Solder mask manufacturing process of high-speed circuit board with low insertion loss and high-speed circuit board

Abstract

According to the low-insertion-loss resistance welding manufacturing process of the high-speed circuit board and the high-speed circuit board, the insertion loss of a manufactured high-speed circuit board product is reduced by optimizing the resistance welding manufacturing process of the high-speed circuit board. Specifically, the whole surface of the high-speed circuit board is printed by adopting a two-time silk-screen process, and in the one-time silk-screen process, after ink is printed on the whole high-speed circuit board, a standing and air-drying process is adopted, and the thickness of the ink on the surface of the outer layer of the high-speed circuit board and between line gaps is reduced; and the problems that the printing ink is cured too early and the line-to-line accumulation is too thick due to high-temperature pre-baking are avoided. Afterwards, the thickness of the ink covering the surface of the circuit is precisely reinforced through secondary silk-screen, the distribution condition of solder resist ink with the thick line surface and the thin line space is formed, the electrical performance of the high-speed circuit board is improved, the insertion loss of the high-speed circuit board product is reduced, meanwhile, the solder resist manufacturing technological process of the high-speed circuit board is simplified, and the manufacturing efficiency is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of printed circuit board manufacturing, and more particularly, to a solder resist manufacturing process of a low insertion loss high-speed circuit board and a high-speed circuit board. BACKGROUND

[0002] With the continuous development of the printed circuit board (PCB) industry, PCB circuit boards are widely used in consumer electronic devices, servers, automotive medical devices, and the quality requirements for PCB signal transmission are gradually increasing. When the signal passes through the connector, part of the energy will be consumed due to electrical characteristics, material loss, etc. For example, when a high-frequency input signal line is connected to a PCB finished board, the signal will be lost when passing through the board material and the circuit, i.e. dielectric, resistance, etc. At this time, if the insertion loss is too large, it will affect the signal transmission effect. Therefore, for the terminal product corresponding to the PCB, the smaller the insertion loss, the less the signal will be affected during transmission, the better the signal quality, and the more ideal the transmission effect.

[0003] In the design of high-speed PCB, usually the signal line design is placed on the inner layer circuit or the outer layer circuit, and the main factors affecting the insertion loss of the PCB product in the process of the outer layer circuit of the PCB are the board material, the circuit and the solder resist; wherein, the outer layer solder resist on the PCB refers to a thin film covering the outer layer copper foil of the PCB, which is used to form an electrical insulation effect on the surface of the PCB, avoiding the mutual contact of different parts of the circuit to cause accidental short circuit or current leakage, and can prevent the short circuit of the outer layer circuit on the PCB, avoid the outer layer copper layer exposed to air easy to oxidize, help to keep the solder joint clean, and prolong the service life of the PCB. In the process of making solder resist on the PCB, the ink material and the thickness of the ink between the lines have a great influence on the insertion loss. Taking the ink material as an example, the ink material can absorb part of the signal energy, at the same time, the thicker the ink coverage thickness of the signal line area, the more the transmission medium, the greater the signal loss. In the existing solder resist manufacturing process of high-speed PCB, the copper thickness of the outer layer circuit of the high-speed PCB is relatively large, usually single silk printing or multiple silk printing is adopted to print sufficient ink on the signal line area to ensure the thickness requirement of the solder resist coverage on the circuit, so as to form an effective protective barrier on the outer layer circuit area, prevent the solder from leaking or flowing between the solder joints in the subsequent soldering process to cause short circuit, and improve the durability of the high-speed PCB. But in the existing solder resist manufacturing process of high-speed PCB, especially in the case of small line gap between the outer layer circuits, when the ink thickness covered on the surface of the outer layer circuit of the high-speed PCB meets the requirements, the ink thickness filled in the line gap will be too thick, basically level with the ink layer covered on the circuit, resulting in failure of the insertion loss test. At the same time, the too thick ink thickness filled in the line gap may also affect the formation of the solder joint on the high-speed PCB, resulting in poor subsequent soldering, poor electrical connection between the circuits, too narrow gap between the circuits, etc., affecting the precision and stability of the high-speed PCB. Therefore, it is necessary to develop a solder resist manufacturing process to accurately control the thickness of the solder resist layer covered on the outer layer circuit of the high-speed PCB and the thickness of the solder resist ink in the line gap, so as to ensure the balance of protection, solderability and electrical performance, and reduce the insertion loss of the manufactured high-speed PCB product. SUMMARY

[0004] The present application aims to overcome at least one of the above-mentioned defects of the prior art, and provides a solder resist manufacturing process for a low insertion loss high-speed circuit board and a high-speed circuit board. By optimizing the solder resist manufacturing process of the high-speed circuit board, the thickness of the solder resist layer covered on the outer layer circuit of the high-speed PCB and the thickness of the solder resist ink in the line gap are accurately controlled, so as to ensure the balance of protection, solderability and electrical performance, and reduce the insertion loss of the manufactured high-speed PCB product.

