Improvement of the processing method for excessive side etching of solder mask on printed circuit boards

Abstract

This invention provides a method for improving the processing of printed circuit boards with excessive solder resist side etching. By using a first transparent solder resist ink and a second colored solder resist ink, the thickness of the first solder resist ink is greater than that of the second solder resist ink. In step S3, the second solder resist ink completely covers the first solder resist ink. By using two layers of solder resist ink, with the first layer being transparent and the surface layer being colored, the overall curing uniformity of the solder resist layer is improved, thereby reducing the undercut caused by incomplete curing of the bottom solder resist ink. Furthermore, by ensuring that the colored ink layer completely covers the transparent ink layer, and by setting the thickness of the transparent ink layer to be greater than that of the colored ink layer, the high-gloss curing characteristics of the transparent ink layer are fully utilized, optimizing the bonding effect between the colored and transparent ink layers and ensuring the overall curing effect of the solder resist layer.

Description

Technical Field

[0001] This invention relates to the field of electronic manufacturing technology, and more specifically, to a processing method for improving excessive solder mask etching on printed circuit boards. Background Technology

[0002] With the increasing demand for printed circuit board (PCB) products, PCBs are developing towards higher precision and higher complexity. How to lay out more lines and components within a limited space is a problem that urgently needs to be solved. Dense component design means that the spacing between pads on the PCB is compressed, and the width of the solder mask layer used to isolate the pads can only be made smaller and smaller.

[0003] like Figure 1 As shown, in the printed circuit board (PCB) manufacturing process, the main function of the solder mask layer is to protect copper traces from oxidation, corrosion, and short circuits. Undercut refers to the excessive removal or etching of the solder mask layer at its edges, resulting in discontinuities or gaps at the edges, exposing the copper traces and damaging the appearance and function of the solder mask layer. This increases the risk of short circuits and corrosion, reducing the long-term reliability of the PCB. Simultaneously, the presence of the solder mask layer ensures the precision of the soldering process. During soldering, the solder mask layer prevents solder from flowing to areas that do not need to be soldered. If the undercut is too large, the solder mask layer may not completely cover specific areas of the PCB, affecting the soldering quality and causing poor soldering, bridging, or cold solder joints. Furthermore, incomplete or uneven coverage of the solder mask layer can cause electrical interference, signal crosstalk, and noise problems on the PCB. Especially in high-frequency applications, an excessive undercut can cause the solder mask layer to be too thin or completely disappear in some areas, affecting insulation performance and potentially impacting circuit stability and signal integrity. Therefore, minimizing the undercut while meeting the requirements for solder mask thickness and width is an important means to ensure the electrical performance, reliability, production efficiency, and quality control of the circuit board.

[0004] In actual production, minimizing the undercut of the solder mask layer is a key technical challenge faced by printed circuit board (PCB) manufacturers. Specifically, during solder mask exposure, light energy attenuates as it penetrates the ink layer. The surface ink has a high photocurability, while the bottom ink has a relatively low photocurability. During development, the chemicals corrode the bottom ink, forming an undercut. The larger the undercut, the more difficult it is to reduce the solder mask layer size. Because undercuts are unavoidable, the minimum thickness for solder mask film design is currently 3 mil. Under normal single-pass screen printing, the undercut of a 3 mil thick ordinary green solder mask is generally around 1.2 mil. For black solder mask, due to the greater difficulty of light penetration to the ink layer, the undercut is around 1.5-2 mil, sometimes exceeding 2 mil, even resulting in solder mask peeling off. Furthermore, for thick copper boards, the thicker the copper, the thicker the solder mask at the copper edge. The solder mask thickness directly affects the undercut; the thicker the solder mask, the larger the undercut. Therefore, in order to minimize the undercut while meeting the requirements for solder resist thickness and width, it is necessary to comprehensively optimize the ink selection, printing process, exposure process, development process, and curing process. Summary of the Invention

[0005] This invention aims to overcome at least one of the shortcomings of the prior art and provide an improved processing method for excessive solder resist side etching on printed circuit boards. By using a combination of transparent ink and colored ink and through a special process, the undercut phenomenon of the solder resist ink can be minimized while ensuring the color and thickness requirements of the solder resist layer.

[0006] The purpose of this invention is to provide a method for improving the processing of printed circuit boards with excessive solder mask etching, comprising the following steps:

[0007] S1. Circuit board pretreatment;

[0008] S2. Print the first solder resist ink on the processed circuit board and pre-cure it;

[0009] S3. Print the second solder resist ink onto the first solder resist ink and pre-cure it;

[0010] S4. Expose and develop the first and second solder resist inks;

[0011] S5. Cure the developed first and second solder resist inks at high temperature;

[0012] The first solder resist ink is a transparent ink, the second solder resist ink is a colored ink, the thickness of the first solder resist ink is greater than that of the second solder resist ink, and in step S3, the second solder resist ink completely covers the first solder resist ink.

