PCB solder mask method for preventing solder mask ghosting

Abstract

The embodiment of the application provides a PCB solder mask method for preventing solder mask ghosting, which comprises the following steps: printing a layer of water film on a ghosting area on a PCB; coating solder mask ink on the whole PCB after the PCB is baked; exposing the PCB; and developing the PCB to remove the un-solidified solder mask ink and water film on the ghosting area. In the process of soldering the PCB, a layer of water film is printed on the ghosting area on the PCB before exposure, and then the solder mask ink is coated, so that the water film becomes a temporary physical shielding layer in the subsequent exposure process of the PCB, the solder mask ink on the ghosting area is prevented from being cured by light transmission in the exposure process, and the un-solidified solder mask ink and the water film with hydrophilicity on the ghosting area can be removed by a developing solution in the subsequent developing stage. Therefore, the ghosting in the window area of the PCB can be effectively avoided, and the process flow is simplified.

Description

Technical Field

[0001] This application relates to, but is not limited to, the field of circuit board manufacturing technology, and in particular to a PCB solder mask method for preventing solder mask ghosting. Background Technology

[0002] In PCB boards, the "windowed area" refers to the area intentionally left uncovered on the solder mask layer (usually green ink, or "green solder mask") to expose the underlying pads or traces for subsequent component soldering, testing, and other operations. During PCB exposure, ultraviolet light can penetrate the solder mask and substrate to expose the ink in the windowed area on the reverse side. This causes the green solder mask in the windowed area, which doesn't need to cure, to partially cure as well. The reverse windowed area is where ghosting occurs, leading to PCB board scrap due to quality issues. Based on this, the existing methods for preventing PCB solder mask ghosting are as follows: (1) Reduce the energy of the PCB board's cover oil layer alignment exposure. However, this method can only improve ghosting and cannot avoid the occurrence of ghosting. In addition, due to insufficient photocuring, it will also cause quality problems such as solder mask bridging and oil loss in other areas of the circuit board, increasing the probability of PCB board scrapping. (2) Set the oil blocking area on the same side of the PCB board to be larger than the opening side of the ghosting area. This method makes the ink outside the oil blocking area after printing, near the edge of the ghosting area, fluid and will seep into the opening position of the ghosting area. After exposure, a small amount of ink residue will appear, forming ghosting. (3) Make a first light blocking area on the core board corresponding to the ghosting area or make a second light blocking area on the PP layer corresponding to the ghosting area. When one side is exposed, the ultraviolet light will be blocked by the first light blocking area or the second light blocking area, and the photosensitive ink on the other side that does not need to be cured will also be cured, so as to effectively avoid the occurrence of ghosting in the opening area. However, the process of this method is complicated. Summary of the Invention

[0003] This application provides a PCB solder mask method to prevent ghosting, which can effectively avoid the formation of ghosting in the window area of ​​the PCB board while simplifying the process.

[0004] In a first aspect, embodiments of this application provide a PCB solder mask method for preventing solder mask ghosting, including: Print a layer of water film in the area where ghosting occurs on the PCB board; After coating the entire PCB board with solder resist ink, the PCB board is baked. The PCB board is exposed; The PCB board is developed to remove uncured solder resist ink and water film from the areas where ghosting occurs.

[0005] In some embodiments, a layer of water-based film is printed on the ghosting area on the PCB board, including: Print the water-film image in the area where the ghost appears; The water film in the area where the ghost image appears is baked.

[0006] In some embodiments, after coating the entire PCB board with solder resist ink, baking the PCB board includes: A layer of the solder resist ink is printed on the PCB board. The PCB board is baked.

[0007] In some embodiments, after coating the entire PCB board with solder resist ink, baking the PCB board includes: The solder resist ink is applied by air pressure spraying or electrostatic spraying on the PCB board. The PCB board is baked.

[0008] In some embodiments, a layer of water-based film is printed on the ghosting area of ​​the PCB board, including: Use a 36T or 39T dot screen printing plate to screen print the water film in the area where the ghost image appears.

[0009] In some embodiments, a layer of water-based film is printed on the ghosting area of ​​the PCB board, including: Using a 77T dot screen printing plate, the water film is silkscreened onto the area where the ghost image appears.

[0010] In some embodiments, baking the PCB board includes: The PCB board is baked at 75°C for 40 to 45 minutes.

[0011] In some embodiments, baking the water film on the area where the ghosting occurs includes: The PCB board is baked at 75°C for 5 to 10 minutes.

