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Acceptability of Conformal Coating Bubbles

Question: We have some PCB cards that are flooded with champagne size encapsulated bubbles. While no single bubble bridges between conductors there are numerous small bubbles similar to Figure 10-131 below, None have popped, as they are all encapsulated. Is Figure 10-131 a Defect Photo? Other than stripping and re-coating , if bubbles are encapsulated would they be considered an acceptable Process Indicator or a Defect?

conformal coating bubbles
*Image (excerpt) Courtesy of IPC-A-610 Standard

Answer: The IPC-A-610 pictures are just there to provide some visual information on the condition being described, in this case the coverage from conformal coating application.

The important issue here is the text and based upon your description and question I would lean towards the condition being a Process Indicator for class 1, 2, and 3.

Please keep in mind that conformal coating is not impervious to the absorption of moisture, so moisture can still impact your product and if the moisture does get into those bubble and the conformal coating cracks or crazes, then you could have a failure, which is why the spanning of conductors is not allowed.