Experimental and FEM study of hygro-thermo reliability of FCPBGA

In this paper, hygro-thermal deformations of a flip-chip-plastic-ball-grid-array (FCPBGA) package are tested using a 3-D optical testing system. It is found that the warpage of the FCPBGA package can even be reversed by moisture absorption of plastic materials. To investigate the thermal stress field of the FCPBGA and its change due to moisture absorption, finite element method (FEM) was employed, the experimental results are used to verify and modify the FEM models. With the FEM simulation,it is verified that the residual stress field of the FCPBGA can be changed greatly by moisture absorption, especially, a high peel stress occurred to the solder balls, which can be used to illustrate the failure mode of UBM opening. Through the simulation and investigation, a usually neglected reliability problem due to moisture absorption is revealed.