Microchannel Design Study for 3D Microelectronics Cooling Using a Hybrid Analytical and Finite Element Method

For microelectronics cooling, microchannels are a potential solution to ensure reliability without sacrificing compactness, as they require relatively small space to remove high heat fluxes compared to air cooling. However, designing microchannels is a complex task where simulation models become a forefront tool to investigate and propose new solutions to increase the chip thermal performances with minimal impact on other aspects. This work evaluates numerically the impact of microchannel cooling in a standalone chip and a 3D assembly of two stacked chips with localized heat sources. To do so, a modeling approach was developed to combine finite element modeling of conduction in the chip using commercial software with analytical relations to capture the heat transfer and fluid flow in the microchannels. This approach leverages the multiphysics and post-processing capabilities of commercial software, but avoids the extensive discretization that would normally be required in microchannels with full finite element modeling. The study shows that increasing the flow rate is not as beneficial as increasing the number of channels (with constant total cross-section area). The effect of heat spreading was also found to be critical, favoring thicker dies. When switching to 3D chip configuration, the interdie underfill layer significantly increases the total thermal resistance and must be considered for thermal design. This effect can be significantly alleviated by increasing the interdie thermal conductivity through adding copper micropillars.

Suppression of Thermocapillary Effect in Evaporating Thin Film of Micro Heat Pipes

This paper presents a theoretical study on the flow mechanism of different types of working fluids incorporated with Marangoni effect in a microelectronics cooling device. It is known that surface tension gradient effect or thermocapillary effect can be induced by temperature gradient which leads to the thermocapillary flow. By adding a small quantity of alcohol into the pure working fluid, the characteristics of surface tension can be altered without changing other thermo physical properties of the working fluid. A theoretical model is employed to focus on the suppression of thermocapillary effect in evaporating thin liquid film. The study reveals the fluid flow mechanism of a working fluid can be altered with thermocapillary effect. Thermal performance of microelectronics cooling devices can also be enhanced by utilizing aqueous solution as the working fluid.