UC Irvine

With the development of modern semiconductor technology, the power density of electronic devices continuously increases, and the performance of electronic devices is now governed by heat dissipation from the heat source to the heat sink, which requires new efficient thermal management solutions. Recent advancements in microfabrication techniques enable the employment of micro- and nanomaterials for next-generation thermal management systems to improve heat transfer efficiency between the device junctions at various length scales. This doctoral research focuses on the application of three-dimensional porous matrix in single- and two-phase thermal management solutions. Thermal interface materials are essential for thermal management in electronics packaging by providing a low resistance thermal pathway between heat sources and heat sinks. Nanostructured materials can be potential candidates for the next-generation interface materials by coupling their high thermal conductivity and mechanical compliances. This research investigates the thermal and mechanical characteristics of a new type of thermal interface materials, consisting of metal/elastomer interpenetrating phase composites. The three-dimensional, highly porous copper scaffolds are fabricated via a fast and simple in situ bubble-templated electrodeposition process without solid templates; subsequently, the void fraction of the composite is filled by elastomer infiltration. The presence of elastomer matrix contributes substantially to the mechanical properties, providing the structural flexibility required. Thermal characteristics are measured upon multiple thermal cycles, confirming the thermal and mechanical stability of the composite. Boiling heat transfer has been a popular topic for decades because of the ability to remove a significant amount of thermal energy while maintaining a low wall superheat during the liquid phase change. New types of heterogeneous boiling surfaces are introduced by integrating vertical gradient micropores on macroscale fins. The gradient morphology and corresponding gradient wettability simultaneously enable bubble nucleation on the top pores and capillary wicking through the bottom pores. With these unique wetting characteristics, the gradient pores installed on the bottom of the copper fin demonstrate the most significant boiling enhancement in critical heat flux and heat transfer coefficients, and this enhancement can be attributed to the microflow-enhanced nature of bubble departures around the fins while isolating bubble nucleation and liquid supply through gradient pores. The results provide fundamental insights into boiling mechanisms using porous media and the potential for future work that can optimize the design of multi-dimensional heterogeneous surfaces to engineer flow patterns and boiling mechanisms accordingly. Finally, the boiling performance are tested with ethanol as working fluid, and the lower latent heat results in limited critical heat flux and heat transfer coefficient. However, the surface temperatures are measured to be 10-20°C lower than those with water under the same dissipated heat flux due to the reduced boiling point of ethanol. Three-dimensional porous structures have been widely utilized in numerous applications as porous structures can offer the unique combination of thermal and structural properties. While various porous structures can be fabricated through templated-electrodeposition methods by employing sacrificial structures, the approach using bubbles as sacrificial templates provides quasi-random porous structures in a rapid and synchronized fashion. The growth mechanisms of bubble-templated porous copper depend on the intrinsic nature of dynamic and everchanging bubbles as well as the combination of surface profiles and deposition time. We reveal the evolution from surface- to bubble dynamics-governing growth mechanisms by quantifying quasi-random characteristics of biporous copper through their electron microscopic images and spectral density functions. This dissertation demonstrates the utilization of a three-dimensional porous matrix in single- and two-phase thermal management solutions. The three-dimensional porous copper with inserted elastomer suggests a unique combination of different property sets depending on their structural information, which can be applied for packaging applications. The use of heterogeneous porous copper also improves boiling performances by engineering bubble nucleation mechanisms and flow-enhanced convection. The optimal morphology of porous media is further discussed and demonstrated by understanding the evolution mechanisms of quasi-random structures through the template-free electrodeposition method. The systematical study can provide guidance for the design of rational porous media for single- and two-phase thermal management systems.