[0013] In this technical solution, the selection of ink materials is optimized to minimize undercut on the solder resist layer of the printed circuit board. Specifically, since undercut usually occurs at the edges of the solder resist ink layer, uneven curing during the exposure curing process can lead to etching or excessive peeling of the ink edges. By using two layers of solder resist ink, the overall curing uniformity of the solder resist ink is improved, thereby reducing undercut caused by excessive etching of the bottom solder resist ink that has not fully cured. Specifically, the first solder resist ink at the bottom layer is a transparent ink, while the solder resist ink on the surface is a colored ink. The colored ink, which has a slower photocuring speed, is placed on the surface of the solder resist layer, allowing it to be fully exposed and cured. Simultaneously, the transparent ink, which has a faster photocuring speed, is placed at the bottom of the colored ink. Because the transparent ink has strong light transmittance and requires less light energy, the light source, even after exposure attenuation through the colored ink layer, can effectively penetrate the transparent ink during exposure and achieve uniform curing of the transparent ink layer. This ensures uniform curing of both the stacked colored ink layer and the transparent ink layer, thereby reducing undercut on the sides or edges of the solder resist layer. Furthermore, to optimize the bonding effect between the color ink layer and the transparent ink layer and improve the overall curing uniformity of the solder resist layer, the transparency and color characteristics of the first and second solder resist inks differ only in the presence or absence of pigment, ensuring compatibility between the first and second solder resist inks during manufacturing. Simultaneously, the color ink layer is designed to completely cover the transparent ink layer, ensuring uniform exposure energy penetrating from the color ink layer to the transparent ink layer while maintaining the appearance of the solder resist layer. The thickness of the transparent ink layer is also set to be greater than that of the color ink layer, fully utilizing the high-gloss curing characteristics of the transparent ink layer to guarantee the overall curing effect of the solder resist layer. This effectively reduces undercut formation while improving the compatibility between the color ink layer and the transparent ink layer.

[0014] Furthermore, the printing method in steps S2 and S3 employs screen printing. The T-number of the screen printing stencil for the first solder resist ink is no greater than that for the second solder resist ink, and the viscosity of the printing ink for the first solder resist ink is greater than that for the second solder resist ink. In this technical solution, the printing process for the first and second solder resist inks is selected and improved according to the inks in the solder resist layer. Specifically, by selecting a small T-number, i.e., a fine mesh screen, transparent ink is printed with precision, thereby ensuring that the thickness of the first solder resist ink layer is moderate, guaranteeing good adhesion and photocuring effect of the first solder resist ink on the printed circuit board. At the same time, a large T-number, i.e., a coarse mesh screen, is used to print the second solder resist ink layer, thereby ensuring that the second solder resist ink layer is thinner. This ensures that during the exposure process of the solder resist layer, the second solder resist ink layer using colored ink allows more light to penetrate to the underlying second solder resist ink layer using transparent ink, thus ensuring the curing effect of the second solder resist ink layer and improving the overall manufacturing quality of the solder resist layer, while reducing the occurrence of undercuts.

[0015] Preferably, the screen printing stencil of the first solder resist ink has a T-number of 20-80T, and the screen printing stencil of the second solder resist ink has a T-number of 50-100T. Further, to improve the adhesion of the first solder resist ink to the printed circuit board and simultaneously enhance the bonding force with the second solder resist ink, the printing ink viscosity of the first solder resist ink is set to 125±25ps, and the printing ink viscosity of the second solder resist ink is set to 30±10dps. By using appropriate viscosities for both the first and second solder resist inks, the uniformity and adhesion of each layer of solder resist ink during coating are ensured, thereby improving the precision and reliability of the solder resist layer fabrication.

[0016] Preferably, in order to further ensure that during the exposure and fabrication of the solder resist layer, the second solder resist ink layer using colored ink allows more light to penetrate to the underlying second solder resist ink layer using transparent ink, thereby ensuring the curing effect of the second solder resist ink layer and improving the overall fabrication quality of the solder resist layer and reducing the occurrence of undercut, the light transmittance of the second solder resist ink is set to be not less than 50%, and the thickness of the second solder resist ink is not greater than 35% of the thickness of the first solder resist ink.

[0017] Furthermore, after step S5, the maximum shrinkage value of either the left or right side of the lateral dimension of the first solder resist ink relative to the second solder resist ink is no greater than 1 mil, thereby ensuring the integrity of the overall appearance of the solder resist layer and ensuring the bonding effect between the first and second solder resist inks, thus improving the precision and reliability of the overall solder resist layer manufacturing.

[0018] Furthermore, after the two layers of solder resist ink are printed, a preliminary pre-curing treatment should be performed to ensure the adhesion of the first solder resist ink to the printed circuit board and the bonding force between the first and second solder resist inks, preventing the solder resist ink from peeling off or moving during subsequent exposure. The pre-curing temperature and time should be optimized according to the characteristics of the ink. Preferably, in step S2, the pre-curing temperature of the first solder resist ink is 60-80℃, and the pre-curing time is 15-30 minutes; in step S3, the pre-curing temperature of the second solder resist ink is 60-80℃, and the pre-curing time is 35-60 minutes.

[0019] Furthermore, in order to further improve the adhesion of the solder resist ink layer on the printed circuit board and improve the precision and reliability of the solder resist layer manufacturing, a pretreatment method for the printed circuit board surface is also included before the solder resist processing. Preferably, the pretreatment method in step S1 is set to volcanic ash grinding plate, which uses a brush and volcanic ash to grind the copper surface to achieve a certain roughness and clean the copper surface.

[0020] Furthermore, to ensure that the light source can uniformly irradiate the surfaces of the two solder resist inks in the formed solder resist layer and that both solder resist inks in the stacked layer can be uniformly cured, it is also necessary to control the exposure parameters of the solder resist layer accordingly. Specifically, the exposure method in step S4 is set to cause the photopolymer in the ink to undergo a cross-linking reaction by irradiating with UV light, exposing the required graphic position, controlling the number of exposure grids to 12±2 grids, and the exposure energy to 350~500mJ. The exposure time is precisely adjusted according to the required thickness of the solder resist ink and the light blocking effect of the color layer, avoiding uneven curing caused by insufficient or excessive exposure, and improving the precision and reliability of the overall solder resist layer manufacturing.

