When discussing the hot topic of LEDs, quality and reliability become two major factors. Without either of these qualities, LEDs would have never become the efficient, breakout star of the world of lighting that they are today.
Q - Quality
To ensure the quality of a solid-state lighting (SSL) product, it is critical to perform a broad spectrum of tests on the luminaire system to accurately determine design margins and predict long-term reliability for the SSL product. It is not the LED alone but the total SSL system that has to be of quality.
Measuring and evaluating an LED luminaire is challenging, particularly to lighting manufacturers that are new to designing with LEDs. A solid-state luminaire comprises many different subassemblies including the LEDs, circuit board, optics, diffuser, current driver, power supply, heat sink, and mechanical enclosure. Any of these components can affect the performance, quality, or lifetime of the SSL product.
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Using a pulse-heat controlled batch eutectic reflow die-attach process is necessary for assembly throughput, LED protection, and high thermal conductivity while providing high-quality, low-risk performance. To ensure time-to-market success in high-volume production, specific methods to achieve throughput and quality are required. Testing materials and equipment before the assembly of deliverable hardware increases quality and reduces manufacturing issues. |
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R – Reliability
Reliability issues with LEDs, which tend to show up in the field, are more costly than yield issues, which are typically captured during in-house testing.
Typically, high-end LED manufacturers inspect the substrates post-epi, taking note of any defects greater than about 0.5mm in size. A virtual die grid is superimposed onto the wafer, and any virtual die containing significant defects will be blocked out. These die are not expected to yield if they contain pits, and are at high risk for reliability issues if they contain cracks. 
Especially with high-end LEDs intended for automotive or solid-state lighting applications, defects cannot be tolerated: reliability for these devices must be very high.
In order to increase yield and reliability, LED manufacturers need to carefully specify the maximum defectivity of the substrate by type and size—assuming the substrates can be manufactured to those specifications without making their selling price so high that it negates the benefit of increased yield.
Sources:
LEDs Magazine: "LED system evaluation yields quality analysis", http://ledsmagazine.com/features/10/9/8.
Solid State Technology Journal: “The gleam of well-polished sapphire”, http://electroiq.com/blog/2013/01/the-gleam-of-well-polished-sapphire/.
Photo credit: http://www.ecopowerlife.com/.
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Janine Hueners
Marketing Specialist
Palomar Technologies, Inc.