1. The main reason for bubbles occurring between two or more lines is primarily attributed to the narrow line spacing and high lines. During screen printing, the solder mask fails to adhere properly to the substrate, resulting in the entrapment of air or moisture between the solder mask and the substrate. Subsequently, during curing and exposure, the trapped gas expands due to heating, causing the lines to elevate excessively. This excessive elevation of the lines leads to an increased angle between the squeegee and the lines, hindering the proper printing of solder resist onto the root of the lines. Consequently, gas accumulates between the side of the line root and the solder mask, resulting in the formation of bubbles after heating.
Solution: To address this issue, it is imperative to visually inspect the screen printing process to ensure complete coverage of the screen printing material on both the substrate and the sidewalls of the lines. Additionally, strict control over the current during electroplating is essential.
2. The primary cause of issues with FPC (Flexible Printed Circuit) boards lies in the delay of paper printing during the screen printing process. This delay leads to an accumulation of excessive residual ink on the screen, which, under the pressure of the squeegee, is transferred into the holes, thereby causing irregularities in the solder mask. Furthermore, inadequate cleanliness of the photographic plate results in areas of the FPC board intended for exposure during the exposure process not receiving sufficient light, consequently resulting in the formation of pinholes in the pattern.
Solution: To mitigate these issues, it is recommended to adhere to a timely paper printing schedule and opt for high-mesh screens for plate making. Regular inspection of the cleanliness of the photographic plate during exposure is also crucial.
3. Inadequate drying of the FPC flexible circuit board after wiping, coupled with splashing of liquid or manual handling before the solder mask printing process, leads to surface contamination.
Solution: Visual inspection of both sides of the printed board for copper foil oxidation during screen printing is advised.
4. Surface contamination, attributed to airborne debris such as flying feathers, and neglecting to timely print paper during screen printing, leading to residual ink accumulation on the screen, result in an uneven surface.
Solution: Maintaining cleanliness in the cleanroom environment, restricting the entry of non-essential personnel, regular cleanroom maintenance, and diligent removal of residual ink using paper during screen printing are recommended measures to address this issue.
5. Ghosting occurs due to inadequate positioning of the FPC flexible circuit board during screen printing and the failure to promptly remove residual ink from the screen plate, leading to its accumulation on the printed circuit board. This accumulation results in the presence of regular ink dots adjacent to the entire FPC pad. Additionally, cracks may appear on the board surface due to insufficient exposure during the FPC exposure process.
Solution: Ensuring firm fixation of the paper with positioning pins and timely removal of residual ink from the screen are essential. Furthermore, precise measurement of exposure parameters, such as the energy of the exposure lamp and exposure time, within the range of 9-11 exposure levels, helps prevent the occurrence of cracks.
Solution: To address this issue, it is imperative to visually inspect the screen printing process to ensure complete coverage of the screen printing material on both the substrate and the sidewalls of the lines. Additionally, strict control over the current during electroplating is essential.
2. The primary cause of issues with FPC (Flexible Printed Circuit) boards lies in the delay of paper printing during the screen printing process. This delay leads to an accumulation of excessive residual ink on the screen, which, under the pressure of the squeegee, is transferred into the holes, thereby causing irregularities in the solder mask. Furthermore, inadequate cleanliness of the photographic plate results in areas of the FPC board intended for exposure during the exposure process not receiving sufficient light, consequently resulting in the formation of pinholes in the pattern.
Solution: To mitigate these issues, it is recommended to adhere to a timely paper printing schedule and opt for high-mesh screens for plate making. Regular inspection of the cleanliness of the photographic plate during exposure is also crucial.
3. Inadequate drying of the FPC flexible circuit board after wiping, coupled with splashing of liquid or manual handling before the solder mask printing process, leads to surface contamination.
Solution: Visual inspection of both sides of the printed board for copper foil oxidation during screen printing is advised.
4. Surface contamination, attributed to airborne debris such as flying feathers, and neglecting to timely print paper during screen printing, leading to residual ink accumulation on the screen, result in an uneven surface.
Solution: Maintaining cleanliness in the cleanroom environment, restricting the entry of non-essential personnel, regular cleanroom maintenance, and diligent removal of residual ink using paper during screen printing are recommended measures to address this issue.
5. Ghosting occurs due to inadequate positioning of the FPC flexible circuit board during screen printing and the failure to promptly remove residual ink from the screen plate, leading to its accumulation on the printed circuit board. This accumulation results in the presence of regular ink dots adjacent to the entire FPC pad. Additionally, cracks may appear on the board surface due to insufficient exposure during the FPC exposure process.
Solution: Ensuring firm fixation of the paper with positioning pins and timely removal of residual ink from the screen are essential. Furthermore, precise measurement of exposure parameters, such as the energy of the exposure lamp and exposure time, within the range of 9-11 exposure levels, helps prevent the occurrence of cracks.
