Improved thermal performance of high-power LED by using low-temperature sintered chip attachment

Abstract

Chip attachment is an important step in packaging light-emitting 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 epoxy-glued 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.