Printed circuit board golden finger coating processing method

Abstract

The invention discloses a printed circuit board golden finger coating processing method, which belongs to the technical field of printed circuit board preparation, and comprises three main steps of first coating processing, non-coating processing, and second and third coating processing. In the first plating layer, a copper layer is deposited on the circuit board hole and the base copper surface through a chemical deposition process, and then the thickness is increased to 20-70 microns. The non-plating layer processing comprises circuit processing, optical detection, resistance welding and character processing. The processing of the second plating layer and the third plating layer relates to pretreatment, oil removal, micro-etching, acid pickling, pre-soaking, activation, post-soaking, deposition of the second plating layer and the third plating layer, and metal recovery. The second plating layer is mainly composed of nickel and phosphorus, and the third plating layer is composed of gold and cobalt, so that abrasion resistance is improved. Compared with the prior art, the plating layer machining method has the advantages of being short in technological process, low in cost and high in plating layer thickness uniformity, and the plating layer hardness and abrasion resistance are remarkably improved.

Description

Technical Field

[0001] The invention relates to the technical field of printed circuit board preparation, and in particular to a method for processing a gold finger plating layer of a printed circuit board. Background Art

[0002] The "gold fingers" of PCB circuit boards refer to the metal connectors covering the edge of the board. These gold fingers are usually gold-plated to improve their conductivity and corrosion resistance. PCB circuit board gold fingers are generally used as interfaces for connectors or slots, which can be easily interconnected with other devices or electronic components. In computer memory and graphics cards, gold fingers also exist as a kind of connector. In PCB design, since its main function is to connect and conduct, it needs to have good conductivity, wear resistance, oxidation resistance and corrosion resistance. According to its performance characteristics, gold fingers are divided into regular gold fingers, long and short gold fingers, and segmented gold fingers.

[0003] Regardless of the type of gold finger, given the functional characteristics of the gold finger, the gold plating thickness generally needs to reach more than 0.5μm, or even higher. Therefore, the traditional gold finger processing technology is to use electroplating. In order to control costs and process requirements, gold finger electroplating generally adopts a selective electroplating process, that is, during the electroplating process, only a part of the area needs to be electroplated. This causes the problem of uneven distribution of power lines during the electroplating process, which in turn leads to excessive differences in the height of the gold finger metal plating after electroplating. The difference in plating thickness can reach 4~10μm, causing problems such as poor contact in some products with high thickness accuracy requirements. On the other hand, the selective electroplating process will require the protection of non-processing areas in the process, which will lengthen the process and make the production process cost very high.

[0004] Chinese invention patent CN109788662A discloses a method for making a gold finger circuit board. The invention first applies adhesive tape to the gold finger area before electroplating the outer layer circuit pattern to enhance the sealing ability of the dry film and prevent the solution from penetrating during copper and tin electroplating to plate copper and tin on the gold finger; before stripping the tin, not only is a gold finger area pattern made to cover the gold finger area, but also adhesive tape is applied to the gold finger area to enhance the sealing ability of the dry film and prevent the solution from penetrating and corroding the gold surface of the gold finger; before nickel-gold plating on the PAD, adhesive tape is applied to the gold finger area to seal the side wall groove of the gold finger to prevent the solution from penetrating and causing the gold finger to form a double layer of nickel-gold, thereby realizing the production of a circuit board with both gold fingers with three sides gold plating and nickel-gold plating PAD. However, the gold finger circuit board prepared by the invention has poor adhesion and flatness, and the quality is not enough to meet the manufacturing requirements. Summary of the invention

[0005] In view of the above problems, the present invention overturns and re-studies the gold finger plating processing technology for gold finger products, and develops a new gold finger product plating processing technology, which is characterized by a short process flow and low processing cost, and the thickness difference of the obtained selective electroplating layer can be controlled within 1.5μm, and the coating under this process has a higher hardness.

[0006] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0007] A processing method for a printed circuit board gold finger plating layer is as follows:

[0008] Step 1: First coating process

[0009] (1) Conductive layer deposition: a conductive layer is deposited on the circuit board holes and the outermost base copper surface through a chemical deposition process;

[0010] (2) Thickening by plating: The first plating layer is thickened by plating through a vertical continuous electroplating line or a gantry line;

[0011] Step 2: Non-plating processing

[0012] (1) Circuit processing: Through pattern transfer, development, copper removal, etching and film stripping are carried out in sequence on the DES line to process the required circuit pattern;

[0013] (2) Optical inspection: Confirm processing defects and quality by comparing the processed graphics with optical graphics;

