PCB (Printed Circuit Board) coplanar resistance welding method for preventing resistance welding bridge defect

Abstract

The invention discloses a PCB (Printed Circuit Board) coplanar resistance welding method for preventing a resistance welding bridge defect, which relates to the field of PCB processing, and comprises the following steps of: coating resistance welding ink on the surface of a PCB to form an ink layer containing a resistance welding bridge and a bonding pad area; covering a first film to expose a solder bridge region and shield other regions, and curing the ink in the region to form a solder bridge by high-parameter first exposure; covering a second film to expose an area except the solder resist bridge and the bonding pad and shield the solder resist bridge and the bonding pad, and performing second exposure with lower parameters to cure the ink in the area; and finally, uncured ink in the pad area is developed and washed out to leak out of the pad. According to the method, regional differentiation exposure is carried out, sufficient curing of the solder bridge is guaranteed, bridge white and bridge falling defects are avoided, excessive curing of printing ink at the edge of the windowing of the bonding pad is prevented, the windowing size is prevented from being reduced, the welding precision is guaranteed, the reject ratio of the PCB is effectively reduced, and the yield is improved.

Description

Technical Field

[0001] This invention relates to the field of PCB processing technology, and in particular to a PCB same-side solder mask method for preventing solder bridge defects. Background Technology

[0002] In the manufacturing process of high-precision PCBs (printed circuit boards), solder mask bridges and pads are often designed on the same surface. The pads are small solder mask openings. The solder mask bridges separate adjacent pads to prevent short circuits during soldering, while the pads are used for precise soldering to component leads. During the exposure stage of the solder mask process, to prevent solder mask bridges from exhibiting "bridge whitening" (i.e., the bottom of the solder mask bridge is suspended, nearing detachment) and detachment defects, and to ensure the solder mask bridges are firmly cured, the industry typically uses high-energy exposure processes. However, because the pads themselves are relatively small, high exposure energy can easily lead to poor exposure, resulting in a smaller opening size. Specifically, excessively high exposure energy causes the solder mask ink at the edge of the pad opening to be over-exposed and cured, exceeding the designed opening boundary. During the development stage, the developer cannot dissolve this over-cured ink, resulting in the actual opening size of the pad being smaller than the designed size, failing to meet the dimensional requirements for component soldering, and ultimately increasing the defect rate of the PCB product. Summary of the Invention

[0003] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a PCB same-sided solder mask method to prevent solder bridge defects, which is beneficial to improving the yield of PCB products.

[0004] A PCB same-sided solder resist method for preventing solder bridge defects according to an embodiment of the present invention includes ink coating, wherein solder resist ink is coated on the surface of the PCB to form an ink layer, the ink layer having a solder bridge region and a pad region; a first film covering, wherein a first film is placed on the ink layer to expose the ink layer at the solder bridge region and to cover other areas of the ink layer except for the solder bridge region; and a first exposure, wherein the PCB is exposed using a first exposure parameter to cure only the ink layer at the solder bridge region and form solder resist. Bridge; Second film overlay, applying a second film over the ink layer to expose areas of the ink layer other than the solder mask bridge area and the pad area, while masking the ink layer in the solder mask bridge area and the pad area; Second exposure, exposing the PCB with a second exposure parameter lower than the first exposure parameter, so that only areas of the ink layer other than the solder mask bridge area and the pad area are cured; Development, washing away the uncured ink layer in the pad area to expose the pads.