[0005] The technical scheme adopted by the present application is to provide a solder resist manufacturing process for a low insertion loss high-speed circuit board, comprising the following steps: S1. Pre-treatment, pre-treating the surface of a circuit board made of outer layer circuit to obtain a high-speed circuit board to be made of solder resist; S2. First screen printing, using solder resist ink to screen print the whole high-speed circuit board, and placing the printed high-speed circuit board to dry naturally; S3. Second screen printing, using solder resist ink to screen print the whole high-speed circuit board after the first screen printing, and placing the printed high-speed circuit board to flow flat and then pre-baking; S4. Developing and curing, exposing and developing the surface of the pre-baked high-speed circuit board, and forming a high-speed circuit board made of solder resist after curing process.

[0006] In the technical solution, the solder resist manufacturing process of the high-speed circuit board is optimized to accurately control the thickness of the solder resist layer covered by the outer layer circuit and the thickness of the solder resist ink in the line gap of the high-speed circuit board, thereby reducing the insertion loss of the manufactured high-speed circuit board product. Specifically, the whole surface of the high-speed circuit board is printed by using a two-time screen printing process, and the ink distribution of the solder resist layer of the high-speed circuit board is significantly optimized by using a natural drying process after the first screen printing, thereby reducing the insertion loss while considering the process efficiency and reliability. In the first screen printing process, the natural drying process is used instead of the traditional pre-baking process after printing the ink on the whole high-speed circuit board, the ink naturally diffuses and thins out in the line gap by using the flowability of the ink itself, and the overall ink thickness of the outer surface of the high-speed circuit board is reduced by the loss of the ink on the surface of the outer layer circuit along the edge of the copper line due to gravity, thereby avoiding the problems of premature curing and excessive accumulation of the ink in the line gap caused by high-temperature pre-baking. Subsequently, the ink thickness covered on the surface of the circuit is precisely reinforced by the second screen printing to form an ideal distribution of "thick on the surface of the line and thin in the line gap", which not only ensures the corrosion resistance and insulation protection of the circuit, but also greatly reduces the dielectric loss during high-frequency signal transmission, thereby improving the electrical performance of the high-speed circuit board and reducing the insertion loss of the high-speed circuit board product. Further, the natural drying process is used instead of the traditional pre-baking process to dynamically control the flowability of the ink, and the screen printing process is used to precisely control the ink thickness on the surface of the high-speed circuit board and the ink thickness in the line gap, thereby optimizing the precision and reliability of the high-speed circuit board, simplifying the solder resist manufacturing process of the high-speed circuit board, and improving the manufacturing efficiency.

[0007] Further, in the step S2, the specific steps of the natural drying are as follows: vertically inserting the high-speed circuit board into a placing rack, and placing the high-speed circuit board and the placing rack under the air outlet of a clean room to dry naturally for 20-30 minutes.

[0008] In the technical solution, the high-speed circuit board is vertically inserted into the stand and placed under the clean room air outlet for 20-30 minutes of air drying, and the synergy of gravity and ink fluidity is used to realize dynamic optimization of ink distribution. Specifically, by vertically placing the high-speed circuit board, the ink between the lines is naturally diffused and thinned downward, reducing the high-frequency signal loss caused by medium accumulation. At the same time, the air outlet directional drying controls the ink curing speed to avoid excessive flow of surface ink, providing an even and moderate ink base for subsequent secondary silk printing. The ink morphology can be precisely controlled simply and conveniently, preventing excessive thickness between lines from causing excessive insertion loss, and ensuring that the surface ink retains sufficient coverage ability, thereby improving the high-frequency signal transmission quality and process stability on the high-speed circuit board.

[0009] Further, in the step S3, the specific step of static leveling is that the high-speed circuit board is naturally parked for 15-30 minutes after secondary silk printing double-sided printing.

[0010] In the technical solution, after secondary silk printing, the static leveling process of natural parking is used to realize uniform spreading and bubble elimination of the surface ink, avoiding ink shrinkage or orange peel defects caused by direct high-temperature pre-baking. The static leveling process realized by natural parking not only retains the moderate fluidity of the ink to fill the fine gap and improve the coverage density, but also stabilizes the ink morphology on the high-speed circuit board in a gentle way, ensuring the formation of a smooth and continuous solder mask layer on the circuit surface. At the same time, the static leveling time after secondary silk printing is 15-30 minutes, which ensures that the ink thickness filled between the lines is optimized in the static air drying process of primary silk printing and the static leveling process of secondary silk printing, finally balancing between low loss and high reliability, providing a stable dielectric environment for high-frequency signal transmission, and meeting the precision and reliability requirements of high-speed and high-density circuit boards.

