Protecting electronic components at harsh environments and applications often requires the use of conformal coatings, underfills or potting compounds. The temperature dependent properties of these materials greatly depend on their chemical formulation. Conformal coatings used for electronic applications are available in a variety of materials ranging from silicones, acrylics, polyurethanes, paralyne and epoxies. The glass transition temperature (Tg) varies for each material and represents a phase change from a hard glassy one to a soft rubbery state. Temperature fluctuations experienced by electronics can span a wide range that can often include the Tg of the encapsulant.
In this paper, thermal cycling simulations are performed on QFN and BGA components using different conformal coating materials. Material characterization is performed to determine the temperature dependent properties of several conformal coating materials. Results illustrate higher damage accumulation during ramp down and cold side of thermal cycles. Information obtained in this study is used to develop a mitigation strategy that enables selection of encapsulants without compromising desired system level encapsulation method to increase overall board level reliability.