PCB copper surface repairing process

Abstract

The invention belongs to the technical field of circuit board repair, and particularly relates to a PCB copper surface repair process. The process comprises the following steps: detecting the copper surface of the PCB, identifying and positioning defects, and generating a three-dimensional damage map; a cleaning solution containing tripotassium citrate, sodium lauroyl sarcosinate, propyl gallate, glycerin and Tr ici ne is used for conducting fixed-point cleaning on the defect area; spraying a functional nano activator dispersion liquid prepared from a layered zirconium oxide nanosheet, carboxymethyl chitosan, ammonium tripolyphosphate, a naringenin-dopamine-maleic acid copolymer and a polyvinyl alcohol aqueous solution to form a nano-structure activation layer; and finally, applying a conductive material for defect filling and repairing. According to the process, the copper surface micro-defects can be accurately repaired, the conductivity and the interface bonding force of the repaired area are enhanced, the repaired PCB has excellent long-term stability, the overall reliability of the PCB is effectively improved, and the service life of the PCB is effectively prolonged.

Description

Technical Field

[0001] The invention belongs to the technical field of circuit board repair, and in particular relates to a copper surface repair process for a PCB board. Background Art

[0002] Printed circuit boards (PCBs) are essential components of modern electronic devices, widely used in a variety of high-tech fields, including communications, automotive, aerospace, and medical electronics. PCBs utilize the copper foil traces on them to achieve electrical connections and signal transmission between electronic components. Therefore, the quality of the copper surface directly determines the overall board's electrical performance and service life.

[0003] During PCB manufacturing, handling, assembly, and subsequent maintenance, copper surfaces are susceptible to various forms of damage, including physical scratches, chemical corrosion, and electromigration fractures. Once defects occur, they can not only cause localized conduction failures and signal interference, but can also create safety hazards such as short circuits due to copper ion migration. Therefore, rapid and accurate detection and efficient repair of copper surface defects are crucial for ensuring PCB functional reliability.

[0004] Currently, industrial repair of PCB copper surface defects mostly relies on manual visual inspection, extensive surface treatment methods, and traditional soldering repair methods. These methods have significant limitations: First, manual inspection cannot accurately identify microcracks or deep corrosion, resulting in a high rate of missed detections; second, conventional repair processes such as overall cleaning, hot pressing welding, or mechanical polishing can easily cause secondary damage to non-damaged areas and even introduce new defects. Furthermore, the lack of specialized repair materials and refined treatment methods results in poor adhesion between the repaired area and the original copper surface, low reliability, and the risk of unstable conductivity or detachment after long-term use.

[0005] In recent years, with the increasing demand for PCB reliability in precision electronics manufacturing, the industry urgently needs a highly efficient copper surface defect repair process that integrates "precision detection, targeted repair, and enhanced integration." Traditionally used acid and alkali reagents are particularly corrosive and have poor selectivity, making it difficult to achieve precise localized treatment. Commonly used roughening agents, such as high-concentration oxidants and micro-etching solutions, can easily lead to excessive corrosion of surrounding circuits, seriously impacting circuit performance.

[0006] Therefore, there is an urgent need to develop a more selective, gentle and functional repair strategy that can achieve accurate identification, gentle removal and efficient regeneration of copper surface micro-defects, providing a better solution for improving the overall reliability of PCB boards and extending their service life. Summary of the Invention

[0007] The present invention aims to provide a PCB copper surface repair process, which can achieve high-precision detection of micro-defects on the copper surface of the circuit board, fixed-point cleaning and surface activation repair, and has the advantages of simple operation, strong selectivity, little damage to the substrate, and high repair bonding strength.