[0005] It has at least the following beneficial effects: When solder mask processing is required on the same surface of a PCB, the process begins with an ink coating step. Solder mask ink is evenly coated onto the PCB surface, forming an ink layer that covers the PCB surface and includes the solder bridge and pad areas. Next, a first film covering step is performed, where a first film is placed over the ink layer on the PCB surface, exposing the solder bridge areas while masking all other areas of the ink layer. Following this, a first exposure step is performed, exposing the PCB to the first exposure parameters. Due to the masking effect of the first film, the exposure light only reaches the ink layer in the solder bridge areas, thus curing only the ink layer in those areas and forming a strong solder bridge. Finally, a second film covering step is performed. In the film exposure step, a second film is placed over the ink layer on the PCB board, exposing areas of the ink layer other than the solder mask bridge and pad areas, while simultaneously shielding the ink layer in the solder mask bridge and pad areas to prevent these areas from being exposed. Next, a second exposure step is performed, using a lower exposure parameter than the first exposure parameter to expose the PCB. With the help of the second film's shielding, the exposure light only acts on areas of the ink layer other than the solder mask bridge and pad areas, curing only the ink layer in these areas. Finally, a development step is performed, which washes away all the uncured solder mask ink in the pad areas, revealing the solder pads on the PCB and completing the entire solder mask processing procedure. By applying film in two stages and using different exposure parameters for regional exposure, the first exposure uses a higher first exposure parameter specifically for the solder mask area. This ensures that the ink layer in the solder mask area is fully cured, effectively preventing whitening and detachment defects. This guarantees the curing strength of the solder mask, thus separating adjacent pads and preventing short circuits. The second exposure uses a lower second exposure parameter for areas other than the solder mask and pads. This ensures the ink layer in these areas is cured, and because the second exposure parameter is lower and the pads are shielded from this exposure, the problem of over-curing of the ink at the pad opening edges due to high exposure energy is avoided. This prevents over-cured ink from being unable to be dissolved by the developer during development, thus preventing the actual opening size of the pads from shrinking. This ensures that the pad opening size meets design requirements, satisfies the need for precise soldering of component leads, and ultimately reduces the defect rate and improves the yield of PCB products.

[0006] According to an embodiment of the present invention, a PCB same-side solder resist method for preventing solder bridge defects includes a first film comprising a first light-transmitting area and a first light-shielding area. The first light-transmitting area is used to expose the ink layer at the solder bridge area, and the first light-shielding area is used to shield other areas of the ink layer except for the solder bridge area.

[0007] According to an embodiment of the present invention, a PCB same-side solder resist method for preventing solder bridge defects includes a second film comprising a second light-transmitting area, a second light-shielding area, and a third light-shielding area. The second light-transmitting area is used to allow the ink layer to pass through areas other than the solder bridge area and the pad area. The second light-shielding area is used to shield the ink layer at the solder bridge area. The third light-shielding area is used to shield the ink layer at the pad area.

[0008] According to an embodiment of the present invention, a PCB same-side solder resist method for preventing solder bridge defects is further provided with a pretreatment before the ink coating, wherein the pretreatment is to remove the oxide layer on the surface of the copper layer on the PCB board.

[0009] According to an embodiment of the present invention, a PCB same-side solder resist method for preventing solder bridge defects includes a pre-baking process between the ink coating and the first film coating. The pre-baking process involves baking the PCB to bring the ink layer to a semi-cured state.

[0010] According to an embodiment of the present invention, a PCB same-side solder resist method for preventing solder bridge defects is further provided after development, wherein the solder resist detection is performed to detect the solder resist condition on the PCB board surface.

[0011] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0012] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein: Figure 1 This is a flowchart illustrating the PCB same-side solder mask method for preventing solder bridge defects according to an embodiment of the present invention. Figure 2 This is a schematic diagram of the first film; Figure 3 This is a schematic diagram of the second film; Icon labels: First film 100; First light-transmitting zone 110; First light-blocking zone 120; Second film 200; Second light-transmitting zone 210; Second light-blocking zone 220; Third light-blocking zone 230. Detailed Implementation

[0013] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, etc., are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0014] In the description of this invention, the use of "first" and "second" is for the purpose of distinguishing technical features only, and should not be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated or the order of the technical features indicated.

[0015] In the description of this invention, unless otherwise explicitly defined, terms such as "set up," "install," and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0016] refer to Figures 1 to 3 This invention discloses a method for preventing solder bridge defects on the same side of a PCB, comprising: ink coating, applying solder resist ink to the surface of the PCB to form an ink layer, the ink layer having solder bridge areas and pad areas; first film coating, applying a first film 100 onto the ink layer to expose the ink layer at the solder bridge areas and masking other areas of the ink layer except for the solder bridge areas; first exposure, exposing the PCB with a first exposure parameter to cure only the ink layer at the solder bridge areas and form solder bridges; second film coating, applying a second film 200 onto the ink layer to expose other areas of the ink layer except for the solder bridge areas and pad areas, and masking the ink layer at the solder bridge areas and pad areas; second exposure, exposing the PCB with a second exposure parameter lower than the first exposure parameter to cure only the ink layer except for the solder bridge areas and pad areas; and development, washing away the uncured ink layer at the pad areas to expose the pads.

[0017] In this embodiment of the invention, the solder mask bridge area and the pad area refer to two specific areas on the same PCB board surface, which are divided by the coated solder mask ink layer. The solder mask bridge area is the area used to form solder mask bridges, which can separate adjacent pads and prevent short circuits during soldering. The pad area is the area corresponding to the pads on the PCB. After the uncured solder mask ink is removed by development, the pads can be exposed to achieve precise soldering with component pins.

