Chemical nickel-gold process of multilayer ceramic substrate

Abstract

The invention relates to the technical field of semiconductor manufacturing, and provides an electroless nickel-gold process of a multilayer ceramic substrate, which comprises the following specific steps: S1, pretreating the multilayer ceramic substrate to obtain a pretreated multilayer ceramic substrate; s2, depositing a copper metal layer on the pretreated multilayer ceramic substrate to obtain a pretreated multilayer ceramic substrate with a metal surface; s3, the pretreated multilayer ceramic substrate with the metal surface is subjected to palladium alloy electroplating and chemical nickel plating to form a nickel plating layer, and a metalized multilayer ceramic substrate is obtained; in the step S1, the pretreatment comprises surface cleaning and activating treatment; in the step S3, when the palladium alloy is electroplated, the adopted electrolyte comprises lanthanum salt and cobalt salt. According to the technical scheme, the problem that the corrosion resistance of chemical nickel plating of the multilayer ceramic substrate is poor in the prior art is solved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, and more specifically, to the chemical nickel-gold process for multilayer ceramic substrates. Background Technology

[0002] Multilayer ceramic substrates, due to their excellent thermal stability, high insulation, thermal expansion coefficient matching that of silicon, and superior high-frequency characteristics, have become indispensable key materials in high-end semiconductor packaging, RF modules, and power electronic devices. In these applications, the metallized circuitry and pads on the substrate surface must possess excellent solderability and long-term stability to ensure a robust, low-resistance, and durable interconnect between the chip and the substrate, thereby guaranteeing the performance and lifespan of the entire electronic component.

[0003] Currently, electroless nickel-gold plating is widely used due to its advantages such as high-temperature oxidation resistance, good solderability, high flatness, and low contact resistance. However, this process still suffers from insufficient nickel layer density and poor interlayer adhesion. During subsequent assembly or long-term use, corrosive media can easily penetrate through the pores of the nickel layer and erode the weakly bonded interfaces, causing corrosion of the nickel layer itself. This corrosion not only reduces the mechanical strength of the solder joints but also generates oxides or corrosion products on the pad surface, severely impairing the solderability of the pads. Ultimately, this affects the lifespan and operational stability of multilayer ceramic substrate packaged devices, making it difficult to meet the packaging reliability requirements of high-end electronics. Summary of the Invention

[0004] This invention proposes a chemical nickel-gold plating process for multilayer ceramic substrates, which solves the problem of poor corrosion resistance in chemical nickel plating of multilayer ceramic substrates in related technologies.

[0005] The technical solution of the present invention is as follows: This invention proposes a chemical nickel-gold process for multilayer ceramic substrates, comprising the following specific steps: S1. After pretreatment, a pretreated multilayer ceramic substrate is obtained. S2. After depositing a copper metal layer on the pretreated multilayer ceramic substrate, a pretreated multilayer ceramic substrate with a metal surface is obtained. S3. The pretreated multilayer ceramic substrate with a metal surface is electroplated with palladium alloy and electroless nickel plating to form a nickel plating layer, thereby obtaining a metallized multilayer ceramic substrate. In step S1, the pretreatment includes surface cleaning and activation treatment; In step S3, the electrolyte used in the electroplating of palladium alloy includes lanthanum salt and cobalt salt.

[0006] As a further technical solution, in step S3, during the electroplating of palladium alloy, the electrolyte is an aqueous solution composed of palladium chloride, nickel sulfate, ethylenediamine, acrylamide, sodium sulfate, boric acid, and additives. The concentration of palladium chloride in the electrolyte is 17~20 g / L, the concentration of nickel sulfate is 0.3~0.5 g / L, the concentration of ethylenediamine is 60~70 mL / L, the concentration of acrylamide is 0.30~0.38 g / L, the concentration of sodium sulfate is 35~50 g / L, the concentration of boric acid is 35~45 g / L, and the concentration of additives is 3.5~4.5 g / L. The additive consists of lanthanum nitrate and cobalt chloride.

[0007] As a further technical solution, the mass ratio of lanthanum nitrate to cobalt chloride is 1:2 to 3, for example, it can be 1:2, 1:2.5, or 1:3, preferably 1:2.5.

