Method for manufacturing dry film mask hole on outer layer pattern of PCB (Printed Circuit Board)

Abstract

The invention discloses a method for manufacturing a dry film mask hole on an outer layer pattern of a PCB (Printed Circuit Board), and belongs to the technical field of printed circuit boards. The method for manufacturing the dry film mask hole on the outer layer pattern of the PCB comprises the following steps of: 1, manufacturing an inner layer pattern: forming a primary PCB; 2, manufacturing an outer layer pattern: carrying out earlier stage processing on the primary PCB, and carrying out dry film pressing and exposure after processing; wet film hole masking is carried out on the dry film hole masking, then wet film drying is carried out, exposure development is carried out, and an intermediate PCB is formed; step 3, curing and checking: the PCB is cured; and step 4, carrying out resistance welding, surface coating and testing on the PCB with the masked hole to form an ultimate complete PCB product. According to the method for manufacturing the dry film mask hole of the PCB outer layer pattern, the wet film is covered outside the dry film at the mask hole, so that the risk that the dry film is broken due to liquid medicine impact during developing and etching of the dry film can be reduced, the risk of poor manufacturing of an outer layer circuit is reduced, and the manufacturing and processing of a precise circuit board are improved.

Description

Technical Field

[0001] The invention relates to the technical field of printed circuit boards, in particular to a method for making dry film mask holes for outer layer graphics of a PCB board. Background Art

[0002] PCB is a support for interconnecting various electronic components. There are different types of holes designed on the PCB, such as through holes, part holes and mounting holes. In the production process of PCB, CCL cuts the material to make the inner layer pattern, and after browning, it is combined with PP and copper foil to stack and press, and then drills, copper plating, outer layer pattern, solder mask, surface coating, testing, etc.

[0003] When making the outer layer graphics of the PCB, from film pasting, exposure to DES development steps, since there are many holes of different apertures on the PCB board, the dry film must cover holes of different sizes to prevent the copper in the holes from being etched away, that is, the dry film is required to have the ability to mask large holes. However, after covering the large holes, the existing dry film is easily broken by the impact of the chemical solution during the subsequent development, etching and other chemical impact steps due to the large aperture of some holes on the PCB, resulting in etching of the copper plating in the holes, and the dry film fragments causing defects such as burrs and open short circuits in the etched circuits. Although pasting multiple layers of dry film or thick dry film can improve the masking ability, the thick dry film coverage is not easy to make fine circuits, which affects the manufacturing and processing of precision circuit boards. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a method for making dry film mask holes on the outer layer graphics of a PCB board, which solves the problem that the dry film at the PCB mask hole is easily damaged by impact due to the large hole diameter, and the multi-layer dry film causes the film thickness at the circuit to affect the processing of fine circuits.

[0005] To achieve the above purpose, the present invention is implemented by the following technical scheme: A method for making a dry film mask hole on the outer layer pattern of a PCB board, comprising the following steps:

[0006] Step 1: Inner layer pattern production: Cut the substrate, make the inner layer pattern, brown it, laminate it with PP and copper foil, then drill and copper electroplate it to form a primary PCB board;

[0007] Step 2: outer layer pattern production: the above primary PCB is pre-processed, and then dry film is pressed and exposed; wet film is masked on the dry film mask, and then the wet film is dried and exposed to form an intermediate PCB board;

[0008] Step 3: Curing and inspection: Use a curing device with a soft gas lamp to cure the above PCB board, control the density of the soft gas lamp and the speed of the conveyor belt to obtain the required heat level, and perform quality inspection;

[0009] Step 4: Perform solder mask, surface coating and testing on the masked PCB to form the ultimate complete PCB product.

[0010] Preferably, the dry film pressing in step 2 is dry film pasting, wherein the dry film thickness is 10-40 μm.

[0011] Preferably, in the step 2, the wet film mask is processed by silk screen printing, wherein the thickness of the wet film is 20-50 μm.

[0012] Preferably, the preliminary processing of the primary PCB in step 2 includes:

[0013] Oxidation treatment: The copper layer is controlled oxidized with brown oxide and black oxide. The oxidation process must be strictly controlled to keep the oxide layer thickness at 0.5-1.0 μm.

