Parametric finite element analysis of solder joint reliability of flip chip on board

Abstract

Numerous studies have indicated that by encapsulating the solder joint with underfill material, the reliability of flip chip on board (FCOB) assemblies can be effectively enhanced. Typical manufacturing processes for FCOB assembly with underfill, however, involve long throughput time and additional equipment sets which are undesirable for high volume manufacturing environments. Hence, design/process simplifications, if not total elimination of underfill from conventional FCOB assemblies, that can directly result in productivity gain should be considered. A comprehensive parametric finite element analysis has been conducted to assess the feasibility of FCOB structures with partial underfill (i.e. only the peripheral joints are encapsulated with underfill material). The effects of some critical design parameters such as die size, joint height, joint diameter, joint pitch, printed circuit board (PCB) thickness and material properties of underfill on the solder joint reliability of FCOB structures were investigated in this study. Two-dimensional nonlinear plane strain finite element models of FCOB packages are employed. Moire and IR Fizeau interferometry techniques are used to measure the thermal deformation of the FCOB for model validation. Elasto-plastic deformation behaviours of solder were simulated under thermal cyclic loading from -55/spl deg/C to 125/spl deg/C. Maximum effective elastic and plastic strains of the solder joint were calculated and used as the indicator for determination of the solder joint reliability.