Processing method for improving overlarge resistance welding lateral erosion of printed circuit board

Abstract

The invention provides a processing method for improving overlarge solder resist lateral erosion of a printed circuit board, first solder resist ink is adopted as transparent ink, second solder resist ink is adopted as color ink, the thickness of the first solder resist ink is greater than that of the second solder resist ink, and the second solder resist ink completely covers the first solder resist ink in the step S3. The two kinds of solder resist ink are arranged in a laminated mode, the first solder resist ink located on the bottom layer is made to be transparent ink, the solder resist ink located on the surface is color ink, the overall curing uniformity of the solder resist layer is improved, and undercut formed by excessive etching of the solder resist ink which is not completely cured at the bottom is reduced. Furthermore, the transparent ink layer is completely covered by the color ink layer, and the thickness of the transparent ink layer is larger than that of the color ink layer, so that the highlight curing characteristic of the transparent ink layer is fully utilized, the combination effect of the color ink layer and the transparent ink layer is optimized, and the overall curing effect of the solder mask layer is ensured.

Description

Technical Field

[0001] The invention relates to the technical field of electronic manufacturing, and more particularly to a processing method for improving excessive side etching of solder resist on a printed circuit board. Background Art

[0002] As the demand for printed circuit board products continues to grow, printed circuit boards are developing towards high precision and high complexity. How to lay out more circuits and components in a limited space is a problem that needs to be solved urgently. The dense component design means that the spacing between pads (PADs) on the printed circuit board is compressed, and the width of the solder mask used to isolate the PADs can only be made smaller and smaller.

[0003] like Figure 1 As shown, in the manufacturing process of printed circuit boards, the main function of the solder mask is to protect the copper circuits from oxidation, corrosion and short circuits. Undercut refers to the excessive removal or etching of the solder mask at the edge, which makes the edge of the solder mask discontinuous or missing, resulting in the exposure of the copper circuit, resulting in damage to the appearance and function of the solder mask, thereby increasing the risk of short circuits and corrosion and reducing the long-term reliability of the printed circuit board; at the same time, the presence of the solder mask can also ensure the accuracy of the welding process. During welding, the solder mask prevents the solder from flowing to areas where welding is not required. If the Undercut is too large, the solder mask may not be able to completely cover specific areas of the circuit board, thereby affecting the welding quality and causing poor welding, bridging or cold welding; further, incomplete or uneven coverage of the solder mask may cause electrical interference, signal crosstalk and noise problems on the circuit board. Especially in high-frequency applications, too large an Undercut will cause the solder mask to be too thin or completely disappear in some areas, affecting the insulation performance, which may in turn affect the stability and signal integrity of the circuit. Therefore, while meeting the requirements for solder mask thickness and width, minimizing the undercut is an important means to ensure the electrical performance, reliability, production efficiency and quality control of the circuit board.

[0004] In the actual production process, how to minimize the undercut of the solder mask is also a technical problem faced by printed circuit board manufacturers. Specifically, due to the attenuation of the energy of light penetrating the ink layer during solder mask exposure, the surface ink has a high degree of photocuring, and the bottom ink has a relatively low degree of photocuring. During development, the liquid medicine corrodes the bottom ink, forming an undercut. The larger the undercut, the more difficult it is to make the solder mask smaller. Since undercut is difficult to avoid, the minimum design of the solder mask film is currently 3mil. Under the current normal screen printing of one-time oil, the undercut of ordinary green solder mask ink with a thickness of 3mil is generally around 1.2mil, while the black solder mask ink has an undercut of around 1.5~2mil because it is more difficult for light to penetrate the bottom layer of the ink. Sometimes the undercut is larger than 2mil and even the phenomenon of solder mask layer being thrown off occurs. In addition, for thick copper plates, the thicker the copper thickness, the thicker the solder mask thickness at the substrate position of the copper edge, and the solder mask thickness has a direct impact on the undercut of the solder mask. The thicker the solder mask thickness, the larger the undercut. Therefore, in order to minimize undercut while meeting the requirements of solder mask thickness and width, it is necessary to comprehensively optimize ink selection, printing process, exposure process, development process and curing process. Summary of the invention

[0005] The present invention aims to overcome at least one of the shortcomings of the above-mentioned prior art and provide a method for improving the processing of excessive undercut of solder mask on printed circuit boards. By adopting a combination of transparent ink and color ink and a special process flow, the undercut phenomenon of the solder mask ink is minimized while ensuring the color and thickness requirements of the solder mask layer.

[0006] The object of the present invention is to provide a method for improving the excessive undercut of solder mask on a printed circuit board, comprising the following steps: S1. Circuit board pre-processing; S2. Printing and pre-curing a first solder resist ink on the treated circuit board; S3. Printing a second solder resist ink on the first solder resist ink and pre-curing it; S4. Exposing and developing the first solder resist ink and the second solder resist ink; S5. Curing the first solder resist ink and the second solder resist ink at high temperature after development; The first solder resist ink is a transparent ink, the second solder resist ink is a color 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.

