Method for chemically plating silver on surface of nickel-plated ceramic copper-clad substrate

Abstract

The invention discloses a method for chemically plating silver on the surface of a nickel-plated ceramic copper-clad substrate, and relates to the technical field of metal surface treatment. The preparation method comprises the following steps: S1, sequentially adding nitric acid, imidazole and a surfactant into deionized water, and uniformly mixing to obtain an activating agent; s2, after the ceramic copper-clad substrate is pretreated, chemical nickel plating treatment is carried out, cleaning and drying are carried out, and a nickel-plated ceramic substrate is obtained; and S3, the nickel-plated ceramic substrate is immersed in an activating agent for activating treatment, chemical silver plating treatment and post-treatment are conducted, and a product is obtained. According to the method provided by the invention, the problem of copper ion migration in the later silver welding process of chemical silver plating on the surface of the ceramic copper-clad substrate can be solved, and the performance of the packaging module is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of metal surface treatment, and specifically to a method for electroless silver plating on the surface of a nickel-plated ceramic copper-clad substrate. Background Art

[0002] DBC (Direct Bonded Copper) and AMB (Active Metal Brazing) are two commonly used ceramic substrate technologies in high-power electronic applications.

[0003] AMB (Active Metal Brazing Ceramic Substrate), that is, an active metal brazing ceramic substrate, is developed on the basis of DBC technology. At a high temperature of about 800°C, an AgCu solder containing active elements Ti and Zr wets and reacts at the interface between the ceramic and the metal, thereby realizing the heterogeneous bonding of the ceramic and the metal. The AMB ceramic copper-clad substrate realizes the bonding by means of a chemical reaction between the ceramic and the active metal solder paste at a high temperature. Therefore, its bonding strength is higher and its reliability is better, which is extremely suitable for connectors or scenarios with high current-carrying capacity and high heat dissipation requirements.

[0004] The DBC ceramic substrate usually directly clads copper on Al2O3 (aluminum oxide) or AlN (aluminum nitride) ceramics. The manufacturing process of this substrate requires the oxidation treatment of the copper foil to make it tightly bonded with the ceramic sheet through a eutectic bonding reaction at a high temperature (about 1065°C). This bonding method makes the DBC substrate have good thermal stability and high thermal conductivity. The AMB ceramic substrate uses a metal solder containing a small amount of active elements to tightly weld the copper foil and the ceramic sheet. Compared with DBC, the AMB has higher bonding strength and better reliability.

[0005] Due to their excellent heat dissipation efficiency and high current-carrying capacity, DBC and AMB ceramic substrates are widely used in the packaging of high-voltage high-power semiconductor modules such as IGBT (Insulated Gate Bipolar Transistor) modules and SiC (Silicon Carbide) power devices. Especially in the fields of new energy vehicles, smart grids, and high-efficiency power electronic devices, these high-performance ceramic substrates provide essential support.

[0006] In the process of metal surface treatment, the main purpose of the metal coating is to improve the corrosion resistance, aesthetics, and functionality of the metal matrix. Generally, different metal coating processes include metallization processes such as electroplating, electroless plating, and vacuum plating:

[0007] Electroplating, also known as electrolytic plating, is a technique that uses electrochemical reactions to deposit metals on the surface of metals. In an electrolytic cell, an anode and a cathode are added to an electrolyte containing metal ions. When an electric current is applied, the metal ions in the electrolyte will move towards the cathode and the metal will precipitate on the cathode surface to form a metal coating. This method is applicable to the coating treatment of large metal parts and the parts must be conductors.

[0008] Electroless plating. Electroless plating is a process in which metal ions are reduced in a chemical reaction to obtain a metal coating. This method is generally used for low-cost, small samples, and conductors, semiconductors, and plastic parts can all be plated.

[0009] Vacuum plating. It is a process in which metal materials are evaporated into gases in a vacuum environment and then plated onto the surface of workpieces through special processing methods to form a uniform metal coating. This method is widely used in the surface treatment of high-end ornaments and the manufacture of optical products such as artificial diamonds.

