A method for preventing discoloration of selective nickel plating on the surface of a ceramic copper-clad substrate

Abstract

The present invention relates to the technical field of selective nickel plating discoloration, and specifically to a method for preventing selective nickel plating discoloration on the surface of a ceramic copper-clad substrate. The method comprises the following steps: S1: subjecting the ceramic copper-clad substrate to a solder etching process, a step etching process, and a local silver plating process in sequence to obtain a ceramic copper-clad substrate A; S2: subjecting the ceramic copper-clad substrate A to pre-treatment cleaning, wet film printing, alignment exposure, development, chemical nickel-gold plating, film stripping cleaning, gold stripping process, cleaning and drying in sequence to obtain a finished product.

Description

Technical Field

[0001] The invention relates to the technical field of ceramic copper-clad boards, in particular to a method for preventing the surface of a ceramic copper-clad substrate from being discolored by selective nickel plating. Background Art

[0002] With the rapid development of microelectronics technology, electronic devices tend to be integrated and multifunctional, and printed circuit boards (electronic substrates) have become an indispensable electronic component; ceramic substrates are widely used in power electronics, electronic packaging, hybrid microelectronics and multi-chip modules due to their good thermal conductivity and airtightness; alumina ceramic substrates have a thermal expansion coefficient that matches that of semiconductor silicon, high thermal stability, chemical stability and low dielectric constant, and are cheap, making them the most popular ceramic substrate material at present; in order to improve the conductivity of alumina ceramic substrates and prevent metal oxidation and other properties, the surface of alumina ceramic substrates needs to be metallized. The current metallization methods mainly include: high-temperature sintering silver coating, vacuum evaporation coating, magnetron sputtering, chemical vapor deposition, chemical plating and other methods.

[0003] In the prior art, selective chemical plating of nickel-phosphorus alloy layer on the surface of ceramic copper-clad substrate is a newly developed process based on the actual needs of product design and packaging. The difficulty of this process lies in the local selective plating of nickel-phosphorus alloy, rather than direct plating of nickel-phosphorus alloy layer on the entire board. Therefore, before the selective plating of nickel-phosphorus alloy layer, it is necessary to use a highly viscous ink to mask the area that does not need the phosphorus alloy layer; after the treatment is completed, chemical nickel-phosphorus plating is carried out, and then the surface masking ink is removed and cleaned. If the product surface is not cleaned thoroughly, it will quickly oxidize and discolor, affecting the weldability and punching linearity of the coating, and ultimately causing module failure during the packaging process.

[0004] Therefore, it is urgent to solve the above problems. Therefore, this patent has obtained a method for selectively chemically plating a nickel-phosphorus alloy layer on the surface of a ceramic copper-clad substrate through research, which effectively prevents the nickel-phosphorus alloy layer from discoloring due to contact with strong alkali and strong acidic substances during the ink removal process. Summary of the invention

[0005] The object of the present invention is to provide a method for preventing the selective nickel plating on the surface of a ceramic copper-clad substrate from changing color, so as to solve the problems raised in the above-mentioned background technology.

[0006] A method for preventing discoloration of selective nickel plating on the surface of a ceramic copper-clad substrate comprises the following steps:

[0007] S1: subjecting the ceramic copper-clad substrate to a solder etching process, a step etching process, and a local silver plating process in sequence to obtain a ceramic copper-clad substrate A;

[0008] S2: The ceramic copper-clad substrate A is sequentially subjected to pre-treatment cleaning, wet film printing, alignment exposure, development, chemical nickel-gold plating, film stripping cleaning, gold stripping process, cleaning and drying to obtain a finished product.

[0009] More optimally, a gold stripping liquid is used during the gold stripping process, which includes a cyanide-containing gold stripping liquid or a cyanide-free gold stripping liquid.

[0010] More preferably, the cyanide-containing gold stripping solution comprises the following components: 18-22 g / L sodium m-nitrobenzene sulfonate, 48-52 g / L sodium cyanide, and 48-52 g / L citric acid.

