High-performance circuit board solder mask printing process

Abstract

The invention belongs to the technical field of circuit board printing, and particularly relates to a high-performance circuit board solder mask printing process. The solder mask printing process for the high-performance circuit board comprises the following steps: S1, pretreatment; s2, solder mask ink is prepared; s3, carrying out silk-screen printing; and S4, curing. Through pretreatment fine micro-etching, solder mask ink preparation, high-precision silk-screen printing and segmented curing processes, the adhesive force, the temperature resistance and the thermal shock resistance of the solder mask layer are remarkably improved, meanwhile, the dielectric loss and the process defect rate are reduced, and the strict requirements of a high-frequency high-speed circuit for reliability and signal integrity are comprehensively met.

Description

Technical Field

[0001] The present invention belongs to the technical field of printed circuit boards, and specifically relates to a solder mask printing process for high-performance circuit boards. Background Art

[0002] With the rapid development of 5G communication, autonomous driving, and high-density integrated circuits, the solder mask layer of circuit boards faces multiple challenges such as high-frequency signal transmission, high-temperature soldering, and reliability in complex environments. Traditional solder mask printing processes mostly use a single resin system combined with mechanical roughening treatment, but there are problems such as insufficient adhesion, high dielectric loss, and poor heat resistance. Conventional micro-etching processes often use sulfuric acid / hydrogen peroxide systems. Although they can roughen the copper surface, it is easy to cause uneven surface roughness due to too fast oxidation rate, and the residual acid solution is difficult to completely remove, leading to interface corrosion defects. In addition, most existing solder mask ink systems use epoxy resin or acrylic resin as a single substrate, and it is difficult to balance high-temperature stability and low dielectric requirements. The epoxy resin system has excellent heat resistance, but the dielectric constant (ε) is generally higher than 3.8, making it difficult to meet the requirements of 5G communication for signal integrity; the acrylic system has excellent dielectric properties, but the heat resistance is less than 220°C and it cannot pass the lead-free reflow soldering certification.

[0003] In terms of the application of fillers, existing technologies mostly rely on a single nano-silica to reduce the dielectric constant. However, its particle size distribution is wide and it is easy to agglomerate, resulting in an increase in filler-resin interface defects and high dielectric loss (Df). At the same time, traditional curing processes use single-stage high-temperature curing, resulting in uneven resin cross-linking density and internal stress accumulation, causing micro-cracks or delamination, and poor thermal shock performance, seriously affecting long-term reliability.

[0004] Therefore, there is an urgent need for a systematic solution to comprehensively improve the performance of the solder mask layer through the collaborative innovation of materials, processes, and structures. Summary of the Invention

[0005] The purpose of the present invention is to provide a solder mask printing process for high-performance circuit boards. Through pre-treatment, fine micro-etching, preparation of solder mask ink, high-precision screen printing, and segmented curing processes, the adhesion, heat resistance, and thermal shock resistance of the solder mask layer are significantly improved, while the dielectric loss and process defect rate are reduced.

[0006] To achieve the above purpose, the present invention provides the following technical solutions:

[0007] The solder mask printing process for high-performance circuit boards includes the following steps:

[0008] S1. Pre-treatment;

[0009] S2. Preparation of solder mask ink;

[0010] S3. Screen printing;

[0011] S4. Curing.

[0012] The specific steps of step S1 are as follows: After removing the oil stain on the surface of the circuit board, the surface of the circuit board is micro-etched with a micro-etchant to obtain a micro-etched circuit board.

[0013] Preferably, the main components of the micro-etchant are: 75 - 85 g / L of sodium persulfate, 35 - 45 g / L of nitric acid, 5 - 10 g / L of tetramethylammonium chloride, 0.5 - 1.0 g / L of benzotriazole, and the solvent is deionized water.

[0014] The preparation steps of the micro-etchant are: Add sodium persulfate and tetramethylammonium chloride into deionized water, stir evenly, control the temperature at room temperature, slowly add nitric acid, stir evenly, then add benzotriazole, and stir evenly to obtain it.

