BEOL thermal characterization for 3-D packaging

Abstract

Little research has been conducted to thermally characterize the Back End of Line (BEOL) interconnects since they play little role in conventional 2-D electronic packages. This is changing with the emergence of 3D packages, which place BEOL layers directly in the primary thermal path when die are stacked. In this study we look at the impact of the BEOL layers on a realistic 3-D stacked package to gauge the thermal penalty and to understand the necessary accuracy for BEOL thermal resistance calculations. We then describe various BEOL structures and evaluate the thermal resistance using detailed finite element micro-models. We compare the results to analytical techniques and simple approximations schemes to find effective resistance values that can be used in conventional package or system level thermal models. The primary goal of the work is to establish suitably accurate ways to account for different BEOL designs in a macro-level model.