A method for processing the gold finger plating of a printed circuit board

Abstract

The present invention discloses a method for processing the gold finger plating layer of a printed circuit board, belonging to the technical field of printed circuit board preparation. The method includes three main steps: the first plating layer processing, non-plating layer processing procedures, and the second and third plating layer processing. In the first plating layer, a copper layer is deposited on the circuit board holes and the base copper surface through a chemical deposition process, and then thickened to 20 - 70 μm. The non-plating layer processing includes circuit processing, optical detection, solder mask and text processing. The second and third plating layer processing involves pretreatment, degreasing, micro-etching, pickling, pre-impregnation, activation, post-impregnation, deposition of the second and third plating layers, 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 to increase wear resistance. Compared with the prior art, the plating layer processing method of the present invention has the advantages of short process flow, low cost, and high uniformity of the plating layer thickness, and the hardness and wear resistance of the plating layer are significantly improved.

Description

Technical Field

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

[0002] The "gold fingers" of a PCB circuit board refer to the metal connectors covering the edge of the board. These gold fingers are usually gold-plated to improve their electrical conductivity and corrosion resistance. The gold fingers of a PCB circuit board are generally used as the interfaces of connectors or slots, enabling convenient interconnection with other devices or electronic components. On computer memory and graphics cards, the 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 electrical conductivity, wear resistance, oxidation resistance, and corrosion resistance. According to its performance characteristics, the gold fingers are divided into conventional gold fingers, long and short gold fingers, and segmented gold fingers.

[0003] Regardless of the type of gold fingers, due to the functional characteristics of the gold fingers, the gold plating thickness generally needs to reach more than 0.5μm, or even higher. Therefore, the traditional gold finger processing process is to process by electroplating. In order to control costs and process requirements, selective electroplating process is generally used for gold finger electroplating, that is, only a part of the area needs to be electroplated during the electroplating process. In this way, the problem of uneven distribution of power lines during electroplating is caused, which in turn leads to too large a height difference in the metal plating layer of the gold fingers after electroplating, and the plating thickness difference can reach 4 - 10μm, resulting in problems such as poor contact in some products with high thickness accuracy requirements. On the other hand, the selective electroplating processing process requires the protection of non-processing areas in the process, which lengthens the process and makes the manufacturing process cost very high.

[0004] Chinese Patent CN109788662A discloses a method for manufacturing a gold finger circuit board. The invention enhances the slot sealing ability of the dry film by pasting a tape on the gold finger area before electroplating the outer layer circuit pattern, preventing copper and tin from being plated on the gold fingers due to the infiltration of the electroplating solution during electroplating copper and electroplating tin; before tin stripping, not only is the gold finger area pattern made to cover the gold finger area, but also a tape is pasted on the gold finger area to enhance the slot sealing ability of the dry film, preventing the tin stripping solution from infiltrating and etching the gold surface of the gold fingers; before electroless nickel immersion gold on the PAD, a tape is pasted on the gold finger area to seal the side wall slots of the gold fingers, preventing the electroless nickel immersion gold solution from infiltrating and causing the gold fingers to form a double-layer nickel gold, thus realizing the manufacture of a circuit board with both three-sided gold-plated gold fingers and electroless nickel immersion gold PADs. However, the adhesion and flatness of the gold finger circuit board prepared by this invention are poor, and the quality is insufficient to meet the manufacturing requirements. Summary of the Invention

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

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

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

[0008] Step 1: First plating layer processing

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

[0010] (2) Additional plating and thickening: Conduct additional plating and thickening on the first plating layer through a vertical continuous plating line or a gantry line;

[0011] Step 2: Non-plating processing procedures

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

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

[0014] (3) Solder mask processing: Coat a solder mask ink layer on the surface of the circuit board, and expose the subsequent required pattern through graphic transfer by developing, facilitating subsequent plating processing;

[0015] (4) Letter processing: Coat a letter ink layer on the surface of the circuit board for subsequent processing and identification;

