PCB copper surface repair process

Abstract

The application 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 a PCB, identifying and positioning defects, and generating a three-dimensional damage atlas; using a cleaning solution containing tri-potassium citrate, sodium lauroyl sarcosinate, propyl gallate, glycerol and Trici ne to perform spot cleaning on the defect area; spraying a functional nano-activating agent dispersion liquid made of layered zirconium oxide nanosheets, carboxymethyl chitosan, ammonium tripolyphosphate, naringenin-dopamine-maleic acid copolymer and polyvinyl alcohol aqueous solution to form a nano-structure activation layer; and finally applying a conductive material to fill and repair the defects. The process can realize accurate repair of copper surface micro-defects, enhance the conductivity and interface bonding force of the repaired area, and the repaired PCB has excellent long-term stability, effectively improving the overall reliability and service life of the PCB.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of circuit board repair, and particularly relates to a PCB copper surface repair process. BACKGROUND

[0002] Printed Circuit Board (PCB) is an indispensable basic component in modern electronic equipment, and is widely used in various high-precision fields such as communication, automobile, aerospace, medical electronics, etc. The copper foil circuit on the PCB realizes the electrical connection and signal transmission between electronic components, so the quality of the copper surface directly determines the conductivity and service life of the whole board.

[0003] In the manufacturing, handling, assembly and later operation and maintenance process of the PCB, the copper surface is easily damaged in various forms such as physical scratching, chemical corrosion, and electromigration fracture. Once a defect occurs, it may not only cause local conduction failure and signal interference, but also cause safety hazards such as short circuit due to copper ion migration. Therefore, the rapid, accurate detection and efficient repair of copper surface defects are important guarantees for ensuring the reliability of the PCB.

[0004] At present, the repair of PCB copper surface defects in the industry mostly relies on manual visual inspection, extensive surface treatment methods and traditional welding repair methods. These methods have obvious limitations: on the one hand, manual detection cannot accurately identify fine cracks or deep corrosion, and the missed detection rate is high; on the other hand, conventional repair processes such as overall cleaning, hot pressure welding or mechanical polishing are easy to cause secondary damage to non-damaged areas, and even cause new defects. In addition, the lack of professional repair materials and fine processing methods leads to poor adhesion between the repaired area and the original copper surface, low reliability, and the risk of unstable conduction or peeling after long-term use.

[0005] In recent years, with the continuous improvement of the reliability requirements of precision electronic manufacturing on PCB, the industry urgently needs an efficient copper surface defect repair process that integrates "accurate detection - point repair - enhanced bonding". In the cleaning and roughening stage, the traditional use of acid and alkali reagents is generally highly corrosive and has poor selectivity, making it difficult to achieve local precise processing. Common roughening agents such as high-concentration oxidizing agents and micro-etching solutions can easily cause excessive corrosion of the surrounding circuit, seriously affecting the circuit performance.

[0006] Therefore, it is urgent to develop a more selective, mild and functional repair strategy that can accurately identify, gently remove and efficiently regenerate micro-defects on the copper surface, providing a better solution for improving the overall reliability and extending the service life of the PCB. SUMMARY

[0007] The application aims to provide a PCB copper surface repair process, which can realize high-precision detection, pinpoint cleaning and surface activation repair of micro-defects on the copper surface of a circuit board, and has the advantages of simple operation, strong selectivity, small damage to the substrate, high repair bonding force and the like.

[0008] In order to achieve the above-mentioned purpose, the application provides the following technical solutions.

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

[0010] (1) performing surface detection on the copper surface of a PCB to be repaired, identifying and positioning defects on the copper surface, and generating a three-dimensional damage map for guiding subsequent repair operations;

[0011] (2) using a cleaning solution to perform pinpoint spraying on the defect area identified in step (1), wherein the cleaning solution comprises tri-potassium citrate, sodium lauroyl sarcosinate, propyl gallate, glycerol and Tricine, and after spraying is completed, a certain time of reaction is performed, then deionized water is used for rinsing and natural drying;

[0012] (3) spraying a functional nano-activator dispersion liquid on the defect area treated in step (2), and standing for drying to form a nano-structured activation layer; the preparation raw materials of the functional nano-activator dispersion liquid comprise, by weight fraction, 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 4-6 w% polyvinyl alcohol aqueous solution;

[0013] (4) applying a conductive material on the nano-structured activation layer formed in step (3), and completing repair after curing.