[0015] The specific conditions of the micro-etching treatment are: The micro-etching temperature in the first 20 s is 28 - 32 °C, then it is cooled to 23 - 25 °C until the surface roughness Ra of the copper surface is 0.35 - 0.45 μm, take it out, neutralize the residual acid with a buffer solution with pH = 6.5 - 7.5, then thoroughly wash it with ultrapure water, immerse it in a silane coupling agent solution, react at 38 - 42 °C for 4 - 6 min and then take it out, and then bake it at 78 - 82 °C for 8 - 12 min.

[0016] Preferably, in the silane coupling agent solution, the mass fraction of the silane coupling agent is 1% - 3%, and the solvent is an ethanol aqueous solution with a mass fraction of 65% - 75%.

[0017] Preferably, the silane coupling agent includes 3-aminopropyltriethoxysilane.

[0018] Through the compounding of sodium persulfate, nitric acid, tetramethylammonium chloride and benzotriazole, the etching uniformity and adhesion are significantly improved. This may be because sodium persulfate, as an oxidant, preferentially etches the grain boundaries of the copper surface to form nanoscale pits; nitric acid dissolves the oxidation products to prevent the formation of a passivation layer, and at the same time complexes copper ions with tetramethylammonium chloride to avoid local over-etching; benzotriazole adsorbs at the low-lying areas of the copper surface to inhibit lateral corrosion. Through the synergistic effect of these four chemical substances, a three-step dynamic balance of oxidation, dissolution and complexation is achieved, so that the surface roughness (Ra) of the copper surface is accurately controlled within 0.35 - 0.45 μm, the mechanical bite area increases, and combined with the treatment of the silane coupling agent, the adhesion is greatly improved. At the same time, uniform etching reduces stress concentration, the circuit breakage rate decreases, and the defect rate decreases.

[0019] Preferably, for the solder mask ink, calculated by weight, its preparation raw materials include 65 - 75 parts of resin matrix, 5 - 10 parts of curing agent, 12 - 20 parts of modified filler, and 0.5 - 1.5 parts of auxiliary agent.

[0020] Preferably, the resin matrix includes epoxy acrylate, phenolic epoxy resin, and polyimide prepolymer.

[0021] Preferably, the mass ratio of the epoxy acrylate, phenolic epoxy resin, and polyimide prepolymer is (7 - 9):(4 - 6):1; more preferably, it is 8:5:1.

[0022] Through the hybrid design of the three components of epoxy acrylate, phenolic epoxy resin, and polyimide prepolymer, the adhesion, heat resistance, and thermal shock resistance are simultaneously improved, while the dielectric constant is reduced. This may be because the hydroxyl groups in bisphenol A epoxy acrylate form hydrogen bonds with the copper surface to provide initial adhesion; the multi-benzene ring structure of bisphenol F phenolic epoxy resin forms a dense cross-linked network to inhibit high-temperature deformation; the rigid chain segments of the polyimide prepolymer are interspersed in the epoxy network to block the slip of molecular chains at high temperatures, while reducing the dielectric constant, reducing signal loss, and improving the transmission speed of high-frequency circuits. The epoxy resin provides interfacial bonding force, the phenolic epoxy constructs the framework, and the polyimide enhances the upper temperature limit of heat resistance. The three cooperate to form a "rigid-flexible combination" composite structure, thereby improving heat resistance and impact resistance, while improving dielectric properties. The rigid-flexible combination structure adapts to the thermal expansion and contraction of the copper surface and improves the adhesion retention rate.

[0023] Preferably, the epoxy acrylate is bisphenol A epoxy resin, with a functionality of 2 - 3, a viscosity of 9000 - 18000 cps at 30 °C, and an acid value ≤ 2.5 mgKOH / g.

[0024] In some preferred embodiments, the epoxy acrylate is from Boxing, B-123.

[0025] Preferably, the epoxy equivalent of the phenolic epoxy resin is 160 - 180 g / eq, and the viscosity at 25 °C is 2000 - 5000 cps.

[0026] In some preferred embodiments, the phenolic epoxy resin is from Nan Ya, NPEF-170.

