Assembly and alignment of Proximity Communication enabled multi-chip packages using elastomeric bump interposers

A MCM enabled by Proximity Communication (P×C) includes a two-dimensional array of facing chips, including island chips and bridge chips that communicate with each other using P×C I/Os placed in the overlapping regions. In order to maintain the relative vertical spacing of these P×C I/O pads as well as to allow Ball-in-Pit self-alignment technology to work, elastomeric bump interposers are placed in cavities in a substrate, which house the bridge chips, to provide a compressive force on the back surfaces of the bridge chips. These interposers contain compressible structures which are precisely placed to make sure that sufficient and symmetric amount of force is applied to the bridge chip to ensure that facing surfaces of the island chips and the bridge chips, as well as connectors on these surfaces, are held securely and reliably and are approximately coplanar without bending the bridge chips. At the same time, the interposer must also allow the bridge chip to be lowered sufficiently to disengage the ball-pit sites during the reflow process of the island chips. In this paper, the design and fabrication of such compliant mechanical interposers are discussed.