[0008] In order to achieve the above object, the present invention provides the following technical solutions:

[0009] A PCB copper surface repair process includes the following steps:

[0010] (1) Perform surface inspection on the copper surface of the PCB to be repaired, identify and locate copper surface defects, and generate a three-dimensional damage map to guide subsequent repair operations;

[0011] (2) using a cleaning solution to spray the defective area identified in step (1) at a fixed point, wherein the cleaning solution contains tripotassium citrate, sodium lauroyl sarcosinate, propyl gallate, glycerin and Tricine, and reacting for a certain time after spraying, and then rinsing with deionized water and drying naturally;

[0012] (3) spraying a functional nano-activator dispersion onto the defective area treated in step (2), and standing to dry to form a nanostructured activation layer; the functional nano-activator dispersion is prepared from the following raw materials, in parts by weight: 1-5 parts of layered zirconium oxide nanosheets, 10-30 parts of carboxymethyl chitosan, 0.5-2 parts of ammonium tripolyphosphate, 1-5 parts of naringenin-dopamine-maleic acid copolymer, and 60-80 parts of a 4-6w% polyvinyl alcohol aqueous solution;

[0013] (4) Applying a conductive material on the nanostructured activation layer formed in step (3) and curing to complete the repair.

[0014] Furthermore, in step (1), the copper surface of the PCB board is inspected by high-resolution optical imaging and micro-resistance scanning.

[0015] High-resolution optical imaging uses a short-wavelength light source and a high-pixel sensor to scan the copper surface of the PCB. It can clearly identify microscopic defects such as surface scratches and corrosion, and generate a detailed surface map through image processing. Micro-resistance scanning helps to detect micro-cracks or hidden short circuits that are difficult to visually identify with optical imaging by measuring the local resistance changes on the copper surface. The combination of the two can not only quickly locate physical damage on the surface, but also detect electrical anomalies. The generated three-dimensional damage map provides data support for subsequent precise repairs, significantly improving the sensitivity, accuracy and reliability of detection. Specifically, high-resolution optical imaging can be achieved through a 3D laser confocal scanner, a white light interferometer or a high-resolution automatic optical inspection (AOI) system; micro-resistance scanning can be achieved through a four-probe micro-resistance tester or a local impedance scanning device.

[0016] Furthermore, the mass percentages of the raw materials in the cleaning solution in step (2) are: tripotassium citrate 5-20%, sodium lauroyl sarcosinate 0.1-2%, propyl gallate 0.05-1%, glycerol 0.5-5%, Tricine 0.5-2%, and the balance is deionized water.

[0017] Furthermore, the reaction time in step (2) is 1-3 minutes.

[0018] In the cleaning solution, tripotassium citrate, as main chelating agent, can effectively complex copper oxide (Cu2O, CuO) and other metal ion deposits on copper surface under neutral or weakly acidic conditions, realizes pollutant gentle peeling by complex desorption mode, avoids the copper surface damage caused by strong acid corrosion. Sodium lauroyl sarcosinate, as a kind of mild anionic surfactant, has good wetting, infiltration and interfacial activation ability, can reduce liquid surface tension, makes cleaning solution spread rapidly in copper surface defect area and penetrate into microcrack inside, simultaneously assists dirt stripping away. Propyl gallate, as the antioxidant functional component in cleaning solution, is rich in polyphenol hydroxyl groups, can capture free radicals, suppresses the reoxidation reaction of copper surface, protects fresh exposed copper surface in cleaning process, reduces the secondary corrosion risk caused by cleaning. Glycerol, as hydrophilic auxiliary agent, can maintain local moist environment at the evaporation rate of buffer solution in cleaning process, and prevents the copper surface from drying and cracking or forming new oxide film in the short time after cleaning by forming thin protective film simultaneously.

[0019] The cleaning solution of the present invention has the comprehensive advantages of mild decontamination, selective complexation, prevention of secondary oxidation, and protection of copper surface integrity. It can achieve accurate and low-damage cleaning of defective areas on the copper surface of a PCB, laying a good foundation for subsequent surface activation and repair operations.

[0020] Furthermore, the functional nano-activator dispersion in step (3) is prepared according to the following method:

[0021] (a) adding layered zirconia nanosheets to a polyvinyl alcohol aqueous solution and ultrasonically dispersing the nanosheets for 10-60 minutes to form a nanoparticle dispersion;

[0022] (b) adding carboxymethyl chitosan, ammonium tripolyphosphate, and naringenin-dopamine-maleic acid copolymer to the dispersion in sequence, stirring and reacting for 1-2 hours to obtain the functional nano activator dispersion.

