Solder resist manufacturing process for high-speed circuit board with low insertion loss and high-speed circuit board

Abstract

The application provides a solder resist manufacturing process of a low-insertion-loss high-speed circuit board and a high-speed circuit board. The solder resist manufacturing process of the high-speed circuit board is optimized, and the insertion loss of the manufactured high-speed circuit board product is reduced. Specifically, the whole surface of the high-speed circuit board is printed by adopting a twice-screen printing process, and a standing air-drying process is adopted after the whole high-speed circuit board is printed with ink in the once-screen printing process, and the ink thickness between the outer surface of the high-speed circuit board and the line gap is reduced, so that the problems of premature solidification of the ink and excessive thickness of the line gap caused by high-temperature pre-baking are avoided. Subsequently, the ink thickness covered on the surface of the line is precisely supplemented by the twice-screen printing, so that the solder resist ink distribution of thick line surface and thin line gap 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, and the solder resist manufacturing process flow of the high-speed circuit board is simplified and the manufacturing efficiency is improved.

Description

Technical Field

[0001] This invention relates to the field of printed circuit board manufacturing, and more specifically, to a solder mask fabrication process for a high-speed circuit board with low insertion loss and the high-speed circuit board itself. Background Technology

[0002] With the continuous development of the printed circuit board (PCB) industry, PCBs are widely used in consumer electronics, servers, automotive, and medical equipment. The requirements for the quality of PCB signal transmission are also gradually increasing. When a signal passes through a connector, some energy is lost due to electrical characteristics and material losses. For example, when a high-frequency input signal line connects to a finished PCB board, the signal experiences losses as it passes through the board material and circuitry, such as dielectric and resistance losses. Excessive insertion loss in this case can affect signal transmission performance. Therefore, for the end products manufactured using PCBs, the lower the insertion loss, the less the signal is affected during transmission, resulting in better signal quality and a more ideal transmission effect.

[0003] In high-speed PCB design, signal lines are typically placed on inner or outer layers. The main factors affecting insertion loss during the manufacturing process of outer layer PCBs are the substrate, the circuitry, and the solder mask. The outer layer solder mask is a thin film covering the outer copper foil of the PCB. It provides electrical insulation, preventing contact between different parts of the circuit, which could cause accidental short circuits or current leakage. Furthermore, it prevents short circuits in the outer layer circuitry, avoids oxidation of the outer copper layer exposed to air, helps maintain the cleanliness of solder joints, and extends the PCB's lifespan. During the solder mask fabrication process, the ink material and the thickness of the ink between lines significantly affect insertion loss. For example, the ink material can absorb some signal energy. Furthermore, the thicker the ink coverage in the signal line area, the more transmission medium is involved, resulting in greater signal loss. In the current solder mask manufacturing process for high-speed PCBs, the outer layer circuitry has a relatively thick copper layer. Typically, a single or multiple silkscreen printing process is used to print sufficient ink on the signal line areas to ensure the required solder mask coverage thickness. This forms an effective protective barrier in the outer layer circuitry area, preventing solder leakage or flow between solder joints and short circuits during subsequent soldering, thus improving the durability of the high-speed PCB. However, in the current high-speed PCB solder mask manufacturing process, especially when the gaps between outer layer circuits are small, even if the ink thickness covering the outer layer circuitry surface meets the requirements, the ink thickness filling the gaps between the circuits can be excessive, almost flush with the ink layer covering the circuitry. This can lead to insertion loss test failure. Furthermore, excessive ink thickness filling the gaps can also affect the formation of solder joints on the high-speed PCB, resulting in subsequent soldering defects, poor electrical connectivity between circuits, and excessively narrow gaps between circuits, affecting the precision and stability of the high-speed PCB.

[0004] Therefore, it is necessary to develop a solder mask manufacturing process to precisely control the thickness of the solder mask layer covering the outer layer circuitry on high-speed PCBs and the thickness of the solder mask ink in the gaps between the lines, so as to ensure a balance in terms of protection, solderability, and electrical performance, and reduce the insertion loss of the manufactured high-speed PCB products. Summary of the Invention

[0005] The present invention aims to overcome at least one of the defects of the prior art and provide a solder mask manufacturing process and a high-speed circuit board with low insertion loss. By optimizing the solder mask manufacturing process of the high-speed circuit board, the thickness of the solder mask layer covering the outer layer circuit on the high-speed PCB and the thickness of the solder mask ink in the gap are precisely controlled to ensure a balance in terms of protection, solderability and electrical performance, and reduce the insertion loss of the manufactured high-speed PCB products.