[0010] In addition to the above three methods, there are also methods such as spray plating and spray electroplating. However, no matter which method is used, the purpose is to improve the appearance, performance, and service life of metal parts. Therefore, through the understanding of the above process methods, only electroless plating is suitable for metallizing the surface of semiconductor (ceramic copper-clad substrate) products.

[0011] When electroless silver plating is performed on the surface of a ceramic copper-clad substrate, the silver coating can effectively improve the electrical conductivity, thermal conductivity, and soldering assistance of the copper substrate. However, it will also bring some problems. Since silver has poor corrosion resistance, especially in some high-temperature / humid or corrosive environments, the silver coating is easily damaged, resulting in the corrosion of the copper substrate and the decline of its service performance. At the same time, in the subsequent silver sintering welding process of directly electroless silver-plated products, when the sintering temperature increases, copper ions will migrate to the electroless silver layer and the silver sintering layer, and even diffuse through the pores of the coating to the surface to form copper oxide (CuO), ultimately leading to the failure of the module's performance at the application end. Therefore, it is important to improve and upgrade on the basis of directly electroless silver plating on the surface of a conventional AMB ceramic copper-clad substrate with an etched circuit pattern to prevent the migration of metal copper ions from causing module failure.

[0012] In summary, to solve the above problems, it is of great significance to provide a method for electroless silver plating on a ceramic copper-clad substrate. Summary of the Invention

[0013] The purpose of the present invention is to provide a method for electroless silver plating on the surface of a nickel-plated ceramic copper-clad substrate to solve the problems proposed in the prior art.

[0014] To achieve the above purpose, the present invention provides the following technical solutions:

[0015] A method for chemically plating silver on the surface of a nickel-plated ceramic copper-clad substrate comprises the following steps:

[0016] S1: adding nitric acid, imidazole and surfactant into deionized water in sequence and mixing them evenly to obtain an activator;

[0017] S2: pre-treating the ceramic copper-clad substrate, subjecting it to chemical nickel plating, and cleaning and drying it to obtain a nickel-plated ceramic substrate;

[0018] S3: immersing the nickel-plated ceramic substrate in an activator for activation treatment, followed by chemical silver plating and post-treatment to obtain a product.

[0019] Preferably, the activator comprises the following raw materials, calculated by mass fraction: 12-15% imidazole, 5-10% surfactant, 2-5% 68wt% nitric acid, and the solvent is deionized water.

[0020] Preferably, the surfactant includes but is not limited to NP-21 type surfactant.

[0021] Preferably, during the activation treatment, the temperature is 20-30° C., the time is 40-60 seconds, and the activator stirring method is filtering circulation stirring.

[0022] Preferably, the pretreatment process includes the following steps: primary chemical pretreatment, film lamination, exposure, primary development, copper foil etching, solder etching, cleaning and drying, solder etching inspection, secondary chemical pretreatment, wet film printing, alignment exposure, and secondary development.

[0023] Preferably, the nickel layer thickness of the nickel-plated ceramic substrate is 4-5 μm; the nickel-plated ceramic substrate needs to be stored in an inert gas for a storage time not exceeding ten hours.

[0024] Preferably, the post-processing process includes the following steps: film stripping, cleaning, drying, cutting, inspection and packaging.

[0025] The process of chemical nickel plating specifically includes the following steps: degreasing, micro-etching, pickling, pre-immersion A, activation A, post-acid immersion, and chemical nickel plating.

[0026] Wherein, during the degreasing process, the temperature is 40-60°C and the time is 3-5 minutes; the degreasing agent includes an organic acid with a concentration of 80-120 mL / L and a non-ionic surfactant of 1-3%;

[0027] During the micro-etching process, the temperature is 28-32° C. and the time is 2-3 min. The micro-etching solution includes the following raw materials: 60-100 g / L of sodium persulfate and 4-6% of 98% sulfuric acid.

[0028] During the pickling process, the temperature is room temperature and the time is 1 - 2 min; the pickling solution includes 98% sulfuric acid with a concentration of 4 - 6%.

[0029] During the pre - immersion A process, the temperature is room temperature and the time is 1 - 2 min; the pre - immersion solution includes 98% sulfuric acid with a concentration of 0.8 - 1.2%.

