Survey of High-Temperature Polymeric Encapsulants for Power Electronic Packaging
Semiconductor encapsulant is crucial to electronic packaging because it protects the packages from mechanical stresses, electrical breakdown, chemical erosions, radiations, etc. Conventional encapsulants, including acrylic-, urethane-, and most epoxy-based polymers, are only applicable below 150°C. However, with increasing demand for high-density and high-temperature packaging, encapsulants that can work beyond 200°C are required. In this survey, four types of encapsulants, including conformal coatings, underfills, molding compounds, and potting compounds, are studied. Recommended properties and selection criteria for each type are listed. Standard testing methods for glass transition temperature (Tg), coefficient of thermal expansion (CTE), dielectric strength, etc. are introduced. Also, commercial products and current research topics for high-temperature encapsulation are surveyed. Novel material compositions, including silicone-, cyanate ester-, bismaleimide (BMI)-, and polyimide-based composites, are identified as potential high-temperature encapsulants for power electronic packaging.