[0011] More optimally, the cyanide-free gold stripping solution includes the following components: 28-32 g / L potassium sulfate, 38-42 g / L sodium carbonate, and 18-22 g / L sodium citrate.

[0012] More optimally, when a cyanide-containing gold stripping solution is used in the gold stripping process, the process parameters are: temperature is 70-80° C., speed is 0.5±0.05 um / min; pH of the gold stripping solution is 10-12.

[0013] More optimally, when cyanide-free gold stripping liquid is used in the gold stripping process, the process parameters are: the temperature is room temperature, the speed is 0.2±0.05um / min; the pH of the gold stripping liquid is 8-12.

[0014] More optimally, the chemical nickel-gold plating includes a nickel-phosphorus layer and a gold layer, and the thickness of the gold layer is 0.01-0.02 um.

[0015] More optimally, the cyanide-free gold stripping solution further includes 5-6 g / L of additives, and the additives include small molecule amino acids and modified amino acids.

[0016] Preferably, the small molecule amino acid comprises one or more of methionine, cystine and cysteine; and the mass ratio of the small molecule amino acid to the modified amino acid is (2-2.5):1.

[0017] The more optimized preparation method of the modified amino acid is: adding 5-aminolysine and cysteine ​​to N,N-dimethylacetamide and stirring for 10 to 20 minutes, adding diphenyl sulfide dianhydride and reacting for 4 to 6 hours to obtain the modified amino acid.

[0018] More optimally, the raw materials of the modified amino acid include the following components: by weight, 2 to 3 parts of cysteine, 1 to 1.5 parts of 5-aminolysine, 30 to 40 parts of N,N-dimethylacetamide, and 1 to 2 parts of diphenyl sulfide dianhydride.

[0019] Compared with the prior art, the beneficial effects achieved by the present invention are: achieving local selective chemical plating of nickel-phosphorus alloy layer while solving the problem of discoloration of the coating caused by the product contacting strong alkali or strong acid solution, and effectively increasing the yield rate of the finished product.

[0020] Among them, by means of the stable chemical properties of the gold plating layer, the nickel-phosphorus alloy plating layer is protected from oxidation discoloration caused by contact with acid and alkaline solutions, and a local selective chemical nickel-phosphorus alloy plating process is realized, which effectively solves the product performance requirements. Specific principle explanation: The local selective nickel-phosphorus alloy plating and local selective silver plating processes on the surface of the ceramic copper-clad substrate, because the nickel-phosphorus alloy is in the process of "film removal" and "pickling" steps, the alkaline solution (5% strong alkaline substance-sodium hydroxide) and the acid solution (3-5% acidic substance-sulfuric acid) contact the surface of the product nickel-phosphorus alloy, causing the local nickel-phosphorus alloy coating to be not cleaned and discolored. Once the coating surface is discolored, it will not be able to be cleaned and removed again. The product function will be greatly affected, resulting in most products being directly scrapped, resulting in high costs, low yields, and frequent quality abnormalities. In this application, a 0.01-0.02um gold layer is pre-plated on the surface of the nickel-phosphorus layer as a protective layer during the film removal process, thereby effectively solving the problem of product oxidation discoloration.

[0021] Among them, there are two types of gold stripping processes after film stripping. One is gold stripping at a certain temperature in a cyanide-containing gold stripping solution; the other is gold stripping at room temperature in a cyanide-free gold stripping solution.

[0022] (1) Cyanide-containing gold stripping solution mainly uses the concentration of cyanide to increase the gold leaching speed, but cyanide is highly toxic. Increasing the dosage will bring difficulties to subsequent sewage treatment. In addition, when the pH of the cyanide-containing gold stripping solution is less than 10, HCN highly toxic gas will be released, thus affecting human health.