[0027] The preparation method of the polyimide prepolymer includes the following steps: Under nitrogen protection, dissolve 4,4'-diaminodiphenyl ether in N-methylpyrrolidone, and after stirring until completely dissolved, add pyromellitic dianhydride in batches, control the reaction temperature ≤ 40 °C, stir at 300 - 500 rpm for 24 h, add benzoic anhydride to obtain a polyamic acid solution, and dehydrate under vacuum at 80 °C until the intrinsic viscosity is 0.4 - 0.6 dL / g to obtain the polyimide prepolymer.

[0028] Preferably, the molar ratio of 4,4'-diaminodiphenyl ether and pyromellitic dianhydride is 1:1.

[0029] Preferably, the addition amount of N-methylpyrrolidone is 2 times the total mass of 4,4'-diaminodiphenyl ether and pyromellitic dianhydride.

[0030] Preferably, the addition amount of benzoic anhydride is 1% - 5% of the molar amount of pyromellitic dianhydride.

[0031] By precisely matching the physical property parameters of epoxy acrylate, phenolic epoxy resin, and polyimide prepolymer, the process adaptability and performance are maximized. Epoxy acrylate with appropriate functionality ensures moderate crosslinking, avoiding brittleness caused by high functionality and affecting thermal shock resistance; phenolic resin with a specific epoxy equivalent extends the operable time, and at the same time reacts with dicyandiamide curing agent in proportion to ensure complete crosslinking, while the lower viscosity can ensure the dispersibility of fillers; polyimide prepolymer is compatible with epoxy resin, preventing interfacial defects caused by phase separation, and at the same time adjusting the thixotropy of the system. Low-viscosity epoxy acrylate ensures the dispersibility of fillers, the high epoxy equivalent of phenolic epoxy improves the crosslinking efficiency, the viscosity matching of polyimide prepolymer avoids sedimentation, the rheological characteristics of the three match to reduce phase separation, reduce the defect rate, improve thermal shock resistance, and also form a homogeneous dielectric network.

[0032] Preferably, the curing agent includes dicyandiamide and 2-ethyl-4-methylimidazole.

[0033] Preferably, the mass ratio of dicyandiamide to 2-ethyl-4-methylimidazole is (13 - 15):1; more preferably, it is 14:1.

[0034] The preparation method of the modified filler includes the following steps: soaking the filler in a silane coupling agent solution, taking it out after treating at 58 - 62 °C for 2 - 3 h, rinsing it with deionized water 2 - 3 times, and then drying it under vacuum to obtain the modified filler.

[0035] Preferably, the filler includes one or more of nano-silica, boron nitride, alumina, graphene, and silver nanowires.

[0036] Preferably, the mass ratio of nano-silica, boron nitride, and alumina is (10 - 14):(2 - 4):1; more preferably, it is 12:3:1.

[0037] Through the functional complementarity of multi-morphology fillers, the synergistic improvement of dielectric properties and reliability is achieved. This may be because nano-silica can fill the free volume of the resin and reduce the polarization rate; the two-dimensional heat conduction path of flaky boron nitride disperses heat and inhibits local heat accumulation; the hard particles of alumina improve wear resistance and prevent crack propagation. Silica reduces dielectric loss, boron nitride improves heat dissipation, and alumina enhances mechanical durability. The three work together to form a "dielectric-thermal conduction-wear resistance" trinity functional network, thus optimizing dielectric properties and thermal shock tolerance.

[0038] Preferably, the nano-silica is spherical, with an average particle size of 15-25 nm and a specific surface area of 145-160 m 2 / g.

[0039] Preferably, the boron nitride has a sheet diameter of 1-5 μm, a thickness <5 nm, a diameter-to-thickness ratio >50, and a bulk density of 0.1-0.3 g / cm 3 .

[0040] Preferably, the alumina is a mixed phase of α and γ, with a particle size of 25-35 nm.

[0041] In some preferred embodiments, the nano-silica, boron nitride, and alumina are all from Jiangsu Xianfeng Nano Materials Technology Co., Ltd.