[0023] Furthermore, the naringenin-dopamine-maleic acid copolymer in step (3) is prepared according to the following method:

[0024] (i) adding naringenin, dopamine hydrochloride, and maleic anhydride to an ethanol-water mixed solvent and stirring to form a prepolymer reaction liquid;

[0025] (ii) heating the prepolymer reaction solution to 50-70° C. under nitrogen protection, and adding an initiator to initiate a copolymerization reaction for 2-6 hours;

[0026] (iii) After the reaction is completed, the product is added dropwise to anhydrous ether for precipitation, and the precipitate is washed, filtered, and dried to obtain the target product, naringenin-dopamine-maleic acid copolymer.

[0027] Furthermore, the molar ratio of naringenin, dopamine hydrochloride and maleic anhydride is 1:(0.8-1.2):(1.5-3.0); the mass ratio of ethanol to water in the ethanol-water mixed solvent is (2-5):1; and the mass ratio of naringenin to the ethanol-water mixed solvent is 1:(50-80).

[0028] Furthermore, the initiator is potassium persulfate or azobisisobutyronitrile, and the mass ratio of the initiator to naringenin is (0.01-0.05):1.

[0029] The present invention introduces a naringenin-dopamine-maleic acid copolymer into a functional nano-activator dispersion. Naringenin is a natural flavonoid polyphenol compound with multiple phenolic hydroxyl groups in its molecular structure. It can form a coordination complex with metal ions and has antioxidant and free radical resistance. Dopamine molecules contain a catechol structure and a primary amine functional group, have good metal surface adhesion and interfacial activity, and are the basic structure of polydopamine-based high-adhesion coatings. Maleic anhydride is a highly reactive bifunctional monomer that can undergo ring-opening acylation or free radical addition reactions with various nucleophilic groups (such as phenolic hydroxyl groups and amino groups) to form stable ester bonds or amide bonds.

[0030] In this process, the three react in an ethanol-water mixture to form a copolymer. Maleic anhydride, under the action of an initiator, undergoes free radical polymerization, triggering a reaction between dopamine and naringenin, forming a chain or network copolymer structure. Controlling the reaction conditions at 50-70°C for 2-6 hours ensures reactivity while avoiding excessive oxidative polymerization of dopamine, which could affect structural control. Adjusting the molar ratio of the three components allows for flexible control of the copolymer's polarity, rigidity, and functional group density, thereby regulating the subsequent surface modification of the nanoparticles.

[0031] This copolymer possesses a multifunctional synergistic structure, particularly phenolic hydroxyl, carboxyl, and amide groups, which can form hydrogen bonds, coordination, or electronic conjugation with zirconium oxide, copper ions, and PVA molecules. This copolymer not only acts as a surfactant to enhance the dispersion stability of inorganic nanosheets but also as an adhesion enhancer on metal surfaces, increasing the material's adhesion to copper surfaces, conductive adhesives, or other organic substrates. Furthermore, the phenolic hydroxyl structure possesses a certain antioxidant capacity, which helps improve the environmental stability of the repair interface.

[0032] The core function of the functional nano-activator dispersion of the present invention is to "reconstruct" defective areas on the copper surface of a PCB through the synergistic effect of its nanoscale structure and multiple functional groups, providing favorable microscopic interface conditions for the subsequent deposition of conductive materials. The five components in the dispersion work synergistically to address the three functional modules of physical roughening, chemical activation, and bonding interface construction. Specifically, the layered zirconium oxide nanosheets provide a controllable two-dimensional layer structure with a microscopic thickness that matches the copper surface and possesses excellent mechanical strength and chemical stability. After ultrasonic dispersion, they can evenly adhere to the copper surface to form a micro-nanostructured roughening layer, increasing the surface area and anchoring sites. Carboxymethyl chitosan has a large number of carboxyl and amino functional groups, which can form hydrogen bonds and electrostatic adsorption with the surface of the ZrO2 layer, while also imparting good colloidal stability to the system. Its adsorption behavior on the copper surface also enhances the interfacial transition strength between the ZrO2 and the copper surface. Ammonium tripolyphosphate introduces a large number of phosphate groups, which can undergo complex adsorption reactions with the copper surface and simultaneously form phosphate zirconate bonds with the ZrO2 surface, enhancing the synergistic bonding of the entire structure. Furthermore, the naringenin-dopamine-maleic acid copolymer plays a role in interfacial activation and surface energy regulation in this system. Its multi-site structure forms a composite adsorption layer on the copper surface, while also chemically and physically bonding with the metal powder or resin in the conductive adhesive, acting as an "interface bridge." As a dispersion medium, the PVA aqueous solution not only provides initial film-forming properties but also forms weak crosslinks with chitosan and the copolymer, enhancing the flexibility and stability of the dried film.

