Micromechanical modelling of SnAgCu solder joint under cyclic loading: Effect of grain orientation

Miniaturisation of SnAgCu solder joints for electronic package results in the diminishment of the number of grains within a single joint, sometimes down to only one or two grains per joint. In this case, solder joints exhibit an anisotropic creep behaviour. Moreover, the crystal structure of β Sn (matrix of SnAgCu eutectics and Sn dendrites) is a contracted version of a diamond cubic, one leading to a body-centred tetragonal structure, which enhances this non-uniform character. These factors affect the character of creep and consequently determine reliability of solder joints for electronic packages. In this study, a crystal visco-plasticity model is developed to capture an anisotropic behaviour of SnAgCu solder joints in cases of single-, bi- and multi-crystals. In order to simulate responses of solder joints under thermal cycling, a multi-scale finite element modelling is performed. In a global model, responses of joints in a flip chip package are simulated. Then results for displacements are adopted in the sub-model of a single joint. The obtained results are compared with those based on the traditional isotropic constitutive descriptions.