[0006] The technical solution adopted in this invention is firstly to provide a solder mask fabrication process for a high-speed circuit board with low insertion loss, including the following steps:

[0007] S1. Pre-treatment: Pre-treatment is performed on the surface of the circuit board made with the outer layer circuitry to obtain the high-speed circuit board to be solder masked.

[0008] S2. One-time screen printing: The high-speed circuit board is screen printed on both sides in one time using solder resist ink, and the printed high-speed circuit board is left to air dry.

[0009] S3. Secondary screen printing: The high-speed circuit board after the first screen printing is printed on both sides using solder resist ink. After the printed high-speed circuit board is left to stand and level, it is pre-baked.

[0010] S4. Development and curing: The surface of the pre-baked high-speed circuit board is exposed and developed, and then cured to form the high-speed circuit board after the solder mask is manufactured.

[0011] In this technical solution, by optimizing the solder mask manufacturing process of high-speed circuit boards, the thickness of the solder mask layer covering the outer layer of the circuit board and the thickness of the solder mask ink in the gaps are precisely controlled, thereby reducing the insertion loss of the manufactured high-speed circuit board products. Specifically, by employing a two-stage screen printing process to print on the entire surface of the high-speed circuit board, and then using a static air-drying process after the first screen printing, the ink distribution of the solder mask layer of the high-speed circuit board is significantly optimized, reducing insertion loss while maintaining process efficiency and reliability. In the first screen printing process, after printing ink on the entire high-speed circuit board, static air-drying is used instead of the traditional pre-baking process. The ink's own fluidity allows the ink filling the gaps to naturally diffuse and thin out, and the ink on the outer layer surface is thinned by gravity flowing along the copper wire edges, thus reducing the overall ink thickness on the outer layer surface of the high-speed circuit board. This avoids the problems of premature ink curing and excessive accumulation between lines caused by high-temperature pre-baking. Subsequently, a second screen printing process precisely reinforces the ink thickness covering the circuit surface, creating an ideal distribution of "thick ink on the surface and thin ink between lines." This ensures both corrosion resistance and insulation protection of the circuit, while significantly reducing dielectric loss during high-frequency signal transmission, thereby improving the electrical performance of the high-speed circuit board and reducing insertion loss. Furthermore, a static air-drying process replaces the traditional pre-baking process to dynamically control ink flow, while simultaneously using screen printing to achieve precise control over the ink thickness on the circuit board surface and between lines. This optimizes the precision and reliability of the high-speed circuit board while simplifying the solder mask fabrication process and improving production efficiency.

[0012] Further, in step S2, the specific steps of the static air drying are as follows: the high-speed circuit board is vertically inserted into the placement rack and placed together below the air outlet of the clean room for static air drying for 20-30 minutes.

[0013] In this technical solution, by vertically inserting the high-speed circuit board and placing it below the cleanroom air outlet for 20-30 minutes to air dry, the synergistic effect of gravity and ink flow is utilized to achieve dynamic optimization of ink distribution. Specifically, by placing the high-speed circuit board vertically, the ink between the lines naturally diffuses downwards and thins, reducing high-frequency signal loss caused by media accumulation. At the same time, directional air drying at the air outlet controls the ink curing speed, preventing excessive ink loss due to excessive flow on the surface. This provides a uniform and appropriate ink base for subsequent secondary screen printing, allowing for simple, convenient, and precise control of the ink form. This prevents excessive insertion loss caused by excessive thickness between lines and ensures that the surface ink retains sufficient coverage, thereby improving the high-frequency signal transmission quality and process stability on the high-speed circuit board.

[0014] Furthermore, in step S3, the specific steps of the static leveling are as follows: after the high-speed circuit board is screen-printed on both sides twice, it is left to stand naturally for 15-30 minutes.

[0015] In this technical solution, a natural resting and leveling process is used after the secondary screen printing to achieve uniform surface spreading and bubble elimination by utilizing the ink's own fluidity, avoiding ink shrinkage or orange peel defects caused by direct high-temperature pre-baking. This natural resting and leveling process retains the ink's appropriate fluidity to fill tiny gaps and improve coverage density, while gently stabilizing the ink form on the high-speed circuit board. This ensures a smooth and continuous solder resist layer on the circuit surface. Furthermore, the resting and leveling time after the secondary screen printing is 15-30 minutes, ensuring that the ink thickness filling the lines is synergistically optimized between the initial screen printing's resting and drying process and the secondary screen printing's resting and leveling process. Ultimately, a balance is achieved 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, high-density circuit boards.

[0016] Furthermore, the solder resist ink is a low Df ink; the viscosity of the solder resist ink is 55-75 dps;

[0017] Furthermore, the mesh count of the screen printing mesh used in the first and second screen printing processes shall not be less than 60T.

