Copper reduction method for resin plug hole plate capable of preventing seepage corrosion of hole opening

Abstract

The invention discloses a resin hole plugging plate copper reduction method for preventing hole seepage corrosion. The method comprises the steps of resin hole plugging and curing, primary grinding, hole activating treatment, hole protection treatment, copper reduction treatment, washing, secondary grinding, electroplating filling and the like. The core is that special acid and alkali resistant protective ink is printed at the orifice through a character jet printing process, a compact protective layer is formed through segmented gradient curing, and a copper foil area at the edge of the orifice is accurately covered; during copper reduction, the protective layer blocks capillary permeation and lateral attack of liquid medicine, and the copper lateral corrosion amount can be dynamically compensated through micro-inward shrinkage of the protective layer; the protective layer can be completely removed through secondary polishing subsequently, and no residue affects electroplating; according to the method, the problem of hole seepage corrosion is fundamentally solved, the reject ratio is reduced to 0% from 80% or above, and the reliability and the mass production stability of the PCB are greatly improved.

Description

Technical Field

[0001] This invention relates to the field of printed circuit board (PCB) manufacturing technology, specifically to a method for reducing copper content in resin-filled vias to prevent corrosion at the orifices. Background Technology

[0002] In existing resin-filled printed circuit board (PCB) manufacturing processes, copper reduction typically employs a sulfuric acid-hydrogen peroxide system to uniformly etch the copper layer of the substrate. A typical process flow is: resin plugging → curing → ceramic polishing → copper reduction → secondary polishing → electroplating. However, this process has revealed serious technical bottlenecks in long-term practice. Due to the strong oxidizing properties of the copper reduction solution and its pH value typically below 1.5, it easily causes lateral corrosion of the copper foil at the resin-filled via opening. More critically, the resin-copper interface forms a preferential corrosion path due to differences in thermal expansion coefficients, surface energy mismatch, and the presence of microscopic gaps. While etching the overall surface copper layer, the copper reduction solution also undergoes capillary penetration and lateral attack along the resin-copper interface, resulting in uneven thinning of the copper layer at the via opening, microscopic depressions, and even complete erosion of some copper layers. This leads to serious quality defects in subsequent electroplating processes, such as incomplete plating at the via opening, depressions, or "no copper plating." In actual production, the defect rate is typically over 80%, severely restricting the reliability and mass production stability of PCBs. The inability to deposit copper here refers to the inability of copper ions to adhere and deposit during electroplating, resulting in localized missing plating layers.

[0003] Current industry attempts to improve the process mainly focus on adjusting the copper reduction solution formula or optimizing electroplating parameters, but none of these methods fundamentally solve the structural problem of local protection at the orifice. To overcome this bottleneck, multiple technical obstacles must be overcome simultaneously: First, a temporary protective layer that can stably exist in a strong acid and oxidizing environment must be applied to the orifice area. However, this protective layer must precisely cover the resin-copper interface area, which is only tens of micrometers wide, and possess sufficient adhesion to resist chemical erosion. Second, the protective material must have good interfacial bonding and thermochemical stability with the resin and copper foil to prevent peeling due to expansion during curing and copper reduction. Third, the protective layer should be able to achieve controllable micro-shrinkage, dynamically compensating for the lateral corrosion of copper and achieving a self-compensating protective effect. Fourth, the protective layer must be completely removed during subsequent secondary polishing without leaving any residue that could affect electroplating. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a method for reducing copper content in resin-plugged orifice plates to prevent orifice corrosion, comprising: S1. Resin plugging and curing: Filling the vias of the printed circuit board with resin and curing the resin. S2. Initial polishing: Polish the surface of the cured substrate to remove excess resin and make the substrate surface smooth; S3. Orifice activation treatment: Micro-etching solution is used to micro-etch the copper foil at the orifice of the resin plug, with a micro-etching depth of 0.5-1.5μm, forming a micro-rough structure on the copper surface at the orifice, which greatly improves the adhesion of the protective ink. S4. Orifice Protection Treatment: Using inkjet printing technology, acid and alkali resistant protective ink is printed at the orifice of the resin plug. The acid and alkali resistant protective ink is cured in stages and gradients: first, it is pre-cured at 60-80℃ for 3-5 minutes, and then cured at 120-150℃ for 20-30 minutes to form a dense chemical corrosion resistant protective layer. The diameter of the protective layer is 0.08-0.15 mm larger than the diameter of the resin plug orifice, covering the copper foil area at the edge of the orifice. The acid and alkali resistant protective ink is composed of the following components: 30-38 wt% bisphenol A type epoxy acrylate, 10-14 wt% phenolic resin, 5-8 wt% photoinitiator, 12-18 wt% filler, 0.5-1.0 wt% leveling agent, 0.3-0.8 wt% defoamer, and the balance is ethylene glycol ether ester organic solvent. S5. Copper Reduction Treatment: The substrate covered with a chemical corrosion resistant protective layer is immersed in a copper reduction solution for chemical copper reduction treatment; S6. Water washing: The copper-reduced substrate is washed in three stages to remove residual copper-reducing chemicals from the substrate surface; S7. Secondary polishing: The surface of the substrate after water washing is polished a second time to remove the chemical corrosion resistant protective layer; S8. Electroplating leveling: Electroplating is performed on the substrate after secondary polishing to achieve leveling of the copper layer on the surface.

