Conformal Coating Challenges: Detection, Rework and Failure Analysis

摘要

To enable rework and FA, various techniques to remove conformal coating were evaluated. Chemical methodologies were found time-consuming and raise health concerns due to certain hazardous stripping agents. The thermal method is quick and simple for conformal coating removal, but the temperature applied must be precise to avoid damage to the product or component. Successful removal of conformal coating using relatively low temperature has been demonstrated. A mechanical method of microabrasion was found best to remove thick coatings (several microns), provided the abrasive material was carefully selected. The removal process was demonstrated on a control board and unit under test where devices maintained functionality. The demonstration of rework on a QFN component was also shown by micro-abrasion. In a specific FA case where issues related to thin conformal coating detection were encountered, new detection techniques were proposed.