Lot-to-lot analysis of molding compound for PQFP package assembly

Abstract

Lot-to-Lot data is needed in order to assure a constant and controlled process. In order to determine the stability of molding compound, we did a full characterization using three lots of material. Elastic modulus, and coefficient of thermal expansion (CTE), glass transition temperature, and filler content were determined using molded test specimens. The same level of understanding is also needed in the area of molding compound rheology. The molding compound viscosity at several shear rates was determined. It was found that lot-to-lot viscosity were similar at high shear rates during the early stage of the reaction. The total heat, rate and %conversion of reaction, and activation energy were calculated. Time and temperature dependence of the molding compound were evaluated by monitoring the rate constant versus time plots. There was no significant difference in CTE and %filler whether the material was molded in 240L PQFP packages or test specimens. However, molded packages were observed to have 10% lower in elastic modulus and 5% lower in Tg than molded test specimens. Finally, effect of moisture ingress in uncured pellets competing of the molding compound was investigated. While information the process capability can be maintained, one critical parameter which can effect the assembly process is moisture. Moisture absorbed by the molding compound showed an influence on a spiral flow test, but it does not appear to significantly change the mechanical properties of the molded packages.