[0005] Preferably, the viscosity of the acid and alkali resistant protective ink is 120-180 dPa·s, and the thixotropic index is 3.0-4.5. High thixotropy ensures that the ink does not flow and the edges are clear during printing; moderate viscosity balances printhead smoothness and film thickness control, ensuring orifice coverage accuracy and film thickness uniformity.

[0006] Preferably, the copper reduction solution comprises the following components: 15-25 wt% sulfuric acid, 3-6 wt% hydrogen peroxide, 0.5-1.5 wt% stabilizer, 1-3 wt% phosphate-citric acid buffer solution, 0.1-0.3 wt% surfactant, and the balance being deionized water; wherein the phosphate-citric acid buffer solution is used to maintain the pH value of the solution between 0.5 and 1.2, and the temperature is controlled at 25-35℃. Adding the phosphate-citric acid buffer solution to the copper reduction solution can maintain a stable low pH environment, ensuring a controllable copper reduction rate and preventing localized over-etching or uneven etching due to pH fluctuations.

[0007] Preferably, the resin used in step S1 is a modified epoxy resin with a viscosity in the range of 15000-25000 mPa·s (25℃) and a glass transition temperature (Tg) greater than 120℃ after curing. The modified epoxy resin has a low coefficient of thermal expansion, a high Tg value, and good compatibility with the copper interface, which can reduce the micro-gaps at the interface between the resin and copper after curing, thereby reducing the risk of corrosion channel formation from the source.

[0008] Preferably, the micro-etching solution used in step S3 consists of the following components: 5-15 wt% sulfuric acid, 20-80 g / L sodium persulfate, and the balance being deionized water. After micro-etching, acid washing, water washing, and pre-baking treatments are required sequentially. The pre-baking temperature is 80-100℃, and the time is 5-10 minutes. Pre-baking removes moisture, prevents bubbles or poor adhesion during the curing of acid and alkali resistant protective inks, and ensures the integrity of the protective layer.

[0009] Preferred text printing process parameters for step S4: printing pressure of 0.3-0.6 MPa, printing speed of 80-120 mm / s, printhead-to-substrate distance of 2-4 mm, and acid- and alkali-resistant protective ink coating thickness of 15-25 μm. Using text printing not only achieves high-precision positioning and ensures the protective layer covers only the edges of the openings without contaminating other areas, but also has a lower cost compared to film printing. Optimizing process parameters achieves complete edge coverage of the protective layer, with a thickness controlled at 15-25 μm, balancing protection and ease of removal.

[0010] Preferably, in step S5, the substrate covered with a chemically resistant protective layer needs to be continuously passed through the copper reduction bath 1-3 times at a speed of 1.5-2.5 m / min, with each dwell time being 3-5 min, and the total copper reduction amount controlled at 10-20 μm. Compared with immersion, this method can effectively reduce local concentration differences, making copper reduction more uniform; the total copper reduction amount is precisely controlled at 10-20 μm to avoid over-etching.

[0011] Preferably, in step S6, the three-stage water washing process involves: first, deionized water rinsing for 1-3 minutes; second, high-pressure spray rinsing at 0.2-0.4 MPa for 30-60 seconds; and third, ultrasonic rinsing at 300-500 W at 40-50℃ for 1-2 minutes. This thoroughly removes residual copper-reducing chemicals. Ultrasonic-assisted rinsing effectively removes residual chemicals from microscopic crevices, preventing further corrosion and subsequent electroplating abnormalities.

[0012] Preferably, both the initial and secondary polishing are performed using a ceramic polishing machine to polish the substrate surface. The ceramic polishing machine includes an 800-1200 grit diamond abrasive belt, a 1000-1500 grit ceramic abrasive block, and a 1200-1800 grit non-woven fabric abrasive pad, arranged sequentially. The polishing pressure is 0.1-0.2 MPa, the polishing speed is 1200-1800 rpm, and the polishing time is 2-4 minutes. This three-step polishing process using diamond abrasive belt, ceramic abrasive block, and non-woven fabric abrasive pad effectively removes resin and the protective layer while ensuring surface smoothness and avoiding damage to the copper layer or leaving polishing marks.

