PCB surface treatment process based on local gold plating and nickel and gold immersion

Abstract

The invention discloses a PCB surface treatment process based on local gold plating and nickel and gold immersion, and relates to the technical field of surface treatment processes. The method is used for processing a PCB which needs local hard gold plating and nickel gold immersion at other positions, and comprises the following steps: S1, pre-processing: processing the PCB to a copper thickness before electroplating; s2, first-layer pattern processing: pasting a dry film on the CS surface of the PCB and etching to form a pattern; s3, gold plating preparation; s4, local gold plating; s5, removing the film and processing a second layer of pattern; s6, removing the wire; s7, resistance welding and protection; and S8, nickel and gold immersion treatment. According to the surface treatment process, the microcosmic roughness of the surface of the substrate is accurately controlled through multi-step pretreatment, and high-pressure water washing and plasma cleaning are combined, so that the mechanical embedding force of a plating layer and a copper layer is ensured, and the problem that the plating layer is not uniform due to too large roughness is avoided. And meanwhile, the current distribution is regulated and controlled by adopting pulse current and a magnetic mask in the copper deposition and electroplating stages, so that the compactness and thickness uniformity of the coating are improved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of surface treatment processes, in particular to a PCB surface treatment process based on local gold plating plus nickel-gold plating. BACKGROUND

[0002] Under the background of rapid development of the electronic information industry, the surface treatment process of a PCB directly affects the reliability, conductivity and service life of a product as a core carrier of electronic components. With the evolution of terminal devices towards high precision, miniaturization and multifunctionalization, the PCB often needs to meet the dual requirements of local high wear resistance and overall oxidation resistance. For example, the high-frequency contact areas of connectors, keys and the like need to use hard gold plating layers with high hardness and strong wear resistance (usually with a Vickers hardness of 200 HV or more), while other areas need to form a uniform nickel-gold alloy layer through nickel-gold plating to improve the oxidation resistance and welding performance.

[0003] In the traditional process, single alkaline degreasing or acid etching is often used for pretreatment of the surface of the substrate, and it is difficult to accurately control the micro roughness of the surface. When the roughness is insufficient, the mechanical embedding force of the plating layer and the copper layer is weakened, and peeling and falling off are prone to occur. When the roughness is too large, the thickness distribution of the plating layer is uneven, and stress concentration is aggravated. In addition, drill chips and organic impurities are not completely removed from the hole wall after drilling, which can cause holes in the plating layer of the hole wall and affect the conduction reliability. Moreover, in the existing process, single pattern transfer or simple shielding is often used to divide the gold plating and nickel-gold plating areas, which is prone to cause the plating solution to penetrate into the non-target area due to bubbles in the dry film and poor edge sealing. For example, during local hard gold plating, if the SS surface (bottom layer) is not properly protected, gold ions may deposit in the non-gold plating area, resulting in a decrease in the purity of the subsequent nickel-gold plating layer. During the nickel-gold plating process, nickel ions may also contaminate the hard gold plated surface, reducing its wear resistance. SUMMARY

[0004] To achieve the above purpose, the application is implemented by the following technical scheme: a PCB surface treatment process based on local gold plating plus nickel-gold plating, which is used to treat a PCB that needs to be plated with hard gold locally and nickel-gold at other positions, and includes the following steps:

[0005] S1, front process treatment: treating the PCB to a copper thickness before electroplating;

[0006] S2, first layer pattern processing: applying a dry film to the CS surface (top layer) of the PCB and etching to form a pattern, and not etching the SS surface (bottom layer);

[0007] S3, gold plating preparation: applying a dry film to the SS surface and leaving the gold plating position exposed on the CS surface;

[0008] S4, local gold plating: plating hard gold on the exposed position of the CS surface;

[0009] S5, film removal and second layer pattern processing: remove the dry film on both sides of the PCB, paste dry film protection on the CS side, and etch the SS side to form a pattern;

[0010] S6, wire removal: remove the wires on the PCB;

[0011] S7, solder mask and protection: after completing the solder mask processing, protect the local gold plating position, and expose the position where nickel plating is required;

[0012] S8, nickel plating processing: perform nickel plating processing on the exposed position, and then complete the surface treatment after post-processing.

[0013] Preferably, the specific steps of step 1 are as follows:

[0014] S11, substrate pretreatment: soak the substrate in a 5-8% sodium hydroxide solution at 50-60°C for 3-5 min to remove oil and oxidation layer on the substrate surface; treat the substrate with a 10-15% ammonium persulfate solution at 25-30°C for 60-90 s to control the micro-roughness of the substrate surface to be 0.1-0.2 μm, and enhance the adhesion between the subsequent plating layer and the substrate;

[0015] S12, drilling and hole wall treatment:

[0016] High-pressure water flushing: for the residual drillings in the holes after drilling, when the hole diameter is >0.2 mm, use deionized water with a pressure of 1.5-2 MPa for flushing; when the hole diameter is ≤0.2 mm, use deionized water with a pressure of 0.8-1.2 MPa for flushing to avoid damage to the small hole structure by high pressure;

[0017] Plasma cleaning: perform plasma treatment in an oxygen atmosphere at a power of 380-450 W for 60-90 s to remove residual organic matter and small impurities on the hole wall, and ensure the cleanliness of the hole wall;

[0018] S13, copper plating: uniformly deposit a conductive copper layer with a thickness of 0.5-1 μm on the substrate surface and hole wall to form a conductive substrate; use pulse current to thicken the copper layer on the whole board, wherein the peak current density is 2-3 A / dm 2 , the forward pulse width is 0.5 ms, the reverse pulse width is 0.2 ms, and the copper layer density is improved; set an adjustable magnetic mask above the area where hard gold plating is required, control the current distribution by a shielding coefficient of 40±5%, so that the final copper thickness of this area is 5-10% higher than that of the non-gold plated area, and the copper thickness deviation of the whole board after local thickening is ≤8%, which provides a basis for the uniformity of the gold layer thickness of the local hard gold plating;

[0019] S14, water washing treatment: flush the substrate with deionized water until the pH value of the substrate surface reaches 6-7, and complete the front process processing.

[0020] Preferably, the step S2 specifically comprises the following steps:

[0021] S21, dry film pretreatment: a photosensitive dry film with a thickness of 35-50 μm and a resolution of ≥25 μm is selected, and is balanced for 24 h in an environment with a temperature of 25°C and a relative humidity of ≤30% to eliminate internal stress generated during storage of the dry film and ensure dimensional stability during lamination;

[0022] S22, dry film lamination on the CS surface: a roller lamination method is used, and the lamination temperature is set to 70-75°C, the roller pressure is set to 0.3-0.4 MPa, and the lamination speed is set to 1.5-2 m / min, so that the dry film is tightly combined with the copper layer on the CS surface, and subsequent pattern distortion caused by poor lamination is avoided;

[0023] S23, exposure and development: exposure is performed by an exposure device with an alignment accuracy of ±5 μm, and the exposure energy is controlled to be 80-100 mJ / cm2; after exposure, baking is performed at 110°C for 2 min to strengthen the photosensitive crosslinking effect of the dry film; a sodium carbonate solution with a mass concentration of 1.5-2.0% is used for spray development at 30-35°C for 90-120 s to accurately remove the unexposed dry film area and expose the pattern to be etched;

[0024] S24, CS surface etching: an ammonia-based alkaline etching solution (Cu 2 + concentration 120-150 g / L, pH value 8.0-8.5) is used for etching at 45-50°C; during etching, gradient spray control is used, and the spray pressure of the edge area is higher than that of the center area by 0.03-0.04 MPa to ensure that the pattern edge perpendicularity is ≥88°, which meets the requirements of subsequent four-side gold plating on pattern accuracy;

[0025] S25, SS surface protection: a fluororubber-based composite film (thermal expansion coefficient CTE = 18±2 ppm / ℃, thickness 15-20 μm) is used to cover the SS surface, which protects the copper layer on the SS surface from the etching solution due to its excellent etching resistance and dimensional stability, and the composite film is removed after the CS surface etching is completed.