[0042] Through the gradient design of the physical parameters of the filler, the beneficial effects of the filler are further optimized. This may be because by controlling the particle size and specific surface area of the silica, the small size can fill the micropores, and the specific surface area is adapted to the coating of the silane coupling agent; the boron nitride sheet with a large diameter-to-thickness ratio can form a continuous heat conduction network, and the specific bulk density ensures the dispersion stability; the alumina mixed with α-phase and γ-phase is selected, the α-phase provides high-temperature stability, the γ-phase improves the dispersibility, reduces the ink viscosity, and balances the performance of the solder mask ink. At the same time, the α-phase can inhibit the high-temperature shrinkage of the γ-phase, improve the heat resistance, and the particle size is distributed in a gradient with the particle size of the silica, reducing the sedimentation and agglomeration of the filler and forming a dense stacking structure, so that the film thickness is uniform and the defect rate is reduced.

[0043] Preferably, the additives include a leveling agent and an antifoaming agent.

[0044] Preferably, the leveling agent is a polyether-modified silicone leveling agent with a viscosity of 500-700 mPa·s at 25°C.

[0045] In some preferred embodiments, the leveling agent is from Shanghai Ziyi Chemical Co., Ltd., ZY-1333.

[0046] Preferably, the antifoaming agent is a silicone polyether antifoaming agent, non-ionic, with a solid content of 29%-31% and a viscosity of 1000-4000 mPa·s at 25°C.

[0047] In some preferred embodiments, the antifoaming agent is from Shanghai Ziyi Chemical Co., Ltd., ZY-2169.

[0048] Preferably, the mass ratio of the leveling agent to the antifoaming agent is (1.5-2.5):1.

[0049] The preparation method of the solder mask ink comprises the following steps: mixing a resin matrix and a modified filler, successively performing shear dispersion and ultrasonic dispersion, adding a curing agent and an auxiliary agent, stirring at 80-100 rpm for 1-5 min, performing vacuum degassing until the bubble residue rate < 0.1%, and passing through a 300-mesh sieve to obtain the product.

[0050] Preferably, the specific conditions for the shear dispersion are as follows: the rotation speed is 2000-3000 rpm, and the time is 10-20 min.

[0051] Preferably, the specific conditions for the ultrasonic dispersion are as follows: the frequency is 25-30 kHz, the power is 200-300 W, and the time is 5-15 min.

[0052] The specific steps of step S3 are as follows: fixing the micro-etched circuit board on the printing table, aligning it with the screen marking, pre-coating with the solder mask ink, and then precisely filling to obtain a wet film.

[0053] Preferably, the screen is a nickel screen, the mesh number is 400 meshes, the wire diameter is 23-27 μm, and the tension is 21-23 N / cm.

[0054] Preferably, the specific conditions for the pre-coating are as follows: the squeegee pressure is 2-4 kg / cm, and the speed is 190-210 mm / s.

[0055] Preferably, the specific conditions for the precise filling are as follows: the squeegee pressure is 4-6 kg / cm, and the speed is 140-160 mm / s.

[0056] Preferably, the thickness of the wet film is as follows: the thickness of the circuit area is 16-20 μm, and the thickness of the solder mask area is 27-33 μm.

[0057] The specific steps of step S4 are as follows: first performing light curing, then performing thermal curing, and finally performing infrared annealing.

[0058] Preferably, the specific conditions for the light curing are as follows: ultraviolet curing, the light intensity is 180-220 mW / cm 2 , and the illumination time is 28-32 s.

[0059] Preferably, the thermal curing is multi-stage gradient temperature rise curing. The temperature in the first stage is 78-82 °C, and the curing time is 12-18 min; the temperature in the second stage is 118-122 °C, and the curing time is 38-42 min; the temperature in the third stage is 178-182 °C, and the curing time is 28-32 min.

[0060] Preferably, the specific conditions for the infrared annealing are as follows: medium-wave infrared, the temperature is 58-62 °C, and the time is 8-12 min.