[0018] In this technical solution, by employing ink with a low dielectric loss factor (low Df), precisely controlling ink viscosity, and using high-mesh-count mesh, the signal transmission performance of high-speed circuit boards is significantly improved. Low Df ink directly reduces signal energy loss and is suitable for high-frequency electric field environments. Moderate viscosity ensures that the ink maintains both controllable flowability and uniform coverage during screen printing, preventing ink overflow between lines or insufficient ink on the surface. High-mesh-count mesh, by limiting the amount of ink transmitted in a single pass and combining it with two screen printing processes, precisely suppresses the ink thickness between lines while ensuring dense protection of the surface solder mask layer. Through the synergistic effect of these three factors, the corrosion resistance and insulation reliability of the solder mask layer covering the outer circuitry of the high-speed circuit board are maintained, while minimizing the impact of dielectric loss caused by the solder mask on the integrity of high-frequency signals.

[0019] Furthermore, in step S2, the squeegee is 10mm thick and has a rubber hardness of 75°. When performing one screen printing, the squeegee angle is 8-10°, the screen printing speed is 180-200mm / s, and the screen printing pressure is 6bar.

[0020] Furthermore, in step S3, when using a squeegee with a thickness of 10mm and a rubber hardness of 75° for secondary screen printing, the squeegee angle is 8-10°, the screen printing speed is 180-200mm / s, and the screen printing pressure is 5bar.

[0021] In this technical solution, precise control of ink thickness in high-speed circuit board areas is achieved quickly and easily through the synergistic effect of precisely controlling squeegee parameters and screen printing process parameters. The squeegee hardness and angle design during the two printing processes—10mm thickness and 75° hardness—maintains ink transfer stability while reducing the impact of squeegee deformation on screen contact. Combined with a constant squeegee angle and screen printing speed of 8-10° and 180-200mm / s, precise control of ink leveling and thickness is achieved. Furthermore, the first screen printing uses 6bar high pressure to ensure that low-viscosity ink forms a thin and uniform coverage layer under high-mesh screen, while appropriately filling the inter-line areas. The second screen printing uses 5bar low pressure to precisely reinforce the surface ink thickness, avoiding secondary thickening between lines. Ultimately, under simple and quick process conditions, sufficient coverage and dense protection of the circuit surface are achieved, along with a thin and low-loss ink distribution between lines, significantly reducing the transmission loss of high-frequency signals on high-speed circuit boards.

[0022] Furthermore, in step S3, the pre-baking temperature is 70-80℃, and the pre-baking time is 40-60 minutes. By setting a pre-baking temperature of 70-80℃ and a mild curing condition of 40-60 minutes, controllable evaporation and initial cross-linking of the ink solvent are achieved after the second screen printing. The selected moderate curing temperature range avoids ink embrittlement or internal stress accumulation caused by high temperatures, and also prevents exposure and development defects caused by solvent residue at low temperatures. The progressive curing process retains the appropriate flexibility of the ink, ensuring the bonding accuracy of the solder resist layer and the circuit in the subsequent exposure process. Furthermore, by extending the pre-baking time window, the thinning morphology of the ink between lines is stabilized, suppressing the risk of backflow or collapse. This not only consolidates the differentiated ink distribution structure between the lines and gaps formed by the two screen printing processes, but also provides a uniform and dense dielectric substrate for final curing, thereby ensuring low loss and long-term reliability of high-frequency signal transmission on high-speed circuit boards.

[0023] Further, in step S4, the number of exposure grids is 11-12, and the exposure energy is 300-400mJ. By reducing the exposure energy control, the accuracy of the solder resist pattern is ensured while avoiding damage to the dielectric properties of the ink from high energy. This allows the exposure energy to complete the photocuring and cross-linking of the ink, ensuring the clarity of the solder resist layer and the circuit edges after development, while also reducing the risk of ink embrittlement or localized carbonization caused by overexposure, maintaining the inherent characteristics of the ink material's low dielectric loss factor. At the same time, the mild exposure conditions and the thin ink structure formed by the two screen printing processes work synergistically to avoid secondary ink flow or thickness fluctuations between lines due to high-energy thermal effects, consolidating the optimized distribution of thin ink between lines and uniform ink on the line surface, further reducing dielectric loss during high-frequency signal transmission, and improving the interfacial bonding strength between the solder resist layer and the circuit.

[0024] Furthermore, in step S4, the developing solution is a 0.8% K2CO3 developing solution, the developing temperature is 29-33℃, the developing time is 70s, and the developing pressure is 2.0 bar.

