Evaluating Vulnerability of Chiplet-Based Systems to Contactless Probing Techniques

Driven by a need for ever-increasing chip performance, a growing number of semiconductor companies are opting for all-inclusive System-on-Chip (SoC) architectures. Increasingly, the solution adopted to minimize the impact of silicon defects on manufacturing yield of larger dies has been to split a design into multiple smaller dies called chiplets, which are then brought together on a silicon interposer. Advanced 2.5D and 3D packaging techniques that enable this kind of integration also promise increased power efficiency and opportunities for heterogeneous integration.However, despite their advantages, chiplets are not without issues. Disaggregating a design into multiple separate dies introduces new security threats, including the possibility of tampering with and probing exposed data lines. In this paper we evaluate the exposure of chiplets to probing by applying laser contactless probing techniques to a chiplet-based AMD/Xilinx VU9P FPGA. First, we identify and map interposer wire drivers, and show that probing them is easier compared to probing internal nodes. Lastly, we demonstrate that delay-based sensors, which can be used to protect against physical probes, are insufficient to protect against laser probing.