High Power Led Package And Its Thermal Substrate

Thermal management is a key issue in the high-power LED package, which has great effect on the output power and lifetime of the device. Metal core printed circuit board(MCPCB), as one of decisive components to solve this problem, is attached great importance in the consideration for the structure and configuration of the LED devices. The reliability and stability, including electric-connecting, physical supporting, heat dissipating ability, the packaging process and the system cost, to a great extent dependents on MCPCB.Functions of several types of MCPCB have been analyzed in detail. From the angle of thermal management and coefficient of temperature expanding (CTE) matching of the packaging materials and the LED chip, two kind of MCPCB were introduced, advantages& disadvantages was investigated respectively, and finite element method (FEM) was adopted to evaluate the temperature distribution of LED package.1. AlN films with thickness of approximately 3μm were deposited by Magnetron sputtering System on 6061 Al substrates. Preferential orientation polycrystalline AlN films were discriminated by XRD and Spectroscopic Ellipsometry. Potential resistance testing showed that breakdown voltage of the AlN film resembles single crystal. The coating -substrate interfacial was investigated on a scratch tester, and the critical load was 6 Newton. Reason of strong adhesion was presented by SEM. The package model of LED was analyzed by FEM, and the internal thermal resistance, was less than 3 K/W.AlN/Al composite make easy to design the internal thermal passage, conducting the heat from the chip efficiently. The problems of this composite include low efficiency thus high cost, and adhesive limit of the AlN films was disbennifit to later package processes. 2. A special MCPCB fabricated by PEO (plasma electrolyte oxidation) is introduced, Excellent Mechanical performance, low cost, good electrical isolation, excellent thermal transfer and its convenience for later package processes is the great advantage. MAO-MCPCB substrate, the internal thermal resistance of the LED package based on which was less than 10 K/W, has a great promise in the future general lighting application. The higher is the thermal conductivity of the MAO coating, or the thinner is the MAO coating, the lower is the internal thermal resistance.The technical Parameter fabricating MAO coatings with thickness from 20μm to 40μm was optimized On the basis of a great deal of experiments, and 20μm±1μm (before grinding or finishing) polycrystalline MAO coatings was acquired, the thermal conductivity reached 2. 3 W K^-1m^-1. Aimed at the application for MCPCB, This paper attached great importance on the efficiency of the MAO-Process and microstructure of MAO coatings, such as uniformity, surface morphology and surface-micro-crack-distribution.MAO coating growth coexists with the dissolution; at the same time strength, sequence, and ubiety of the discharge has great effect on the uniformity and microstructure of MAO coatings. So the discharge characteristic(I) and quenching process of the micro-melting pool( II) was deeply investigated.(I)As to the uniformity of MAO Coatings and efficiency of MAO Process, assumption aboat breakdown was brought up. From microcosmic viewpoint, the Al₂O₃/Al interface was accidented. Because of skin effect, protuberant region is electric-charge-rich (electron-pool) region and concave region electric-charge-pool (electron-rich) region at the anode-positive-loaded half cycle. As like electric charge species repel and unlike attract each other, the distribution of positive electrical charge on the Al interface impact on the distribution of negative ion on the Al₂O₃/solution interface. The Electric Field on electric-charge-rich region was stronger than other region, so this position has more probability to breakdown. When the MAO Coating grow to even enough, and Electric Field was relatively equilibrium, the frequency of discharge events gradually die away.(II )The convection heat transfer coefficient on Al₂O₃ coating during microarc oxidation process was estimated by experiment and simulation. The Al₂O₃/Al interface was found to be a heat-transfer passage. During quenching, most heat of the micro-melting-pool was transferred through the Al substrate and the Al₂O₃ coating nearby. The micro-melting-pool was modeled by finite element method (FEM), and the process of quenching was characterized by the simulated temperature-time curves of the nodes along the depth, respectively. The effects of the quenching on the distribution ofα-Al₂O₃ and surface morphology of Al₂O₃ coating were discussed by comparing the relative cooling rate at different positions. The influence of pressure on the microstructure of MAO coating was also discussed briefly.