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

[0015] The high-resolution optical imaging uses a short-wavelength light source and a high-pixel sensor to scan the PCB copper surface, can clearly identify micro-defects such as surface scratches and corrosion, and generates a surface map with rich details through image processing. The micro-resistance scanning measures the local resistance change of the copper surface, and assists in finding micro-cracks or hidden open circuits that are difficult to visually identify by optical imaging. The combination of the two can quickly locate surface physical damage and detect electrical abnormalities, and the generated three-dimensional damage map provides data support for subsequent accurate repair, significantly improving the sensitivity, accuracy and reliability of detection. Specifically, the high-resolution optical imaging can be realized by a 3D laser confocal scanner, a white light interferometer or a high-resolution automatic optical inspection (AOI) system; the micro-resistance scanning can be realized by a four-probe micro-resistance tester or a local impedance scanning device.

[0016] Further, the mass percentage of each raw material in the cleaning solution in step (2) is: 5-20% of tri-potassium citrate, 0.1-2% of sodium lauroyl sarcosinate, 0.05-1% of propyl gallate, 0.5-5% of glycerol, 0.5-2% of Tricine, and the rest is deionized water.

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

[0018] The tri-potassium citrate in the cleaning solution serves as a main complexing agent, which can effectively complex copper oxide (Cu2O, CuO) and other metal ion deposits on the surface of the copper under neutral or weakly acidic conditions, and realize mild stripping of pollutants through complexation desorption, thereby avoiding damage to the copper surface caused by strong acid corrosion. The sodium lauroyl sarcosinate, as a mild anionic surfactant, has good wetting, penetration and interfacial activation capabilities, can reduce the surface tension of the liquid, and make the cleaning solution rapidly spread and penetrate into the micro-cracks in the defect area of the copper surface, while assisting in stripping and removing the dirt. The propyl gallate, as an antioxidant functional component in the cleaning solution, is rich in polyphenolic hydroxyl groups, can capture free radicals, inhibit the re-oxidation reaction of the copper surface, and protect the freshly exposed copper surface during the cleaning process, thereby reducing the risk of secondary corrosion caused by cleaning. The glycerol, as a hydrophilic aid, can buffer the evaporation speed of the solution during the cleaning process, maintain a local humid environment, and prevent the copper surface from drying and cracking or forming a new oxide film in a short time after cleaning by forming a thin protective film.

[0019] The cleaning solution has the comprehensive advantages of mild decontamination, selective complexation, prevention of secondary oxidation, and protection of the integrity of the copper surface, and can realize precise and low-damage cleaning of the defect area of the PCB copper surface, thereby laying a good foundation for subsequent surface activation and repair operations.

[0020] Further, the functional nano activator dispersion liquid in step (3) is prepared as follows:

[0021] (a) adding layered zirconium oxide nanosheets into a polyvinyl alcohol aqueous solution, ultrasonic dispersion for 10-60 minutes to form a nanoparticle dispersion;

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

[0023] Further, the naringenin-dopamine-maleic acid copolymer in step (3) is prepared as follows:

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

[0025] (ii) under the protection of nitrogen, the prepolymer reaction solution is heated to 50-70℃, and an initiator is added to initiate the copolymerization reaction, and the reaction time is 2-6 hours;

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

[0027] Further, 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; the mass ratio of naringenin to the ethanol-water mixed solvent is 1:(50-80).

