Mechanical characterization of epoxy moulding compound in pressurized steam

摘要

Epoxy Molding Compounds (EMCs), commonly based on epoxy resin, are used widely for encapsulation of chips in electronic devices for protection against mechanical, environmental, and chemical attack. The thermo-mechanicai properties of these compounds are important for the assessment of package reliability. These properties are highly dependent on the temperature and moisture. EMCs absorb water when exposed to a humid environment. The trapped water generates steam in the compounds during the soldering reflow part of the packaging assembly process, which may drastically change the viscoelastic and adhesion behavior of the compound. The present research focuses on the characterization of mechanical properties of an epoxy molding compound in steam at elevated pressure (temperature above 100 °C and relative humidity equal to 100%). A special steam chamber with a highly accurate tensile setup for force and displacement measurements is designed and manufactured. The chamber is equipped with a 3 Point Bending (3PB) loading setup. The setup can also be modified to mixed mode bending for investigating the effect of temperature and steam on the molding compound-to-lead frame interface strength. In this paper, the viscoelastic creep compliance of a molding compound in dry and wet environment is measured in 3 point bending mode. It is shown that steam significantly affects the thermo-mechanicai properties of the molding compound. The glassy and rubbery modulus of the molding compound were seen to decrease almost by 20%. Furthermore the glass transition temperature decreased by about 30 C and the creep process was seen to be about a factor 40 faster in a hot steam environment.