The Effect of Acrylic Conformal Coating in the Reliability of Solder Joints

Abstract

During the product life, electronic components are subjected to environmental conditions, such as humidity or temperature fluctuations. Solder joints, which allow the electrical and mechanical connection, are one of the most critical spots to have failures due to environmental conditions. Conformal coating, a thin layer that encapsulates all components and consequently solder joints, is one of the techniques that allows the protection of the component against these detrimental effects. Nevertheless, the application of conformal coating has not been recommended in some components, namely in ball grid arrays (BGAs) and quad-flat-no-leads (QFN), since it can compromise the reliability of their solder joints when exposed to temperature fluctuations. Herein, by using an accelerative test, the reliability of BGA- and QFN-coated solder joints with an acrylic conformal coating was studied. A thermal cycle test of temperature ranging from −40 °C to +125 °C comprising 837 cycles demonstrated no failures (confidence level of 0.99; <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R = 4$ </tex-math></inline-formula> ppm/year; <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\beta = 3$ </tex-math></inline-formula> ) to occur due to acrylic conformal-coating application. However, the solder joints analysis indicated that conformal coating causes an excess of deformations on solder joints, compromising their reliability. Therefore, this study suggests that this acrylic conformal coating is not suitable for these electronic components.