[0026] Preferably, in the step S3, the process of lamination of the dry film on the SS surface adopts multi-parameter collaborative control to exclude bubbles, and specifically comprises the following steps:

[0027] S31, an acrylate-based photoresist dry film (Tg = 65±5°C) is used, and is preheated to 60-70°C to soften it, and then dry film lamination is performed after the protective film on the SS surface is removed;

[0028] S32, in the environment of vacuum degree -0.08 to -0.1 MPa, a gradient pressure from the center to the edge is applied: the initial pressure of the center is 0.1-0.15 MPa, the final pressure of the edge is 0.2-0.25 MPa, and the increasing rate is 0.05 MPa / 5 cm;

[0029] S33, a dry film edge is provided with a flow guide groove with a width of 0.1±0.02 mm and a depth of 0.05±0.02 mm to form a directional exhaust passage.

[0030] Preferably, the gradient pressure from the center to the edge is applied by using a dynamic control logic, which specifically includes: taking the center of the PCB board as the origin, dividing the center area (radius ≤1 / 3 board length), the transition area (1 / 3 board length < radius ≤2 / 3 board length), and the edge area (radius > 2 / 3 board length);

[0031] 1) The pressure in the center area starts from 0.1-0.12 MPa and increases at a rate of 0.05 MPa / 5 cm;

[0032] 2) The initial pressure in the transition area is the final pressure in the center area, and the increasing rate is 0.06-0.07 MPa / 5 cm; and when it is detected that there are dense pads (spacing ≤0.2 mm) in the area, the pressure is temporarily increased by 0.02 MPa;

[0033] 3) The initial pressure in the edge area (including the area where the flow guide groove is located) is the final pressure in the transition area, and the final pressure is controlled at 0.23-0.25 MPa. The pressure increasing rate is dynamically adjusted according to the distance from the flow guide groove: when the distance is ≤5 mm, the rate is increased to 0.08 MPa / 5 cm to accelerate the convergence of bubbles to the flow guide groove; when the distance is >5 mm, the rate is maintained at 0.06 MPa / 5 cm; when the pressure in the edge area reaches 0.2 MPa, the vacuum degree is simultaneously increased to -0.095 to -0.1 MPa.

[0034] Preferably, the local hard gold plating in step S4 includes the following specific steps:

[0035] S41, plating solution configuration: prepare a hard gold plating solution with a gold ion concentration of 6-8 g / L, ammonium citrate of 80-100 g / L, and a pH value controlled at 3.8-4.5; add 0.5-1 g / L of cobalt salt to increase the hardness of the gold layer, and add 0.1 g / L of polyvinylpyrrolidone as a dispersant to make the gold ions uniformly deposit;

[0036] S42, plating parameter control: carry out plating at the position where the gold plating leaks from the CS surface, set the current density at 2-3 A / dm2, the temperature at 45-50℃, and the stirring rate at 300-400 r / min; conduct the current through the plating network connected in series on the non-gold-plated surface of the SS surface to make the current distribution uniformity deviation ≤5% and ensure the consistency of the gold plating layer thickness in the area without wires.

[0037] S43, thickness gradient control: using regional current density control, the current density of the gold-plated edge region is 8-10% higher than that of the central region, forming a thickness gradient: the gold thickness of the gold-plated edge region reaches 0.8-1.0 μm, the gold thickness of the central region is 0.5-0.7 μm, and the total gold thickness of the gold-plated edge region is ≤1.2 μm, meeting the integrity requirement of four-side gold plating;

[0038] S44, post-gold plating treatment: first, ultrasonic cleaning with deionized water (power 200-300 W, time 3-5 min) to remove surface residual plating solution; then neutralizing with 2-3% citric acid solution at 35-40°C for 40-60 s to eliminate surface alkaline residues.

[0039] Preferably, the film stripping and second layer pattern processing of step S5 include the following specific steps:

[0040] S51, double-sided film stripping: using a 5-8% sodium hydroxide solution, soaking at 50-60°C for 2-3 min, while assisted by 150-200 W ultrasonic vibration, to remove the dry film on the CS side and the SS side, and the residual glue area is controlled to be ≤0.1 mm 2 ;

[0041] S52, CS side protection: covering a 40-50 μm thick corrosion-resistant dry film on the entire CS side, using a vacuum degree of -0.09 to -0.1 MPa vacuum lamination process to make the dry film tightly adhere to the CS side pattern, and the edge sealing width is ≥1 mm to prevent the subsequent etching solution from penetrating in;

[0042] S53, SS side pattern etching: using an alkaline copper chloride etching solution (Cu 2+ concentration 160±10 g / L, pH value 8.8±0.2) to etch at 48-50°C, and the etching rate is controlled at 18-22 μm / min; real-time monitoring of the etching progress is performed by a CCD vision system, and the pattern edge deviation is controlled to be ≤0.02 mm according to the IPC-TM-650 2.2.22 standard;

[0043] S54, damage detection: using a lock-in infrared thermal imager to scan the CS side (temperature resolution 0.1°C), and when the detected regional temperature difference is >0.5°C, it is determined as potential etching damage to ensure that the local gold-plated area is intact.

[0044] Preferably, the lead removal of step S6 includes the following specific steps:

[0045] S61, lead identification and positioning: scanning the PCB board by an AOI automatic optical detection system to identify the leads (including etched leads and isolated leads) to be removed with an accuracy of ±0.005 mm, and mark the lead position and width information;

[0046] S62, removing the conductive wire by etching: for the etchable conductive wire, a local spraying process is adopted, the spraying liquid is ammonium persulfate solution with a mass concentration of 10-15% (add 0.05% sodium dodecyl sulfate), the spraying pressure is controlled to be 0.2-0.3 MPa, and etching is only performed on the conductive wire area to avoid damaging the surrounding patterns;

[0047] S63, removing the isolated conductive wire by laser: for the isolated conductive wire that cannot be etched, laser cutting is adopted to remove it, the laser power is set to be 6-8 W, the pulse frequency is set to be 20 kHz, and the spot diameter is set to be 0.02-0.03 mm; the cutting path is along the position 0.03-0.05 mm away from the edge of the conductive wire, and 5-8 L / min of nitrogen gas is introduced for auxiliary cooling to prevent thermal damage;

[0048] S64, removing effect acceptance: the conductive wire removal area is checked by a 50 times microscope to ensure that there is no conductive wire residue and carbonization damage, and the cleanliness meets the cleanliness requirements of subsequent surface treatment.

