Studbump Interconnects for High-power LED Assembly

High-power LEDs have penetrated high-volume consumer markets including automotive, signaling, LED television, backlighting and portable electronics. Some of these market segments are specifically demanding Pb-free solutions to meet various legal Pb-free initiatives, miniaturization of package components as well as SMT compatibility. In conventional LED packages, typical die-interconnection materials are solder/Ag-epoxy-based materials that cannot meet all of the above requirements. These interconnects also lead to high package thermal resistance, which limits the maximum allowable operating temperature of the LED. To accommodate the mandatory attributes of future high-power LED packages, Lumileds has pioneered the implementation of Au-Au interconnections (GGI) using studbumps for high-power LED assembly.

This paper presents two breakthrough LED packages that use studbumping technology in high-volume production - LUXEONŽ Flash and LUXEONŽ K2. LUXEONŽ Flash is the world's thinnest and lightest high-power LED package based on die-on-ceramic technology. Used in a cell-phone camera flash application, a single Luxeon Flash solution can generate up to 79 lux of light at one meter, compared to just 6-7 lux produced by conventional LEDs. LUXEONŽ K2, based on die-on-silicon technology, is the world's best LED light output with 140 or more lumens in white, highest maximum junction temperature at 185^oC, highest allowable drive current at 1500mA and lowest thermal resistance at 9^oC/W and industry's best moisture tolerance with a JEDEC level 2a rating. Both solutions offer simpler manufacturing through the use of surface mount technology, lead-free package and assembly capabilities.

Aspects of the studbump interconnects in high-volume manufacturing are discussed in this paper. Experimental results showing superior thermal performance and reliability under high temperature and high current density operation of the Au studbumps are also illustrated.