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

[0029] The present application introduces naringenin-dopamine-maleic acid copolymer into the functional nano-activator dispersion liquid. Naringenin is a natural flavonoid polyphenol compound, which contains multiple phenolic hydroxyl groups in the molecular structure and can form coordination complex with metal ions, and has antioxidant and anti-free radical ability. Dopamine molecule contains o-diphenol structure and primary amine functional group, has good metal surface adhesion and interfacial activity, and is the basic structure of polydopamine high adhesion coating. Maleic anhydride is a high-reactivity bifunctional monomer, which can undergo ring-opening acylation or free radical addition reaction with various nucleophilic groups (such as phenolic hydroxyl group and amine group) to form stable ester bond or amide bond.

[0030] In the present process, the three components form a copolymer through copolymerization in an ethanol-water mixed solution. Maleic anhydride undergoes free radical polymerization under the action of an initiator to initiate the reaction of dopamine and naringenin, generating a chain or network copolymer structure. The reaction conditions are controlled at 50-70℃ and 2-6 hours, which can ensure the reaction activity while avoiding excessive oxidation polymerization of dopamine to affect the structure control. By adjusting the molar ratio of the three components, the polarity, rigidity and functional group density of the copolymer can be flexibly controlled, thereby producing a regulating effect on the subsequent surface modification behavior of nanoparticles.

[0031] The copolymer has a multi-functional group synergistic structure, especially the phenolic hydroxyl group, carboxyl group and amide group, which can form hydrogen bond, coordination or electron conjugation with zirconium oxide, copper ion and PVA molecule. This copolymer not only can be used as an interfacial active agent to improve the dispersion stability of inorganic nanosheets, but also can be used as an adhesion enhancer for metal surface to increase the adhesion strength of the material to copper surface, conductive adhesive or other organic substrates. At the same time, the phenolic hydroxyl structure also has certain antioxidant ability, which helps to improve the environmental stability of the repaired interface.

[0032] The core function of the functional nano-activator dispersion solution of the present application is to perform "surface reconstruction" on the defect area of the PCB copper surface through the synergistic effect of nano-scale structure and multi-functional groups, so as to provide good micro-interface conditions for the deposition of subsequent conductive materials. The five components in the dispersion solution cooperate synergistically, taking into account three functional modules of physical roughening, chemical activation and adhesive interface construction. Specifically, the layered zirconium oxide nanosheet provides a controllable two-dimensional sheet structure, the micro-thickness of which can match the copper surface and has good mechanical strength and chemical stability. After ultrasonic dispersion, it can uniformly adhere to the copper surface to form a micro-nano structure roughening layer, increase the surface specific area and anchor site. The carboxymethyl chitosan has a large number of carboxyl and amino functional groups, which can form hydrogen bonds and electrostatic adsorption with the surface of ZrO2 sheet, and at the same time, it can also give the system good colloidal stability. The adsorption behavior of carboxymethyl chitosan on the copper surface also enhances the interfacial transition strength between ZrO2 and the copper surface. The introduction of ammonium tripolyphosphate into a large number of phosphate groups can occur complex adsorption reaction with the copper surface, and at the same time, it can also occur zirconium phosphate salt bonding with the surface of ZrO2, thereby improving the synergistic combination of the whole structure. In addition, the naringenin-dopamine-maleic acid copolymer plays a role in interface activation and surface energy adjustment in the system. The multi-site structure of the copolymer forms a composite adsorption layer with the copper surface, and can also form chemical / physical combination with metal powder or resin in the conductive adhesive, thereby playing a role in "interface bridging". The PVA aqueous solution as a dispersion medium not only provides preliminary film-forming ability, but also forms weak cross-linking with chitosan and copolymer, thereby improving the flexibility and stability of the film layer after drying.

[0033] The functionalized structure layer formed by drying the dispersion solution of the present application after spraying on the copper surface can effectively improve the adhesion and electrical path stability of the subsequent conductive material, and at the same time, can avoid secondary corrosion or interface peeling of the copper surface in an oxidizing atmosphere at high temperature.

