We introduce GI-core multimode polymer optical waveguides as a promising component triggering the migration of optical interconnects from inter-racks to PCBs in high performance computers and servers. In particular, we spotlight "the Mosquito methoda" we developed for simultaneous fabrication and integration for the GI-core polymer waveguides on-board. For high density channel alignment, small-core waveguides are desirable so that single-mode waveguides are regarded as an ideal component. In this paper, we show the Mosquito method is capable of fabricating single-mode polymer waveguides. Furthermore, we focus on polymer waveguide circuits on PCBs in which horizontally and vertically (three-dimensionally) curved cores are aligned.