[0011] Further, the solder mask ink uses low Df ink; the viscosity of the solder mask ink is 55-75 dps; and the mesh number of the silk screen used in primary silk printing and secondary silk printing is not less than 60T.

[0012] In the technical solution, the ink with low Df, precise control of ink viscosity and high mesh screen are used to significantly improve the signal transmission performance of high-speed circuit board. The ink with low Df can directly reduce signal energy loss and adapt to high-frequency electric field environment. Moderate viscosity ensures the controllability and uniformity of ink flowability during screen printing, avoiding ink overflow between lines or surface oil shortage. High mesh screen limits the amount of ink penetration at a time, and combined with the twice screen printing process, the thickness of ink between lines is precisely controlled, while the surface solder resist layer is protected. Under the synergistic effect of the three, the corrosion resistance and insulation reliability of the solder resist layer covering the outer circuit of the high-speed circuit board are maintained, and the influence of the dielectric loss caused by the solder resist on the integrity of the high-frequency signal is minimized.

[0013] Further, in the step S2, the doctor blade with a thickness of 10 mm and a rubber hardness of 75° is used for one-time screen printing, the doctor blade angle is 8-10°, the screen printing speed is 180-200 mm / s, and the screen printing pressure is 6 bar.

[0014] Further, in the step S3, the doctor blade with a thickness of 10 mm and a rubber hardness of 75° is used for two-time screen printing, the doctor blade angle is 8-10°, the screen printing speed is 180-200 mm / s, and the screen printing pressure is 5 bar. In the technical solution, the precise control of the doctor blade parameters and the screen printing process parameters is realized simply and quickly, and the hardness and angle of the doctor blade in two printing are designed, the thickness is 10 mm, the hardness is 75°, which maintains the stability of ink transfer and reduces the influence of doctor blade deformation on screen contact. Combined with constant doctor blade angle and screen printing speed, the angle is 8-10° and the speed is 180-200 mm / s, the precise control of ink flow and thickness is realized. Further, one-time screen printing uses 6 bar high pressure to ensure that low viscosity ink forms a thin and uniform covering layer under high mesh screen, while moderately filling the interline area. Two-time screen printing precisely reinforces the surface ink thickness by 5 bar low pressure to avoid interline thickening, and finally realizes the distribution of dense protection and light and low loss ink on the surface of the circuit under simple and fast process conditions, thereby significantly reducing the transmission loss of high-frequency signals on the high-speed circuit board.

[0015] Further, in the step S3, the pre-baking temperature is 70-80℃, and the pre-baking time is 40-60min. By setting the pre-baking temperature of 70-80℃ and the mild curing condition of 40-60min, the controllable volatilization of the ink solvent and the preliminary cross-linking after the second silk printing are realized. The selected moderate curing temperature interval avoids the brittleness of the ink or the accumulation of internal stress caused by high temperature, and prevents the exposure and development defects caused by the residual solvent at low temperature. The gradual curing process retains the moderate flexibility of the ink, ensures the bonding accuracy of the solder mask and the circuit in the subsequent exposure process, and stabilizes the thinning form of the ink between the lines by extending the pre-baking time window, thereby suppressing the risk of reflow or collapse. It not only consolidates the differentiated ink distribution structure between the line and the line gap formed by the two silk printing, but also provides a uniform and dense dielectric substrate for the final curing, thereby ensuring the low loss and long-term reliability of high-frequency signal transmission of the high-speed circuit board.

[0016] Further, in the step S4, the exposure grid number is 11-12 grids, and the exposure energy is 300-400mJ. By reducing the exposure energy control, the precision of the solder mask pattern is ensured while avoiding the damage to the dielectric properties of the ink caused by high energy. The exposure energy can not only complete the photocuring cross-linking of the ink and ensure the clarity of the solder mask and the circuit edge after development, but also reduce the risk of ink brittleness or local carbonization caused by excessive exposure, thereby maintaining the inherent characteristics of the ink material with low dielectric loss factor. At the same time, the mild exposure condition and the thin layer of ink structure formed by the two silk printing work together to avoid the secondary flow or thickness fluctuation of the ink between the lines caused by high energy thermal effect, consolidate the optimized distribution form of the thin oil between the lines and the uniform oil on the line surface, further reduce the dielectric loss during high-frequency signal transmission, and improve the interface bonding strength of the solder mask and the circuit.

[0017] Further, in the step S4, the development uses K2CO3 developer with a concentration of 0.8%, the development temperature is 29-33℃, the development time is 70s, and the development pressure is 2.0bar.

