Effects of a Conformal Coating on the Signal Integrity of Space Electronics Systems

The working environment of aerospace loads is harsh, so conformal coatings are applied to the surface of printed circuit boards (PCBs) to improve the reliability of space electronics systems. However, the effects of a conformal coating on the electrical signal are still unclear. This work studies the effects of a conformal coating on signal integrity from the perspective of the characteristic impedance and scattering parameters (
$S_{21}$
). It includes building a correlation model between coating parameters and the characteristic impedance using the conformal mapping method, calculating and simulating the changes in the characteristic impedance and
$S_{21}$
based on finite element analysis software, and testing the effects of the coating on signal integrity under different working conditions in temperature cycling experiments. The results show that an increase in the coating thickness to 1.5 mm results in a
$4.2~\Omega $
reduction in the characteristic impedance and a 0.53 dB increase in
$S_{21}$
at 1 GHz for a 10-in long and 25-mil wide transmission line. Additionally, the coating has different effects on different size transmission lines and different component packages. This study clarifies the mechanism and magnitude of the effects of conformal coatings on signal integrity, which can provide a reference for future coating thickness selection, circuit impedance matching design, and signal integrity optimization.