[0018] Understandably, when solder mask processing is required on the same surface of a PCB, an ink coating step is performed first. Solder mask ink is evenly coated onto the PCB surface, forming an ink layer covering the PCB surface and including the solder bridge and pad areas. Next, a first film covering step is performed, where a first film 100 is placed over the ink layer on the PCB surface, exposing the solder bridge areas while masking all other areas of the ink layer. Following this, a first exposure step is performed, exposing the PCB to the first exposure parameters. Due to the masking effect of the first film 100, the exposure light only reaches the ink layer in the solder bridge areas, thus curing only the ink layer in those areas and forming a strong solder bridge. Afterwards, the process continues... In the second film coating step, a second film 200 is applied to the ink layer on the PCB board, exposing areas of the ink layer other than the solder mask bridge area and the pad area. Simultaneously, the ink layer in the solder mask bridge area and the pad area is blocked to prevent these areas from being exposed. Next, a second exposure step is performed, using a second exposure parameter lower than the first exposure parameter to expose the PCB. With the help of the second film 200, the exposure light only acts on areas of the ink layer other than the solder mask bridge area and the pad area, curing only the ink layer in these areas. Finally, a development step is performed, which washes away all the uncured solder mask ink in the pad area, revealing the pads on the PCB and completing the entire solder mask processing procedure. By applying film in two stages and using different exposure parameters for regional exposure, the first exposure uses a higher first exposure parameter specifically for the solder mask area. This ensures that the ink layer in the solder mask area is fully cured, effectively preventing whitening and detachment defects. This guarantees the curing strength of the solder mask, thus separating adjacent pads and preventing short circuits. The second exposure uses a lower second exposure parameter for areas other than the solder mask and pads. This ensures the ink layer in these areas is cured, and because the second exposure parameter is lower and the pads are shielded from this exposure, the problem of over-curing of the ink at the pad opening edges due to high exposure energy is avoided. This prevents over-cured ink from being unable to be dissolved by the developer during development, thus preventing the actual opening size of the pads from shrinking. This ensures that the pad opening size meets design requirements, satisfies the need for precise soldering of component leads, and ultimately reduces the defect rate and improves the yield of PCB products.

[0019] refer to Figure 2The first film 100 includes a first light-transmitting area 110 and a first light-shielding area 120. The first light-transmitting area 110 is used to expose the ink layer at the solder resist bridge area, and the first light-shielding area 120 is used to shield other areas of the ink layer except for the solder resist bridge area. It is understood that the first film 100 is used in the first film covering step. The first light-transmitting area 110 is positioned corresponding to the solder resist bridge area on the ink layer, exposing the ink layer at that area so that light during the first exposure can smoothly reach that area, ensuring that the ink layer in the solder resist bridge area can be cured to form a solder resist bridge. The first light-shielding area 120 covers all other areas of the ink layer except for the solder resist bridge area, shielding these areas during the first exposure to prevent them from being exposed to the exposure light and curing prematurely, ensuring that the first exposure only affects the solder resist bridge area.

[0020] refer to Figure 3 The second film 200 includes a second light-transmitting area 210, a second light-shielding area 220, and a third light-shielding area 230. The second light-transmitting area 210 exposes areas of the ink layer other than the solder resist bridge area and the pad area. The second light-shielding area 220 blocks the ink layer in the solder resist bridge area, and the third light-shielding area 230 blocks the ink layer in the pad area. It is understood that the second film 200 is adapted for use in the second film coating step. The second light-transmitting area 210 corresponds to areas of the ink layer other than the solder resist bridge area and the pad area, and is used to expose the ink layer in these areas so that light can reach them and cure them during the second exposure. The second light-shielding area 220 corresponds to the solder resist bridge area on the ink layer and is used to block this area, since the solder resist bridge area has already been cured and formed in the first exposure step using the first exposure parameters. If the area is not shielded during the second exposure, it will be exposed to light again. Although the second exposure uses lower parameters than the first exposure, repeated exposure may still cause the solder mask to over-cur, leading to defects such as embrittlement and cracking. Therefore, the ink layer of the solder mask area needs to be shielded during the second exposure step. The third shielding area 230 corresponds to the pad area on the ink layer and is used to shield this area to prevent the second exposure light from shining on the pad area and causing the ink to cure. This provides a guarantee for the subsequent development step to wash away the uncured ink in this area and expose the pad.