[0008] In the chemical nickel-gold process for multilayer ceramic substrates of this invention, the mass ratio of lanthanum nitrate to cobalt chloride in the electrolyte is limited to 1:2~3 during the palladium alloy electroplating process. Lanthanum can refine the palladium alloy coating grains and purify the plating solution, thereby improving the density, corrosion resistance, and adhesion to the substrate of the coating. Cobalt further enhances corrosion resistance by promoting densification and alloy strengthening. If the proportion of cobalt is too low, the coating structure will be loose and insufficiently dense, reducing its protective effect as a barrier layer and decreasing corrosion resistance. If the proportion of cobalt is too high, although it can increase hardness, it will cause increased internal stress and brittleness, making it prone to microcracks, providing channels for the penetration of corrosive media, which will reduce corrosion resistance and ultimately affect the stability of the substrate performance.

[0009] As a further technical solution, when electroplating palladium alloy, the sputtering power of palladium alloy is 15~20kw, the sputtering gas pressure is 0.4Pa, the negative bias voltage is 470V, the deposition temperature is 230℃, and the deposition time is 20~30min.

[0010] As a further technical solution, in step S1, the pretreatment step includes: degreasing, first water washing, acid washing, second water washing, drying and preheating.

[0011] As a further technical solution, the degreasing is performed by soaking in an aqueous solution containing 5wt% to 8wt% phosphoric acid and 5wt% to 8wt% sulfuric acid for 4 to 6 minutes.

[0012] As a further technical solution, the pickling is to soak in an aqueous solution containing 0.5wt% to 1wt% sulfuric acid for 0.5 to 1.5 minutes.

[0013] As a further technical solution, in step S3, the electroless nickel plating solution is an aqueous solution composed of nickel oxide, reducing agent, complexing agent, and stabilizer. The concentration of nickel oxide in the electroless nickel plating solution is 25~30 g / L, the concentration of reducing agent is 15~20 g / L, the concentration of complexing agent is 35~45 g / L, and the concentration of stabilizer is 1~3 g / L.

[0014] As a further technical solution, the reducing agent includes one or more of sodium hypophosphite, dimethylamine borane, and ammonium hypophosphite.

[0015] As a further technical solution, the stabilizer includes one or more of sodium thiosulfate, ammonium chloride, and thioglycolic acid.

[0016] As a further technical solution, the complexing agent includes sodium citrate and sodium 2-mercaptobenzimidazole-5-sulfonate dihydrate.

[0017] In the electroless nickel-gold process for multilayer ceramic substrates of this invention, sodium citrate and sodium 2-mercaptobenzimidazole-5-sulfonate dihydrate are added as complexing agents during the electroless nickel plating step. This significantly improves the density and bonding strength of the electroless nickel plating layer, effectively reduces the porosity of the plating layer, and thus greatly enhances the corrosion resistance of the multilayer ceramic substrate. At the same time, this composite complexing agent system promotes the uniform deposition of the nickel layer. While improving the surface smoothness and solderability stability of the plating layer, it also increases the microhardness of the plating layer itself, thereby enhancing the corrosion resistance of the metallized area on the surface of the multilayer ceramic substrate.

[0018] As a further technical solution, the mass ratio of sodium citrate to sodium 2-mercaptobenzimidazole-5-sulfonate dihydrate is 8:1.5~3.5.

[0019] As a further technical solution, the electroless nickel plating temperature is 70~85℃, the electroless nickel plating time is 3~5min, and the electroless nickel plating can be repeated 2~4 times depending on the required coating thickness.

[0020] As a further technical solution, the thickness of the nickel plating layer is 8~14μm.

[0021] As a further technical solution, in step S1, the multilayer ceramic substrate comprises the following raw materials in parts by weight: 100 parts alumina, 3-5 parts sintering aid, 1-3 parts plasticizer, 1-2 parts dispersant, 7-10 parts binder, and 40-45 parts water.

[0022] As a further technical solution, the sintering aid includes one or more of calcium oxide, yttrium oxide, and strontium oxide.

[0023] As a further technical solution, the plasticizer includes one or both of polyacrylol and polyethylene glycol.

[0024] As a further technical solution, the dispersant includes one or both of polyacrylamide and polyvinylpyrrolidone.

[0025] As a further technical solution, the adhesive includes one or both of polyvinyl alcohol and hydroxypropyl methylcellulose.

[0026] As a further technical solution, the method for preparing the multilayer ceramic substrate is as follows: A1. Mix all raw materials except the binder evenly, add the binder, and ball mill to obtain the cast slurry; A2. The cast slurry is degassed, cast, and dried to obtain ceramic blanks; A3. After punching, surface printing, laminating, connecting the upper and lower parts, and cutting the ceramic blank, hot pressing and sintering are performed to obtain a multilayer ceramic substrate.

