Preparation and Packaging Performance of Chip on Board Ceramic Substrate for High-power LED
|School||Nanjing University of Aeronautics and Astronautics|
|Keywords||High-Power LED Thick Film Process COB (Chip On Board) Package CeramicSubstrate Package Structure Thermal Resistance|
In this paper, on the basis of COB package structure and substrate for the high-power LED, thethick film process which without a glass phase Cu slurry system of reactive bonded method was used.The metallization of ceramic substrate was realized though sintering and reduction heat treatment, andthe densification process was also tried. On the basis of thick film technique, the screen was designedby the existing LED substrate graphic, and prepared by screen printing process. The electroplatingfixture was designed to dense the circuit graphics which was prepared by thick film technique.Then,the high performance ceramic substrate for COB package was prepared. The package structure wasimproved which use solder replace the thermal plastic, and then self-made COB ceramic substratewas packaged. The phase composition and morphology of samples were analysised by X-raydiffraction (XRD) and scanning electron microscopy (SEM).The mechanical and electrical propertieswere tested and analysised, and the optimization of substrate preparation process was made. ANSYSthermal simulation was used to forecast heat dissipation performance of the improved packagestructure. The thermal performance of the COB ceramic substrate using new structure was also testedand evaluated.The results show:1) The Cu slurry had good rheological properties, which viscosity can becontrolled at100~300Pa·s, and the thickness was also controlled according viscosity regulation.2)The thick film Cu layer can be prepared upon sintering and reduction heat treatment.The optimumsubstrate surface was obtained by sintering at1050℃and reducting heat treatment at900℃. Thequality of surface Cu layer was further improved by bright plating copper process.3) After design andscreen printing circuit graphics, the best COB ceramic substrate was obtained under the conditionsthat the mass of coated slurry was0.08g, sintering temperature was1050℃, reducting temperaturewas900℃, which bonding strength was94N, and the surface sheet resistance was2.78m/□.4) Thesurface sheet resistance of COB substrate can further reduce that use the bright plating copper processbase on the designed electroplating fixture.When the current is0.3A, it only was0.9m/□.5)According to simulation analysis, the improved package structure can enhance the heat dissipation ofthe substrate. Thermal resistance fell to28.33K/W from50.69K/W.6) The package of COB ceramicsubstrate use welding method, its interface was dense without hole defects. The peel strength was8.66N/cm, and wasn’t failed after500thermal shock. The COB substrate with improved package wasapplied to LED systems, it was found that thermal resistance was only33.5K/W. The trend was consistent with simulation results.