[0025] Preferably, the ink thickness covering the outer layer lines on the high-speed circuit board is 0.8-1.5 mil, and the ink thickness between adjacent outer layer lines is 0.5-1.0 mil. By precisely controlling the differential distribution of the ink thickness (0.8-1.5 mil) on the surface of the outer layer lines and the ink thickness (0.5-1.0 mil) between adjacent line gaps, the requirements of high-frequency signal transmission performance and line protection on the high-speed circuit board are systematically balanced. The ink thickness on the line surface fully covers the lines to ensure corrosion resistance and mechanical strength, while the significant reduction in ink thickness between line gaps greatly reduces dielectric loss in the high-frequency electric field region, avoiding excessive absorption of signal energy. Through precise control and synergistic optimization between the two, the physical protection capability of the solder mask layer for complex lines is strengthened, and the core cause of high-frequency insertion loss is minimized to the greatest extent, ensuring a stable and controllable dielectric environment for the signal transmission path and improving the electrical performance of the high-speed circuit board.

[0026] Another object of the present invention is to provide a high-speed circuit board with low insertion loss manufactured using the solder resist fabrication process described in this technical solution.

[0027] Preferably, the outer copper foil thickness of the low insertion loss high-speed circuit board provided by this technical solution is 0.5-2oz, the outer circuit thickness is 2.5-3.0mil, the line width is 5-15mil, the line spacing is 3-5mil, the ink thickness covering the outer circuit on the high-speed circuit board is 0.8-1.5mil, and the ink thickness between adjacent outer circuits is 0.5-1.0mil.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] 1. By optimizing the solder mask manufacturing process of high-speed circuit boards, a two-stage screen printing process is adopted to print on the entire surface of the high-speed circuit board. After the first screen printing, a static air-drying process is used to significantly optimize the ink distribution of the solder mask layer, reducing insertion loss while ensuring process efficiency and reliability. Specifically, in the first screen printing process, after printing ink on the entire high-speed circuit board, static air-drying is used instead of the traditional pre-baking process. The ink's own fluidity allows the ink filling the lines to naturally diffuse and thin out. The ink on the outer layer surface is also thinned by gravity due to the loss of ink along the copper wire edges, avoiding the problems of premature ink curing and excessive accumulation between lines caused by high-temperature pre-baking. Subsequently, the ink thickness covering the circuit surface is precisely reinforced through the second screen printing, forming an ideal distribution of "thick on the surface, thin between lines." This ensures the corrosion resistance and insulation protection of the circuits while significantly reducing 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.

[0030] 2. The static air-drying process replaces the traditional pre-baking process to dynamically control the ink flow. At the same time, the screen printing process is superimposed to achieve precise control of the ink thickness on the surface of the high-speed circuit board and the ink thickness between lines. While optimizing the precision and reliability of the high-speed circuit board, it also simplifies the solder mask manufacturing process of the high-speed circuit board and improves the manufacturing efficiency. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the solder mask fabrication process and the flow chart of the low insertion loss high-speed circuit board provided by the present invention.

[0032] Figure 2 This is a schematic diagram of the high-speed circuit board and its solder resist layer prepared in Example 2.

[0033] Figure 3 This is a schematic diagram of the high-speed circuit board and its solder mask layer prepared in Comparative Example 1.

[0034] Figure 4 This is a schematic diagram of the insertion loss test results of the high-speed circuit board prepared in Example 2.

[0035] Figure 5 This is a schematic diagram showing the test results of the insertion loss of the high-speed circuit board prepared in Comparative Example 1. Detailed Implementation

[0036] The accompanying drawings are for illustrative purposes only and should not be construed as limiting the invention. To better illustrate the following embodiments, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions; it is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0037] Example 1

[0038] like Figure 1 As shown, this embodiment provides a solder mask fabrication process for a high-speed circuit board with low insertion loss, specifically including the following steps:

[0039] S1. Pre-treatment: Pre-treatment is performed on the surface of the circuit board made with the outer layer circuitry to obtain the high-speed circuit board to be solder masked.

[0040] S2. One-time screen printing: The high-speed circuit board is screen printed on both sides in one time using solder resist ink, and the printed high-speed circuit board is left to air dry.

[0041] S3. Secondary screen printing: The high-speed circuit board after the first screen printing is printed on both sides using solder resist ink. After the printed high-speed circuit board is left to stand and level, it is pre-baked.

[0042] S4. Development and curing: The surface of the pre-baked high-speed circuit board is exposed and developed, and then cured to form the high-speed circuit board after the solder mask is manufactured.

