Improved slim sector model for analysis of solder joint reliability

Within the next three years, it is likely that the interconnection pitch of the advanced flip chip will come down to 100 micron. In order to study the solder joint reliability more efficiently, a slim sector model has been developed to handle the large number of interconnects involved [1]. The number of nodes and elements of the slim sector model is much lesser than that of the traditional one-eighth model. However, more effort, are required in the preprocessing. This paper presents an improved slim sector model. The intermediate layer between chip and substrate is treated as a continuum layer since the solder joints are distributed evenly. The advantage of transversely isotropic behaviour is taken into account. The effective mechanical properties of the equivalent continuum layer are evaluated using a 3-D representative volume element (RVE) based on continuum mechanics and a numerical homogenization method. Formulae to extract the effective material constants are derived using elasticity theory. With finite element analysis of four cases of loading to the RVE, transversely isotropic plasticity model are obtained. Characteristic parameters for Hill's formulation are extracted from the numerical experiments. Temperature dependent mechanical properties are taken into account. Thermal reliability analysis of a 6x6mm(2) flip chip package was carried out using the continuum layer with effective mechanical properties and heterogeneous structure. Numerical results show that the difference of displacement is 3 similar to 5%. As a result, the error percentage of maximum inelastic shear strain and fatigue life prediction is 5% and 9%, respectively. The improvement of time efficiency in terms of preprocessing and computational time is significant.