[0030] During the activation A process, the temperature is room temperature and the time is 2 - 3 min; the activation solution includes the following raw materials: 19 - 27 mg / L palladium sulfate, 8 - 24 g / L of 98% sulfuric acid.

[0031] During the post - acid pickling process, the temperature is room temperature and the time is 1 - 2 min; the acid pickling solution is 98% sulfuric acid with a concentration of 2 - 4%.

[0032] During the electroless nickel plating process, the temperature is 78 - 82 °C and the time is 20 - 25 min; the nickel plating solution includes nickel sulfate, sodium hypophosphite, complexing agent, stabilizer, pH adjuster; among them, the nickel ion concentration is 4.6 - 5.3 g / L, the sodium hypophosphite concentration is 20 - 35 g / L, the pH value is 4.5 - 4.8, and the phosphorus content is 5 - 9%.

[0033] Among them, in each example and comparative example, during the electroless silver plating process, it specifically includes the following steps: pre - immersion B, electroless silver plating.

[0034] Among them, during the pre - immersion B process, the temperature is room temperature and the time is 1 - 2 min; the pre - immersion solution includes the following raw materials: 68% nitric acid with a concentration of 0.05 - 0.3 mol / L, 8 - 12% complexing agent, 1 - 3% wetting agent.

[0035] During the silver plating process, the temperature is 45 - 55 °C and the time is 2 - 4 min; the silver plating solution includes silver nitrate, complexing agent, wetting agent, brightening agent, copper ion; among them, the silver ion concentration is 0.6 - 0.9 g / L, the complexing agent concentration is 28 - 32 mL / L, and the wetting agent concentration is 4 - 6 mL / L.

[0036] Compared with the prior art, the beneficial effects of this application are as follows:

[0037] The present invention first electrolessly plates a layer of metal nickel on the surface of the ceramic - clad copper substrate as a barrier layer between the copper substrate and the silver - plated layer, and then performs electroless silver plating, which can prevent the migration of metal copper ions and solve the problem of module failure caused by copper ion migration during the silver sintering welding process of the product at the client side; however, the nickel - plated layer is prone to generate a passivation film and an oxide film, resulting in difficulty in depositing a silver layer on the nickel layer during the subsequent electroless silver plating process.

[0038] Therefore, the present invention also provides a preparation method of an activator for electroless silver plating on a nickel layer. The use of this activator can effectively inhibit the formation of a passivation film and an oxidation film on the nickel plating layer, greatly improve the wettability of the nickel surface, and play a "catalyst" role between the nickel and the silver plating layer. In this way, when electroless silver plating is directly carried out on the surface of the nickel plating layer, problems such as corrosion of the nickel layer by silver nitrate solution, resulting in no silver plating layer, blackening of the silver plating layer, and missing plating are solved, and finally, the plating process of nickel-silver combination on the surface of the ceramic copper-clad substrate is realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Silver plating effect diagram of the product of Comparative Example 1 of the present invention;

[0040] Figure 2 Silver plating effect diagram of the product of Comparative Example 2 of the present invention;

[0041] Figure 3 Silver plating effect diagram of the product of Example 1 of the present invention;

[0042] Figure 4 High-temperature test effect diagram of the product of Example 1 of the present invention;

[0043] Figure 5 High-temperature test effect diagram of the product of Example 2 of the present invention;

[0044] Figure 6 High-temperature soldering test effect diagram of the product of Example 1 of the present invention;

[0045] Figure 7 High-temperature soldering test effect diagram of the product of Example 2 of the present invention;

[0046] Figure 8 Wire bonding force (wire tying) test effect diagram of the product of Example 1 of the present invention;

[0047] Figure 9 Wire bonding force (wire tying) test effect diagram of the product of Example 2 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0048] Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0049] It should be noted that there are no special restrictions on the purchase manufacturers of all raw materials involved in the present invention. Exemplarily, the CAS number of imidazole is 288-32-4. In the following embodiments, parts are parts by mass, and the above-mentioned and unmentioned raw materials are all commercially available.

[0050] Among them, in the following examples and comparative examples, the surfactant is NP-21.