[0021] Furthermore, it also includes the control of the development process. To ensure that the unexposed parts of the ink can be completely removed and to avoid undercut due to incomplete development, the liquid temperature and time during development need to be precisely controlled. Specifically, the development method in step S4 is set to wash away the unexposed ink that has not undergone cross-linking reaction with a weakly alkaline solution to expose a clean copper surface. The development speed is controlled between 3-4.5 m / min, the development time is controlled between 40-60 s, the development pressure is controlled between 1.8-2.3 bar, the concentration of the developing solution is 0.8±0.2%, and the solution temperature is 31±2℃.

[0022] Furthermore, it also includes the control of the final curing process. The final curing of the solder resist ink layer needs to be carried out at a high temperature to ensure the stability of the ink layer. By optimizing the curing temperature and time, quality problems in the solder resist layer production caused by over-curing or under-curing are avoided. Specifically, the method for high-temperature curing in step S5 is to heat-cur the ink on the board surface through high-temperature hot air circulation. During the curing process, 1-3% of the solvent by weight of the ink is lost to achieve a permanent insulating and anti-corrosion protective film. The high-temperature curing temperature is controlled between 140-170℃, and the time is controlled between 60-80 minutes.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] 1. By optimizing the selection of ink materials, undercut on the solder resist layer of printed circuit boards can be minimized. Specifically, since undercut usually occurs at the edges of the solder resist ink layer, uneven curing during the exposure curing process can lead to etching or excessive peeling of the ink edges. By using two layers of solder resist ink, the overall curing uniformity of the solder resist ink is improved, thereby reducing undercut caused by excessive etching of the bottom solder resist ink that has not fully cured. Specifically, the first solder resist ink at the bottom layer is a transparent ink, while the solder resist ink on the surface is a colored ink. The colored ink, which has a slower photocuring speed, is placed on the surface of the solder resist layer, allowing it to be fully exposed and cured. Simultaneously, the transparent ink, which has a faster photocuring speed, is placed at the bottom of the colored ink. Because the transparent ink has strong light transmittance and requires less light energy, the light source, even after exposure attenuation through the colored ink layer, can effectively penetrate the transparent ink during the exposure process, achieving uniform curing of the transparent ink layer. This ensures uniform curing of both the stacked colored and transparent ink layers, thereby reducing undercut on the sides or edges of the solder resist layer. Furthermore, in order to optimize the bonding effect between the color ink layer and the transparent ink layer and improve the overall curing uniformity of the solder resist layer, the color ink layer is designed to completely cover the transparent ink layer. This ensures that the exposure energy penetrating from the color ink layer to the transparent ink layer remains uniform while maintaining the appearance of the solder resist layer. In addition, the thickness of the transparent ink layer is set to be greater than that of the color ink layer, thereby making full use of the high-gloss curing characteristics of the transparent ink layer and ensuring the overall curing effect of the solder resist layer. This effectively improves the undercut and enhances the compatibility between the color ink layer and the transparent ink layer.

[0025] 2. Regarding the selection and improvement of inks in the solder resist layer, the printing process for both the first and second solder resist inks was optimized. Specifically, a small T-count (fine mesh) was selected for fine printing of the transparent ink, ensuring a moderate thickness of the first solder resist ink layer and guaranteeing good adhesion and photocuring effect on the printed circuit board. Simultaneously, a large T-count (coarse mesh) was used for printing the second solder resist ink layer, ensuring a thinner layer. This allows more light to penetrate the colored ink layer to the underlying transparent ink layer during solder resist exposure, ensuring better curing of the second solder resist layer, improving the overall quality of the solder resist layer, and reducing undercuts. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the structure of the solder mask layer on a printed circuit board in the prior art.

[0027] Figure 2 This is a flowchart illustrating the improved processing method for excessive solder resist etching on printed circuit boards according to the present invention.

[0028] Figure 3 This is a schematic diagram of the printed circuit board structure during the printing of the first solder resist ink in the improved processing method for excessive solder resist side etching of printed circuit boards according to the present invention.

[0029] Figure 4 This is a schematic diagram of the printed circuit board structure during the printing of the second solder resist ink in the improved processing method for excessive solder resist side etching of printed circuit boards according to the present invention.

[0030] Figure 5 This is a schematic diagram of the structure of the printed circuit board after high-temperature curing in the improved processing method for excessive solder resist etching of the printed circuit board of the present invention. Detailed Implementation

[0031] 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.

[0032] Example 1

[0033] like Figure 2 As shown, this embodiment provides a method for improving the processing of printed circuit boards with excessive solder mask etching, including the following steps:

[0034] S1. Circuit board pretreatment;

[0035] S2. Print the first solder resist ink on the processed circuit board and pre-cure it;

[0036] S3. Print the second solder resist ink onto the first solder resist ink and pre-cure it;

[0037] S4. Expose and develop the first and second solder resist inks;

[0038] S5. Cure the developed first and second solder resist inks at high temperature;

[0039] The first solder resist ink is a transparent ink, and the second solder resist ink is a colored ink. By making the first solder resist ink at the bottom layer a transparent ink and the solder resist ink at the surface a colored ink, the colored ink with a slower photocuring speed is placed on the surface of the solder resist layer so that it can be fully exposed and cured. At the same time, the transparent ink with a faster photocuring speed is placed at the bottom of the colored ink. Since the transparent ink has strong light transmittance and requires less light energy, the light source after exposure attenuation of the colored ink layer can also effectively penetrate the transparent ink during the exposure process and achieve uniform curing of the transparent ink layer. This ensures the uniform curing of the stacked colored ink layer and the transparent ink layer as a whole, thereby reducing the undercut phenomenon on the sides or edges of the solder resist layer. Furthermore, to optimize the bonding effect between the color ink layer and the transparent ink layer and improve the overall curing uniformity of the solder resist layer, the transparency and color characteristics of the first solder resist ink and the second solder resist ink are only different depending on whether colorant is added, which is used to ensure the compatibility of the first solder resist ink and the second solder resist ink during manufacturing; at the same time, the color ink layer is set to completely cover the transparent ink layer, so as to ensure the appearance of the solder resist layer while ensuring that the exposure energy penetrating the color ink layer to the transparent ink layer remains uniform, and the thickness of the transparent ink layer is set to be greater than the thickness of the color ink layer, thereby making full use of the high-gloss curing characteristics of the transparent ink layer and ensuring the overall curing effect of the solder resist layer.

