Thermal stresses of conformal coatings on printed circuit boards

As part of the drive towards lighter aircraft and reduced fuel consumption, power electronics are expected to replace mechanical and hydraulic systems on aircraft necessitating a move to higher operation voltages. The combination of higher operating voltages. The aerospace environment introduces the potential for a number of failure mechanisms including regular temperature cycles, low atmospheric pressure, chemical contamination, a higher likelihood of partial discharge and condensing humidity that could reduce the performance or cause failure of the power electronics. Conformal coatings have previously been used to protect power electronics but the long term performance of the coatings on circuit boards in an aerospace environment is unclear. This paper will describe how the thermal cycles experienced by aircraft and the rapid temperature rise due to the switch-on of the electronics affects the development of mechanical stresses in the components of a printed circuit board. With the aid of thermogravimetric analysis, an assessment of whether the thermal cycles and switch-on of the electronics is likely to have an effect on the ageing of the conformal coating is made.