[0014] Preferably, the dry film lamination in step 2 includes:

[0015] Dehumidification: Use a high-pressure hair dryer to physically remove water from the surface and holes of the circuit board.

[0016] Lamination: Cover the dry film on the primary PCB board and make the dry film fit tightly with the PVB board.

[0017] Preferably, the wet film masking in step 2 comprises:

[0018] Material preparation: ensure that the required slurry, screen, scraper, cleaning agent, and circuit board are ready;

[0019] Screen printing: Make a screen that matches the hole layout of the circuit board, pour the slurry on the screen, and then use a scraper to evenly scrape the slurry across the screen so that the slurry enters the holes of the circuit board through the openings of the screen and adheres to the dry film. The slurry is in the holes, and its surface is flush with the surface of the circuit board or slightly higher than the opening.

[0020] Preferably, in step 2, the wet film is dried by a heating box, the temperature of the heating box is controlled at 50-75° C., and the drying time is 30 minutes.

[0021] Preferably, in the step 2, the ring width when the dry film is used to mask the holes is ≥ 0.1 mm, and the ring width when the wet film is used to mask the holes is ≤ the ring width when the dry film is used to mask the holes.

[0022] Preferably, the exposure and imaging in step 2 includes:

[0023] Exposure: When the dry film is just pressed, the required exposure energy is low. It increases rapidly with the increase of holding time and gradually stabilizes to a constant value. The holding time after pressing should be kept at a constant value to avoid drastic changes in exposure time. After the wet film is dried, the exposure dose is directly stabilized at 50mJ / cm2, and the exposure time is set to 5 seconds.

[0024] Development: The unexposed solder resist is washed off from the surface of the printed circuit board. The chemicals used for development are aqueous solution and developer. In aqueous solution development, a diluted sodium carbonate solution is added to 99% pure water. The operating temperature is 45°C. After using this solution, the flushing distance experienced by the printed circuit board during full development accounts for between 40% and 60% of the length of the developing chamber.

[0025] Preferably, in step three, the curing time of the curing equipment is 2 minutes, and the curing temperature is 100-130°C.

[0026] The present invention discloses a method for making dry film mask holes on the outer layer pattern of a PCB board, which has the following beneficial effects:

[0027] The present invention can solve the problem that the dry film at the PCB mask hole is easily damaged by impact due to the large hole diameter, and the film thickness at the circuit caused by the multi-layer dry film affects the processing of fine circuits through the setting mode of matching the dry film and the wet film. The wet film has good fluidity and can effectively fill the pits and protrusions on the surface of the dry film covering the hole, thereby improving the coverage. By covering the dry film at the mask hole with the wet film, the mask hole is thickened, which can reduce the risk of the dry film being broken due to the impact of the chemical solution during development and etching, thereby reducing the risk of poor production of the outer layer circuit and improving the manufacturing and processing of precision circuit boards.

[0028] The present invention uses multiple exposure and imaging to allow the dry film and the wet film to be exposed and imaged separately, so that double protection is formed, which is convenient for forming accurate circuit patterns and solder mask patterns on the PCB board, and is convenient for forming the characteristics of thick film at the mask hole and thin film at the circuit on the PCB, thereby improving the integrity and stability of the outer layer pattern production of the PCB board, reducing the risk of thin dry film mask hole breakage, and improving the yield of the outer layer pattern production. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0030] Figure 1 This is a step diagram of the PCB processing process of the present invention;

[0031] Figure 2 This is a schematic diagram of the PCB processing flow of the present invention;

[0032] Figure 3 This is a schematic diagram of making the outer layer pattern of the PCB of the present invention;

[0033] Figure 4 This is a schematic diagram of the PCB after completion of the present invention. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] The embodiment of the present application provides a method for making a dry film mask hole on the outer layer pattern of a PCB board, so as to solve the problem that the dry film at the mask hole of the PCB is easily damaged by impact due to the large hole diameter, and the film thickness at the circuit caused by the multi-layer dry film affects the processing of fine circuits. The method achieves that the mask hole is thickened by covering the dry film with a wet film outside the mask hole. The good fluidity of the wet film can effectively fill the pits and protrusions on the surface of the dry film covering the hole, thereby improving the coverage, and reducing the risk of the dry film being broken due to the impact of the chemical solution during development and etching, so as to facilitate the formation of the characteristics of thick film at the mask hole and thin film at the circuit on the PCB, thereby improving the integrity and stability in the production of the outer layer pattern of the PCB board, reducing the risk of thin dry film mask hole damage, and improving the yield of the outer layer pattern production, thereby reducing the risk of defective outer layer circuit production, and improving the manufacturing and processing of precision circuit boards.

