Search

We developed a hybrid single- and two-phase capillary-based microcooler consisting of parallel microchannels with hydrophilic wicks for power electronics. The presented approach overcomes the conventional pumped-only flow two-phase cooling limitations, such as flow instabilities and large temperature superheat in confined microchannels. We further conducted a parametric study of the microcooler and investigated the boiling dynamics of capillary flow using high-speed imaging. While the proof-of-concept microcooler is demonstrated on a copper substrate and free-form liquid supply setup, it can be easily implemented in the copper layer of a direct bonded copper (DBC) substrate of the power module package. The capillary-driven microchannel cooler demonstrates a significant performance improvement compared to conventional single/two-phase closed-microchannel coolers, achieving maximum heat flux ~700 W/cm2, superheat ~30 °C, and the target two-phase thermal resistance ~0.043 cm $^{2}\cdot ^{\circ }\text{C}$ /W. The capillary-based microcooler achieves vapor quality > 0.9, utilizing $50\times $ smaller flowrates compared to two/single-phase conventional microchannel coolers. Successful implementation of the capillary-driven microcooler would result in significant downsizing of the cooling system for electric vehicles.

A microchannel heat sink integrated with a three-dimensional manifold using direct bonded copper (DBC) is promising for high power density electronics due to the combination of low thermal resistance and reduced pressure drop. However, this requires much progress on the fabrication and high-quality point-contact bonding processes of the microchannel substrate and three-dimensional manifold DBCs. In this study, we have developed processing techniques for surface preparations and high-quality point-contact solder bonding between the two DBC substrates. We utilized chemical polishing followed by electroless plating to prevent excess solder from blocking the microchannels. We performed a parametric study to investigate the impact of bonding time and surface roughness on the tensile strength of the bonding interface. The bonding strength increased from 1.8 MPa to 2.3 MPa as the bonding time increased from 10 to 30 min while reducing the surface roughness from Rz = 0.21 to 0.05 μm, resulting in increasing the bonding strength from 0.16 MPa to 2.07 MPa. We successfully tested the microcooler up to the inlet pressure of 70 kPa and pressure drop of 30 kPa, which translates to the tensile strength at the bonding point contacts, which remains well below the 2.30 MPa. We achieved the junction-to-coolant thermal resistance of 0.2 cm2 K/W at chip heat flux of 590 W/cm2. Thus, our study provides an important proof-of-concept demonstration toward enabling high power density modules for power conversion applications.

Better thermal management is a key enabler of higher power density in traction inverter power modules. For the first time, we successfully fabricated and tested a microchannel with a three-dimensional (3D) manifold cooler (MMC) using aluminum nitride (AlN)-based directed bonded copper (DBC) substrates. The microchannels (width ∼300 μm and height ∼450 μm) and 3D manifold fluidic passages (width ∼300 μm and height ∼600 μm) were fabricated in two DBC substrates using the femtosecond laser and subsequently bonded using transition liquid phase (TLP) bonding. In this study, the hydraulic and thermal performance of the 3D MMC is measured and validated with numerical simulation. The proposed 3D MMC is capable of removing heat at 600 W/cm2 with a 10 kPa pressured drop at the thermal thermal resistance of 0.2 cm2 K/W. The optimized designs via geometric and layout rearrangement were conducted, which indicates the pressure drop can be further reduced by 10× while maintaining the same thermal performance.

Silicon-based embedded microchannel with three-dimensional (3D) manifold (MF) μ-cooler offers lower pressure drop and increased heat removal capability (>1 kW/cm2) for microprocessors and power electronics cooling using single-phase water. In this paper, we present a thermal–fluidic numerical analysis of silicon-embedded microchannel cooling. We develop a full-scale computational fluid dynamics (CFD) model of a large footprint (24 × 24 mm2) device having embedded microchannels and a 3D manifold. It is found that the pressure/velocity distributions at three different critical regions inside the inlet manifold have a significant impact on the temperature distribution. A previous study reported a shift of the chip temperature hot-spot at high flow rates; this study delves deep into the flow and pressure variations within the MF and cold plate (CP) that leads to this shift. This study also investigates the degree of flow maldistribution, first between the manifold channels caused by the plenum and then between the cold plate channels caused by individual MF channels. Finally, this study concludes with a comparison between two different 3D manifold inlet channel heights. The comparison reveals that the manifold with 1.5 mm thickness can reduce the pressure drop by a factor of 4 while maintaining the same thermal resistance of 0.04 K cm2/W, thus indicating an increase in the coefficient of performance (COP) by a factor of 4, compared with a manifold thickness of 0.7 mm.