This vendor from China was in the process of qualification. There are solder dross and conductive flux underneath the conformal coating. Solder dross is highly conductive and flux will activate as an ionic conductor across leads, pads, terminals, etc.
Conformal coatings inhibit the crosstalk and ionic migration across the PCB surface. If, however, these contaminants reside on the board surface, the conformal coating cannot make contact with the solder mask and does not bond properly. This lack of bonding creates a void like space at the interface of the conformal coating and the board surface. This space is where electromigration can occur. This PCB failed many of the IPC-A-610 criteria in addition to many of the test methods used to evaluate ionic contamination.
Gideon can inspect printed circuit boards for potential problems. We can cross-section to demonstrate how well the fillets are formed, show cracks, or voids. We can x-ray to show the internal structure, voiding, delamination, and components mounted to the PCB. We also perform quality checks on a regular basis. Improve your yields and confidence in your assembly house by using Gideon Analytical Laboratories as the quality control house.