Chiplet Interconnect Design is the engineering discipline of creating high-bandwidth, low-latency, energy-efficient die-to-die communication interfaces that connect multiple chiplets within an advanced package, enabling disaggregated chip architectures where specialized dies from potentially different process nodes are integrated into a single system.

The die-to-die interface must provide bandwidth density approaching on-die interconnect while operating across a package-level physical channel with impedance discontinuities, crosstalk, and power constraints.

UCIe (Universal Chiplet Interconnect Express) has emerged as the industry standard:

PHY Architecture: Die-to-die PHY designs differ fundamentally from chip-to-chip SerDes. Short reach allows: parallel interfaces (wide data buses rather than high-speed serial), simplified equalization (1-2 tap FFE), forwarded clock (eliminates CDR latency and power), and single-ended signaling at advanced package pitches (saving 2x bump count versus differential).

Protocol Layer: UCIe supports PCIe for I/O, CXL for cache-coherent memory, and streaming for custom protocols. The link layer provides: CRC error detection with replay, credit-based flow control, and link training. Latency targets <2ns for coherent traffic.

Physical Design Challenges: Bump-to-circuit routing at fine pitch with impedance control; power distribution through interposer (IR drop); crosstalk mitigation between dense parallel lanes; ESD protection with low capacitance; and KGD testing requiring loopback and BIST modes.

Emerging Directions: Optical chiplet interconnects using silicon photonics, 3D stacking with Cu-Cu hybrid bonding for maximum bandwidth density, and chiplet-native protocols optimized for AI/ML workloads.

Chiplet interconnect design is the enabling technology for the disaggregated silicon era — its bandwidth density, energy efficiency, and standardization determine whether multi-chiplet systems can match monolithic alternatives.