[SEMI Theater] High Brightness LEDs: Assembly/Materials Challenges/Opportunities
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Transcript of [SEMI Theater] High Brightness LEDs: Assembly/Materials Challenges/Opportunities
hbLEDSW7.10 © 2010 TechSearch International, Inc.
High Brightness LEDs: Assembly and Materials Challenges/Opportunities
E. Jan VardamanDr. Frank Bachner
TechSearch International, Inc.
www.techsearchinc.com
hbLEDSW7.10 © 2010 TechSearch International, Inc.
Overview• HB LEDs have high
potential growth rates, BUT to reach the full market potential
– Must be reliable– Must have good
performance (lumens/$, lumens/watt)
– Must have lower prices
• Key patents and technology around the diode itself, phosphor, LED epitaxial layer, electrical contact material on die
• Material selection, packaging, and assembly are becoming the key differentiators in LED performance, reliability, and cost
Source: OSRAM GmbH
hbLEDSW7.10 © 2010 TechSearch International, Inc.
High Brightness LED Module Structures• Materials to fabricate LEDs
– InGaN– AlInGaP
• LED mounted on various substrates– Leadframe– Silicon– Ceramic (AlN, Al2O3)– Metal core board
• Die attach• Interconnect• Application of phosphor• Encapsulation of LED
– Epoxy mold– Silicone
• Focus light– Glass lens– Plastic lens
• Mount LED package or mount LED directly to metal core board
• Cooling
Source: LUMILEDS
hbLEDSW7.10 © 2010 TechSearch International, Inc.
Issues for LED Packaging and Assembly
• There are no standard packages– No standard footprints
• Optimize (try not to degrade) optical performance of LED– Reflectivity– Transmissivity– Index of Refraction
• Thermal dissipation (how do we get the heat out more efficiently)– Die attach material– Metals used in package (leadframe, metal core board, AlN,
alumina)• Reliability of package over lifetime
hbLEDSW7.10 © 2010 TechSearch International, Inc.
Thermal Issues• LED emits light, but heat is not radiated• Controlling the LED Tj to 50 to 100°C is critical to performance
– Change in junction temperature changes the wavelength of emitted light (making color control difficult)
– With high Tj, the active regions of LED and electrodes of the device can degrade—leading to changing light output of the device
• Good thermal dissipation is required because heat can degrade the phosphors in the LED package as well as packaging materials
– Yellowing of encapsulation materials– TCE and Tg of materials can change (reduces lumens and decreases
efficiency)
Source: CoreSEM
hbLEDSW7.10 © 2010 TechSearch International, Inc.
LED Lifetime with Junction Temperature
If the junction temperature changes from 74oC to 63oC, the lifetime increase from 15,000 to 40,000 hours
More light output in same used hours
More longer time if junction temp decrease
Source: CoreSEM
hbLEDSW7.10 © 2010 TechSearch International, Inc.
Material Selection Key in Thermal Dissipation
LED package(Die attach + Heat slug)
Metal plate
TIM
Heat sink
SolderPCB bonding pad (Cu)
LED package
Metal Core PCB(CoreSEM)
Heat sinkH
eat f
low
Thermal bottleneck(dielectric layer)
Source: CoreSEM
hbLEDSW7.10 © 2010 TechSearch International, Inc.
Copper Circuit Layer
CoreSEM’s Metal PCB (CoolRATE®)
High thermal conductive
dielectric layer
Advantage : High thermal transfer characteristics of dielectric layer (4~10 W/mK thermal conductivity grade)
Very low thermal resistance with thin dielectric layer (50~120um)High operating temperature and good adhesionEasy control of dielectric breakdown voltageEasy thickness control from 0.5 mm ~ 2 mm
Aluminum plateAluminum plate Aluminum plate
Source: CoreSEM
hbLEDSW7.10 © 2010 TechSearch International, Inc.