[0023] (2) In order to improve the environmental friendliness of the process, the present invention further uses a cyanide-free gold stripping solution including 28-32 g / L potassium sulfate, 38-42 g / L sodium carbonate, and 18-22 g / L sodium citrate for room temperature gold stripping. In order to further improve the gold stripping efficiency and reduce the residue while ensuring the yield rate; the present invention further adds small molecule amino acids and modified amino acids to the cyanide-free gold stripping solution. The carbon side chain structure and the type of donor atom of the amino acid determine the gold leaching ability of the amino acid, but the presence of only one carboxyl group in the carbon side chain does not increase the gold leaching amount; amino acids with N and S donor atoms on the side chain are more capable of being used as gold leaching agents. Compared with the introduction of a single amino acid, the synergistic modified amino acid has better gold stripping performance. The present invention connects cysteine ​​and 5-aminolysine through the anhydride on diphenyl sulfide dianhydride to increase the reaction site of the amino acid carbon side chain, thereby enhancing the gold leaching speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0025] Figure 1 The ceramic copper-clad substrate with a gold-plated layer of Example 3;

[0026] Figure 2 This is the ceramic copper-clad substrate after the gold stripping treatment of Example 3. DETAILED DESCRIPTION

[0027] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] It should be noted that the purchase manufacturers of all raw materials involved in the present invention are not subject to any special restrictions and exemplarily include: in the following embodiments, the CAS number of sodium m-nitrobenzene sulfonate is 127-68-4, the CAS number of sodium cyanide is 143-33-9, the CAS number of sodium hypophosphite is 7681-53-0, the CAS number of 5-aminolysine is 98961-95-6, the CAS number of N,N-dimethylacetamide is 127-19-5, and the CAS number of diphenyl sulfide dianhydride is 25884-43-9.

[0029] Preparation method of modified amino acid: add 1.5 parts of 5-aminolysine and 3 parts of cysteine ​​to 30 parts of N,N-dimethylacetamide and stir for 10 to 20 minutes, add 2 parts of diphenyl sulfide dianhydride and react for 5 hours to obtain modified amino acid.

[0030] Embodiment 1: A method for preventing discoloration of the surface of a ceramic copper-clad substrate by selective nickel plating, comprising the following steps:

[0031] S1: After cleaning the ceramic copper-clad substrate, printing ink, drying, alignment exposure, and development are performed to expose the required copper shape; the ceramic copper-clad substrate with the required copper shape exposed is placed in a chemical etching solution (3% sulfuric acid and 50g / L sodium sulfate aqueous solution), treated at 35°C for 40 minutes, placed in a solder etching at 40°C for 30 minutes, and washed with deionized water to obtain a basic ceramic copper-clad substrate;

[0032] The solder etching solution comprises: 4wt% sodium hydroxide, 5wt% ammonia water, 6wt% hydrogen peroxide, and 3wt% stabilizer;

[0033] S2: placing the base ceramic copper-clad substrate in a step etching solution at 40°C for etching for 25 minutes, washing with water, printing ink, drying, alignment exposure, developing, placing in a silver plating solution at 50°C for 30 minutes, washing with deionized water, stripping, and drying to obtain a ceramic copper-clad substrate A;

[0034] The components of the step etching solution include: 5wt% copper corrosion inhibitor, 10wt% sodium dodecyl sulfate, and 30wt% hydrogen peroxide; the components of the silver plating solution include: 0.36mol / L silver ammonia complex solution, 0.42mol / L glucose solution, and 4g / L dispersant solution;

[0035] S3: The ceramic copper-clad substrate A is sequentially subjected to pre-treatment cleaning, wet film printing, alignment exposure, development, chemical nickel plating at 80° C., deionized water washing, chemical gold plating at 85° C., and then placed in a 5wt% sodium hydroxide aqueous solution for stripping and washing for 3 minutes, then placed in a 3wt% sulfuric acid aqueous solution for neutralization and washing, deionized water washing, placed in a cyanide-containing gold stripping solution, and then treated at 70° C. for 40 minutes, washed and dried to obtain a finished product;

[0036] Among them, the components of the nickel plating solution include: 4.2g / L nickel ions, 25g / L sodium hypophosphite, 6wt% P, pH=4.5, and the nickel layer thickness is 10μm; the components of the gold plating solution include: 1.1g / L gold, 180mL / LTCL-61-M5, pH=4.6, and the gold layer thickness is 0.01μm; the cyanide-containing gold stripping solution includes the following components: 18g / L sodium m-nitrobenzene sulfonate, 48g / L sodium cyanide, and 48g / L citric acid.

