29 May 2018
Imec, the research and innovation hub based in Leuven, Belgium, has demonstrated for the first time a low-cost impingement-based solution for cooling chips at package level.
The announcement is being described as an important innovation in tackling the cooling demands of high-performance 3D chips and systems.
Conventional solutions cool through combining heat exchangers that are bonded to heat spreaders that are then attached to the back of the chip. These are all interconnected with thermal interface materials (TIM) that create a fixed thermal resistance that can’t be overcome by introducing more efficient cooling solutions. Direct cooling could be more efficient, but current direct cooling microchannel solutions create a temperature gradient across the chip surface.
According to imec the ideal chip cooler is an impingement-based cooler with distributed coolant outlets. It puts the cooling liquid in direct contact with the chip and sprays the liquid perpendicular to the chip surface. This ensures that all the liquid on the chip surface has the same temperature and reduces the contact time between coolant and chip.
Current impingement coolers, however, have the drawback that they are silicon-based and therefore expensive, or that their nozzle diameters and use processes are not compatible with the chip packaging process flow.
The new impingement chip cooler from imec, uses polymers instead of silicon, to achieve a cost-effective fabrication. The solution features nozzles of only 300µm, made by high-resolution stereolithography 3D printing. The use of 3D printing allows the customisation of the nozzle pattern design to match the heat map and the fabrication of complex internal structures. Moreover, 3D printing allows to efficiently print the whole structure in one part, reducing production cost and time.
“Our new impingement chip cooler is actually a 3D printed ‘showerhead’ that sprays the cooling liquid directly onto the bare chip,” clarifies Herman Oprins, senior engineer at imec. “3D prototyping has improved in resolution, making it available for realizing microfluidic systems such as our chip cooler. 3D printing enables an application-specific design, instead of using a standard design.”
Imec’s impingement cooler achieves a high cooling efficiency, with a chip temperature increase of less than 15°C per 100W/cm2 for a coolant flow rate of 1 l/min. Moreover, it features a pressure drop as low as 0.3 bar, thanks to the smart internal cooler design. It outperforms benchmark conventional cooling solutions in which the thermal interface materials alone already cause a 20-50°C temperature increase.
Next to its high efficiency and its cost-effective fabrication, imec’s cooling solution is much smaller compared to existing solutions, matching the footprint of the chip package enabling chip package reduction and more efficient cooling.