Single-Phase and Evaporating Two-Phase Flow Microchannel Cooling of Power Modules for Temporary Overcurrent Operation

Evaporating two-phase flows are usually avoided in cooling applications due to the potential inception of flow instabilities, which result in worse cooling performance. However, the substantial latent heat of liquid evaporation presents a compelling source in power electronics cooling when temporary overcurrent is needed. In this study, we utilise water evaporation to enhance the cooling performance under temporary module overcurrent conditions, while the water remains in its liquid phase during nominal operation. The proof-of-concept is demonstrated for a Si IGBT/diode half-bridge module cooled with a microchannel array integrated below the direct bonded copper ceramic. The microchannel cooling solution is evaluated in terms of reduction in the junction-to-case thermal resistance and of an increase in the temporary overcurrent capability. The thermal resistance is extracted for different flow rates using Simcenter Micred Power Tester. Infrared and visible spectrum cameras are used to simultaneously record the junction temperature and the evaporating flow in the microchannel array. Flow regimes with parts of individual channels occupied by the flow of vapor have been observed in the overcurrent duration, resulting in heat transported downstream from the chip location, where liquid evaporates, to the outlet of the manifold. Results indicate that evaporation enhances the cooling performance for the tested conditions, with no signs of boiling crisis in the microchannel flow.