[0040] Furthermore, the printing method in steps S2 and S3 employs screen printing. The T-number of the screen printing stencil for the first solder resist ink is no greater than that for the second solder resist ink, and the viscosity of the printing ink for the first solder resist ink is greater than that for the second solder resist ink. In this technical solution, the printing process for the first and second solder resist inks is selected and improved according to the inks in the solder resist layer. Specifically, by selecting a small T-number, i.e., a fine mesh screen, transparent ink is printed with precision, thereby ensuring that the thickness of the first solder resist ink layer is moderate, guaranteeing good adhesion and photocuring effect of the first solder resist ink on the printed circuit board. At the same time, a large T-number, i.e., a coarse mesh screen, is used to print the second solder resist ink layer, thereby ensuring that the second solder resist ink layer is thinner. This ensures that during the exposure process of the solder resist layer, the second solder resist ink layer using colored ink allows more light to penetrate to the underlying second solder resist ink layer using transparent ink, thus ensuring the curing effect of the second solder resist ink layer and improving the overall manufacturing quality of the solder resist layer, while reducing the occurrence of undercuts.

[0041] Preferably, the screen printing stencil of the first solder resist ink has a T-number of 20-80T, and the screen printing stencil of the second solder resist ink has a T-number of 50-100T. Further, to improve the adhesion of the first solder resist ink to the printed circuit board and simultaneously enhance the bonding force with the second solder resist ink, the printing ink viscosity of the first solder resist ink is set to 125±25ps, and the printing ink viscosity of the second solder resist ink is set to 30±10dps. By using appropriate viscosities for both the first and second solder resist inks, the uniformity and adhesion of each layer of solder resist ink during coating are ensured, thereby improving the precision and reliability of the solder resist layer fabrication.

[0042] Preferably, in order to further ensure that during the exposure and fabrication of the solder resist layer, the second solder resist ink layer using colored ink allows more light to penetrate to the underlying second solder resist ink layer using transparent ink, thereby ensuring the curing effect of the second solder resist ink layer and improving the overall fabrication quality of the solder resist layer and reducing the occurrence of undercut, the light transmittance of the second solder resist ink is set to be not less than 50%, and the thickness of the second solder resist ink is not greater than 35% of the thickness of the first solder resist ink.

[0043] Furthermore, after step S5, the maximum shrinkage value of either the left or right side of the lateral dimension of the first solder resist ink relative to the second solder resist ink is no greater than 1 mil, thereby ensuring the integrity of the overall appearance of the solder resist layer and ensuring the bonding effect between the first and second solder resist inks, thus improving the precision and reliability of the overall solder resist layer manufacturing.

[0044] Furthermore, after the two layers of solder resist ink are printed, a preliminary pre-curing treatment should be performed to ensure the adhesion of the first solder resist ink to the printed circuit board and the bonding force between the first and second solder resist inks, preventing the solder resist ink from peeling off or moving during subsequent exposure. The pre-curing temperature and time should be optimized according to the characteristics of the ink. Preferably, in step S2, the pre-curing temperature of the first solder resist ink is 60-80℃, and the pre-curing time is 15-30 minutes; in step S3, the pre-curing temperature of the second solder resist ink is 60-80℃, and the pre-curing time is 35-60 minutes.

[0045] Furthermore, in order to further improve the adhesion of the solder resist ink layer on the printed circuit board and improve the precision and reliability of the solder resist layer manufacturing, a pretreatment method for the printed circuit board surface is also included before the solder resist processing. Preferably, the pretreatment method in step S1 is set to volcanic ash grinding plate, which uses a brush and volcanic ash to grind the copper surface to achieve a certain roughness and clean the copper surface.

[0046] Furthermore, to ensure that the light source can uniformly irradiate the surfaces of the two solder resist inks in the formed solder resist layer and that both solder resist inks in the stacked layer can be uniformly cured, it is also necessary to control the exposure parameters of the solder resist layer accordingly. Specifically, the exposure method in step S4 is set to cause the photopolymer in the ink to undergo a cross-linking reaction by irradiating with UV light, exposing the required graphic position, controlling the number of exposure grids to 12±2 grids, and the exposure energy to 350~500mJ. The exposure time is precisely adjusted according to the required thickness of the solder resist ink and the light blocking effect of the color layer, avoiding uneven curing caused by insufficient or excessive exposure, and improving the precision and reliability of the overall solder resist layer manufacturing.

[0047] Furthermore, it also includes the control of the development process. To ensure that the unexposed parts of the ink can be completely removed and to avoid undercut due to incomplete development, the liquid temperature and time during development need to be precisely controlled. Specifically, the development method in step S4 is set to wash away the unexposed ink that has not undergone cross-linking reaction with a weakly alkaline solution to expose a clean copper surface. The development speed is controlled between 3-4.5 m / min, the development time is controlled between 40-60 s, the development pressure is controlled between 1.8-2.3 bar, the concentration of the developing solution is 0.8±0.2%, and the solution temperature is 31±2℃.

