Phase change materials (PCMs) are an attractive alternative to thermal greasedpads. While their thermal conductivity is not as good as greases, they are more manufacturable. This paper reports on evaluation of PCMs for high power electronic applications. Conductivity measurements were carried out for several OEM PCMs. In addition experiments were carried out to determine process parameters (to attain target thermal impedance). A few candidates were then evaluated in a single chip module, under different environmental stresses and the results are presented here. The design concept was then extended to an MCM test vehicle and two candidate PCMs were evaluated. Differences in the reliability performance between SCM and MCM form factor are explained. 50-60 ParaffinWaX

In 2001, IBM delivered to the marketplace a high-performance UNIX ® -class eServer based on a four-chip multichip module (MCM) code named Regatta. This MCM supports four POWER4 chips, each with 170 million transistors, which utilize the IBM advanced copper back-end interconnect technology. Each chip is attached to the MCM through 7018 flip-chip solder connections. The MCM, fabricated using the IBM high-performance glass-ceramic technology, features 1.7 million internal copper vias and high-density topsurface contact pad arrays with 100-m pads on 200-m centers. Interconnections between chips on the MCM and interconnections to the board for power distribution and MCM-to-MCM communication are provided by 190 meters of co-sintered copper wiring. Additionally, the 5100 off-module connections on the bottom side of the MCM are fabricated at a 1-mm pitch and connected to the board through the use of a novel land grid array technology, thus enabling a compact 85-mm ؋ 85-mm module footprint that enables 8-to 32-way systems with processors operating at 1.1 GHz or 1.3 GHz. The MCM also incorporates advanced thermal solutions that enable 156 W of cooling per chip. This paper presents a detailed overview of the fabrication, assembly, testing, and reliability qualification of this advanced MCM technology.

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