[0043] Specifically, by employing a two-stage screen printing process to print ink onto the entire surface of the high-speed circuit board, and then using a static air-drying process after the first screen printing, the ink distribution of the solder mask layer on the high-speed circuit board is significantly optimized. This reduces insertion loss while maintaining process efficiency and reliability. In the first screen printing process, after printing ink onto the entire high-speed circuit board, static air-drying is used instead of the traditional pre-baking process. The ink's own fluidity allows the ink filling the lines to naturally diffuse and thin, and the ink on the outer layer surface is thinned by gravity flowing along the copper wire edges, thus reducing the overall ink thickness on the outer surface of the high-speed circuit board. This avoids the problems of premature ink curing and excessive ink buildup between lines caused by high-temperature pre-baking. Subsequently, the second screen printing precisely reinforces the ink thickness covering the circuit surface, forming an ideal distribution of "thick on the surface, thin between lines." This ensures the corrosion resistance and insulation protection of the circuits while significantly reducing 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. Furthermore, by replacing the traditional pre-baking process with a static air-drying process to dynamically regulate ink flow, and simultaneously adding a screen printing process to achieve precise control over the ink thickness on the high-speed circuit board surface and between lines, the precision and reliability of the high-speed circuit board are optimized, while also simplifying the solder mask manufacturing process and improving production efficiency.

[0044] Further, in step S2, the specific steps of the static air-drying are as follows: the high-speed circuit board is vertically inserted into the placement rack and placed below the air outlet of the clean room for static air-drying for 20-30 minutes. Specifically, by placing the high-speed circuit board vertically, the ink between the lines naturally diffuses downwards and thins out, reducing high-frequency signal loss caused by media accumulation. At the same time, the directional air-drying at the air outlet controls the ink curing speed, preventing excessive ink loss due to excessive flow on the surface. This provides a uniform and appropriate ink base for subsequent secondary screen printing, allowing for simple, convenient, and precise control of the ink form. This prevents excessive insertion loss caused by excessive thickness between lines and ensures that the surface ink retains sufficient coverage, thereby improving the high-frequency signal transmission quality and process stability on the high-speed circuit board.

[0045] Further, in step S3, the specific steps of the static leveling process are as follows: after the double-sided screen printing of the entire high-speed circuit board, it is left to rest naturally for 15-30 minutes. This static leveling process, achieved through natural resting, retains the appropriate fluidity of the ink to fill tiny gaps and improve coverage density, while gently stabilizing the ink morphology on the high-speed circuit board. This ensures a smooth and continuous solder resist protective layer is formed on the circuit surface. Simultaneously, the 15-30 minute static leveling time after the second screen printing ensures that the ink thickness filling the lines is synergistically optimized in both the static drying process of the first screen printing and the static leveling process of the second screen printing. Ultimately, a balance is achieved 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, high-density circuit boards.

[0046] Furthermore, the solder resist ink is a low Df ink; the viscosity of the solder resist ink is 55-75 dps;

[0047] Furthermore, the mesh count of the screen printing mesh used in the first and second screen printing processes shall not be less than 60T.

[0048] By employing inks with low dielectric loss factor (low Df), precisely controlling ink viscosity, and using high-mesh-count screen printing, the signal transmission performance of high-speed circuit boards has been significantly improved. Low Df inks directly reduce signal energy loss and are suitable for high-frequency electric field environments. Moderate viscosity ensures that the ink maintains both controllable flowability and uniform coverage during screen printing, preventing ink overflow between lines or insufficient ink on the surface. High-mesh-count screen printing limits the amount of ink transmitted in a single pass, and combined with two screen printing processes, precisely suppresses the ink thickness between lines while ensuring dense protection of the surface solder mask layer, minimizing the impact of dielectric loss caused by solder mask on the integrity of high-frequency signals.

[0049] Furthermore, in step S2, the squeegee is 10mm thick and has a rubber hardness of 75°. When performing one screen printing, the squeegee angle is 8-10°, the screen printing speed is 180-200mm / s, and the screen printing pressure is 6bar.

[0050] Furthermore, in step S3, when using a squeegee with a thickness of 10mm and a rubber hardness of 75° for secondary screen printing, the squeegee angle is 8-10°, the screen printing speed is 180-200mm / s, and the screen printing pressure is 5bar.