[0033] The functionalized structural layer formed by drying the dispersion after spraying on the copper surface can effectively improve the adhesion of subsequent conductive materials and the stability of the electrical path, while preventing secondary corrosion or interface shedding of the copper surface under high temperature and oxidizing atmosphere.

[0034] Furthermore, the conductive material in step (4) is a conductive composite material that can form a conductive path by thermal curing or photocuring, including but not limited to nano silver conductive glue, nano copper conductive paste, conductive glue containing low melting point alloy particles, etc.

[0035] Among them, nanosilver conductive adhesive contains silver particles with a particle size of 10-100nm and an epoxy or acrylic resin matrix, suitable for heat curing at 80-150°C or UV curing. Nanocopper conductive paste contains copper particles with a particle size of less than 100nm and an alcohol dispersion medium. It can achieve sintering and conduction after heat treatment at 150-200°C in a protective atmosphere. Conductive adhesive containing low-melting-point alloy particles has a melting point of 60-180°C and can form a stable conductive path by heating and melting and then cooling.

[0036] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0037] The present invention achieves precise positioning of copper surface defects through high-resolution optical imaging and micro-resistance scanning technology, avoiding the problem of missed detection in traditional manual detection and improving the accuracy of repair. A mild cleaning solution containing chelating, antioxidant and wetting ingredients is used to effectively remove local oxidation contamination on the copper surface, while avoiding secondary corrosion and substrate damage, laying a good foundation for subsequent repair. The functional nano-activator dispersion significantly improves the adhesion and interface stability of the conductive material on the copper surface through nanostructure coarsening and surface functional group modification, thereby enhancing the mechanical reliability and electrical performance of the repaired area. Performance testing shows that the PCB board repaired by the present invention has good conductivity recovery and high interface adhesion. After aging for 500 hours in a high temperature and high humidity environment, the resistance change rate is still less than 15%, showing excellent long-term stability. The process of the present invention can significantly reduce resistance growth, avoid interface shedding, and greatly improve the overall performance and service life of the PCB board, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is the SEM image of the repaired surface in Example 1.

[0039] Figure 2 This is the SEM image of the repaired surface in Example 2.

[0040] Figure 3 This is the SEM image of the repaired surface in Example 3.

[0041] Figure 4 This is the SEM image of the repaired surface of Comparative Example 1.

[0042] Figure 5 This is the SEM image of the repaired surface of comparative example 2.

[0043] Figure 6 This is the SEM image of the repaired surface of comparative example 3.

[0044] Figure 7 This is the SEM image of the repaired surface of comparative example 4. DETAILED DESCRIPTION

[0045] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0046] Unless otherwise specified, the raw materials used in the examples are all common commercially available products. The following sources are for illustrative purposes only:

[0047] Layered zirconia nanosheets were purchased from Nanjing Hepurui New Materials Co., Ltd., ZrO2YSZ-CZP-007, with a particle size of 200-300 nm.

[0048] Carboxymethyl chitosan was purchased from Shanghai Jizhi Biochemical Technology Co., Ltd. with a molecular weight of 9600-11000 and a degree of substitution of 70%-75%.

[0049] Ammonium tripolyphosphate was purchased from Hubei Shishun Biotechnology Co., Ltd.

[0050] Nano-silica was purchased from Nanjing Hepury New Materials Co., Ltd. with a particle size of 7-15 nm.

[0051] Polyethyleneimine was purchased from Shanghai Hanluo New Materials Co., Ltd. with a molecular weight of 1000-1500.

