Surface treatment process of mini LED circuit board

Abstract

The present application relates to the field of circuit board, and particularly relates to a surface treatment process of MiniLED circuit board. The surface treatment process of MiniLED circuit board comprises the following steps: pretreatment, chemical nickel plating, chemical palladium plating and chemical gold plating. By adding complex pyridine-2-carboxylic acid and thiomalic acid in the gold plating solution, pyridine-2-carboxylic acid is used as the main heterocyclic complexing agent, can form a stable five-membered ring chelate with Au⁺ in sodium sulfite gold, effectively inhibits the spontaneous reduction of gold ions in the plating solution, and the agglomeration and precipitation of gold. Thiomalic acid is used as an auxiliary complexing agent and a grain refiner, the carboxyl and mercapto groups contained in the thiomalic acid can form a weak coordination bond with Au⁺, which can further stabilize the plating solution system with pyridine-2-carboxylic acid, prolong the service life of the plating solution, refine the gold grain size, fill the micro-pores of the plating layer, and make the plating layer more flat and dense, thereby significantly improving the mounting yield and long-term reliability of the MiniLED circuit board pad.

Description

Technical Field

[0001] This invention relates to the field of circuit boards, and more specifically to a surface treatment process for MiniLED circuit boards. Background Technology

[0002] MiniLED, as a next-generation display technology, is widely used in high-end displays, automotive electronics, and smart terminals due to its advantages of high contrast, high brightness, and low power consumption. MiniLED circuit boards are characterized by tiny pad sizes and dense spacing, requiring surface treatment to form a uniform and dense protective coating to ensure soldering reliability, prevent corrosion, and meet precision mounting requirements.

[0003] Currently, the most common surface treatment process for MiniLED circuit boards is ENIG (chemical nickel-gold plating). However, this process is prone to black pad defects. The root cause is the excessive corrosion of the nickel layer by the gold plating solution during the immersion gold process, which generates black nickel oxides or sulfides, leading to brittle fracture of the solder joints and insufficient shear strength. In addition, the stability of the plating solution in the existing process is poor. For example, sodium gold sulfite in the cyanide-free gold plating system is prone to spontaneous reduction and gold precipitation, resulting in uneven gold layer deposition and poor coverage on high-density micro pads, which can easily lead to missed plating, short circuits, or tombstoning.

[0004] Therefore, a surface treatment process for MiniLED circuit boards needs to be proposed to improve soldering reliability. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a surface treatment process for MiniLED circuit boards.

[0006] This invention provides a surface treatment process for a MiniLED circuit board, comprising the following steps: S1: Preprocessing The copper-clad laminate is subjected to alkaline treatment, acid treatment, micro-etching, pre-immersion and activation in sequence to obtain a pretreated substrate; S2: Electroless nickel plating Heat the nickel plating solution to 70-80℃, then turn on the air agitation, vertically immerse the pretreated substrate into the nickel plating solution, keep it at the temperature for 30-40 minutes, then wash it with water for 120-140 seconds and dry it with hot air at 70-75℃ for 10-12 minutes to obtain the nickel-plated substrate. S3: Electroless palladium plating Heat the palladium plating solution to 50-55℃, then turn on the air agitation, vertically immerse the above nickel-plated substrate into the palladium plating solution, keep it at the temperature for 6-8 minutes, then wash it with water for 120-140 seconds and dry it with hot air at 65-70℃ for 10-12 minutes to obtain the palladium-plated substrate. S4: Chemical gold plating Heat the gold plating solution to 45-50℃, then turn on the air agitation, vertically immerse the palladium-plated substrate into the gold plating solution, keep it at the temperature for 3.5-4.5 minutes, then wash it with water for 120-140 seconds and dry it with hot air at 65-70℃ for 10-12 minutes to obtain the gold-plated substrate.