[0027] The working principle and beneficial effects of this invention are as follows: This invention provides a chemical nickel-gold plating process for multilayer ceramic substrates. Lanthanum and cobalt are added to the palladium alloy used in the electroplating process, significantly improving the adhesion between the palladium alloy layer and the subsequent nickel plating layer, thereby effectively enhancing the corrosion resistance of the coating on the surface of the multilayer ceramic substrate. Lanthanum, as an active rare earth element, refines the grain structure of the palladium alloy and nickel plating, fills grain boundary pores, and improves the density of the coating. Simultaneously, its segregation effect at the interface with the substrate purifies the bonding interface and enhances the adhesion of the coating. The addition of cobalt synergistically enhances the interfacial bonding strength and the overall continuity of the coating with lanthanum. Together, they form a denser and stronger barrier layer, effectively blocking the penetration of corrosive media and avoiding solderability degradation caused by interfacial corrosion. Ultimately, this results in a chemical nickel-gold plating layer with excellent corrosion resistance, improving the welding reliability of the multilayer ceramic substrate. Detailed Implementation

[0028] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0029] In the following embodiments and comparative examples: The viscosity of hydroxypropyl methylcellulose is 100,000 mPa·s; Polyvinylpyrrolidone, model: K90, manufacturer: Guangdong Yuemei Chemical Co., Ltd.; The polyethylene glycol is designated as PEG-1000.

[0030] Example 1 The electroless nickel-gold process for multilayer ceramic substrates includes the following specific steps: S1. Weigh 100 parts alumina, 3 parts yttrium oxide, 1 part polyethylene glycol, 1 part polyvinylpyrrolidone, and 40 parts water according to the weight ratio. After mixing evenly, add 7 parts hydroxypropyl methylcellulose and ball mill at 4000 r / min for 0.5 h to obtain a casting slurry. The casting slurry is degassed, cast, and dried to obtain a ceramic blank. The ceramic blank is punched, surface printed, laminated (30 layers), connected to the top and bottom, and cut. It is sintered at 25 MPa and 1400℃ for 3 h and cooled to obtain a multilayer ceramic substrate. S2. Soak the multilayer ceramic substrate in an aqueous solution containing 5wt% phosphoric acid and 5wt% sulfuric acid for 6 min, wash with water, soak in an aqueous solution containing 0.5wt% sulfuric acid for 1.5 min, wash with water, and dry at 70℃ to obtain the pretreated multilayer ceramic substrate. S3. After depositing a copper metal layer on the pretreated multilayer ceramic substrate, a multilayer ceramic substrate with a metal surface is obtained. S4. After electroplating the multilayer ceramic substrate with palladium alloy, a multilayer ceramic substrate with palladium alloy electroplating is obtained. The sputtering power of palladium alloy is 15 kW, the sputtering gas pressure is 0.4 Pa, the negative bias voltage is 470 V, the deposition temperature is 230 °C, and the deposition time is 30 min. S5. After the multilayer ceramic substrate with palladium alloy electroplating is washed and dried, the palladium alloy is activated and immersed in nickel plating solution. Nickel plating is performed at 70°C for 5 minutes as one time. The nickel plating is repeated until the thickness of the nickel plating layer is 8μm. After the nickel plating is completed, it is taken out and dried to remove the photoresist covering and the excess nickel layer, thus obtaining the metallized ceramic substrate. The electrolyte for electroplating palladium alloys is an aqueous solution composed of palladium chloride, nickel sulfate, ethylenediamine, acrylamide, sodium sulfate, boric acid, and additives. The concentrations of palladium chloride, nickel sulfate, ethylenediamine, acrylamide, sodium sulfate, boric acid, and additives in the electrolyte are 17 g / L, 0.3 g / L, 60 mL / L, 0.30 g / L, 35 g / L, 35 g / L, and 3.5 g / L. The additives consist of lanthanum nitrate and cobalt chloride in a mass ratio of 1:2. The electroless nickel plating solution is an aqueous solution composed of nickel oxide, sodium hypophosphite, sodium citrate, and sodium thiosulfate. The concentration of nickel oxide in the electroless nickel plating solution is 25 g / L, the concentration of sodium hypophosphite is 15 g / L, the concentration of sodium citrate is 35 g / L, and the concentration of sodium thiosulfate is 1 g / L.