[0052] Nanosilver was purchased from Xi'an Qiyue Biotechnology Co., Ltd. with a particle size of 20-50 nm.

[0053] Epoxy resin was purchased from Baling Petrochemical Co., Ltd., model CYDCN-200.

[0054] Example 1

[0055] This embodiment provides a PCB copper surface repair process, including the following steps:

[0056] (1) The PCB to be repaired is placed on an automatic optical inspection (AOI) device for surface imaging inspection. The device used is a Gryphon SL automatic optical inspection device produced by Camtek, Israel. The scanning speed is set to 100 mm / s and the lateral resolution is 1 μm. The abnormal area is extracted and a preliminary defect map is generated through the built-in image recognition algorithm. Subsequently, the PCB is transferred to a four-probe micro-resistance scanner for electrical continuity detection. The device used is a QuadPro-2000 four-probe tester produced by Crest Systems. The applied current is 0.5 mA and the probe spacing is 1 mm. The surface resistance distribution is recorded by grid scanning to identify the local resistance abnormal area to assist in the detection of microcracks or hidden circuits. The optical imaging results are superimposed and fused with the resistance scanning results to generate a three-dimensional damage map to clarify the defect location, type and severity, providing accurate guidance for subsequent targeted repairs.

[0057] (2) According to the defect area information of the PCB board detected in step (1), the PCB board is fixed on the operating platform, and a micro-injection system equipped with a 0.1mm diameter nozzle (applied air pressure 0.2MPa) is used to spray the cleaning liquid at the defect points marked by the detection. The amount of cleaning liquid sprayed at each defect point is 0.05mL. After the spraying is completed, it is allowed to stand for 2 minutes, and then the cleaning area is immediately rinsed with room temperature deionized water using a handheld low-pressure flushing gun. The flushing time is controlled to be 10 seconds. After the flushing is completed, the PCB board is placed in a natural air-drying environment at room temperature to dry, ensuring that there are no visible water marks and stains on the surface;

[0058] The cleaning solution used was prepared from the following components (by mass percentage): 10% tripotassium citrate, 1% sodium lauroyl sarcosinate, 0.2% propyl gallate, 2% glycerol, 1% Tricine, and the balance was deionized water.

[0059] (3) Place the PCB board after cleaning in step (2) on the spraying platform, and use a spray gun (nozzle aperture 0.1mm, air pressure 0.15MPa) to evenly spray the functional nano activator dispersion on the surface of the defect area. The spraying amount of each defect point is controlled to be about 0.05mL. After the spraying is completed, let it stand and dry naturally for 5 minutes to allow the dispersion to form a uniform and continuous nanostructured activation film on the copper surface.

[0060] Functional nano-activator dispersion was prepared as follows:

[0061] (a) 2 g of layered zirconia nanosheets (LDH-ZrO2) were added to 70 g of a 5 wt% aqueous solution of polyvinyl alcohol (PVA 17-88). The mixture was ultrasonically dispersed in an ultrasonic disperser (power 300 W, frequency 40 kHz) for 30 min to form a nanoparticle dispersion.

[0062] (b) Under stirring conditions, 20 g of carboxymethyl chitosan, 1 g of ammonium tripolyphosphate, and 3 g of naringenin-dopamine-maleic acid copolymer were added to the dispersion in sequence. The reaction was continued under magnetic stirring for 90 minutes. The system was maintained at room temperature (25°C). After the reaction was completed, a functional nano-activator dispersion was obtained.

[0063] The naringenin-dopamine-maleic acid copolymer was prepared according to the following method:

[0064] (i) In a 250 mL three-necked flask, 3.7 mmol (approximately 1.0 g) of naringenin, 3.0 mmol (approximately 0.57 g) of dopamine hydrochloride, and 7.4 mmol (approximately 0.76 g) of maleic anhydride were added, and 100 mL of an ethanol-water mixed solvent (the mass ratio of ethanol to water was 3:1) was added and stirred to form a uniform prepolymer reaction solution;

[0065] (ii) Under a nitrogen atmosphere, the reaction solution was heated to 60° C., and potassium persulfate initiator (3% of the mass of naringenin) was added to initiate a free radical copolymerization reaction for 4 hours;

[0066] (iii) After the reaction is complete, the reaction solution is slowly added dropwise to 500 mL of anhydrous ether to form a yellow flocculent precipitate. The precipitate is washed twice with ethanol and twice with deionized water, filtered, and dried in a vacuum oven at 40°C for 12 hours to obtain a naringenin-dopamine-maleic acid copolymer.

