Assessment of FOWLP process dependent wafer warpage using parametric FE study

The paper presents the steps for the parametric finite element model creation of the wafer, material characterization of the adhesive tape, analytical and finite element study of the wafer warpage considering the bifurcation, gravity effect on the wafer bow assessing the warpage of mold/Si bilayered structure under thermal loading. The analytical results are compared to finite element analyses (FEA) considering the linear and nonlinear deflection. Consequently, the FEA approach has been used to study the deformation of 12” reconstituted wafers in their FOWLP fabrication process. By changing the temperature, the deformation of the wafer shows a bifurcation point, at which the warpage changes between the spherical and cylindrical shapes. The bifurcation region has been analyzed for the relevant range of overmold thicknesses in order to provide the guidance to optimum wafer and process designs that avoid the excessive warpage. For different wafer structures, the study determines also the effects of the gravitational force on the wafer bow as well as its influence in combination with the thermal mismatch. Finally, the FOWLP process induced warpage has been demonstrated by FEA incorporating the geometrical nonlinearity, gravity and ground support by means of contact elements.