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A source synchronous I/O system based on high-density silicon carrier interconnects is introduced. Benefiting from the advantages of advanced silicon packaging technologies, the system uses 50 μm-pitch μC4s to reduce I/O cell size and fine-pitch interconnects on silicon carrier to achieve record-breaking interconnect density. An I/O architecture is introduced with link redundancy such that any link can be taken out of service for periodic recalibration without interrupting data transmission. A timing recovery system using two phase rotators shared across all bits in a receive bus is presented. To demonstrate these concepts, an I/O chipset using this architecture is fabricated in 45 nm SOI CMOS technology. It includes compact DFE-IIR equalization in the receiver, as well as a new all-CMOS phase rotator. The chipset is mounted to a silicon carrier tile via Pb-free SnAg μ C4 solder bumps. Chip-to-chip communication is achieved over ultra-dense interconnects with pitches of between 8 μm and 22 μm. 8 × 10-Gb/s data is received over distances up to 4 cm with a link energy efficiency of 5.3 pJ/bit from 1 V TX and RX power supplies. 8 × 9-Gb/s data is recovered from a 6-cm link with 16.3 dB loss at 4.5 GHz with an efficiency of 6.1 pJ/bit.