[0031] Example 2 The electroless nickel-gold process for multilayer ceramic substrates includes the following specific steps: S1. Weigh 100 parts alumina, 4 parts yttrium oxide, 2 parts polyethylene glycol, 1.5 parts polyvinylpyrrolidone, and 43 parts water according to the weight ratio. Mix them evenly, then add 8 parts hydroxypropyl methylcellulose. Ball mill the mixture for 0.5 hours at a speed of 4000 r / min to obtain a casting slurry. The casting slurry is degassed, cast, and dried to obtain a ceramic blank. The ceramic blank is punched, surface printed, laminated (30 layers), connected to the top and bottom, cut, and sintered at 25 MPa and 1400℃ for 3 hours. After cooling, a multilayer ceramic substrate is obtained. S2. Soak the multilayer ceramic substrate in an aqueous solution containing 7wt% phosphoric acid and 7wt% sulfuric acid for 5 min, wash with water, soak in an aqueous solution containing 0.7wt% sulfuric acid for 1.0 min, wash with water, and dry at 75°C to obtain the pretreated multilayer ceramic substrate. S3. After depositing a copper metal layer on the pretreated multilayer ceramic substrate, a multilayer ceramic substrate with a metal surface is obtained. S4. After electroplating the multilayer ceramic substrate with palladium alloy, a multilayer ceramic substrate with palladium alloy electroplating is obtained. The sputtering power of palladium alloy is 18 kW, the sputtering gas pressure is 0.4 Pa, the negative bias voltage is 470 V, the deposition temperature is 230 °C, and the deposition time is 25 min. S5. After the multilayer ceramic substrate with palladium alloy electroplating is washed and dried, the palladium alloy is activated and immersed in nickel plating solution. Nickel plating is performed at 78°C for 4 minutes as one time. The nickel plating is repeated until the thickness of the nickel plating layer is 10μm. After the nickel plating is completed, it is taken out and dried to remove the photoresist covering and the excess nickel layer, thus obtaining the metallized ceramic substrate. The electrolyte for electroplating palladium alloys is an aqueous solution composed of palladium chloride, nickel sulfate, ethylenediamine, acrylamide, sodium sulfate, boric acid, and additives. The concentrations of palladium chloride, nickel sulfate, ethylenediamine, acrylamide, sodium sulfate, boric acid, and additives in the electrolyte are 18 g / L, 0.4 g / L, 65 mL / L, 0.34 g / L, 43 g / L, 40 g / L, and 4.0 g / L. The additives consist of lanthanum nitrate and cobalt chloride in a mass ratio of 1:2. The electroless nickel plating solution is an aqueous solution composed of nickel oxide, sodium hypophosphite, sodium citrate, and sodium thiosulfate. The concentration of nickel oxide in the electroless nickel plating solution is 27 g / L, the concentration of sodium hypophosphite is 18 g / L, the concentration of sodium citrate is 40 g / L, and the concentration of sodium thiosulfate is 2 g / L.

