Challenges and Solutions for Interoperability in BoW-based Multi-Chip Module Systems

The Bunch of Wires (BoW) standard has emerged as a scalable and open solution for chiplet-to-chiplet communication, enabling the integration of dies fabricated in heterogeneous technology nodes. Despite its robust physical interface, BoW adoption in multi-chip modules (MCM) faces challenges related to performance degradation, standard compliance, and mismatched operating voltage domains, which can compromise interface reliability and efficiency. This work investigates these challenges with a primary focus on voltage-domain mismatch in BoW-based Die-to-Die (D2D) interfaces. A comparative analysis of transmitter implementations in 130 nm and 22 nm technologies is performed to study process-dependent behavior. Based on this analysis, a configurable low-swing transmitter architecture is implemented in 130 nm to enable PHY-level voltage adaptation. Simulation results demonstrate that controlled swing reduction enables safe cross-node interfacing while improving energy efficiency. These findings highlight the importance of voltage-domain management for reliable heterogeneous BoW integration and support its broader adoption in chiplet-based systems.