[0014] (3) Solder mask processing: Coat the solder mask ink layer on the surface of the circuit board, and expose the required graphics through development through pattern transfer to facilitate subsequent plating processing;

[0015] (4) Text processing: Coating a text ink layer on the surface of the circuit board to facilitate subsequent processing and identification;

[0016] Step 3: Second and third coating processing

[0017] (1) Pretreatment: including but not limited to sandblasting, micro-etching, and roughening processes;

[0018] (2) Degreasing: Use acidic or alkaline degreasing agent to remove the residual oil on the surface of the circuit board;

[0019] (3) Water washing: including but not limited to hot water washing, pure water washing, and multi-stage water washing;

[0020] (4) Micro-etching: Use micro-etching liquid to treat the first coating to ensure that residual oxides and other impurities are removed to facilitate subsequent coating processing;

[0021] (5) Pickling: Use 4~6wt% sulfuric acid solution to soak and stir to remove oxides, keep the plate surface clean, and remove excess impurity ions;

[0022] (6) Pre-immersion: Use a 4-6% volume percent sulfuric acid aqueous solution to remove excess impurity ions and maintain the acidity of the activation tank;

[0023] (7) Activation: Depositing a medium layer on the first coating layer as a trigger medium for the processing reaction exchange of the second coating layer;

[0024] (8) Post-immersion: In the post-immersion process, first add water to 1 / 2~3 / 4 of the total volume, add the post-immersion agent at a concentration of 30~50ml / L, stir thoroughly until completely mixed, then add water to the total volume, put the printed circuit board in, and soak it at 20~30℃ for 2~5 minutes. The purpose is to remove oxides to keep the board surface clean and remove excess impurity ions;

[0025] (9) Second coating process: The coating is gradually deposited by displacement reaction. Side reaction products will be produced during the coating deposition process. The processing temperature is not less than 70°C.

[0026] (10) Third coating process: The coating first deposits a highly conductive metal layer through a replacement reaction at an operating temperature of not less than 80°C, and then further thickens the third coating layer by changing the method of power supply to a redox reaction at an operating temperature of not more than 45°C. The main metal layer obtained by this method is the same as the metal layer obtained by the replacement reaction, and is accompanied by the deposition of new metal elements to increase the wear resistance of the coating;

[0027] (11) Metal recovery: recovery of metals removed;

[0028] (12) Water washing: including but not limited to hot water washing, pure water washing, and multi-stage water washing to obtain the gold finger plating layer of the printed circuit board.

[0029] The main material of the conductive layer includes but is not limited to copper and silver.

[0030] The total thickness of the first coating after thickening by plating in step 1 is between 20 and 70 μm.

[0031] The medium layer includes but is not limited to one or more of rhodium, iridium, platinum and palladium.

[0032] The main material of the coating in the second coating process includes but is not limited to one or more of nickel and phosphorus, and the normalized weight percentage of phosphorus is 5% to 14%.

[0033] The side reaction product in the second coating process is in a gaseous state.

[0034] The main high-conductivity metal layer in the third plating process includes but is not limited to one or more of gold and platinum.

[0035] The new metal elements in the third plating process include but are not limited to one or more of cobalt, iron, and nickel.

[0036] The normalized weight percentage of new metal elements in the third coating process is less than 3%.

[0037] The preparation method of the post-infusion agent is as follows, in parts by weight:

[0038] First, 4 to 6 parts of glycyrrhizic acid and 3 to 5 parts of 4,4'-diaminodicyclohexylmethane are mixed evenly to form a pretreatment solution, and the solution is set aside for use; then, 80 to 120 parts of water are heated to 60 to 80°C, and then 40 to 60 parts of crocetin are added, and the mixture is stirred for 2 to 4 hours to form an acid solution; thereafter, 8 to 12 parts of pentaethylenehexamine are added to the acid solution, and the mixture is stirred for 50 to 70 minutes to ensure uniform mixing, thereby obtaining a reaction solution; next, 30 to 50 parts of humic acid are added to the reaction solution, and the mixture is stirred for 40 to 60 minutes to achieve complete mixing, thereby forming a post-treatment solution; finally, the prepared pre-treatment solution is added to the post-treatment solution, and the mixture is stirred at 50 to 70°C for 60 to 100 minutes to complete the final mixing, thereby obtaining the desired post-infusion agent.

[0039] The functions of the various substances described in the present invention are as follows:

[0040] The conductive layer (copper) is used as the first plating layer on the circuit board holes and the outermost base copper surface to provide the conductive properties required for circuit connection.

[0041] Vertical continuous plating lines or gantry lines are used to add additional plating to the first layer to ensure that the coating reaches the required thickness.

