铝基板表面微弧氧化膜厚度对其导电导热性的影响

Effect of Oxide Film Thickness on Electrical and Thermal Conductivity of Micro-arc Oxidize Aluminium Substrates

目的对LED封装用铝基板表面进行微弧氧化处理,用以调控其界面的导电导热行为,并构建微弧氧化膜的厚度与其导电性及导热性之间的关联性。方法采用XRD表征了不同厚度微弧氧化膜的相结构,借助SEM观察了不同厚度膜层的表面微观形貌,利用高阻计测试了不同外加电压下膜层的电阻率,采用闪光法测定了不同温度下膜层的热扩散系数。结果微弧氧化膜主要由γ-Al_2O_3相组成,随膜层厚度的增加,膜层的相结构无显著变化,但其表面多孔结构出现了明显变化。膜层电阻率随膜厚的增大而升高,在膜厚从10μm增至40μm的过程中,电阻率增大了4~8倍。膜层电阻率随测试电压的升高而降低,当测试电压从50 V升至100 V时,电阻率降幅达1~2个数量级。膜层的热扩散系数随膜厚的增大出现波动,当膜厚为10~40μm时,热扩散系数的变化量为21.6~24.8 m^2/s。膜层热扩散系数随测试温度的升高而降低,降幅最高可达8.9 m^2/s。结论厚度为40μm的微弧氧化膜既具有高的电阻率(7.1×1012?·cm),又具有高的热扩散系数(98.0 m^2/s),有望满足LED铝基板的界面绝缘与散热要求。

The work aims to control interfacial electrical and thermal conductivity, and establish relevancy between thick- ness of micro-arc oxide film and its electrical and thermal conductivity by performing micro-arc oxidation to aluminum sub- strate for LED packaging use. Phase structure in micro-arc oxidation coatings of different thickness was characterized by XRD. Surface morphology of the coatings was observed using SEM. Electrical resistivity of the coatings was tested at different testing voltage with a high resistance meter. Thermal diffusivity of the coatings at different temperature was measured in laser flash method. The micro-arc oxidation coating was mainly composed of γ-Al2O3 phase. With the increase of coating thickness, phase structure of the coatings changed slightly while porous structure on surfaces of the coatings changed remarkably. Electrical re- sistivity of the coatings increased as the coating thickness increased. The resistivity increased by 4-8 times as the coating thick- ens ranged from 10 μm to 40 μm. The resistivity decreased as the testing voltage increased. The resistivity decreased by 1-2 or- ders of magnitude when the voltage ranged from 50 V to 100 V. Furthermore, fluctuation was present in the thermal diffusivity of micro-arc oxidation coatings as the coating thickness increased. Variation of the thermal diffusivity was 21.6-24.8 m^2/s at the coating thickness of 10-40 μm. The diffusivity might decreased （by up to 8.9 m^2/s） as the testing temperature increased. The 40 μm-thick micro-arc oxidation coating not only exhibits high electrical resistivity of 7.1 × 10^12 Ω· cm, but also high thermal dif- fusivity of 98.0 m^2/s, thus meeting the requirements of interfacial insulation and heat dissipation of LED aluminum substrate.