Numerical investigation on the influence of different substrate materials on the viscoplastic behaviour of flip chip solder bumps

The finite element method was used to simulate the thermo-mechanical behaviour of a flip chip under thermocyclic loading between -55/spl deg/C (-67/spl deg/F) and 125/spl deg/C (257/spl deg/F). In order to simulate realistically the inelastic material response of the solder bump, Chaboche's viscoplastic material model instead of a classical ORNL-theory was implemented into the finite element code ABAQUS and applied to a flip chip configuration. This so-called unified constitutive model is able to describe the Bauschinger effect as well as the creep/plasticity interaction. Herewith the influence of the substrate material on the inelastic deformation behaviour of a tin-lead solder bump was analysed. A comparison is given with respect to the influence of the two substrate materials namely Al/sub 2/O/sub 3/ and our self-developed Low Temperature Co-fired Ceramics (LTCC) on the inelastic response of the Sn60Pb40 eutectic solder material. It may be shown that the thermoelastic behaviour of the LTCC substrate significantly reduces the cyclic stresses in the bump compared to Al/sub 2/O/sub 3/ as well as the cumulative inelastic strain which is responsible for the development of damage and hence flip chip failure.