[0051] Among them, in each example and comparative example, during the electroless nickel plating process, the following steps are specifically included: degreasing, micro-etching, pickling, pre-immersion A, activation A, post-acid immersion, and electroless nickel plating.

[0052] Among them, during the degreasing process, the temperature is 50 °C and the time is 4 min; the degreasing agent includes 100 mL / L of organic acid and 2% of non-ionic surfactant;

[0053] During the micro-etching process, the temperature is 30 °C and the time is 2.5 min; the micro-etching solution includes the following raw materials: 80 g / L of sodium persulfate, 5% of 98% sulfuric acid;

[0054] During the pickling process, the temperature is room temperature and the time is 1.5 min; the pickling solution includes 5% of 98% sulfuric acid;

[0055] During the pre-immersion A process, the temperature is room temperature and the time is 1.5 min; the pre-immersion solution includes 1% of 98% sulfuric acid;

[0056] During the activation A process, the temperature is room temperature and the time is 2.5 min; the activation solution includes the following raw materials: 23 mg / L of palladium sulfate, 16 g / L of 98% sulfuric acid;

[0057] During the post-acid immersion process, the temperature is room temperature and the time is 1.5 min; the acid immersion solution is 3% of 98% sulfuric acid;

[0058] During the electroless nickel plating process, the temperature is 80 °C and the time is 25 min; the nickel plating solution includes nickel sulfate, sodium hypophosphite, complexing agent, stabilizer, and pH adjuster; among them, the nickel ion concentration is 4.9 g / L, the sodium hypophosphite concentration is 28 g / L, the pH value is 4.5 - 4.8, and the phosphorus content is 7%.

[0059] Among them, in each example and comparative example, during the electroless silver plating process, the following steps are specifically included: pre-immersion B, electroless silver plating.

[0060] Among them, during the pre-immersion B process, the temperature is room temperature and the time is 1 - 2 min; the pre-immersion solution includes the following raw materials: 0.1 mol / L of 68% nitric acid, 10% of complexing agent, 2% of wetting agent;

[0061] During the silver plating process, the temperature is 20 °C and the time is 3 min; the silver plating solution includes silver nitrate, complexing agent, wetting agent, brightening agent, and copper ion; among them, the silver ion concentration is 0.7 g / L, the complexing agent concentration is 30 mL / L, and the wetting agent concentration is 5 mL / L.

[0062] Example 1: The method for electroless silver plating on the surface of nickel-plated ceramic copper-clad substrate includes the following steps:

[0063] S1: Add nitric acid, imidazole, and surfactant to deionized water in sequence and mix evenly to obtain an activator. Among them, the activator includes the following raw materials, by mass fraction: 12% of imidazole, 8% of surfactant, 3% of 68 wt% nitric acid, and the solvent is deionized water;

[0064] S2: Subject the ceramic copper-clad substrate to primary chemical pretreatment, film laminating, exposure, primary development, copper foil etching, solder etching, cleaning and drying, solder etching inspection, secondary chemical pretreatment, wet film printing, alignment exposure, and secondary development in sequence, then transfer it to a vertical electroless nickel plating equipment for electroless nickel plating treatment, cleaning and drying to obtain a nickel-plated ceramic substrate;

[0065] S3: Immerse the nickel-plated ceramic substrate in the activator for activation treatment at 25°C for 50 seconds, with the stirring method being circulating filtration stirring, transfer it to a horizontal electroless silver plating equipment for electroless silver plating treatment, stripping, cleaning, drying, cutting, inspection and packaging to obtain the product.

[0066] Example 2: The method for electroless silver plating on the surface of a nickel-plated ceramic copper-clad substrate includes the following steps:

[0067] S1: Add nitric acid, imidazole, and surfactant to deionized water in sequence and mix evenly to obtain an activator. Among them, the activator includes the following raw materials, by mass fraction: 12% of imidazole, 5% of surfactant, 2% of 68 wt% nitric acid, and the solvent is deionized water;

[0068] S2: Subject the ceramic copper-clad substrate to primary chemical pretreatment, film laminating, exposure, primary development, copper foil etching, solder etching, cleaning and drying, solder etching inspection, secondary chemical pretreatment, wet film printing, alignment exposure, and secondary development in sequence, then transfer it to a vertical electroless nickel plating equipment for electroless nickel plating treatment, cleaning and drying to obtain a nickel-plated ceramic substrate;

[0069] S3: Immerse the nickel-plated ceramic substrate in the activator for activation treatment at 25°C for 50 seconds, with the stirring method being circulating filtration stirring, transfer it to a horizontal electroless silver plating equipment for electroless silver plating treatment, stripping, cleaning, drying, cutting, inspection and packaging to obtain the product.