[0037] Embodiment 2: A method for preventing discoloration of the surface of a ceramic copper-clad substrate by selective nickel plating, comprising the following steps:

[0038] S1: After cleaning the ceramic copper-clad substrate, printing ink, drying, alignment exposure, and development are performed to expose the required copper shape; the ceramic copper-clad substrate with the required copper shape exposed is placed in a chemical etching solution (3% sulfuric acid and 50g / L sodium sulfate aqueous solution), treated at 35°C for 40 minutes, placed in a solder etching at 40°C for 30 minutes, and washed with deionized water to obtain a basic ceramic copper-clad substrate;

[0039] The solder etching solution comprises: 4wt% sodium hydroxide, 5wt% ammonia water, 6wt% hydrogen peroxide, and 3wt% stabilizer;

[0040] S2: placing the base ceramic copper-clad substrate in a step etching solution at 40°C for etching for 25 minutes, washing with water, printing ink, drying, alignment exposure, developing, placing in a silver plating solution at 50°C for 30 minutes, washing with deionized water, stripping, and drying to obtain a ceramic copper-clad substrate A;

[0041] The components of the step etching solution include: 5wt% copper corrosion inhibitor, 10wt% sodium dodecyl sulfate, and 30wt% hydrogen peroxide; the components of the silver plating solution include: 0.36mol / L silver ammonia complex solution, 0.42mol / L glucose solution, and 4g / L dispersant solution;

[0042] S3: The ceramic copper-clad substrate A is sequentially subjected to pre-treatment cleaning, wet film printing, alignment exposure, development, chemical nickel plating at 80°C, deionized water cleaning, chemical gold plating at 85°C, and then placed in a 5wt% sodium hydroxide aqueous solution for stripping and cleaning for 3 minutes, then placed in a 3wt% sulfuric acid aqueous solution for neutralization and cleaning, deionized water cleaning, placed in a cyanide-free gold stripping solution, and then treated at 70°C for 40 minutes, cleaned and dried to obtain a finished product; the components of the nickel plating solution include: 4.2g / L nickel ions, 25g / L sodium hypophosphite, 6wt% P, pH=4.5, nickel layer thickness is 10μm; the components of the gold plating solution include: 1.1g / L gold, T180mL / LCL-61-M5, pH=4.6, gold layer thickness is 0.01μm; cyanide-free gold stripping solution includes the following components: 28g / L potassium sulfate, 38g / L sodium carbonate, 18g / L sodium citrate, 5g / L additives (the mass ratio of glutamic acid to modified amino acid is 2.2:1), and the pH is adjusted to 12.

[0043] Embodiment 3: A method for preventing discoloration of the surface of a ceramic copper-clad substrate by selective nickel plating, comprising the following steps:

[0044] S1: After cleaning the ceramic copper-clad substrate, printing ink, drying, alignment exposure, and development are performed to expose the required copper shape; the ceramic copper-clad substrate with the required copper shape exposed is placed in a chemical etching solution (3% sulfuric acid and 50g / L sodium sulfate aqueous solution), treated at 35°C for 40 minutes, placed in a solder etching at 40°C for 30 minutes, and washed with deionized water to obtain a basic ceramic copper-clad substrate;

[0045] The solder etching solution comprises: 4wt% sodium hydroxide, 5wt% ammonia water, 6wt% hydrogen peroxide, and 3wt% stabilizer;

