Research on Properties of Liquid Crystalline Epoxy for High-Voltage and Large-Power IGBT (Part 1 ): Thermal Conductivity and Heat Resistance Performance
Wang Zhengdong, Cao Xiaolong, Yang Ganqiu, Luo Meng, Zhou Yuanhang
School of Mechanical and Electrical Engineering Xi' an University of Architecture and Technology Xi' an 710055 China
Abstract：With the increasingly widespread application of high-voltage and large-power insulated gate bipolar transistors (IGBT) and the increasingly complex application environment, stricter requirements have been put forward for its insulation packaging materials. The thermal conductivity and electrical insulation properties of traditional epoxy resins and silicone materials currently used in IGBT are difficult to meet the requirements of future power devices, and there is an urgent need to develop a new type of encapsulation material with high thermal conductivity, outstanding thermal resistance and electrical insulation properties. This study attempts to simultaneously enhance the electrical insulating and thermal properties of materials by constructing ordered self-assembly liquid crystalline domains in epoxy materials. The influence of liquid crystalline domains on material properties was studied by blending liquid crystalline epoxy with traditional epoxy. A biphenyl epoxy and liquid crystalline curing agent were innovatively proposed to prepare a novel highly ordered liquid crystalline epoxy (named TMB-5+) based on dual crystalline units. Because of the length limitation of research article in this journal, our work referring to electrical insulating and thermal properties will be reported via two papers. The current first paper mainly investigates the related heat resistance and thermal conductivity properties of the prepared liquid crystalline epoxy. The ordered structures formed by the π-π stacking of biphenyl liquid crystalline units result in a typical spherical liquid crystalline morphology in the epoxy film. As the content of biphenyl epoxy increases, the quantity of liquid crystalline domains also increases. The highly ordered liquid crystalline domains and numerous rigid structures inside the material can theoretically achieve a synergistic improvement in thermal conductivity and heat resistance. Firstly, the heat resistance of liquid crystalline epoxy films was studied. The study found that the TMB-5+ sample exhibited a ultrahigh glass transition temperature (Tg), reaching 247℃, which was 76.4% higher than that of traditional epoxy. By molecular dynamics simulation, the theoretical Tg of the novel liquid crystalline epoxy can reach (310±20)℃, and high Tg allows the material to maintain stable physical and chemical properties at high temperatures. Based on the mean square displacement (MSD) simulation, it was found that the motion ability of molecular chain segments in the liquid crystalline epoxy cross-linking model is relatively weaker, indicating stronger thermal stability of the material. Secondly, thermal conductivity of the liquid crystalline epoxy film was studied, and the new epoxy with dual liquid crystalline units showed an improved thermal conductivity of 0.351 W/(m·K), which was 64.0% bigger than taht of traditional bisphenol A epoxy resin. At the same time, the liquid crystalline epoxy showed an improved thermal conductivity at high temperatures. The highly ordered orientation structure in liquid crystalline polymers becomes an effective pathway for phonon conduction, where phonon scattering hardly occurs. In addition, the thermal conductivity of the liquid crystalline epoxy crosslinking model was simulated using the resistance to disturbance non-equilibrium molecular dynamics (RNEMD) method, and the simulated values were consistent with the experimental results.
王争东, 曹晓龙, 杨淦秋, 罗盟, 周远航. 高压大功率IGBT用液晶环氧性能研究（一）：热导率与耐热特性[J]. 电工技术学报, 2025, 40(1): 273-284.
Wang Zhengdong, Cao Xiaolong, Yang Ganqiu, Luo Meng, Zhou Yuanhang. Research on Properties of Liquid Crystalline Epoxy for High-Voltage and Large-Power IGBT (Part 1 ): Thermal Conductivity and Heat Resistance Performance. Transactions of China Electrotechnical Society, 2025, 40(1): 273-284.
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