[0016] Step 3: Second and third plating layer processing

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

[0018] (2) Degreasing: Use an 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: Treat the first plating layer with a micro-etching solution to ensure the removal of residual oxides and other impurities, facilitating subsequent plating processing;

[0021] (5)Pickling: Immerse and agitate in a 4 - 6 wt% sulfuric acid solution to remove oxides, keep the board surface clean, and remove excess impurity ions;

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

[0023] (7)Activation: Deposit a medium layer on the first plating layer as a trigger medium for the processing reaction exchange of the second plating 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 - 50 ml / L, stir well until completely mixed, then add water to the total amount, put the printed circuit board in, and soak at 20 - 30 °C for 2 - 5 minutes. The purpose is to remove oxides, keep the board surface clean, and remove excess impurity ions;

[0025] (9)Second plating layer processing: The plating layer is gradually deposited by displacement reaction. By - products will be generated during the plating layer deposition process, and the processing temperature is not lower than 70 °C;

[0026] (10)Third plating layer processing: First, deposit a high - conductivity metal layer on the plating layer by displacement reaction, with the operating temperature not lower than 80 °C. Then, change to redox reaction by electrifying to further thicken the third plating layer, with the operating temperature not higher than 45 °C. The main metal layer obtained by this method is the same as the metal layer obtained by displacement reaction, and new metal elements are deposited, so as to increase the wear - resistance of the plating layer;

[0027] (11)Metal recovery: Recover the metal carried out;

[0028] (12)Water washing: Includes but is 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 materials of the conductive layer include but are not limited to copper and silver materials.

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

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

[0032] In the second plating layer processing, the main materials of the plating layer include but are not limited to one or several of nickel and phosphorus elements, and the normalized weight percentage of phosphorus element is 5% - 14%.

[0033] In the second plating layer processing, the by - products are in a gaseous state.

[0034] In the processing of the third coating layer, the main highly conductive metal layer includes but is not limited to one or more of gold and platinum.

[0035] In the processing of the third coating layer, the new metal elements include but are not limited to one or more of cobalt, iron, and nickel.

[0036] The normalized weight percentage of the new metal elements in the processing of the third coating layer is < 3%.

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

[0038] First, mix 4 - 6 parts of glycyrrhizic acid and 3 - 5 parts of 4,4'-diaminodicyclohexylmethane evenly to form a pretreatment solution, and set it aside; then, heat 80 - 120 parts of water to 60 - 80 °C, and then add 40 - 60 parts of crocetin, and continuously stir for 2 - 4 hours to form an acid solution; after that, add 8 - 12 parts of pentaethylenehexamine to the acid solution and stir for 50 - 70 minutes to ensure uniform mixing to obtain a reaction solution; next, add 30 - 50 parts of humic acid to the reaction solution and stir for 40 - 60 minutes to achieve complete mixing to form a post-treatment solution; finally, add the prepared pretreatment solution to the post-treatment solution and stir at 50 - 70 °C for 60 - 100 minutes to complete the final mixing to obtain the required post-soaking agent.

[0039] The functions of each substance in the present invention are as follows:

[0040] The conductive layer (copper), as the first coating layer on the holes of the circuit board and the outermost base copper surface, provides the conductive performance required for circuit connection.

[0041] The vertical continuous electroplating line or gantry line is used to electroplate and thicken the first coating layer to ensure that the coating layer reaches the required thickness.

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

[0043] Optical detection confirms the defects and quality of the processed patterns through optical graphic comparison to ensure product quality.

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

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

[0046] The pre-treatment processes such as sandblasting, micro-etching, and roughening are used to improve the adhesion and surface roughness of the coating layer.

[0047] Acidic or alkaline degreasing agents are used to remove the residual oil stains on the surface of the circuit board, preparing for the subsequent plating process.

[0048] The micro-etching solution is used to treat the first plating layer to remove residual oxides and other impurities.

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

[0050] Aqueous sulfuric acid solution (volume fraction of 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 plating layer as a trigger medium for the reaction exchange in the second plating layer processing.

[0052] The post - immersion agent is used in the post - immersion process to remove oxides, keep the board surface clean, and remove excess impurity ions.