[0007] Furthermore, S1 specifically includes the following steps: S1.1: Immerse the copper-clad laminate in an alkaline degreasing solution, treat it at 45-55℃ for 4-6 minutes, and then wash it with water for 1-2 minutes to obtain an alkaline-treated substrate. S1.2: Immerse the above-mentioned alkaline-treated circuit board in an acidic treatment solution, treat it at 30-35°C for 30-60 seconds, and then wash it with water for 1-2 minutes to obtain an acid-treated substrate. S1.3: Immerse the above acid-treated circuit board in a micro-etching solution, treat it at 25-30℃ for 30-40s, and then wash it with water for 80-100s to obtain a micro-etched substrate. S1.4: Immerse the micro-etched substrate in the pre-impregnation solution for 20-30 seconds, then transfer it to the activation solution and treat it at 30-35°C for 40-60 seconds. Wash it with water for 2-3 minutes, and then dry it with hot air at 70-80°C for 10-15 minutes to obtain the pre-treated substrate.

[0008] Furthermore, the alkaline degreasing solution includes: 20-30 g / L sodium hydroxide, 30-40 g / L sodium carbonate, and 2-3 g / L fatty alcohol polyoxyethylene ether.

[0009] Furthermore, the acidic treatment solution includes 80 mL / L concentrated sulfuric acid; the micro-etching solution includes 80-120 g / L sodium persulfate and 20-30 mL / L concentrated sulfuric acid.

[0010] Furthermore, the pre-impregnation solution includes 20-30 mL / L concentrated sulfuric acid; the activation solution includes 10-20 ppm palladium chloride, 5-10 mL / L concentrated hydrochloric acid, and 0.5 g / L potassium iodide.

[0011] Furthermore, the nickel plating solution comprises: 25-35 g / L nickel sulfate hexahydrate, 15-20 g / L sodium hypophosphite monohydrate, 8-10 g / L citric acid, 5-8 g / L lactic acid, 5-7 g / L sodium acetate, and 0.1-0.2 g / L sodium dodecyl sulfate, and the pH of the nickel plating solution is 4.

[0012] Furthermore, the palladium plating solution comprises: 1.2-1.4 g / L palladium chloride, 15-20 g / L ammonium aminosulfonate, 20-25 g / L sodium citrate, 2-3 g / L sodium hypophosphite, and 0.3-0.5 g / L composite stabilizer, and the pH of the palladium plating solution is 7.2-7.8. The composite stabilizer is composed of benzotriazole and polyethylene glycol 2000 in a mass ratio of 1:1.

[0013] Furthermore, the gold plating solution comprises: 1.3-1.5 g / L sodium gold sulfite, 20-30 g / L sodium sulfite, 8-10 g / L pyridine-2-carboxylic acid, 1-2 g / L thiomalic acid, 2-3 g / L thiourea, and 20-30 g / L sodium hypophosphite, and the pH of the palladium plating solution is 4.5.

[0014] The present invention has the following advantages: 1. In this invention, by setting a palladium layer between the nickel plating layer and the gold plating layer, the gold plating solution can be isolated from the underlying nickel-phosphorus plating layer, blocking the displacement corrosion reaction between gold and nickel, avoiding the nickel layer from being etched, and fundamentally eliminating the black pad problem. During soldering, the palladium element will be incorporated into the solder system, forming a Ni-Sn-Pd ternary intermetallic compound at the interface, causing the solder joint to exhibit ductile fracture, improving the soldering strength and reliability, while improving the corrosion resistance of the plating layer, realizing the deposition of an ultra-thin gold layer, and adapting to the precision mounting requirements of MiniLED high-density pads.

[0015] 2. In this invention, by adding a compound of pyridine-2-carboxylic acid and thiomalic acid to the gold plating solution, pyridine-2-carboxylic acid is used as the main heterocyclic complexing agent to form a stable five-membered ring chelate with Au⁺ in sodium gold sulfite. This effectively inhibits the spontaneous reduction and precipitation of gold ions in the plating solution, as well as their agglomeration and precipitation. Thiomalic acid, as an auxiliary complexing agent and grain refiner, contains carboxyl and thiol groups that can form weak coordination bonds with Au⁺. This not only synergistically stabilizes the plating solution system with pyridine-2-carboxylic acid and extends the service life of the plating solution, but also refines the gold grain size, fills the micropores in the plating layer, and makes the plating layer more flat and dense, thereby significantly improving the mounting yield and long-term reliability of MiniLED circuit board pads. Attached Figure Description

[0016] Figure 1 This is a flow chart of the surface treatment process of the MiniLED circuit board used in an embodiment of the present invention. Detailed Implementation

[0017] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of this invention.

