Imec, the renowned Belgian research center has demonstrated a new and cost-effective method of cooling chips at the package level. This technique is a good solution for today’s power-hungry high performance chips.

Powerful electronic systems have high cooling requirements for integrated semiconductor chips. Conventional solutions operate with various passive (or occasionally active) heat sinks, the bottleneck in the heat-transfer path occurs at the interface between the substrate and the heat sink. Direct cooling on the back of the chip is more efficient, but current microchannel solutions with direct cooling result in stress and a temperature gradient across the chip surface.

The ideal solution is to use an impingement-based cooler with coolant outlets distributed across the chip’s surface area. This arrangement directs the liquid perpendicular to the chip surface and ensures the liquid is at the same temperature throughout, reducing contact time between the coolant and the chip. Until now, cooling solutions based on this principle have the disadvantage that they are fabricated from silicon and are therefore very expensive. In some other alternative implementations, the nozzle diameter and necessary fabrication techniques are not compatible with chip packaging processes.
 
 
The principle of direct chip cooling. Source: Imec.
Imec has developed a low-cost novel impingement chip cooler made from polymer rather than silicon. The Imec chip cooler solution squirts the coolant through 0.3 mm diameter nozzles, which are produced using high-resolution stereolithography 3D printing. 3D printing allows the nozzle design to be adapted to the shape of the heat source and allows the creation of complex internal structures. In addition, this allows the efficient printing of the entire structure in one process, reducing production costs and time.
The new Imec chip cooler looks almost like a tiny 3D-printed shower head, which injects the coolant through an array of fine nozzles directly onto the bare chip surface. Improvements to the resolution achievable with 3D printing has now made the process suitable for the production of microfluidic systems such as chip coolers on this scale. The Imec cooler achieves a high cooling efficiency keeping the chip temperature rise to less than 15 °C for a power dissipation of 100 W / cm² and a coolant flow rate of 1 l / min. The performance is achieved with a coolant pressure drop of just 0.3 bar. This compares with conventional cooling solutions where a temperature rise of 20 to 50 °C can be expected at the thermal interface. As well as the improvements in cooling efficiency and low-cost the Imec cooling solution is also much smaller, since the heat exchanger is basically contained within the chip package outline.