Moulding compounds are epoxy resins filled with inorganic (silica) particles, carbon black, and processing aids. They have become one of the prime fundamental elements in the electronics industry because of their wide-spread use as an encapsulating material for electronic components. However, because of their viscoelastic nature, thermo-mechanical characterization of such materials is a big challenge. The mechanical properties required in finite element codes are usually the shear modulus and the bulk modulus (resistance to compression). Data for the shear modulus is relatively easy accessible from measurements but (time dependent) data for the bulk modulus of moulding compounds has hardly been reported. The probable reason could be that the bulk modulus measurements involve very small deformations and, particularly for moulding compounds, their very high incompressibility (or low compressibility) makes it more challenging to characterize them for bulk deformations.

This research investigated time and temperature dependency of bulk modulus for moulding compounds using transient bulk creep experiments. These, so called pressure jump volume relaxation experiments, were done by applying positive and negative pressure jumps followed by a holding period at those pressure levels and the whole set of experiments was repeated at different temperatures. For negative pressure jumps (or expansion experiments) the bulk modulus was found to be almost independent of time. For positive pressure jumps (or compression experiments) time dependent volume decrease was very slow. Compared to time and pressure, temperature dependency was of highest influence. In another set of measurements, using standard PvT experiments temperature dependent bulk modulus, ignoring time dependency, was measured for different moulding compounds with different filler contents. A Gnomix PvT apparatus was used for these characterizations. The apparatus was adopted for PvT measurements of highly incompressible materials.

The other important property of interest to researchers is cure shrinkage, which is exhibited by the materials during their curing process. This shrinkage causes residual stress and warpage, which is one of the core issues concerning reliability of package. Proper establishment of the materials model during the curing process demands fairly accurate estimations of volumetric shrinkage. Another part of this research performed, volumetric cure shrinkage measurements for the same set of moulding compounds. Approximate linear relation with conversion was observed in all the tested moulding compounds.