[0018] Example 1: A surface treatment process for a MiniLED circuit board, such as... Figure 1 As shown, it includes the following steps: S1: Preprocessing S1.1: Immerse the copper-clad laminate in an alkaline degreasing solution, treat it at 45°C for 4 minutes, and then wash it with water for 1 minute to obtain an alkaline-treated substrate. The alkaline degreasing solution includes: 20 g / L sodium hydroxide, 30 g / L sodium carbonate, and 2 g / L fatty alcohol polyoxyethylene ether. S1.2: Immerse the above-mentioned alkaline-treated circuit board in an acidic treatment solution, treat it at 30°C for 30 seconds, and then wash it with water for 1 minute to obtain an acid-treated substrate. The acidic treatment solution includes 80 mL / L concentrated sulfuric acid. S1.3: Immerse the above acid-treated circuit board in a micro-etching solution, treat it at 25°C for 30 seconds, and then wash it with water for 80 seconds to obtain a micro-etched substrate. The micro-etching solution includes 80 g / L sodium persulfate and 20 mL / L concentrated sulfuric acid. S1.4: Immerse the above micro-etched substrate in the pre-impregnation solution and treat for 20 seconds. Then, transfer it to the activation solution and treat it at 30°C for 40 seconds. Wash it with water for 2 minutes and then dry it with hot air at 70°C for 10 minutes to obtain the pre-treated substrate. The pre-impregnation solution includes 20 mL / L concentrated sulfuric acid, and the activation solution includes 10 ppm palladium chloride, 5 mL / L concentrated hydrochloric acid, and 0.5 g / L potassium iodide. S2: Electroless nickel plating The nickel plating solution is heated to 70°C, and then air agitation is turned on. The pretreated substrate is vertically immersed in the nickel plating solution and kept at the temperature for 30 minutes. Then it is washed with water for 120 seconds and dried with hot air at 70°C for 10 minutes to obtain a nickel-plated substrate. The nickel plating solution includes: 25 g / L nickel sulfate hexahydrate, 15 g / L sodium hypophosphite monohydrate, 8 g / L citric acid, 5 g / L lactic acid, 5 g / L sodium acetate and 0.1 g / L sodium dodecyl sulfate, and the pH of the nickel plating solution is 4. S3: Electroless palladium plating The palladium plating solution was heated to 50°C, and then air stirring was turned on. The nickel-plated substrate was vertically immersed in the palladium plating solution and kept at the temperature for 6 minutes. Then it was washed with water for 120 seconds and dried with hot air at 65°C for 10 minutes to obtain the palladium-plated substrate. The palladium plating solution included: 1.2 g / L palladium chloride, 15 g / L ammonium aminosulfonate, 20 g / L sodium citrate, 2 g / L sodium hypophosphite, and 0.3 g / L composite stabilizer. The pH of the palladium plating solution was 7.2. The composite stabilizer was composed of benzotriazole and polyethylene glycol 2000 in a mass ratio of 1:1. S4: Chemical gold plating The gold plating solution was heated to 45°C, and then air agitation was turned on. The palladium-plated substrate was vertically immersed in the gold plating solution and kept at the temperature for 3.5 minutes. Then it was washed with water for 120 seconds and dried with hot air at 65°C for 10 minutes to obtain the gold-plated substrate. The gold plating solution included: 1.3 g / L sodium gold sulfite, 20 g / L sodium sulfite, 8 g / L pyridine-2-carboxylic acid, 1 g / L thiomalic acid, 2 g / L thiourea and 20 g / L sodium hypophosphite, and the pH of the palladium plating solution was 4.5.

