Optoelectronic interconnections and packaging: A materials challenge

The need for increased speed and functionality by electronic components has pushed traditional electronic packages to the limit of their capabilities. Typically, the electronic device is electrically connected by wires or solder bumps in a package that gives the device environmental isolation and acts as a space transformer to transfer the electronic signals down leads to other discrete packaged devices on a printed circuit board. The discrete spacing of the devices and the time needed to propagate electronic signals along the wiring (that has a finite resistance and slows electron travel to a fraction of the speed of light) on the printed circuit board restricts the speed of the circuit. A promising solution is to use light, rather than electrons, to enhance signal transmission. The use of light, generated by lightemitting diodes (LEDs) or lasers, in these applications is called optoelectronic packaging. Applications in which optoelectronic packaging has had a significant impact include telecommunications (fiberoptic lines), optical reading devices (scanners), and supercomputers. The physics of transmitting signals via optics is well understood. However, there is a significant challenge in the area of interconnects. Interconnects are the interface between a transmission optics line and a device (Le., a laser or LED); they must be manufacturable and have excellent reliability. The difficulty with (and most expensive aspect of) optical interconnections is thatalignmentis critical. For multiple-mode optical interconnects, the alignment between the light source and the transmission line must be between 5 /lm and 10 /lm. In a singlemode interconnect, the alignment must be on the order of 1 /lm or less. The interconnects currently used for traditional electronic packages have nowhere near this requirement of alignment, being in the range of 50 to 100 /lm. Furthermore, accurate optical alignments represent up to 80 percent of the cost of the entire package. Therefore,innovativeapproaches to the materials used in optoelectronic packages-and their processing-are needed to enhance reliabil