[0021] refer to Figure 1Before ink coating, a pretreatment process is performed to remove the oxide layer from the copper layer surface of the PCB board. This pretreatment step is performed before ink coating and involves treating the copper layer surface of the PCB board to completely remove the oxide layer, ensuring a clean and oxide-free surface. The oxide layer on the copper layer affects the adhesion between the solder resist ink and the copper layer. Removing the oxide layer allows the subsequently applied solder resist ink to adhere more tightly and firmly to the copper layer of the PCB board, preventing defects such as solder resist peeling or lifting during subsequent exposure, development, and processing. It also ensures the strength of the cured solder bridges and the soldering reliability of the pad areas, further improving the yield rate of PCB products.

[0022] refer to Figure 1 A pre-baking process is performed between the ink coating and the first film coating. This pre-baking involves baking the PCB to bring the ink layer to a semi-cured state. Specifically, the pre-baking step is performed between the ink coating and the first film coating steps. The process involves baking the PCB that has been coated with solder resist ink to form an ink layer. The baking intensity is controlled to bring the ink layer to a semi-cured state, meaning the ink layer is partially cured, has a certain degree of adhesion and shaping ability, but is not completely cured. This semi-cured ink layer prevents the first film 100 from adhering to the ink layer during subsequent film coating, which could damage or cause the ink layer to fall off. It also fixes the shape of the ink layer, preventing it from flowing or spreading, ensuring uniform thickness and clear boundary lines. This provides a guarantee for precise positioning of the first film coating and accurate implementation of the first exposure, avoiding the impact of an uncured ink layer on the forming accuracy of the solder resist bridge.

[0023] refer to Figure 1After development, a solder mask inspection is performed to check the solder mask condition on the PCB board. It is understood that the solder mask inspection step is performed after the development step. The specific process involves a comprehensive inspection of the solder mask condition on the developed PCB board, including solder bridge inspection, pad inspection, overall board solder mask inspection, and appearance and dimensional inspection. Solder mask bridge inspection: Checking whether the solder mask bridges are fully formed, without missing material, or broken, with no bubbles or pinholes on the surface, and whether the curing is sufficient, without defects such as whitening, detachment, or embrittlement and cracking. The spacing between adjacent solder mask bridges meets design requirements. Pad inspection: Checking whether uncured ink in the pad area has been completely removed, ensuring the pads are completely exposed without residual ink, and that the pad opening size and shape are consistent with design specifications, without shrinkage or deformation. Overall board surface solder mask inspection: Checking whether the solder mask ink on the PCB board surface, excluding the pad area, is uniformly and completely cured, without defects such as missed coating, incomplete coating, peeling, lifting, or scratches. The ink layer thickness is uniform, with no significant differences in thickness, and the solder mask ink coverage area perfectly matches design requirements. Appearance and dimensional inspection: Checking whether the PCB board surface has no developer residue, stains, or other impurities, and whether the positional accuracy of solder mask-related structures meets the processing requirements of high-precision PCBs. By inspecting the solder mask on the PCB board, various defects that occur during the solder mask processing after development can be detected in a timely manner. This prevents defective PCBs from entering subsequent soldering and assembly processes, effectively reducing problems such as short circuits in components, poor soldering, and shortened PCB lifespan caused by solder mask defects. It also allows for the selection of qualified products, further improving the yield rate of PCB products and ensuring that the PCB products leaving the factory meet design standards and usage requirements.

[0024] In this embodiment of the invention, the pretreatment step uses copper oxide layer removal equipment (such as pickling equipment, plasma cleaning equipment); the ink coating step uses solder resist ink coating equipment (such as screen printing machine, spraying machine); the pre-baking step uses baking equipment (such as constant temperature oven, tunnel oven); the first exposure and second exposure steps use an exposure machine; the developing step uses a developing machine; and the solder resist detection step uses PCB inspection equipment (such as AOI automatic optical inspection instrument, magnifying glass-assisted manual inspection equipment). In this invention, the exposure machine can use a first exposure parameter and a second exposure parameter to expose the PCB respectively; as a preferred embodiment of the invention, the solder resist ink is Rongda green ink H9100-GH40, the first exposure parameter is 300mJ / cm², and the second exposure parameter is 200mJ / cm².