[0046] S2: placing the base ceramic copper-clad substrate in a step etching solution at 40°C for etching for 25 minutes, washing with water, printing ink, drying, alignment exposure, developing, placing in a silver plating solution at 50°C for 30 minutes, washing with deionized water, stripping, and drying to obtain a ceramic copper-clad substrate A;

[0047] The components of the step etching solution include: 5wt% copper corrosion inhibitor, 10wt% sodium dodecyl sulfate, and 30wt% hydrogen peroxide; the components of the silver plating solution include: 0.36mol / L silver ammonia complex solution, 0.42mol / L glucose solution, and 4g / L dispersant solution;

[0048] S3: The ceramic copper-clad substrate A is sequentially subjected to pre-treatment cleaning, wet film printing, alignment exposure, development, chemical nickel plating at 80° C., deionized water washing, chemical gold plating at 85° C., and then placed in a 5wt% sodium hydroxide aqueous solution for stripping and washing for 3 minutes, then placed in a 3wt% sulfuric acid aqueous solution for neutralization and washing, deionized water washing, placed in a cyanide-free gold stripping solution, and then treated at 70° C. for 40 minutes, washed and dried to obtain a finished product;

[0049] Among them, the components of the nickel plating solution include: 4.2g / L nickel ions, 25g / L sodium hypophosphite, 6wt% P, pH=4.5, and the nickel layer thickness is 10μm; the components of the gold plating solution include: 1.1g / L gold, 180mL / LTCL-61-M5, pH=4.6, and the gold layer thickness is 0.01μm; the cyanide-free gold stripping solution includes the following components: 28g / L potassium sulfate, 38g / L sodium carbonate, 18g / L sodium citrate, 6g / L additives (the mass ratio of glutamic acid to modified amino acids is 2.2:1), and the pH is adjusted to 10.

[0050] Embodiment 4: A method for preventing discoloration of the surface of a ceramic copper-clad substrate by selective nickel plating, comprising the following steps:

[0051] S1: After cleaning the ceramic copper-clad substrate, printing ink, drying, alignment exposure, and development are performed to expose the required copper shape; the ceramic copper-clad substrate with the required copper shape exposed is placed in a chemical etching solution (3% sulfuric acid and 50g / L sodium sulfate aqueous solution), treated at 35°C for 40 minutes, placed in a solder etching at 40°C for 30 minutes, and washed with deionized water to obtain a basic ceramic copper-clad substrate;

[0052] The solder etching solution comprises: 4wt% sodium hydroxide, 5wt% ammonia water, 6wt% hydrogen peroxide, and 3wt% stabilizer;

[0053] S2: placing the base ceramic copper-clad substrate in a step etching solution at 40°C for etching for 25 minutes, washing with water, printing ink, drying, alignment exposure, developing, placing in a silver plating solution at 50°C for 30 minutes, washing with deionized water, stripping, and drying to obtain a ceramic copper-clad substrate A;

[0054] The components of the step etching solution include: 5wt% copper corrosion inhibitor, 10wt% sodium dodecyl sulfate, and 30wt% hydrogen peroxide; the components of the silver plating solution include: 0.36mol / L silver ammonia complex solution, 0.42mol / L glucose solution, and 4g / L dispersant solution;

[0055] S3: The ceramic copper-clad substrate A is sequentially subjected to pre-treatment cleaning, wet film printing, alignment exposure, development, chemical nickel plating at 80° C., deionized water washing, chemical gold plating at 85° C., and then placed in a 5wt% sodium hydroxide aqueous solution for stripping and washing for 3 minutes, then placed in a 3wt% sulfuric acid aqueous solution for neutralization and washing, deionized water washing, placed in a cyanide-free gold stripping solution, and then treated at 70° C. for 40 minutes, washed and dried to obtain a finished product;

[0056] Among them, the components of the nickel plating solution include: 4.2g / L nickel ions, 25g / L sodium hypophosphite, 6wt% P, pH=4.5, and the nickel layer thickness is 10μm; the components of the gold plating solution include: 1.1g / L gold ions, 180mL / LTCL-61-M, pH=4.6, and the gold layer thickness is 0.01μm; the cyanide-free gold stripping solution includes the following components: 28g / L potassium sulfate, 38g / L sodium carbonate, 18g / L sodium citrate, 5.5g / L additives (the mass ratio of glutamic acid to modified amino acids is 2.2:1), and the pH is adjusted to 12.

