Introdution Electronic materials are often evaluated according to properties such as thermal resistance, dielectric performance, mechanical strength and moisture resistance. But another factor can have a major influence on long-term reliability: mobile ionic impurities. Trace ions such as chloride (Cl⁻), sodium (Na⁺), potassium (K⁺) and other ionic species may originate from resins, fillers, additives, synthesis residues, processing equipment or environmental contamination. Their concentration may be extremely low. However, when moisture, elevated temperature and electrical bias are present, some of these ions can become mobile and migrate through polymeric materials or along interfaces. Research on microelectronic encapsulants has shown that epoxy