[0032] Example 3 The electroless nickel-gold process for multilayer ceramic substrates includes the following specific steps: S1. Weigh 100 parts alumina, 5 parts yttrium oxide, 3 parts polyethylene glycol, 2 parts polyvinylpyrrolidone, and 45 parts water according to the weight ratio. Mix them evenly, then add 10 parts hydroxypropyl methylcellulose. Ball mill the mixture for 0.5 hours at a speed of 4000 r / min to obtain a casting slurry. The casting slurry is degassed, cast, and dried to obtain a ceramic blank. The ceramic blank is punched, surface printed, laminated (30 layers), connected to the top and bottom, cut, and sintered at 25 MPa and 1400℃ for 3 hours. After cooling, a multilayer ceramic substrate is obtained. S2. Soak the multilayer ceramic substrate in an aqueous solution containing 8wt% phosphoric acid and 8wt% sulfuric acid for 4 min, wash with water, soak in an aqueous solution containing 1wt% sulfuric acid for 0.5 min, wash with water, and dry at 80℃ to obtain the pretreated multilayer ceramic substrate. S3. After depositing a copper metal layer on the pretreated multilayer ceramic substrate, a multilayer ceramic substrate with a metal surface is obtained. S4. After electroplating the multilayer ceramic substrate with palladium alloy, a multilayer ceramic substrate with palladium alloy electroplating is obtained. The sputtering power of palladium alloy is 20 kW, the sputtering gas pressure is 0.4 Pa, the negative bias voltage is 470 V, the deposition temperature is 230 °C, and the deposition time is 30 min. S5. After the multilayer ceramic substrate with palladium alloy electroplating is washed and dried, the palladium alloy is activated and immersed in nickel plating solution. Nickel plating is performed at 85°C for 3 minutes as one time. The nickel plating is repeated until the thickness of the nickel plating layer is 14μm. After the nickel plating is completed, it is taken out and dried to remove the photoresist covering and the excess nickel layer, thus obtaining the metallized ceramic substrate. The electrolyte for electroplating palladium alloys is an aqueous solution composed of palladium chloride, nickel sulfate, ethylenediamine, acrylamide, sodium sulfate, boric acid, and additives. The concentrations of palladium chloride, nickel sulfate, ethylenediamine, acrylamide, sodium sulfate, boric acid, and additives in the electrolyte are 20 g / L, 0.5 g / L, 70 mL / L, 0.38 g / L, 50 g / L, 45 g / L, and 4.5 g / L. The additives consist of lanthanum nitrate and cobalt chloride in a mass ratio of 1:2. The electroless nickel plating solution is an aqueous solution composed of nickel oxide, sodium hypophosphite, sodium citrate, and sodium thiosulfate. The concentration of nickel oxide in the electroless nickel plating solution is 30 g / L, the concentration of sodium hypophosphite is 20 g / L, the concentration of sodium citrate is 45 g / L, and the concentration of sodium thiosulfate is 3 g / L.

[0033] Example 4 The only difference between this embodiment and Embodiment 2 is that the additive in this embodiment is composed of lanthanum nitrate and cobalt chloride in a mass ratio of 1:2.5.

[0034] Example 5 The only difference between this embodiment and Embodiment 2 is that the additive in this embodiment is composed of lanthanum nitrate and cobalt chloride in a mass ratio of 1:3.

[0035] Example 6 The only difference between this embodiment and Embodiment 4 is that sodium citrate is replaced with equal amounts of sodium citrate and ethylenediamine in a mass ratio of 8:1.5.

[0036] Example 7 The only difference between this embodiment and Example 4 is that sodium citrate is replaced with equal amounts of sodium citrate and 2-mercaptobenzimidazole-5-sulfonate sodium dihydrate in a mass ratio of 8:1.5.

[0037] Example 8 The only difference between this embodiment and Example 4 is that sodium citrate is replaced with equal amounts of sodium citrate and 2-mercaptobenzimidazole-5-sulfonate sodium dihydrate in a mass ratio of 8:2.5.

[0038] Example 9 The only difference between this embodiment and Embodiment 4 is that sodium citrate is replaced with equal amounts of sodium citrate and 2-mercaptobenzimidazole-5-sulfonate sodium dihydrate in a mass ratio of 8:3.5.

[0039] Comparative Example 1 The only difference between this comparative example and Example 1 is that the auxiliary agent in this comparative example is only lanthanum nitrate.

[0040] Comparative Example 2 The only difference between this comparative example and Example 1 is that the auxiliary agent in this comparative example is only cobalt chloride.

[0041] Comparative Example 3 The only difference between this comparative example and Example 1 is that no additives are added in this comparative example.

[0042] Experimental Example (1) The test was conducted according to the neutral salt spray test standard in GB / T 10125-2021 "Artificial Salt Spray Corrosion Test Method". The spray was a 5wt% NaCl aqueous solution at a temperature of 35℃. Spraying was performed for 15 minutes at 15-minute intervals. The corrosion of the sample surface was observed and the time when corrosion began to appear on the sample surface was recorded. The test results are shown in Table 1.

[0043] (2) The hardness of the ceramic substrate was tested according to GB / T 4340.1-2024 "Metallic materials Vickers hardness test - Part 1: Test method" and the test results are shown in Table 2.

[0044] Table 1. Corrosion resistance test results of Examples 1-5 and Comparative Examples 1-3

[0045] As shown in Table 1, the salt spray resistance time of the metallized ceramic substrates prepared in Examples 1-5 is higher than that of Comparative Examples 1-3, indicating that by incorporating lanthanum nitrate and cobalt chloride into the palladium alloy, the corrosion resistance of electroless nickel plating can be improved, thereby improving the product quality and reliability of multilayer ceramic substrates.