[0019] Example 2: A surface treatment process for a MiniLED circuit board, such as... Figure 1 As shown, it includes the following steps: S1: Preprocessing S1.1: Immerse the copper-clad laminate in an alkaline degreasing solution, treat it at 50°C for 5 minutes, and then wash it with water for 1.5 minutes to obtain an alkaline-treated substrate. The alkaline degreasing solution includes: 25 g / L sodium hydroxide, 35 g / L sodium carbonate, and 2.5 g / L fatty alcohol polyoxyethylene ether. S1.2: Immerse the above-mentioned alkaline-treated circuit board in an acidic treatment solution, treat it at 32°C for 45 seconds, and then wash it with water for 1.5 minutes to obtain an acid-treated substrate. The acidic treatment solution includes 80 mL / L concentrated sulfuric acid. S1.3: Immerse the above acid-treated circuit board in a micro-etching solution, treat it at 27.5°C for 35 seconds, and then wash it with water for 90 seconds to obtain a micro-etched substrate. The micro-etching solution includes 100 g / L sodium persulfate and 25 mL / L concentrated sulfuric acid. S1.4: Immerse the above micro-etched substrate in the pre-impregnation solution and treat for 25 seconds. Then, transfer it to the activation solution and treat it at 32.5°C for 50 seconds. Wash it with water for 2.5 minutes and then dry it with hot air at 75°C for 12.5 minutes to obtain the pre-treated substrate. The pre-impregnation solution includes 25 mL / L concentrated sulfuric acid, and the activation solution includes 15 ppm palladium chloride, 7.5 mL / L concentrated hydrochloric acid, and 0.5 g / L potassium iodide. S2: Electroless nickel plating The nickel plating solution was heated to 75°C, and then air agitation was turned on. The pretreated substrate was vertically immersed in the nickel plating solution and kept at the temperature for 35 minutes. Then it was washed with water for 130 seconds and dried with hot air at 72°C for 11 minutes to obtain a nickel-plated substrate. The nickel plating solution included: 30 g / L nickel sulfate hexahydrate, 17.5 g / L sodium hypophosphite monohydrate, 9 g / L citric acid, 6.5 g / L lactic acid, 6 g / L sodium acetate and 0.3 g / L sodium dodecyl sulfate, and the pH of the nickel plating solution was 4. S3: Electroless palladium plating The palladium plating solution was heated to 52.5℃, and then air stirring was turned on. The nickel-plated substrate was vertically immersed in the palladium plating solution and kept at the temperature for 7 minutes. Then it was washed with water for 130 seconds and dried with hot air at 67.5℃ for 11 minutes to obtain the palladium-plated substrate. The palladium plating solution included: 1.3 g / L palladium chloride, 17.5 g / L ammonium aminosulfonate, 22.5 g / L sodium citrate, 2.5 g / L sodium hypophosphite, and 0.4 g / L composite stabilizer. The pH of the palladium plating solution was 7.5. The composite stabilizer was composed of benzotriazole and polyethylene glycol 2000 in a mass ratio of 1:1. S4: Chemical gold plating The gold plating solution was heated to 47.5°C, and then air agitation was turned on. The palladium-plated substrate was vertically immersed in the gold plating solution and kept at the temperature for 4 minutes. Then it was washed with water for 130 seconds and dried with hot air at 67.5°C for 11 minutes to obtain the gold-plated substrate. The gold plating solution included: 1.4 g / L sodium gold sulfite, 25 g / L sodium sulfite, 9 g / L pyridine-2-carboxylic acid, 1.5 g / L thiomalic acid, 2.5 g / L thiourea and 25 g / L sodium hypophosphite, and the pH of the palladium plating solution was 4.5.

