Application of (Electrochemical) Impedance Spectroscopy to Investigate the Degradation of Epoxy Mold Compounds for Plastic Encapsulation of Power Electronics - A Feasibility Study

The present work investigates the suitability of impedance spectroscopy to characterize typical plastic encapsulation materials in electronic packaging. In a first approach, a commercially available epoxy mold compound (EMC) after processing to millimeters thick free-standing samples is studied. The use of free-standing samples avoids any influence of substrate/encapsulation interaction and enables the investigation of the intrinsic properties before and after harsh conditions of exposition in a Pressure Cooker Test (PCT). The change of properties of the mold material and the uptake of water is characterized with impedance spectroscopy in a 2-electrode design. Complementary material diagnostic (FTIR) confirms the results of the impedance spectroscopy. The free-standing mold failed dramatically and degraded under the conditions of the PCT due to embrittlement of the polymer and a fast water uptake. The study impressively demonstrates the (electrochemical) impedance spectroscopy as a powerful tool for qualifying and characterizing materials with extremely high impedance, such as plastic encapsulations.