The accuracy of structural approximations employed in analysis of area array packages

At the present time, area-array packages are a very common electronics packaging approach. One of the major concerns in designing such packages is the reliability of solder joints, die, and the various material interfaces present in the package. Currently, analytical, numerical, and experimental methods are employed in the analysis of thermo-mechanical stresses/strains in area array packages. The sources of error in these analytical and numerical models may be broadly characterized as being due to geometry representation, material behavior, solution procedure, and due to the accuracy in representing the load history. In this paper we assess the errors in package models due to geometry representation and material behavior using a representative area-array package, namely the 225 input/output (I/O) plastic ball grid array (PBGA). The package deformation due to a fixed temperature change is experimentally characterized using Moire interferometry and numerically simulated using both two- and three-dimensional finite element models. The difference in behavior between the finite element prediction and experimental results is explained using solder material behavior data available in the literature. A comparison of accuracy as well as efficiency is made between the different finite element models. Finally, conclusions are drawn on the aspects of package construction and material that influence behavior, and on the most efficient finite element model to accurately capture this behavior.