[0007] In the technical scheme, the selection of ink materials is optimized to minimize the undercut of the solder mask layer on the printed circuit board. Specifically, since undercut usually occurs at the edge of the solder mask ink layer, when the ink fails to be uniformly cured during the exposure and curing process, the ink edge will be etched or over-peeled. The two solder mask inks are stacked to improve the overall curing uniformity of the solder mask ink, thereby reducing the undercut caused by the bottom solder mask ink being over-etched due to incomplete curing. Among them, the first solder mask ink located at the bottom layer is transparent ink, and the solder mask ink located on the surface is color ink. The color ink with a slower light curing speed is set on the surface of the solder mask layer so that it can be fully exposed and cured. At the same time, the transparent ink with a faster light curing speed is set at the bottom of the color ink. Since the transparent ink has strong light penetrability and less light energy demand, the light source after the color ink layer is exposed and attenuated can also effectively penetrate the transparent ink during the exposure process and realize the uniform curing of the transparent ink layer, thereby ensuring the uniform curing of the stacked color ink layer and the transparent ink layer as a whole, thereby reducing the undercut phenomenon on the side or edge of the overall solder mask layer. Furthermore, in order to optimize the combination effect of the color ink layer and the transparent ink layer and improve the overall curing uniformity of the solder mask layer, the transparency and color characteristics between the first solder mask ink and the second solder mask ink are only the differences in whether the colorant is added or not, which is used to ensure the compatibility of the first solder mask ink and the second solder mask ink during production; at the same time, the color ink layer is arranged to completely cover the transparent ink layer, so as to ensure that the exposure energy penetrating the color ink layer to the transparent ink layer remains uniform while ensuring the appearance of the solder mask layer, and the thickness of the transparent ink layer is arranged to be greater than the thickness of the color ink layer, thereby making full use of the high light curing characteristics of the transparent ink layer, ensuring the overall curing effect of the solder mask layer, and effectively improving the Undercut generation while improving the compatibility between the color ink layer and the transparent ink layer.

[0008] Furthermore, the printing method in steps S2 and S3 adopts screen printing, the T number of the screen printing screen of the first solder resist ink is not greater than that of the second solder resist ink, and the viscosity of the printing ink of the first solder resist ink is greater than that of the second solder resist ink. In the present technical solution, the ink in the solder resist layer is selected and the printing process of the first solder resist ink and the second solder resist ink is improved. Specifically, by selecting a small T number, that is, a fine mesh gauze to finely print transparent ink, the thickness of the first solder resist ink layer formed is ensured to be moderate, and the good adhesion and light curing effect of the first solder resist ink on the printed circuit board are ensured. At the same time, a large T number, that is, a coarse mesh gauze is used to print the second solder resist ink layer, so as to ensure that the second solder resist ink layer is thinner, so as to ensure that when the solder resist layer is exposed and made, the second solder resist ink layer using color ink allows more light to penetrate into the second solder resist ink layer using transparent ink set at the bottom, thereby ensuring the curing effect of the second solder resist ink layer and improving the overall production quality of the solder resist layer and reducing the occurrence of undercut.

[0009] Preferably, the T number of the silk screen printing screen of the first solder resist ink is 20-80T, and the T number of the silk screen printing screen of the second solder resist ink is 50-100T; further, in order to improve the adhesion of the first solder resist ink on the printed circuit board and improve the bonding force with the second solder resist ink, the printing ink viscosity of the first solder resist ink is set to 125±25dps, and the printing ink viscosity of the second solder resist ink is set to 30±10dps. By adopting appropriate viscosities for both the first solder resist ink and the second solder resist ink, the uniformity and adhesion of each layer of solder resist ink during coating are ensured, thereby improving the precision and reliability of solder resist layer production.

[0010] Preferably, in order to further ensure that when the solder mask layer is exposed and produced, the second solder mask ink layer using colored ink allows more light to penetrate into the second solder mask ink layer using transparent ink arranged at the bottom layer, thereby ensuring the curing effect of the second solder mask ink layer and improving the overall production quality of the solder mask layer and reducing the occurrence of Undercut, it is arranged that the transmittance of the second solder mask ink is not less than 50%, and the thickness of the second solder mask ink is not greater than 35% of the thickness of the first solder mask ink.

[0011] Furthermore, it is arranged that after step S5, the maximum shrinkage of the lateral dimension of the first solder resist ink on either side relative to the second solder resist ink is not greater than 1 mil, thereby ensuring the integrity of the overall appearance of the manufactured solder resist layer, while ensuring the bonding effect between the first solder resist ink and the second solder resist ink, thereby improving the precision and reliability of the overall manufacturing of the solder resist layer.

[0012] Furthermore, after the two layers of solder resist ink are printed, they should be pre-cured to ensure the adhesion of the first solder resist ink on the printed circuit board and the bonding between the first solder resist ink and the second solder resist ink, so as to prevent the solder resist ink from falling off or moving during the subsequent exposure process. The pre-curing temperature and time should be optimized according to the characteristics of the ink. Preferably, the pre-curing temperature of the first solder resist ink in step S2 is 60-80°C and the pre-curing time is 15-30 minutes; the pre-curing temperature of the second solder resist ink in step S3 is 60-80°C and the pre-curing time is 35-60 minutes.

[0013] Furthermore, in order to further improve the adhesion of the solder mask ink layer on the printed circuit board and improve the precision and reliability of the solder mask production, a pre-treatment method for the printed circuit board surface is also included before the solder mask processing. Preferably, the pre-treatment method in step S1 is set to be a volcanic ash grinding plate, and the copper surface is treated by grinding with a brush and volcanic ash to achieve a certain roughness of the copper surface and clean the copper surface.

[0014] Furthermore, in order to ensure that the light source can evenly irradiate the surfaces of the two solder resist inks forming the solder resist layer and that the two solder resist inks in the stacked arrangement can be evenly cured, it is also necessary to control the exposure parameters of the solder resist layer accordingly. Specifically, the method of setting the exposure in step S4 is to cause a cross-linking reaction of the photopolymer in the ink by UV light irradiation, expose the required graphic position, control the number of exposure grids at 12±2 grids, and the exposure energy at 350~500mj. The exposure time is accurately adjusted according to the required thickness of the solder resist ink and the light-blocking effect of the color layer setting, thereby avoiding uneven curing caused by insufficient or excessive exposure and improving the precision and reliability of the overall production of the solder resist layer.

