A cleaner path to cool chips

Phase-change materials help heat sinks do their job, without thermal grease. Chomerics, a division of Parker Hannifin Corp. PCMs bond to microprocessors, cache chips, relays, and rectifiers in desktop and laptop computers, telecom, networking, and industrial gear. PCMs are also used in dc/dc converters and other power-module components. Outdoor telephone equipment housings use PCMs to control thermal loads from solar heating and daytime peak usage. Aluminum foilbacked phase change pads preapplied to laptop cooling modules. The metal foil allows easy heat sink removal for PCB access. Solid PCM films boost thermal conductivity by filling asparities and flatness mismatch between parts. PCMs can let metal surfaces touch one another and therefore don't provide electrical isolation. Ever faster microprocessors run hotter while the packages surrounding them continue to shrink. Little room remains for heat sinks, spreaders, or cooling fans. That's why electronics packaging these days often focuses on controlling component temperature. In particular, attention is on interfaces where hot components join cooling hardware. An example is the space between the top surface of a Pentium III package and the bottom surface of an attached heat sink. No matter how tightly the heat sink screws onto the processor, heat will not flow efficiently without a thermally conductive material sandwiched between. This is because tiny air gaps remain between the mating surfaces and air is a poor thermal conductor. One scheme fills these gaps with a highly thermally conductive material such as thermal grease, which is effective but messy. Elastomer-based thermal pads are another, cleaner option. They consist of a binder such as silicone filled with fine particles of heat-conducting ceramic. Elastomer pads work for many applications, though thermal greases are still needed to cool more powerful, hotter processors. Another option is thermally conductive adhesive tape. Tapes can eliminate mechanical mounting hardware but, like elastomer