A high-power light-emitting diode (LED) is commonly defined as an LED package that operates at one watt of power or higher. LEDs are semiconductor-based diodes that emit light when a forward voltage is applied. This allows for the production of a lot of light from a small form factor while maintaining excellent efficiency, thus allowing a single LED to pump out hundreds, or even thousands, of lumens. High-power LEDs have the ability to provide much higher levels of light than traditional LEDs. They also provide higher levels of performance which lead to a longer lifetime of the device, but the trade-off is that a large amount of heat is generated—and in a small localized area. Since the temperature per unit is so high with high-power LEDs, a high-melting and high-reliability solder is required for assembly. Also critical to the LED assembly process is a void-free solder interface between the diode and its substrate. This provides the thermal and electrical connections needed to generate a stable transmission of light, and allows for efficient heat transfer to maintain the temperature stability of the device.
While there is a high upfront cost of investing in luminaires that use high-power LEDs as the light source, the optical power, lumen maintenance, and reliability of high-power LEDs often translate to a return on investment that is significantly higher than that of using mid-power LEDs. In fact, higher operating temperatures and the compact footprint of high-power ceramic packages enable a heat-sink design that is reduced in size and offer tremendous savings in PCB, TIR reflectors, and diffuser optics, which account for a large portion of the BOM cost for systems using mid-power LEDs.
The high-power LED market thrives on the widening application base of LEDs, specifically in the automobile industry, and due to the increasing number of government initiatives that promote energy conservation and efficiency. Other factors that contribute to their desired use include small size; long-life and continuous usage; less power consumption and low voltage; and increasing high brightness applications. High-power LEDs, especially those used for automotive headlamps, tend to use AuSn solder paste as a solder material due to its high-melting temperature and reliability in high-volume production. Indium Corporation has developed specially formulated AuSn solder pastes—AuLTRA™ 3.2 and AuLTRA™ 5.1—ideal for higher processing temperatures and assembly needs required for use in high-power LED module array applications. Available in both a water-soluble option (AuLTRA™ 3.2) and a no-clean formulation (AuLTRA™ 5.1), these AuSn solder pastes offer consistent printing and reflow, in addition to exceptional wetting and low-voiding. AuLTRA™ 3.2 and AuLTRA™ 5.1 solder pastes are available in these alloy compositions: 80Au/20Sn, 79Au/21Sn, 78Au/22Sn, and 77Au/23Sn, and powder sizes 2 to 7SGS.