[0061] Through three-step sequential curing of photocuring, thermal curing, and infrared annealing, and energy field coupling, the contradiction between curing efficiency and interfacial stress is solved, thereby improving the temperature resistance, thermal shock resistance, and dielectric properties, while reducing the defect rate. This may be because firstly, through UV pre-curing, the surface rapidly gels to lock the filler distribution, avoiding dielectric inhomogeneity caused by sedimentation; then gradient thermal curing, in the first stage, gentle heating causes the solvent to slowly volatilize, avoiding microbubbles formed by sudden boiling, in the second stage, the decomposition temperature of dicyandiamide is matched to trigger the main cross-linking reaction, in the third stage, it promotes the imidization of polyimide to form a high-temperature dense network, and the gradient heating makes the cross-linking reaction proceed step by step, avoiding interfacial delamination caused by drastic temperature changes, thereby improving the temperature resistance and thermal shock tolerance; finally, infrared annealing, mid-wave infrared targets to eliminate the residual stress at the resin-copper interface. Photocuring maintains the shape, thermal curing densifies, and infrared annealing eliminates stress, and the energy input shows a gradient distribution of "surface → bulk → whole", thereby reducing the defect rate and improving the temperature resistance and thermal shock resistance.

[0062] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0063] 1. The present invention provides a solder mask printing process for high-performance circuit boards. Through pretreatment of fine etching, preparation of solder mask ink, high-precision screen printing, and segmented curing process, the adhesion, temperature resistance, and thermal shock resistance of the solder mask layer are significantly improved, while reducing the dielectric loss and process defect rate, fully meeting the stringent requirements of high-frequency and high-speed circuits for reliability and signal integrity.

[0064] 2. The present invention significantly improves the etching uniformity and adhesion through the compounding of sodium persulfate, nitric acid, tetramethylammonium chloride, and benzotriazole.

[0065] 3. Through the hybrid design of three components of epoxy acrylate, phenolic epoxy resin, and polyimide prepolymer, the adhesion, temperature resistance, and thermal shock resistance are simultaneously improved, while reducing the dielectric constant; through the precise matching of the physical property parameters of epoxy acrylate, phenolic epoxy resin, and polyimide prepolymer, the process adaptability and performance are maximized.

[0066] 4. Through the complementary functions of multi-morphology fillers, the synergistic improvement of dielectric properties and reliability is achieved; through the gradient design of the physical parameters of each filler, the beneficial effects of the fillers are further optimized.

[0067] 5. Through three-step sequential curing of photocuring, thermal curing, and infrared annealing, and energy field coupling, the contradiction between curing efficiency and interfacial stress is solved, thereby improving the temperature resistance, thermal shock resistance, and dielectric properties, while reducing the defect rate. Detailed implementation manners

[0068] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Apparently, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0069] The raw materials used in the present invention are all commercially available. Specifically:

[0070] The epoxy acrylate is bisphenol A type epoxy resin, with a functionality of 2-3, a viscosity of 9000-18000 cps at 30 °C, an acid value ≤ 2.5 mgKOH / g, from Boxing, B-123.

[0071] The phenolic epoxy resin has an epoxy equivalent of 160-180 g / eq and a viscosity of 2000-5000 cps at 25 °C, from Nan Ya, NPEF-170.

[0072] The nano-silica is spherical, with an average particle size of 15-25 nm and a specific surface area of 145-160 m 2 / g; the sheet diameter of boron nitride is 1-5 μm, the thickness < 5 nm, the aspect ratio > 50, and the bulk density is 0.1-0.3 g / cm 3 ; the alumina is a mixed phase of α and γ, with a particle size of 25-35 nm; all from Jiangsu Xianfeng Nano Materials Technology Co., Ltd.

[0073] The leveling agent is a polyether-modified silicone leveling agent, with a viscosity of 500-700 mPa·s at 25 °C, from Shanghai Ziyi Chemical Co., Ltd., ZY-1333.

[0074] The defoaming agent is a silicone polyether defoaming agent, non-ionic, with a solid content of 29%-31% and a viscosity of 1000-4000 mPa·s at 25 °C, from Shanghai Ziyi Chemical Co., Ltd., ZY-2169.

[0075] Example 1

[0076] This example provides a high-performance solder mask printing process for printed circuit boards, and the steps are as follows:

[0077] S1. After removing the oil stain on the surface of the printed circuit board by pretreatment, the surface of the printed circuit board is micro-etched with a micro-etchant to obtain a micro-etched printed circuit board;

[0078] S2. Prepare the solder mask ink;

[0079] S3. Screen printing: Fix the micro-etched printed circuit board on the printing table, align it with the screen mark, pre-coat it with the solder mask ink, and then accurately fill it to obtain a wet film;

[0080] S4. Curing.

