PACKAGING OF POWER LEDS USING THERMOSONIC BONDING OF Au-Au INTERCONNECTS
Authors: Seck-Hoe Wong, Mooi Guan Ng, Mee-Lee Yong, Noorals Company: Philips Lumileds Lighting Company Date Published: 9/24/2006
Abstract: Packaging of power LEDs targeted for consumer electronics market segment must comply with various legal Pb-free initiatives along with continued miniaturization and SMT assembly compatibility. Many proposed lead-free solder alloys are worse thermal conductors than lead-based solders. One of the most promising techniques emerging from the lead-free quest is gold-gold interconnection (GGI), where gold stud bumps are thermosonically attached to gold pads of the substrate/package/die. Prior experimental results have shown that thermal performance of a GGI-based package is significantly improved (greater than 50% reduction of junction to case thermal resistance) compared to solder-based LED package. The high thermal conductivity of gold interconnects allow higher temperature operation than conventional LED packages. Most importantly, the maximum allowable junction temperature of an LED, which determines light output, is no longer limited by the device interconnects. This paper presents process overview, process optimization and process control aspects of thermosonic die-attach in a high volume manufacturing setting.
Keywords: Au stud bumping, thermosonic bonding, flipchip die-attach, surface mount LED package, LED packaging