Last week, we discussed what the causes of bubbles in conformal coating are. Now, let’s go through the various ways to remedy the bubbles.
- When applying the conformal coating ensure the wet film surface is not too thick. This is particularly important when spray coating. It is better to apply multiple thin layers than one thick layer. Also, check curing in case elevated temperature is causing the coating to bubble.
- Bubbles becoming entrapped in the coating before they dissipate because too thick a layer is applied can be prevented by applying thinner individual layers and allowing a flash off time between coats.
- To avoid air entrapment under PCB components try:
- Dipping slower into the conformal coating dip tank
- Adding a dwell time to allow penetration of the coating
- Using a lower viscosity version of the conformal coating to under fill the area more effectively
- When using pressure pots with conformal coating inside try to avoid leaving the pots pressurized for long periods of time when not being used or avoid running the pressure pots more than 50% full and letting them stand. This will minimize the champagne effect in the coating.
- When brush coating try to blend the coating so it flows easily and “flow” the material onto the PCB. Do not work the coating into the PCB as it creates bubbles.