[0048] Furthermore, it also includes the control of the final curing process. The final curing of the solder resist ink layer needs to be carried out at a high temperature to ensure the stability of the ink layer. By optimizing the curing temperature and time, quality problems in the solder resist layer production caused by over-curing or under-curing are avoided. Specifically, the method for high-temperature curing in step S5 is to heat-cur the ink on the board surface through high-temperature hot air circulation. During the curing process, 1-3% of the solvent by weight of the ink is lost to achieve a permanent insulating and anti-corrosion protective film. The high-temperature curing temperature is controlled between 140-170℃, and the time is controlled between 60-80 minutes.

[0049] Example 2

[0050] like Figure 2-Figure 5 As shown, this embodiment also provides a method for improving the processing of printed circuit boards with excessive solder mask etching, including the following steps:

[0051] S1. Circuit board pretreatment;

[0052] S2. Print the first solder resist ink on the processed circuit board and pre-cure it;

[0053] S3. Print the second solder resist ink onto the first solder resist ink and pre-cure it;

[0054] S4. Expose and develop the first and second solder resist inks;

[0055] S5. Cure the developed first and second solder resist inks at high temperature;

[0056] In step S1, the pretreatment method is volcanic ash grinding plate. The copper surface is treated by grinding with a brush and volcanic ash to achieve a certain roughness and clean the copper surface, thereby increasing the adhesion between the solder resist ink and the copper layer.

[0057] like Figure 3 As shown, in step S2, a 36T screen printing stencil is used to cover the copper surface and substrate of the printed circuit board with a layer of first solder resist ink made of transparent ink. The viscosity of the first solder resist ink is 125 dps. The screen printing machine pressure is controlled at 2~6 bar. A 10mm wide squeegee with a Shore hardness of 70 is used, and the squeegee angle is 5-15°. After the first solder resist ink is evenly coated, the first solder resist ink layer is pre-cured. Specifically, the board surface is dried by heating in a tunnel oven and circulating hot air, so that the first solder resist ink changes from a wet, flowable state to a semi-dry state, which prepares for the next step of printing the second solder resist ink. The pre-curing temperature is 75℃, and the pre-baking time for double-sided printing is 21 minutes.

[0058] like Figure 4As shown, in step S3, a 36T screen printing stencil is used to cover the pre-cured first solder resist ink layer with a layer of black second solder resist ink. The viscosity of the second solder resist ink is 125 dps. The difference in transparency and color between the first and second solder resist inks is only due to the presence or absence of pigment, which is used to ensure the compatibility of the first and second solder resist inks during manufacturing. After the second solder resist ink is printed, the second solder resist ink layer is pre-cured by heating it in a tunnel oven and drying the board surface with circulating hot air. This evaporates some of the solvent in the ink, changing the ink from a wet, flowable state to a semi-dry state, preparing it for the next exposure step. The temperature is controlled at 75℃, and the pre-baking time for double-sided printing is 48 minutes.

[0059] In step S4, the pre-cured, stacked solder resist ink layer is exposed using a C-SUN manual exposure machine. Specifically, after manually applying yellow film to the board surface, the board is placed in the exposure machine for exposure. The exposure scale is controlled at 12±2 divisions, and the exposure energy is 350~500mJ. UV light irradiation causes the photopolymer in the ink to undergo a cross-linking reaction, exposing the desired pattern positions. Subsequently, a development process is performed. The solder resist ink that has not undergone UV light irradiation and has not undergone a cross-linking reaction is washed away with a weakly alkaline solution such as K2CO3 / Na2CO3, exposing a clean copper surface. The development speed is controlled at 3.8m / min, the development time is 50s, the development pressure is 2.0bar, the developing solution concentration is 0.8±0.2%, and the solution temperature is 31±2℃.

[0060] In step S5, the ink on the board surface is thermally cured by high-temperature hot air circulation. During the curing process, 1-3% of the solvent by weight of the ink is lost to achieve a permanent insulating and anti-corrosion protective film. Specifically, the high temperature is 155°C and the baking time is 70 minutes.

[0061] like Figure 5 As shown, after high-temperature curing, the printed circuit board undergoes surface treatment to form its final shape.

[0062] Example 3

[0063] like Figure 2-Figure 5 As shown, this embodiment also provides a method for improving the processing of printed circuit boards with excessive solder mask etching, including the following steps:

[0064] S1. Circuit board pretreatment;

[0065] S2. Print the first solder resist ink on the processed circuit board and pre-cure it;

[0066] S3. Print the second solder resist ink onto the first solder resist ink and pre-cure it;

[0067] S4. Expose and develop the first and second solder resist inks;

[0068] S5. Cure the developed first and second solder resist inks at high temperature;

[0069] In step S1, the pretreatment method is volcanic ash grinding plate. The copper surface is treated by grinding with a brush and volcanic ash to achieve a certain roughness and clean the copper surface, thereby increasing the adhesion between the solder resist ink and the copper layer.

[0070] like Figure 3 As shown, in step S2, a 62T screen printing stencil is used to cover the copper surface and substrate of the printed circuit board with a layer of first solder resist ink made of transparent ink. The viscosity of the first solder resist ink is 125 dps. The screen printing machine pressure is controlled at 2~6 bar. A 10mm wide squeegee with a Shore hardness of 70 is used, and the squeegee angle is 5-15°. After the first solder resist ink is evenly coated, the first solder resist ink layer is pre-cured. Specifically, the board surface is dried by heating in a tunnel oven and circulating hot air, so that the first solder resist ink changes from a wet, flowable state to a semi-dry state, which prepares for the next step of printing the second solder resist ink. The pre-curing temperature is 75℃, and the pre-baking time for double-sided printing is 21 minutes.