[0053] Nickel and phosphorus elements constitute the main materials of the second plating layer.

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

[0055] New metal elements (cobalt, iron, nickel) are deposited during the third plating layer processing to increase the wear - resistance of the plating layer.

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

[0057] These substances and process steps work together to form a new method for processing the gold finger plating layer of printed circuit boards, aiming to improve the plating layer quality, control the plating layer thickness difference, and reduce the manufacturing cost.

[0058] Compared with the existing technology, it has the following beneficial effects:

[0059] 1) Through the finely tuned plating layer processing steps and the specific post - immersion agent formula of the present invention, the adhesion and flatness of the gold finger plating layer are significantly improved, thus enhancing the overall quality of the plating layer. This helps to reduce plating layer defects such as burrs, nodules, notches, 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 plating layer within 1.5 μm, which is crucial for products with high thickness precision requirements and can avoid problems such as poor contact caused by uneven plating layer 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 the processing defects and quality by comparing the processed patterns through optical pattern comparison;

[0076] (3)Solder mask processing: Coating a solder mask ink layer on the surface of the circuit board, and exposing the subsequent required patterns through the way of pattern transfer by developing, which is convenient for subsequent plating processing;

[0077] (4)Text processing: Coating a text ink layer on the surface of the circuit board, which is convenient for subsequent processing and identification;

[0078] Step 3, Second and third plating processing

[0079] (1)Pretreatment: Adopting sandblasting process, the sandblasting process uses compressed air as power to form a high-speed jet beam to spray copper ore sand onto the surface of the workpiece to be processed at high speed, so that the surface of the workpiece obtains a certain cleanliness and different roughness;

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

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

[0082] (4)Micro-etching: Treating the first plating layer with a micro-etching solution to ensure the removal of residual oxides and other sundries, which is convenient for subsequent plating processing;

[0083] (5)Pickling: Soaking and stirring with a 5wt% sulfuric acid solution to remove oxides, keep the board surface clean, and remove excess impurity ions;

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

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

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

[0087] (9)Second plating layer processing: The plating layer is gradually deposited through the way of displacement reaction. The main materials of the plating layer include nickel and phosphorus elements. The thickness of the nickel layer is 2.54μm, and the normalized weight percentage of phosphorus element is 10%. By-products will be generated during the plating layer deposition process, and the by-products are in a gaseous state. The processing temperature is 80°C;

[0088] (10) Third plating layer processing: First, a high-conductive metal layer is deposited on the plating layer through a displacement reaction. The main high-conductive metal layer includes gold, with a gold layer thickness of 0.1 μm and an operating temperature of 90°C. Then, the third plating layer is further thickened through an oxidation-reduction reaction by applying an electric current, with an operating temperature of 40°C. The main metal layer obtained by this method is the same as the metal layer obtained by the displacement reaction, and new metal elements are deposited, including cobalt, to increase the wear resistance of the plating layer. The normalized weight percentage of the new metal element is 2.1%;

[0089] (11) Metal recovery: Recover the metal carried out;

[0090] (12) Water washing: Wash with hot water to obtain the gold finger plating layer of the printed circuit board.

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

[0092] First, mix 5 g of glycyrrhizic acid and 4 g of 4,4'-diaminodicyclohexylmethane evenly to form a pretreatment solution and set it aside. Then, heat 100 mL of water to 70°C, add 50 g of crocetin, and continuously stir for 3 hours to form an acid solution. After that, add 10 g of pentaethylenehexamine to the acid solution and stir for 60 minutes to ensure uniform mixing, obtaining a reaction solution. Next, add 40 g of humic acid to the reaction solution and stir for 50 minutes to achieve complete mixing, forming a post-treatment solution. Finally, add the prepared pretreatment solution to the post-treatment solution and stir at 60°C for 80 minutes to complete the final mixing, obtaining the required post-soaking agent.