[0013] Preferably, step S8 employs a pulse electroplating leveling process with process parameters of a forward current density of 3-7 A / dm². 2 The negative current density is 0.5-1.5 A / dm². 2 The duty cycle is 1:1-3, and the frequency is 50-150Hz. Pulse electroplating has better deep plating capability and uniform plating performance, and can effectively fill the micro-depressions that may be formed due to copper reduction, achieving high-quality filling of the surface copper layer and improving the integrity of the plating layer in the orifice area.

[0014] The beneficial effects are as follows: This application uses a text inkjet printing process to print a specially formulated acid and alkali resistant protective ink onto the orifice of the resin-filled hole, forming a brim-like protective layer covering the copper foil area at the edge of the orifice. This achieves precise local protection at the interface between the resin and copper, effectively blocking capillary penetration and lateral attack of the copper reduction solution. During the copper reduction process, the protective layer undergoes a slight inward shrinkage of 0.5-1.5μm. This shrinkage dynamically compensates for the lateral loss of the copper foil at the orifice during etching, achieving a self-compensating protection effect and avoiding protection failure caused by lateral etching. The protective ink forms a dense protective layer through segmented gradient curing. The protective layer, combined with orifice activation treatment, significantly improves the adhesion between ink and copper foil, ensuring its stability even in strong acid and oxidizing environments, resisting chemical erosion and interface peeling. The protective layer can be completely removed during secondary polishing without leaving any residue that could affect subsequent electroplating, guaranteeing the cleanliness of the surface copper layer and the quality of electroplating. It fundamentally solves the problems of uneven thinning, depression, and even erosion of the copper layer at the orifice, significantly improving the integrity and uniformity of the orifice plating in subsequent electroplating processes. The defect rate caused by orifice corrosion has been reduced from over 80% to 0%, greatly improving the reliability and mass production stability of PCB boards. Attached Figure Description

[0015] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1The images show a comparison of the via opening conditions using the conventional process and the process described in this application. The upper image shows that the via opening under the conventional process has obvious corrosion and depressions due to capillary penetration of the chemical solution (incomplete copper layer at the edge and significant corrosion marks). The lower image shows the effect after treatment by the process described in this application (the copper layer at the edge of the via opening is complete and uniform, without corrosion or depressions, and is in a regular and smooth state). Detailed Implementation

[0016] The present invention will now be described in further detail with reference to specific embodiments, so that those skilled in the art can more clearly understand the present invention.

[0017] The following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. All other embodiments obtained by those skilled in the art based on the specific embodiments of the invention without inventive effort are within the protection scope of the invention.

[0018] In the embodiments of the present invention, unless otherwise specified, all raw material components are commercially available products well known to those skilled in the art; in the embodiments of the present invention, unless specifically specified, the technical means used are conventional means well known to those skilled in the art.

[0019] Raw material source: Modified epoxy resin, brand DIC, model EPICLON HP-4710, purchased from DIC Synthetic Resins (Zhongshan) Co., Ltd. Bisphenol A type epoxy acrylate, purchased from Shandong Suihua Biotechnology Co., Ltd. Phenolic epoxy acrylate, purchased from Wuhan Lanabai Pharmaceutical Chemical Co., Ltd. Phenolic resin, purchased from Jinan Huijinchuan Chemical Co., Ltd.; Photoinitiators: benzophenone, purchased from Hubei Shiteng Chemical Technology Co., Ltd.; 2,4-diethylthioxanthone, purchased from Hubei Dali Chemical Co., Ltd. The packing material was purchased from Hangzhou Hengna New Materials Co., Ltd. The leveling agent, brand BASF, model BASF Efka FL3600, was purchased from Anhui Jingzhicai New Material Co., Ltd. Defoamers, brand Dow Corning, models AFE-1410, AFE-3168, and AFE-1247, were all purchased from Shanghai Guangbai New Materials Co., Ltd. Propylene glycol methyl ether acetate and propylene glycol ethyl ether acetate were both purchased from Jinan Shuangying Chemical Co., Ltd. Butyl acetate, purchased from Shandong Chuangying Chemical Co., Ltd.; All other reagents were commercially available.