[0018] Preferably, the ink thickness on the outer layer circuit of the high-speed circuit board is 0.8-1.5 mil, and the ink thickness between adjacent outer layer circuits is 0.5-1.0 mil. By precisely controlling the differential distribution of the ink thickness on the surface of the outer layer circuit (0.8-1.5 mil) and the ink thickness between adjacent circuits (0.5-1.0 mil), the demand for high-frequency signal transmission performance and circuit protection on the high-speed circuit board is systematically balanced. The ink thickness on the surface of the circuit sufficiently covers and protects the circuit from corrosion and mechanical strength, and the significant thinning of the ink thickness between the circuits greatly reduces the dielectric loss in the high-frequency electric field area, avoiding excessive absorption of signal energy. Through precise control and synergistic optimization between the two, the physical protection capability of the solder resist layer for the complex circuit is consolidated, and the core cause of high-frequency insertion loss is maximally weakened, ensuring the stable and controllable dielectric environment of the signal transmission path and improving the electrical performance of the high-speed circuit board.

[0019] Another object of the present application is to provide a low-insertion-loss high-speed circuit board made by the solder resist manufacturing process as described in the technical solution.

[0020] Preferably, the low-insertion-loss high-speed circuit board provided by the present technical solution has an outer layer copper foil thickness of 0.5-2 oz, an outer layer circuit thickness of 2.5-3.0 mil, a line width of 5-15 mil, a circuit gap of 3-5 mil, an ink thickness on the outer layer circuit of the high-speed circuit board of 0.8-1.5 mil, and an ink thickness between adjacent outer layer circuits of 0.5-1.0 mil.

[0021] Compared with the prior art, the present application has the following advantages: 1. By optimizing the solder resist manufacturing process of the high-speed circuit board, the entire surface of the high-speed circuit board is printed by two times of silk screen printing, and after the first time of silk screen printing, a standing air drying process is used to significantly optimize the ink distribution of the solder resist layer of the high-speed circuit board, which reduces the insertion loss while taking into account the process efficiency and reliability. Specifically, in the first silk screen printing process, after printing ink on the high-speed circuit board, standing air drying is used instead of the traditional pre-baking process. The ink naturally spreads and thins out between the lines by taking advantage of its own flowability, and the ink thickness on the surface of the outer layer circuit is reduced by the loss of ink along the edge of the copper line due to gravity, which avoids the problems of premature solidification and excessive thickness of the ink between the lines caused by high-temperature pre-baking. Subsequently, the ink thickness covered on the surface of the circuit is precisely supplemented by the second silk screen printing, forming an ideal distribution of "thick on the surface of the line and thin between the lines", which not only ensures the corrosion resistance and insulation protection of the circuit, but also greatly reduces the dielectric loss during high-frequency signal transmission, thereby improving the electrical performance of the high-speed circuit board and reducing the insertion loss of the high-speed circuit board product.

[0022] 2. The over-static air drying process replaces the traditional pre-baking process to dynamically control the ink fluidity, and the silk screen printing process is superimposed to realize precise control of the ink thickness on the high-speed circuit board surface and the ink thickness between lines, thereby optimizing the precision and reliability of the high-speed circuit board, simplifying the solder resist manufacturing process of the high-speed circuit board, and improving the manufacturing efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 A flowchart of the solder resist manufacturing process of the low-insertion-loss high-speed circuit board and the high-speed circuit board provided by the present application.

[0024] Figure 2 A structure diagram of the high-speed circuit board and its solder resist layer prepared in Example 2.

[0025] Figure 3 A structure diagram of the high-speed circuit board and its solder resist layer prepared in Comparative Example 1.

[0026] Figure 4 A test result diagram of the insertion loss of the high-speed circuit board prepared in Example 2.

[0027] Figure 5 A test result diagram of the insertion loss of the high-speed circuit board prepared in Comparative Example 1. DETAILED DESCRIPTION

[0028] The drawings of the present application are only used for illustrative explanation, and cannot be understood as a limitation of the present application. In order to better illustrate the following examples, some components in the drawings may be omitted, enlarged or reduced, and do not represent the actual product size; it is understandable for those skilled in the art that some well-known structures and their descriptions in the drawings may be omitted.

[0029] Example 1 As shown in the drawings, the present embodiment provides a solder resist manufacturing process of a low-insertion-loss high-speed circuit board, specifically comprising the following steps: Figure 1 S1. Pretreatment, pretreating the surface of the circuit board manufactured with an outer layer circuit to obtain a high-speed circuit board to be manufactured with solder resist; S2. First silk screen printing, printing the entire high-speed circuit board with solder resist ink by first silk screen printing, and air drying the printed high-speed circuit board; S3. Second silk screen printing, printing the entire high-speed circuit board after the first silk screen printing with solder resist ink by second silk screen printing, and air drying the printed high-speed circuit board after leveling; S4. Development and curing, exposing and developing the surface of the high-speed circuit board after pre-baking, and forming a high-speed circuit board after solder resist manufacturing through a curing process.