[0057] Comparative Example 1 is based on Example 2, but no additives are added.

[0058] S1: After cleaning the ceramic copper-clad substrate, printing ink, drying, alignment exposure, and development are performed to expose the required copper shape; the ceramic copper-clad substrate with the required copper shape exposed is placed in a chemical etching solution (3% sulfuric acid and 50g / L sodium sulfate aqueous solution), treated at 35°C for 40 minutes, placed in a solder etching at 40°C for 30 minutes, and washed with deionized water to obtain a basic ceramic copper-clad substrate;

[0059] The solder etching solution comprises: 4wt% sodium hydroxide, 5wt% ammonia water, 6wt% hydrogen peroxide, and 3wt% stabilizer;

[0060] S2: placing the base ceramic copper-clad substrate in a step etching solution at 40°C for etching for 25 minutes, washing with water, printing ink, drying, alignment exposure, developing, placing in a silver plating solution at 50°C for 30 minutes, washing with deionized water, stripping, and drying to obtain a ceramic copper-clad substrate A;

[0061] The components of the step etching solution include: 5wt% copper corrosion inhibitor, 10wt% sodium dodecyl sulfate, and 30wt% hydrogen peroxide; the components of the silver plating solution include: 0.36mol / L silver ammonia complex solution, 0.42mol / L glucose solution, and 4g / L dispersant solution;

[0062] S3: The ceramic copper-clad substrate A is sequentially subjected to pre-treatment cleaning, wet film printing, alignment exposure, development, chemical nickel plating at 80°C, deionized water cleaning, chemical gold plating at 85°C, and then placed in a 5wt% sodium hydroxide aqueous solution for stripping and cleaning for 3 minutes, then placed in a 3wt% sulfuric acid aqueous solution for neutralization and cleaning, deionized water cleaning, placed in a cyanide-free gold stripping solution, and then treated at 70°C for 40 minutes, cleaned and dried to obtain a finished product; the components of the nickel plating solution include: 4.2g / L nickel ions, 25g / L sodium hypophosphite, pH=4.5, 6wt% P, and a nickel layer thickness of 10μm; the components of the gold plating solution include: 1.1g / L gold ions, 180mL / L TCL-61-M5, pH=4.6, and a gold layer thickness of 0.01μm; the cyanide-free gold stripping solution includes the following components: 28g / L potassium sulfate, 38g / L sodium carbonate, 18g / L sodium citrate, and the pH is adjusted to 12.

[0063] Comparative Example 2 is based on Example 2, except that a single amino acid is introduced.

[0064] S1: After cleaning the ceramic copper-clad substrate, printing ink, drying, alignment exposure, and development are performed to expose the required copper shape; the ceramic copper-clad substrate with the required copper shape exposed is placed in a chemical etching solution (3% sulfuric acid and 50g / L sodium sulfate aqueous solution), treated at 35°C for 40 minutes, placed in a solder etching at 40°C for 30 minutes, and washed with deionized water to obtain a basic ceramic copper-clad substrate;

[0065] The solder etching solution comprises: 4wt% sodium hydroxide, 5wt% ammonia water, 6wt% hydrogen peroxide, and 3wt% stabilizer;

[0066] S2: placing the base ceramic copper-clad substrate in a step etching solution at 40°C for etching for 25 minutes, washing with water, printing ink, drying, alignment exposure, developing, placing in a silver plating solution at 50°C for 30 minutes, washing with deionized water, stripping, and drying to obtain a ceramic copper-clad substrate A;

