Molding temperature, molding pressure, and time are three major parameters affecting the curing quality of molding materials. In this article, the effect of molding pressure on warpage of HVQFN packages is studied. The typical map-chips with 65% silica particle-filled epoxy resin are manufactured under five molding pressure levels from 1.8 to 12.3 MPa. The curvature measurements are performed for the packages after demolding and postcuring, respectively. The viscoelastic tensile relaxation modulus of molding materials is obtained by using dynamic mechanical analysis. The characterization of evolution of equilibrium moduli is analyzed for future modification of the model. The experimental results show that the molding pressure has a significant effect on the warpage after molding as well as after postcuring of HVQFN packages. The curvatures of HVQFN packages at both lower (1.8 MPa) and higher molding pressures (12.27 MPa) are about 45% less than the average max curvature at 3.6-8.66 MPa. The molding pressure has obvious influences on the glassy Young's modulus but has little effects on the rubbery modulus and relaxation time of the package materials. (c) 2008 Wiley Periodicals, Inc.