Conformal coating challenges: Detection, rework and failure analysis

Conformal coating application is essential to enhance the lifetime and reliability of electronics made to operate in harsh environments. These polymer based coatings provide a barrier to air-borne contaminants from the operating environment thus preventing attack from moisture, aggressive chemicals, salt sprays, etc. While conformal coatings are mostly used on printed circuit boards (PCBs), they could also be used to protect discrete components mounted on PCBs such as packages, capacitors, passive components, etc. This in turn presents risk when the coating needs to be removed for component rework without deteriorating component functionality. The removal of conformal coating is very important when there is any process or product related issues that requires failure analysis (FA). The main factors to be considered when choosing the coating removal technique are simple and safe technique, low cost process and zero damage to the products. Therefore understanding coating chemistry dictates the removal strategy. This paper addresses the challenges of conformal coating removal and describes the design of experiments (DOE) for conformal coating removal in order to enable rework/FA. Special cases where conventional detection of the conformal coating fails are also addressed.