[0049] Preferably, the solder resist and protection of step S7 comprises the following specific steps:

[0050] S71, solder resist ink coating: a 300-400 mesh silk screen is used to print a photosensitive solder resist ink to form an ink layer with a thickness of 15-20 μm on the surface of the PCB, ensuring that there is no ink accumulation on the edge of the local gold plating area and the nickel immersion gold area, and ensuring the subsequent protection accuracy;

[0051] S72, solder resist layer step curing: 60°C pre-baking for 10 min, exposure (energy 150-200 mJ / cm2), 70°C post-baking for 15 min, 1.5-2.0% sodium carbonate solution development, 130°C final curing for 30 min, to form a solder resist layer;

[0052] S73, local gold plating area protection: an acid-resistant adhesive tape with a thickness of 80-100 μm is used to cover the local gold plating area, and the edge of the adhesive tape exceeds the gold plating area by ≥0.5 mm; the adhesive tape is sealed by a hot pressing process at 60-70°C and 0.1-0.15 MPa to prevent the nickel immersion gold solution from eroding;

[0053] S74, activation of the nickel immersion gold area: for the leaked nickel immersion gold area, a 0.5% citric acid solution is used for activation at 25-30°C for 30-60 s to remove the surface oxide layer and enhance the adhesion of the subsequent nickel immersion gold layer.

[0054] Preferably, the nickel immersion gold treatment of step S8 comprises:

[0055] S81, gradient nickel layer deposition: in the first stage, the current density is 0.5-0.8 A / dm2, and the soft nickel layer (thickness 2-3 mu m, Vickers hardness 180-200 HV, measured according to ISO6507-1 standard) is deposited for 10-15 min; in the second stage, the current density is 1.8-2.2 A / dm2, and the hard nickel layer (thickness 1-2 mu m, Vickers hardness 300-350 HV) is deposited for 5-8 min; the thickness ratio of the soft nickel layer to the hard nickel layer is 1.5:1 to 2:1, and the current density difference is 1.3-1.5 A / dm2; 2

[0056] S82, micro-roughening of the palladium layer: deposit a palladium layer under the conditions of a palladium salt concentration of 0.5-1 g / L and a current density of 0.1-0.3 A / dm2, and the surface roughness is 0.1-0.3 mu m; 2

[0057] S83, pre-plating of a soft gold transition layer: deposit a 0.1-0.2 mu m soft gold layer (purity > 99.9%) on the surface of the palladium layer at a current density of 0.2 A / dm2, and the pre-plated soft gold layer is not included in the total thickness of the local hard gold plating.

[0058] The application discloses a PCB surface treatment process based on local gold plating and nickel-gold plating, which has the following beneficial effects:

[0059] (1) The application precisely controls the micro-roughness (0.1-0.2 mu m) of the substrate surface through multiple pretreatment steps, combines high-pressure water flushing (pore diameter regulation pressure) and plasma cleaning (oxygen atmosphere removes pore wall impurities), ensures the mechanical embedding force of the plating layer and the copper layer, and avoids the problem of uneven plating layer caused by excessive roughness. At the same time, pulse current and magnetic mask are used to regulate current distribution in the copper plating and electroplating stages, so that the density and thickness uniformity of the plating layer are improved, effectively solving the problems of peeling, falling and pore wall cavitation in the traditional process, and significantly enhancing the structural stability and conduction reliability of the PCB;

[0060] (2) The application realizes precise isolation of the gold-plated area of the CS surface (top layer) and the non-gold-plated area of the SS surface (bottom layer) through the layered pattern processing and multi-parameter collaborative dry film lamination process (gradient pressure lamination in a vacuum environment, edge flow groove exhaust). The special protection (acid-resistant tape hot pressing sealing) of the local gold-plated position in the nickel-gold plating stage further blocks the penetration path of the plating solution in different areas, effectively solves the problems of gold ion pollution of the nickel-gold layer and nickel ion erosion of the hard gold surface caused by poor shielding in the traditional process, and ensures the wear resistance of the hard gold plating layer and the purity of the nickel-gold layer. BRIEF DESCRIPTION OF DRAWINGS

[0061] ​​In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced. Obviously, the accompanying drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0062] Figure 1 For the industrial process block diagram of the present application; DETAILED DESCRIPTION

[0063] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application are described clearly and completely. Obviously, the described embodiments are some 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 skilled in the art without creative labor are within the protection scope of the present application.

[0064] In order to better understand the above technical solutions, the above technical solutions will be described in detail in combination with the accompanying drawings and specific embodiments.

[0065] The present application provides a method for preparing a compound of formula (I) Figure 1The process is used for processing PCB boards which need to be plated with hard gold in local area and plated with nickel in other area, and comprises the following steps: S1, front process treatment: processing the PCB board to the copper thickness before electroplating; S2, first layer pattern processing: pasting dry film on the CS surface (top layer) of the PCB board and etching to form a pattern, and the SS surface (bottom layer) is not etched; S3, gold plating preparation: pasting dry film on the SS surface and leaving out the gold plating position of the CS surface; S4, local gold plating: plating hard gold on the left-out position of the CS surface; S5, film removal and second layer pattern processing: removing the double-side dry film of the PCB board, pasting dry film on the whole CS surface for protection, and etching the SS surface to form a pattern; S6, lead removal: removing the leads on the PCB board; S7, solder resist and protection: after completing the solder resist treatment, protecting the local gold plating position and leaving out the position which needs to be plated with nickel; and S8, nickel plating treatment: plating nickel on the left-out position, and then completing the surface treatment through post-process. In the traditional process, it is difficult to meet the area isolation requirements of local gold plating and overall nickel plating through single pattern processing, and the plating layer boundary is often blurred and mutually contaminated. The process ensures that the local hard gold plating is only performed in the target area of the CS surface through S2 step of etching the pattern on the CS surface alone (the SS surface is not etched) and S3 step of pasting dry film on the SS surface for protection to leave out the gold plating position of the CS surface. The process realizes the independent formation of two layer patterns through S5 step of pasting dry film on the whole CS surface for protection and etching the SS surface to form a pattern. This layered processing mode controls the boundary precision between the gold plating area and the nickel plating area within ±0.02 mm, completely avoids the cross-contamination of plating layers caused by unclear area division in the traditional process, and ensures the purity of the local hard gold plating layer and the welding performance of the nickel plating layer. In the traditional process, if the nickel plating is performed first and then the gold plating, the gold ions are prone to replacement reaction with the nickel layer, resulting in the decrease of the bonding force of the gold plating layer; if the two types of plating layers are performed simultaneously, it is difficult to control the thickness difference between the two types of plating layers. The process completes the local hard gold plating through S4 step, ensures that the gold layer is deposited only in the target area by using dry film shielding, and controls the thickness deviation of the gold layer to be ≤0.1 μm through current distribution regulation. The process performs the nickel plating treatment through S8 step after the special protection of the gold plating area through S7 step, so that the nickel plating layer (the thickness of the nickel layer is 3-5 μm, and the thickness of the gold layer is 0.05-0.1 μm) uniformly covers the non-gold plating area. This process design ensures the high wear resistance of the hard gold plating layer and the oxidation resistance of the nickel plating layer, and solves the problem of mutual interference of the plating layer performance in the traditional process. In the traditional process, multiple etching and plating layer processing easily causes over-corrosion or mechanical damage to the copper layer of the substrate and the already-formed pattern. The process protects the SS surface through fluororubber-based composite film in S2 step to avoid damage during etching of the CS surface; protects the CS surface through vacuum pasting dry film in S5 step to prevent corrosion during etching of the SS surface; and seals the gold plating area through acid-resistant adhesive tape in S7 step to avoid erosion of the nickel plating solution.It is detected that the PCB treated by the process has high verticality of pattern edge, etching deviation of copper layer is less than or equal to 0.01 mm, and substrate damage rate is reduced, which solves the substrate damage problem caused by insufficient protection in the traditional process, and significantly improves the mechanical strength and electrical performance stability of the PCB.