[0036] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0037] The embodiment of the invention discloses a method for making dry film mask holes on the outer layer pattern of a PCB board.

[0038] Embodiment 1

[0039] According to the attached Figure 1 -4, including the following steps:

[0040] Step 1: Inner layer pattern production: The substrate is cut, the inner layer pattern is browned and then laminated with PP and copper foil, and then drilled and copper plated to form a primary PCB board. Cutting, lamination, drilling and copper plating are all existing mature steps, which can stably produce a primary PCB board with an inner layer pattern.

[0041] Step 2: outer layer pattern production: the above primary PCB is pre-processed, and then dry film lamination is performed. Dry film lamination is to paste dry film, wherein the thickness of dry film is 10-40μm, and then exposure is performed; wet film masking is performed on the dry film mask, and the wet film masking is processed by silk screen printing, wherein the thickness of wet film is 20-50μm, and then the wet film is dried, and the wet film is dried by a heating box, the temperature of the heating box is controlled at 75℃, and the drying time is 30min, and then exposure and imaging are performed, that is, exposure is performed twice, exposure once when the dry film is pasted, and exposure of the wet film again after the wet film is dried, and the second exposure only exposes the wet film, and the intermediate PCB board is formed after the second exposure and imaging;

[0042] When the dry film is used to mask the holes, the ring width is ≥0.1mm, and when the wet film is used to mask the holes, the ring width is ≤ the ring width when the dry film is used to mask the holes. Since the wet film has good fluidity, it can effectively fill the pits and protrusions on the surface, thereby improving the coverage on the dry film. The wet film is thinner, so the wet film has excellent performance in image resolution and is suitable for PCB applications with high precision requirements.

[0043] The preliminary processing of primary PCB includes:

[0044] Oxidation: The copper layer is oxidized with brown oxide and black oxide to increase the adhesion between the surface and the solder mask. The oxidation process must be strictly controlled to keep the thickness of the oxide layer at 0.5-1.0 μm. If the oxidized circuit board is stored for too long, the surface must be thoroughly degreased before lamination.

[0045] Dry film lamination includes:

[0046] Dehumidification: Use a high-pressure hair dryer to physically remove water from the surface and holes of the circuit board. You can also bake the circuit board at 120°C for 15 minutes to remove the moisture absorbed by the circuit board, or use an infrared oven equipped with a conveyor belt to bake at 100°C for 30 seconds. Circuit boards with different substrates and circuit boards of different thicknesses require different drying times. Too long baking time and baking temperature should be avoided to avoid increasing the formation of copper oxides and causing poor adhesion.

[0047] Lamination: Cover the dry film on the primary PCB board and make the dry film fit tightly with the PVB board. The width of the dry film should be selected according to the width of the process board. The width of the dry film should not exceed 10mm of the process board to avoid edge trimming loss.

[0048] Wet film masking includes:

[0049] Material preparation: ensure that the required slurry, screen, scraper, cleaning agent, and circuit board are ready;

[0050] Screen printing: Make a screen that matches the hole layout of the circuit board, pour the slurry on the screen, and then use a scraper to evenly scrape the slurry across the screen so that the slurry enters the holes of the circuit board through the openings of the screen and adheres to the dry film. The slurry is in the holes, and its surface is flush with the surface of the circuit board or slightly higher than the opening.

[0051] Exposure imaging includes:

[0052] Exposure: When the dry film lamination is just completed, the required exposure energy is low, which increases rapidly with the growth of the holding time and gradually stabilizes to a constant value. The holding time after lamination should be kept at a constant value to avoid drastic changes in the exposure time. After the wet film is dried, the exposure dose is directly stabilized at 50mJ / cm2, the exposure time is set to 5 seconds, and the photosensitive polymer solder mask works negatively, requiring a positive film for exposure.