[0015] Furthermore, it also includes the control of the development process. In order to ensure that the unexposed part of the ink can be completely removed and to avoid undercut caused by incomplete development, the liquid temperature and time during development need to be precisely controlled. Specifically, the method of setting the development in step S4 is to wash away the ink that has not been exposed and has not undergone a cross-linking reaction with a weakly alkaline solution to expose a clean copper surface. The development speed is controlled between 3-4.5m / min, the development time is controlled between 40-60S, the development pressure is controlled between 1.8-2.3bar, the concentration of the developing solution is 0.8±0.2%, and the solution temperature is 31±2℃.

[0016] Furthermore, it also includes the control of the final curing process. The final curing of the solder mask 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, the quality problems of the solder mask layer caused by over-curing or under-curing are avoided. Specifically, the method of setting the high-temperature curing in step S5 is to heat-cure the ink on the board surface through high-temperature hot air circulation, and lose 1-3% of the solvent of the total weight of the ink during the curing process to achieve a permanent insulating anti-corrosion protective film. The temperature of the high-temperature curing is controlled between 140-170°C and the time is controlled between 60-80min.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. By optimizing the selection of ink materials, the undercut of the solder mask layer on the printed circuit board can be minimized. Specifically, since undercut usually occurs at the edge of the solder mask ink layer, when the ink fails to be uniformly cured during the exposure and curing process, the ink edge will be etched or over-peeled. The two solder mask inks are stacked to improve the overall curing uniformity of the solder mask ink, thereby reducing the undercut caused by the bottom solder mask ink being over-etched due to incomplete curing. Among them, the first solder mask ink located at the bottom layer is transparent ink, and the solder mask ink located on the surface is color ink. The color ink with a slower light curing speed is set on the surface of the solder mask layer so that it can be fully exposed and cured. At the same time, the transparent ink with a faster light curing speed is set at the bottom of the color ink. Since the transparent ink has strong light penetrability and less light energy demand, the light source after the color ink layer is exposed and attenuated can also effectively penetrate the transparent ink during the exposure process and realize the uniform curing of the transparent ink layer, thereby ensuring the uniform curing of the stacked color ink layer and the transparent ink layer as a whole, thereby reducing the undercut phenomenon on the side or edge of the overall solder mask layer. Furthermore, in order to optimize the combination effect of the color ink layer and the transparent ink layer and improve the overall curing uniformity of the solder mask layer, the color ink layer is arranged to completely cover the transparent ink layer, so as to ensure the appearance of the solder mask 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 arranged to be greater than the thickness of the color ink layer, thereby making full use of the high light curing characteristics of the transparent ink layer, ensuring the overall curing effect of the solder mask layer, and effectively improving the Undercut generation while improving the compatibility between the color ink layer and the transparent ink layer.

[0018] 2. Select the ink in the corresponding solder mask layer and improve the printing process of the first solder mask ink and the second solder mask ink when making it. Specifically, by selecting a small T number, that is, a fine mesh screen to finely print the transparent ink, it is ensured that the thickness of the first solder mask ink layer formed is moderate, and the good adhesion and light curing effect of the first solder mask ink on the printed circuit board are ensured. At the same time, a large T number, that is, a coarse mesh screen is used to print the second solder mask ink layer, so as to ensure that the second solder mask ink layer is thinner, so as to ensure that when the solder mask layer is exposed, the second solder mask ink layer using the color ink allows more light to penetrate the second solder mask ink layer using the transparent ink set at the bottom, thereby ensuring the curing effect of the second solder mask ink layer and improving the overall production quality of the solder mask layer and reducing the occurrence of undercut. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The present invention is a schematic diagram of the structure of the solder mask layer on the printed circuit board in the prior art.

[0020] Figure 2 The present invention is a flow chart of a method for improving the excessive side etching of solder mask on a printed circuit board.

[0021] Figure 3 The present invention is a schematic diagram of the structure of a printed circuit board when the first solder resist ink is printed in the method for improving the excessive solder resist undercut of a printed circuit board.

[0022] Figure 4 The present invention is a schematic diagram of the structure of a printed circuit board when the second solder resist ink is printed in the processing method for improving the excessive undercut of the solder resist on the printed circuit board.

[0023] Figure 5 The present invention is a schematic structural diagram of a printed circuit board after high temperature curing in a method for improving the excessive side erosion of solder mask on a printed circuit board. DETAILED DESCRIPTION

[0024] The drawings of the present invention are only for illustrative purposes and should not be construed as limiting the present invention. In order to better illustrate the following embodiments, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of the actual product; it is understandable to those skilled in the art that some well-known structures and their descriptions in the drawings may be omitted.

[0025] Example 1 like Figure 2 As shown, this embodiment provides a method for improving the excessive side etching of solder mask on a printed circuit board, comprising the following steps: S1. Circuit board pre-processing; S2. Printing and pre-curing a first solder resist ink on the treated circuit board; S3. Printing a second solder resist ink on the first solder resist ink and pre-curing it; S4. Exposing and developing the first solder resist ink and the second solder resist ink; S5. Curing the first solder resist ink and the second solder resist ink at high temperature after development; The first solder resist ink is a transparent ink, and the second solder resist ink is a color ink. The first solder resist ink located at the bottom layer is a transparent ink, and the solder resist ink located on the surface is a color ink. The color ink with a slower light curing speed is set 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 light curing speed is set at the bottom of the color ink. Since the transparent ink has strong light penetrability and requires less light energy, the light source after exposure attenuation of the color ink layer can also effectively penetrate the transparent ink during the exposure process and realize uniform curing of the transparent ink layer, thereby ensuring the uniform curing of the stacked color ink layer and the transparent ink layer as a whole, thereby reducing the Undercut phenomenon on the side or edge of the overall solder resist layer. Furthermore, in order to optimize the combination effect of the color ink layer and the transparent ink layer and improve the overall curing uniformity of the solder mask layer, the transparency and color characteristics between the first solder mask ink and the second solder mask ink are only the differences in whether colorant is added or not, which is used to ensure the compatibility of the first solder mask ink and the second solder mask ink during production; at the same time, the color ink layer is arranged to completely cover the transparent ink layer, so as to ensure that the exposure energy penetrating the color ink layer to the transparent ink layer remains uniform while ensuring the appearance of the solder mask layer, and the thickness of the transparent ink layer is arranged to be greater than the thickness of the color ink layer, thereby making full use of the high light curing characteristics of the transparent ink layer and ensuring the overall curing effect of the solder mask layer.

