Development of electro-optical PCBs with embedded waveguides for data center and high performance computing applications

Power consumption and scaling the performance and quantity of electrical interconnects for data traffic inside boards and backplanes are one of the critical barriers envisaged in next‐generation Data Center (DC) and High‐Performance Computing (HPC) applications. In this paper, we report developments of electro-optical PCBs (EO-PCB) with embedded polymer waveguide layers. We show results for fabricating realistic product emulator test vehicles that comprise of reasonable form factor PCBs with optical and electrical layers. The optical layer comprise of multiple waveguides exhibiting a full range of geometric configurations required to meet practical optical routing functions. Test patterns include varied cross-sectional sizes, 90° bends of varying radii (40mm – 2mm), cascaded bends with varying radii, waveguide crossings with varied crossing angles (90° - 20°), splitters, tapered waveguides and waveguide interconnect to midboard interface slots. Moreover, results for fabricating electrical interconnect structures (e.g. tracing layers, vias, plated vias) top/bottom and through optical layers in OE-PCB stack are shown. The purpose of the complex routed copper layers is to enable the crucial demonstration of the fabrication and thermal robustness challenges inherent to electro-optical PCBs with optical layers. Process compatibility with accepted practices and challenges in production scale up for high volumes are key concerns to meet the yield target and cost efficiency. Results include waveguide characterization, waveguide transmission loss, misalignment tolerance, and effect of lamination. Moreover, we show results on waveguide termination by in-plane edge connector and with 90° out-of-plane couplers.