[0053] Development: The unexposed solder resist is washed off from the surface of the printed circuit board. The development time of a specific type of photosensitive polymer depends on the chemical substances used. The correct development time is usually determined by controlling the time point when the unexposed resist can be completely washed off from the surface of the printed circuit board. The chemical substances used for development are aqueous solution and developer. In aqueous solution development, diluted sodium carbonate solution is added to 99% pure water, and its use temperature is 45°C. After using this solution, the flushing distance experienced by the printed circuit board during complete development accounts for between 40% and 60% of the length of the developing chamber.

[0054] Step 3: Curing and inspection: Use a curing device with a soft gas lamp to cure the above PCB board. The required heat level is obtained by controlling the density of the soft gas lamp and the speed of the conveyor belt. The curing time of the curing device is 2 minutes, and the curing temperature is 100-130°C. A quality inspection is also performed to check the quality of the dry film masking to ensure that there are no broken hole defects.

[0055] Step 4: Conduct solder mask, surface coating and testing on the masked PCB to form the ultimate complete PCB product;

[0056] The purpose of solder mask is to cover the copper surface that does not need soldering with a layer of solder mask ink to prevent the reaction of tin liquid or solder paste with solder mask ink during DIP and SMT process, thereby avoiding problems such as tin short circuit; solder mask includes:

[0057] Pretreatment: The main function is to clean and roughen the copper surface in order to increase the bonding force between the ink and the copper surface during subsequent processing;

[0058] Ink coverage: The ink is covered on the entire board surface by screen printing or spraying. Since the screen printing ink is liquid (with a certain viscosity), it needs to be pre-baked (pre-dried) before the next process. Since the ink spraying is an online operation, the pre-baking section is connected to the spraying section, so no additional handling is required;

[0059] Curing: Use IR light source to cure the ink that needs to be retained;

[0060] Development: Use sodium carbonate solution to remove the uncured ink and expose the copper surface.

[0061] Surface coating usually refers to the surface treatment process of PCB, that is, the process of coating molten tin-lead solder on the surface of PCB and leveling it with heated compressed air to form a coating layer that is both resistant to copper oxidation and provides good solderability. Hot air leveling forms a copper-tin metal compound between solder and copper at the junction, with a thickness of about 1-2 mils; or on the surface of clean bare copper, a layer of organic film is grown by chemical methods. This film has anti-oxidation, heat shock resistance, and moisture resistance, which is used to protect the copper surface from rusting (oxidation or sulfide, etc.) in a normal environment; at the same time, it must be easily removed by flux in the subsequent high temperature of welding for welding;

[0062] The test includes: Appearance inspection: Check whether there are scratches, stains, uneven ink, etc. on the PCB surface;

[0063] Electrical performance test: Use multimeter, oscilloscope and other instruments to test the electrical performance of the PCB, such as resistance, capacitance, inductance and other parameters to see if they meet the design requirements;

[0064] Functional test: According to the design requirements of the PCB, test each functional module to ensure its normal function;

[0065] Reliability test: Conduct reliability tests under high temperature, low temperature, humidity and other environments to ensure that the PCB can work normally in different environments.

[0066] The above-mentioned PCB products have the characteristics of thick film at the mask hole and thin film at the circuit. Through the double thickening of the dry film and the wet film at the mask hole, the risk of dry film breakage caused by the impact of chemical solution during development and etching can be reduced, thereby reducing the defective production of outer layer circuits and avoiding the problem of inconvenience in the production and processing of outer layer precision circuits caused by multiple films or thick films, facilitating the production and processing of precision circuits and improving the yield of outer layer graphic production.

[0067] Embodiment 2

[0068] According to the attached Figure 1 -4, including the following steps:

[0069] Step 1: Inner layer pattern production: The substrate is cut, the inner layer pattern is browned and then laminated with PP and copper foil, and then drilled and copper plated to form a primary PCB board. Cutting, lamination, drilling and copper plating are all existing mature steps, which can stably produce a primary PCB board with an inner layer pattern.

