Ayar Labs and GUC Joint Thermal Co-Simulation: Co-Packaged Optics Requires Liquid Cooling to Meet Spec in a 3 kW AI Package

Whether co-packaged optics (CPO) can operate reliably alongside high-power AI processors has been one of the central concerns blocking deployment of the technology. Ayar Labs and GUC (Global Unichip Corp.) jointly conducted a thermal co-simulation targeting a multi-chip package with a total power envelope exceeding 3 kW, testing how optical engines perform thermally when coexisting with high-power AI dies. The conclusion is clear: conventional air cooling fails to meet spec, while liquid cooling works.

The package measures 105 mm × 140 mm and houses 2 XPUs (25.69 mm × 32.40 mm each), 8 HBM4 memory modules, 4 I/O chiplets, and 8 TeraPHY optical engines (12.5 mm × 13.0 mm each). The optical engines are attached directly to the MCP organic substrate and communicate with the I/O chiplets via UCIe-S, replacing traditional electrical interconnects and enabling a full-duplex optical interface of more than 100 Tbps. The AI processors alone consume 1,500 W, with the entire package exceeding 3 kW.

The simulation proceeded in three steps. First, a standard air fin heatsink was tested at airspeeds of 5–6 m/s and an ambient temperature of 25 °C; the result showed that all components except the I/O die significantly exceeded their temperature specifications. Second, a thermal resistance analysis determined the conditions needed to meet spec: ASIC thermal resistance must be ≤ 0.008 K/W and optical engine thermal resistance must be ≤ 0.15 K/W. Third, an impingement-type cold plate was tested at a flow rate of 4.5 LPM, and all components fell within their temperature limits—HBM4 below 95 °C, SoC below 125 °C, and optical engines below 100 °C.