[0030] ​Specifically, the entire surface of the high-speed circuit board is printed using two silk-screen processes, and a static air-drying process is used after the first silk-screening is completed to significantly optimize the ink distribution of the high-speed circuit board's solder mask layer, thereby reducing insertion loss while balancing process efficiency and reliability. In the first silk-screening process, after the ink is printed on the entire high-speed circuit board, a static air-drying process is used instead of the traditional pre-baking process. The ink's inherent fluidity is utilized to naturally diffuse and thin the ink filling between the wires. The ink on the outer layer of the circuit surface flows along the edges of the copper wires due to gravity, reducing the overall ink thickness on the outer surface of the high-speed circuit board. This avoids the problems of premature curing of the ink and excessive accumulation between wires caused by high-temperature pre-baking. Subsequently, the ink thickness covering the circuit surface is precisely reinforced through a second silk-screening process, forming an ideal distribution of "thick lines on the surface and thin lines between lines." This not only ensures corrosion resistance and insulation protection for the circuit, but also significantly reduces dielectric loss during high-frequency signal transmission, thereby improving the electrical performance of the high-speed circuit board and reducing the insertion loss of high-speed circuit board products. Furthermore, the static air-drying process replaces the traditional pre-baking process to dynamically control the ink fluidity, and the silk-screen printing process is superimposed to achieve precise control of the ink thickness on the high-speed circuit board surface and the ink thickness between lines. While optimizing the precision and reliability of the high-speed circuit board, it also simplifies the solder mask production process of the high-speed circuit board and improves production efficiency.

[0031] Furthermore, in step S2, the specific step of allowing the circuit board to air dry is as follows: inserting the high-speed circuit board vertically onto a rack and placing the board below the cleanroom air outlet to allow the board to air dry naturally for 20-30 minutes. Specifically, by placing the high-speed circuit board vertically, the ink between the lines naturally diffuses downward and becomes thinner, reducing high-frequency signal loss caused by dielectric accumulation. At the same time, directional air drying at the air outlet controls the ink curing speed, preventing excessive loss of surface ink due to excessive flow, and providing a uniform and appropriate ink base for subsequent secondary screen printing. The ink morphology can be precisely and easily controlled, preventing excessive insertion loss caused by excessive thickness between lines while ensuring that the surface ink retains sufficient coverage, thereby improving the high-frequency signal transmission quality and process stability on the high-speed circuit board.

[0032] Further, in the step S3, the specific step of the static leveling is that the whole high-speed circuit board is naturally placed for 15-30 minutes after the double-side printing of the secondary silk screen printing. The process of static leveling by natural placement not only retains the moderate fluidity of the ink to fill the fine gap and improve the coverage density, but also stabilizes the ink form on the high-speed circuit board in a mild way, ensuring the formation of a smooth and continuous solder resist protective layer on the circuit surface. At the same time, the static leveling time after the secondary silk screen printing is 15-30 minutes, so as to ensure the collaborative optimization of the ink thickness between the lines in the static air-drying process of the primary silk screen printing and the static leveling process of the secondary silk screen printing, finally balancing between low loss and high reliability, providing a stable dielectric environment for high-frequency signal transmission, and adapting to the precision and reliability requirements of high-speed and high-density circuit boards.

[0033] Further, the solder resist ink adopts a low Df ink; the viscosity of the solder resist ink is 55-75 dps; and the mesh number of the silk screen printing mesh used in the primary silk screen printing and the secondary silk screen printing is not less than 60T.

[0034] By using the low Df ink, precisely controlling the viscosity of the ink, and using the high-mesh silk screen printing mesh, the signal transmission performance of the high-speed circuit board is significantly improved. The low Df ink can directly reduce the signal energy loss and adapt to the high-frequency electric field environment. The moderate viscosity ensures the controllability of the ink flow and the uniformity of the coverage in the silk screen printing process, avoiding ink overflow between lines or surface oil shortage. The high-mesh silk screen printing mesh limits the single ink penetration amount, and in combination with the two silk screen printing processes, the ink thickness between lines is precisely controlled, while the surface solder resist layer is densely protected, and the influence of the dielectric loss caused by the solder resist on the integrity of the high-frequency signal is minimized.

[0035] Further, in the step S2, the rubber scraper with a thickness of 10 mm and a rubber hardness of 75° is used for the primary silk screen printing, the rubber scraping angle is 8-10°, the silk screen printing speed is 180-200 mm / s, and the silk screen printing pressure is 6 bar.