[0042] Pattern transfer, development, copper removal, etching and film stripping are carried out sequentially on the DES line for circuit processing to produce the required circuit patterns.

[0043] Optical inspection confirms the defects and quality of processed graphics through optical image comparison to ensure product quality.

[0044] The solder mask ink layer is coated on the surface of the circuit board, and the required graphics are exposed through development to facilitate subsequent plating processing.

[0045] The text ink layer is coated on the surface of the circuit board to facilitate subsequent processing and identification.

[0046] Sandblasting, micro-etching and roughening are pre-treatment steps used to improve the adhesion and surface roughness of the coating.

[0047] Acidic or alkaline degreasers remove residual oil stains on the surface of the circuit board to prepare for subsequent plating processing.

[0048] The first coating layer is treated with a micro-etching solution to remove residual oxides and other impurities.

[0049] Sulfuric acid solution (4~6wt%) is used for pickling to remove oxides, keep the board surface clean, and remove excess impurity ions.

[0050] Aqueous sulfuric acid solution (volume fraction 4~6%) is used for pre-immersion to remove excess impurity ions and maintain the acidity of the activation tank.

[0051] The intermediate layer (rhodium, iridium, platinum, palladium) is deposited on the first coating layer and acts as a trigger for the exchange of the processing reaction of the second coating layer.

[0052] Post-dip agents are used in the post-dip process to remove oxides, keep the board surface clean, and remove excess impurity ions.

[0053] Nickel and phosphorus elements constitute the main material of the second coating.

[0054] The highly conductive metal layer constitutes the main metal layer of the third plating layer.

[0055] New metallic elements (cobalt, iron, nickel) are deposited in the third coating process to increase the wear resistance of the coating.

[0056] Glycyrrhizic acid, 4,4'-diaminodicyclohexylmethane, crocetin, pentaethylenehexamine and humic acid are used to prepare post-immersion agents. The specific combination and preparation method of these substances play a key role in improving the adhesion and flatness of the coating.

[0057] These substances and process steps work together to form a new method for processing printed circuit board gold finger plating, which aims to improve plating quality, control plating thickness differences, and reduce manufacturing costs.

[0058] Compared with the prior art, it has the following beneficial effects:

[0059] 1) The present invention significantly improves the adhesion and flatness of the gold finger coating through finely controlled coating processing steps and a specific post-dip formulation, thereby improving the overall quality of the coating. This helps reduce coating defects such as burrs, bumps, gaps and adhesions, ensuring that the gold finger has excellent electrical conductivity, wear resistance, oxidation resistance and corrosion resistance.

[0060] 2) The process flow of the present invention can control the thickness difference of the selective electroplating layer within 1.5 μm, which is crucial for products with high thickness accuracy requirements and can avoid problems such as poor contact caused by uneven plating thickness.

[0061] 3) The process flow of the present invention is short and the processing cost is low. The optimized coating processing method reduces the need for protection of non-processed areas, simplifies the manufacturing process, and thus reduces production costs while maintaining the high performance standards of the gold finger coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 This is a diagram of the gold finger plating structure of a printed circuit board according to Example 1 of the present invention. DETAILED DESCRIPTION

[0063] Main sources of substances:

[0064] Acid degreaser, PH value: 4, product number: 8401, category: circuit board cleaning agent, brand: Lijieshi.

[0065] Micro-etching liquid, model: 855KBX, Shenzhen Kebaoxin Technology Co., Ltd., micro-etching liquid with hydrogen peroxide and sulfuric acid as main components.

[0066] The remaining raw materials in the examples and comparative examples of the present invention are all commercially available products.

[0067] The design idea of ​​the present invention is to provide a new type of printed circuit board gold finger plating processing method, which optimizes the plating processing technology, shortens the process flow, reduces the manufacturing cost, and at the same time realizes the control of the thickness difference of the selective electroplating layer within 1.5μm, so as to obtain a gold finger plating with higher precision and better performance. In particular, through a specific post-immersion agent formula and finely controlled plating processing steps, the adhesion and flatness of the plating are significantly improved, ensuring that the gold finger has excellent conductivity, wear resistance, oxidation resistance and corrosion resistance.

