A novel tool for cure dependent viscoelastic characterization of packaging polymers

This paper concerns the dynamic mechanical shear characterization of curing thermosets. During curing, thermosets change from a viscous liquid to a viscoelastic solid. This solidification process is attended by chemical shrinkage, a combination leading to residual stresses in the package where the resin is applied. Thermo-viscoelastic characterization is one of the main subjects in studying the residual stress development during thermoset cure. Experiments for thermo-viscoelastic characterization usually take place at several temperatures, where the material is in the glassy as well as in the rubbery or liquid state. The modulus range to be measured is thus huge; the difference between glassy and rubbery modulus is usually of the order of 10³. Furthermore, in the transition from the liquid state to the glassy state the shear modulus changes from almost zero to roughly 1 (GPa). It is generally rather difficult to measure such modulus changes using just one set-up. Usually, these type of problems are solved by the use of different sample geometries in different modulus ranges. In the present work, two shear tools, giving complementary results, are discussed.