[0020] Example 1 A method for reducing copper content in a resin-plugged orifice plate to prevent orifice corrosion includes the following steps: S1. Resin plugging and curing: The vias of the printed circuit board are filled with resin and the resin is cured; the resin is a modified epoxy resin with a viscosity in the range of 15000-25000mPa·s (25℃) and a glass transition temperature (Tg) greater than 120℃ after curing. S2. Initial polishing: The surface of the cured substrate is polished using a ceramic polishing machine to remove excess resin and make the substrate surface smooth. The ceramic polishing machine includes an 800-grit diamond abrasive belt, a 1000-grit ceramic abrasive block and a 1200-grit non-woven abrasive pad arranged in sequence. The polishing pressure is 0.1 MPa, the polishing speed is 1200 rpm and the polishing time is 2 minutes. S3. Orifice Activation Treatment: The copper foil at the orifice of the resin-filled orifice is micro-etched with a micro-etching solution to a depth of 0.5 μm, forming a micro-rough structure on the copper surface at the orifice. The micro-etching solution used in step S3 consists of the following components: 5 wt% sulfuric acid, 20 g / L sodium persulfate, and the balance being deionized water. After micro-etching, acid washing, water washing, and pre-baking treatment are required in sequence. The pre-baking temperature is 80℃ and the time is 5 min. S4. Orifice Protection Treatment: Using inkjet printing, acid and alkali resistant protective ink is printed onto the orifice of the resin-filled orifice. The ink undergoes segmented gradient curing: pre-curing at 60℃ for 3 minutes, followed by curing at 120℃ for 20 minutes, forming a dense, chemically resistant protective layer. The diameter of this layer is 0.08 mm larger than the orifice diameter, covering the copper foil area at the orifice edge. The acid and alkali resistant protective ink consists of the following components: 30 wt% bisphenol A type epoxy acrylate, 10 wt%... The ink consists of phenolic resin, 5 wt% photoinitiator benzophenone, 12 wt% filler hydrophobic nano-silica, 0.5 wt% leveling agent, 0.3 wt% defoamer, and the balance being organic solvent propylene glycol methyl ether acetate; the viscosity of the acid and alkali resistant protective ink is 120-180 dPa·s, and the thixotropic index is 3.0-4.5; the text printing process parameters are: printing pressure 0.3 MPa, printing speed 80 mm / s, printhead-substrate distance 2 mm, and acid and alkali resistant protective ink coating thickness 15 μm; S5. Copper Reduction Treatment: The substrate covered with a chemical corrosion resistant protective layer is immersed in a copper reduction solution for chemical copper reduction treatment; the specific operation is to continuously pass the substrate covered with a chemical corrosion resistant protective layer through the copper reduction tank once at a speed of 1.5m / min, with a dwell time of 3min each time, and the total copper reduction is controlled at 10μm. The copper-reducing solution consists of the following components: 15wt% sulfuric acid, 3wt% hydrogen peroxide, 0.5wt% stabilizer, 1wt% phosphate-citric acid buffer, 0.1wt% surfactant, and the balance being deionized water; the phosphate-citric acid buffer is used to maintain the pH of the solution between 0.5 and 1.2, and the temperature is controlled at 25-35℃. S6. Water washing: The copper-reduced substrate is subjected to three stages of water washing to remove residual copper-reducing chemicals from the substrate surface. The first stage is deionized water rinsing for 1 minute; the second stage is high-pressure spray water washing with a spray pressure of 0.2 MPa and a rinsing time of 30 seconds; the third stage is ultrasonic water washing with an ultrasonic power of 300 W, a water washing temperature of 40℃, and a water washing time of 1 minute. S7. Secondary polishing: A ceramic polishing machine is used to polish the surface of the substrate after water washing to remove the chemical corrosion resistant protective layer. The ceramic polishing machine includes an 800-mesh diamond abrasive belt, a 1000-mesh ceramic abrasive block and a 1200-mesh non-woven abrasive pad arranged in sequence. The polishing pressure is 0.1MPa, the polishing speed is 1200rpm and the polishing time is 2min. S8. Electroplating leveling: A pulse electroplating leveling process is used to electroplat the substrate after secondary polishing to achieve leveling of the surface copper layer; the pulse electroplating process parameters are a forward current density of 3A / dm². 2 The negative current density is 0.5 A / dm. 2 The duty cycle is 1:1 and the frequency is 50Hz.

