3D study of thermal stresses in lead-free surface mount devices

The paper presents the study of non-uniform temperature distributions in a flip chip electronic assembly, and the use of these temperature distributions to analyse the thermal stresses in lead-free solder joints in surface mount devices. The thermal stresses in the solder joints are mainly due to the mismatch in the coefficients of thermal expansions between the component and substrate materials, and temperature gradient in the electronic assembly. The thermo-elasto-visco-plastic finite element analysis is carried out to investigate the extent of thermal stresses induced in solder joints between a surface mount component and a FR4 circuit board (substrate) under conditions of thermal cycling with the chip resistor operating at its full power condition. Three different cases of spatial temperature distributions are considered including one with an experimentally obtained non-uniform temperature distribution. A comparative study of thermal stresses is performed using a near-eutectic SnAgCu solder material for three different thermal cases.