As well as enhancements in processing power and speed, the latest integrated chips have exhibited a commensurate rise in their operating temperatures. Current output levels of 50W/sq cm can be handled by heat sinks; but the anticipated rise to a circuit-melting 100W/sq cm needs a fresh approach, hence the recent surge of heat pipe research.
Thermal management is becoming a serious problem as size demands and packaging constraints set identical challenges as a greater number of more powerful chips are packed into smaller spaces. "Space, military and consumer applications are all bumping up against a thermal barrier," says Sandia National Laboratory's Mike Rightly, whose recently patented heat pipes offer light at the end of the tunnel for thermal management problems. His solution, a remarkably simple heat pipe technology, will transfer heat to edges of a computer where it can be dissipated using fins or a much smaller, quieter fan.
The simple, self powered mechanism uses finely etched lines, about as deep as a finger print, to wick methanol between several locations and an arbitrary end point. Using capillary action methanol wicks along the lines to the point of heat generation where it turns to vapour it then travels along the centre of the tube to a cooling point where it reverts back to liquid, expelling the heat and then wicks back to the point of heat generation. Woking by capillary action, it consists of a ring of copper which separates two copper plates. Sixty-micron tall curving, copper lines, slightly less thick than the diameter of a human hair, made with photolithographic techniques allow material wicking along the surface, defying gravity.
"An isotropic method (one that sends out heat in all directions) doesn't work because it only cools the first heat source; you need anisotropic capability to cool all sources of heat directionally," says Rightley. "We use laws of fluid mechanics to derive the optimum wick path to each heat source." The curvilinear guides can be patterned to go around holes drilled through the plate necessary to package it within the computer. The beauty of the design is that the heatpipes can move heat from point A to point B without any directional geometrical relation between the two points; meaning that the heat can be displaced to any location.
The technology is being licensed to a start up company "that has a very interested large customer in the (civilian) laptop market" says Rightley. "And no internal redesign of laptops is needed. The new design exactly duplicates in external form the heat transfer mechanism already in place in laptops, industry won't even see the difference." The military has also expressed an interest as it envisages wearable computers with the smallest possible cooling fans – powerful fans are electronically noisy and give away the location of the user. In colder climates, the heat could also be dumped into hand warmers rather than into fabric and the flesh beneath.
Sandia Labs
Pointers
The heat pipes can cater for the additional thermal problems created by more powerful ICs
The technology mirrors existing external thermal management methods so a redesign is not necessary
The does not have to be any geometrical relation between the heated point and the cooled point
