Parallel optical interconnect between ceramic BGA packages on FR4 board using embedded waveguides and passive optical alignments

We have studied technologies to design and fabricate high-bit-rate chip-to-chip optical interconnects on printed circuit boards (PCBs) using board-embedded polymer waveguides and surface-mounted component packages or modules. In order to demonstrate the developed technologies, a 4times10 Gb/s optical interconnect was completely integrated on a standard FR4 PCB. The optical link demonstrator consists of 4-channel BGA-mounted transmitter and receiver modules as well as of four parallel multimode optical waveguides fabricated on top of the solder mask of the PCB using lithographic patterning. The transmitters and receivers built on low-temperature co-fired ceramic (LTCC) substrates include 4times10 Gb/s flip-chip mounted VCSEL or photodiode array, wire-bonded driver and receiver ICs, and optical coupling structures. Two microlens arrays and a micro-mirror enable optical coupling between the optoelectronic devices and the waveguide array. The passive optical alignment was based on the marks and structures fabricated both in the LTCC process and in the patterning of the optical layers. The characterized optical alignment tolerances are in the limits of accuracy of the surface-mount technology. The demonstrated technology is suitable for interconnecting CBGA-packaged ICs or multi-chip-modules