Novel process warpage modeling of matrix stacked-die BGA

A comprehensive warpage analysis is performed on the matrix stacked-die ball grid array BGA (SDBGA) by means of finite-element modeling and experimental warpage measurements. By comparing the block warpage results from conventional linear small deformation simulation and the experimental measurement results, it is found that the linear method is not able to capture the warpage behavior of the SDBGA matrix, because the change of the centroidal moment of inertia of cross section after deformation cannot be considered due to small deformation assumption. The nonlinear large deformation analysis must be taken instead. Based on the nonlinear analysis, an advanced warpage prediction methodology for matrix SDBGA is established. This methodology is then used to characterize the warpage behavior of matrix SDBGA and to study the different effects on the warpage. Warpage of matrix SDBGA during the whole assembly processes is also predicted. For the SDBGA matrix investigated, the crossbow dominant warpage and buckling phenomena are observed for the matrix after bottom die bonding and after interposer bonding, which are new findings in the warpage study for electronic packages. It is also found that not only the total die length, but also the dice distribution will affect the warpage pattern of the matrix. For the matrix after top die bonding and after molding, normal warpage patterns are observed, i.e., both crossbow and coilset warpage are comparable. "Bending interaction" and the "warpage competition" mechanisms are proposed to explain the warpage characteristic for matrix SDBGA.