THERMOMECHANICAL MODELS FOR LEADLESS SOLDER INTERCONNECTIONS IN FLIP-CHIP ASSEMBLIES

Analytical thermomechanical models have been developed in order to cal culate the thermally induced stresses in leadless solder interconnecti on systems. Two different analytical models are highlighted: the perip heral and area array thermomechanical model which describe the thermal ly induced stresses for two components connected to each other with a peripheral, respectively, area array of joints, The analytical models are based on structural mechanics and have the ability to characterize the nature and estimate the magnitude of the joint stresses. Using th ese models, structural design optimization of interconnection systems can be performed very quickly in order to reduce time consuming experi ments and finite element simulations. It is found that the largest str esses in the solder joints of flip chip assemblies are at the top and bottom surface of the: connection and that they are especially caused by bending moments subjected to the joints, Comparisons with finite el ement simulations have proved a good accuracy of the thermomechanical models.