[0066] In the step 1, the specific steps are as follows: S11, substrate pretreatment: a sodium hydroxide solution with a mass concentration of 5-8% is used to soak the substrate at 50-60℃ for 3-5 min to remove oil stains and oxide layer on the substrate surface; an ammonium persulfate solution with a mass concentration of 10-15% is used to treat the substrate at 25-30℃ for 60-90 s to control the micro roughness of the substrate surface to be 0.1-0.2 μm, and to enhance the bonding force between the subsequent plating layer and the substrate; S12, drilling and hole wall treatment: high-pressure water flushing: for the residual drill chips in the hole after drilling, when the hole diameter is greater than 0.2 mm, deionized water with a pressure of 1.5-2 MPa is used for flushing; when the hole diameter is less than or equal to 0.2 mm, deionized water with a pressure of 0.8-1.2 MPa is used for flushing to avoid high-pressure damage to the small hole structure; plasma cleaning: plasma treatment is carried out in an oxygen atmosphere at a power of 380-450 W for 60-90 s to remove residual organic matter and small impurities on the hole wall and ensure the cleanliness of the hole wall; S13, copper deposition and electroplating: a conductive copper layer with a thickness of 0.5-1 μm is uniformly deposited on the substrate surface and the hole wall to form a conductive substrate; pulse current is used for copper layer thickening, in which the peak current density is 2-3 A / dm 2, the forward pulse width is 0.5 ms, the reverse pulse width is 0.2 ms, and the copper layer density is improved; an adjustable magnetic mask is arranged above the area where hard gold plating is required in the subsequent process, the current distribution is regulated by a shielding coefficient of 40±5%, so that the final copper thickness of the area is 5-10% higher than that of the non-gold plating area, the local thickening causes the copper thickness deviation of the whole board to be ≤8%, and provides a basis for the thickness uniformity of the gold layer for local hard gold plating; S14, water washing treatment: the substrate is washed with deionized water until the pH value of the substrate surface reaches 6-7, and the front process treatment is completed. The process ensures the surface cleanliness through the hierarchical treatment in step S11, and enhances the mechanical interlocking force between the plated layer and the substrate through the moderate micro-rough structure, so that the plated layer peeling strength is increased to ≥0.8 N / mm, solving the problem of easy peeling and falling of the plated layer in the traditional process; in step S12, the deionized water is washed at a pressure of 1.5-2 MPa for the holes with a diameter >0.2 mm, and the deionized water is washed at a pressure of 0.8-1.2 MPa for the holes with a diameter ≤0.2 mm, avoiding damage to small holes by high pressure; at the same time, the holes are treated by plasma under an oxygen atmosphere at a power of 380-450 W for 60-90 s, so that the residual organic matter and small impurities on the hole wall are completely removed. There is no drill chip residue in the hole, the hole wall plated layer has a low cavity rate, solving the problem of insufficient reliability of the hole wall plated layer in the traditional process, and ensuring the conduction performance of the PCB board; in step S13, a conductive copper layer of 0.5-1 μm is first deposited to form a uniform substrate, and then the copper layer is thickened by pulse current to improve the copper layer density (porosity ≤0.1 per / mm 2 ); at the same time, the current distribution is regulated by the adjustable magnetic mask, so that the copper thickness of the area where hard gold plating is required is 5-10% higher than that of the non-gold plating area, and the copper thickness deviation of the whole board is ≤8%. This local thickening design provides a basis for the thickness uniformity of the gold layer for subsequent local hard gold plating, so that the gold layer thickness deviation is controlled to be ≤0.1 μm, solving the problem of gold layer thickness fluctuation caused by uneven copper layer in the traditional process.

[0067] In the step S2, the following steps are included: S21, dry film pretreatment: a photosensitive dry film with a thickness of 35-50 μm and a resolution of ≥25 μm is selected, and is balanced for 24 h in an environment with a temperature of 25℃ and a relative humidity of ≤30% to eliminate internal stress generated during storage of the dry film and ensure dimensional stability during lamination; S22, dry film lamination on the CS surface: a roller lamination method is used, the lamination temperature is set to 70-75℃, the roller pressure is set to 0.3-0.4 MPa, and the lamination speed is set to 1.5-2 m / min, so that the dry film is tightly combined with the copper layer on the CS surface, and subsequent pattern distortion caused by poor lamination is avoided; S23, exposure and development: exposure is performed by using an exposure device with an alignment accuracy of ±5 μm, the exposure energy is controlled to be 80-100 mJ / cm2, and after exposure, baking is performed at 110℃ for 2 min to strengthen the photosensitive cross-linking effect of the dry film; a sodium carbonate solution with a mass concentration of 1.5-2.0% is used for spraying and developing at 30-35℃ for 90-120 s to accurately remove the unexposed dry film area and expose the pattern to be etched; S24, CS surface etching: an ammonia-based alkaline etching solution (wherein Cu 2+ concentration 120-150 g / L, pH value 8.0-8.5), etching is carried out at 45-50°C; gradient spraying control is adopted during etching, the spraying pressure of the edge area is 0.03-0.04 MPa higher than that of the center area, to ensure that the verticality of the pattern edge is ≥ 88°, meeting the requirements of the pattern accuracy for subsequent four-side gold plating; S25, SS surface protection: fluororubber-based composite film (coefficient of thermal expansion CTE = 18 ± 2 ppm / °C, thickness 15-20 μm) is used to cover the SS surface, to protect the SS surface copper layer from the etching liquid by virtue of its excellent etching resistance and dimensional stability, and the composite film is removed after the CS surface etching is completed. In the traditional process, the dry film is directly used without sufficient pretreatment, which is easy to cause dimensional change after lamination due to internal stress, and improper lamination parameter control will cause the dry film and the copper layer to be not tightly combined, affecting the subsequent pattern accuracy. In this process, the photosensitive dry film is balanced in a specific temperature and humidity environment for 24 h in the S21 step, to eliminate internal stress and ensure dimensional stability; the dry film and the CS surface copper layer are tightly combined by setting appropriate lamination temperature, pressure and speed in the S22 step. This process avoids pattern distortion caused by poor dry film lamination, and lays a foundation for the accuracy of subsequent pattern etching. In the traditional exposure and development process, unstable exposure energy and improper development parameters are easy to cause poor photosensitive crosslinking effect of the dry film, and incomplete removal of the unexposed area, resulting in blurred pattern edges. In the S23 step of this process, high-precision exposure equipment is used to control the exposure energy, and post-exposure baking is used to strengthen the crosslinking effect, followed by spraying and developing with a specific concentration of sodium carbonate solution at a suitable temperature. This operation accurately removes the unexposed dry film area, making the exposed pattern edge clear and improving the pattern accuracy. In the S24 step of this process, ammonia alkaline etching liquid is used, and gradient spraying control is adopted to make the spraying pressure of the edge area higher than that of the center area, to ensure that the verticality of the pattern edge meets the requirements; meanwhile, in the S25 step, fluororubber-based composite film is used to cover the SS surface, to protect the SS surface copper layer by virtue of its etching resistance and dimensional stability. This design not only meets the requirements of the pattern accuracy for subsequent four-side gold plating, but also avoids damage to the SS surface during CS surface etching.

