Printed Wiring Assemblies (PWAs)
Fiber contamination in comformal coating

When this board was conformally coated a fiber was trapped in the coating creating a possible short potential.

Reference :
NASA-STD-8739.1
11.8 Acceptance/Rejection Criteria for Conformal Coating
3. Rejection Criteria. The following are some characteristics of unsatisfactory conditions, any of which is cause for rejection: f. Any signs of contamination (e.g., flux, loose particles, or foreign material)