The effect of improper conformal coating on SnPb and Pb-free BGA solder joints during thermal cycling: Experiments and modeling

Electronic components, such as ball grid array (BGA), chip scale packages (CSP) and bottom terminated components (BTC) used in harsh use environments often require the use of conformal coatings to meet reliability requirements. In certain coating application methods, the conformal coating materials can flow underneath the component and cause solder joint failure during thermal expansion and contraction of the electronic assembly. In this study, BGA components were coated with an acrylic conformal coating material using two application methods and subjected to two different thermal cycling profiles to assess the integrity of SnPb and Pb-free BGA components. To better understand the observed failure modes, Finite Element Analysis (FEA) was performed on the conformally coated BGA packages. Material characterization was performed using Dynamic Mechanical Analysis (DMA) and Thermal Mechanical Analysis (TMA) to capture the temperature dependent properties of the conformal coating to better correlate simulation and experimental results. Failure modes were found to greatly depend on the conformal coating material properties around the glass transition temperature (Tg) rather than temperature cycle range. Significant differences in the failure mode were found between the Pb-free and SnPb BGA components with acrylic conformal coating materials and temperatures profiles.