[0012] This application provides a method for preventing ghosting on a PCB. The method includes: printing a layer of water-based film on the ghosting area of ​​the PCB; coating the entire PCB with solder resist ink and then baking the PCB; exposing the PCB; and developing the PCB to remove the uncured solder resist ink and water-based film on the ghosting area. According to the solution provided in this application, during the solder resist process on the PCB, before exposure, a layer of water-based film is printed on the ghosting area of ​​the PCB before coating with solder resist ink. This allows the water-based film to act as a temporary physical shielding layer during subsequent exposure, preventing the solder resist ink on the water-based film (i.e., the solder resist ink on the ghosting area) from curing during exposure. In the subsequent developing stage, the uncured solder resist ink and the hydrophilic water-based film on the ghosting area can be removed by the developing solution. This effectively prevents ghosting in the windowed area of ​​the PCB while simplifying the process. Attached Figure Description

[0013] Figure 1 This is a flowchart of the steps of a PCB solder mask method for preventing solder mask ghosting provided in one embodiment of this application; Figure 2 This is a schematic diagram of a PCB board before development, provided in one embodiment of this application; Figure 3 This is a schematic diagram of a developed PCB board according to one embodiment of this application. Detailed Implementation

[0014] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0015] It is understandable that although functional modules are divided in the device schematic diagram and a logical order is shown in the flowchart, in some cases, the steps shown or described may be performed in a different order than the module division in the device or the order in the flowchart. The terms "first," "second," etc., in the specification, claims, or the aforementioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0016] In PCB boards, the "windowed area" refers to the area intentionally left uncovered on the solder mask layer (usually green ink, or "green solder mask") to expose the underlying pads or traces for subsequent component soldering, testing, and other operations. During PCB exposure, ultraviolet light can penetrate the solder mask and substrate to expose the ink in the windowed area on the reverse side. This causes the green solder mask in the windowed area, which doesn't need to cure, to partially cure as well. The reverse windowed area is where ghosting occurs, leading to PCB board scrap due to quality issues. Based on this, the existing methods for preventing PCB solder mask ghosting are as follows: (1) Reduce the energy of the PCB board's cover oil layer alignment exposure. However, this method can only improve ghosting and cannot avoid the occurrence of ghosting. In addition, due to insufficient photocuring, it will also cause quality problems such as solder mask bridging and oil loss in other areas of the circuit board, increasing the probability of PCB board scrapping. (2) Set the oil-blocking area on the same side of the PCB board to be larger than the opening side of the ghosting area. This method makes the ink outside the oil-blocking area after printing, near the edge of the ghosting area, fluid and will seep into the opening position of the ghosting area. After exposure, a small amount of ink residue will appear, forming ghosting. (3) Make a first light-blocking area on the core board corresponding to the ghosting area or make a second light-blocking area on the PP layer corresponding to the ghosting area. When one side is exposed, the ultraviolet light will be blocked by the first light-blocking area or the second light-blocking area, and the photosensitive ink on the other side that does not need to be cured will also be cured, so as to effectively avoid the occurrence of ghosting in the opening area. However, the process of this method is complicated.

[0017] To address the aforementioned problems, this application provides a PCB solder mask method to prevent ghosting. The method includes: printing a layer of water-based film on the ghosting area of ​​the PCB; coating the entire PCB with solder mask ink and then baking the PCB; exposing the PCB; and developing the PCB to remove the uncured solder mask ink and water-based film on the ghosting area. According to the solution provided in this application, during the solder masking process on the PCB, before exposure, a layer of water-based film is printed on the ghosting area of ​​the PCB before coating with solder mask ink. This allows the water-based film to act as a temporary physical shielding layer during subsequent exposure, preventing the solder mask ink on top of the water-based film (i.e., the solder mask ink on the ghosting area) from curing during exposure. In the subsequent developing stage, the uncured solder mask ink and the hydrophilic water-based film on the ghosting area can be removed by the developing solution. This effectively prevents ghosting in the windowed areas of the PCB while simplifying the process.

[0018] The embodiments of this application will be further described below with reference to the accompanying drawings.

