Thermal Characteristics of Phase Change Liquid Immersion Packaged SiC MOSFET under Overcurrent Conditions
Peng Cheng’ao1, Wang Zhiqiang1,2, Tang Lewen1
1. School of Electrical and Electronic Engineering Huazhong University of Science and Technology Wuhan 430074 China; 2. State Key Laboratory of Advanced Electromagnetic Technology Huazhong University of Science and Technology Wuhan 430074 China
Abstract：Silicon carbide (SiC) power devices are susceptible to critical thermal failure under transient overcurrent conditions. Conventional packaging, characterized by a top-down stacked heat dissipation path, is inadequate for managing the transient thermal shock and asymmetric heat source distribution inherent to SiC devices. This inadequacy frequently leads to excessively rapid local temperature increases, initiating detrimental electrothermal coupling positive feedback that accelerates thermal instability and device failure. This paper presents a packaging solution that integrates electrical insulation with thermal management, specifically designed to mitigate transient thermal shock in SiC MOSFETs. A novel packaging approach, termed phase change liquid immersion packaged SiC MOSFET (PCL-IM SiC MOSFET), is presented. This method replaces the traditional silicone encapsulation layer with a high-insulation phase change liquid, forming a dual-functional structure. The significant latent heat of the phase change liquid (>135 kJ/kg) is harnessed to establish an effective thermal buffering mechanism. To accurately simulate the associated thermal behavior, a dual-dimensional phase change modeling strategy based on the Cauer thermal network model is introduced. This strategy employs the equivalent thermal conductivity method for modeling heat transfer within the nucleate boiling zone and the equivalent heat capacity method for the high-temperature zone, overcoming limitations of traditional phase change interface tracking in simulations. Validation of the dual-dimensional modeling strategy shows high accuracy. The equivalent thermal conductivity method achieves prediction errors of less than 5.6% in the nucleate boiling zone (Δt<70℃. The equivalent heat capacity method yields errors below 4.0% in the high-temperature zone, demonstrating higher performance in this region. Experimental results confirm the efficacy of the PCL-IM packaging. Under 2.5 times overcurrent conditions (500 ms duration), the PCL-IM SiC MOSFET exhibits a junction temperature reduction of 27.36℃ compared to commercially packaged devices, equating to a temperature rise suppression rate of 24.78%. A junction temperature reduction of 40.15℃ is observed under 3 times overcurrent conditions. Testing over 50 cycles with varying overcurrent multiples reveals a junction temperature rise difference of less than 1℃ between the first and last cycles. A phase change liquid packaging design incorporating a threefold safety margin effectively maintains gas-liquid dynamic equilibrium throughout the cycling tests. The PCL-IM packaging technology significantly attenuates transient thermal shock in SiC MOSFETs, substantially reducing junction temperature rise under overcurrent conditions. The integrated phase change liquid provides robust thermal buffering through efficient absorption of latent heat. The proposed dual-dimensional phase change modeling strategy, comprising the equivalent thermal conductivity and equivalent heat capacity methods, provides a reliable and efficient framework for simulating complex phase change heat transfer. Stable performance over 50 testing cycles, supported by maintained gas-liquid dynamic balance, confirms the cycling reliability of the PCL-IM SiC MOSFET under extreme operating conditions. This packaging approach demonstrates a potential alternative for enhancing transient thermal management and reliability in power devices that are vulnerable to short-term, strong overcurrent.
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2026, Vol. 41 
