1. Thermal management is crucial for solid state lighting applications using LEDs as temperature greatly impacts LED performance and lifetime. 2. A three-step approach is recommended to analyze thermal challenges: analytical modeling, computational fluid dynamics modeling, and experimental testing. 3. An example thermal analysis of an LED downlighter demonstrated good agreement between the three analysis methods, validating the thermal management solution.

1. Thermal Challenges and Solutions
for Industrial Solid State Lighting
Applications
Peter Resca
Sr. Director of Product Development
Advanced Thermal Solutions
Presented at: APEC 2016 Long Beach CA

2. Agenda
1.Challenges of thermal management in
Industrial lighting
2.Implications of temperature stress on
the system
3.Tools to manage the thermal stress
4.Application Example
5.Conclusion
2

3. Comparison of LED to Incandescent Lamp
8%
73%
19%
Incandescent
Visible Light
IR
Heat
20%
80%
LED
Visible Light
IR
Heat
• Most of the energy is infrared
• Energy losses are mainly lost by
Radiation heat transfer
• No radiation
• Conduction heat
transfer dominant
3

4. 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
management
Luxeon K2 power LED (courtesy of Lumileds)
4

5. Conduction - junction to heatsink
Metal core
1.6mm
Prepreg
150um
Copper
70um
Heatslug
Solderpaste
150um
Rslug-solder pad
Rjunct-heatslug
Rmetal core
Interface material
Heatsink base
Rinterface
Rhs, (material and spreading resista
Ths
Tjunct.
P
5

6. 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!
6

7. 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
7

8. Lifetime vs. Temperature
(B50, L70) lifetimes against junction temperature for LUXEON Rebel LED
Temperature can directly impact the life of
the LED
8

9. Thermal Analysis Process
9
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
Sinks
Standard
Heat Sinks
Results

10. 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
10

11. Example Thermal Management
of LED Based Down-lighter
11

12. LED Based Downlighter
Heat Sink
LEDsLens
Lens housing
and protective
cover
12

13. Three modes of heat transfer
• Conduction
• Convection
• Radiation
Convection
Radiation
Radiation
Internally conduction
13

14. Impedance Model
Metal core
1.6mm
Prepreg
150um
Copper
70um
Heatslug
Solderpaste
150um
Rslug-solder pad
Rjunct-heatslug
Rmetal core
9 K/W (see spec)
0.13 K/W
(k=50W/mK, 22.5mm
1.8 K/W
(spreading resistance + mate
Interface material
Heatsink base
Rinterface 0.2 K/W
Rhs, base, spreading0 K/W
Ths
Tjunct.
P
14

15. Conduction and Spreading
15
Heat
LED
Good x-y Thermal
conductivity(3 W/m-K
Dielectric)
Poor x-y Thermal
Conductivity (0.3 W/m-K
Dielectric)
Dielectric
Copper
Metal Base

16. Conduction and Spreading
Spreading in copper
Spreading in prepreg
16

17. Convection/ Radiation
)*(
1
* rrcc
hs
AhAh
R


Km
W
hc
2
10
Km
W
hr
2
3.6
W
K
R
RRR
totalhs
rctotalhs
6.424.038.4,
int,

 
W
K
EE
Rhs 38.4
22.5*3.696.1*10
1
32


 
Base
Fins
Interface base to fins
Phs
Rconv
Rrad
Tambient
Rbase bot-top 0.006 K/W
Contact resistance
base to fins 433 mm2
h' screw contact 1.1 [K-cm2/W]
Rinterface 0.25 K/W DThs-air@9.6W =
44.4K
17

18. Convection/ Radiation
WKWRhs
KWT
/86.5)6.9(
3.56)6.9(


No. of Fins 12
Weight (grams) 45
Length (L) 45
Base thickness (t) 7
Heat Sink Configuration Dimensions [mm]
Diameter (D) 45
Thermal Performance Graph
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
4.00 5.00 6.00 7.00 8.00 9.00 10.00 11.00 12.00
Power Dissipation [W]
Ths-ambient[K]
Vertical mounted
• Performance based on analytical DThs-air@9.6W = 44.4K
• Assume free inflow of air to fin area
18

19. Analytical Analyses LED Downlighter
Ths, base
64/
84°C
Tpcb =72/
92°C
Tcore
66/
86°C
Rj-pcb =
9.1K/W
Rspr, pcb = 1.8K/W
Rinterface
0.2K/W
Rsp, hs
0K/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 + rad
4.6K/W
Light efficiency LED 1000mA@108°C ~9.4% => 3.53x0.91 =
3.20W dissipation
Tj, life = 101°C < 114°C => OK
19

20. Computional Analyses (CFD)
heatsink
base
MCPCB
Compact
Model
LED
Interface
material
3D Modeling downlighter in free air.
Solved for Conduction/ convection/ radiation
Side of housing
not shown
Troom 20°C
Tj, max =113°C
20

21. Experimental Test Setup
21
Measurement of junction
temperature
based on
Forward Voltage
Test setup
Infrared
picture
downlighter

22. Results
Paramater Units
Analytical,
with
experimental
hs-data
Analytical,
only CFD Experiment
Tambient °C 20 20 20 20
Iforward mA 1000 1000 1000 1000
Light efficiency % 9% 9% 9% 9%
Tdissipated total °C 9.6 9.6 9.6 9.6
Theatsink base °C 76 66 75 71
Tboard, copper led °C 84 74 84 78
Tj, led °C 113 103 113 107
Comparison methods 106% 96% 105% 100%
Results of different solution methods show good
comparison, within 6%.
22

23. 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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24. 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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25. Thank You
• For more information:
• www.qats.com
• http://www.qats.com/Applications/LED
-Applications
• Peter Resca – presca@qats.com
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