[0068] Example 1

[0069] A processing method for a printed circuit board gold finger plating layer is as follows:

[0070] Step 1: First coating process

[0071] (1) Conductive layer deposition: A conductive layer is deposited on the circuit board holes and the outermost base copper surface through a chemical deposition process. The main material of the conductive layer is copper;

[0072] (2) Thickening by plating: The first plating layer is thickened by plating through a vertical continuous electroplating line, using copper as the thickening material. The total thickness of the first plating layer after processing is 50 μm;

[0073] Step 2: Non-plating processing

[0074] (1) Circuit processing: Through pattern transfer, development, copper removal, etching and film stripping are carried out in sequence on the DES line to process the required circuit pattern;

[0075] (2) Optical inspection: Confirm processing defects and quality by comparing the processed graphics with optical graphics;

[0076] (3) Solder mask processing: Coat the solder mask ink layer on the surface of the circuit board, and expose the required graphics through development through pattern transfer to facilitate subsequent plating processing;

[0077] (4) Text processing: Coating a text ink layer on the surface of the circuit board to facilitate subsequent processing and identification;

[0078] Step 3: Second and third coating processing

[0079] (1) Pre-treatment: sand blasting is used, wherein the sand blasting process uses compressed air as a power source to form a high-speed spray beam to spray copper ore sand at high speed onto the surface of the workpiece to be treated, so that the workpiece surface has a certain degree of cleanliness and different degrees of roughness;

[0080] (2) Degreasing: Use an acidic degreasing agent to remove the residual oil on the surface of the circuit board;

[0081] (3) Water washing: Using hot water for washing helps remove grease and certain types of dirt;

[0082] (4) Micro-etching: Use micro-etching liquid to treat the first coating to ensure that residual oxides and other impurities are removed to facilitate subsequent coating processing;

[0083] (5) Pickling: Use 5wt% sulfuric acid solution to soak and stir to remove oxides, keep the plate surface clean, and remove excess impurity ions;

[0084] (6) Pre-immersion: Use 5% sulfuric acid aqueous solution to remove excess impurity ions and maintain the acidity of the activation tank;

[0085] (7) Activation: Depositing a medium layer on the first coating layer as a trigger medium for the second coating layer processing reaction exchange, the medium layer is rhodium;

[0086] (8) Post-immersion: In the post-immersion process, first add water to 2 / 3 of the total volume, add the post-immersion agent at a concentration of 40 ml / L, stir thoroughly until completely mixed, then add water to the total volume, put the printed circuit board in, and soak it at 25°C for 3 minutes to remove oxides, keep the board surface clean, and remove excess impurity ions;

[0087] (9) Second coating process: The coating is gradually deposited by substitution reaction. The main materials of the coating include nickel and phosphorus. The thickness of the nickel layer is 2.54 μm, and the normalized weight percentage of phosphorus is 10%. Side reaction products are generated during the deposition of the coating. The side reaction products are in gaseous state. The processing temperature is 80°C.

[0088] (10) Third coating process: The coating first deposits a highly conductive metal layer by substitution reaction, the main highly conductive metal layer includes gold, the thickness of the gold layer is 0.1 μm, and the operating temperature is 90°C. Then, the third coating is further thickened by changing the way of electricity to oxidation-reduction reaction, and the operating temperature is 40°C. The main metal layer obtained by this method is the same as the metal layer obtained by the substitution reaction, and is accompanied by the deposition of new metal elements, the new metal elements including cobalt, to increase the wear resistance of the coating, and the normalized weight percentage of the new metal elements is 2.1%;

[0089] (11) Metal recovery: recovery of metals removed;

[0090] (12) Water washing: Use hot water to wash and obtain the gold finger coating of the printed circuit board.

[0091] The preparation method of the post-infusion agent is as follows:

[0092] First, 5g of glycyrrhizic acid and 4g of 4,4'-diaminodicyclohexylmethane were mixed evenly to form a pretreatment solution, and the solution was set aside for use; then, 100mL of water was heated to 70°C, and then 50g of crocetin was added and stirred for 3 hours to form an acid solution; thereafter, 10g of pentaethylenehexamine was added to the acid solution and stirred for 60 minutes to ensure uniform mixing to obtain a reaction solution; next, 40g of humic acid was added to the reaction solution and stirred for 50 minutes to achieve complete mixing to form a post-treatment solution; finally, the prepared pretreatment solution was added to the post-treatment solution and stirred at 60°C for 80 minutes to complete the final mixing to obtain the desired post-infusion agent.

[0093] Example 2

[0094] A processing method for a gold finger plating layer of a printed circuit board is basically the same as that of Example 1, the only difference being that the preparation method of the post-dip agent is different.

[0095] The preparation method of the post-infusion agent is as follows:

[0096] First, 5g of citric acid and 4g of 4,4'-diaminodicyclohexylmethane were mixed evenly to form a pretreatment solution, and the solution was set aside for use; then, 100mL of water was heated to 70°C, and then 50g of crocetin was added and stirred for 3 hours to form an acid solution; thereafter, 10g of pentaethylenehexamine was added to the acid solution and stirred for 60 minutes to ensure uniform mixing to obtain a reaction solution; next, 40g of humic acid was added to the reaction solution and stirred for 50 minutes to achieve complete mixing to form a post-treatment solution; finally, the prepared pretreatment solution was added to the post-treatment solution and stirred at 60°C for 80 minutes to complete the final mixing to obtain the desired post-infusion agent.