[0067] (4) Nanosilver particles and epoxy resin matrix are uniformly dispersed to prepare nanosilver conductive glue, and conductive glue is applied to the defective area after treatment in step (3) using precision micro-dispensing equipment. The amount of glue dispensed is controlled to be 0.03 mL per defect point. After the dispensing is completed, the PCB board is placed in a hot air circulation oven and thermally cured at 120°C for 30 minutes to achieve the construction of a conductive path in the repair area, and then naturally cooled to room temperature to complete the repair.

[0068] The SEM image of the repaired surface of Example 1 is as follows: Figure 1 As shown in the figure, it can be seen that the surface of the repaired position is smooth and flat.

[0069] Example 2

[0070] This embodiment provides a PCB copper surface repair process, which differs from Example 1 in that the cleaning solution used is prepared from the following components (by mass percentage): 18% tripotassium citrate, 2% sodium lauroyl sarcosinate, 0.1% propyl gallate, 1% glycerol, 1% tricine, and the balance is deionized water.

[0071] The SEM image of the repaired surface of Example 2 is as follows: Figure 2 As shown in the figure, it can be seen that the surface of the repaired position is smooth and flat.

[0072] Example 3

[0073] This embodiment provides a PCB copper surface repair process, which differs from Embodiment 1 in that:

[0074] Functional nano-activator dispersion was prepared as follows:

[0075] (a) 4 g of layered zirconia nanosheets (LDH-ZrO2) were weighed and added to 70 g of a 5 wt% aqueous solution of polyvinyl alcohol (PVA 17-88). The mixture was treated in an ultrasonic disperser (power 300 W, frequency 40 kHz) for 30 min to form a nanoparticle dispersion.

[0076] (b) 15 g of carboxymethyl chitosan, 1 g of ammonium tripolyphosphate, and 5 g of naringenin-dopamine-maleic acid copolymer were sequentially added to the dispersion under stirring. The reaction was continued under magnetic stirring for 90 minutes while the system was maintained at room temperature (25°C). After the reaction was completed, a functional nano-activator dispersion was obtained.

[0077] The SEM image of the repaired surface of Example 3 is as follows: Figure 3 As shown in the figure, it can be seen that the surface of the repaired position is smooth and flat.

[0078] Comparative Example 1

[0079] This comparative example provides a PCB copper surface repair process, which differs from Example 1 in that the cleaning solution used is prepared from the following components (by mass percentage): 30% tripotassium citrate, 1% sodium lauroyl sarcosinate, 0.01% propyl gallate, 7% glycerol, 2% tricine, and the balance is deionized water.

[0080] The SEM image of the repaired surface of Comparative Example 1 is as follows: Figure 4 As shown in the figure, it can be seen that there is a slight step difference in the repair position.

[0081] Comparative Example 2

[0082] This comparative example provides a PCB copper surface repair process, which differs from Example 1 in that the cleaning solution used is prepared from the following components (by mass percentage): 10% sodium citrate, 1% sodium lauroyl glutamate, 0.2% propyl gallate, 2% glycerol, 1% tricine, and the balance is deionized water.

[0083] The SEM image of the repaired surface of Comparative Example 2 is as follows: Figure 5 As shown in the figure, it can be seen that there is a slight step difference in the repair position.

[0084] Comparative Example 3

[0085] This comparative example provides a PCB copper surface repair process, which differs from Example 1 in that the functional nano-activator dispersion is prepared according to the following method:

[0086] (a) 10 g of layered zirconia nanosheets (LDH-ZrO2) were added to 70 g of a 5 wt% aqueous solution of polyvinyl alcohol (PVA 17-88). The mixture was treated in an ultrasonic disperser (power 300 W, frequency 40 kHz) for 30 min to form a nanoparticle dispersion.