[0025] The PCB same-side solder mask method for preventing solder bridge defects according to the present invention is roughly as follows: The pretreatment step involves using a copper oxide layer removal device to treat the PCB board, thoroughly removing the oxide layer on the copper surface of the PCB board to ensure that the copper surface is clean and free of oxide residue. In the ink coating step, solder resist ink is uniformly coated onto the PCB surface using solder resist ink coating equipment to form an ink layer; The pre-baking step involves placing the PCB with the ink layer into a baking equipment for baking treatment, and controlling the baking parameters to keep the ink layer in a semi-cured state. In the first film covering step, the first film 100 is covered on the ink layer, so that the first light-transmitting area 110 of the first film 100 exposes the ink layer at the solder bridge area, and the first light-blocking area 120 blocks other areas of the ink layer except for the solder bridge area. In the first exposure step, an exposure machine is used and the first exposure parameters are set to expose the PCB. With the help of the light-shielding and light-transmitting effects of the first film 100, the ink layer in the solder mask area is cured and forms a solder mask bridge. In the second film covering step, the second film 200 is covered on the ink layer, so that the second light-transmitting area 210 of the second film 200 exposes the other areas of the ink layer except for the solder mask area and the pad area, the second light-shielding area 220 blocks the ink layer in the solder mask area, and the third light-shielding area 230 blocks the ink layer in the pad area. In the second exposure step, the same exposure machine is used and the second exposure parameters are set to be lower than those of the first exposure parameters to expose the PCB. With the help of the light-shielding and light-transmitting effects of the second film 200, only the areas of the ink layer other than the solder bridge area and the pad area are cured. The developing step involves placing the PCB into a developing machine for developing. The developing solution thoroughly removes the uncured ink layer in the pad area, allowing the pads to be exposed. The solder mask inspection step involves using PCB inspection equipment to comprehensively inspect the solder mask condition on the PCB board surface. This includes detailed inspection of solder mask bridges, pads, overall board surface solder mask, and external dimensions, etc., to screen out qualified products and complete the entire PCB same-side solder mask processing process.

[0026] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0027] Of course, the present invention is not limited to the above-described embodiments. Those skilled in the art can make equivalent modifications or substitutions without departing from the spirit of the present invention. All such equivalent modifications or substitutions are included within the scope defined by the claims of this application.

Claims

1. A method for preventing solder bridge defects on the same side of a PCB using solder mask, characterized in that, include: Ink coating: Solder resist ink is coated on the surface of the PCB to form an ink layer, the ink layer having solder bridge areas and pad areas; First film covering: The first film (100) is placed on the ink layer to expose the ink layer at the solder bridge area and to cover other areas of the ink layer except for the solder bridge area. In the first exposure, the PCB is exposed using the first exposure parameters, so that only the ink layer in the solder mask area is cured and forms a solder mask bridge. A second film is applied, and a second film (200) is applied to the ink layer to expose the ink layer except for the solder bridge area and the pad area, while covering the ink layer at the solder bridge area and the pad area. The second exposure uses a second exposure parameter to expose the PCB. The second exposure parameter is lower than the first exposure parameter, so that only the areas of the ink layer other than the solder bridge area and the pad area are cured. The developing process removes the uncured ink layer in the pad area to expose the pad.

2. The PCB same-side solder mask method for preventing solder bridge defects according to claim 1, characterized in that: The first film (100) includes a first light-transmitting area (110) and a first light-shielding area (120). The first light-transmitting area (110) is used to expose the ink layer at the solder bridge area, and the first light-shielding area (120) is used to shield the ink layer from other areas except the solder bridge area.

3. The PCB same-side solder mask method for preventing solder bridge defects according to claim 1, characterized in that: The second film (200) includes a second light-transmitting area (210), a second light-shielding area (220), and a third light-shielding area (230). The second light-transmitting area (210) is used to expose areas of the ink layer other than the solder mask area and the pad area. The second light-shielding area (220) is used to shield the ink layer at the solder mask area. The third light-shielding area (230) is used to shield the ink layer at the pad area.

4. The PCB same-side solder mask method for preventing solder bridge defects according to claim 1, characterized in that: A pretreatment is performed before the ink coating, which involves removing the oxide layer on the copper layer surface of the PCB board.

5. The PCB same-side solder mask method for preventing solder bridge defects according to claim 1, characterized in that: A pre-baking process is also provided between the ink coating and the first film coating. The pre-baking is to bake the PCB to make the ink layer in a semi-cured state.

6. The PCB same-side solder mask method for preventing solder bridge defects according to claim 1, characterized in that: After development, a solder resist detection is performed, which involves detecting the solder resist condition on the PCB board surface.

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