[0067] The components of the step etching solution include: 5wt% copper corrosion inhibitor, 10wt% sodium dodecyl sulfate, and 30wt% hydrogen peroxide; the components of the silver plating solution include: 0.36mol / L silver ammonia complex solution, 0.42mol / L glucose solution, and 4g / L dispersant solution;

[0068] S3: The ceramic copper-clad substrate A is sequentially subjected to pre-treatment cleaning, wet film printing, alignment exposure, development, chemical nickel plating at 80°C, deionized water cleaning, chemical gold plating at 85°C, and then placed in a 5wt% sodium hydroxide aqueous solution for stripping and cleaning for 3 minutes, then placed in a 3wt% sulfuric acid aqueous solution for neutralization and cleaning, deionized water cleaning, placed in a cyanide-free gold stripping solution, and then treated at 70°C for 40 minutes, cleaned and dried to obtain a finished product; the components of the nickel plating solution include: 4.2g / L nickel ions, 25g / L sodium hypophosphite, 6wt% P, pH=4.5, and the nickel layer thickness is 10μm; the components of the gold plating solution include: 1.1g / L gold ions, 180mL / LTCL-61-M5, pH=4.6, and the gold layer thickness is 0.01μm; the cyanide-free gold stripping solution includes the following components: 28g / L potassium sulfate, 38g / L sodium carbonate, 18g / L sodium citrate, 6g / L glutamic acid, and the pH is adjusted to 12.

[0069] Comparative Example 3 is based on Example 2, but an excess amount of additives is added.

[0070] S1: After cleaning the ceramic copper-clad substrate, printing ink, drying, alignment exposure, and development are performed to expose the required copper shape; the ceramic copper-clad substrate with the required copper shape exposed is placed in a chemical etching solution (3% sulfuric acid and 50g / L sodium sulfate aqueous solution), treated at 35°C for 40 minutes, placed in a solder etching at 40°C for 30 minutes, and washed with deionized water to obtain a basic ceramic copper-clad substrate;

[0071] The solder etching solution comprises: 4wt% sodium hydroxide, 5wt% ammonia water, 6wt% hydrogen peroxide, and 3wt% stabilizer;

[0072] S2: placing the base ceramic copper-clad substrate in a step etching solution at 40°C for etching for 25 minutes, washing with water, printing ink, drying, alignment exposure, developing, placing in a silver plating solution at 50°C for 30 minutes, washing with deionized water, stripping, and drying to obtain a ceramic copper-clad substrate A;

[0073] The components of the step etching solution include: 5wt% copper corrosion inhibitor, 10wt% sodium dodecyl sulfonate, and 30wt% hydrogen peroxide; the components of the silver plating solution include: 0.36mol / L silver ammonia complex solution concentration, 0.42mol / L glucose solution concentration, and 4g / L dispersant solution;

[0074] S3: The ceramic copper-clad substrate A is sequentially subjected to pre-treatment cleaning, wet film printing, alignment exposure, development, chemical nickel plating at 80°C, deionized water washing, chemical gold plating at 85°C, and then placed in a 5wt% sodium hydroxide aqueous solution for stripping and washing for 3 minutes, then placed in a 3wt% sulfuric acid aqueous solution for neutralization and washing, deionized water washing, placed in a cyanide-free gold stripping solution, and then treated at 70°C for 40 minutes, washed and dried to obtain a finished product; the components of the nickel plating solution include: 4.2g / L nickel ions, 25 g / L sodium hypophosphite, pH=4.5, 6wt%P, nickel layer thickness is 10μm; the components of the gold plating solution include: 1.1g / L gold ions, 180mL / LTCL-61-M5, pH=4.6, gold layer thickness is 0.01μm; the cyanide-free gold stripping solution includes the following components: 28g / L potassium sulfate, 38g / L sodium carbonate, 18g / L sodium citrate, 20g / L additives (the mass ratio of glutamic acid to modified amino acids is 2.2:1), and the pH is adjusted to 12.