[0026] Furthermore, the printing method in steps S2 and S3 adopts screen printing, the T number of the screen printing screen of the first solder resist ink is not greater than that of the second solder resist ink, and the viscosity of the printing ink of the first solder resist ink is greater than that of the second solder resist ink. In the present technical solution, the ink in the solder resist layer is selected and the printing process of the first solder resist ink and the second solder resist ink is improved. Specifically, by selecting a small T number, that is, a fine mesh gauze to finely print transparent ink, the thickness of the first solder resist ink layer formed is ensured to be moderate, and the good adhesion and light curing effect of the first solder resist ink on the printed circuit board are ensured. At the same time, a large T number, that is, a coarse mesh gauze is used to print the second solder resist ink layer, so as to ensure that the second solder resist ink layer is thinner, so as to ensure that when the solder resist layer is exposed and made, the second solder resist ink layer using color ink allows more light to penetrate into the second solder resist ink layer using transparent ink set at the bottom, thereby ensuring the curing effect of the second solder resist ink layer and improving the overall production quality of the solder resist layer and reducing the occurrence of undercut.

[0027] Preferably, the T number of the silk screen printing screen of the first solder resist ink is 20-80T, and the T number of the silk screen printing screen of the second solder resist ink is 50-100T; further, in order to improve the adhesion of the first solder resist ink on the printed circuit board and improve the bonding force with the second solder resist ink, the printing ink viscosity of the first solder resist ink is set to 125±25dps, and the printing ink viscosity of the second solder resist ink is set to 30±10dps. By adopting appropriate viscosities for both the first solder resist ink and the second solder resist ink, the uniformity and adhesion of each layer of solder resist ink during coating are ensured, thereby improving the precision and reliability of solder resist layer production.

[0028] Preferably, in order to further ensure that when the solder mask layer is exposed and produced, the second solder mask ink layer using colored ink allows more light to penetrate into the second solder mask ink layer using transparent ink arranged at the bottom layer, thereby ensuring the curing effect of the second solder mask ink layer and improving the overall production quality of the solder mask layer and reducing the occurrence of Undercut, it is arranged that the transmittance of the second solder mask ink is not less than 50%, and the thickness of the second solder mask ink is not greater than 35% of the thickness of the first solder mask ink.

[0029] Furthermore, it is arranged that after step S5, the maximum shrinkage of the lateral dimension of the first solder resist ink on either side relative to the second solder resist ink is not greater than 1 mil, thereby ensuring the integrity of the overall appearance of the manufactured solder resist layer, while ensuring the bonding effect between the first solder resist ink and the second solder resist ink, thereby improving the precision and reliability of the overall manufacturing of the solder resist layer.

[0030] Furthermore, after the two layers of solder resist ink are printed, they should be pre-cured to ensure the adhesion of the first solder resist ink on the printed circuit board and the bonding between the first solder resist ink and the second solder resist ink, so as to prevent the solder resist ink from falling off or moving during the subsequent exposure process. The pre-curing temperature and time should be optimized according to the characteristics of the ink. Preferably, the pre-curing temperature of the first solder resist ink in step S2 is 60-80°C and the pre-curing time is 15-30 minutes; the pre-curing temperature of the second solder resist ink in step S3 is 60-80°C and the pre-curing time is 35-60 minutes.

[0031] Furthermore, in order to further improve the adhesion of the solder mask ink layer on the printed circuit board and improve the precision and reliability of the solder mask production, a pre-treatment method for the printed circuit board surface is also included before the solder mask processing. Preferably, the pre-treatment method in step S1 is set to be a volcanic ash grinding plate, and the copper surface is treated by grinding with a brush and volcanic ash to achieve a certain roughness of the copper surface and clean the copper surface.

[0032] Furthermore, in order to ensure that the light source can evenly irradiate the surfaces of the two solder resist inks forming the solder resist layer and that the two solder resist inks in the stacked arrangement can be evenly cured, it is also necessary to control the exposure parameters of the solder resist layer accordingly. Specifically, the method of setting the exposure in step S4 is to cause a cross-linking reaction of the photopolymer in the ink by UV light irradiation, expose the required graphic position, control the number of exposure grids at 12±2 grids, and the exposure energy at 350~500mj. The exposure time is accurately adjusted according to the required thickness of the solder resist ink and the light-blocking effect of the color layer setting, thereby avoiding uneven curing caused by insufficient or excessive exposure and improving the precision and reliability of the overall production of the solder resist layer.

[0033] Furthermore, it also includes the control of the development process. In order to ensure that the unexposed part of the ink can be completely removed and to avoid undercut caused by incomplete development, the liquid temperature and time during development need to be precisely controlled. Specifically, the method of setting the development in step S4 is to wash away the ink that has not been exposed and has not undergone a cross-linking reaction with a weakly alkaline solution to expose a clean copper surface. The development speed is controlled between 3-4.5m / min, the development time is controlled between 40-60S, the development pressure is controlled between 1.8-2.3bar, the concentration of the developing solution is 0.8±0.2%, and the solution temperature is 31±2℃.