[0036] Further, in the step S3, the rubber scraper with a thickness of 10 mm and a rubber hardness of 75° is used for the secondary silk screen printing, the rubber scraping angle is 8-10°, the silk screen printing speed is 180-200 mm / s, and the silk screen printing pressure is 5 bar. The precise control of the glue scraping parameters and the silk printing process parameters is simple and fast to realize the precise control of the ink thickness of the high-speed circuit board area. The hardness and angle of the glue scraping in the two printing are designed as 10 mm and 75°, which maintains the stability of the ink transfer and reduces the influence of the scraper deformation on the screen contact. Combined with the constant glue scraping angle and silk printing speed, the angle is 8-10° and the speed is 180-200 mm / s, which realizes the precise control of the ink leveling and thickness. Further, the first silk printing adopts 6 bar high pressure to ensure that the low viscosity ink forms a thin and uniform covering layer under the high mesh screen, and at the same time, it is filled with the line area; the second silk printing precisely reinforces the surface ink thickness through 5 bar low pressure, avoids the secondary thickening of the line, and finally realizes the sufficient coverage and dense protection of the line surface and the light and thin ink distribution of the line under the simple and fast process conditions, thereby significantly reducing the transmission loss of high-frequency signals on the high-speed circuit board.

[0037] Further, in the step S3, the pre-baking temperature is 70-80℃, and the pre-baking time is 40-60 min. By setting the pre-baking temperature of 70-80℃ and the mild curing condition of 40-60 minutes, the differential ink distribution structure between the line surface and the line gap formed by the two silk printing is consolidated, and a uniform and dense dielectric substrate is provided for the final curing, thereby ensuring the low loss and long-term reliability of high-frequency signal transmission of the high-speed circuit board.

[0038] Further, in the step S4, the exposure grid number is 11-12 grids, and the exposure energy is 300-400 mJ. By reducing the exposure energy control, the precision of the solder mask pattern is ensured while avoiding the damage of high energy to the dielectric properties of the ink. At the same time, the mild exposure condition and the thin layer ink structure formed by the two silk printing work together to avoid the secondary flow or thickness fluctuation of the ink between the lines caused by high energy thermal effect, consolidate the optimized distribution form of thin oil between the lines and uniform oil on the line surface, further reduce the dielectric loss during high-frequency signal transmission, and at the same time, improve the interface bonding strength of the solder mask layer and the circuit.

[0039] Further, in the step S4, K2CO3 developer with a concentration of 0.8% is used for development, the development temperature is 29-33℃, the development time is 70 s, and the development pressure is 2.0 bar.

[0040] Preferably, the ink coating thickness on the outer layers of the high-speed circuit board is 0.8-1.5 mils, and the ink thickness between adjacent outer layers is 0.5-1.0 mils. By precisely controlling the differential distribution of ink thickness on the outer layers and between adjacent lines, a systematic balance is achieved between the high-frequency signal transmission performance and line protection requirements on the high-speed circuit board. This precise control and coordinated optimization of the two not only strengthens the solder mask's physical protection capabilities for complex lines, but also minimizes the core cause of high-frequency insertion loss, ensuring a stable and controllable dielectric environment in the signal transmission path and improving the electrical performance of the high-speed circuit board.

[0041] Example 2 like Figures 1-2 As shown, this embodiment provides a solder mask manufacturing process for a high-speed circuit board with low insertion loss, specifically, comprising the following steps: S1. Pre-treatment: After the outer layer circuits are fabricated, the high-speed circuit board undergoes a series of processes, including pickling, water washing, volcanic ash grinding, ultrasonic water washing, high-pressure water washing, and heat drying, to clean the board surface. After the pre-treatment, the high-speed circuit board is naturally cooled to room temperature before being screen-printed. The pickling process uses 5% sulfuric acid to remove oxides from the copper surface. The volcanic ash grinding process uses a 500-mesh needle roller with 20% volcanic ash to polish the copper surface.

[0042] S2. Screen printing is performed once, using a high-mesh screen, low-viscosity ink, and high printing pressure to print a thin layer of ink on the entire high-speed circuit board. The screen printing screen uses a 62T dot screen and the screen printing ink uses low Df performance ink, preferably Taiyo's PSR4000 LT02G. When the screen printing ink is diluted, a diluent is added to dilute it, and the ink viscosity is controlled at 55-75dps. The squeegee has a thickness of 10mm and a rubber hardness of 75°. When performing a screen printing, the squeegee angle is 8-10°, the screen printing speed is 180-200mm / s, and the screen printing pressure is 6bar. After the screen printing is completed once, the high-speed circuit board is vertically inserted into the PCB placement rack. Next, place the PCB in the vertical rack below the cleanroom's air outlet and air dry for 20-30 minutes. During this time, the ink around the circuits will flow and diffuse due to the ink's inherent fluidity, thinning the ink between the circuits. Simultaneously, the ink on the circuit surface will flow along the copper edges, thinning the surface and requiring a second print to completely cover the circuit surface. The drying time should be neither too long nor too short. Excessive drying time will cause the ink to dry and become viscous, making it easy for the second screen print to stick to the screen and cause uneven ink thickness. Excessive drying time will cause the ink to remain highly fluid, leading to significant ink loss during the second screen print. The ink thickness on the circuit surface will be too low, resulting in thin lines.

