Warpage and Reliability of a 3D-MCM on an Embedded Substrate With Multiple Interconnection Method

In this paper, the warpage of 3-D multichip module (3D-MCM) on an embedded substrate with flip-chip and wirebonding interconnection method was studied by finite element (FE) simulation and moire fringes measurement. Simulation results showed that the warpage of 3D-MCM without underfill presents double-bow-shaped (W-shaped) mode, which is because of the cavity in substrate and the viscoplasticity behavior of solder balls. For the same reason, the warpage of substrate with temperature change has an inflexion around 75 °C, which indicated that the cavity in the substrate center may decrease the warpage of the substrate. The FE model and simulation results were validated through moire fringes measurement. Based on this model, the effect of underfill on warpage was discussed. It turned out that using suitable underfill could strengthen the interconnection between component and substrate, and then protect the solder balls and decrease the warpage of module. However, underfill with high coefficient of thermal expansion (CTE) may increase the stress, strain and plastic work density of solder ball, therefore result in the solder ball failure and lower the reliability of the module. The optimal CTE of the underfill, which is the mean magnitude of CTEs of the materials at both sides of unferfill layer, was determined with multiobjective method.