[0081] The composition of the micro-etchant is: 80 g / L sodium persulfate, 40 g / L nitric acid, 8 g / L tetramethylammonium chloride, 0.8 g / L benzotriazole, and the balance solvent is deionized water.

[0082] The preparation steps of the micro-etchant are as follows: Add sodium persulfate and tetramethylammonium chloride to deionized water, stir evenly, control the temperature at room temperature, slowly add nitric acid, stir evenly, add benzotriazole, and stir evenly to obtain it.

[0083] The specific conditions of the micro-etching treatment are as follows: The micro-etching temperature in the first 20 s is 30 °C, then it is cooled to 25 °C until the surface roughness Ra of the copper surface is 0.4 μm, taken out, neutralize the residual acid with a buffer solution with pH = 7.0, then thoroughly wash it with ultrapure water, immerse it in a silane coupling agent solution, react at 40 °C for 5 min and then take it out, and then bake it at 80 °C for 10 min.

[0084] In the silane coupling agent solution, the mass fraction of the silane coupling agent is 2%, and the solvent is an ethanol aqueous solution with a mass fraction of 70%.

[0085] The silane coupling agent is 3-aminopropyltriethoxysilane.

[0086] The solder mask ink, by weight, its preparation raw materials are 70 parts of resin matrix, 8 parts of curing agent, 16 parts of modified filler, and 1 part of auxiliary agent.

[0087] The resin matrix is epoxy acrylate, phenolic epoxy resin, and polyimide prepolymer, and the mass ratio is 8:5:1.

[0088] The preparation method of the polyimide prepolymer has the following steps: Under nitrogen protection, dissolve 4,4'-diaminodiphenyl ether in N-methylpyrrolidone, stir until completely dissolved, add pyromellitic dianhydride in batches, control the reaction temperature ≤ 40 °C, stir at 400 rpm for 24 h, add benzoic anhydride to obtain a polyamic acid solution, and vacuum dehydrate at 80 °C until the intrinsic viscosity is 0.5 dL / g to obtain the polyimide prepolymer.

[0089] The molar ratio of 4,4'-diaminodiphenyl ether to pyromellitic dianhydride is 1:1.

[0090] The addition amount of N-methylpyrrolidone is 2 times the total mass of 4,4'-diaminodiphenyl ether and pyromellitic dianhydride.

[0091] The addition amount of benzoic anhydride is 3% of the molar amount of pyromellitic dianhydride.

[0092] The curing agent is dicyandiamide and 2-ethyl-4-methylimidazole, and the mass ratio is 14:1.

[0093] The preparation method of the modified filler comprises the steps of: soaking the filler in a silane coupling agent solution, taking it out after treating at 60 °C for 2.5 h, rinsing it three times with deionized water, and then drying it under vacuum to obtain the modified filler.

[0094] The filler is nano-silica, boron nitride, and alumina, and the mass ratio is 12:3:1.

[0095] The additives are a leveling agent and an antifoaming agent, and the mass ratio is 2:1.

[0096] The preparation method of the solder mask ink comprises the steps of: mixing the resin matrix and the modified filler, successively performing shear dispersion and ultrasonic dispersion, adding a curing agent and additives, stirring at 90 rpm for 3 min, then performing vacuum degassing until the bubble residue rate is 0.05%, and passing through a 300-mesh sieve to obtain the solder mask ink.

[0097] The specific conditions for the shear dispersion are: the rotation speed is 2500 rpm and the time is 15 min.

[0098] The specific conditions for the ultrasonic dispersion are: the frequency is 28 kHz, the power is 250 W, and the time is 10 min.

[0099] The wire mesh is a nickel mesh, with a mesh number of 400 meshes, a wire diameter of 25 μm, and a tension of 22 N / cm.

[0100] The specific conditions for the pre-coating are: the blade pressure is 3 kg / cm and the speed is 200 mm / s.

[0101] The specific conditions for the precise filling are: the blade pressure is 5 kg / cm and the speed is 150 mm / s.