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

[0035] The nano-silver conductive adhesive contains silver particles with a particle size of 10-100 nm and an epoxy resin or acrylic resin matrix, and is suitable for thermal curing or UV curing at 80-150 DEG C. The nano-copper conductive paste contains copper particles with a particle size of less than 100 nm and an alcohol dispersion medium, and can realize sintering conduction by heat treatment in a protective atmosphere at 150-200 DEG C. The conductive adhesive containing low-melting-point alloy particles has an alloy particle melting point of 60-180 DEG C, and can form a stable conductive channel by heating, melting and cooling.

[0036] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0037] The present application realizes accurate positioning of copper surface defects through high-resolution optical imaging and micro-resistance scanning technology, avoids the missed detection problem of traditional manual detection, and improves the accuracy of repair. The mild cleaning solution containing complexing, antioxidant and wetting components can effectively remove local oxidation pollution on the copper surface, while avoiding secondary corrosion and substrate damage, laying a good foundation for subsequent repair. The functional nano activator dispersion liquid significantly improves the adhesion and interface stability of conductive materials on the copper surface through nano structure roughening and surface functional group modification, thereby enhancing the mechanical reliability and electrical performance of the repair area. After performance testing, the repaired PCB board of the present application has good conductivity recovery, high interface adhesion, and 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 application can significantly reduce resistance growth, avoid interface peeling, greatly improve the overall performance and service life of the PCB board, and has wide application prospects. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 SEM image of the repair surface of Example 1.

[0039] Figure 2 SEM image of the repair surface of Example 2.

[0040] Figure 3 SEM image of the repair surface of Example 3.

[0041] Figure 4 SEM image of the repair surface of Comparative Example 1.

[0042] Figure 5 SEM image of the repair surface of Comparative Example 2.

[0043] Figure 6 SEM image of the repair surface of Comparative Example 3.

[0044] Figure 7 SEM image of the repair surface of Comparative Example 4. DETAILED DESCRIPTION

[0045] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0046] The raw materials used in the examples are all ordinary commercially available products unless otherwise specified. The following sources are exemplary:

[0047] Layered zirconium oxide nanosheets were purchased from Nanjing Hupu New Material Co., Ltd., Zr02YSZ-CZP-007, particle size 200-300 nm.

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

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

[0050] Nanosilica was purchased from Nanjing Hupu New Material Co., Ltd., particle size 7-15 nm.

[0051] Polyethyleneimine was purchased from Shanghai Hanluo New Material Co., Ltd., molecular weight 1000-1500.

[0052] Nanosilver was purchased from Xi'an Qiyue Biological Technology Co., Ltd., particle size 20-50 nm.

[0053] Epoxy resin was purchased from Balin Petroleum Chemical Industry Co., Ltd., model CYDCN-200.

[0054] Example 1

[0055] The present embodiment provides a PCB copper surface repair process, comprising the following steps:

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

[0057] (2) According to the PCB defect area information detected in step (1), the PCB is fixed on the operation platform, and a micro-injection system (0.2 MPa air pressure) equipped with a 0.1 mm caliber nozzle is used to spray cleaning liquid at the detected defect points. The amount of cleaning liquid sprayed at each defect point is 0.05 mL. After spraying is completed, the reaction is allowed to stand for 2 minutes, and then a handheld low-pressure flushing gun is immediately used to flush the cleaning area with normal temperature deionized water. The flushing time is controlled to be 10 seconds. After flushing is completed, the PCB is placed in a room temperature natural drying environment for drying, to ensure that the surface is free of visible water marks and stains;

[0058] The cleaning liquid used is prepared from the following components (by mass percentage): 10% of tri-potassium citrate, 1% of sodium lauroyl sarcosinate, 0.2% of propyl gallate, 2% of glycerol, 1% of Tricine, and the balance being deionized water.

[0059] (3) The PCB after cleaning treatment in step (2) is placed on a spraying platform, and a spray gun (nozzle caliber 0.1 mm, air pressure 0.15 MPa) is used to uniformly spray a functional nano activator dispersion liquid on the surface of the defect area. The spraying amount at each defect point is controlled to be about 0.05 mL. After spraying is completed, the dispersion liquid is allowed to stand and dry naturally for 5 minutes, to form a uniform and continuous nano structure activation film on the copper surface.

