A hybrid equivalent-layer model for analysis of solder joint reliability of ultra-fine pitch packages

Abstract

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 (Zhao and Tay, 2003). The number of nodes and elements of the slim sector model is much lesser than that of the traditional one-eighth model. In order to save the efforts in the preprocessing, a hybrid slim sector model was developed. The intermediate layer between chip and substrate was homogenized in terms of mechanical properties, with the application of representative volume element (RVE) and homogenisation method. This paper presents a hybrid equivalent layer model for analysis of solder joint reliability of ultra-fine pitch package. The intermediate layer between chip and substrate is treated as a continuum layer since the solder joints are distributed evenly. 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. An energy-based method is developed to obtain the effective plasticity. Temperature-dependent mechanical properties are taken into account. A general creep model was also developed to describe both the transient creep and secondary steady state creep. Thermal reliability analysis of a 4 times 4mm 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 ~ 5%