[0051] By precisely controlling the synergistic effect of squeegee parameters and screen printing process parameters, accurate control of ink thickness in high-speed circuit board areas is achieved simply and quickly. The hardness and angle design of the squeegee during the two printing processes—10mm thickness and 75° hardness—maintains ink transfer stability while reducing the impact of squeegee deformation on screen contact. Combined with a constant squeegee angle and screen printing speed of 8-10° and 180-200mm / s, precise control of ink leveling and thickness is achieved. Furthermore, the first screen printing uses 6bar high pressure to ensure that low-viscosity ink forms a thin and uniform coverage layer under high-mesh screen, while appropriately filling the inter-line areas. The second screen printing uses 5bar low pressure to precisely reinforce the surface ink thickness, avoiding secondary thickening between lines. Ultimately, under simple and quick process conditions, sufficient coverage and dense protection of the circuit surface, and a thin, low-loss ink distribution between lines are achieved, thus significantly reducing the transmission loss of high-frequency signals on high-speed circuit boards.

[0052] Furthermore, in step S3, the pre-baking temperature is 70-80℃, and the pre-baking time is 40-60 minutes. By setting the pre-baking temperature to 70-80℃ and the mild curing conditions to 40-60 minutes, the differentiated ink distribution structure between the lines and gaps formed by the two screen printing processes is consolidated, and a uniform and dense dielectric substrate is provided for final curing, thereby ensuring low loss and long-term reliability of high-frequency signal transmission on high-speed circuit boards.

[0053] Furthermore, in step S4, the number of exposure grids is 11-12, and the exposure energy is 300-400mJ. By reducing the exposure energy, the accuracy of the solder resist pattern is ensured while avoiding damage to the dielectric properties of the ink from high energy. At the same time, the mild exposure conditions and the thin ink structure formed by the two screen printing processes work together to avoid secondary ink flow or thickness fluctuations between lines due to high-energy thermal effects. This consolidates the optimized distribution of thin ink between lines and uniform ink on the line surface, further reducing dielectric loss during high-frequency signal transmission, and simultaneously improving the interfacial bonding strength between the solder resist layer and the circuit.

[0054] Furthermore, in step S4, the developing solution is a 0.8% K2CO3 developing solution, the developing temperature is 29-33℃, the developing time is 70s, and the developing pressure is 2.0 bar.

[0055] Preferably, the ink thickness covering the outer layer lines on the high-speed circuit board is 0.8-1.5 mil, and the ink thickness between adjacent outer layer lines is 0.5-1.0 mil. By precisely controlling the differential distribution of ink thickness on the outer layer lines and between adjacent lines, the requirements of high-frequency signal transmission performance and line protection on the high-speed circuit board are systematically balanced. Through precise control and synergistic optimization between the two, the physical protection capability of the solder mask layer for complex lines is strengthened, and the core cause of high-frequency insertion loss is minimized to the greatest extent, ensuring a stable and controllable dielectric environment for the signal transmission path and improving the electrical performance of the high-speed circuit board.

[0056] Example 2

[0057] like Figures 1-2 As shown, this embodiment provides a solder mask fabrication process for a high-speed circuit board with low insertion loss, specifically including the following steps:

[0058] S1. Pre-treatment: After the outer layer circuitry is fabricated, the high-speed circuit board undergoes processes such as acid pickling, water washing, volcanic ash grinding, ultrasonic water washing, high-pressure water washing, and hot drying to clean the board surface. After the pre-treatment, the high-speed circuit board is naturally cooled to room temperature before screen printing. The acid pickling uses 5% sulfuric acid to remove copper oxides; the volcanic ash grinding uses a 500-grit needle roller with 20% volcanic ash to polish the copper surface.

[0059] S2. One-time screen printing: Using high-mesh-count mesh, low-viscosity ink, and high printing pressure, a thin layer of ink is printed onto the entire high-speed circuit board. The screen printing stencil uses a 62T dot-blocking screen, and the screen printing ink uses low Df performance ink, preferably Taiyo's PSR4000 LT02G. The ink is diluted with thinner during ink preparation to maintain a viscosity of 55-75 dps. The squeegee is 10mm thick with a rubber hardness of 75°. During the first screen printing, the squeegee angle is 8-10°, the screen printing speed is 180-200mm / s, and the screen printing pressure is 6 bar. After the first screen printing is completed, the high-speed circuit board is vertically inserted into the PCB placement rack. Next, the PCB board with the vertical mounting bracket is placed below the air outlet of the clean room and air-dried for 20-30 minutes. During this time, the ink around the circuits flows and spreads due to its own flow characteristics, and the ink between the circuits becomes thinner. However, at the same time, the ink on the surface of the circuits also flows along the copper edges, making the surface thinner, requiring a second printing to completely cover the circuit surface. The drying time should not be too long or too short. If the drying time is too long, the ink will dry and become viscous, making it easy for the screen to stick during the second screen printing, resulting in uneven ink thickness. If the drying time is too short, the ink will still be in a highly fluid state, and during the second screen printing, a lot of ink will still be lost from the circuit surface, resulting in insufficient ink thickness and the problem of thin ink on the circuit surface.