[0021] Example 2 A method for reducing copper content in a resin-plugged orifice plate to prevent orifice corrosion includes the following steps: S1. Resin plugging and curing: The vias of the printed circuit board are filled with resin and the resin is cured; the resin is a modified epoxy resin with a viscosity in the range of 15000-25000mPa·s (25℃) and a glass transition temperature (Tg) greater than 120℃ after curing. S2. Initial polishing: A ceramic polishing machine is used to polish the surface of the cured substrate to remove excess resin and make the substrate surface smooth. The ceramic polishing machine includes a 1000-grit diamond abrasive belt, a 1200-grit ceramic abrasive block and a 1500-grit non-woven fabric abrasive pad arranged in sequence. The polishing pressure is 0.15MPa, the polishing speed is 1500rpm and the polishing time is 3min. S3. Orifice Activation Treatment: The copper foil at the orifice of the resin-filled orifice is micro-etched with a micro-etching solution to a depth of 1 μm, forming a micro-rough structure on the copper surface at the orifice. The micro-etching solution used in step S3 consists of the following components: 10 wt% sulfuric acid, 50 g / L sodium persulfate, and the balance being deionized water. After micro-etching, acid washing, water washing, and pre-baking treatment are required in sequence. The pre-baking temperature is 90℃ and the time is 7 min. S4. Orifice Protection Treatment: Using inkjet printing, acid and alkali resistant protective ink is printed onto the orifice of the resin-filled orifice. The ink undergoes segmented gradient curing: first pre-curing at 70℃ for 4 minutes, then curing at 135℃ for 25 minutes to form a dense, chemically resistant protective layer. The diameter of this protective layer is 0.11 mm larger than the orifice diameter, covering the copper foil area at the orifice edge. The acid and alkali resistant protective ink consists of the following components: 34 wt% bisphenol A type epoxy acrylate, 12 wt% phenolic resin, ... The ink consists of 6 wt% photoinitiator 2,4-diethylthioxanthrone, 15 wt% filler hydrophobic nano-silica, 0.75 wt% leveling agent, 0.55 wt% defoamer, and the balance being organic solvent propylene glycol ethyl ether acetate; the viscosity of the acid and alkali resistant protective ink is 120-180 dPa·s, and the thixotropic index is 3.0-4.5; the text printing process parameters are: printing pressure of 0.5 MPa, printing speed of 100 mm / s, printhead-substrate distance of 3 mm, and acid and alkali resistant protective ink coating thickness of 20 μm; S5. Copper Reduction Treatment: The substrate covered with a chemical corrosion resistant protective layer is immersed in a copper reduction solution for chemical copper reduction treatment; the specific operation is to pass the substrate covered with a chemical corrosion resistant protective layer through the copper reduction tank twice at a speed of 2m / min, with a dwell time of 4min each time, and the total copper reduction is controlled at 15μm. The copper-reducing solution consists of the following components: 20wt% sulfuric acid, 4wt% hydrogen peroxide, 1wt% stabilizer, 2wt% phosphate-citric acid buffer solution, 0.2wt% surfactant, and the balance being deionized water; the phosphate-citric acid buffer solution is used to maintain the pH value of the solution between 0.5 and 1.2, and the temperature is controlled at 25-35℃. S6. Water washing: The copper-reduced substrate is subjected to three stages of water washing to remove residual copper-reducing chemicals from the substrate surface; the first stage is deionized water rinsing for 2 minutes; the second stage is high-pressure spray water washing with a spray pressure of 0.3 MPa and a rinsing time of 45 seconds; the third stage is ultrasonic water washing with an ultrasonic power of 400 W and a water washing temperature of 45℃ for 2 minutes. S7. Secondary polishing: A ceramic polishing machine is used to polish the surface of the substrate after water washing to remove the chemical corrosion resistant protective layer. The ceramic polishing machine includes a 1000-grit diamond abrasive belt, a 1200-grit ceramic abrasive block and a 1500-grit non-woven abrasive pad arranged in sequence. The polishing pressure is 0.15MPa, the polishing speed is 1500rpm and the polishing time is 3min. S8. Electroplating leveling: A pulse electroplating leveling process is used to electroplat the substrate after secondary polishing to achieve leveling of the surface copper layer; the pulse electroplating process parameters are a forward current density of 5A / dm². 2 The negative current density is 1 A / dm 2 The duty cycle is 1:2 and the frequency is 100Hz.