[0019] refer to Figures 1 to 3 , Figure 1This is a flowchart illustrating the steps of a PCB solder mask method for preventing solder mask ghosting according to an embodiment of this application. Figure 2 This is a schematic diagram of a PCB board before development, provided in one embodiment of this application; Figure 3 This is a schematic diagram of a PCB board after development, provided in one embodiment of this application. This application provides a method for preventing solder mask ghosting on a PCB, which includes, but is not limited to, the following steps: Step S10: Print a layer of water film on the area where the ghosting appears on the PCB board; Step S20: After coating the entire PCB board with solder resist ink, bake the PCB board. Step S30: Expose the PCB board; Step S40: Develop the PCB board to remove uncured solder mask ink and water film from the areas where ghosting occurs.

[0020] It is understandable that during the solder mask application process on a PCB board, before exposure, a layer of water-based film is printed on the area where ghosting occurs on the PCB board, and then solder mask ink (such as...) is applied. Figure 2 As shown in the diagram, the water-film acts as a temporary physical shielding layer during the subsequent exposure of the PCB board, preventing the solder resist ink on top of the water-film (i.e., the solder resist ink in the ghosting areas) from curing during exposure. In the subsequent development stage, the uncured solder resist ink and the hydrophilic water-film in the ghosting areas can be removed by the developing solution. The developed PCB board appears as shown in the diagram. Figure 3 As shown. In this way, ghosting can be effectively avoided in the window area of ​​the PCB board, while simplifying the process.

[0021] Specifically, in some embodiments, Figure 1 Step S10 includes, but is not limited to, the following steps: Step S11: Print the water film on the area where the ghost appears; Step S12: Bake the PCB board.

[0022] It is understood that, in this embodiment, the method of printing water film in the ghosting area specifically includes two types: one is to screen print the water film in the ghosting area and then bake the PCB board to bake the water film on the PCB board; the other is to screen print the water film in the ghosting area without baking the board.

[0023] Specifically, referring to the description of the above embodiments, when the method of printing water-based film in the ghosting area involves silkscreening the water-based film onto the ghosting area and then baking the PCB board, step S20 includes, but is not limited to, the following steps: Step S21: Print a layer of solder resist ink on the PCB board. Step S22: Bake the PCB board.

[0024] Specifically, referring to the description of the above embodiments, the method of printing water film in the ghosting area is to screen print the water film on the ghosting area, and without baking the plate, step S20 includes, but is not limited to, the following steps: Step S23: Apply solder resist ink to the PCB board by air pressure spraying or electrostatic spraying. Step S24: Bake the PCB board.

[0025] That is to say, there are two schemes for sequentially printing water film and coating solder resist ink on the PCB board in this embodiment: Scheme (1): After screen printing the water film on the ghosting area, bake the water film on the PCB board to cure the water film; then screen print a layer of solder resist ink on the whole board, so that a layer of solder resist ink is covered on the water film that has been cured in the ghosting area; then bake the PCB board again to semi-cur the solder resist ink, which is convenient for subsequent exposure processing; Scheme (2): After screen printing the water film on the ghosting area, do not bake the board, spray the solder resist ink on the whole board with air pressure or electrostatic spraying, so that the solder resist ink is sprayed on the water film that has not been cured in the ghosting area, and then bake the board again.

[0026] It should be noted that this embodiment does not limit the screen printing parameters of the water film. The mesh count of the screen corresponding to scheme (2) in this embodiment is greater than that of scheme (1). For example, scheme (1) uses a 36T or 39T screen to screen the water film in the ghosting area, while scheme (2) uses a 77T screen to screen the water film in the ghosting area. It can be understood that the larger the mesh count of the screen, the thinner the screen-printed water film and the slower it flows; the smaller the mesh count of the screen, the thicker the screen-printed water film and the faster it flows.

[0027] It is understandable that the water-based film that has just been screen-printed is in a wet film state, containing moisture or solvents and having fluidity. For scheme (1), baking the ghosting area of ​​the printed water-based film can quickly evaporate the solvent, allowing the water-based film to initially form a film and lose its fluidity. At this time, screen printing a layer of solder resist ink can effectively prevent the solder resist ink and the fluid water-based film from mixing and failing to achieve their respective functions, thus providing an effective guarantee to prevent the ghosting area from forming ghosts after subsequent exposure. For scheme (2), after screen printing the water-based film on the ghosting area, no baking is performed. Referring to the description of the above embodiment, the thickness of the water-based film layer here is relatively thin and the fluidity is relatively small. At this time, the solder resist ink is sprayed evenly on the uncured, less fluid water-based film in the ghosting area by air pressure spraying or electrostatic spraying before the water-based film flows. Only one baking operation is required afterward. The operation process of scheme (2) is more simplified than that of scheme (1), which can effectively improve the solder resist efficiency of the PCB board.