[0102] The wet film thickness is: the thickness of the circuit area is 18 μm, and the thickness of the solder mask area is 30 μm.

[0103] The specific steps of step S4 are: first performing photocuring, then performing thermal curing, and finally performing infrared annealing.

[0104] The specific conditions for the photocuring are: ultraviolet curing, the light intensity is 200 mW / cm 2 , and the light irradiation time is 30 s.

[0105] The thermal curing is multi-stage gradient temperature rising curing. The temperature in the first stage is 80 °C and the curing time is 15 min; the temperature in the second stage is 120 °C and the curing time is 40 min; the temperature in the third stage is 180 °C and the curing time is 30 min.

[0106] The specific conditions for the infrared annealing are: medium-wave infrared, the temperature is 60 °C, and the time is 10 min.

[0107] Example 2

[0108] The difference between this embodiment and Embodiment 1 is that the resin matrix is epoxy acrylate, phenolic epoxy resin, and polyimide prepolymer, and the mass ratio is 9:6:1.

[0109] Comparative Example 1

[0110] The difference between this comparative example and Embodiment 1 is that the components of the micro-etchant are: 80 g / L sodium persulfate, 40 g / L nitric acid, and the balance solvent is deionized water.

[0111] Comparative Example 2

[0112] The difference between this comparative example and Embodiment 1 is that the resin matrix is epoxy acrylate.

[0113] Comparative Example 3

[0114] The difference between this comparative example and Embodiment 1 is that the resin matrix includes polyester acrylate, phenolic epoxy resin, and polyimide prepolymer, and the mass ratio is 8:5:1.

[0115] The polyester acrylate has a functionality of 4, a viscosity of 1600 - 2450 mPa·s at 60 °C, and an acid value of ≤ 9 mgKOH / g.

[0116] The polyester acrylate is from UCB, Ebecryl 811.

[0117] The phenolic epoxy resin has an epoxy equivalent of 175 - 182 g / eq and a viscosity of 20000 - 50000 cps at 25 °C.

[0118] The phenolic epoxy resin is from Changchun Co., Ltd., Taiwan Province, EPN 1138.

[0119] Comparative Example 4

[0120] The difference between this comparative example and Embodiment 1 is that the filler is nano-silica.

[0121] Comparative Example 5

[0122] The difference between this comparative example and Embodiment 1 is that the nano-silica is spherical, with an average particle size of 100 nm, and is from Nanjing Dongna Biotechnology Co., Ltd.

[0123] The boron nitride has a flake diameter of 1 - 3 μm, a thickness of < 100 nm, is from Beijing Decod Island Gold Technology Co., Ltd., and is flaky nano-boron nitride.

[0124] The alumina is of γ-phase, with a particle size of 10 - 15 nm, and is from Jiangsu Xianfeng Nano Materials Technology Co., Ltd.

[0125] Comparative Example 6

[0126] The difference between this comparative example and Example 1 is that the specific steps of step S4 are as follows: just perform thermal curing.

[0127] Comparative Example 7

[0128] The difference between this comparative example and Example 1 is that the temperature of the thermal curing is 180 °C and the curing time is 60 min.

[0129] Performance test

[0130] Test the adhesion force by referring to the method in ASTM D3359. Test the dielectric constant at 10 GHz by referring to the method in GB / T 12636-1990. Test the heat resistance by referring to the method in IPC-TM-650. Immerse the sample into the molten solder (Sn96.5 / Ag3.0 / Cu0.5) at (288 ± 5) °C for 10 seconds each time; repeat 5 times, and cool to room temperature at intervals each time; check for delamination and blistering under a microscope, and detect internal cracks by X-ray. Thermal shock resistance: Place the sample in a high and low temperature test chamber, keep it at -55 °C for 10 minutes and 125 °C for 10 minutes with a cycle of 15 minutes, and the conversion time ≤ 1 minute. After every 5 cycles, use a blade to pry the edge of the solder mask layer to check for cracking. Defect rate: Randomly detect 10 areas of 10 mm × 10 mm on the circuit board with a 50-fold optical microscope, count the number of voids (diameter > 0.1 mm) and cracks (length > 0.5 mm), and the defect rate = (number of defect points / total detection area) × 100%. The results are shown in Table 1.

