Are you using high-temp masking tape during your board processing? Take a look at 3M’s new 2538 and 2538UV High Temperature Masking Liquid. This is an efficient alternative to conventional masking techniques.
The only difference between the two part numbers is the 2538UV allows users to pull off the adhesive under UV lighting (blacklight illumination) making visual inspection easier when removing masking materials.
Take a look at the video: https://www.digikey.com/en/videos/3/3m/3m-hightemp-masking-liquid-2538-and-2538uv