[0046] Table 2. Test results of corrosion resistance and hardness in Examples 4, 6-9.

[0047] The metallized multilayer ceramic substrates prepared in Examples 7-9 have higher salt spray resistance and hardness than those in Examples 4 and 6, indicating that the addition of sodium citrate and sodium 2-mercaptobenzimidazole-5-sulfonate dihydrate can improve the corrosion resistance of electroless nickel plating and the hardness of the ceramic substrate, allowing the metal surface to retain excellent welding performance for a long time.

[0048] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A chemical nickel-gold process for multilayer ceramic substrates, characterized in that, The specific steps include the following: S1. After pretreatment, a pretreated multilayer ceramic substrate is obtained. S2. After depositing a copper metal layer on the pretreated multilayer ceramic substrate, a pretreated multilayer ceramic substrate with a metal surface is obtained. S3. The pretreated multilayer ceramic substrate with a metal surface is electroplated with palladium alloy and electroless nickel plating to form a nickel plating layer, thereby obtaining a metallized multilayer ceramic substrate. In step S1, the pretreatment includes surface cleaning and activation treatment; In step S3, the electrolyte used in the electroplating of palladium alloy includes lanthanum salt and cobalt salt.

2. The electroless nickel-gold process for multilayer ceramic substrates according to claim 1, characterized in that, In step S3, during the electroplating of palladium alloy, the electrolyte is an aqueous solution composed of palladium chloride, nickel sulfate, ethylenediamine, acrylamide, sodium sulfate, boric acid, and additives. The concentrations of palladium chloride, nickel sulfate, ethylenediamine, acrylamide, sodium sulfate, boric acid, and additives in the electrolyte are 17-20 g / L, 0.3-0.5 g / L, 60-70 mL / L, 0.30-0.38 g / L, 35-50 g / L, 35-45 g / L, and 3.5-4.5 g / L. The additive consists of lanthanum nitrate and cobalt chloride.

3. The electroless nickel-gold process for multilayer ceramic substrates according to claim 1, characterized in that, In step S1, the pretreatment steps include: degreasing, first water washing, acid washing, second water washing, drying, and preheating.

4. The electroless nickel-gold process for multilayer ceramic substrates according to claim 1, characterized in that, In step S3, the electroless nickel plating solution is an aqueous solution composed of nickel oxide, reducing agent, complexing agent, and stabilizer. The concentration of nickel oxide in the electroless nickel plating solution is 25~30 g / L, the concentration of reducing agent is 15~20 g / L, the concentration of complexing agent is 35~45 g / L, and the concentration of stabilizer is 1~3 g / L.

5. The electroless nickel-gold process for multilayer ceramic substrates according to claim 4, characterized in that, The reducing agent includes one or more of sodium hypophosphite, dimethylamine borane, and ammonium hypophosphite.

6. The electroless nickel-gold process for multilayer ceramic substrates according to claim 4, characterized in that, The stabilizer includes one or more of sodium thiosulfate, ammonium chloride, and thioglycolic acid.

7. The electroless nickel-gold process for multilayer ceramic substrates according to claim 4, characterized in that, The complexing agent includes sodium citrate and sodium 2-mercaptobenzimidazole-5-sulfonate dihydrate.

8. The electroless nickel-gold process for multilayer ceramic substrates according to claim 7, characterized in that, The mass ratio of sodium citrate to sodium 2-mercaptobenzimidazole-5-sulfonate dihydrate is 8:1.5~3.

5.

9. The electroless nickel-gold process for multilayer ceramic substrates according to claim 1, characterized in that, In step S1, the multilayer ceramic substrate comprises the following raw materials in parts by weight: 100 parts alumina, 3-5 parts sintering aid, 1-3 parts plasticizer, 1-2 parts dispersant, 7-10 parts binder, and 40-45 parts water.

10. The electroless nickel-gold process for multilayer ceramic substrates according to claim 9, characterized in that, The method for preparing the multilayer ceramic substrate is as follows: A1. Mix all raw materials except the binder evenly, add the binder, and ball mill to obtain the cast slurry; A2. The cast slurry is degassed, cast, and dried to obtain ceramic blanks; A3. After punching, surface printing, laminating, connecting the upper and lower parts, and cutting the ceramic blank, hot pressing and sintering are performed to obtain a multilayer ceramic substrate.

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