Thermomechanical models for leadless solder interconnections in flip chip assemblies

Analytical thermomechanical models have been developed in order to calculate the thermally induced stresses in leadless solder interconnection systems. Two different analytical models are highlighted: the peripheral and area array thermomechanical model which describe the thermally 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 these models, structural design optimization of interconnection systems can be performed very quickly in order to reduce time consuming experiments and finite element simulations. It is found that the largest stresses 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 element simulations have proved a good accuracy of the thermomechanical models.