[0097] Example 3

[0098] A processing method for a gold finger plating layer of a printed circuit board is basically the same as that of Example 1, the only difference being that the preparation method of the post-dip agent is different.

[0099] The preparation method of the post-infusion agent is as follows:

[0100] First, 5g of sebacic acid and 4g of 4,4'-diaminodicyclohexylmethane were mixed evenly to form a pretreatment solution, and the solution was set aside for use; then, 100mL of water was heated to 70°C, and then 50g of crocetin was added and stirred for 3 hours to form an acid solution; thereafter, 10g of pentaethylenehexamine was added to the acid solution and stirred for 60 minutes to ensure uniform mixing to obtain a reaction solution; next, 40g of humic acid was added to the reaction solution and stirred for 50 minutes to achieve complete mixing to form a post-treatment solution; finally, the prepared pretreatment solution was added to the post-treatment solution and stirred at 60°C for 80 minutes to complete the final mixing to obtain the desired post-infusion agent.

[0101] Example 4

[0102] A processing method for a gold finger plating layer of a printed circuit board is basically the same as that of Example 1, the only difference being that the preparation method of the post-dip agent is different.

[0103] The preparation method of the post-infusion agent is as follows:

[0104] First, 5g of glycyrrhizic acid and 4g of 1,4-cyclohexanediamine were mixed evenly to form a pretreatment solution, and the solution was set aside for use; then, 100mL of water was heated to 70°C, and then 50g of crocetin was added and stirred for 3 hours to form an acid solution; thereafter, 10g of pentaethylenehexamine was added to the acid solution and stirred for 60 minutes to ensure uniform mixing to obtain a reaction solution; next, 40g of humic acid was added to the reaction solution and stirred for 50 minutes to achieve complete mixing to form a post-treatment solution; finally, the prepared pretreatment solution was added to the post-treatment solution and stirred at 60°C for 80 minutes to complete the final mixing to obtain the desired post-infusion agent.

[0105] Example 5

[0106] A processing method for a gold finger plating layer of a printed circuit board is basically the same as that of Example 1, the only difference being that the preparation method of the post-dip agent is different.

[0107] The preparation method of the post-infusion agent is as follows:

[0108] First, 5g of glycyrrhizic acid and 4g of 4,4'-diaminodicyclohexylmethane were mixed evenly to form a pretreatment solution, and the solution was set aside for use; then, 100mL of water was heated to 70°C, and then 50g of 2,5-dimethyl-2,4-hexadienedicarboxylic acid was added, and the mixture was stirred for 3 hours to form an acid solution; thereafter, 10g of pentaethylenehexamine was added to the acid solution and stirred for 60 minutes to ensure uniform mixing to obtain a reaction solution; next, 40g of humic acid was added to the reaction solution and stirred for 50 minutes to achieve complete mixing to form a post-treatment solution; finally, the prepared pre-treatment solution was added to the post-treatment solution and stirred at 60°C for 80 minutes to complete the final mixing to obtain the desired post-infusion agent.

[0109] Example 6

[0110] A processing method for a gold finger plating layer of a printed circuit board is basically the same as that of Example 1, the only difference being that the preparation method of the post-dip agent is different.

[0111] The preparation method of the post-infusion agent is as follows:

[0112] First, 5g of glycyrrhizic acid and 4g of 4,4'-diaminodicyclohexylmethane were mixed evenly to form a pretreatment solution, and the solution was set aside for use; then, 100mL of water was heated to 70°C, and then 50g of sorbic acid was added and stirred for 3 hours to form an acid solution; thereafter, 10g of pentaethylenehexamine was added to the acid solution and stirred for 60 minutes to ensure uniform mixing to obtain a reaction solution; next, 40g of humic acid was added to the reaction solution and stirred for 50 minutes to achieve complete mixing to form a post-treatment solution; finally, the prepared pretreatment solution was added to the post-treatment solution and stirred at 60°C for 80 minutes to complete the final mixing to obtain the desired post-infusion agent.

[0113] Comparative Example 1

[0114] A processing method for a gold finger plating layer of a printed circuit board is basically the same as that of Example 1, the only difference being that the preparation method of the post-dip agent is different.

