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Active Demonstration of a Passively Self-Aligned, Multi-Chip Package using Proximity Communication in a Switching Fabric
Keywords: passive self alignment chips, Si micromaching in CMOS, Capacitive Proximity Interconnects
Recently, we introduced a novel chip packaging platform based on the passive self- alignment of chips into 2D arrays, which extends fully integrated CMOS silicon beyond the single chip reticle [1]. We report the first active demonstration of this packaging concept, in which functional chips are configured in a face-to-face geometry with sufficient alignment accuracy to enable Proximity Communication (PxC): chip-to-chip capacitively coupled communication between overlapping metal pads [2]. Contemporary chip to chip PxC has been demonstrated on an optical bench using mechanical nano-precision stages with on-chip electronic feedback to overcome six degrees of chip misalignment and to position chips precisely for high fidelity PxC signaling. The key advance reported here is a low-cost packaging application of self-aligning precision micro-spheres and etched pits in CMOS for successful PxC signaling. Creating these pyramidal wafer pits required co-integrating silicon micromachining into a 180 nm CMOS technology. In this paper we report on our multichip package, the fabrication of alignment mechanism, global positioning metrology measurements and validation of PxC signaling in a package by BER measurements. Our demonstration vehicle is an active switching fabric consisting of a four chip linear vector array [3]. Atop these four face-up “island” chips sit face-down “bridge” chips, such that data can be coupled between four islands via overlapping bridges. Inverse pyramidal pits on both bridge and island chips are photolithographically defined relative to the capacitive micropads. When the appropriate diameter microspheres are deployed in the pits, the bridges precisely align to their facing islands. This assembly has relaxed manufacturing tolerances: up to half the microsphere diameter in placement inaccuracy still leads to precise self-alignment to within a couple of microns. In our demonstration 300 micron diameter microspheres precisely lock the chips in global alignment to within a micron and PxC signaling is achieved across array without error. 1. Cunningham, et al., “Optical Proximity Communication in Packaged SiPhotonics,” International Conference on Group IV Photonics, September, 2008. 2. Drost, et al.,
John E Cunningham, Distinguished Engineer
SUN Microsystems
San Diego, CA

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