Thermal tech addresses power mgmt issues in IC packaging

Nextreme Inc. claims to have solved the overheating problem with modern flip-chips with its thermal copper pillar bumps. The technology embeds a thermoelectric cooler into each bump, which can either help cool chips, or can be used in reverse to generate energy from waste heat.

"Over the last decade, thermal power management has become one of the most important issues in semiconductor packaging," said Jeff Doubrava, managing partner of Prismark Partners LLC. "Nextreme's technology is addressing this problem, and we believe they are heading in the right direction."

Nextreme's thermal copper pillar technology studs the backside of flip-chips with solder bumps that not only make an electrical connection, but also help transfer heat out of the chip. The copper pillars are made thermally active by incorporating a proprietary nanoscale thermoelectric thin film into each bump. When current passes through the bumps, one end of the thermoelectrically active structure cools faster than the other, creating a thermal differential that cools chips faster.

The process also works in reverse?that is, temperature differentials can be harnessed to actually generate small amounts of energy for power scavenging applications. Nextreme claims that a temperature difference of 60?C can be generated across a 60?m-high pillar by running a current through it?enabling a maximum power-pumping capability of 150W/cm?, 10-times more than the 15W/cm? typical of flip-chips today. For power-generation applications, the same temperature differential can generate more than 3W/cm??about 10mW of power per bump.

"We want to change how thermal and power management are implemented in semiconductors," said Nextreme CEO Jesko von Windheim. "Our technology delivers both cooling and energy-harvesting functionality that can be designed into the standard flip-chip solder-bumping process."

Nextreme's proprietary thin film enables an embedded thermoelectric cooler (eTEC) to harness the Seebeck effect, whereby electricity is generated from a temperature differential, which induces a difference in the Fermi energy across the thermoelectric material, yielding a voltage potential that can drive a current.

The process is currently in GR-468 reliability testing and will be in pilot production by the end of 2007. Applications include microprocessors, display drivers, radio-frequency discretes, watch chips, smart cards and mixed-signal devices.

- R. Colin Johnson
EE Times