[0115] The preparation method of the post-infusion agent is as follows:

[0116] First, 5g of decanoic acid and 4g of 4,4'-diaminodicyclohexylmethane were mixed evenly to form a pretreatment solution, and the solution was set aside for use; then, 100mL of water was heated to 70°C, and then 50g of crocetin was added and stirred for 3 hours to form an acid solution; thereafter, 10g of pentaethylenehexamine was added to the acid solution and stirred for 60 minutes to ensure uniform mixing to obtain a reaction solution; next, 40g of humic acid was added to the reaction solution and stirred for 50 minutes to achieve complete mixing to form a post-treatment solution; finally, the prepared pretreatment solution was added to the post-treatment solution and stirred at 60°C for 80 minutes to complete the final mixing to obtain the desired post-infusion agent.

[0117] Comparative Example 2

[0118] A processing method for a gold finger plating layer of a printed circuit board is basically the same as that of Example 1, the only difference being that the preparation method of the post-dip agent is different.

[0119] The preparation method of the post-infusion agent is as follows:

[0120] First, 5g of glycyrrhizic acid and 4g of cyclohexylamine were mixed evenly to form a pretreatment solution, and the solution was set aside for use; then, 100mL of water was heated to 70°C, and then 50g of crocetin was added, and the mixture was stirred for 3 hours to form an acid solution; thereafter, 10g of pentaethylenehexamine was added to the acid solution and stirred for 60 minutes to ensure uniform mixing to obtain a reaction solution; next, 40g of humic acid was added to the reaction solution and stirred for 50 minutes to achieve complete mixing to form a post-treatment solution; finally, the prepared pretreatment solution was added to the post-treatment solution and stirred at 60°C for 80 minutes to complete the final mixing to obtain the desired post-infusion agent.

[0121] Comparative Example 3

[0122] A processing method for a gold finger plating layer of a printed circuit board is basically the same as that of Example 1, the only difference being that the preparation method of the post-dip agent is different.

[0123] The preparation method of the post-infusion agent is as follows:

[0124] First, 5g of glycyrrhizic acid and 4g of 4,4'-diaminodicyclohexylmethane were mixed evenly to form a pretreatment solution, and the solution was set aside for use; then, 100mL of water was heated to 70°C, and then 50g of benzoic acid was added and stirred for 3 hours to form an acid solution; thereafter, 10g of pentaethylenehexamine was added to the acid solution and stirred for 60 minutes to ensure uniform mixing to obtain a reaction solution; next, 40g of humic acid was added to the reaction solution and stirred for 50 minutes to achieve complete mixing to form a post-treatment solution; finally, the prepared pretreatment solution was added to the post-treatment solution and stirred at 60°C for 80 minutes to complete the final mixing to obtain the desired post-infusion agent.

[0125] Comparative Example 4

[0126] A processing method for a gold finger plating layer of a printed circuit board is substantially the same as that of Example 1, the only difference being that the post-immersion agent is replaced with an equal amount of a 5% by volume sulfuric acid aqueous solution.

[0127] Test Example 1

[0128] Adhesion assay

[0129] Use a grid test device to make 100 square patterns with a size of 1mm×1mm on the surface of the gold finger coating prepared in the embodiments of the present invention and the comparative examples. Then, stick the model 600 transparent tape produced by 3M Company of the United States on these squares evenly. Then, peel off the tape at the fastest vertical speed. In this process, it is necessary to check whether there is any coating shedding on the edges of the scratches and the edges of the circuit patterns. According to the amount of debris that falls off, evaluate the adhesion level of the coating: if the shedding rate is 0-5%, it is rated as 5B; 5-10% is 4B; 10-20% is 3B; 20-30% is 2B; 30-50% is B; if it exceeds 50%, it is rated as 0B. The specific test data are shown in Table 1.

[0130] Table 1

[0131] Experimental protocol Adhesion grade Example 1 5B Example 2 4B Example 3 3B Example 4 4B Example 5 4B Example 6 4B Comparative Example 1 2B Comparative Example 2 3B Comparative Example 3 3B Comparative Example 4 1B

[0132] Test Example 2

[0133] Flatness test

[0134] On the gold finger coating of the embodiment of the present invention and the comparative example, 100 square areas with a side length of 5 mm were marked out using a grid tool. Subsequently, the burrs, protruding particles, gaps and adhesions in each area were counted. According to the counting results, the quality of the coating was graded: if the number of defects is less than 1, it is rated as level 1; if the number of defects is between 2 and 5, it is rated as level 2; if the number of defects is between 6 and 10, it is rated as level 3; if the number of defects is between 11 and 15, it is rated as level 4; if the number of defects is more than 16, it is rated as level 5. The test results are shown in Table 2.

