Development of electro-optical PCBs with polymer waveguides for high-speed intra-system interconnects

Purpose - The purpose of this paper is to study fabrication of optical-PCBs on panel scale boards in a conventional modern PCB process environment. It evaluates impacts on board design and manufacturing with the developed optical board verifiers outlining challenges and requirements for manufacturing low-loss waveguide structures and optical building blocks. The study aims to expand the current knowledge in the field by adding results obtained by utilizing industrial production infrastructure and developed scalable manufacturing processes to fabricate optical-PCBs and board assemblies in high-volumes and low-cost manner. Design/methodology/approach - Impacts on board design and manufacturing were studied with the developed optical technology verifiers. One verifier is optical-PCB with embedded waveguides, integrated i/o couplers and optical vias. Another verifier is large size PCB with optical layer. A system-level optical board assembly with 12.5 Gb/s Tx/Rx devices on surface mounted ball grid array (BGA) modules is designed for optical link analysis. Fabricated optical structures on verifiers are evaluated of their physical characteristics utilizing optical, SEM, LSCM analysis methods. Performance testing is conducted using standard optical transmission measurement methods and equipment. Findings - The paper provides empirical results about fabrication of multimode optical waveguides with conventional PCB process equipment. Results suggest that current coating and imaging equipments are capable of producing optical waveguide patterns with high resolution and size accuracy. However, fabricators would require larger process window and defect tolerance for processing optical materials to obtain low-loss waveguides with sufficient yields. Research limitations/implications - Because of the limited amount of design variants in production verifiers evaluated in this paper, some impacts like effect of base material, board construction, optical layer location and beam coupling solution were not evaluated. Likewise, impacts on long-term stability and cost were not addressed. These factors however require further investigation to address technical feasibility of optical PCBs technology prior commercial high volume production. Practical implications - The paper includes implications for the development of a fabrication methods and testing procedures for optical polymer waveguide layers on PCBs. Originality/value - This paper fulfils need to provide results on design, fabrication and characterization of optical PCBs and backplanes from industrial fabricator's perspective. The paper provides input for end-user and developers to evaluate technical performance, robustness, and maturity of building blocks and supply chain to support polymer waveguide based technology for intra-system optical links.