Material analysis and process characterization of super high thermal performance die attach epoxy towards package reliability, thermal and electrical performance

Abstract

Super high thermal die attach adhesive towards better thermal resistance and RDSON is highly desired in green robust package development. Novel inventions, include new basic resin, new type and distribution of silver filler, unique blend solvent to enhance silver filler compactness. Thermal and electrical conductivity are directly proportional to degree of silver compactness. Seven high thermal epoxies with thermal conductivity 20 to 65W/K.m and volume resistivity 0.01×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-8</sup> to 7.62Ø10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> are formulated, and assembled into TO263 package. Package thermal resistance, RDSON and SAM have been carried out to assess the glue robustness after MSL3@260dC, 1000 cycle thermal cycling and pressure cooker test. This paper studies the adhesive key challenges to dispensability, wire bond and reliability test. High viscosity due to high filler loading and resin type raise the concern of inconsistent dispensing. Writing dispensing and viscosity lower than 9.5Pa.s are recommended to achieve good dispensability. Higher silver filler to resin ratio enhances compactness of filler, however interfacial adhesion may be weaken which induce lifted die in wire bond. It is shown that minimum 0.16kg/mm2 strength with cohesive mode are sufficient to prevent die lifted. Good interfacial adhesion is also important to improve package thermal resistance by 12%. New thermoset resin and high silver filler loading tend to increase adhesive elastic modulus. This increases the concern of die attach material crack in reliability test. Addition of thermoplastic as resin effectively reduces elastic modulus of epoxy glue. Adhesive's thermal conductivity exceeding 20W/K.m is sufficient to meet TO263 thermal resistance. Thermal conductivity can be improved 11% with addition of spherical silver filler. RDSON test reveals all adhesives have good electrical conductivity in TO263 package.