[0135] Table 2

[0136] Experimental protocol Flatness grade Example 1 1 Example 2 2 Example 3 3 Example 4 2 Example 5 2 Example 6 2 Comparative Example 1 3 Comparative Example 2 3 Comparative Example 3 3 Comparative Example 4 5

[0137] It can be seen from the data of test examples 1 and 2 that the gold finger coating prepared in Example 1 has the best adhesion and flatness.

[0138] Because of its complex molecular structure and multiple active groups, glycyrrhizic acid can react more effectively with other ingredients when forming a post-immersion agent to generate a compound with a larger molecular structure. This macromolecular structure helps to form a uniform and dense protective film on the surface of the gold finger coating of the printed circuit board, which can effectively reduce the contact between the coating and the air, thereby reducing the generation of oxides. At the same time, this uniform film structure also helps to form a protective barrier on the surface of the coating, reduce the attachment of impurity ions, and improve the cleanliness of the coating. Thereby enhancing the adhesion between the coating and the substrate and improving the adhesion of the coating. At the same time, this uniform film structure also helps to reduce defects on the surface of the coating, such as burrs, bumps, gaps and adhesion, and further improves the flatness of the coating. In contrast, other organic acids such as citric acid, sebacic acid and capric acid may not be able to form the same uniform and dense film due to their relatively simple molecular structures, so they are not as good as glycyrrhizic acid in terms of adhesion and flatness. This difference at the molecular level directly affects the macroscopic properties of the coating, so that Example 1 using glycyrrhizic acid performs best in the adhesion and flatness test.

[0139] The molecular structure of 4,4'-diaminodicyclohexylmethane contains two amino groups and two cyclohexyl groups, which enables it to form a complex macromolecular network. In the post-immersion agent, this structure of 4,4'-diaminodicyclohexylmethane helps to form a uniform and dense film on the surface of the gold finger plating of the printed circuit board. This film can reduce the contact between the plating and the air, thereby reducing the formation of oxides, and at the same time provide a smooth surface on the surface of the plating, which helps to improve the flatness of the plating. In addition, the cyclohexyl structure of 4,4'-diaminodicyclohexylmethane provides better steric hindrance, which helps to reduce defects on the surface of the plating, such as burrs and protruding particles, thereby improving the overall quality of the plating. In contrast, the molecular structures of 1,4-cyclohexanediamine and cyclohexylamine are relatively simple, they contain fewer functional groups, and do not have as many cyclohexyl structures as 4,4'-diaminodicyclohexylmethane, so they are not as good as 4,4'-diaminodicyclohexylmethane in the ability to form a uniform and dense film. This may result in a less than smooth coating surface, increasing the risk of oxide formation and surface defects, which in turn affects the adhesion and flatness of the coating.

[0140] The molecular structure of crocetin contains two carboxyl groups and multiple carbon-carbon double bonds, which gives it strong reactivity and complex intermolecular interaction capabilities. In the post-immersion agent, the dicarboxyl groups of crocetin can form macromolecular compounds with pentaethylenehexamine, and the carbon-carbon double bonds can also participate in addition reactions to enhance the binding force with the metal surface. This structure helps to form a uniform and dense protective film on the surface of the gold finger plating of the printed circuit board, effectively reducing the contact between the plating and the air, reducing the formation of oxides, and providing a smooth surface on the surface of the plating, which helps to improve the overall flatness of the plating. In contrast, other organic acids such as 2,5-dimethyl-2,4-hexadienedicarboxylic acid, sorbic acid and benzoic acid have simpler molecular structures, contain fewer functional groups, and lack multiple carbon-carbon double bonds like crocetin, so they are not as good as crocetin in the ability to form a uniform and dense film. This may result in the surface of the coating being not smooth enough, increasing the risk of oxide formation and surface defects, thereby affecting the adhesion and flatness of the coating.