[0071] like Figure 4 As shown, in step S3, a 62T screen printing stencil is used to cover the pre-cured first solder resist ink layer with a layer of black second solder resist ink. The viscosity of the second solder resist ink is 125 dps. The difference in transparency and color between the first and second solder resist inks is only due to the presence or absence of pigment, which is used to ensure the compatibility of the first and second solder resist inks during manufacturing. After the second solder resist ink is printed, the second solder resist ink layer is pre-cured by heating it in a tunnel oven and drying the board surface with circulating hot air. This evaporates some of the solvent in the ink, changing the ink from a wet, flowable state to a semi-dry state, preparing it for the next exposure step. The temperature is controlled at 75℃, and the pre-baking time for double-sided printing is 48 minutes.

[0072] In step S4, the pre-cured, stacked solder resist ink layer is exposed using a C-SUN manual exposure machine. Specifically, after manually applying yellow film to the board surface, the board is placed in the exposure machine for exposure. The exposure scale is controlled at 12±2 divisions, and the exposure energy is 350~500mJ. UV light irradiation causes the photopolymer in the ink to undergo a cross-linking reaction, exposing the desired pattern positions. Subsequently, a development process is performed. The solder resist ink that has not undergone UV light irradiation and has not undergone a cross-linking reaction is washed away with a weakly alkaline solution such as K2CO3 / Na2CO3, exposing a clean copper surface. The development speed is controlled at 3.8m / min, the development time is 50s, the development pressure is 2.0bar, the developing solution concentration is 0.8±0.2%, and the solution temperature is 31±2℃.

[0073] In step S5, the ink on the board surface is thermally cured by high-temperature hot air circulation. During the curing process, 1-3% of the solvent by weight of the ink is lost to achieve a permanent insulating and anti-corrosion protective film. Specifically, the high temperature is 155°C and the baking time is 70 minutes.

[0074] like Figure 5 As shown, after high-temperature curing, the printed circuit board undergoes surface treatment to form its final shape.

[0075] Example 4

[0076] like Figure 2-Figure 5 As shown, this embodiment also provides a method for improving the processing of printed circuit boards with excessive solder mask etching, including the following steps:

[0077] S1. Circuit board pretreatment;

[0078] S2. Print the first solder resist ink on the processed circuit board and pre-cure it;

[0079] S3. Print the second solder resist ink onto the first solder resist ink and pre-cure it;

[0080] S4. Expose and develop the first and second solder resist inks;

[0081] S5. Cure the developed first and second solder resist inks at high temperature;

[0082] In step S1, the pretreatment method is volcanic ash grinding plate. The copper surface is treated by grinding with a brush and volcanic ash to achieve a certain roughness and clean the copper surface, thereby increasing the adhesion between the solder resist ink and the copper layer.

[0083] like Figure 3As shown, in step S2, a 36T screen printing stencil is used to cover the copper surface and substrate of the printed circuit board with a layer of first solder resist ink made of transparent ink. The viscosity of the first solder resist ink is 125 dps. The screen printing machine pressure is controlled at 2~6 bar. A 10mm wide squeegee with a Shore hardness of 70 is used, and the squeegee angle is 5-15°. After the first solder resist ink is evenly coated, the first solder resist ink layer is pre-cured. Specifically, the board surface is dried by heating in a tunnel oven and circulating hot air, so that the first solder resist ink changes from a wet, flowable state to a semi-dry state, which prepares for the next step of printing the second solder resist ink. The pre-curing temperature is 75℃, and the pre-baking time for double-sided printing is 21 minutes.

[0084] like Figure 4 As shown, in step S3, a 62T screen printing stencil is used to cover the pre-cured first solder resist ink layer with a layer of black second solder resist ink. The viscosity of the second solder resist ink is 30 dps. The difference in transparency and color between the first and second solder resist inks is only due to the presence or absence of pigment, which ensures the compatibility of the first and second solder resist inks during manufacturing. After the second solder resist ink is printed, the second solder resist ink layer is pre-cured by heating it in a tunnel oven and drying the board surface with circulating hot air. This evaporates some of the solvent in the ink, changing the ink from a wet, flowable state to a semi-dry state, preparing it for the next exposure step. The temperature is controlled at 75℃, and the pre-baking time for double-sided printing is 48 minutes.

[0085] In step S4, the pre-cured, stacked solder resist ink layer is exposed using a C-SUN manual exposure machine. Specifically, after manually applying yellow film to the board surface, the board is placed in the exposure machine for exposure. The exposure scale is controlled at 12±2 divisions, and the exposure energy is 350~500mJ. UV light irradiation causes the photopolymer in the ink to undergo a cross-linking reaction, exposing the desired pattern positions. Subsequently, a development process is performed. The solder resist ink that has not undergone UV light irradiation and has not undergone a cross-linking reaction is washed away with a weakly alkaline solution such as K2CO3 / Na2CO3, exposing a clean copper surface. The development speed is controlled at 3.8m / min, the development time is 50s, the development pressure is 2.0bar, the developing solution concentration is 0.8±0.2%, and the solution temperature is 31±2℃.

[0086] In step S5, the ink on the board surface is thermally cured by high-temperature hot air circulation. During the curing process, 1-3% of the solvent by weight of the ink is lost to achieve a permanent insulating and anti-corrosion protective film. Specifically, the high temperature is 155°C and the baking time is 70 minutes.

[0087] like Figure 5 As shown, after high-temperature curing, the printed circuit board undergoes surface treatment to form its final shape.

