In the production of circuit board solder resist, there is often the phenomenon of solder resist hole, causing unnecessary rework, time-consuming and laborious, then what causes the solder resist hole and what preventive measures are there, the following editor will explain in detail One said.
Five reasons for solder mask entry holes
1. During solder mask printing, the process uses air-screen printing, which leads to solder mask holes. During development, there are many solder mask holes and smaller apertures, so they are not developed during development.
2. When pre-baking the board after printing the solder mask, the pre-baking time is too long and the temperature is too high, which will cause the solder mask in the hole to be over-cured, resulting in poor development during development.
3. During development, the development parameters were set improperly and the concentration of the chemical solution was too low, which caused the solder mask in the hole to not be cleaned.
4. When the inspector was inspecting, due to improper inspection method, the board with solder resist hole was not inspected and flowed to the client.
5. The inspector is not clear about the standard of solder mask into the via, which causes the problem board to leak to the customer .
Preventive measures for solder mask entry holes
1. For plug-in holes with small apertures, the project will make stop point film, and use stop point nets for solder mask printing in the solder mask process. Make sure that the solder mask does not enter the hole or enters very little ink during printing to avoid unclean development.
2. Before pre-baking, the staff will set the oven parameters according to the requirements of different solder mask colors for the pre-baking time and temperature, and the equipment department and solder mask process will determine the temperature uniformity and temperature difference of the pre-baking oven every week. Measure to check whether the temperature difference is within the control range.
3. Before developing, it is required to confirm the various parameters of the developing machine (including: developing temperature, developing pressure, developing speed) and the concentration analysis of the developer by the chemical laboratory on the day to ensure that the parameters and the concentration of the developer are in the controlled range. Carry out development production.
4. The supervisor of the final inspection will train the inspectors on the inspection method. For the inspection method of the hole, during the inspection, stack two or three boards together and look at the light at a 50-degree angle to confirm the inside of the hole. Is there a solder mask?
5. The final inspection supervisor regularly trains employees on product acceptance standards and conducts examinations to ensure that employees are clear about the acceptance standards for each defect.