MCM LGA Package with Optical I/O Passively Aligned to Dual Layer Polymer Waveguides in PCB

Over the past 30 years, IBM has provided leadership in high density wiring and high I/O density and I/O count packaging as has been necessary for the high end symmetrical multiple processor (SMP) chips in servers. For example, IBM introduced the multi-chip modules (MCMs) in the 1970s, thermal conduction modules (TCMs) in the 1980s and 1990s, and advanced organic micro-via buildup-layer technology in the 1990s and 2000s [11]. Typical multi-chip modules are necessary to provide the significant increases in bandwidth between chips on the module, compared to the alternative route of lower bandwidth resulting from chip-tochip bandwidth going through the printed circuit board (PCB) for single chip modules. This results from CMOS chip-topackage pad scaling outpacing the package-to-printed circuit board (PCB) pad scaling. For example, today’s mainstream IC–to-package C4 bonding uses 4 mil (thousands of an inch) square pads on 8 mil pitch, with 3-on-6 ramping up, while the package-to-PCB ball- or land grid array (BGA or LGA) pitch uses 1-mm pitch, an areal density as much as 64 times higher. However, even with the larger bandwidth advantage of MCMs, more complex chips such as multi-processor cores and higher bandwidth cache will require a relatively larger number of signal I/Os, as well as more power and ground I/Os. Faster I/O clocks will further exacerbate the need for more package I/O by forcing the transition from previous single ended I/Os to differential signal I/Os to satisfy the higher frequency bit error rate specifications on SMP busses. Our goal is to alleviate the I/O bottleneck at the packaging level in the most cost effective manner, while providing the lowest risk, most flexible development package. To this end, we will present our work on an electrical LGA field replaceable package with optical components. These optical components enable larger I/O bandwidth density between the MCM and PCB than does the electrical I/O bandwidth density.

By: F. R. Libsch; R. Budd; P. Chiniwalla, P. C. D. Hobbs; M. Mastro; J. L. Sanford; J. Xu

Published in: RC23904 in 2006


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