TSV-less Power Delivery for Wafer-scale Assemblies and Interposers

Wafer-scale engines are gaining popularity amidst the rapidly rising demand for high-performance computing (HPC). Large interposers, such as Silicon Interconnect Fabric (Si-IF)[1], enable wafer-scale systems via dense integration of heterogeneous known-good-dielet (KGD) on a single silicon substrate. As a result, one can build an HPC processor as large as a 300 mm wafer. To deliver power and achieve external communication for such a large system, the conventional solution is to use through-silicon vias (TSVs) in the interposer substrate. In this work, we propose an alternative novel solution in which power and signals are routed around the die, in the inter-die gap, and then are routed on the substrate under the die and uniformly delivered to the dies. This solution has the following advantages: (1) TSV-less process which is inexpensive and reduces process complexity; (2) enablement of fine-pitch power/signal paths. This work focuses on power delivery of the novel structure, and a detailed simulation framework compares the power distribution network (PDN) electrical performance of the dielet-side method to the substrate-side method. We show that dielet sizes determine which PDN (TSV or dielet-side) should be used to reliably supply power to the assemblies. Based on our model, dielet-side power delivery is acceptable under conditions in which die sizes are smaller than 25 mm² and the power density is lower than 0.5 W/mm². A preliminary fabrication process was developed for power/ground paths of the dielet-side PDN in which through-polymer vias (TPVs) are employed. To demonstrate the compatibility of this novel integration methodology to thin (100 μm) dielet, a surrogate structure was designed and fabricated to mimic die-to-wafer assembly with 100 μm dielet. System encapsulation was achieved by thin Al2O3 deposition. Low-stress inter-die polymer isolation walls were built, and 500 μm width TPVs were fabricated by Cu electrochemical deposition.