[0088] Example 5

[0089] like Figure 2-Figure 5 As shown, this embodiment also provides a method for improving the processing of printed circuit boards with excessive solder mask etching, including the following steps:

[0090] S1. Circuit board pretreatment;

[0091] S2. Print the first solder resist ink on the processed circuit board and pre-cure it;

[0092] S3. Print the second solder resist ink onto the first solder resist ink and pre-cure it;

[0093] S4. Expose and develop the first and second solder resist inks;

[0094] S5. Cure the developed first and second solder resist inks at high temperature;

[0095] In step S1, the pretreatment method is volcanic ash grinding plate. The copper surface is treated by grinding with a brush and volcanic ash to achieve a certain roughness and clean the copper surface, thereby increasing the adhesion between the solder resist ink and the copper layer.

[0096] like Figure 3 As shown, in step S2, a 62T screen printing stencil is used to cover the copper surface and substrate of the printed circuit board with a layer of first solder resist ink made of transparent ink. The viscosity of the first solder resist ink is 30 dps. The screen printing machine pressure is controlled at 2~6 bar. A 10mm wide squeegee with a Shore hardness of 70 is used, and the squeegee angle is 5-15°. After the first solder resist ink is evenly coated, the first solder resist ink layer is pre-cured. Specifically, the board surface is dried by heating in a tunnel oven and circulating hot air, so that the first solder resist ink changes from a wet, flowable state to a semi-dry state, which prepares for the next step of printing the second solder resist ink. The pre-curing temperature is 75℃, and the pre-baking time for double-sided printing is 21 minutes.

[0097] like Figure 4As shown, in step S3, a 32T screen printing stencil is used to cover the pre-cured first solder resist ink layer with a layer of black second solder resist ink. The viscosity of the second solder resist ink is 30 dps. The difference in transparency and color between the first and second solder resist inks is only due to the presence or absence of pigment, which ensures the compatibility of the first and second solder resist inks during manufacturing. After the second solder resist ink is printed, the second solder resist ink layer is pre-cured by heating it in a tunnel oven and drying the board surface with circulating hot air. This evaporates some of the solvent in the ink, changing the ink from a wet, flowable state to a semi-dry state, preparing it for the next exposure step. The temperature is controlled at 75℃, and the pre-baking time for double-sided printing is 48 minutes.

[0098] In step S4, the pre-cured, stacked solder resist ink layer is exposed using a C-SUN manual exposure machine. Specifically, after manually applying yellow film to the board surface, the board is placed in the exposure machine for exposure. The exposure scale is controlled at 12±2 divisions, and the exposure energy is 350~500mJ. UV light irradiation causes the photopolymer in the ink to undergo a cross-linking reaction, exposing the desired pattern positions. Subsequently, a development process is performed. The solder resist ink that has not undergone UV light irradiation and has not undergone a cross-linking reaction is washed away with a weakly alkaline solution such as K2CO3 / Na2CO3, exposing a clean copper surface. The development speed is controlled at 3.8m / min, the development time is 50s, the development pressure is 2.0bar, the developing solution concentration is 0.8±0.2%, and the solution temperature is 31±2℃.

[0099] In step S5, the ink on the board surface is thermally cured by high-temperature hot air circulation. During the curing process, 1-3% of the solvent by weight of the ink is lost to achieve a permanent insulating and anti-corrosion protective film. Specifically, the high temperature is 155°C and the baking time is 70 minutes.

[0100] like Figure 5 As shown, after high-temperature curing, the printed circuit board undergoes surface treatment to form its final shape.

[0101] Example 6

[0102] like Figure 2-Figure 5 As shown, this embodiment also provides a method for improving the processing of printed circuit boards with excessive solder mask etching, including the following steps:

[0103] S1. Circuit board pretreatment;

[0104] S2. Print the first solder resist ink on the processed circuit board and pre-cure it;

[0105] S3. Print the second solder resist ink onto the first solder resist ink and pre-cure it;

[0106] S4. Expose and develop the first and second solder resist inks;

[0107] S5. Cure the developed first and second solder resist inks at high temperature;

[0108] In step S1, the pretreatment method is volcanic ash grinding plate. The copper surface is treated by grinding with a brush and volcanic ash to achieve a certain roughness and clean the copper surface, thereby increasing the adhesion between the solder resist ink and the copper layer.

[0109] like Figure 3 As shown, in step S2, a 62T screen printing stencil is used to cover the copper surface and substrate of the printed circuit board with a layer of first solder resist ink made of transparent ink. The viscosity of the first solder resist ink is 30 dps. The screen printing machine pressure is controlled at 2~6 bar. A 10mm wide squeegee with a Shore hardness of 70 is used, and the squeegee angle is 5-15°. After the first solder resist ink is evenly coated, the first solder resist ink layer is pre-cured. Specifically, the board surface is dried by heating in a tunnel oven and circulating hot air, so that the first solder resist ink changes from a wet, flowable state to a semi-dry state, which prepares for the next step of printing the second solder resist ink. The pre-curing temperature is 75℃, and the pre-baking time for double-sided printing is 21 minutes.

[0110] like Figure 4 As shown, in step S3, a 62T screen printing stencil is used to cover the pre-cured first solder resist ink layer with a layer of black second solder resist ink. The viscosity of the second solder resist ink is 30 dps. The difference in transparency and color between the first and second solder resist inks is only due to the presence or absence of pigment, which ensures the compatibility of the first and second solder resist inks during manufacturing. After the second solder resist ink is printed, the second solder resist ink layer is pre-cured by heating it in a tunnel oven and drying the board surface with circulating hot air. This evaporates some of the solvent in the ink, changing the ink from a wet, flowable state to a semi-dry state, preparing it for the next exposure step. The temperature is controlled at 75℃, and the pre-baking time for double-sided printing is 48 minutes.