[0022] Example 3 A method for reducing copper content in a resin-plugged orifice plate to prevent orifice corrosion includes the following steps: S1. Resin plugging and curing: The vias of the printed circuit board are filled with resin and the resin is cured; the resin is a modified epoxy resin with a viscosity in the range of 15000-25000mPa·s (25℃) and a glass transition temperature (Tg) greater than 120℃ after curing. S2. Initial polishing: A ceramic polishing machine is used to polish the surface of the cured substrate to remove excess resin and make the substrate surface smooth. The ceramic polishing machine includes a 1200-grit diamond abrasive belt, a 1500-grit ceramic abrasive block and an 1800-grit non-woven abrasive pad arranged in sequence. The polishing pressure is 0.2MPa, the polishing speed is 1800rpm and the polishing time is 4min. S3. Orifice Activation Treatment: The copper foil at the orifice of the resin plug is micro-etched using a micro-etching solution to a depth of 1.5 μm, forming a micro-rough structure on the copper surface at the orifice. The micro-etching solution used in step S3 consists of the following components: 15 wt% sulfuric acid, 80 g / L sodium persulfate, and the balance being deionized water. After micro-etching, acid washing, water washing, and pre-baking treatment are required in sequence. The pre-baking temperature is 100℃ and the time is 10 min. S4. Orifice Protection Treatment: Using inkjet printing, acid and alkali resistant protective ink is printed onto the orifice of the resin-filled orifice. The ink undergoes segmented gradient curing: first pre-curing at 80℃ for 5 minutes, then curing at 150℃ for 30 minutes to form a dense, chemically resistant protective layer. The diameter of this layer is 0.15 mm larger than the orifice diameter, covering the copper foil area at the orifice edge. The acid and alkali resistant protective ink consists of the following components: 38 wt% bisphenol A type epoxy acrylate and 14 wt% phenolic resin. The ink consists of 8 wt% photoinitiator 2,4-diethylthioxanthrone, 18 wt% filler hydrophobic nano-silica, 1.0 wt% leveling agent, 0.8 wt% defoamer, and the balance being organic solvent propylene glycol methyl ether acetate; the viscosity of the acid and alkali resistant protective ink is 120-180 dPa·s, and the thixotropic index is 3.0-4.5; the text printing process parameters are: printing pressure 0.6 MPa, printing speed 120 mm / s, printhead-substrate distance 4 mm, and acid and alkali resistant protective ink coating thickness 25 μm; S5. Copper Reduction Treatment: The substrate covered with a chemical corrosion resistant protective layer is immersed in a copper reduction solution for chemical copper reduction treatment; the specific operation is to pass the substrate covered with a chemical corrosion resistant protective layer through the copper reduction tank 3 times at a speed of 2.5m / min, with a dwell time of 5min each time, and the total copper reduction is controlled at 20μm. The copper-reducing solution consists of the following components: 25wt% sulfuric acid, 6wt% hydrogen peroxide, 1.5wt% stabilizer, 3wt% phosphate-citric acid buffer, 0.3wt% surfactant, and the balance being deionized water; the phosphate-citric acid buffer is used to maintain the pH of the solution between 0.5 and 1.2, and the temperature is controlled between 25 and 35℃. S6. Water washing: The copper-reduced substrate is subjected to three stages of water washing to remove residual copper-reducing chemicals from the substrate surface; the first stage is deionized water rinsing for 3 minutes; the second stage is high-pressure spray water washing for 60 seconds at a spray pressure of 0.4 MPa; and the third stage is ultrasonic water washing for 2 minutes at an ultrasonic power of 500 W and a water temperature of 50°C. S7. Secondary polishing: A ceramic polishing machine is used to polish the surface of the substrate after water washing to remove the chemical corrosion resistant protective layer. The ceramic polishing machine includes a 1200-grit diamond abrasive belt, a 1500-grit ceramic abrasive block and an 1800-grit non-woven abrasive pad arranged in sequence. The polishing pressure is 0.2MPa, the polishing speed is 1800rpm and the polishing time is 4min. S8. Electroplating leveling: A pulse electroplating leveling process is used to electroplat the substrate after secondary polishing to achieve leveling of the surface copper layer; the pulse electroplating process parameters are a forward current density of 7A / dm². 2 The negative current density is 1.5 A / dm. 2 The duty cycle is 1:3 and the frequency is 150Hz.

[0023] Comparative Example 1 (Verifying the Importance of Orifice Protection Treatment) The difference from Example 2 is that no orifice protection treatment was performed.

[0024] Comparative Example 2 (Verifying the importance of acid and alkali resistant protective ink formulations) The difference from Example 2 is that in the acid and alkali resistant protective ink formulation, bisphenol A type epoxy acrylate is replaced with phenolic epoxy acrylate, and ethylene glycol ether ester organic solvent is replaced with ester organic solvent (butyl acetate).

