System design and characterisation of integrated liquid cooling solutions for 3D-stacked modules.
Tan, Siow Pin.
Date of Issue2009
School of Mechanical and Aerospace Engineering
INSTITUTE OF MICROELECTRONICS, DARPA
Heat densities for electronic packages are increasing as the demand for many functionalities on a single package had resulted in single chip modules being stacked vertically to increase the amount of transistors that can be put on a given footprint. In this study, a liquid cooling solution is proposed to remove the heat from a stacked package with two modules each dissipating 100 W/cm2. A first order estimate of the thermal resistance using thermal network modeling showed that the resistance across the solderjoints (interconnects) and the microchannel heat sink are of equal magnitude and hence focus is placed on minimising these two resistances. In a closed loop system design, when an external heat exchanger is included, the thermal resistance across it also becomes critical. A compact modeling approach is used to replace the interconnect layer with an effective material conductivity obtained from detailed modelling of a solderball considering the spreading/constriction effects. For the microchannel heat sink, a dual inlet/outlet configuration had been shown to have significant advantages over a single inlet/outlet. Flow distribution in the microchannel heat sink had been demonstrated to have a significant impact on its thermal performance. Plenum designs are used to influence the flow distribution within the microchannels to achieve lower temperature gradients and better thermal performance. The thermal performance of the carrier with a dual inlet/outlet with a reducing plenum had been shown numerically to have a thermal resistance of 0.15 ºC/W at the design flowrate of 230 ml/min. Temperature variation on the die is also less than at 7°C. The pressure drop from inlet to outlet is also relatively low at 326.3 mbar.