[0075] (1) Result comparison: 100 ceramic copper-clad substrates were tested according to Examples 1 and 3, and the yield rate was calculated:

[0076] Results: The yield rate of the cyanide gold stripping solution in Example 1 was 90%, and the yield rate of the cyanide-free gold stripping solution in Example 3 was 96%.

[0077] (2) Test 1: The gold-plated samples of Example 2 and Comparative Examples 1 to 3 were cleaned, dried, and cut into 8 mm × 150 mm test pieces, 6 in each group, and placed in the gold stripping solution of Example 2 and Comparative Examples 1 to 3 for 8 hours. The gold stripping rate and the gold-free plating residue are shown in Table 1.

[0078] Stripping rate (μm / min) No gold plating residue (%) Example 2 0.31 0.81 Comparative Example 1 0.20 1.07 Comparative Example 2 0.26 1.03 Comparative Example 3 0.32 0.87

[0079] Table 1

[0080] Conclusion: Example 2 uses amino acids and modified amino acids as additives for cyanide-free gold stripping liquid; Comparative Example 1 is based on Example 2, without adding additives, which leads to a decrease in the gold stripping rate and increases in time cost and gold residue; Comparative Example 2 is based on Example 2, and a single amino acid is introduced, which reduces the rate, because the amino acid is modified to introduce multiple reaction sites on its side chain, thereby reducing time cost and gold residue; Comparative Example 3 is based on Example 2, and the content of the additive is increased. It is found that the gold stripping rate is not improved with the increase in the content of the additive, resulting in waste of materials and increased costs.

[0081] Finally, it should be noted that the above description is only a preferred example of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preventing discoloration of selective nickel plating on the surface of a ceramic copper-clad substrate, characterized in that: The steps include: S1: subjecting the ceramic copper-clad substrate to a solder etching process, a step etching process, and a local silver plating process in sequence to obtain a ceramic copper-clad substrate A; S2: The ceramic copper-clad substrate A is sequentially subjected to pre-treatment cleaning, wet film printing, alignment exposure, development, chemical nickel-gold plating, film stripping and cleaning, gold stripping process, cleaning and drying to obtain a finished product; In the process of the gold stripping process, a gold stripping liquid is used, and the gold stripping liquid is a cyanide-free gold stripping liquid; The cyanide-free gold stripping solution comprises the following components: 28-32 g / L potassium sulfate, 38-42 g / L sodium carbonate, 18-22 g / L sodium citrate, 5-6 g / L additives; the additives include small molecule amino acids and modified amino acids; The small molecule amino acid includes one or more of methionine, cystine and cysteine; the mass ratio of the small molecule amino acid to the modified amino acid is (2-2.5):1; The preparation method of the modified amino acid is as follows: 5-aminolysine and cysteine ​​are added to N,N-dimethylacetamide and stirred for 10 to 20 minutes, and diphenyl sulfide dianhydride is added to react for 4 to 6 hours to obtain the modified amino acid; In the step etching process, the components of the step etching solution include: 5wt% copper corrosion inhibitor, 10wt% sodium dodecyl sulfate, and 30wt% hydrogen peroxide.

2. A method for preventing discoloration of selective nickel plating on the surface of a ceramic copper-clad substrate according to claim 1, characterized in that: When cyanide-free gold stripping liquid is used in the gold stripping process, the process parameters are: the temperature is room temperature, the speed is 0.2±0.05um / min; the pH of the gold stripping liquid is 8~12.

3. The method for preventing discoloration of selective nickel plating on the surface of a ceramic copper-clad substrate according to claim 1, characterized in that: The chemical nickel-gold plating comprises a nickel-phosphorus layer and a gold layer, and the thickness of the gold layer is 0.01-0.02 μm.

4. The method for preventing discoloration of selective nickel plating on the surface of a ceramic copper-clad substrate according to claim 1, characterized in that: The raw materials of the modified amino acid include the following components: by weight, 2-3 parts of cysteine, 1-1.5 parts of 5-aminolysine, 30-40 parts of N,N-dimethylacetamide, and 1-2 parts of diphenyl sulfide dianhydride.

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