Prediction of Solder Joint Reliability with Applied Acrylic Conformal Coating

Abstract

The exposure of miniaturized components to the environment leads to new failure analysis as a result of environmental conditions and constant innovation of the component materials and dimensions. Generally, these failures occur on the solder joints, which ensure the mechanical and electrical connection between the printed circuit board and the component. Conformal coating is a thin layer of a polymeric material that encapsulates the components and consequently their solder joints to protect against harsh environments. However, this application is not recommended in some components such as ball grid array and quad flat no-lead (QFN) packages, since it can reduce the reliability of the solder joints when exposed to temperature fluctuations. Therefore, by using a finite element analysis, a thermal cycle test was simulated with and without conformal coating. The simulation output was extrapolated to lifetime theoretical methods with the aim of predicting the number of cycles until the failure of the solder joints. Therefore, this study demonstrates that for both components without conformal coating, solder joint lifetime was a precise approximation. Coated solder joints reveal a drastic reduction in their reliability due to the influence of the conformal coating behavior and its thermomechanical properties.