[0070] Example 3: The method for electroless silver plating on the surface of a nickel-plated ceramic copper-clad substrate includes the following steps:

[0071] S1: Add nitric acid, imidazole, and surfactant to deionized water in sequence and mix evenly to obtain an activator. Among them, the activator includes the following raw materials, by mass fraction: 15% of imidazole, 10% of surfactant, 5% of 68 wt% nitric acid, and the solvent is deionized water;

[0072] S2: The ceramic copper-clad substrate is successively subjected to a primary chemical pretreatment, film lamination, exposure, primary development, copper foil etching, solder etching, cleaning and drying, solder etching inspection, secondary chemical pretreatment, wet film printing, alignment exposure, and secondary development, and then transferred to a vertical electroless nickel plating device for electroless nickel plating treatment, cleaning and drying to obtain a nickel-plated ceramic substrate;

[0073] S3: Immerse the nickel-plated ceramic substrate in an activator for activation treatment at 25 °C for 50 seconds. The stirring method is circulating filtration stirring. Then transfer it to a horizontal electroless silver plating device for electroless silver plating treatment, film stripping, cleaning, drying, cutting, inspection and packaging to obtain the product.

[0074] Comparative Example 1: Based on Example 1, in step S3, no activator is used for treatment, and the rest of the processes remain unchanged. The specific steps are as follows:

[0075] S1: The ceramic copper-clad substrate is successively subjected to a primary chemical pretreatment, film lamination, exposure, primary development, copper foil etching, solder etching, cleaning and drying, solder etching inspection, secondary chemical pretreatment, wet film printing, alignment exposure, and secondary development, and then transferred to a vertical electroless nickel plating device for electroless nickel plating treatment, cleaning and drying to obtain a nickel-plated ceramic substrate;

[0076] S2: Transfer the nickel-plated ceramic substrate to a horizontal electroless silver plating device for electroless silver plating treatment, film stripping, cleaning, drying, cutting, inspection and packaging to obtain the product.

[0077] Comparative Example 2: Based on Example 1, adjust the content of each substance in the activator, and the rest of the processes remain unchanged. The specific steps are as follows:

[0078] S1: Add nitric acid, imidazole, and surfactant to deionized water in sequence and mix evenly to obtain an activator. The activator includes the following raw materials, calculated by mass fraction: 6% imidazole, 4% surfactant, 3% 68 wt% nitric acid, and the solvent is deionized water;

[0079] S2: The ceramic copper-clad substrate is successively subjected to a primary chemical pretreatment, film lamination, exposure, primary development, copper foil etching, solder etching, cleaning and drying, solder etching inspection, secondary chemical pretreatment, wet film printing, alignment exposure, and secondary development, and then transferred to a vertical electroless nickel plating device for electroless nickel plating treatment, cleaning and drying to obtain a nickel-plated ceramic substrate;

[0080] S3: Immerse the nickel-plated ceramic substrate in the activator for activation treatment at 20 - 30 °C for 40 - 60 seconds. The stirring method is circulating filtration stirring. Then transfer it to a horizontal electroless silver plating device for electroless silver plating treatment, film stripping, cleaning, drying, cutting, inspection and packaging to obtain the product.

[0081] Comparative Example 3: Based on Example 1, increase the temperature of the activation treatment, and the rest of the processes remain unchanged. The specific steps are as follows:

[0082] S1: Add nitric acid, imidazole, and surfactant to deionized water in sequence and mix evenly to obtain an activator. Among them, the activator includes the following raw materials, by mass fraction: 13% imidazole, 8% surfactant, 3% of 68 wt% nitric acid, and the solvent is deionized water.

