Thermo-mechanical study of a 2.5D passive silicon interposer technology: Experimental, numerical and In-Situ stress sensors developments

Thermo-mechanical stresses have proven to be a critical issue in a typical interposer integration and assembly flow. However the nature of passive interposer makes the integration of MOS-based stress sensors impossible. New methods are required. Using a coupling strategy between 3D Finite Element Models (FEM) and physical characterization, a method based on electrical measurement of passive stress sensors is presented here to assess stress at die- and wafer-level. Innovative combination of passive stress sensors based on rosettes of serpentine resistors have been developed and embedded to quantify local strain states in a typical interposer die. Their principle and implementation at a copper interconnect level of interposer are presented in this paper. Preliminary results are depicted, including first electrical measurements of these sensors. Electrical characterization has been performed after the back-side interconnection fabrication of the interposer. A local sensibility of each copper serpentine is highlighted. Discrepancies in the resistance values of orthogonal resistors could indicate local deformations to the environment of sensors, such as TSV´s and bump pads. However, the order of magnitude of relative variation of resistance values is unexpectedly high and requires further investigations.