[0068] In step S3, the process of pasting dry film on the SS surface adopts multi-parameter collaborative control to exclude bubbles, specifically including the following steps: S31, using an acrylate-based photoresist dry film (Tg=65±5℃), preheating to 60-70℃ to soften it, and then pasting the dry film after removing the protective film on the SS surface; S32, in a vacuum degree of-0.08 to-0.1 MPa environment, applying a gradient pressure from the center to the edge: the initial pressure at the center is 0.1-0.15 MPa, the final pressure at the edge is 0.2-0.25 MPa, and the incremental rate is 0.05 MPa / 5 cm; S33, a guide groove with a width of 0.1±0.02 mm and a depth of 0.05±0.02 mm is set at the edge of the dry film to form a directional exhaust channel. In the traditional process, when the dry film is directly pasted, its own hardness may cause it not to be tightly pasted with the substrate surface, especially when there are small concave-convex on the substrate, which is easy to produce gaps. In step S31 of the process, the acrylate-based photoresist dry film is preheated to 60-70℃ to soften it, and then pasted after removing the protective film on the SS surface. The softened dry film is more adaptable to the surface state of the substrate, reducing the fitting gap caused by the over-hardness of the dry film, and laying a foundation for subsequent bubble exclusion. In the traditional pasting process, improper pressure application method can easily lead to local insufficient pressure, so that bubbles cannot be discharged and remain between the dry film and the substrate, affecting the quality of the subsequent plating layer. In step S32 of the process, a gradient pressure is applied from the center to the edge in a vacuum environment, with a low initial pressure at the center, a high final pressure at the edge, and a gradual increase. This pressure control method can promote the movement of bubbles to the edge and discharge them, avoiding the residual of bubbles under the dry film and ensuring the tight combination of the dry film and the SS surface. In step S33 of the process, a guide groove with a specific size is set at the edge of the dry film to form a directional exhaust channel. When the bubbles are pushed to the edge by the gradient pressure, the guide groove can guide the bubbles to be quickly discharged, avoiding the retention of edge bubbles and ensuring the pasting quality of the dry film edge, providing a guarantee for the effective protection of the SS surface in the subsequent local gold plating process.

[0069] The gradient pressure application process from the center to the edge adopts a zoning dynamic control logic, specifically including: taking the center of the PCB board as the origin, dividing the center zone (radius ≤ 1 / 3 board length), transition zone (1 / 3 board length < radius ≤ 2 / 3 board length), and edge zone (radius > 2 / 3 board length); 1) the center zone pressure starts from 0.1-0.12 MPa and increases at a rate of 0.05 MPa / 5 cm; 2) the transition zone pressure starts at the final pressure of the center zone and increases at a rate of 0.06-0.07 MPa / 5 cm; and when it is detected that there are dense pads (spacing ≤ 0.2 mm) in the region, the pressure is temporarily increased by 0.02 MPa; 3) the edge zone (including the area where the flow guide groove is located) pressure starts at the final pressure of the transition zone and is controlled at 0.23-0.25 MPa, and the pressure increase rate is dynamically adjusted according to the distance from the flow guide groove: when the distance from the flow guide groove is ≤ 5 mm, the rate is increased to 0.08 MPa / 5 cm to accelerate the bubble convergence to the flow guide groove; when the distance from the flow guide groove is > 5 mm, the rate is maintained at 0.06 MPa / 5 cm; when the edge zone pressure reaches 0.2 MPa, the vacuum degree is simultaneously increased to -0.095 to -0.1 MPa. In the traditional process, the gradient pressure application often uses a unified starting value and increasing rate, which is difficult to adapt to the different lamination requirements of the PCB board center, transition zone, and edge zone, and is prone to cause insufficient or excessive pressure in some areas. This process divides the PCB board into center zone, transition zone, and edge zone, and sets appropriate pressure starting value and increasing rate for each zone. The center zone starts from a lower pressure and slowly increases, and the transition zone starts from the final pressure of the center zone and appropriately increases the increasing rate. This zoning setting makes the pressure better match the lamination characteristics of each region, avoiding the problem of loose lamination caused by inappropriate pressure. When the process detects dense pads in the transition zone, the pressure is temporarily increased, enhancing the lamination intensity in the dense pad area and promoting the bubble to be expelled, ensuring the tight combination of dry film and substrate in the dense pad area. In the traditional process, the edge zone pressure control is relatively fixed and not coordinated with the vacuum degree, making it difficult for bubbles near the edge zone, especially the flow guide groove, to be quickly expelled. This process dynamically adjusts the pressure increasing rate according to the distance of the edge zone from the flow guide groove, increases the rate when the distance is close to the flow guide groove to accelerate the bubble convergence, and increases the vacuum degree when the edge zone pressure reaches a certain value, enhancing the bubble expulsion effect and ensuring the lamination quality near the edge zone and the flow guide groove, providing further protection for the effective protection of the SS surface dry film.

[0070] Specifically, the partial hard gold plating of step S4 includes the following specific steps: S41, plating solution configuration: prepare a hard gold plating solution, wherein the gold ion concentration is 6-8 g / L, the ammonium citrate is 80-100 g / L, and the pH value is controlled at 3.8-4.5; 0.5-1 g / L of cobalt salt is added to improve the hardness of the gold layer, and 0.1 g / L of polyvinylpyrrolidone is added as a dispersant to make the gold ions uniformly deposit; S42, plating parameter control: carry out electroplating at the position where the gold plating leaks from the CS surface, set the current density at 2-3 A / dm 2 , the temperature at 45-50℃, and the stirring rate at 300-400 r / min; conduct the current through the electroplating network connected in series by the non-gold-plated surface of the SS surface to make the current distribution uniformity deviation ≤5%, and ensure the thickness consistency of the gold-plated layer in the area without wires; S43, thickness gradient regulation: adopt regionalized current density control, the current density of the gold-plated edge area is 8-10% higher than that of the central area, and a thickness gradient is formed: the gold thickness of the gold-plated edge reaches 0.8-1.0 μm, the gold thickness of the central area is 0.5-0.7 μm, and the total gold thickness of the gold-plated edge is ≤1.2 μm, meeting the integrity requirement of four-side gold plating; S44, post-plating treatment: first, ultrasonic cleaning is carried out with deionized water (power 200-300 W, time 3-5 min) to remove the surface residual plating solution; then, 2-3% citric acid solution is used for neutralization at 35-40℃ for 40-60 s to eliminate the surface alkaline residue. Traditional gold plating solution is single in composition, which leads to uneven deposition of gold ions and low hardness of the gold layer, and it is difficult to meet the high wear resistance requirement. In step S41, by reasonably adjusting the gold ion concentration, ammonium citrate content, and adding cobalt salt and polyvinylpyrrolidone in the gold plating solution, the uniform dispersion of gold ions is promoted, the uniform deposition of the gold layer is ensured, and the hardness of the gold layer is improved, so that the hard gold plating layer can withstand high-frequency contact wear. In step S42, by setting appropriate current density, temperature and stirring rate, and using the electroplating network connected in series by the non-gold-plated surface of the SS surface to conduct the current, the current distribution is more uniform, the thickness deviation of the gold-plated layer in the area without wires is effectively controlled, and the thickness consistency of the gold layer is ensured. In step S43, by using regionalized current density control, the current density of the gold-plated edge area is higher than that of the central area, a reasonable thickness gradient is formed, the thickness of the gold-plated edge is ensured, the integrity requirement of four-side gold plating is met, and material waste caused by excessive thickness of the gold layer in the central area is avoided. If the post-plating treatment is not proper, the surface is easy to be left with plating solution and alkaline substances, which affects the performance of the gold layer and subsequent processing. In step S44, the surface residual plating solution is removed by ultrasonic cleaning first, and then the surface alkaline residue is eliminated by citric acid solution, which ensures the cleanliness of the gold layer surface and provides a good foundation for the smooth progress of subsequent processes.