[0025] Small-batch tests were conducted on Examples 1-3, using model K6F22028C0, quantity 200 PNL (each PNL = 12 PCS), board thickness 1.5mm, and via diameter 0.35mm. Inspection using a magnifying glass / section revealed no corrosion at the via openings. After electroplating, the FQC (Final Quality Control) finished product AVI (Automated Visual Inspection) showed a 0% defect rate of 0 / 200 / 10 = 0% (where 0 indicates 0 defective holes found during inspection; 200 indicates 200 vias sampled per batch; and 10 indicates a total of 10 batches inspected). No dents or copper plating defects were observed. Comparative Example 1 underwent a small-batch follow-up test with model K6F22028C0, quantity 200 PNL, board thickness 1.5mm, and via diameter 0.35mm. Inspection using a magnifying glass / section revealed no corrosion at the via openings. After electroplating, the finished product underwent FQC (Final Quality Control) AVI (Automated Visual Inspection) with a 100% defect rate of 1700 / 200 / 10 = 85% (in this formula, 1700 represents the number of defective vias found during inspection; 200 represents 200 vias sampled from each batch; and 10 represents a total of 10 batches inspected). Comparative Example 2 underwent a small-batch follow-up test with model K6F22028C0, quantity 200 PNL, board thickness 1.5mm, and via diameter 0.35mm. Inspection using a magnifying glass / section revealed no corrosion at the via openings. After electroplating, the finished product underwent FQC (Final Quality Control) AVI (Automated Visual Inspection) with a 100% defect rate of 85%. The full inspection defect rate is 1240 / 200 / 10 = 62% (in this formula, 1240 represents the number of defective holes found during the inspection process; 200 represents the number of through holes sampled from each batch; and 10 represents the number of batches inspected in total). Further follow-up large-scale testing was conducted on Examples 1-3, model K6F23747C0, quantity 1000 PNL. Inspection using a magnifying glass / section revealed no corrosion at the orifices. After electroplating and leveling, the FQC finished product AVI full inspection showed a defect rate of 0 / 1000 / 10=0% (where 0 indicates 0 defective holes were found during inspection; 1000 indicates 1000 vias were sampled per batch; and 10 indicates a total of 10 batches were inspected). No dents or copper ingress were observed. For example, a large-scale test was conducted on model K6F23747C0, with a quantity of 1000 PNLs. Inspection using a magnifying glass / section revealed no corrosion at the orifices. After electroplating and leveling, the FQC finished product AVI full inspection showed a defect rate of 8722 / 1000 / 10 = 87.22% (in this formula, 8722 represents the number of defective holes found during inspection; 1000 represents 1000 vias sampled from each batch; and 10 represents a total of 10 batches inspected). Comparative Example 2 was tested in large batches with model K6F23747C0, quantity 1000 PNL. Inspection using a magnifying glass / section revealed no corrosion at the orifices. After electroplating and leveling, the FQC finished product AVI full inspection showed a defect rate of 6413 / 1000 / 10 = 64.13% (in this formula, 6413 represents the number of defective holes found during inspection; 1000 represents 1000 vias sampled per batch; and 10 represents a total of 10 batches inspected). Experiments have shown that the process described in this application fundamentally solves the problem of orifice corrosion in resin-plugged plates. In both small-batch and large-batch production verifications, no uneven copper layer thinning, microscopic depressions, or erosion were observed in the orifice area. After electroplating, the integrity and uniformity of the orifice plating were significantly improved, with no quality defects such as "non-coppering." The defect rate due to orifice corrosion decreased from over 80% in traditional processes to 0%. This demonstrates that the acid- and alkali-resistant protective ink layer formed by the inkjet printing process precisely covers the resin-copper interface, blocking the capillary penetration of the copper-reducing agent. The protective layer undergoes slight inward shrinkage during copper reduction, dynamically compensating for copper foil lateral corrosion loss and preventing localized erosion. Segmented gradient curing and micro-etching activation treatment enhance the adhesion of the protective layer, ensuring it does not peel off in a strong acid environment. Figure 1 As shown, using traditional processes, the edges of vias exhibit obvious depressions and corrosion defects; after adopting the process of this application, the copper layer at the edges of the vias is complete and uniform, with no traces of corrosion; this directly demonstrates the effective suppression of corrosion by the process of this application. In summary, the process of this application not only reduces the defect rate to zero, but also significantly improves the reliability and mass production stability of PCB boards, providing key technical support for the high-quality manufacturing of resin-filled PCB boards.

[0026] The above are merely embodiments of the present invention and are not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A method for reducing copper content in resin-plugged orifice plates to prevent orifice corrosion, characterized in that, include: S1. Resin plugging and curing: Resin is used to fill the vias of the printed circuit board and the resin is cured. S2. Initial polishing: Polish the surface of the cured substrate to remove excess resin and make the substrate surface smooth; S3. Orifice activation treatment: Micro-etching solution is used to micro-etch the copper foil at the orifice of the resin plug, with a micro-etching depth of 0.5-1.5μm, forming a micro-rough structure on the copper surface at the orifice. S4. Orifice Protection Treatment: Using a text inkjet printing process, acid and alkali resistant protective ink is printed at the orifice of the resin plug. The acid and alkali resistant protective ink is then subjected to segmented gradient curing: first, pre-curing at 60-80℃ for 3-5 minutes, and then curing at 120-150℃ for 20-30 minutes to form a dense chemical corrosion resistant protective layer. The diameter of the protective layer is 0.08-0.15 mm larger than the diameter of the resin plug orifice, covering the copper foil area at the edge of the orifice. The acid and alkali resistant protective ink is composed of the following components: 30-38 wt% bisphenol A type epoxy acrylate, 10-14 wt% phenolic resin, 5-8 wt% photoinitiator, 12-18 wt% filler, 0.5-1.0 wt% leveling agent, 0.3-0.8 wt% defoamer, and the balance being ethylene glycol ether ester organic solvent. S5. Copper Reduction Treatment: The substrate covered with the chemical corrosion resistant protective layer is immersed in a copper reduction solution for chemical copper reduction treatment; S6. Water washing: The copper-reduced substrate is washed in three stages to remove residual copper-reducing chemicals from the substrate surface; S7. Secondary polishing: The chemical corrosion resistant protective layer is removed by secondary polishing of the substrate surface after water washing; S8. Electroplating leveling: Electroplating is performed on the substrate after the secondary polishing to achieve leveling of the surface copper layer.