[0020] Example 3: A surface treatment process for a MiniLED circuit board, such as... Figure 1 As shown, it includes the following steps: S1: Preprocessing S1.1: Immerse the copper-clad laminate in an alkaline degreasing solution, treat it at 55°C for 6 minutes, and then wash it with water for 2 minutes to obtain an alkaline-treated substrate. The alkaline degreasing solution includes: 30 g / L sodium hydroxide, 40 g / L sodium carbonate, and 3 g / L fatty alcohol polyoxyethylene ether. S1.2: Immerse the above-mentioned alkaline-treated circuit board in an acidic treatment solution, treat it at 35°C for 60 seconds, and then wash it with water for 2 minutes to obtain an acid-treated substrate. The acidic treatment solution includes 80 mL / L concentrated sulfuric acid. S1.3: Immerse the above acid-treated circuit board in a micro-etching solution, treat it at 30°C for 40 seconds, and then wash it with water for 100 seconds to obtain a micro-etched substrate. The micro-etching solution includes 120 g / L sodium persulfate and 30 mL / L concentrated sulfuric acid. S1.4: Immerse the above micro-etched substrate in the pre-impregnation solution and treat for 30 seconds. Then, transfer it to the activation solution and treat it at 35°C for 60 seconds. Wash it with water for 3 minutes and then dry it with hot air at 80°C for 15 minutes to obtain the pre-treated substrate. The pre-impregnation solution includes 30 mL / L concentrated sulfuric acid, and the activation solution includes 20 ppm palladium chloride, 10 mL / L concentrated hydrochloric acid, and 0.5 g / L potassium iodide. S2: Electroless nickel plating The nickel plating solution is heated to 80°C, and then air agitation is turned on. The pretreated substrate is vertically immersed in the nickel plating solution and kept at the temperature for 40 minutes. Then it is washed with water for 140 seconds and dried with hot air at 75°C for 12 minutes to obtain a nickel-plated substrate. The nickel plating solution includes: 35 g / L nickel sulfate hexahydrate, 20 g / L sodium hypophosphite monohydrate, 10 g / L citric acid, 8 g / L lactic acid, 7 g / L sodium acetate and 0.2 g / L sodium dodecyl sulfate, and the pH of the nickel plating solution is 4. S3: Electroless palladium plating The palladium plating solution was heated to 55°C, and then air stirring was turned on. The nickel-plated substrate was vertically immersed in the palladium plating solution and kept at the temperature for 8 minutes. Then it was washed with water for 140 seconds and dried with hot air at 70°C for 12 minutes to obtain the palladium-plated substrate. The palladium plating solution included: 1.4 g / L palladium chloride, 20 g / L ammonium aminosulfonate, 25 g / L sodium citrate, 3 g / L sodium hypophosphite, and 0.5 g / L composite stabilizer. The pH of the palladium plating solution was 7.8. The composite stabilizer was composed of benzotriazole and polyethylene glycol 2000 in a mass ratio of 1:1. S4: Chemical gold plating The gold plating solution was heated to 50°C, and then air agitation was turned on. The palladium-plated substrate was vertically immersed in the gold plating solution and kept at the temperature for 4.5 minutes. Then it was washed with water for 140 seconds and dried with hot air at 70°C for 12 minutes to obtain the gold-plated substrate. The gold plating solution included: 1.5 g / L sodium gold sulfite, 30 g / L sodium sulfite, 10 g / L pyridine-2-carboxylic acid, 2 g / L thiomalic acid, 3 g / L thiourea and 30 g / L sodium hypophosphite, and the pH of the palladium plating solution was 4.5.

[0021] Comparative Example 1 differs from Example 1 in that step S3 is removed, and the nickel-plated substrate is directly immersed in the gold plating solution for chemical gold plating.

[0022] Comparative Example 2 differs from Example 1 in that the thiomalic acid in the gold plating solution is replaced with an equal amount of pyridine-2-carboxylic acid.

[0023] Comparative Example 3 differs from Example 1 in that pyridine-2-carboxylic acid in the gold plating solution is replaced with an equal amount of thiomalic acid.

[0024] Comparative Example 4 differs from Example 1 in that pyridine-2-carboxylic acid and thiomalic acid are removed from the gold plating solution.

[0025] Test example: Test 1: The surface morphology of the gold-plated substrate pads prepared in Examples 1-3 and Comparative Example 1 was observed using a metallographic microscope, and the occurrence rate of black pads was statistically analyzed. The results are shown in Table 1.

[0026] Sampling rules: 10 complete substrates are randomly selected from each group, and 20 independent 50μm×50μm pads are selected on each substrate. The total number of pads observed in each group is 200.

[0027] Calculation method: Black pad occurrence rate = total number of failed pads in each group / total number of observed pads × 100%.

[0028] Black disk judgment criteria: 1. Obvious black or dark gray areas appear on the surface of the pads, with an area ≥ 5% of the total area of ​​the pads; 2. Pitted corrosion pits and mesh corrosion patterns appear on the pads, and the underlying nickel layer is exposed. 3. Plating defects, exposed copper / nickel, are present at the edges or center of the solder pads; 4. The surface is dull, rough, and lacks metallic luster, showing a significant difference in appearance from a normal gold plating layer; If any of the above conditions are met, the pad is determined to be a failed pad with a black disk.