[0071] In the step S5, the film stripping and the second layer pattern processing include the following specific steps: S51, double-sided film stripping: using a sodium hydroxide solution with a mass concentration of 5-8%, soaking at 50-60°C for 2-3min, and meanwhile, assisting with 150-200W ultrasonic vibration, removing the dry film on the CS surface and the SS surface, and controlling the residual glue area to be ≤0.1mm 2 ; S52, CS surface protection: sticking a 40-50μm thick corrosion-resistant dry film on the whole CS surface, using a vacuum degree of-0.09 to-0.1MPa vacuum sticking process to make the dry film closely stick to the CS surface pattern, and the edge sealing width is ≥1mm to prevent the subsequent etching liquid from penetrating; S53, SS surface pattern etching: using an alkaline copper chloride etching liquid (wherein Cu 2 + concentration 160±10g / L, pH value 8.8±0.2), etching at 48-50°C, and controlling the etching rate to be 18-22μm / min; real-time monitoring the etching progress through a CCD vision system, and according to the IPC-TM-6502.2.22 standard, controlling the pattern edge deviation to be ≤0.02mm; S54, damage detection: scanning the CS surface by using a phase-locked infrared thermal imager (temperature resolution 0.1°C), and when detecting that the regional temperature difference is >0.5°C, it is determined as potential etching damage, so as to ensure the integrity of the local gold plating area. The traditional film stripping process often causes dry film residue to form residual glue due to improper solution concentration or processing time, which affects the subsequent processing. In the step S51, the process uses a sodium hydroxide solution with a specific concentration to soak at a suitable temperature, and meanwhile, assists with ultrasonic vibration, which can quickly and completely remove the dry film on the CS surface and the SS surface, reduces the residual glue, and provides a clean substrate surface for the subsequent pattern processing. In the step S52, the process sticks a corrosion-resistant dry film on the whole CS surface, and uses a vacuum sticking process to make the dry film closely combine with the CS surface pattern and the edge sealing is good, which effectively blocks the etching liquid from eroding the CS surface and protects the local gold plating area. In the step S53, the process uses an etching liquid with a specific composition, controls the suitable temperature and etching rate, and real-time monitors the etching progress through a vision system, which can accurately control the pattern edge deviation and meet the requirements of high-precision patterns. In the step S54, the process scans the CS surface by using a phase-locked infrared thermal imager, identifies potential etching damage through detecting the regional temperature difference, which can find problems in time and handle them, and ensures the integrity of the local gold plating area and the substrate.

[0072] Specifically, the lead removal of step S6 includes the following specific steps: S61, lead identification and positioning: scanning the PCB board by an AOI automatic optical detection system to identify the leads (including etched leads and isolated leads) to be removed with an accuracy of ±0.005 mm, and mark the lead position and width information; S62, etching method to remove leads: for etchable leads, a local spraying process is adopted, the spraying liquid is ammonium persulfate solution with a mass concentration of 10-15% (add 0.05% sodium dodecyl sulfate), the spraying pressure is controlled at 0.2-0.3 MPa, and only the lead area is etched to avoid damaging the surrounding patterns; S63, laser method to remove isolated leads: for isolated leads that cannot be etched, laser cutting is used for removal, the laser power is set to 6-8 W, the pulse frequency is 20 kHz, and the spot diameter is 0.02-0.03 mm; the cutting path is along the edge of the lead at a distance of 0.03-0.05 mm, and 5-8 L / min of nitrogen gas is introduced for auxiliary cooling to prevent thermal damage; S64, removal effect acceptance: the lead removal area is checked by a 50 times microscope to ensure that there is no lead residue and carbonization damage, and the cleanliness meets the cleanliness requirements of subsequent surface treatment. In traditional processes, lead identification relies on manual work, which is not only low in efficiency, but also prone to positioning deviation due to human factors, affecting the subsequent removal effect. In step S61 of the process, the AOI automatic optical detection system is used to scan the PCB board, which can accurately identify the leads to be removed and mark their position and width information, providing accurate positioning basis for subsequent accurate lead removal. In step S62 of the process, a local spraying process is used for etchable leads, and the spraying liquid is precisely applied to the lead area to avoid erosion of the surrounding patterns and protect the integrity of the non-lead area. In step S63 of the process, laser cutting is used to remove isolated leads that cannot be etched, by setting appropriate laser parameters and cutting paths, and introducing nitrogen gas for auxiliary cooling, which can accurately remove isolated leads and avoid the influence of thermal damage on the substrate and surrounding patterns. In step S64 of the process, the lead removal area is checked by a microscope to ensure that there is no lead residue and carbonization damage, providing a clean substrate surface for subsequent surface treatment. The AOI automatic optical detection system is a key equipment for accurate lead identification and positioning. Its core function is to scan the surface of the PCB board comprehensively through optical imaging and image analysis technology, thereby quickly and accurately identifying the leads to be removed, including etched leads and isolated leads. When the system is working, it first uses a high-resolution camera to image the surface of the PCB board to obtain clear surface pattern information. Then, through the built-in image algorithm, the collected image is processed and analyzed, and the lead features in the image are compared with the preset lead standard features to accurately determine which leads need to be removed. At the same time, the system can accurately position the identified leads and mark their specific position and width information, and the positioning accuracy can meet the accuracy requirements of the process for lead removal.With the help of AOI automatic optical detection system, the traditional manual identification method is replaced, not only the efficiency of wire identification is improved, more importantly, the error that may be produced by manual identification is avoided, which provides reliable basis for subsequent etching method or laser method precise removal of wire, ensures that the wire removal process can accurately act on the target area, reduces the impact on the surrounding graphics, and guarantees the quality of PCB board surface treatment.

