Cure Shrinkage and Bulk Modulus Determination for Moulding Compounds

In the electronic industry thermoset polymers are used as moulding compounds, underfill materials coatings and adhesives. A good knowledge of the cure shrinkage and material properties is needed to do reliable predictions of the stresses induced during packaging. In this paper, a novel technique using a new PVT (pressure-volume-temperature) apparatus is applied for measuring these quantities. The PVT apparatus can measure specific volume changes of the order of plusmn10^-3 cm³ /g with a programmable temperature range of 20-400degC and pressure range of 0-200MPa. A hybrid approach is then used together with differential scanning calorimeter (DSC) measurements for the kinetic modeling of these thermoset systems. The results show that the actual shrinkage during curing can reach values as high as 3.5% by volume for an unfilled epoxy Novolac system. It is furthermore shown that the common shrinkage definition which compares the specific volumes at room temperature before and after curing underestimates the actual shrinkage at the curing temperature by a factor of about 6. In addition a bulk modulus versus temperature curve was established. The bulk modulus was seen to drop by a factor of 1.5 during the glass transition