A new technique for fabricating liquid cooling channels onto the backs of high-performance integrated circuits (ICs) that allows for denser packaging of chips, better temperature control and more reliability was developed by the Georgia Institute of Technology. The wafer-level fabrication technique includes polymer pipes that will allow electronic and cooling interconnections to be made simultaneously using an automated manufacturing process. The new technology was introduced at the IEEE International Interconnect Conference in San Francisco.

The low-temperature technique is compatible with conventional microelectronics manufacturing processing, allowing fabrication of the microfluidic cooling channels without damage to ICs.

“This scheme offers a simple, compact solution to transfer cooling liquid directly into a gigascale integrated (GSI) chip and is fully compatible with conventional flip-chip packaging,” said Bing Dang, a graduate research assistant in the university's school of electrical and computer engineering. “By integrating the cooling microchannels directly into the chip, we can eliminate a lot of the thermal-interface issues that are of great concern.”

Conventional cooling techniques, which depend on heat sinks on the backs of ICs to transfer heat into streams of forced air, will be unable to meet the needs of future power-hungry devices - especially 3-D multichip modules that will pack more processing power into less space.

High temperatures can cause early failure of the devices due to electromigration. By controlling average operating temperature and cooling hot-spots, liquid cooling can enhance reliability of the ICs, Dang noted. Lower operating temperatures also mean a smaller thermal-excursion between silicon and low-cost organic package substrates that expand at different rates.

In addition to the cooling channels, the researchers have also built through-chip holes and polymer pipes that would allow the on-chip cooling system to be connected to embedded fluidic channels built into a printed wiring board.

The system would use buffered, deionized water as its coolant. Self-contained cooling systems would circulate coolant using a centimeter-size micropump, while more complex equipment could use a centralized circulation system. The researchers have so far demonstrated that the microchannels can withstand pressure of more than 35 psi.

Calculations show that the system, which can have either straight-line or serpentine microchannel configurations, should be able to cool 100 W/cm2. Heat-removal capacity depends on the flow rate of the coolant and its pressure, with smaller diameter microchannels more efficient at heat transfer.