2. The method for reducing copper content in resin-plugged orifice plates to prevent orifice corrosion according to claim 1, characterized in that, The acid and alkali resistant protective ink has a viscosity of 120-180 dPa·s and a thixotropic index of 3.0-4.

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3. The method for reducing copper content in resin-plugged orifices by preventing corrosion according to claim 1, characterized in that, The copper-reducing solution is composed of the following components: 15-25 wt% sulfuric acid, 3-6 wt% hydrogen peroxide, 0.5-1.5 wt% stabilizer, 1-3 wt% phosphate-citric acid buffer solution, 0.1-0.3 wt% surfactant, and the balance being deionized water; wherein the phosphate-citric acid buffer solution is used to maintain the pH value of the solution between 0.5 and 1.2, and the temperature is controlled at 25-35℃.

4. The method for reducing copper content in resin-plugged orifice plates to prevent orifice corrosion according to claim 1, characterized in that, The resin used in step S1 is a modified epoxy resin with a viscosity in the range of 15000-25000 mPa·s (25℃) and a glass transition temperature (Tg) greater than 120℃ after curing.

5. The method for reducing copper content in resin-plugged orifice plates to prevent orifice corrosion according to claim 1, characterized in that, The micro-etching solution used in step S3 consists of the following components: 5-15 wt% sulfuric acid, 20-80 g / L sodium persulfate, and the balance being deionized water. After micro-etching, acid washing, water washing, and pre-baking treatment are required in sequence. The pre-baking temperature is 80-100℃ and the time is 5-10 min.

6. The method for reducing copper content in resin-plugged orifice plates to prevent orifice corrosion according to claim 1, characterized in that, The text printing process parameters for step S4 are as follows: printing pressure is 0.3-0.6MPa, printing speed is 80-120mm / s, the distance between the printhead and the substrate is 2-4mm, and the thickness of the acid and alkali resistant protective ink coating is 15-25μm.

7. The method for reducing copper content in resin-plugged orifice plates to prevent orifice corrosion according to claim 1, characterized in that, In step S5, the substrate covered with the chemical corrosion resistant protective layer needs to be continuously passed through the copper reduction tank 1-3 times at a speed of 1.5-2.5 m / min, with a dwell time of 3-5 min each time, and the total copper reduction amount is controlled at 10-20 μm.

8. The method for reducing copper content in resin-plugged orifice plates to prevent orifice corrosion according to claim 1, characterized in that, In step S6, the three-stage water washing process consists of three stages: the first stage is deionized water rinsing, with a rinsing time of 1-3 minutes; the second stage is high-pressure spray water washing, with a spray pressure of 0.2-0.4 MPa and a rinsing time of 30-60 seconds; and the third stage is ultrasonic water washing, with an ultrasonic power of 300-500 W, a water washing temperature of 40-50℃, and a water washing time of 1-2 minutes.

9. The method for reducing copper content in resin-plugged orifice plates to prevent orifice corrosion according to claim 1, characterized in that, Both the initial and secondary polishing are performed using a ceramic polishing machine to polish the substrate surface. The ceramic polishing machine includes an 800-1200 grit diamond abrasive belt, a 1000-1500 grit ceramic abrasive block, and a 1200-1800 grit non-woven fabric abrasive pad arranged in sequence. The polishing pressure is 0.1-0.2 MPa, the polishing speed is 1200-1800 rpm, and the polishing time is 2-4 minutes.

10. The method for reducing copper content in a resin-plugged orifice plate to prevent orifice corrosion according to claim 1, characterized in that, Step S8 employs a pulse electroplating leveling process with process parameters of a forward current density of 3-7 A / dm². 2 The negative current density is 0.5-1.5 A / dm². 2 The duty cycle is 1:1-3, and the frequency is 50-150Hz.

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