Claims

1. A method for processing a gold finger coating of a printed circuit board, characterized in that: Here’s how: Step 1: First coating process (1) Conductive layer deposition: a conductive layer is deposited on the circuit board holes and the outermost base copper surface through a chemical deposition process; (2) Thickening by plating: The first plating layer is thickened by plating through a vertical continuous electroplating line or a gantry line; Step 2: Non-plating processing (1) Circuit processing: Through pattern transfer, development, copper removal, etching and film stripping are carried out in sequence on the DES line to process the required circuit pattern; (2) Optical inspection: Confirm processing defects and quality by comparing the processed graphics with optical graphics; (3) Solder mask processing: Coat the solder mask ink layer on the surface of the circuit board, and expose the required graphics through development through pattern transfer to facilitate subsequent plating processing; (4) Text processing: Coating a text ink layer on the surface of the circuit board to facilitate subsequent processing and identification; Step 3: Second and third coating processing (1) Pretreatment: including but not limited to sandblasting, micro-etching, and roughening processes; (2) Degreasing: Use acidic or alkaline degreasing agent to remove the residual oil on the surface of the circuit board; (3) Water washing: including but not limited to hot water washing, pure water washing, and multi-stage water washing; (4) Micro-etching: Use micro-etching liquid to treat the first coating to ensure that residual oxides and other impurities are removed to facilitate subsequent coating processing; (5) Pickling: Use 4~6wt% sulfuric acid solution to soak and stir to remove oxides, keep the plate surface clean, and remove excess impurity ions; (6) Pre-immersion: Use a 4-6% volume percent sulfuric acid aqueous solution to remove excess impurity ions and maintain the acidity of the activation tank; (7) Activation: Depositing a medium layer on the first coating layer as a trigger medium for the processing reaction exchange of the second coating layer; (8) Post-immersion: In the post-immersion process, first add water to 1 / 2~3 / 4 of the total volume, add the post-immersion agent at a concentration of 30~50ml / L, stir thoroughly until completely mixed, then add water to the total volume, put the printed circuit board in, and soak it at 20~30℃ for 2~5 minutes. The purpose is to remove oxides to keep the board surface clean and remove excess impurity ions; (9) Second coating process: The coating is gradually deposited by displacement reaction. Side reaction products will be produced during the coating deposition process. The processing temperature is not less than 70°C. (10) Third coating process: The coating first deposits a highly conductive metal layer through a replacement reaction at an operating temperature of not less than 80°C, and then further thickens the third coating layer by changing the method of power supply to a redox reaction at an operating temperature of not more than 45°C. The main metal layer obtained by this method is the same as the metal layer obtained by the replacement reaction, and is accompanied by the deposition of new metal elements to increase the wear resistance of the coating; (11) Metal recovery: recovery of metals removed; (12) Water washing: including but not limited to hot water washing, pure water washing, and multi-stage water washing to obtain the gold finger plating layer of the printed circuit board.

2. The method for processing the gold finger plating of a printed circuit board according to claim 1, characterized in that: The main material of the conductive layer includes but is not limited to copper and silver.

3. The method for processing the gold finger plating of a printed circuit board according to claim 1, characterized in that: The total thickness of the first coating after thickening by plating in step 1 is between 20 and 70 μm.

4. The method for processing the gold finger plating of a printed circuit board according to claim 1, characterized in that: The medium layer includes but is not limited to one or more of rhodium, iridium, platinum and palladium.

5. The method for processing the gold finger plating of a printed circuit board according to claim 1, characterized in that: The main material of the coating in the second coating process includes but is not limited to one or more of nickel and phosphorus, and the normalized weight percentage of phosphorus is 5% to 14%.

6. The method for processing the gold finger plating of a printed circuit board according to claim 1, characterized in that: The side reaction product in the second coating process is in a gaseous state.

7. The method for processing the gold finger plating of a printed circuit board according to claim 1, characterized in that: The main high-conductivity metal layer in the third plating process includes but is not limited to one or more of gold and platinum.

8. The method for processing the gold finger plating of a printed circuit board according to claim 1, characterized in that: The new metal elements in the third plating process include but are not limited to one or more of cobalt, iron, and nickel.

9. The method for processing the gold finger plating of a printed circuit board according to claim 1, characterized in that: The normalized weight percentage of new metal elements in the third coating process is less than 3%.

10. The method for processing the gold finger plating of a printed circuit board according to claim 1, characterized in that: The preparation method of the post-infusion agent is as follows, in parts by weight: 4-6 parts of glycyrrhizic acid and 3-5 parts of 4,4'-diaminodicyclohexylmethane are mixed evenly to form a pretreatment solution, and the solution is set aside for use; then, 80-120 parts of water are heated to 60-80°C, and then 40-60 parts of crocetin are added, and the mixture is stirred for 2-4 hours to form an acid solution; thereafter, 8-12 parts of pentaethylenehexamine are added to the acid solution, and the mixture is stirred for 50-70 minutes to ensure uniform mixing, thereby obtaining a reaction solution; next, 30-50 parts of humic acid are added to the reaction solution, and the mixture is stirred for 40-60 minutes to achieve complete mixing, thereby forming a post-treatment solution; finally, the prepared pre-treatment solution is added to the post-treatment solution, and the mixture is stirred at 50-70°C for 60-100 minutes to complete the final mixing, thereby obtaining the desired post-infusion agent.

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