[0028] It should be noted that this embodiment does not limit the specific method of baking the PCB board. In this embodiment, the first baking operation in scheme (1) is to bake the PCB board at 75°C for 5 to 10 minutes to achieve pre-curing of the water film; while the second baking operation in scheme (1) and the baking operation in scheme (2) is to bake at 75°C for 40 to 45 minutes.

[0029] Understandably, after sequentially printing water-based films on the PCB board, the PCB board is baked at 75°C for 5 to 10 minutes. 75°C is sufficient to evaporate moisture, allowing the water-based films to form a film that adheres to the ghosting areas of the PCB board, creating a physical masking layer for the solder resist ink layer during exposure, while also maintaining the water solubility of the water-based film layer. Thus, after development in step S40, the developing solution can remove the uncured solder resist ink and water-based films on the ghosting areas, exposing the ghosting areas (i.e., the open windows).

[0030] In summary, in this embodiment, during the solder mask application process on the PCB board, before exposure, a layer of water-based film is printed on the area where ghosting occurs on the PCB board, and then solder mask ink (such as...) is applied. Figure 2 As shown), this allows the water-film to act as a temporary physical shielding layer during the subsequent exposure of the PCB board, preventing the solder resist ink on top of the water-film (i.e., the solder resist ink in the ghosting areas) from curing during exposure. In the subsequent development stage, the uncured solder resist ink and the hydrophilic water-film in the ghosting areas can be removed in one step by the developing solution. The developed PCB board looks like... Figure 3As shown. Thus, compared to existing methods where the ink-blocking area on one side of the PCB board is larger than the ghosting area on a single side, this method allows the ink outside the ink-blocking area near the edge of the ghosting area to flow after printing, allowing it to seep into the window position of the ghosting area. This results in a small amount of ink residue after exposure, forming a ghosting effect. Alternatively, a first light-blocking area can be created on the core board corresponding to the ghosting area, or a second light-blocking area can be created on the PP layer corresponding to the ghosting area. This ensures that when one side is exposed, the ultraviolet light is blocked by the first or second light-blocking area, preventing the photosensitive ink on the other side from curing. This effectively avoids ghosting in the window area, simplifies the process, and reduces the time cost of the PCB board.

Claims

1. A PCB solder mask method for preventing solder mask ghosting, characterized in that, include: Print a layer of water film in the area where ghosting occurs on the PCB board; After coating the entire PCB board with solder resist ink, the PCB board is baked. The PCB board is exposed; wherein the water film is used as a temporary physical shielding layer to prevent the solder resist ink on the ghosting area from being cured by light during the exposure process; The PCB board is developed to remove uncured solder resist ink and water film from the areas where ghosting occurs.

2. The PCB solder mask method for preventing solder mask ghosting according to claim 1, characterized in that, A layer of water-based film is printed on the area where ghosting occurs on the PCB board, including: The water-film screen is printed in the area where the ghost image appears; The water film in the area where the ghost image appears is baked.

3. The PCB solder mask method for preventing solder mask ghosting according to claim 2, characterized in that, After coating the entire PCB board with solder resist ink, the PCB board is then baked, including: A layer of the solder resist ink is printed on the PCB board. The PCB board is baked.

4. The PCB solder mask method for preventing solder mask ghosting according to claim 1, characterized in that, After coating the entire PCB board with solder resist ink, the PCB board is then baked, including: The solder resist ink is applied by air pressure spraying or electrostatic spraying on the PCB board. The PCB board is baked.

5. The PCB solder mask method for preventing solder mask ghosting according to claim 3, characterized in that, A layer of water film is printed on the area where ghosting occurs on the PCB board, including: Use a 36T or 39T dot screen printing plate to screen print the water film in the area where the ghost image appears.

6. The PCB solder mask method for preventing solder mask ghosting according to claim 4, characterized in that, A layer of water film is printed on the area where ghosting occurs on the PCB board, including: Using a 77T dot screen printing plate, the water film is silkscreened onto the area where the ghost image appears.

7. The PCB solder mask method for preventing solder mask ghosting according to claim 1, characterized in that, The process of baking the PCB board includes: The PCB board is baked at 75°C for 40 to 45 minutes.

8. The PCB solder mask method for preventing solder mask ghosting according to claim 2, characterized in that, Baking the water film in the area where the ghosting occurs includes: The PCB board is baked at 75°C for 5 to 10 minutes.

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