Chip attachment is an important step in packaging lightemitting diode (LED) chips. The attachment material provides mechanical support and heat dissipation. As high-power LED chips are targeted at general illumination applications, the thermal property of the die-attach material is critical to the light output and degradation of the lighting device. Silver epoxy, lead-free solder paste, and nanosilver paste, were evaluated as the attachment material for LED chips. The interconnected chips were tested at current-density levels up to 3×102A/cm2. We found that at high levels of current density, the chips that attached using the nanosilver paste had a significantly higher light output than the lead-free soldered chips, which in turn had a higher light output than the epoxyglued chips. This can be explained by the higher thermal conductivity of the sintered silver than that of solder and epoxy. Higher thermal conductivity of the attachment material results in a lower junction temperature at a given level of current density, thus causing a higher light output. Our results suggest that LED performance can be significantly improved with a die-attached nanosilver paste.
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