Thermal ions diffusion on printed circuit board

Abstract

Reliability of PCB is of paramount importance during high temperature application in the field. Good integration among all PCB components is essential to ensure robust PCB performance. Imperfection in the PCB assembly may activate ion diffusion and induce board level contamination, which are detrimental to the device functionality. In this paper, we show that magnesium ions can be thermal-electrically excited from a heat fin. Under the influence of electric field, these ions diffuse through thermal glue and cause fatal failure to the adjacent electronic device. The movement of the ions is governed by various diffusion mechanisms such as interstitial diffusion, grain boundary diffusion, and surface diffusion. The PCB assembly process must be properly controlled and by isolating the thermal glue from the heat fin, the failure risk can be reduced.