[0083] S2: Subject the ceramic copper-clad substrate to primary chemical pretreatment, film laminating, exposure, primary development, copper foil etching, solder etching, cleaning and drying, solder etching inspection, secondary chemical pretreatment, wet film printing, alignment exposure, and secondary development in sequence, then transfer it to a vertical electroless nickel plating equipment for electroless nickel plating treatment, cleaning and drying to obtain a nickel-plated ceramic substrate.

[0084] S3: Immerse the nickel-plated ceramic substrate in the activator for activation treatment at 40°C for 50 seconds, with the stirring method being circulating filtration stirring. Then transfer it to a horizontal electroless silver plating equipment for electroless silver plating treatment, film stripping, cleaning, drying, cutting, inspection, and packaging to obtain the product.

[0085] Comparative Example 4: Based on Example 1, increase the activation treatment time and keep the rest of the processes unchanged. Specifically as follows:

[0086] S1: Add nitric acid, imidazole, and surfactant to deionized water in sequence and mix evenly to obtain an activator. Among them, the activator includes the following raw materials, by mass fraction: 13% imidazole, 8% surfactant, 3% of 68 wt% nitric acid, and the solvent is deionized water.

[0087] S2: Subject the ceramic copper-clad substrate to primary chemical pretreatment, film laminating, exposure, primary development, copper foil etching, solder etching, cleaning and drying, solder etching inspection, secondary chemical pretreatment, wet film printing, alignment exposure, and secondary development in sequence, then transfer it to a vertical electroless nickel plating equipment for electroless nickel plating treatment, cleaning and drying to obtain a nickel-plated ceramic substrate.

[0088] S3: Immerse the nickel-plated ceramic substrate in the activator for activation treatment at 25°C for 80 seconds, with the stirring method being circulating filtration stirring. Then transfer it to a horizontal electroless silver plating equipment for electroless silver plating treatment, film stripping, cleaning, drying, cutting, inspection, and packaging to obtain the product.

[0089] Performance test: (1) High-temperature test: Place the samples of Example 1 and Example 2 on a heating platform at 350°C and bake for 5 minutes, and observe whether there are any problems of blistering and peeling of each coating layer. The experimental data are as Figure 4 and 5 shown;

[0090] (2) Solder Test: Apply solder paste of tin-silver-copper (Sn 96 wt%, Ag 0.5 wt%, Cu 3.5 wt%) to partial areas on the surfaces of the products of Example 1 and Example 2, melt the solder on a heating platform at 288 °C, and observe the soldering effect. The experimental data are as Figure 6 and Figure 7 shown;

[0091] (3) Bonding Wire Force Test: Conduct a bonding wire force test on the surfaces of the products of Example 1 and Example 2. The experimental data are as Figure 8 、 Figure 9 and Table 1 shown;

[0092] (4) Nickel-Silver Coating Thickness Test: Observe the appearance of the coatings of Example 1, Comparative Example 1, and 2, and test the nickel-silver coating thickness of Examples 1-3 and Comparative Examples 1-4. The experimental data are as Figures 1 to 3 and Table 2 shown.

[0093] Table 1

[0094]

[0095]

[0096] Table 2

[0097]

[0098] Conclusion: From Figure 4 、 Figure 5 , it can be seen that under the condition of baking at 350 °C for 5 minutes, no coating blistering or peeling problems are found between the nickel coatings and silver coatings of the products of Example 1 and Example 2 of the present invention; from Figure 6 、 Figure 7 , it can be seen that the soldering of the products of Example 1 and Example 2 of the present invention is full and smooth, and no bad phenomena such as peeling, tin shrinkage, and false soldering are found; from Table 1 and Figure 8 、 Figure 9 , it can be seen that the bonding wire force tests of the products of the present invention can all meet the judgment requirements;