[0060] The functional nano activator dispersion liquid is prepared according to the following method:

[0061] (a) 2 g of layered zirconium oxide nanosheets (LDH-ZrO2) is added to 70 g of a 5 wt% polyvinyl alcohol (PVA 17-88) aqueous solution, and is treated in an ultrasonic disperser (power 300 W, frequency 40 kHz) for 30 minutes, to form a nanoparticle dispersion;

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

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

[0064] (i) 3.7 mmol (about 1.0 g) of naringenin, 3.0 mmol (about 0.57 g) of dopamine hydrochloride and 7.4 mmol (about 0.76 g) of maleic anhydride are added to a 250 mL three-necked flask, and 100 mL of an ethanol-water mixed solvent (mass ratio of ethanol to water 3:1) is added, to form a uniform prepolymer reaction liquid under stirring;

[0065] (ii) under the protection of nitrogen atmosphere, the reaction solution is heated to 60℃, and potassium persulfate initiator (3% of the mass of naringin) is added to initiate the free radical copolymerization, and the reaction time is 4 hours;

[0066] (iii) after the reaction is completed, the reaction solution is slowly added dropwise into 500 mL of anhydrous ether to form a yellow flocculent precipitate, the precipitate is washed twice with ethanol and deionized water, and then filtered and dried in a 40℃ vacuum drying oven for 12 hours to obtain the naringin-dopamine-maleic acid copolymer.

[0067] (4) The nano-silver particles are uniformly dispersed in the epoxy resin matrix to prepare a nano-silver conductive adhesive. A precise micro-droplet dispensing device is used to apply the conductive adhesive to the defect area treated in step (3) at a fixed point. The amount of droplet dispensing is controlled to be 0.03 mL per defect point. After the droplet dispensing is completed, the PCB board is placed in a hot air circulating oven and heat cured at 120℃ for 30 minutes to realize the construction of the conductive path in the repaired area. Then, the repaired PCB board is naturally cooled to room temperature, and the repair is completed.

[0068] The SEM image of the repaired surface of Example 1 is shown in Figure 1 The repaired surface is smooth and flat.

[0069] Example 2

[0070] The PCB copper surface repair process provided in this embodiment is different from that of Example 1 in that the cleaning solution used is prepared from the following components (by mass percentage): potassium citrate 18%, sodium lauroyl sarcosinate 2%, propyl gallate 0.1%, glycerol 1%, Tricine 1%, and the balance is deionized water.

[0071] The SEM image of the repaired surface of Example 2 is shown in Figure 2 The repaired surface is smooth and flat.

[0072] Example 3

[0073] The PCB copper surface repair process provided in this embodiment is different from that of Example 1 in that:

[0074] The functional nano-activator dispersion liquid is prepared as follows:

[0075] (a) 4 g of layered zirconium oxide nanosheets (LDH-ZrO2) is added to 70 g of a 5wt% polyvinyl alcohol (PVA 17-88) aqueous solution, and treated in an ultrasonic disperser (power 300 W, frequency 40 kHz) for 30 minutes to form a nanoparticle dispersion;

[0076] (b) under stirring, 15 g of carboxymethyl chitosan, 1 g of ammonium tripolyphosphate and 5 g of naringin-dopamine-maleic acid copolymer were sequentially added into the dispersion, and the magnetic stirring reaction was continued for 90 minutes, the system was kept 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 shown in Figure 3 It can be seen from the image that the repaired position is smooth and flat.

[0078] Comparative Example 1

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

[0080] The SEM image of the repaired surface of Comparative Example 1 is shown in Figure 4 It can be seen from the image that the repaired position has a slight step difference.

[0081] Comparative Example 2

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

[0083] The SEM image of the repaired surface of Comparative Example 2 is shown in Figure 5 It can be seen from the image that the repaired position has a slight step difference.

