Warpage of plastic IC packages as a function of processing conditions

Variation of processing conditions on warpage prediction of a plastic quad flat package (PQFP) is examined. Thermal mismatch between package constitue nt materials is the major cause of IC package warpage. To minimize the warp age problem, a thorough understanding of epoxy,, molding compound (EMC) pro perties with molding parameters is necessary as EMC is epoxy-based with tim e and temperature dependent viscoelastic properties. This paper first addre ssed the thermal characterization of encapsulating material. Degree-of-cure (DOC or beta), coefficient of thermal expansion (CTE or a), glass transiti on temperature T-g, and shear modulus G' and G of the molded specimens were measured by various thermal analysis techniques. The glass transition temp erature was shown to be a good and direct measure of the degree-of-cure. Th e CTEs (alpha (1) and alpha (2)), G' and G" were found to be decreasing fun ctions of degree-of-cure. Viscoelastic EMC material models with DOC (i.e., T-g) dependent were formulated. Package warpage predictions against differe nt processing conditions were performed via finite element analyses. Out-of -plane displacement measurements were performed on plastic quad flat packag e (PQFP) to validate the numerical results. Warpage prediction by the visco elastic material model was found to agree with the measured data better tha n the thermoelastic one. For a given cured content, less warpage was found in packages molded at low temperature and longer molding time OR high tempe rature and shorter molding time.