[0034] Furthermore, it also includes the control of the final curing process. The final curing of the solder mask 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, the quality problems of the solder mask layer caused by over-curing or under-curing are avoided. Specifically, the method of setting the high-temperature curing in step S5 is to heat-cure the ink on the board surface through high-temperature hot air circulation, and lose 1-3% of the solvent of the total weight of the ink during the curing process to achieve a permanent insulating anti-corrosion protective film. The temperature of the high-temperature curing is controlled between 140-170°C and the time is controlled between 60-80min.

[0035] Example 2 like Figure 2-Figure 5 As shown, this embodiment also provides a method for improving the excessive side etching of solder mask on a printed circuit board, comprising the following steps: S1. Circuit board pre-processing; S2. Printing and pre-curing a first solder resist ink on the treated circuit board; S3. Printing a second solder resist ink on the first solder resist ink and pre-curing it; S4. Exposing and developing the first solder resist ink and the second solder resist ink; S5. Curing the first solder resist ink and the second solder resist ink at high temperature after development; In step S1, the pretreatment method is volcanic ash grinding plate, and the copper surface is treated by grinding with a brush and volcanic ash to make the copper surface reach a certain roughness and clean the copper surface, thereby increasing the bonding strength between the solder mask ink and the copper layer.

[0036] like Figure 3 As shown, in step S2, a screen printing screen with a mesh of 36T is used to cover the copper surface and substrate position of the printed circuit board with a first solder resist ink using transparent ink, and the viscosity of the first solder resist ink is 125dps, the pressure of the screen printer is controlled at 2-6bar, and the screen printing squeegee uses a 10mm wide squeegee with a Shore hardness of 70, and the squeegee angle is 5-15°; after the first solder resist ink is evenly applied, the first solder resist ink layer is pre-cured, specifically, the first solder resist ink layer is heated by a tunnel furnace oven, and the board surface is dried by circulating hot air, so that the first solder resist ink changes from a wet flowable state to a semi-dry state, so as to prepare for the next step of printing the second solder resist ink, the pre-curing temperature is 75°C, and the pre-baking time for double-sided printing is 21min.

[0037] like Figure 4 As shown, in step S3, a 36T screen is used to cover the pre-cured first solder resist ink layer with a layer of black second solder resist ink, and the viscosity of the second solder resist ink is 125dps, wherein the transparency and color characteristics between the first solder resist ink and the second solder resist ink are only the difference in whether the colorant is added or not, which is used to ensure the compatibility of the first solder resist ink and the second solder resist ink in the production; after the second solder resist ink is printed, the second solder resist ink layer is pre-cured, heated by a tunnel furnace oven, and the board surface is dried by circulating hot air to volatilize part of the solvent in the ink, so that the ink changes from a wet flowable state to a semi-dry state, so as to prepare for the next step of exposure, and the temperature is controlled at 75°C, and the pre-baking time for double-sided printing is 48min.

[0038] In step S4, a C-SUN manual exposure machine is used to expose the pre-cured stacked solder mask ink layer. Specifically, a yellow film is hand-patted on the board surface and then placed in the exposure machine for exposure. The exposure scale number is controlled at 12±2 grids, and the exposure energy is 350~500mj. The photopolymer in the ink undergoes a cross-linking reaction through UV light irradiation, and the required graphic position is exposed. Then, a development process is performed to expose the solder mask ink that has not been exposed to UV light and has not undergone a cross-linking reaction with a weakly alkaline solution such as K 2 CO 3 / Na 2 CO 3 Wash it off to expose a clean copper surface; wherein, the developing speed is controlled at 3.8m / min, the developing time is 50s, the developing pressure is 2.0bar, the developing solution concentration is 0.8±0.2%, and the solution temperature is 31±2℃.

[0039] In step S5, the ink on the board surface is thermally cured by high-temperature hot air circulation, and 1-3% of the total weight of the ink solvent is lost during the curing process to achieve a permanent insulating anti-corrosion protective film; specifically, the high temperature is 155°C and the baking time is 70 minutes.

[0040] like Figure 5 As shown, after high temperature curing is completed, the printed circuit board is finally formed into its final shape after surface treatment.

[0041] Example 3 like Figure 2-Figure 5 As shown, this embodiment also provides a method for improving the excessive side etching of solder mask on a printed circuit board, comprising the following steps: S1. Circuit board pre-processing; S2. Printing and pre-curing a first solder resist ink on the treated circuit board; S3. Printing a second solder resist ink on the first solder resist ink and pre-curing it; S4. Exposing and developing the first solder resist ink and the second solder resist ink; S5. Curing the first solder resist ink and the second solder resist ink at high temperature after development; In step S1, the pretreatment method is volcanic ash grinding plate, and the copper surface is treated by grinding with a brush and volcanic ash to make the copper surface reach a certain roughness and clean the copper surface, thereby increasing the bonding strength between the solder mask ink and the copper layer.

[0042] like Figure 3 As shown, in step S2, a screen printing screen with a mesh of 62T is used to cover the copper surface and substrate position of the printed circuit board with a first solder resist ink using transparent ink, and the viscosity of the first solder resist ink is 125dps, the pressure of the screen printer is controlled at 2-6bar, and the screen printing squeegee uses a 10mm wide squeegee with a Shore hardness of 70, and the squeegee angle is 5-15°; after the first solder resist ink is evenly applied, the first solder resist ink layer is pre-cured, specifically, the first solder resist ink layer is heated by a tunnel furnace oven, and the board surface is dried by circulating hot air, so that the first solder resist ink changes from a wet flowable state to a semi-dry state, so as to prepare for the next step of printing the second solder resist ink, the pre-curing temperature is 75°C, and the pre-baking time for double-sided printing is 21min.