[0060] S3. Secondary screen printing: After allowing the circuit board to air dry, the same screen printing parameters as the first screen printing are used, including the screen printing plate, ink, and squeegee. The screen printing pressure is reduced to 5 bar, and the entire high-speed circuit board is screen printed a second time to increase the ink thickness on the circuit surface. After the second screen printing, the printed high-speed circuit board is allowed to rest naturally for 15-30 minutes to allow the ink on the board surface to settle, level, and defoam. Then, a pre-baking process is performed on the high-speed circuit board. The high-speed circuit board, after settling, leveling, and defoaming, is heated in a tunnel oven to evaporate some of the solvent in the ink, pre-curing the ink and drying it to prepare it for exposure. The pre-baking temperature is controlled at 75℃, and the pre-baking time is 48 minutes.

[0061] S4. Development and Curing: The pre-baked high-speed circuit board is exposed using a DI exposure machine with an LED light source to induce a cross-linking reaction in the photopolymers in the ink. The exposure grid is controlled at 11-12 grids, and the exposure energy is 300-400mJ. Immediately afterward, the ink that has not been exposed to light and has not undergone a cross-linking reaction is washed away with a 0.8% K₂CO₃ solution, exposing a clean copper surface. The development temperature is 31±2℃, the development time is 70s, and the development pressure is 2.0 bar. Finally, the ink on the board surface is thermally cured using high-temperature hot air circulation in an oven, allowing the solvents in the ink to evaporate completely, achieving a permanent insulating and anti-corrosion protective film. The high-temperature curing temperature is 155℃, and the curing time is 70 minutes, forming the high-speed circuit board after solder mask fabrication.

[0062] Example 3

[0063] This embodiment provides a high-speed circuit board with low insertion loss, manufactured using the solder resist fabrication process provided in Embodiment 1 or Embodiment 2. The high-speed circuit board provided in this embodiment has an outer copper foil thickness of 0.5-2 oz, an outer circuit thickness of 2.5-3.0 mil, a line width of 5-15 mil, a line spacing of 3-5 mil, an ink thickness of 0.8-1.5 mil covering the outer circuit on the high-speed circuit board, and an ink thickness of 0.5-1.0 mil between adjacent outer circuits.

[0064] Comparative Example 1

[0065] like Figure 3 As shown, this comparative example provides a solder mask fabrication process for a high-speed circuit board and a high-speed circuit board thereof, which differs from Example 2 in that:

[0066] S2. One-time LMS screen printing: A layer of ink is printed on the entire outer layer of the high-speed circuit board. A 51T screen printing stencil is used for the printed circuit areas. The screen printing ink is PSR4000 G23K with a viscosity of 55-75 dps. A 10mm thick 75° hardness squeegee is used for screen printing, with the squeegee angle controlled at 8-10°. Double-sided printing is performed using a bed of nails. The screen printing speed is controlled at 200-240mm / s, and the screen printing pressure is controlled at 4-6 bar. After screen printing, the PCB board is vertically inserted into the vehicle frame. Immediately afterward, the printed high-speed circuit board is allowed to rest naturally for 15-30 minutes to allow the ink on the board surface to settle, level, and defoam. Then, a pre-baking process is performed on the high-speed circuit board. After settling and defoaming, the high-speed circuit board is heated in a tunnel oven to evaporate some of the solvent in the ink, pre-curing the ink and drying it to prepare it for exposure. The pre-baking temperature is controlled at 75℃, and the pre-baking time is 21 minutes.

[0067] S3. Secondary screen printing: After the first screen printing and pre-baking, the same squeegee, screen printing pressure, and other printing parameters as the first screen printing are used. A 43T screen printing screen is used for the printed circuit lines, and PSR4000 G23K ink with a viscosity of 115-135 dps is used for the secondary screen printing on the outer layer of the high-speed circuit board to thicken the ink on the circuit surface. After the secondary screen printing, the printed high-speed circuit board is allowed to rest naturally for 15-30 minutes to allow the ink on the board surface to settle, level, and defoam. Then, a pre-baking process is performed on the high-speed circuit board. After settling, leveling, and defoaming, the high-speed circuit board is heated in a tunnel oven to evaporate some of the solvent in the ink, pre-curing the ink and drying it to prepare it for exposure. The pre-baking temperature is controlled at 75℃, and the pre-baking time is 48 minutes.

