Al₂O₃ Film Fabricated Using Anodic Oxidation Method On Al Substrate For LED Packaging

LEDs are gradually replacing the traditional lighting, and the market demand for high-power LED increases. The traditional package technique and substrate reach to the bottleneck of heat dissipation, so the thermal diffusion of LED is mainly based on the heat sink through packaging substrate. The common substrates including MCPCB, DBC, and et al have some problems such as low-thermal conductivity, high-cost and technical limitation. This work focus on researching a new kind of packaging substrate based on aluminum anodic oxidation with high-insulation, high-thermal conductivity, and low-cost.The anodic oxidation films were prepared in sulfuric acid and oxalic acid solution. The influences of current density, concentration, treatment time, and distance between electrodes were studied. Results showed that when the Al substrate anodized in 0.8mol/L sulfuric acid solution for 40min, keeping electrode distance in 3.0cm and current density of 3.5A/dm2, the surface morphology of Al2O3 film was in uniform hole shape. In this case the average pore size is 22nm, pore density 40/200nm * 200nm, thickness 11μm.Flexible steel plate was used as the cathode, and highly-ordered Al2O3 thin film was also prepared. Aluminum oxide film had good insulating properties. The breakdown voltage was up to 2.4kV. The heat-dissipation performance was improved.To improve reflectivity of the Al2O3 film, TiO2 film was prepared using electrophoresis, screen printing, dipping and other methods. The reflectivity of the substrate was improved with the substrate insulation and thermal performance being maintained. It was beneficial for the LED package application.