[0043] like Figure 4As shown, in step S3, a 62T screen printing screen is used to cover a layer of black second solder resist ink on the pre-cured first solder resist ink layer, and the viscosity of the second solder resist ink is 125dps, wherein the transparency and color characteristics between the first solder resist ink and the second solder resist ink are only the difference in whether the colorant is added or not, which is used to ensure the compatibility of the first solder resist ink and the second solder resist ink in the production; after the second solder resist ink is printed, the second solder resist ink layer is pre-cured, heated by a tunnel furnace oven, and the board surface is dried by circulating hot air to volatilize part of the solvent in the ink, so that the ink changes from a wet flowable state to a semi-dry state, so as to prepare for the next step of exposure, and the temperature is controlled at 75°C, and the pre-baking time for double-sided printing is 48min.

[0044] In step S4, a C-SUN manual exposure machine is used to expose the pre-cured stacked solder mask ink layer. Specifically, a yellow film is hand-patted on the board surface and then placed in the exposure machine for exposure. The exposure scale number is controlled at 12±2 grids, and the exposure energy is 350~500mj. The photopolymer in the ink undergoes a cross-linking reaction through UV light irradiation, and the required graphic position is exposed. Then, a development process is performed to expose the solder mask ink that has not been exposed to UV light and has not undergone a cross-linking reaction with a weakly alkaline solution such as K 2 CO 3 / Na 2 CO 3 Wash it off to expose a clean copper surface; wherein, the developing speed is controlled at 3.8m / min, the developing time is 50s, the developing pressure is 2.0bar, the developing solution concentration is 0.8±0.2%, and the solution temperature is 31±2℃.

[0045] In step S5, the ink on the board surface is thermally cured by high-temperature hot air circulation, and 1-3% of the total weight of the ink solvent is lost during the curing process to achieve a permanent insulating anti-corrosion protective film; specifically, the high temperature is 155°C and the baking time is 70 minutes.

[0046] like Figure 5 As shown, after high temperature curing is completed, the printed circuit board is finally formed into its final shape after surface treatment.

[0047] Example 4 like Figure 2-Figure 5 As shown, this embodiment also provides a method for improving the excessive side etching of solder mask on a printed circuit board, comprising the following steps: S1. Circuit board pre-processing; S2. Printing and pre-curing a first solder resist ink on the treated circuit board; S3. Printing a second solder resist ink on the first solder resist ink and pre-curing it; S4. Exposing and developing the first solder resist ink and the second solder resist ink; S5. Curing the first solder resist ink and the second solder resist ink at high temperature after development; In step S1, the pretreatment method is volcanic ash grinding plate, and the copper surface is treated by grinding with a brush and volcanic ash to make the copper surface reach a certain roughness and clean the copper surface, thereby increasing the bonding strength between the solder mask ink and the copper layer.

[0048] like Figure 3 As shown, in step S2, a screen printing screen with a mesh of 36T is used to cover the copper surface and substrate position of the printed circuit board with a first solder resist ink using transparent ink, and the viscosity of the first solder resist ink is 125dps, the pressure of the screen printer is controlled at 2-6bar, and the screen printing squeegee uses a 10mm wide squeegee with a Shore hardness of 70, and the squeegee angle is 5-15°; after the first solder resist ink is evenly applied, the first solder resist ink layer is pre-cured, specifically, the first solder resist ink layer is heated by a tunnel furnace oven, and the board surface is dried by circulating hot air, so that the first solder resist ink changes from a wet flowable state to a semi-dry state, so as to prepare for the next step of printing the second solder resist ink, the pre-curing temperature is 75°C, and the pre-baking time for double-sided printing is 21min.

[0049] like Figure 4 As shown, in step S3, a 62T screen printing screen is used to cover a layer of black second solder resist ink on the pre-cured first solder resist ink layer, and the viscosity of the second solder resist ink is 30dps, wherein the transparency and color characteristics between the first solder resist ink and the second solder resist ink are only the difference in whether the colorant is added or not, which is used to ensure the compatibility of the first solder resist ink and the second solder resist ink in the production; after the second solder resist ink is printed, the second solder resist ink layer is pre-cured, heated by a tunnel furnace oven, and the board surface is dried by circulating hot air to volatilize part of the solvent in the ink, so that the ink changes from a wet flowable state to a semi-dry state, so as to prepare for the next step of exposure, and the temperature is controlled at 75°C, and the pre-baking time for double-sided printing is 48min.

[0050] In step S4, a C-SUN manual exposure machine is used to expose the pre-cured stacked solder mask ink layer. Specifically, a yellow film is hand-patted on the board surface and then placed in the exposure machine for exposure. The exposure scale number is controlled at 12±2 grids, and the exposure energy is 350~500mj. The photopolymer in the ink undergoes a cross-linking reaction through UV light irradiation, and the required graphic position is exposed. Then, a development process is performed to expose the solder mask ink that has not been exposed to UV light and has not undergone a cross-linking reaction with a weakly alkaline solution such as K 2 CO 3 / Na 2 CO 3Wash it off to expose a clean copper surface; wherein, the developing speed is controlled at 3.8m / min, the developing time is 50s, the developing pressure is 2.0bar, the developing solution concentration is 0.8±0.2%, and the solution temperature is 31±2℃.

[0051] In step S5, the ink on the board surface is thermally cured by high-temperature hot air circulation, and 1-3% of the total weight of the ink solvent is lost during the curing process to achieve a permanent insulating anti-corrosion protective film; specifically, the high temperature is 155°C and the baking time is 70 minutes.

[0052] like Figure 5 As shown, after high temperature curing is completed, the printed circuit board is finally formed into its final shape after surface treatment.