[0043] S3, after the first silk screen printing, the printed board is left to dry, and then a second silk screen printing is performed on the whole board using the same silk screen, ink and squeegee as the first printing, but with a reduced pressure of 5 bar to thicken the ink on the surface of the circuit. After the second printing, the printed board is left to stand for 15-30 minutes to allow the ink to flow and defoam, and then the board is pre-baked to evaporate part of the solvent in the ink and to pre-cure the ink, providing preparation for exposure. The pre-baking temperature is controlled at 75°C, and the pre-baking time is 48 minutes.

[0044] S4, after the pre-baking, the printed board is exposed to light using a DI exposure machine with LED light source to cause cross-linking reaction of the photopolymer in the ink. The exposure grid number is controlled at 11-12, and the exposure energy is 300-400 mJ. Then, the ink that has not been exposed to light and has not undergone cross-linking reaction is cleaned off using 0.8% K2CO3 solution to expose the clean copper surface. The developing temperature is 31±2°C, the developing time is 70 seconds, and the developing pressure is 2.0 bar. Finally, the ink on the board is heat-cured using the high-temperature hot air circulation of an oven to evaporate the solvent in the ink completely to form a permanent insulating and corrosion-resistant protective film. The high-temperature curing temperature is 155°C, and the curing time is 70 minutes to form the finished high-speed circuit board.

[0045] Example 3 The example provides a low-insertion-loss high-speed circuit board made by the solder mask manufacturing process provided in Example 1 or Example 2. The thickness of the outer copper foil of the high-speed circuit board provided in the example is 0.5-2 oz, the thickness of the outer circuit is 2.5-3.0 mil, the line width is 5-15 mil, the line gap is 3-5 mil, the thickness of the ink covering the outer circuit on the high-speed circuit board is 0.8-1.5 mil, and the thickness of the ink between adjacent outer circuits is 0.5-1.0 mil.

[0046] Comparative Example 1 As shown in Figure 3 , the comparative example provides a solder mask manufacturing process for high-speed circuit board and a high-speed circuit board made by the process. The difference between the comparative example and Example 2 is that: S2, one silk printing LMS, on the entire high-speed circuit board on the outer layer of the circuit area printed a layer of ink, printed circuit position screen printing using 51T, silk printing ink using ink viscosity of 55-75 dps PSR4000 G23K, silk printing using 10mm thickness 75° hardness of the glue scraping, scraping angle control in 8-10°, and using the nail bed tool double-sided printing, silk printing speed control in 200-240mm / s, silk printing pressure control in 4-6bar. After silk printing, the PCB board is vertically inserted into the vehicle. Immediately, the printed high-speed circuit board is naturally placed for 15-30 minutes, the high-speed circuit board ink is allowed to stand and flow flat and defoaming, and then the high-speed circuit board is pre-baked. The high-speed circuit board after standing, flowing flat and defoaming is heated by a tunnel oven to volatilize part of the solvent in the ink, pre-curing the ink, and drying the ink to provide preparation for exposure. The pre-baking temperature is controlled at 75℃, and the pre-baking time is 21min.

[0047] S3, secondary silk printing, after the first silk printing and pre-baking, using the same scraper, silk printing pressure and other printing parameters as the first silk printing, printed circuit position screen printing using 43T, silk printing ink using ink viscosity of 115-135 dps PSR4000 G23K, secondary silk printing is performed on the outer layer of the high-speed circuit board to thicken the ink thickness on the surface of the circuit. After secondary silk printing, the printed high-speed circuit board is naturally placed for 15-30 minutes, the high-speed circuit board ink is allowed to stand and flow flat and defoaming, and then the high-speed circuit board is pre-baked. The high-speed circuit board after standing, flowing flat and defoaming is heated by a tunnel oven to volatilize part of the solvent in the ink, pre-curing the ink, and drying the ink to provide preparation for exposure. The pre-baking temperature is controlled at 75℃, and the pre-baking time is 48min.

[0048] S4, development and curing, the high-speed circuit board after secondary silk printing and pre-baking is exposed to light by a DI exposure machine. The exposure uses LED light source to cause cross-linking reaction of the photopolymer in the ink. The exposure energy is 350-450mJ. Then, the ink which has not been exposed to light and has not undergone cross-linking reaction is cleaned with 0.8% K2CO3 solution to expose clean copper surface. The development temperature is 31±2℃, the development time is 70-80s, and the development pressure is 2.0bar. Finally, the ink on the board surface is heat cured by high temperature hot air circulation of an oven, and the solvent in the ink is completely volatilized to achieve permanent insulation and corrosion protection film. The high temperature curing temperature is 155℃, the curing time is 70min, and the high-speed circuit board after solder mask manufacturing is formed.