[0073] In the process, the solder resist and protection of step S7 includes the following specific steps: S71, solder resist ink coating: using 300-400 mesh screen printing photosensitive solder resist ink to form an ink layer with a thickness of 15-20 μm on the surface of the PCB board, ensuring that there is no ink accumulation on the edge of the local gold plating area and the nickel plating area, and ensuring the accuracy of subsequent protection; S72, solder resist layer step curing: pre-baking at 60°C for 10 min, exposure (energy 150-200 mJ / cm2), post-baking at 70°C for 15 min, developing with 1.5-2.0% sodium carbonate solution, and final curing at 130°C for 30 min to form a solder resist layer; S73, local gold plating area protection: using acid-resistant tape with a thickness of 80-100 μm to cover the local gold plating area, and the edge of the tape exceeds the gold plating area by ≥0.5 mm; sealing the tape by hot pressing process at 60-70°C and 0.1-0.15 MPa to prevent the nickel plating solution from eroding; S74, activation of the nickel plating area: using 0.5% citric acid solution to activate the leaked nickel plating area at 25-30°C for 30-60 s to remove the surface oxide layer and enhance the adhesion of the subsequent nickel plating layer. In the traditional process, ink accumulation often occurs on the edge of the local gold plating area and the nickel plating area during the solder resist ink coating, which affects the subsequent protection and plating quality. In the process, specific mesh number of screen printing photosensitive solder resist ink is used in step S71 to control the thickness of the ink layer and ensure that there is no ink accumulation on the edge of the local gold plating area and the nickel plating area, providing a flat basis for subsequent protection and plating treatment. In step S72, the process uses a step-by-step curing process, including pre-baking, exposure, post-baking, developing, and final curing, to fully cure the solder resist layer and improve its insulation and adhesion, better playing the role of solder resist. In step S73, acid-resistant tape with a specific thickness is used to cover the local gold plating area, and the hot pressing process is used for sealing, ensuring that the edge of the tape exceeds the gold plating area by a sufficient width, effectively preventing the nickel plating solution from eroding the gold plating area and protecting the performance of the local gold plating layer. In step S74, citric acid solution is used to activate the leaked nickel plating area, remove the surface oxide layer, and make the subsequent nickel plating layer adhere more closely to the substrate, enhancing the stability of the plating layer.

[0074] The nickel-gold plating process in step S8 includes: S81, gradient nickel layer deposition: In the first stage, the current density is 0.5-0.8 A / dm², and deposition lasts for 10-15 min to form a soft nickel layer (thickness 2-3 μm, Vickers hardness 180-200 HV, measured according to ISO 6507-1 standard); In the second stage, the current density is 1.8-2.2 A / dm². 2 A hard nickel layer (1-2 μm thick, Vickers hardness 300-350 HV) is formed by deposition for 5-8 min; the thickness ratio of the soft nickel layer to the hard nickel layer is 1.5:1 to 2:1, and the current density difference is 1.3-1.5 A / dm²; S82, palladium layer micro-roughening: palladium salt concentration 0.5-1 g / L, current density 0.1-0.3 A / dm² 2 Palladium layers were deposited under specific conditions with a surface roughness of 0.1-0.3 μm; S83, a pre-plated soft gold transition layer: a 0.2 A / dm² layer was deposited on the palladium layer surface. 2 A 0.1-0.2 μm soft gold layer (purity ≥99.9%) is deposited at a current density, and the pre-plated soft gold layer is not included in the total thickness of the localized hard gold plating. In traditional nickel plating processes, nickel layers with a single hardness are either too flexible and prone to brittleness, or too wear-resistant and prone to wear. In step S81 of this process, soft and hard nickel layers are deposited in stages using different current densities. By reasonably controlling the thickness ratio and current density difference between the two layers, the soft nickel layer provides good flexibility, while the hard nickel layer ensures sufficient wear resistance, allowing the nickel layer to have both good toughness and wear resistance. In step S82, the palladium layer deposition parameters are controlled to create a certain roughness on the palladium layer surface, increasing the contact area with subsequent plating layers, improving interlayer adhesion, and reducing the risk of plating peeling. In step S83, a soft gold transition layer is first deposited on the palladium layer surface. Utilizing the good compatibility between soft gold and the palladium and hard gold layers, it serves as a transition layer, making the overall plating structure more stable without affecting the total thickness control of the localized hard gold plating.

[0075] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A PCB board surface treatment process based on local gold plating plus nickel-gold plating, characterized in that, A method for processing PCBs requiring partial hard gold plating and nickel gold plating in other positions, comprising the following steps: S1, front process treatment: processing the PCB to a copper thickness before plating; S2, first layer pattern processing: dry film is pasted on the CS surface of the PCB and etching is performed to form a pattern, and the SS surface is not etched; S3, gold plating preparation: dry film is pasted on the SS surface, and the CS surface is exposed for gold plating; S4, partial gold plating: hard gold plating is performed on the exposed position of the CS surface; S5, film removal and second layer pattern processing: removing the double-sided dry film of the PCB, pasting dry film on the whole CS surface for protection, and etching the SS surface to form a pattern; S6, lead removal: removing the leads on the PCB; S7, solder resist and protection: after completing the solder resist processing, the partial gold plating position is protected, and the position requiring nickel plating is exposed; S8, nickel plating processing: nickel plating is performed on the exposed position, and then the surface treatment is completed through the post-process.

2. The PCB surface treatment process based on partial gold plating plus nickel-gold plating according to claim 1, characterized in that, The specific steps of step 1 are: S11, substrate pretreatment: soaking in a 5-8% sodium hydroxide solution at 50-60°C for 3-5 min; treating with a 10-15% ammonium persulfate solution at 25-30°C for 60-90 s, and controlling the micro-roughness of the substrate surface to be 0.1-0.2 μm; S12, drilling and hole wall treatment: high-pressure water flushing: for the residual drillings in the holes after drilling, when the hole diameter is >0.2 mm, deionized water with a pressure of 1.5-2 MPa is used for flushing; when the hole diameter is ≤0.2 mm, deionized water with a pressure of 0.8-1.2 MPa is used for flushing; plasma cleaning: plasma treatment is performed in an oxygen atmosphere at a power of 380-450 W for 60-90 s; S13, copper deposition and electroplating: uniformly depositing a conductive copper layer with a thickness of 0.5-1 μm on the substrate surface and hole wall to form a conductive substrate; The pulse current is used to thicken the whole copper layer, wherein the peak current density is 2-3 A / dm 2 , the forward pulse width is 0.5 ms, and the reverse pulse width is 0.2 ms; an adjustable magnetic mask is arranged above the area which needs to be plated with hard gold, the current distribution is controlled through a shielding coefficient of 40±5%, so that the copper thickness of the area is finally 5-10% higher than that of the non-gold-plated area, and the copper thickness deviation of the whole plate after local thickening is ≤8%. S14, water washing treatment: rinsing the substrate with deionized water until the pH value of the substrate surface reaches 6-7, and completing the front process treatment.

3. The PCB surface treatment process based on partial gold plating plus nickel-gold plating of claim 1, wherein, The specific steps in step S2 include the following steps: S21, dry film pretreatment: selecting a photosensitive dry film with a thickness of 35-50 μm and a resolution ≥25 μm, and equilibrating in an environment with a temperature of 25°C and a relative humidity ≤30% for 24 h; S22, CS surface dry film pasting: using roll pasting, setting the pasting temperature to 70-75°C, the roll pressure to 0.3-0.4 MPa, and the pasting speed to 1.5-2 m / min, so that the dry film is tightly combined with the CS surface copper layer; S23, exposure and development: exposure is performed by an exposure device with an alignment accuracy of ±5 μm, and the exposure energy is controlled to be 80-100 mJ / cm2; after exposure, baking is performed at 110°C for 2 min; and spraying development is performed at 30-35°C for 90-120 s using a 1.5-2.0% sodium carbonate solution; S24, CS surface etching: using an ammonia-based alkaline etching solution, etching is performed at 45-50°C; during etching, gradient spraying control is adopted, and the spraying pressure in the edge area is 0.03-0.04 MPa higher than that in the center area; S25, SS surface protection: using fluorine rubber-based composite film to cover the SS surface, and removing the composite film after the etching of the CS surface is completed.