[0070] Step 2: outer layer pattern production: the above primary PCB is pre-processed, and then dry film lamination is performed. Dry film lamination is to paste dry film, wherein the thickness of dry film is 10-40μm, and then exposure is performed; wet film masking is performed on the dry film mask, and the wet film masking is processed by silk screen printing, wherein the thickness of wet film is 20-50μm, and then the wet film is dried, and the wet film is dried by a heating box, the temperature of the heating box is controlled at 50℃, and the drying time is 30min, and then exposure and imaging are performed, that is, exposure is performed twice, exposure once when the dry film is pasted, and exposure of the wet film again after the wet film is dried, and the second exposure only exposes the wet film, and the intermediate PCB board is formed after the second exposure and imaging;

[0071] When the dry film is used to mask the hole, the ring width is ≥0.1mm, and when the wet film is used to mask the hole, the ring width is ≤ the ring width when the dry film is used to mask the hole, so that the wet film increases the thickness of the dry film where the hole is masked, and reduces the thickening effect of the wet film on other circuits. Moreover, since the wet film has good fluidity, it can effectively fill the pits and protrusions on the surface, thereby improving the coverage on the dry film. The thinner the wet film is, the better the image resolution of the wet film is, and it is suitable for PCB applications with high precision requirements.

[0072] The preliminary processing of primary PCB includes:

[0073] Oxidation: The copper layer is oxidized with brown oxide and black oxide to increase the adhesion between the surface and the solder mask. The oxidation process must be strictly controlled to keep the thickness of the oxide layer at 0.5-1.0 μm. If the oxidized circuit board is stored for too long, the surface must be thoroughly degreased before lamination.

[0074] Dry film lamination includes:

[0075] Dehumidification: Use a high-pressure hair dryer to physically remove water from the surface and holes of the circuit board. You can also bake the circuit board at 100°C for 20 minutes to remove the moisture absorbed by the circuit board, or use an infrared oven equipped with a conveyor belt to bake at 120°C for 30 seconds. Circuit boards with different substrates and circuit boards of different thicknesses require different drying times. Too long baking time and baking temperature should be avoided to avoid increasing the formation of copper oxides and causing poor adhesion.

[0076] Lamination: Cover the dry film on the primary PCB board and make the dry film fit tightly with the PVB board. The width of the dry film should be selected according to the width of the process board. The width of the dry film should not exceed 10mm of the process board to avoid edge trimming loss.

[0077] Wet film masking includes:

[0078] Material preparation: ensure that the required slurry, screen, scraper, cleaning agent, and circuit board are ready;

[0079] Screen printing: Make a screen that matches the hole layout of the circuit board, pour the slurry on the screen, and then use a scraper to evenly scrape the slurry across the screen so that the slurry enters the holes of the circuit board through the openings of the screen and adheres to the dry film. The slurry is in the holes, and its surface is flush with the surface of the circuit board or slightly higher than the opening.

[0080] Exposure imaging includes:

[0081] Exposure: When the dry film lamination is just completed, the required exposure energy is low, which increases rapidly with the growth of the holding time and gradually stabilizes to a constant value. The holding time after lamination should be kept at a constant value to avoid drastic changes in the exposure time. After the wet film is dried, the exposure dose is directly stabilized at 50mJ / cm2, the exposure time is set to 5 seconds, and the photosensitive polymer solder mask works negatively, requiring a positive film for exposure.

[0082] Development: The unexposed solder resist is washed off from the surface of the printed circuit board. The development time of a specific type of photosensitive polymer depends on the chemical substances used. The correct development time is usually determined by controlling the time point when the unexposed resist can be completely washed off from the surface of the printed circuit board. The chemical substances used for development are aqueous solution and developer. In aqueous solution development, diluted sodium carbonate solution is added to 99% pure water, and its use temperature is 45°C. After using this solution, the flushing distance experienced by the printed circuit board during complete development accounts for between 40% and 60% of the length of the developing chamber.

[0083] Step 3: Curing and inspection: Use a curing device with a soft gas lamp to cure the above PCB board. The required heat level is obtained by controlling the density of the soft gas lamp and the speed of the conveyor belt. The curing time of the curing device is 2 minutes and the curing temperature is 120°C. A quality inspection is also performed to check the quality of the dry film mask to ensure that there are no defects such as broken holes and plating.

[0084] Step 4: Perform solder mask, surface coating and testing on the masked PCB to form the ultimate complete PCB product.

