Measurement of residual stresses in flip chip underfill resins

Flip chip interconnection technology provides a solution to the increasing demands for miniaturisation and weight reduction for applications in portable electronics. The technology enables direct attachment of chips to printed circuit boards through solder joints. The gap between the chip and board is encapsulated with an underfill resin to improve the mechanical/ thermal performance and thus the reliability of package. During the curing process of underfill, large residual stresses are generated due to the chemical shrinkage of polymer and the thermal mismatches between the various package components. The rheological/thermornechanical properties and curing kinetics of underfill resin are important factors that affect the magnitude and distribution of residual stresses. These thermal stresses are the principle cause of device failure after temperature cyclic tests.