4. The PCB surface treatment process based on partial gold plating plus nickel-gold plating of claim 1, wherein, In the step S3, the process of pasting the dry film on the SS surface adopts multi-parameter collaborative control to eliminate bubbles, and specifically includes the following steps. S31, using an acrylate-based photoresist dry film, preheating to 60-70°C to soften it, and pasting the dry film after removing the SS surface protection film; S32, under the vacuum degree of -0.08 to -0.1 MPa, a gradient pressure is applied from the center to the edge: the initial pressure at the center is 0.1-0.15 MPa, the final pressure at the edge is 0.2-0.25 MPa, and the increasing rate is 0.05 MPa / 5 cm; S33, the dry film edge is provided with a flow guide groove with a width of 0.1±0.02 mm and a depth of 0.05±0.02 mm to form a directional exhaust channel.

5. The PCB surface treatment process based on partial gold plating plus nickel-gold plating according to claim 4, characterized in that, The process of applying the gradient pressure from the center to the edge adopts a zoning dynamic control logic, specifically including: taking the center of the PCB board as the origin, dividing the center zone, the transition zone, and the edge zone; 1) the pressure in the center zone starts from 0.1-0.12 MPa and increases at a rate of 0.05 MPa / 5 cm; 2) the initial pressure in the transition zone is the final pressure in the center zone, and the increasing rate is 0.06-0.07 MPa / 5 cm; and when it is detected that there are dense pads in the region, the pressure is temporarily increased by 0.02 MPa; 3) the initial pressure in the edge zone is the final pressure in the transition zone, and the final pressure is controlled at 0.23-0.25 MPa, and the pressure increasing rate is dynamically adjusted with the distance from the flow guide groove: when the distance from the flow guide groove is ≤5 mm, the rate is increased to 0.08 MPa / 5 cm; when the distance from the flow guide groove is >5 mm, the rate is maintained at 0.06 MPa / 5 cm; when the pressure in the edge zone reaches 0.2 MPa, the vacuum degree is simultaneously increased to -0.095 to -0.1 MPa.

6. The PCB surface treatment process based on partial gold plating plus nickel-gold plating of claim 1, wherein, The local hard gold plating in the step S4 includes the following specific steps: S41, gold plating solution configuration: preparing a hard gold plating solution with a gold ion concentration of 6-8 g / L, ammonium citrate of 80-100 g / L, and a pH value controlled at 3.8-4.5; adding 0.5-1 g / L of cobalt salt to increase the hardness of the gold layer, and adding 0.1 g / L of polyvinylpyrrolidone as a dispersant; S42, plating parameter control: plating at the leaked gold plating position on the CS surface, setting the current density at 2-3 A / dm2, the temperature at 45-50°C, and the stirring rate at 300-400 r / min; conducting current through the plating network connected in series on the non-gold-plated surface of the SS surface to make the current distribution uniformity deviation ≤5%; S43, thickness gradient control: using regional current density control, the current density in the gold-plated edge region is 8-10% higher than that in the center region, forming a thickness gradient: the gold thickness at the gold-plated edge is 0.8-1.0 μm, the gold thickness in the center region is 0.5-0.7 μm, and the total gold thickness at the gold-plated edge is ≤1.2 μm; S44, post-plating treatment: first, ultrasonic cleaning with deionized water to remove surface residual plating solution; then, neutralizing with 2-3% citric acid solution at 35-40°C for 40-60 s to eliminate surface alkaline residues.

7. The PCB surface treatment process based on partial gold plating plus nickel-gold plating of claim 1, wherein, The film removing and second layer pattern processing of step S5 include the following specific steps: S51, double-sided film removing: using 5-8% sodium hydroxide solution, soaking for 2-3 min at 50-60℃, and assisting with 150-200W ultrasonic vibration to remove dry film on CS and SS surfaces, and the residual glue area is controlled to be ≤0.1mm2; S52, CS surface protection: covering 40-50μm thick etching-resistant dry film on the whole CS surface, and using vacuum degree-0.09-0.1MPa vacuum laminating process to make the dry film closely laminated with the CS surface pattern, and the edge sealing width is ≥1mm; S53, SS surface pattern etching: using alkaline copper chloride etching solution to etch at 48-50℃, and the etching rate is controlled to be 18-22μm / min; real-time monitoring the etching progress by CCD vision system, and controlling the pattern edge deviation to be ≤0.02mm; S54, damage detection: using lock-in infrared thermal imager to scan the CS surface, and when the detected regional temperature difference is >0.5℃, it is determined as potential etching damage, so as to ensure the local gold plating area to be intact.

8. The PCB surface treatment process based on partial gold plating plus nickel-gold plating of claim 1, wherein, The wire removing of step S6 includes the following specific steps: S61, wire identification and positioning: scanning the PCB by AOI automatic optical detection system to identify the wires to be removed with the accuracy of ±0.005mm, and marking the wire position and width information; S62, etching method to remove the wire: for the etchable wire, using local spraying process, the spraying liquid is 10-15% ammonium persulfate solution, the spraying pressure is controlled to be 0.2-0.3MPa, and only the wire area is etched; S63, laser method to remove isolated wire: for the isolated wire which cannot be etched, laser cutting is used for removal, the laser power is set to be 6-8W, the pulse frequency is 20kHz, and the spot diameter is 0.02-0.03mm; the cutting path is along the position 0.03-0.05mm away from the wire edge, and 5-8L / min nitrogen gas is introduced for auxiliary cooling; S64, removal effect acceptance: checking the wire removing area by 50 times microscope to ensure no wire residue and carbonization damage.

9. The PCB surface treatment process based on partial gold plating plus nickel-gold plating of claim 1, wherein, The solder resist and protection of step S7 includes the following specific steps: S71, solder resist ink coating: using 300-400 mesh silk screen to print photosensitive solder resist ink on the PCB surface to form 15-20μm thick ink layer; S72, solder resist layer step curing: 60℃ pre-baking for 10min, exposure, 70℃ post-baking for 15min, 1.5-2.0% sodium carbonate solution development, and 130℃ final solidification for 30min to form the solder resist layer; S73, local gold plating area protection: using 80-100μm thick acid-resistant adhesive tape to cover the local gold plating area, and the tape edge exceeds the gold plating area by ≥0.5mm; the tape is sealed by 60-70℃, 0.1-0.15MPa hot pressing laminating process; S74, activation of nickel and gold plating area: using 0.5% citric acid solution to activate the leaked nickel and gold plating area at 25-30℃ for 30-60s to remove the surface oxide layer.

10. The PCB surface treatment process based on partial gold plating plus nickel-gold plating of claim 1, wherein, The nickel and gold plating processing of step S8 includes: S81, gradient nickel layer deposition: in the first stage, the current density is 0.5-0.8 A / dm2, and the deposition time is 10-15 min to form a soft nickel layer; in the second stage, the current density is 1.8-2.2 A / dm2, and the deposition time is 5-8 min to form a hard nickel layer; the thickness ratio of the soft nickel layer to the hard nickel layer is 1.5:1 to 2:1, and the current density difference is 1.3-1.5 A / dm2 2 ; S82, roughening of the palladium layer: deposition of the palladium layer at a palladium salt concentration of 0.5-1 g / L and a current density of 0.1-0.3 A / dm 2 0.1-0.3 μm under the conditions given above; S83, pre-plated soft gold transition layer: 0.2 A / dm2 2 A 0.1-0.2 μm layer of soft gold is deposited at a current density of 0.2 A / dm2 and the pre-plated soft gold layer is not included in the total thickness of the local hard gold plating.

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