[0084] Comparative Example 3

[0085] This comparative example provides a PCB copper surface repair process, which is different from Example 1 in that the functional nano-activator dispersion is prepared as follows:

[0086] (a) 10 g of layered zirconium oxide nanosheets (LDH-ZrO2) were weighed and added to 70 g of a 5 wt% polyvinyl alcohol (PVA 17-88) aqueous solution, and treated in an ultrasonic disperser (power 300 W, frequency 40 kHz) for 30 minutes 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 sequentially added to the dispersion, and the magnetic stirring reaction was continued for 90 minutes, and the system was kept at room temperature (25℃). After the reaction was completed, a functional nano-activator dispersion was obtained.

[0088] The SEM image of the repaired surface of Comparative Example 4 is shown in Figure 6 It can be seen from the image that there is a slight step difference in the repaired position.

[0089] Comparative Example 4

[0090] This comparative example provides a PCB copper surface repair process, which is different from Example 1 in that the functional nano-activator dispersion is prepared as follows:

[0091] (a) 2 g of nano-silica was weighed and added to 70 g of a 5wt% polyvinyl alcohol (PVA 17-88) aqueous solution, and 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, 5 g of ammonium tripolyphosphate and 0.3 g of naringenin-dopamine-maleic acid copolymer were sequentially added to the dispersion, and the magnetic stirring reaction was continued for 90 minutes, and the system was kept at room temperature (25℃). 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 shown in Figure 7 It can be seen from the image that there is a slight step difference in the repaired position.

[0094] Performance test

[0095] The repaired PCBs of the examples and comparative examples of the present application were tested for performance, and the conductivity, interface adhesion and long-term stability of the repaired defect area were evaluated. The interface adhesion was tested in accordance with the standard GB / T 5270-2005, the conductivity was tested in accordance with the standard GB / T 4677-2002, and the long-term stability was tested in accordance with the standard GB / T 2423.3-2016.

[0096] The test method is as follows: after the repair process of each example and comparative example is completed, the test point with a repair area of 5 mm x 5 mm is taken, and the resistance value of the repair area is determined by a four-probe micro-resistance tester (Quad Pro-2000, Crest Systems). After the repair area is pasted with a test tape special for copper foil pasting, the interfacial peeling strength is determined by a tensile tester (Instron 3365 universal testing machine), the tensile speed is set to 50 mm / min, and the maximum peeling force value is recorded to evaluate the interfacial adhesion of the repair area. The repaired PCB board is placed in a constant temperature and humidity box (85℃ / 85% RH) for aging for 500 hours, and the resistance value test is repeated, and the resistance change percentage is recorded. The resistance test and the peeling strength test are randomly sampled for 5 points, and the average value 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 repair area of the PCB copper surface repair process of the application is basically consistent with the normal copper surface resistance (0.003-0.005 Ω / cm), the interfacial adhesion strength is high, the interface is firmly combined, and there is no obvious delamination or peeling phenomenon, the resistance change rate after aging is less than 15%, the conductive performance is good, and the long-term stability is excellent. The average resistance value of the repair area of Comparative Example 1 is higher than the normal range, indicating that the conductive performance is significantly reduced; the interfacial adhesion strength is low, and the interface is prone to peeling, indicating that the excessive complex corrosion caused by the excessive proportion of tripotassium citrate in the cleaning solution damages the integrity of the copper surface. The average resistance of the repair area of Comparative Example 2 is significantly higher than that of the examples, the interfacial adhesion strength is significantly reduced, and the copper surface is seriously contaminated, resulting in poor surface combination. The average resistance value of the repair area of Comparative Example 3 is also higher than the normal range, and the conductive performance is reduced; the interfacial adhesion strength is significantly lower than that of the examples, the excessive amount of nanosheets in the activator formula causes serious agglomeration, the coating structure is uneven, and the interfacial combination effect is poor. The average resistance value of the repair area of Comparative Example 4 is also higher than the normal range, and the conductive performance is poor; the interfacial adhesion strength is significantly reduced, the silica particles and polyethyleneimine in the dispersion liquid cannot form an effective and stable interfacial activation structure, and the sedimentation is serious, resulting in discontinuous coating and significantly weakened interfacial combination. The resistance change rate of the aging sample of Comparative Example is generally higher than 50%, and the conductive performance is significantly reduced, indicating that the long-term stability is obviously insufficient.