[0049] According to Figure 2As shown in the high-speed circuit board prepared by the solder resist manufacturing process in Example 2, the thickness of the solder resist ink covering the whole board in the outer layer circuit area is thin, the thickness of the ink on the line surface is thin and uniform, and the thickness of the ink between the lines is thin, which has a significant height difference with the ink layer on the line surface. Figure 3 As shown in the high-speed circuit board prepared by the solder resist manufacturing process in Comparative Example 1, the thickness of the solder resist ink covering the whole board in the outer layer circuit area is thick, the thickness of the ink on the line surface is thick, and the thickness of the ink between the lines is thick, which has a small height difference with the ink layer on the line surface. The high-speed circuit boards prepared in Example 2 and Comparative Example 1 were respectively tested for insertion loss, and the test results showed that, as shown in Figure 4 the high-speed circuit board prepared in Example 2 had a fitted insertion loss of 0.627323 dB / inch; and as shown in Figure 5 the high-speed circuit board prepared in Comparative Example 1 had a fitted insertion loss of 1.051669 dB / inch, which was reduced by 0.424346 dB / inch, indicating that the insertion loss of the high-speed circuit board prepared in Example 2 after the solder resist manufacturing process was reduced by about 40% compared with the insertion loss of the high-speed circuit board prepared by the conventional solder resist manufacturing process.

[0050] Obviously, the above examples of the present application are only examples for clearly illustrating the technical solutions of the present application, and are not intended to limit the specific embodiments of the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A solder resist manufacturing process for a high-speed circuit board with low insertion loss, characterized by, The process comprises the following steps: S1. Pre-treatment, pre-treating the surface of a circuit board made of outer layer circuits to obtain a high-speed circuit board to be made of solder resist; S2. First screen printing, printing the entire high-speed circuit board by using solder resist ink for first screen printing, and then placing the printed high-speed circuit board for air drying; S3. Second screen printing, printing the entire high-speed circuit board after the first screen printing by using solder resist ink for second screen printing, and then placing the printed high-speed circuit board for leveling and pre-baking after the leveling; S4. Developing and curing, exposing and developing the surface of the high-speed circuit board after pre-baking, and then forming a high-speed circuit board made of solder resist after a curing process.

2. The low insertion loss high speed circuit board's solder resist manufacturing process according to claim 1, wherein, In the step S2, the specific steps of air drying are as follows: vertically inserting the high-speed circuit board on a placing rack, and then placing the high-speed circuit board and the placing rack under the air outlet of a clean room for natural air drying for 20-30 minutes.

3. The low insertion loss high speed circuit board's solder resist manufacturing process according to claim 1, wherein, In the step S3, the specific steps of leveling are as follows: naturally placing the high-speed circuit board for 15-30 minutes after the second screen printing.

4. The solder resist manufacturing process for a low insertion loss high speed circuit board according to any one of claims 1 to 3, wherein The solder resist ink is a low Df ink, and the viscosity of the solder resist ink is 55-75 dps. The mesh number of the screen printing screen used in the first screen printing and the second screen printing is not less than 60T.

5. The solder resist manufacturing process for a low insertion loss high speed circuit board according to any one of claims 1 to 3, wherein In the step S2, the squeegee has a thickness of 10 mm and a rubber hardness of 75°, and the squeegee angle is 8-10°, the screen printing speed is 180-200 mm / s, and the screen printing pressure is 6 bar when the first screen printing is performed.

6. The solder resist manufacturing process for a low insertion loss high speed circuit board according to any one of claims 1 to 3, wherein In the step S3, the squeegee has a thickness of 10 mm and a rubber hardness of 75°, and the squeegee angle is 8-10°, the screen printing speed is 180-200 mm / s, and the screen printing pressure is 5 bar when the second screen printing is performed.

7. The solder resist manufacturing process for a low insertion loss high speed circuit board according to any one of claims 1 to 3, wherein In the step S3, the pre-baking temperature is 70-80°C, and the pre-baking time is 40-60 minutes.

8. The solder resist manufacturing process for a low insertion loss high speed circuit board according to any one of claims 1 to 3, wherein In the step S4, the exposure grid number is 11-12, and the exposure energy is 300-400 mJ. The developing is performed by using a K2CO3 developing solution with a concentration of 0.8%, a developing temperature of 29-33°C, a developing time of 70 seconds, and a developing pressure of 2.0 bar.

9. The solder resist manufacturing process for a low insertion loss high speed circuit board according to any one of claims 1 to 3, wherein The ink thickness on the outer layer circuits of the high-speed circuit board is 0.8-1.5 mil, and the ink thickness between adjacent outer layer circuits is 0.5-1.0 mil.

10. A low-insertion-loss high-speed circuit board made by using the solder resist making process according to any one of claims 1-9.

Images