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High Thermal, High Temperature Interconnects for Ultra High Power LEDs
For high performance applications, ultra-high power offers cost reduction through fewer LEDs, smaller PCBs, smaller heat sinks and lighter load bearing.
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Authored By:
Ravi M. Bhatkal, Ph.D. and Ranjit Pandher, Ph.D.
Alpha Assembly Solutions
South Plainfield, NJ, USA
Summary
Use of super/ultra-high power LEDs is increasing. For high performance applications such as street lighting and ultrahigh power density illumination, use of ultra-high power can enable significant systems cost reduction through use of fewer LEDs, smaller PCBs, smaller heat sinks and lighter load bearing structures. In order to be able to drive the LEDs harder and to increase light output in a smaller footprint, one needs efficient thermal performance at the LED die-to-package connection. The ultra-high power density, combined with high thermal metal substrates, (which have high CTE mismatch with ceramic sub-mount LEDs) necessitates use of ultra-high reliability interconnects for elevated temperature operation at the package-to-board connection.
This paper presents two technology platforms: 1. Sintered silver, which enables significant increase in light output at package level, and 2. High temperature creep resistant solder alloys that provide high thermal cycling reliability under high temperature and high CTE mismatch conditions.
Conclusions
1. For high and ultra-high power LEDs, for a given LED package structure and board material used, it is beneficial to use solder joints with improved mechanical and thermal fatigue/creep and vibration resistance. A new class of creep-resistant and vibration resistant alloys has been developed, that can provide this capability, via a micro-structural control approach. These advanced alloys have been developed with special additives for improved thermal stability for high temperature operation and higher thermal fatigue and vibration resistance.
2. Sintered silver technology has several benefits for high and ultra-high power LEDs, including enabling higher light output while maintaining junction temperature, enabling excellent control of tilt, directionality and optical axis, and providing very high thermal cycling reliability.
3. These emerging technologies are enabling us to push the envelope in implemeting ultra-high power LEDs in several applications.
Initially Published in the SMTA Proceedings
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