[0085] The above-mentioned PCB products have the characteristics of thick film at the mask hole and thin film at the circuit. Through the double thickening of the dry film and the wet film at the mask hole, the risk of dry film breakage caused by the impact of chemicals during development and etching can be reduced, and the problem of inconvenience in manufacturing and processing of outer layer precision circuits caused by multiple films or thick films can be avoided.

[0086] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for making dry film mask holes on the outer layer of a PCB board, characterized in that: The following steps are involved: Step 1: Inner layer pattern production: Cut the substrate, make the inner layer pattern, brown it, laminate it with PP and copper foil, then drill and copper electroplate it to form a primary PCB board; Step 2: outer layer pattern production: the above primary PCB is pre-processed, and then dry film is pressed and exposed; wet film is masked on the dry film mask, and then the wet film is dried and exposed to form an intermediate PCB board; Step 3: Curing and inspection: Use a curing device with a soft gas lamp to cure the above PCB board, control the density of the soft gas lamp and the speed of the conveyor belt to obtain the required heat level, and perform quality inspection; Step 4: Perform solder mask, surface coating and testing on the masked PCB to form the ultimate complete PCB product.

2. The method for making dry film mask holes on the outer layer pattern of a PCB board according to claim 1, characterized in that: The dry film pressing in step 2 is dry film pasting, wherein the dry film thickness is 10-40 μm.

3. The method for making dry film holes on the outer layer of a PCB according to claim 1, characterized in that: In the step 2, the wet film mask is processed by silk screen printing, wherein the thickness of the wet film is 20-50 μm.

4. The method for making dry film mask holes on the outer layer pattern of a PCB board according to claim 1, characterized in that: The preliminary processing of the primary PCB in step 2 includes: Oxidation treatment: The copper layer is controlled oxidized with brown oxide and black oxide. The oxidation process must be strictly controlled to keep the oxide layer thickness at 0.5-1.0 μm.

5. The method for making dry film mask holes on the outer layer pattern of a PCB board according to claim 1, characterized in that: The dry film lamination in step 2 includes: Dehumidification: Use a high-pressure hair dryer to physically remove water from the surface and holes of the circuit board; Lamination: Cover the dry film on the primary PCB board and make the dry film fit tightly with the PVB board.

6. The method for making dry film holes on the outer layer of a PCB according to claim 1, characterized in that: The wet film masking in step 2 includes: Material preparation: ensure that the required slurry, screen, scraper, cleaning agent, and circuit board are ready; Screen printing: Make a screen that matches the hole layout of the circuit board, pour the slurry on the screen, and then use a scraper to evenly scrape the slurry across the screen so that the slurry enters the holes of the circuit board through the openings of the screen and adheres to the dry film. The slurry is in the holes, and its surface is flush with the surface of the circuit board or slightly higher than the opening.

7. The method for making dry film holes on the outer layer of a PCB according to claim 1, characterized in that: In the step 2, the wet film is dried by a heating box, the temperature of the heating box is controlled at 50-75° C., and the drying time is 30 minutes.

8. The method for making dry film mask holes on the outer layer pattern of a PCB board according to claim 1, characterized in that: In the step 2, the ring width when the dry film is used to mask the holes is ≥0.1 mm, and the ring width when the wet film is used to mask the holes is ≤ the ring width when the dry film is used to mask the holes.

9. The method for making dry film mask holes on the outer layer pattern of a PCB board according to claim 1, characterized in that: The exposure and imaging in step 2 includes: Exposure: When the dry film is just pressed, the required exposure energy is low, which increases rapidly with the increase of holding time and gradually stabilizes to a constant value. The holding time after pressing should be kept at a constant value to avoid drastic changes in exposure time. After the wet film is dried, the exposure dose is directly stabilized at 50mJ / cm 2 , the exposure time is set to 5 seconds; Development: The unexposed solder resist is washed off from the surface of the printed circuit board. The chemicals used for development are aqueous solution and developer. In aqueous solution development, a diluted sodium carbonate solution is added to 99% pure water. The operating temperature is 45°C. After using this solution, the flushing distance experienced by the printed circuit board during full development accounts for between 40% and 60% of the length of the developing chamber.

10. The method for making dry film mask holes on the outer layer pattern of a PCB board according to claim 1, characterized in that: The curing time of the curing equipment in step 3 is 2 minutes, and the curing temperature is 100-130°C.

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