PBGA Package Finite Element Analysis Based on the Physical Geometry Modeling using X-ray Micro CT Digital Volume Reconstruction

The Ball-grid array BGA package can fail under thermo-mechanical loading such as thermal cycling. It is important to study the strain and stress of an electronic package using Finite Element Analysis (FEA) that is based on physical geometry and dimension. One can precisely view the real package dimension under the CT scan. Use of CT data for FE model creation will allow for greater ability to capture the actual structure. Currently, many people try to take geometrical measurements with calipers or micrometers, which only measures the surface and outline. CT has been widely used for medical imaging. Previous researchers have used medical CT-based femur model to find stress concentration in the femur under mechanical stress (Vulovic, Korunovic, & Trajanovic, 2011), and CT-Scan data to model the vertebra geometry and its properties in the FEA (D.Jovanovic & Lj. Jovanovic, 2010), creating FE models of the human feet (Antunes & Dias, 2008). In the electronic packaging field, it is worthwhile to create the finite element model based on a real geometry rather than assumed nominal dimensions. The ability to capture and port the actual geometry into the FE platform allows for studies which target the effect of manufacturing variabilities and dimensional variations on the reliability and performance of the semiconductor assembly. In this paper, a generalized scheme of FEA model creation using the X-ray micro CT has been put forward. Firstly, a procedure for micro CT scan and a technique for volume reconstruction have been developed. Secondly, the CT data structure has been demonstrated, and a FEA global and local model from the scan has been incorporated into the analysis. Thirdly, the Annand Visco-plasticity model of SAC-305 has been utilized and merged into the FEA software to model material behavior. In the end, a model of a void solder joint under thermal cycling has been presented. The cumulative plastic work and stress-strain hysteresis loop have been plotted.