Analysis of long-term stability of capacitors embedded in printed circuit boards

This paper presents studies of long-term stability of capacitors embedded in printed circuit boards. Planar capacitors fabricated from FaradFlex dielectric foil with copper plates laminated to FR-4 substrate served as test structures. The dielectric was BaTiO₃ ceramic/polymer composition with various fillers and consequently various dielectric constants. Moreover test samples differed in composition thickness and surface size. The investigated capacitors were covered with LDP 2×106 (Laser Drillable Prepreg) protective layers to achieve embedded structures. The behaviour of capacitance as well as dissipation factor was investigated for two values of frequency (1 and 10 kHz) in order to determine their long-term stability. The in-situ accelerated ageing process (capacitance and dissipation factor of test samples performed directly at the ageing conditions) was carried out to perform long-term behaviour analysis. Temperature characteristics both before and after aging process were performed for determination of influence of environmental exposure. Additionally insulation resistance under voltage and temperature stress was monitored and analyzed.