[0131] Table 1 Measurement results

[0132]

[0133]

[0134] According to statistics, the processes of Examples 1-2 of the present invention have significantly improved the adhesion force, heat resistance and thermal shock resistance of the solder mask layer, while reducing the dielectric loss and process defect rate. In Comparative Example 1, tetramethylammonium chloride and benzotriazole were not added; in Comparative Example 2, the resin matrix was only epoxy acrylate; in Comparative Example 3, polyester acrylate was used to replace epoxy acrylate, and at the same time, the functionality and viscosity of the resin matrix did not match; in Comparative Example 4, the filler was only nano-silica; in Comparative Example 5, the particle size and aspect ratio of the filler did not match; in Comparative Example 6, there was only thermal curing, and in Comparative Example 7, there was only single-stage thermal curing. All performances are relatively poor compared with Example 1. Therefore, the circuit board prepared by the method described in this application has significantly improved the adhesion force, heat resistance and thermal shock resistance of the solder mask layer, while reducing the dielectric loss and process defect rate, and fully meets the stringent requirements of high-frequency and high-speed circuits for reliability and signal integrity.

[0135] The above are the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A solder mask printing process for high-performance circuit boards, characterized in that, It includes the following steps: S1. Pretreatment; S2. Preparation of solder mask ink; S3. Screen printing; S4. Curing; The specific steps of step S1 are: after removing the oil stain on the surface of the circuit board, the surface of the circuit board is micro-etched with a micro-etchant to obtain a micro-etched circuit board; The main components of the micro-etchant are: 75 - 85 g / L of sodium persulfate, 35 - 45 g / L of nitric acid, 5 - 10 g / L of tetramethylammonium chloride, 0.5 - 1.0 g / L of benzotriazole, and the solvent is deionized water.

2. The solder mask printing process for high-performance circuit boards according to claim 1, characterized in that, The solder mask ink, by weight, its preparation raw materials include 65 - 75 parts of resin matrix, 5 - 10 parts of curing agent, 12 - 20 parts of modified filler, and 0.5 - 1.5 parts of auxiliary agent.

3. The solder mask printing process for high-performance circuit boards according to claim 2, characterized in that, The resin matrix includes epoxy acrylate, phenolic epoxy resin, and polyimide prepolymer; the mass ratio of the epoxy acrylate, phenolic epoxy resin, and polyimide prepolymer is (7 - 9):(4 - 6):

1.

4. The solder mask printing process for high-performance circuit boards according to claim 3, wherein The epoxy acrylate is bisphenol A type epoxy resin, with a functionality of 2 - 3, a viscosity of 9000 - 18000 cps at 30 °C, and an acid value ≤ 2.5 mgKOH / g.

5. The solder mask printing process for high-performance circuit boards according to claim 3, characterized in that, The epoxy equivalent of the phenolic epoxy resin is 160 - 180 g / eq, and the viscosity at 25 °C is 2000 - 5000 cps.

6. The solder mask printing process for high-performance circuit boards according to claim 2, characterized in that The preparation method of the modified filler includes the following steps: soaking the filler in a silane coupling agent solution, taking it out after treating at 58 - 62 °C for 2 - 3 h, rinsing it with deionized water 2 - 3 times, and then drying it in vacuum to obtain it.

7. The solder mask printing process for high-performance circuit boards according to claim 6, wherein The filler includes one or more of nano-silica, boron nitride, alumina, graphene, and silver nanowires.

8. The solder mask printing process for high-performance circuit boards according to claim 7, characterized in that, The nano-silica is spherical, with an average particle size of 15-25 nm and a specific surface area of 145-160 m 2 / g.

9. The solder mask printing process for high-performance circuit boards according to claim 7, characterized in that, The diameter of the boron nitride flakes is 1-5 μm, the thickness is <5 nm, the diameter-to-thickness ratio is >50, and the bulk density is 0.1-0.3 g / cm 3 .

10. A product prepared by the high-performance circuit board solder mask printing process according to any one of claims 1 to 9.

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