning solution is 0.1-0.3 mol / L.

5. The method according to any one of claims 1-4, characterized in that, The temperature of the alkaline washing is 30-90℃; Preferably, the alkaline washing time is 2-15 minutes.

6. The method according to any one of claims 1-5, characterized in that, The etching solution includes an aqueous solution of barium hydroxide; Preferably, the concentration of barium hydroxide in the etching solution is 28-170 g / L.

7. The method according to any one of claims 1-6, characterized in that, The etching time is 1-9 minutes; Preferably, the etching temperature is 30-90°C.

8. The method according to any one of claims 1-7, characterized in that, The activation solution includes a palladium activation solution and water; Preferably, the palladium activation solution comprises a palladium chloride solution and a dichlorotetraamminepalladium solution; Preferably, the concentration of palladium ions in the activation solution is 10-30 ppm.

9. The method according to any one of claims 1-8, characterized in that, The activation temperature is 30-90℃; Preferably, the activation time is 1-6 minutes.

10. The method according to any one of claims 1-9, characterized in that, The concentration of the boron reducing agent solution is 60-110 mg / L; Preferably, the concentration of the additive solution is 2-18 mg / L.

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