Substrate Solutions for HB LEDs
Copper Signal LayerThermal DielectricCopper or Aluminum Plate
Single Layer
Copper Signal LayerThermal Dielectric
Copper or Aluminum Plate
Two-Layer
Copper Signal LayerThermal Dielectric
Copper Signal LayerThermal DielectricCopper or Aluminum Plate
Copper Signal LayerThermal Dielectric
Copper or Aluminum Plate
Multilayer(one of many variants)
Copper Signal LayerThermal DielectricCopper Signal Layer
Thermal Dielectric
Most Common
Less Common Thermal DielectricCopper Signal Layer
LTCCMLamina
DBC
IMSBergquist
MCS SteelHeatron
Graphtech Z Spreader
MCS AluminumFerro/Heatron
hbLEDSW7.10 © 2010 TechSearch International, Inc.
MCS on Aluminum for Thermal Cooling
Aluminum 3003 alloy( 4 to 5 mm thickness)
DL13-168
ConductorCN33-479 (lead free)
@ 500°C (12 min) peak firing
CN50-101 @580oC
Dielectrics3 coats & 3 fire
@ 600°C ( 12 min) peak firing
DL13-169
DL13-169
OverglazeOG15-313@ 500°C (12 min)peak firing
Aluminum thickness of 4-5 mm prevents warping
hbLEDSW7.10 © 2010 TechSearch International, Inc.
T-clad Metal Core Substrate
Source: Bergquist
hbLEDSW7.10 © 2010 TechSearch International, Inc.
hbLEDSW7.10 © 2010 TechSearch International, Inc.
One Big Die
• Some companies use one large die– Lighting applications– Die range from 0.7mm to 1.5 mm on a side– Power dissipations 1-4 Watts
• Packaging structure vary– LED package– Package mounted on a metal core board
Source: Lumileds
hbLEDSW7.10 © 2010 TechSearch International, Inc.
Trend to COB• Many companies mounting LEDs directly to the metal core board
– Simpler structure– Less packaging materials– Fewer thermal interfaces
• Small die size (0.2-0.4mm, 0.1-0.3 W)• Example with multiple LEDs
– LEDs are wire bonded– Security bond with stud bump
Source: T. Onishi
hbLEDSW7.10 © 2010 TechSearch International, Inc.
Problems with LED Packaging Materials
DelaminationDisconnectionCrack
Reduced LumensShort circuitVisual defects
Moisture Reflow
DelaminationDisconnection
Reduced LumensShort circuit
Heat Cycle-40˚C~100˚C/200cyc
Resin color shiftMetal oxidation
Reduced LumensIncreased current leakage
Biased Temp. & Humidity85˚C/85%/20mA/300hr
Chip degradationReduced LumensLow Temp. Bias
Resin color shiftReduced LumensRoom Temp. Bias25˚C/20mA/1000hr
CauseProblemTest
Source: SANYU REC Co., Ltd.
hbLEDSW7.10 © 2010 TechSearch International, Inc.
Packaging Material Needs
• Encapsulants (Silicone or Epoxy) material properties affect the number of lumens out of the package– Materials with high reflectivity– Materials with a high index of refraction– Materials must stable with exposure to elevated temperatures, UV, and
other wavelength radiation• Lenses (Glass or Plastic)
– High transmission rate– High index of refraction– Low moisture absorption– Low thermal expansion
• Die attach materials– Solder (Pb-free)
• Thermal Interface Materials– Bond well – Conduct well– No degradation with age or use
hbLEDSW7.10 © 2010 TechSearch International, Inc.
Current Encapsulation Materials
Poor adhesionSurface tackinessHigh moisture permeabilityExpensivePoor physical strength
Poor UV light durabilityColor change due to heatPoor heat shock stability
Cons
Good radiation durabilityHeat stableGood electrical propertiesGood shock stability
Good adhesionGood electrical propertiesPhysically toughFairly good heat stabilityLess expensive
Pros
SiliconeEpoxy
Source: SANYU REC Co., Ltd.
hbLEDSW7.10 © 2010 TechSearch International, Inc.
Conclusions• Industry is experiencing rapid growth, but need reliable, long lasting, low cost
products• No standard packages—footprints of LED packages not even the same• Continued room for improvement in packaging and assembly
– New designs– New materials– New assembly methods
• Understanding optical, thermal, and material science trade-offs– Key to making reliable, low-cost products
Source: T. Onishi