Impact of water absorption on electrical properties of epoxy composite polymers: Suppressed charge trapping and enhanced ion transport

Epoxy-based molding compounds (EMCs) are nowadays widely used as encapsulating materials in integrated circuits (ICs) due to their excellent mechanical and electrical properties. Their application to smart power high-voltage ICs is under intensive study as harsh environment conditions exacerbate their performance. More specifically, the presence of a leakage current and the accumulation of space charge under high humidity can affect their long-term reliability, leading to die-level and package-level failures. In this work, by performing transient current measurements and employing numerical simulations, the role of moisture on the EMC properties is investigated. Experiments show that dry samples exhibit the expected current decrease with time before reaching a steady-state regime. Simulations confirm the key role of charge trapping and trap-assisted recombination in the definition of the final leakage current. In contrast, wet samples show unique behavior when subjected to sufficiently high electric fields: the usual reduction of the current is followed by a strong current increase without reaching an equilibrium condition. Simulations reveal that suppressed trapping phenomena allow for a reduction of the net space charge leading to the observed current rise. Moreover, the absence of a steady state and the sharp current increase at large stress times are attributed to enhanced ion transport because of the large presence of water molecules.