[0093] Example 2

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

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

[0096] First, mix 5 g of citric acid and 4 g of 4,4'-diaminodicyclohexylmethane evenly to form a pretreatment solution and set it aside. Then, heat 100 mL of water to 70°C, add 50 g of crocetin, and continuously stir for 3 hours to form an acid solution. After that, add 10 g of pentaethylenehexamine to the acid solution and stir for 60 minutes to ensure uniform mixing, obtaining a reaction solution. Next, add 40 g of humic acid to the reaction solution and stir for 50 minutes to achieve complete mixing, forming a post-treatment solution. Finally, add the prepared pretreatment solution to the post-treatment solution and stir at 60°C for 80 minutes to complete the final mixing, obtaining the required post-soaking agent.

[0097] Example 3

[0098] A processing method for the gold finger plating of a printed circuit board is basically the same as that of Example 1, and the only difference lies in the preparation method of the post-dipping agent.

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

[0100] First, mix 5 g of sebacic acid and 4 g of 4,4'-diaminodicyclohexylmethane evenly to form a pretreatment solution and set it aside; then, heat 100 mL of water to 70 °C, add 50 g of crocetin, and continuously stir for 3 hours to form an acid solution; after that, add 10 g of pentaethylenehexamine to the acid solution and stir for 60 minutes to ensure uniform mixing, obtaining a reaction solution; next, add 40 g of humic acid to the reaction solution and stir for 50 minutes to achieve complete mixing, forming a post-treatment solution; finally, add the prepared pretreatment solution to the post-treatment solution and stir at 60 °C for 80 minutes to complete the final mixing, obtaining the required post-dipping agent.

[0101] Example 4

[0102] A processing method for the gold finger plating of a printed circuit board is basically the same as that of Example 1, and the only difference lies in the preparation method of the post-dipping agent.

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

[0104] First, mix 5 g of glycyrrhizic acid and 4 g of 1,4-cyclohexanediamine evenly to form a pretreatment solution and set it aside; then, heat 100 mL of water to 70 °C, add 50 g of crocetin, and continuously stir for 3 hours to form an acid solution; after that, add 10 g of pentaethylenehexamine to the acid solution and stir for 60 minutes to ensure uniform mixing, obtaining a reaction solution; next, add 40 g of humic acid to the reaction solution and stir for 50 minutes to achieve complete mixing, forming a post-treatment solution; finally, add the prepared pretreatment solution to the post-treatment solution and stir at 60 °C for 80 minutes to complete the final mixing, obtaining the required post-dipping agent.

[0105] Example 5

[0106] A processing method for the gold finger plating of a printed circuit board is basically the same as that of Example 1, and the only difference lies in the preparation method of the post-dipping agent.

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

[0108] First, mix 5 g of glycyrrhizic acid and 4 g of 4,4'-diaminodicyclohexylmethane evenly to form a pretreatment solution, and set it aside for later use; then, heat 100 mL of water to 70 °C, and then add 50 g of 2,5-dimethyl-2,4-hexadiene dicarboxylic acid, and continuously stir for 3 hours to form an acid solution; after that, add 10 g of pentaethylenehexamine to the acid solution and stir for 60 minutes to ensure uniform mixing, obtaining a reaction solution; next, add 40 g of humic acid to the reaction solution and stir for 50 minutes to achieve complete mixing, forming a post-treatment solution; finally, add the prepared pretreatment solution to the post-treatment solution and stir at 60 °C for 80 minutes to complete the final mixing, obtaining the required post-soaking agent.

[0109] Example 6

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

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

[0112] First, mix 5 g of glycyrrhizic acid and 4 g of 4,4'-diaminodicyclohexylmethane evenly to form a pretreatment solution, and set it aside for later use; then, heat 100 mL of water to 70 °C, and then add 50 g of sorbic acid, and continuously stir for 3 hours to form an acid solution; after that, add 10 g of pentaethylenehexamine to the acid solution and stir for 60 minutes to ensure uniform mixing, obtaining a reaction solution; next, add 40 g of humic acid to the reaction solution and stir for 50 minutes to achieve complete mixing, forming a post-treatment solution; finally, add the prepared pretreatment solution to the post-treatment solution and stir at 60 °C for 80 minutes to complete the final mixing, obtaining the required post-soaking agent.