[0111] In step S4, the pre-cured, stacked solder resist ink layer is exposed using a C-SUN manual exposure machine. Specifically, after manually applying yellow film to the board surface, the board is placed in the exposure machine for exposure. The exposure scale is controlled at 12±2 divisions, and the exposure energy is 350~500mJ. UV light irradiation causes the photopolymer in the ink to undergo a cross-linking reaction, exposing the desired pattern positions. Subsequently, a development process is performed. The solder resist ink that has not undergone UV light irradiation and has not undergone a cross-linking reaction is washed away with a weakly alkaline solution such as K2CO3 / Na2CO3, exposing a clean copper surface. The development speed is controlled at 3.8m / min, the development time is 50s, the development pressure is 2.0bar, the developing solution concentration is 0.8±0.2%, and the solution temperature is 31±2℃.

[0112] In step S5, the ink on the board surface is thermally cured by high-temperature hot air circulation. During the curing process, 1-3% of the solvent by weight of the ink is lost to achieve a permanent insulating and anti-corrosion protective film. Specifically, the high temperature is 155°C and the baking time is 70 minutes.

[0113] like Figure 5 As shown, after high-temperature curing, the printed circuit board undergoes surface treatment to form its final shape.

[0114] The printed circuit boards prepared in Examples 2-6 were used, and the undercut of the solder resist layer formed on them was measured. Their appearance was evaluated to determine if it was acceptable. Specifically, the appearance evaluation of the solder resist layer included the following: the presence of the solder resist layer, uniform coverage, the shape and width of the solder resist layer meeting design requirements, consistent color, and no ink dripping. If all these conditions were met, the appearance was considered acceptable. The test comparison results are as follows:

[0115]

[0116] Through the above comparative tests, it is evident that the solder resist processing method provided by this technical solution generally results in a smaller undercut in the formed solder resist layer. This suggests that the use of layered color inks and transparent inks improves the curing performance of the solder resist layer, reduces undercut formation, and enhances the precision and reliability of the solder resist layer fabrication. Furthermore, it was found that in Example 4, the best results were achieved when the first solder resist ink using transparent ink was produced using a high-viscosity, low-mesh-count printing process, while the second solder resist ink using black ink was produced using a low-viscosity, high-mesh-count printing process. Under the same conditions, the undercut was minimized. This indicates that by correspondingly controlling the printing process parameters of different solder resist ink layers, the curing performance of the formed solder resist layer can be further improved, the undercut formation reduced, and the precision and reliability of the solder resist layer fabrication enhanced.

[0117] 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 method for improving the processing of printed circuit boards with excessive solder mask etching, comprising the following steps: S1. Circuit board pretreatment; S2. Print the first solder resist ink on the processed circuit board and pre-cure it; S3. Print the second solder resist ink onto the first solder resist ink and pre-cure it; S4. Expose and develop the first and second solder resist inks; S5. Cure the developed first and second solder resist inks at high temperature; It is characterized in that The first solder resist ink is a transparent ink, the second solder resist ink is a colored ink, the thickness of the first solder resist ink is greater than that of the second solder resist ink, and in step S3, the second solder resist ink completely covers the first solder resist ink. The printing method in steps S2 and S3 is screen printing. The T-number of the screen printing plate of the first solder resist ink is not greater than that of the second solder resist ink, and the printing ink viscosity of the first solder resist ink is greater than that of the second solder resist ink. The screen printing stencil of the first solder resist ink has a T number of 20-80T, the screen printing stencil of the second solder resist ink has a T number of 50-100T, the printing ink viscosity of the first solder resist ink is 125±25dps, and the printing ink viscosity of the second solder resist ink is 30±10dps. The light transmittance of the second solder resist ink is not less than 50%, and the thickness of the second solder resist ink is not greater than 35% of the thickness of the first solder resist ink.

2. The improved processing method for excessive solder resist etching on printed circuit boards according to claim 1, characterized in that, After step S5, the maximum shrinkage of either the left or right side of the lateral dimension of the first solder resist ink relative to the second solder resist ink is no greater than 1 mil.

3. The improved processing method for excessive solder resist etching on printed circuit boards according to claim 1, characterized in that, In step S2, the pre-curing temperature of the first solder resist ink is 60-80℃, and the pre-curing time is 15-30 min; in step S3, the pre-curing temperature of the second solder resist ink is 60-80℃, and the pre-curing time is 35-60 min.

4. The improved processing method for excessive solder mask etching on printed circuit boards according to claim 1, characterized in that, The pretreatment method in step S1 is volcanic ash grinding plate, which uses a brush and volcanic ash to grind the copper surface to achieve a certain roughness and clean the copper surface.

5. The improved processing method for excessive solder mask etching on printed circuit boards according to claim 1, characterized in that, The exposure method in step S4 is to cause the photopolymer in the ink to undergo a cross-linking reaction by irradiating it with UV light, thereby exposing the desired graphic position. The number of exposure grids is controlled at 12±2 grids, and the exposure energy is 350~500mJ.

6. The improved processing method for excessive solder resist etching on printed circuit boards according to claim 1, characterized in that, The development method in step S4 involves washing away the unexposed and uncrosslinked ink with a weakly alkaline solution to expose a clean copper surface. The development speed is controlled between 3-4.5 m / min, the development time is controlled between 40-60 s, the development pressure is controlled between 1.8-2.3 bar, the concentration of the developing solution is 0.8±0.2%, and the solution temperature is 31±2℃.

7. The improved processing method for excessive solder resist etching on printed circuit boards according to claim 1, characterized in that, The high-temperature curing method in step S5 involves using high-temperature hot air circulation to heat-cur the ink on the board surface. During the curing process, 1-3% of the total weight of the ink is lost as solvent, in order to achieve a permanent insulating and anti-corrosion protective film. The high-temperature curing temperature is controlled between 140-170℃ and the time is controlled between 60-80 minutes.

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