[0087] (b) Under stirring conditions, 20 g of carboxymethyl chitosan, 5 g of ammonium tripolyphosphate, and 0.3 g of naringenin-dopamine-maleic acid copolymer were added to the dispersion in sequence. The reaction was continued under magnetic stirring for 90 minutes. The system was maintained at room temperature (25°C). After the reaction was completed, a functional nano-activator dispersion was obtained.

[0088] The SEM image of the repaired surface of Comparative Example 3 is as follows: Figure 6 As shown in the figure, it can be seen that there is a slight step difference in the repair position.

[0089] Comparative Example 4

[0090] This comparative example provides a PCB copper surface repair process, which differs from Example 1 in that the functional nano-activator dispersion is prepared according to the following method:

[0091] (a) 2 g of nano-silica was weighed and added to 70 g of a 5 wt % aqueous solution of polyvinyl alcohol (PVA 17-88). The mixture was treated in an ultrasonic disperser (power 300 W, frequency 40 kHz) for 30 minutes to form a nanoparticle dispersion.

[0092] (b) Under stirring conditions, 20 g of carboxymethyl chitosan, 1 g of ammonium tripolyphosphate, and 3 g of polyethyleneimine were added to the dispersion in sequence, and the reaction was continued under magnetic stirring for 90 minutes. The system was maintained at room temperature (25° C.). After the reaction was completed, a functional nano-activator dispersion was obtained.

[0093] The SEM image of the repaired surface of Comparative Example 4 is as follows: Figure 7 As shown in the figure, it can be seen that there is a slight step difference in the repair position.

[0094] Performance Testing

[0095] Performance tests were conducted on the repaired PCBs of the present invention and comparative examples to evaluate the conductivity, interfacial adhesion, and long-term stability of the repaired defective areas. Interfacial adhesion was tested according to the GB / T 5270-2005 standard, conductivity was tested according to the GB / T 4677-2002 standard, and long-term stability was tested according to the GB / T 2423.3-2016 standard.

[0096] The test method is as follows: after completing the repair process of each embodiment and comparative example, a test point of 5mm×5mm in the repair area is taken, and the resistance value of the repair area is measured by a four-probe micro-resistance tester (QuadPro-2000, Crest Systems). After the repair area and the copper foil are pasted with a special test tape, a tensile tester (Instron 3365 universal testing machine) is used to measure the interface peel strength, the tensile speed is set to 50mm / min, and the maximum peel force value is recorded to evaluate the interface adhesion of the repair area. The repaired PCB board is placed in a constant temperature and humidity chamber (85℃ / 85% RH) for aging for 500 hours, the resistance value test is repeated, and the percentage change of resistance is recorded. Five points are randomly sampled for both the resistance test and the peel strength test, and the average value of the results is taken as the evaluation standard. The test results are shown in Table 1.

[0097] Table 1: Test results

[0098]

[0099] The above results show that the average resistance value of the repaired area of the PCB copper surface repair process of the present invention is basically consistent with the normal copper surface resistance (0.003~0.005Ω / cm), the interface adhesion strength is high, the interface bonding is firm, no obvious delamination or falling off occurs, the resistance change rate after aging is less than 15%, the conductive performance remains good, and it has excellent long-term stability. The average resistance value of the repaired area of Example 1 is higher than the normal range, indicating that the conductive performance is significantly reduced; the interface adhesion strength is low, and the interface is prone to peeling, indicating that the excessive proportion of tripotassium citrate in the cleaning solution causes excessive complex corrosion and destroys the integrity of the copper surface. The average resistance value of the repaired area of Example 2 is significantly higher than that of the embodiment, the interface adhesion strength is significantly reduced, the residual contamination on the copper surface is serious, and the surface bonding is not firm. The average resistance value of the repaired area of Example 3 is also higher than the normal range, and the conductive performance is reduced; the interface adhesion strength is significantly lower than that of the embodiment, the excessive amount of nanosheets in the activator formula causes serious agglomeration, the coating structure is uneven, and the interface bonding effect is poor. The average resistance of the repaired area in Comparative Example 4 was also higher than normal, indicating poor conductivity. The interfacial adhesion strength was significantly reduced, as the silica particles and polyethyleneimine in the dispersion were unable to form an effective and stable interfacial activation structure. Severe sedimentation resulted in a discontinuous coating and significantly weakened interfacial bonding. The resistance change rate of the comparative samples after aging was generally greater than 50%, and the conductivity decreased significantly, indicating a significant lack of long-term stability.