[0053] Example 5 like Figure 2-Figure 5 As shown, this embodiment also provides a method for improving the excessive side etching of solder mask on a printed circuit board, comprising the following steps: S1. Circuit board pre-processing; S2. Printing and pre-curing a first solder resist ink on the treated circuit board; S3. Printing a second solder resist ink on the first solder resist ink and pre-curing it; S4. Exposing and developing the first solder resist ink and the second solder resist ink; S5. Curing the first solder resist ink and the second solder resist ink at high temperature after development; In step S1, the pretreatment method is volcanic ash grinding plate, and the copper surface is treated by grinding with a brush and volcanic ash to make the copper surface reach a certain roughness and clean the copper surface, thereby increasing the bonding strength between the solder mask ink and the copper layer.

[0054] like Figure 3 As shown, in step S2, a screen printing screen with a mesh of 62T is used to cover the copper surface and substrate position of the printed circuit board with a first solder resist ink using transparent ink, and the viscosity of the first solder resist ink is 30dps, the pressure of the screen printer is controlled at 2-6bar, and the screen printing squeegee uses a 10mm wide squeegee with a Shore hardness of 70, and the squeegee angle is 5-15°; after the first solder resist ink is evenly applied, the first solder resist ink layer is pre-cured, specifically, the first solder resist ink layer is heated by a tunnel furnace oven, and the board surface is dried by circulating hot air, so that the first solder resist ink changes from a wet flowable state to a semi-dry state, so as to prepare for the next step of printing the second solder resist ink, the pre-curing temperature is 75°C, and the pre-baking time for double-sided printing is 21min.

[0055] like Figure 4As shown, in step S3, a 32T mesh screen is used to cover the pre-cured first solder resist ink layer with a layer of black second solder resist ink, and the viscosity of the second solder resist ink is 30dps, wherein the transparency and color characteristics between the first solder resist ink and the second solder resist ink are only the difference in whether the colorant is added or not, which is used to ensure the compatibility of the first solder resist ink and the second solder resist ink in the production; after the second solder resist ink is printed, the second solder resist ink layer is pre-cured, heated by a tunnel furnace oven, and the board surface is dried by circulating hot air to volatilize part of the solvent in the ink, so that the ink changes from a wet flowable state to a semi-dry state, so as to prepare for the next step of exposure, and the temperature is controlled at 75°C, and the pre-baking time for double-sided printing is 48min.

[0056] In step S4, a C-SUN manual exposure machine is used to expose the pre-cured stacked solder mask ink layer. Specifically, a yellow film is hand-patted on the board surface and then placed in the exposure machine for exposure. The exposure scale number is controlled at 12±2 grids, and the exposure energy is 350~500mj. The photopolymer in the ink undergoes a cross-linking reaction through UV light irradiation, and the required graphic position is exposed. Then, a development process is performed to expose the solder mask ink that has not been exposed to UV light and has not undergone a cross-linking reaction with a weakly alkaline solution such as K 2 CO 3 / Na 2 CO 3 Wash it off to expose a clean copper surface; wherein, the developing speed is controlled at 3.8m / min, the developing time is 50s, the developing pressure is 2.0bar, the developing solution concentration is 0.8±0.2%, and the solution temperature is 31±2℃.

[0057] In step S5, the ink on the board surface is thermally cured by high-temperature hot air circulation, and 1-3% of the total weight of the ink solvent is lost during the curing process to achieve a permanent insulating anti-corrosion protective film; specifically, the high temperature is 155°C and the baking time is 70 minutes.

[0058] like Figure 5 As shown, after high temperature curing is completed, the printed circuit board is finally formed into its final shape after surface treatment.

[0059] Example 6 like Figure 2-Figure 5 As shown, this embodiment also provides a method for improving the excessive side etching of solder mask on a printed circuit board, comprising the following steps: S1. Circuit board pre-processing; S2. Printing and pre-curing a first solder resist ink on the treated circuit board; S3. Printing a second solder resist ink on the first solder resist ink and pre-curing it; S4. Exposing and developing the first solder resist ink and the second solder resist ink; S5. Curing the first solder resist ink and the second solder resist ink at high temperature after development; In step S1, the pretreatment method is volcanic ash grinding plate, and the copper surface is treated by grinding with a brush and volcanic ash to make the copper surface reach a certain roughness and clean the copper surface, thereby increasing the bonding strength between the solder mask ink and the copper layer.

[0060] like Figure 3 As shown, in step S2, a screen printing screen with a mesh of 62T is used to cover the copper surface and substrate position of the printed circuit board with a first solder resist ink using transparent ink, and the viscosity of the first solder resist ink is 30dps, the pressure of the screen printer is controlled at 2-6bar, and the screen printing squeegee uses a 10mm wide squeegee with a Shore hardness of 70, and the squeegee angle is 5-15°; after the first solder resist ink is evenly applied, the first solder resist ink layer is pre-cured, specifically, the first solder resist ink layer is heated by a tunnel furnace oven, and the board surface is dried by circulating hot air, so that the first solder resist ink changes from a wet flowable state to a semi-dry state, so as to prepare for the next step of printing the second solder resist ink, the pre-curing temperature is 75°C, and the pre-baking time for double-sided printing is 21min.

[0061] like Figure 4 As shown, in step S3, a 62T screen printing screen is used to cover a layer of black second solder resist ink on the pre-cured first solder resist ink layer, and the viscosity of the second solder resist ink is 30dps, wherein the transparency and color characteristics between the first solder resist ink and the second solder resist ink are only the difference in whether the colorant is added or not, which is used to ensure the compatibility of the first solder resist ink and the second solder resist ink in the production; after the second solder resist ink is printed, the second solder resist ink layer is pre-cured, heated by a tunnel furnace oven, and the board surface is dried by circulating hot air to volatilize part of the solvent in the ink, so that the ink changes from a wet flowable state to a semi-dry state, so as to prepare for the next step of exposure, and the temperature is controlled at 75°C, and the pre-baking time for double-sided printing is 48min.

