led engin lps 2013 presentation
DESCRIPTION
This is the presentation made by LED's Engin's Head of Europe, Gerrit-Willem Prins, at LpS 2013, a leading lighting industry conference held in Austria. The show is organised by the same team responsible for LED Professional magazine. Many thanks to the organisers.TRANSCRIPT
Threats to LED lifetime performance and proven techniques to secure reliabilityGerrit-Willem PrinsVP, Europe
Presentation made at the LpS Symposium, September 26, 2013
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LED lighting adoption
• LEDs will replace traditional light sources when performance + reliability is met
Threats to LED lifetime performance and proven techniques to secure reliability
Gerrit-Willem Prins, LED Engin
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LED lighting adoption
• Design needs for accent + downlighting– Lumen density – Beam control– Efficiencies – lm/W– Light quality – Long lifetime
Threats to LED lifetime performance and proven techniques to secure reliability
Gerrit-Willem Prins, LED Engin
Dark spots from defects
Localised hot spots
Blue die Yellow phosphor
Glass lens
Eutectic bondSilicon
Packaging design: compact, multi-die LED light source
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LED reliability expectations
Threats to LED lifetime performance and proven techniques to secure reliability
Gerrit-Willem Prins, LED Engin
Colour quality + consistency
Stability of light levels over time
Long service life
Good beam quality for accent + downlighting
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Stability and consistency of light
Threats to LED lifetime performance and proven techniques to secure reliability
Gerrit-Willem Prins, LED Engin
Results based on independent LM80 test results
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Stability and consistency of light
Threats to LED lifetime performance and proven techniques to secure reliability
Gerrit-Willem Prins, LED Engin
Results based on independent LM80 test results
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Threats to reliability of LED sources
Threats to LED lifetime performance and proven techniques to secure reliability
Gerrit-Willem Prins, LED Engin
Browning
Cracking
Lumen degradation of the source• Degradation of optical material absorbs more light• Cracking and delamination of optical material• Degradation of the LED chip reduces light emission
Colour temperature shift over time• Degradation of optical material Δ emission
spectrum
Functional failure• LED thermal or electrical overstress• Mechanical failure
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Contributing factors – heating of optical material
Threats to LED lifetime performance and proven techniques to secure reliability
Gerrit-Willem Prins, LED Engin
• High-index silicones can boost initial efficiency, but they are typically more susceptible to degradation due to heat
• Common effects are a breakdown of the silicone causing diminished light extraction and CCT shift over time
Photonics.com
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Contributing factors – heating of optical material
Threats to LED lifetime performance and proven techniques to secure reliability
Gerrit-Willem Prins, LED Engin
Solutions: • Silicone materials which balance index of refraction
and stable high transmission rates at temperature
• Direct phosphor on die-top application
• Efficient thermal designs extracting heat away from the silicone
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Contributing factors – thermal stress on die
Threats to LED lifetime performance and proven techniques to secure reliability
Gerrit-Willem Prins, LED Engin
• Material CTE mismatch at higher temperatures puts stress on the material lattice
• Micro stress fractures develop over time that don’t generate light
• Result: Lifetimes decrease with rise in junction temperature
LED device under test
Dark spots from defects
Localized hot spots
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Contributing factors – thermal stress on die
Threats to LED lifetime performance and proven techniques to secure reliability
Gerrit-Willem Prins, LED Engin
Solutions: • Thermally match materials CTE
• Maximise overall system thermal efficiency
to extract heat away from die junction
• Minimise localised hotspots from cracks, voids and delamination in interface materials throughout the system’s thermal path
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Package design considerations
Threats to LED lifetime performance and proven techniques to secure reliability
Gerrit-Willem Prins, LED Engin
• Silicone selection– Lower index silicone
over higher index• LED initially less bright
but benefits from stability over time
• Doesn’t brown or crack in high temperatures and humidity
• CCT stable over time
Thin Siliconelayer
LED Engin LZC White Emitter
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Package design considerations
Threats to LED lifetime performance and proven techniques to secure reliability
Gerrit-Willem Prins, LED Engin
• Phosphor adhesion process– Deposit phosphor directly
onto die-top• Direct contact with die;
no adhesive layer• Thermally efficient path
to back of die• Reduces localised heating of
silicone from phosphor emissions• No voids under phosphor layer
that create localised hot spots
Phosphor die top
LED Engin LZC White Emitter
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Package design considerations
Threats to LED lifetime performance and proven techniques to secure reliability
Gerrit-Willem Prins, LED Engin
• Die attach material and process– Eutectic Die attach
• Die attach material and process are key in thermal path to substrate
• Eutectic die attach have high thermal conductivity compared to Ag epoxies
• Minimises voids between die and substrate to avoid localised heating
Eutectic die attach
LED Engin LZC White Emitter
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Package design considerations
Threats to LED lifetime performance and proven techniques to secure reliability
Gerrit-Willem Prins, LED Engin
• Substrate design– Multi-layer ceramic
• Multiple layers of metal into ceramic substrate offer lowest thermal resistance
• CTE-matched to die creates stress-free environment – no localised hot spots
• Maximises power density and reliability
LED Engin LZC White Emitter
Multi-layer ceramic substrate
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Package design considerations
Threats to LED lifetime performance and proven techniques to secure reliability
Gerrit-Willem Prins, LED Engin
• Primary lens design– Select glass primary lens
over silicone lens• Interlocking design adds
structural package integrity• No degradation from self-heating• Added moisture protection barrier
reduces browning of siliconeLED Engin LZC White Emitter
Solid interlocking glass lens
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System design to maximise heat flow
Threats to LED lifetime performance and proven techniques to secure reliability
Gerrit-Willem Prins, LED Engin
Considerations to capitalise on high flux emitter for long-term reliability
Metal Core PCB Metal acts as a heat spreader Lowest thermal resistance ESD protection Avoid over winding mounting screws to prevent
LED substrate cracking from MCPCB warping
Pedestal Design Emitter in direct contact with base material
eliminating dielectric barrier
Heat Sink Interface material and surface flatness key to minimise air pockets Sized properly to dissipate
heat from system
High flux emitter High power density Low thermal resistance
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Other system design considerations
Threats to LED lifetime performance and proven techniques to secure reliability
Gerrit-Willem Prins, LED Engin
• Driver design considerations• Protect against surge currents• Ensure accuracy of output current • Driver should not add to the
overall system heat• Drivers with thermal feedback
and protection can protect the LED from thermal overstress
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Other system design considerations
Threats to LED lifetime performance and proven techniques to secure reliability
Gerrit-Willem Prins, LED Engin
• Optics– Optimise for specific sources
for best lumens in beam results
– Positioned properly for most efficient light output
• Off-center lenses can put stress on primary lens
• Method of clamping lens to leadframe or substrate can create torque and cracking of the substrate
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Other system design considerations
Threats to LED lifetime performance and proven techniques to secure reliability
Gerrit-Willem Prins, LED Engin
• Mechanical– Mounting techniques should
prevent stress on package that can lead to cracks and delamination
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Conclusions
Threats to LED lifetime performance and proven techniques to secure reliability
Gerrit-Willem Prins, LED Engin
Reliability is key to the value proposition of LED lighting
Reliability designs include:– Design for thermal efficiency
–Materials selection–Process Design
Seek ways to maximise Lux on Target and light quality over time