[0068] S4. Development and Curing: The high-speed circuit board after secondary screen printing and pre-baking is exposed using a DI exposure machine with an LED light source to induce a cross-linking reaction in the photopolymers of the ink. The exposure energy is 350-450 mJ. Immediately afterward, the ink that has not been exposed to light and has not undergone a cross-linking reaction is washed away with a 0.8% K₂CO₃ solution, exposing a clean copper surface. The development temperature is 31±2℃, the development time is 70-80 seconds, and the development pressure is 2.0 bar. Finally, the ink on the board surface is thermally cured using high-temperature hot air circulation in an oven, allowing the solvents in the ink to evaporate completely, achieving a permanent insulating and anti-corrosion protective film. The high-temperature curing temperature is 155℃, and the curing time is 70 minutes, forming the high-speed circuit board after solder mask fabrication.

[0069] according to Figure 2As shown, in the high-speed circuit board manufactured using the solder resist fabrication process in Example 2, the thickness of the solder resist ink covering the entire outer circuit area is relatively thin, the thickness of the ink on the line surface is relatively thin and uniform, and the ink between lines is relatively thin, with a significant height difference between the ink layer and the ink layer on the line surface; according to Figure 3 As shown, in the high-speed circuit board manufactured using the solder resist fabrication process in Comparative Example 1, the thickness of the solder resist ink covering the entire outer circuit area is relatively thick, the thickness of the ink on the line surface is relatively thick, and the ink between lines is also relatively thick, with little difference in height between the ink layers on the line surface and the ink layer on the line surface. Insertion loss tests were performed on the high-speed circuit boards manufactured in Example 2 and Comparative Example 1, and the test results show that: Figure 4 As shown, the insertion loss of the high-speed circuit board fabricated in Example 2 after fitting is 0.627323 dB / inch; Figure 5 As shown, the insertion loss of the high-speed circuit board fabricated in Comparative Example 1 after fitting is 1.051669 dB / inch, and the insertion loss is reduced by 0.424346 dB / inch. This suggests that the insertion loss of the high-speed circuit board fabricated in Example 2 after solder mask fabrication is reduced by about 40% compared to the insertion loss of the conventional solder mask fabrication process.

[0070] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the technical solution of the present invention, and are not intended to limit the specific implementation of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the claims of the present invention should be included within the protection scope of the claims of the present invention.

Claims

1. A solder resist manufacturing process for a high-speed circuit board with low insertion loss, characterized by, It comprises the following steps: S1. Pretreatment, pretreating the surface of the circuit board made of outer layer circuit to obtain a high-speed circuit board to be made of solder resist; S2. First screen printing, printing the whole high-speed circuit board by using solder resist ink for first screen printing, and placing the printed high-speed circuit board for air drying; S3. Second screen printing, printing the whole high-speed circuit board after first screen printing by using solder resist ink for second screen printing, and placing the printed high-speed circuit board for leveling after air drying and pre-baking; S4. Developing and curing, exposing and developing the surface of the high-speed circuit board after pre-baking, and forming the high-speed circuit board after solder resist making through curing process; The solder resist ink uses ink with low dielectric loss factor; 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; The ink thickness on the outer layer circuit on 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; In the step S2, the specific steps of the air drying are as follows: vertically inserting the high-speed circuit board on the placing rack, and placing them together under the clean room air outlet for air drying for 20-30 min; In the step S3, the specific steps of the leveling are as follows: naturally placing the high-speed circuit board for 15-30 min after printing the whole high-speed circuit board by using solder resist ink for second screen printing.

2. The low insertion loss high speed circuit board's solder resist manufacturing process according to claim 1, wherein, In the step S2, the rubber scraper with a thickness of 10 mm and a rubber hardness of 75° is used for first screen printing, the rubber scraping angle is 8-10°, the screen printing speed is 180-200 mm / s, and the screen printing pressure is 6 bar.

3. The low insertion loss high speed circuit board's solder resist manufacturing process according to claim 1, wherein, In the step S3, the rubber scraper with a thickness of 10 mm and a rubber hardness of 75° is used for second screen printing, the rubber scraping angle is 8-10°, the screen printing speed is 180-200 mm / s, and the screen printing pressure is 5 bar.

4. The low insertion loss high speed circuit board's solder resist manufacturing process according to claim 1, wherein, In the step S3, the pre-baking temperature is 70-80℃, and the pre-baking time is 40-60 min.

5. The low insertion loss high speed circuit board's solder resist manufacturing process according to claim 1, wherein, In the step S4, the exposure grid number is 11-12, and the exposure energy is 300-400 mJ; The developing uses K2CO3 developing solution with a concentration of 0.8%, the developing temperature is 29-33℃, the developing time is 70 s, and the developing pressure is 2.0 bar.

6. A low-insertion-loss high-speed circuit board made by using the solder resist making process according to any one of claims 1-5.

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