[0029] Table 1: Results of Black Disk Occurrence Rate Test Example 1 0 Example 2 0 Example 3 0 Comparative Example 1 89.6 As shown in Table 1, after removing the palladium plating layer in Comparative Example 1, the black disk occurrence rate of the gold-plated substrate was much higher than that in Example 1. This shows that by setting a palladium layer between the nickel plating layer and the gold plating layer, the gold plating solution can be isolated from the underlying nickel-phosphorus plating layer, blocking the displacement corrosion reaction between gold and nickel, avoiding the nickel layer from being etched, and fundamentally eliminating the black disk problem. During soldering, the palladium element will be incorporated into the solder system, forming a Ni-Sn-Pd ternary intermetallic compound at the interface, causing the solder joint to exhibit ductile fracture, improving the soldering strength and reliability, while improving the corrosion resistance of the plating layer, realizing the deposition of an ultra-thin gold layer, and adapting to the precision mounting requirements of MiniLED high-density pads.

[0030] Test 2: The gold plating solutions prepared in Examples 1-3 and Comparative Examples 2-4 were continuously heated and stirred at 50°C for 24 hours. Then, the gold ion concentration before and after stirring was measured using a UV-Vis spectrophotometer, and the gold ion concentration retention rate was calculated. The test was repeated 3 times, and the average value was taken. The results are shown in Table 2.

[0031] Calculation formula: Gold ion concentration retention rate = gold ion concentration in the gold plating solution after continuous heating and stirring at 50℃ for 24 hours / initial gold ion concentration in the gold plating solution × 100%.

[0032] Table 2: Results of Gold Ion Concentration Retention Rate Test Example 1 98.2 Example 2 98.7 Example 3 99.3 Comparative Example 2 92.1 Comparative Example 3 84.6 Comparative Example 4 81.5 As shown in Table 2, in Comparative Examples 2 and 3, when only one of pyridine-2-carboxylic acid or thiomalic acid was added to the gold plating solution, the gold ion concentration retention rate of the prepared gold plating solution was higher than that of Comparative Example 4, but lower than that of Example 1. It can be seen that by adding a compound of pyridine-2-carboxylic acid and thiomalic acid to the gold plating solution, pyridine-2-carboxylic acid can be used as the main heterocyclic complexing agent to form a stable five-membered ring chelate with Au⁺ in sodium gold sulfite, which can effectively inhibit the spontaneous reduction and precipitation of gold ions in the plating solution and the agglomeration and precipitation. Thiomalic acid, as an auxiliary complexing agent, contains carboxyl and thiol groups that can form weak coordination bonds with Au⁺, which can work synergistically with pyridine-2-carboxylic acid to further stabilize the plating solution system and extend the service life of the plating solution.

[0033] Test 3: The pore area of ​​the gold-plated substrates prepared in Examples 1-3 and Comparative Example 2 was observed using a scanning electron microscope, and the porosity was calculated. The test was repeated 3 times, and the average value was taken. The results are shown in Table 3.

[0034] Calculation formula: Porosity = Total pore area / Total test area × 100%.

[0035] Table 3: Results of Coating Porosity Test Example 1 0.12 Example 2 0.11 Example 3 0.08 Comparative Example 2 0.58 As shown in Table 3, in Comparative Example 2, when only pyridine-2-carboxylic acid was added to the gold plating solution, the surface porosity of the gold-plated substrate was higher than that in Example 1. This shows that thiomalic acid, as a grain refiner, can refine the size of gold grains, fill the micropores in the plating layer, and make the plating layer more flat and dense, thereby significantly improving the mounting yield and long-term reliability of the MiniLED circuit board pads.

