Si Substrate Backside—An Emerging Physical Attack Surface for Secure ICs in Flip Chip Packaging

Semiconductor integrated circuit (IC) chips are regularly exposed to physical attacks and faced to the compromise of information security. An attacker leverages Si substrate backside as the open surface of an IC chip in flip-chip packaging and explores the points of information leakage over the entire backside without being hampered by physical obstacles as well as applying invasive treatments. Physical side channels (SCs), e.g., voltage potentials, current flows, electromagnetic (EM) waves, and photons, are transparent through Si substrate and attributed to the operation of security ICs. An attacker measures SCs using probes as well as antennas and correlates them with secret information, such as secret key bytes, used in a cryptographic processor or analog quantities at the frontend of Internet of Things (IoT) gadgets. This article defines and elucidates the emerging threats of Si-substrate backside attacks on flipped IC chips, demonstrates attacks and proposes countermeasures.