Characterization of the rheological properties of epoxy-molding compound

Wire-sweep is a common defect in IC packages and becomes more critical in high-density packages. Due to the thermal-setting and shear-thinning nature of epoxy-molding compound (EMC) the usual rheological measurement methods used in characterizing the flow property of EMC (i.e., spiral flow test and Shimadzu flow tester) cannot be used to verify the wire-sweep problem during chip encapsulation. The shear rate for the spiral flow test is around several hundred reciprocal seconds (approximating to flow rate in the runner), end the shear rate is a couple of thousand reciprocal seconds for the Shimadzu flow tester (closing to flow rate in the gate), Since the shear rate in cavity is around 10-50 reciprocal seconds the two equipments mentioned above cannot provide valuable rheological information at this shear rate range. In this paper, the viscosity of EMC on the sheer rate range of wire-sweep is characterized by using a disk-flow-type measurement method. The high-shear viscosity data is obtained by a Shimadzu flow tester, the medium-shear viscosity information is obtained by spiral flow test, and the low-shear viscosity is obtained by disk flow test, By combining results from these measurements, the viscosity of the EMC is obtained over the typical processing range of shear rates encountered during chip encapsulation, i.e., low-shear for cavity flow, medium-shear for runner flow, and high-shear for gate flow.