[0036] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A surface treatment process for a MiniLED circuit board, characterized in that, Includes the following steps: S1: Preprocessing The copper-clad laminate is subjected to alkaline treatment, acid treatment, micro-etching, pre-immersion and activation in sequence to obtain a pretreated substrate; S2: Electroless nickel plating Heat the nickel plating solution to 70-80℃, then turn on the air agitation, vertically immerse the pretreated substrate into the nickel plating solution, keep it at the temperature for 30-40 minutes, then wash it with water for 120-140 seconds and dry it with hot air at 70-75℃ for 10-12 minutes to obtain the nickel-plated substrate. S3: Electroless palladium plating Heat the palladium plating solution to 50-55℃, then turn on the air agitation, vertically immerse the above nickel-plated substrate into the palladium plating solution, keep it at the temperature for 6-8 minutes, then wash it with water for 120-140 seconds and dry it with hot air at 65-70℃ for 10-12 minutes to obtain the palladium-plated substrate. S4: Chemical gold plating Heat the gold plating solution to 45-50℃, then turn on the air agitation, vertically immerse the palladium-plated substrate into the gold plating solution, keep it at the temperature for 3.5-4.5 minutes, then wash it with water for 120-140 seconds and dry it with hot air at 65-70℃ for 10-12 minutes to obtain the gold-plated substrate.

2. The surface treatment process for a MiniLED circuit board according to claim 1, characterized in that, S1 specifically includes the following steps: S1.1: Immerse the copper-clad laminate in an alkaline degreasing solution, treat it at 45-55℃ for 4-6 minutes, and then wash it with water for 1-2 minutes to obtain an alkaline-treated substrate. S1.2: Immerse the above-mentioned alkaline-treated circuit board in an acidic treatment solution, treat it at 30-35°C for 30-60 seconds, and then wash it with water for 1-2 minutes to obtain an acid-treated substrate. S1.3: Immerse the above acid-treated circuit board in a micro-etching solution, treat it at 25-30℃ for 30-40s, and then wash it with water for 80-100s to obtain a micro-etched substrate. S1.4: Immerse the micro-etched substrate in the pre-impregnation solution for 20-30 seconds, then transfer it to the activation solution and treat it at 30-35°C for 40-60 seconds. Wash it with water for 2-3 minutes, and then dry it with hot air at 70-80°C for 10-15 minutes to obtain the pre-treated substrate.

3. The surface treatment process for a MiniLED circuit board according to claim 2, characterized in that, The alkaline degreasing solution includes: 20-30 g / L sodium hydroxide, 30-40 g / L sodium carbonate, and 2-3 g / L fatty alcohol polyoxyethylene ether.

4. The surface treatment process for a MiniLED circuit board according to claim 2, characterized in that, The acidic treatment solution includes 80 mL / L concentrated sulfuric acid; the micro-etching solution includes 80-120 g / L sodium persulfate and 20-30 mL / L concentrated sulfuric acid.

5. The surface treatment process for a MiniLED circuit board according to claim 2, characterized in that, The pre-soaking solution includes 20-30 mL / L concentrated sulfuric acid; the activation solution includes 10-20 ppm palladium chloride, 5-10 mL / L concentrated hydrochloric acid, and 0.5 g / L potassium iodide.

6. The surface treatment process for a MiniLED circuit board according to claim 1, characterized in that, The nickel plating solution includes: 25-35 g / L nickel sulfate hexahydrate, 15-20 g / L sodium hypophosphite monohydrate, 8-10 g / L citric acid, 5-8 g / L lactic acid, 5-7 g / L sodium acetate, and 0.1-0.2 g / L sodium dodecyl sulfate, and the pH of the nickel plating solution is 4.

7. The surface treatment process for a MiniLED circuit board according to claim 1, characterized in that, The palladium plating solution includes: 1.2-1.4 g / L palladium chloride, 15-20 g / L ammonium aminosulfonate, 20-25 g / L sodium citrate, 2-3 g / L sodium hypophosphite, and 0.3-0.5 g / L composite stabilizer. The pH of the palladium plating solution is 7.2-7.

8. The composite stabilizer is a mixture of benzotriazole and polyethylene glycol 2000 in a 1:1 mass ratio.

8. The surface treatment process for a MiniLED circuit board according to claim 1, characterized in that, The gold plating solution includes: 1.3-1.5 g / L sodium gold sulfite, 20-30 g / L sodium sulfite, 8-10 g / L pyridine-2-carboxylic acid, 1-2 g / L thiomalic acid, 2-3 g / L thiourea, and 20-30 g / L sodium hypophosphite, and the pH of the palladium plating solution is 4.5.

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