[0113] Comparative Example 1

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

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

[0116] First, mix 5 g of capric acid and 4 g of 4,4'-diaminodicyclohexylmethane evenly to form a pretreatment solution, and set it aside for later use. Then, heat 100 mL of water to 70 °C, add 50 g of crocetin, and continuously stir for 3 hours to form an acid solution. After that, add 10 g of pentaethylenehexamine to the acid solution and stir for 60 minutes to ensure uniform mixing, obtaining a reaction solution. Next, add 40 g of humic acid to the reaction solution and stir for 50 minutes to achieve complete mixing, forming a post-treatment solution. Finally, add the prepared pretreatment solution to the post-treatment solution and stir at 60 °C for 80 minutes to complete the final mixing, obtaining the required post-soaking agent.

[0117] Comparative Example 2

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

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

[0120] First, mix 5 g of glycyrrhizic acid and 4 g of cyclohexylamine evenly to form a pretreatment solution, and set it aside for later use. Then, heat 100 mL of water to 70 °C, add 50 g of crocetin, and continuously stir for 3 hours to form an acid solution. After that, add 10 g of pentaethylenehexamine to the acid solution and stir for 60 minutes to ensure uniform mixing, obtaining a reaction solution. Next, add 40 g of humic acid to the reaction solution and stir for 50 minutes to achieve complete mixing, forming a post-treatment solution. Finally, add the prepared pretreatment solution to the post-treatment solution and stir at 60 °C for 80 minutes to complete the final mixing, obtaining the required post-soaking agent.

[0121] Comparative Example 3

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

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

[0124] First, mix 5 g of glycyrrhizic acid and 4 g of 4,4'-diaminodicyclohexylmethane evenly to form a pretreatment solution, and set it aside for later use. Then, heat 100 mL of water to 70 °C, add 50 g of benzoic acid, and continuously stir for 3 hours to form an acid solution. After that, add 10 g of pentaethylenehexamine to the acid solution and stir for 60 minutes to ensure uniform mixing, obtaining a reaction solution. Next, add 40 g of humic acid to the reaction solution and stir for 50 minutes to achieve complete mixing, forming a post-treatment solution. Finally, add the prepared pretreatment solution to the post-treatment solution and stir at 60 °C for 80 minutes to complete the final mixing, obtaining the required post-soaking agent.

[0125] Comparative Example 4

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

[0127] Test Example 1

[0128] Adhesion measurement

[0129] Use a cross-cut test device to make 100 square patterns with a size of 1 mm × 1 mm on the surface of the gold finger plating prepared in the examples and comparative examples of the present invention. Then, evenly paste the type 600 transparent tape produced by 3M Company of the United States on these squares. Subsequently, peel off the tape at the fastest vertical speed. During this process, it is necessary to check whether there is any coating peeling at the edge of the scratch and the edge of the circuit pattern. According to the amount of exfoliated debris, evaluate the adhesion grade of the coating: if the exfoliation rate is 0-5%, it is rated as grade 5B; 5-10% is grade 4B; 10-20% is grade 3B; 20-30% is grade 2B; 30-50% is grade B; if it exceeds 50%, it is rated as grade 0B. The specific test data are shown in Table 1.

[0130] Table 1

[0131] Experimental scheme 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 plating of the examples and comparative examples of the present invention, use a cross-cut tool to draw 100 square areas with a side length of 5 mm. Subsequently, count the burrs, raised particles, notches, and adhesion in each area. According to the counting results, grade the quality of the plating: if the number of defects is less than 1, it is rated as grade 1; if the number of defects is between 2 and 5, it is grade 2; if the number of defects is between 6 and 10, it is grade 3; if the number of defects is between 11 and 15, it is rated as grade 4; if the number of defects is more than 16, it is rated as grade 5. The test results are shown in Table 2.

[0135] Table 2

[0136] Experimental scheme 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 in Test Examples 1 to 2 that the gold finger plating prepared in Example 1 has the best adhesion and flatness.

