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Improvement of High-Power LED Performance with a Novel Thermal Interface Material
Keywords: LED packaging, sintered nanoscale silver attachment, thermal management
High-power (HP), high-brightness (HB) light-emitting diodes are progressively making their way into the general illumination applications. Now, interconnection and packaging of the LED chips are being recognized as potential barriers for the advancement of LED lamps. Chip attachment is usually the first and important step in packaging LED lamps. The attachment material provides mechanical support, heat dissipation, and current flow for vertically conducting diodes. Since LED light output decreases rapidly with increasing chip temperature and the lamp degrades faster at high temperature, thermal performance of the chip attachment is critically important to performance and reliability of the lamps. In this study, we tested three different die-attach materials with their corresponding processes: silver epoxy processed by curing; lead-free solder by solder-reflow; and nanosilver paste by low-temperature sintering. The attached chips were tested at varying current density up to 3A/mm2. We found that the chips attached using the nanoscale silver paste had a significantly higher light output than the lead-free soldered chips, which in turn had higher light output than the epoxied chips. This is explained by the higher thermal conductivity of the sintered silver than those of the solder and epoxy. Higher thermal conductivity of the sintered silver attachment resulted in a lower junction temperature at a given level of current density, thus higher light output.
Dr. Guo-Quan Lu, Student
Virginia Polytechnic Institute and State University
Blacksburg, VA

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