[0100] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A PCB copper surface repair process, comprising the following steps: (1) Perform surface inspection on the copper surface of the PCB to be repaired, identify and locate copper surface defects, and generate a three-dimensional damage map to guide subsequent repair operations; (2) using a cleaning solution to spray the defective area identified in step (1) at a fixed point, wherein the cleaning solution contains tripotassium citrate, sodium lauroyl sarcosinate, propyl gallate, glycerin and Tricine, and reacting for a certain time after spraying, and then rinsing with deionized water and drying naturally; (3) spraying a functional nano-activator dispersion onto the defective area treated in step (2), and allowing it to dry to form a nanostructured activation layer; the raw materials for preparing the functional nano-activator dispersion include, by weight: 1-5 parts of layered zirconia nanosheets, 10-30 parts of carboxymethyl chitosan, 0.5-2 parts of ammonium tripolyphosphate, 1-5 parts of naringenin-dopamine-maleic acid copolymer, and 60-80 parts of a 4-6w% polyvinyl alcohol aqueous solution; (4) Applying a conductive material on the nanostructured activation layer formed in step (3) and curing to complete the repair.

2. The repair process according to claim 1, characterized in that: In step (1), the copper surface of the PCB board is inspected by high-resolution optical imaging and micro-resistance scanning.

3. The repair process according to claim 1, characterized in that: The mass percentages of the raw materials in the cleaning solution in step (2) are: 5-20% tripotassium citrate, 0.1-2% sodium lauroyl sarcosinate, 0.05-1% propyl gallate, 0.5-5% glycerol, 0.5-2% Tricine, and the balance is deionized water.

4. The repair process according to claim 1, characterized in that: The reaction time in step (2) is 1-3 minutes.

5. The repair process according to claim 1, characterized in that: The functional nano-activator dispersion in step (3) is prepared as follows: (a) adding layered zirconia nanosheets to a polyvinyl alcohol aqueous solution and ultrasonically dispersing the nanosheets for 10-60 minutes to form a nanoparticle dispersion; (b) adding carboxymethyl chitosan, ammonium tripolyphosphate, and naringenin-dopamine-maleic acid copolymer to the dispersion in sequence, stirring and reacting for 1-2 hours to obtain the functional nano activator dispersion.

6. The repair process according to claim 5, characterized in that: The naringenin-dopamine-maleic acid copolymer was prepared according to the following method: (i) adding naringenin, dopamine hydrochloride, and maleic anhydride to an ethanol-water mixed solvent and stirring to form a prepolymer reaction liquid; (ii) heating the prepolymer reaction solution to 50-70° C. under nitrogen protection, and adding an initiator to initiate a copolymerization reaction for 2-6 hours; (iii) After the reaction is completed, the product is added dropwise to anhydrous ether for precipitation, and the precipitate is washed, filtered, and dried to obtain the target product, naringenin-dopamine-maleic acid copolymer.

7. The repair process according to claim 6, characterized in that: The molar ratio of naringenin, dopamine hydrochloride and maleic anhydride is 1: (0.8-1.2): (1.5-3.0).

8. The repair process according to claim 6, characterized in that: The mass ratio of ethanol to water in the ethanol-water mixed solvent is (2-5):1; the mass ratio of naringenin to the ethanol-water mixed solvent is 1:(50-80).

9. The repair process according to claim 6, characterized in that: The initiator is potassium persulfate or azobisisobutyronitrile, and the mass ratio of the initiator to naringenin is (0.01-0.05):

1.

10. The repair process according to claim 1, characterized in that: The conductive material in step (4) is a conductive composite material that can form a conductive path by thermal curing or photocuring.

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