[0062] In step S4, a C-SUN manual exposure machine is used to expose the pre-cured stacked solder mask ink layer. Specifically, a yellow film is hand-patted on the board surface and then placed in the exposure machine for exposure. The exposure scale number is controlled at 12±2 grids, and the exposure energy is 350~500mj. The photopolymer in the ink undergoes a cross-linking reaction through UV light irradiation, and the required graphic position is exposed. Then, a development process is performed to expose the solder mask ink that has not been exposed to UV light and has not undergone a cross-linking reaction with a weakly alkaline solution such as K 2 CO 3 / Na 2 CO 3Wash it off to expose a clean copper surface; wherein, the developing speed is controlled at 3.8m / min, the developing time is 50s, the developing pressure is 2.0bar, the developing solution concentration is 0.8±0.2%, and the solution temperature is 31±2℃.

[0063] In step S5, the ink on the board surface is thermally cured by high-temperature hot air circulation, and 1-3% of the total weight of the ink solvent is lost during the curing process to achieve a permanent insulating anti-corrosion protective film; specifically, the high temperature is 155°C and the baking time is 70 minutes.

[0064] like Figure 5 As shown, after high temperature curing is completed, the printed circuit board is finally formed into its final shape after surface treatment.

[0065] Take the printed circuit boards prepared in Examples 2-6 and measure the Undercut of the solder mask formed thereon respectively, and evaluate whether the appearance is qualified. Specifically, the appearance evaluation of the solder mask includes the following contents: the solder mask exists, the coverage is uniform, the shape and width of the solder mask meet the design requirements, the color is consistent, and there is no ink sagging. All of them meet the appearance. The test comparison results are as follows:

[0066] Through the above test comparison, it can be seen that when the solder mask processing method provided by the technical solution is adopted, the Undercut of the formed solder mask layer is generally small, indicating that the use of the stacked color ink and transparent ink improves the curing performance of the solder mask layer, reduces the generation of Undercut, and improves the precision and reliability of the solder mask layer. Further, it is found that in Example 4, the first solder mask ink using transparent ink is produced using a high viscosity, small mesh T number printing process, while the second solder mask ink using black ink is produced using a low viscosity, large mesh T number printing process. The effect is best, and the Undercut made under the same conditions is the smallest, indicating that the curing performance of the solder mask layer can be further improved by correspondingly controlling the printing process parameters of different solder mask ink layers, reducing the generation of Undercut, and improving the precision and reliability of the solder mask layer.

[0067] 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 methods of the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the claims of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. A method for improving the excessive side etching of solder mask on a printed circuit board, comprising the following steps: S1. Circuit board pre-processing; S2. Printing and pre-curing a first solder resist ink on the treated circuit board; S3. Printing a second solder resist ink on the first solder resist ink and pre-curing it; S4. Exposing and developing the first solder resist ink and the second solder resist ink; S5. Curing the first solder resist ink and the second solder resist ink at high temperature after development; It is characterized in that The first solder resist ink is a transparent ink, the second solder resist ink is a color 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.

2. The method for improving the over-etching of solder mask on printed circuit boards according to claim 1, characterized in that: The printing method in steps S2. and S3. adopts 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.

3. The method for improving the over-etching of solder mask on printed circuit boards according to claim 2, characterized in that: The T number of the silk screen printing screen of the first solder resist ink is 20-80T, the T number of the silk screen printing screen of the second solder resist ink is 50-100T, the printing ink viscosity of the first solder resist ink is 125±25ps, and the printing ink viscosity of the second solder resist ink is 30±10dps.

4. The method for improving the over-etching of solder mask on printed circuit boards according to any one of claims 1 to 3, characterized in that: 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.

5. The method for improving the over-etching of solder mask on printed circuit boards according to claim 4, characterized in that: After step S5., the maximum contraction value of the lateral dimension of the first solder resist ink relative to the second solder resist ink is no more than 1 mil on either side.

6. The method for improving the over-etching of solder mask on printed circuit boards according to any one of claims 1 to 3, characterized in that: In the step S2., the pre-curing temperature of the first solder resist ink is 60-80° C., and the pre-curing time is 15-30 minutes; in the step S3., the pre-curing temperature of the second solder resist ink is 60-80° C., and the pre-curing time is 35-60 minutes.

7. The method for improving the over-cutting of solder mask on printed circuit boards according to any one of claims 1 to 3, characterized in that: The pre-treatment method in step S1. is a volcanic ash grinding plate, and the copper surface is treated by grinding with a brush and volcanic ash to achieve a certain roughness of the copper surface and clean the copper surface.

8. The method for improving the over-cutting of solder mask on printed circuit boards according to any one of claims 1 to 3, characterized in that: The exposure method in step S4. is to cause a cross-linking reaction of the photopolymer in the ink by UV light irradiation, and expose the required graphic position, the exposure grid number is controlled at 12±2 grids, and the exposure energy is 350~500mj.

9. The method for improving the over-etching of solder mask on printed circuit boards according to any one of claims 1 to 3, characterized in that: The developing method in step S4. is to wash away the ink that has not been exposed and has not undergone cross-linking reaction with a weak alkaline solution to expose a clean copper surface, the developing speed is controlled between 3-4.5m / min, the developing time is controlled between 40-60S, the developing pressure is controlled between 1.8-2.3bar, the concentration of the developing solution is 0.8±0.2%, and the solution temperature is 31±2°C.

10. The method for improving the over-cutting of solder mask on printed circuit boards according to any one of claims 1 to 3, characterized in that: The method of medium and high temperature curing in step S5. is to thermally cure the ink on the board surface through high temperature hot air circulation, and 1-3% of the solvent of the total weight of the ink is lost during the curing process to achieve a permanent insulating anti-corrosion protective film. The temperature of the high temperature curing is controlled between 140-170°C, and the time is controlled between 60-80 minutes.

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