New technology for electrical/optical systems on module and board level: the EOCB approach

Besides the optical wide and local area networks (WAN and LAN) there is a growing request for short-distance solutions like in backplanes, boards, and modules. Optical interconnections within systems and packages transmit data rates up to some Gbit/s with low loss, crosstalk, EMV sensitivity or reflections. But here the fibers provide no satisfying assembling strategies. To find a more efficient solution, the Fraunhofer IZM has developed a packaging concept, which is based on a hybrid carrier containing both, electrical and optical interconnects: the EOCB (Electrical Optical Circuit Board). The key element is an additional optical layer with waveguide structures. This layer is handled by standard PCB technology. The result is, that waveguides are incorporated into the circuit board. For first tests we used the hot embossing process for foil structuring. After core filling and sealing it with an overcladding, the optical layer is given into the PCB process. But other solutions for the waveguide structuring are possible too. They are currently under development. The EOCB uses multimode waveguides to relax assembly tolerances. It has an interface to common SMD technology. Therefore the EOCB concept merges-with current methods of manufacturing equipment. Special optoelectronic components have been designed and fabricated to demonstrate the concept. First results will be presented on the integration of the future information medium "light" into the board.