[0138] Due to its complex molecular structure and multiple active groups, glycyrrhizic acid can react more effectively with other components when forming the post-dip agent, generating compounds with a larger molecular structure. This macromolecular structure helps to form a uniform and dense protective film on the surface of the gold finger plating of the printed circuit board. This film can effectively reduce the contact between the plating and air, thereby reducing the formation of oxides. At the same time, this uniform film structure also helps to form a protective barrier on the surface of the plating, reducing the attachment of impurity ions and improving the cleanliness of the plating. Thereby enhancing the adhesion between the plating and the substrate and improving the adhesion of the plating. At the same time, this uniform film structure also helps to reduce defects on the surface of the plating, such as burrs, protrusions, notches and adhesions, further improving the flatness of the plating. 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 inferior to glycyrrhizic acid in terms of adhesion and flatness. This difference at the molecular level directly affects the macroscopic properties of the plating, making Example 1 using glycyrrhizic acid perform best in the adhesion and flatness tests.

[0139] The molecular structure of 4,4'-diaminodicyclohexylmethane contains two amino groups and two cyclohexyl groups. This structure enables it to form a complex macromolecular network. In the post-dip 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 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. Therefore, they are inferior to 4,4'-diaminodicyclohexylmethane in the ability to form a uniform and dense film. This may result in an uneven surface of the plating, increasing the risk of oxide formation and surface defects, thereby affecting the adhesion and flatness of the plating.

[0140] The molecular structure of crocetin contains two carboxyl groups and multiple carbon-carbon double bonds, which endow it with strong reactivity and complex intermolecular interaction capabilities. In the post-impregnating agent, the two carboxyl groups of crocetin can form a macromolecular compound with pentaethylenehexamine, and the carbon-carbon double bonds can also participate in addition reactions, enhancing 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 air, reducing the generation of oxides, and at the same time providing a smooth surface on the plating surface, which helps to improve the overall flatness of the plating. In contrast, the molecular structures of other organic acids such as 2,5-dimethyl-2,4-hexadienedicarboxylic acid, sorbic acid, and benzoic acid are relatively simple, with fewer functional groups and lacking multiple carbon-carbon double bonds like crocetin. Therefore, they are not as good as crocetin in the ability to form a uniform and dense film. This may result in an uneven surface of the plating, increasing the risk of oxide generation and surface defects, thereby affecting the adhesion and flatness of the plating.

Claims

1. A method for processing the gold finger plating 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 fraction of 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 coating of the printed circuit board; The preparation method of the post-infusion agent is as follows, in parts by weight: Mix 4 - 6 parts of glycyrrhizic acid with 3 - 5 parts of 4,4'-diaminodicyclohexylmethane evenly to form a pretreatment solution and set it aside for use. Then, heat 80 - 120 parts of water to 60 - 80 °C, and then add 40 - 60 parts of crocetin and continuously stir for 2 - 4 hours to form an acid solution. After that, add 8 - 12 parts of pentaethylenehexamine to the acid solution and stir for 50 - 70 minutes to ensure uniform mixing to obtain a reaction solution. Next, add 30 - 50 parts of humic acid to the reaction solution and stir for 40 - 60 minutes to achieve complete mixing to form a post-treatment solution. Finally, add the prepared pretreatment solution to the post-treatment solution and stir at 50 - 70 °C for 60 - 100 minutes to complete the final mixing to obtain the required post-infusion agent.

2. The method for processing the gold finger plating layer of a printed circuit board according to claim 1, wherein, The main materials of the conductive layer include, but are not limited to, copper and silver materials.

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

4. The method for processing the gold finger plating layer of a printed circuit board according to claim 1, wherein, 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 layer of a printed circuit board according to claim 1, characterized in that, In the processing of the second coating, the main materials of the coating include, but are not limited to, one or more of nickel and phosphorus elements, and the normalized weight percentage of phosphorus element is 5% - 14%.

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

7. The method for processing the gold finger plating layer of a printed circuit board according to claim 1, wherein In the processing of the third coating, the main highly conductive metal layer includes, but is not limited to, one or more of gold and platinum.

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

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

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