[0099] From Table 2, it can be seen that the examples of the present invention can all meet the requirements that the nickel coating thickness is 3-7 μm and the silver coating ≥ 0.3 μm; in Comparative Example 1, no activator was used for activation, and silver was directly electroless plated on the surface of the electroless nickel substrate, resulting in a decrease in the nickel layer thickness, and from Figure 1 it can also be seen that in Comparative Example 1, basically no silver layer was deposited, instead, the nickel coating was etched by the silver nitrate solution, resulting in large-area blackening and corrosion; in Comparative Example 2, the ratio of the activator was adjusted, and the thickness of the silver plating layer increased significantly compared with Comparative Example 1, but it was not as good as that of Example 1. The reason is that this ratio was used in the research and was not the optimal ratio. From Figure 2It can also be seen that in Comparative Example 2, the improvement effect is obvious when using the newly configured "activator" on the surface of the electroless nickel plating substrate. However, there is no silver plating layer on some areas of the ceramic copper-clad substrate, and it is corroded by the silver plating solution of the silver nitrate system. In Comparative Example 3, the temperature of the activation treatment is increased, and the thickness of the silver plating layer decreases. In Comparative Example 4, the time of the activation treatment is increased, the thickness of the silver plating layer increases, but the thickness of the single nickel plating layer decreases significantly. Therefore, the solution of Example 1 is the best.

[0100] It can be Figure 6 seen that Example 1 is a process that further improves the formula of the "activator" and continuously optimizes it during use. As can be seen from the figure, the nickel plating surface is completely covered by the electroless silver plating layer, and the thickness of the silver plating layer can reach ≥ 0.3 um or more. The plating layer meets all test indicators. During the subsequent silver sintering welding process of the product, there is no problem of package module failure caused by the migration of metal copper ions.

[0101] In summary, the present invention combines the preparation of an activator with the electroless nickel plating process and the electroless silver plating process, successfully solving the problem of copper ion migration during the later silver soldering process of electroless silver plating on the surface of the ceramic copper-clad substrate, and improving the performance of the package module.

[0102] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for electroless silver plating on the surface of a nickel-plated ceramic copper-clad substrate, characterized in that: The following steps are involved: S1: adding nitric acid, imidazole and surfactant into deionized water in sequence and mixing evenly to obtain an activator; S2: pre-treating the ceramic copper-clad substrate, subjecting it to chemical nickel plating, and cleaning and drying it to obtain a nickel-plated ceramic substrate; S3: immersing the nickel-plated ceramic substrate in an activator for activation treatment, followed by chemical silver plating and post-treatment to obtain a product.

2. A method for electroless silver plating on the surface of a nickel-plated ceramic copper-clad substrate according to claim 1, characterized in that: The activator comprises the following raw materials, calculated by mass fraction: 12-15% of imidazole, 5-10% of surfactant, 2-5% of 68wt% nitric acid, and the solvent is deionized water.

3. A method for electroless silver plating on the surface of a nickel-plated ceramic copper-clad substrate according to claim 1, characterized in that: The surfactant includes NP-21 type surfactant.

4. A method for electroless silver plating on the surface of a nickel-plated ceramic copper-clad substrate according to claim 1, characterized in that: During the activation treatment, the temperature is 20-30° C., the time is 40-60 seconds, and the activator stirring method is filtering circulation stirring.

5. A method for electroless silver plating on the surface of a nickel-plated ceramic copper-clad substrate according to claim 1, characterized in that: The pretreatment process includes the following steps: primary chemical pretreatment, film lamination, exposure, primary development, copper foil etching, solder etching, cleaning and drying, solder etching inspection, secondary chemical pretreatment, wet film printing, alignment exposure, and secondary development.

6. A method for electroless silver plating on the surface of a nickel-plated ceramic copper-clad substrate according to claim 1, characterized in that: The nickel layer thickness of the nickel-plated ceramic substrate is 4-5 μm; the nickel-plated ceramic substrate needs to be stored in an inert gas for a storage time not exceeding ten hours.

7. A method for electroless silver plating on the surface of a nickel-plated ceramic copper-clad substrate according to claim 1, characterized in that: The silver plating thickness of the product is ≥0.3 μm.

8. A method for electroless silver plating on the surface of a nickel-plated ceramic copper-clad substrate according to claim 1, characterized in that: The post-processing process includes the following steps: film stripping, cleaning, drying, cutting, inspection and packaging.

9. A product prepared by the method for chemically plating silver on the surface of a nickel-plated ceramic copper-clad substrate according to any one of claims 1 to 8.

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