[0100] The above is a preferred embodiment of the application, and it should be pointed out that for ordinary skilled persons in the art, several improvements and refinements can be made without departing from the principles of the application, and these improvements and refinements should also be considered as the protection scope of the application.

Claims

1. A PCB copper surface repair process, comprising the following steps: (1) Surface detection is performed on the copper surface of the PCB to be repaired, and the copper surface defects are identified and located to generate a three-dimensional damage map for guiding the subsequent repair operation; (2) A cleaning solution is used to spray the defect area identified in step (1) at a fixed point, and after spraying, the solution is reacted for a certain period of time, then washed with deionized water and naturally dried; The mass percentage of raw materials in the cleaning solution is: 5-20% of tri-potassium citrate, 0.1-2% of sodium lauroyl methylamino acid, 0.05-1% of propyl gallate, 0.5-5% of glycerol, 0.5-2% of Tricine, and the rest is deionized water; (3) spraying a functional nano-activator dispersion liquid on the defect area treated in step (2), and standing and drying to form a nano-structured activation layer; the preparation raw materials of the functional nano-activator dispersion liquid include, by weight fraction: 1-5 parts of layered zirconium oxide nanosheet, 10-30 parts of carboxymethyl chitosan, 0.5-2 parts of ammonium tripolyphosphate, 1-5 parts of naringin-dopamine-maleic acid copolymer, and 60-80 parts of 4-6wt% polyvinyl alcohol aqueous solution; (4) A conductive material is applied on the nano-structured activation layer formed in step (3), and after curing, the repair is completed; The naringin-dopamine-maleic acid copolymer is prepared by the following method: (i) Naringin, dopamine hydrochloride and maleic anhydride are added to an ethanol-water mixed solvent in a molar ratio of 1:(0.8-1.2):(1.5-3.0), and the mixture is stirred to form a prepolymer reaction solution; (ii) The prepolymer reaction solution is heated to 50-70℃ under nitrogen protection, and an initiator is added to initiate the copolymerization reaction, and the reaction time is 2-6 hours; (iii) After the reaction is completed, the product is added dropwise into anhydrous ether for precipitation, and the precipitate is washed, filtered and dried to obtain the target product naringin-dopamine-maleic acid copolymer.

2. The repair process of claim 1, wherein: In step (1), the copper surface of the PCB is detected by high-resolution optical imaging and micro-resistance scanning.

3. The repair process of claim 1, wherein: The reaction time in step (2) is 1-3 minutes.

4. The repair process of claim 1, wherein: In step (3), the functional nano-activator dispersion liquid is prepared by the following method: (a) Layered zirconium oxide nanosheet is added to polyvinyl alcohol aqueous solution, and ultrasonic dispersion is performed for 10-60 minutes to form a nano-particle dispersion; (b) Carboxymethyl chitosan, ammonium tripolyphosphate and naringin-dopamine-maleic acid copolymer are sequentially added to the dispersion, and stirring reaction is performed for 1-2 hours to obtain the functional nano-activator dispersion liquid.

5. The repair process of claim 4, wherein: The mass ratio of ethanol to water in the ethanol-water mixed solvent is (2-5):1; the mass ratio of naringin to the ethanol-water mixed solvent is 1:(50-80).

6. The repair process of claim 5, wherein: The initiator is potassium persulfate or azobisisobutyronitrile, and the mass ratio of initiator to naringin is (0.01-0.05):

1.

7. The repair process of claim 1, wherein: In step (4), the conductive material is a conductive composite material that forms a conductive path through thermal curing or photocuring.

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