apec 2016 industry session-thermal challenges and solutions for ssl applications
TRANSCRIPT
Thermal Challenges and Solutions for Industrial Solid State Lighting ApplicationsPeter RescaSr. Director of Product DevelopmentAdvanced Thermal SolutionsPresented at: APEC 2016 Long Beach CA
Agenda1.Challenges of thermal management in Industrial lighting2.Implications of temperature stress on the system3.Tools to manage the thermal stress4.Application Example5.Conclusion
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Comparison of LED to Incandescent Lamp
8%
73%
19%
Incandescent
Visible LightIRHeat
20%
80%
LED
Visible LightIRHeat
• Most of the energy is infrared• Energy losses are mainly lost by Radiation heat transfer• No radiation• Conduction heat transfer dominant
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LED - inside view
• The efficiency is dependent on many parameters• Not all of these parameters can be influenced by the user• The most important parameter that can be influenced is the junction temperature of the LED, by applying effective thermal managementLuxeon K2 power LED (courtesy of Lumileds) 4
Conduction - junction to heatsink
Metal core 1.6mmPrepreg
150umCopper70um
HeatslugSolderpaste 150um
Rslug-solder padRjunct-heatslug
Rmetal coreInterface material
Heatsink baseRinterface
Rhs, (material and spreading resistance)Ths
Tjunct.
P
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LED Parameters vs. Temperature• Light output is strongly dependent on temperature• Temperature has an effect on forward voltage• Temperature reduces lifetime• Exceeding Tj, max may permanently damage LED=> Thermal Management for LED based solutions is imperative!
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Light Output vs. Temperature
http://cree.com/~/media/Files/Cree/LED-Components-and-Modules/XLamp/Data-and-Binning/XLampMCE.pdf
Temperature can directly impact the output of the emitting light
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Lifetime vs. Temperature
(B50, L70) lifetimes against junction temperature for LUXEON Rebel LED
Temperature can directly impact the life of the LED
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Thermal Analysis Process
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DFM Solution
Analytical Modeling • Fundamental based modeling for quick results• Generate models for what-if scenarios• Physics based results
Computational Modeling• Flotherm• Cfdesign• Icepak• CAD tools
Empirical Modeling• Liquid & air flow testing• JEDEC testing• IR & LC thermography• Temperature measurement• Velocity measurement• Pressure measurement
Validated Prototype
Ready for high volume, low cost production
Custom Heat SinksStandard Heat Sinks
Results
What Does Thermal Management Entail?Objective: To maintain device junction below specified temperature for worst case environment.
Hierarchy (level) of modelling:• Environment: Where the system resides• Enclosure: Houses the electronics• Board: Housing the components• Component: Housing the dies (chip)• Chip: Housing the electronics parts
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Example Thermal Managementof LED Based Down-lighter
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LED Based DownlighterHeat Sink
LEDsLens
Lens housing and protective cover
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Three modes of heat transfer• Conduction• Convection• Radiation
Convection
RadiationRadiation
Internally conduction
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Impedance Model
Metal core 1.6mmPrepreg
150umCopper70um
HeatslugSolderpaste 150um
Rslug-solder padRjunct-heatslug
Rmetal core
9 K/W (see spec)0.13 K/W (k=50W/mK, 22.5mm1.8 K/W (spreading resistance + material)
Interface materialHeatsink base
Rinterface 0.2 K/WRhs, base, spreading0 K/W
Ths
Tjunct.
P
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Conduction and Spreading
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Heat
LED
Good x-y Thermal conductivity(3 W/m-K Dielectric)Poor x-y Thermal Conductivity (0.3 W/m-K Dielectric)
DielectricCopper Metal Base
Conduction and Spreading
Spreading in copperSpreading in prepreg
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Convection/ Radiation)*(
1* rrcc
hs AhAhR
KmWhc 210
KmWhr 23.6
WKR
RRRtotalhs
rctotalhs
6.424.038.4,
int,
WK
EERhs 38.422.5*3.696.1*101
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BaseFins
Interface base to fins
Phs
RconvRrad
Tambient
Rbase bot-top 0.006 K/WContact resistance base to fins 433 mm2h' screw contact 1.1 [K-cm2/W]Rinterface 0.25 K/W [email protected] =
44.4K17
Convection/ Radiation
WKWRhsKWT
/86.5)6.9(3.56)6.9(
No. of Fins 12Weight (grams) 45
Length (L) 45Base thickness (t) 7
Heat Sink Configuration Dimensions [mm]Diameter (D) 45
Thermal Performance Graph
0.0010.0020.0030.0040.0050.0060.0070.0080.00
4.00 5.00 6.00 7.00 8.00 9.00 10.00 11.00 12.00Power Dissipation [W]
Ths-a
mbien
t [K]
Vertical mounted
• Performance based on analytical [email protected] = 44.4K • Assume free inflow of air to fin area18
Analytical Analyses LED Downlighter
Ths, base64/ 84°C
Tpcb =72/ 92°C
Tcore66/ 86°C
Rj-pcb = 9.1K/W
Rspr, pcb = 1.8K/W
Rinterface0.2K/WRsp, hs0K/W
P=3.20W (3x)
Tj =101/ 121°C
Pc+r=9.6W
20/ 40°C
Tj, max = 121°C < 139°C => OK
All resistances are calculated by using Analytical based formula
Rhs. Conv + rad4.6K/W
Light efficiency LED 1000mA@108°C ~9.4% => 3.53x0.91 = 3.20W dissipationTj, life = 101°C < 114°C => OK
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Computional Analyses (CFD)
heatsink
base
MCPCBCompact
ModelLED
Interfacematerial3D Modeling downlighter in free air.Solved for Conduction/ convection/ radiation
Side of housing not shown
Troom 20°CTj, max =113°C
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Experimental Test Setup
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Measurement of junction temperature based on Forward Voltage
Test setup
Infrared picture downlighter
Results
Paramater Units
Analytical, with
experimental hs-data
Analytical, only CFD Experiment
Tambient °C 20 20 20 20Iforward mA 1000 1000 1000 1000Light efficiency % 9% 9% 9% 9%Tdissipated total °C 9.6 9.6 9.6 9.6Theatsink base °C 76 66 75 71Tboard, copper led °C 84 74 84 78Tj, led °C 113 103 113 107Comparison methods 106% 96% 105% 100%
Results of different solution methods show good comparison, within 6%.22
Other Considerations• Power Dissipation – LED components, multichip modules and fixtures• Solar Loading• Heat Sink Materials - Copper, Aluminum• Interface Material – Grease, Phase Change, Gap Pad• Process – Cast, Skiving, Extrusions
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Conclusion• LED’s by their construction and application pose unique thermal challenges.• Proper thermal management a critical variable that can be established and controlled in the design.• Impedance diagrams are a helpful tool for understanding, modeling and analyzing a thermal management problem.• Always calculate/measure the junction temperature; Use the three step approach to the analyze the problem (Analytical/ Computational/ Experimental)• Measure the light efficiency or ask the supplier for input to have the real dissipated power.• Example did show good comparison between three methods providing a solution right the first time.
LEDs can never be cool enough!!
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Thank You• For more information:• www.qats.com• http://www.qats.com/Applications/LED-Applications• Peter Resca – [email protected]
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