Budapest University of Technology and Economics eet.bme.hu Department of Electron Devices Diagnostics of LED-based streetlighting luminaires by means of thermal transient method Gábor Marosy, Zoltán Kovács, András Poppe The 16 th THERMINIC Workshop, 6-8 October 2010, Barcelona, Spain
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Budapest University of Technology and Economics
eet.bme.hu
Department of Electron Devices
Diagnostics of LED-based streetlighting luminaires by means of thermal transient method Gábor Marosy, Zoltán Kovács, András Poppe
The 16th THERMINIC Workshop, 6-8 October 2010, Barcelona, Spain
6 October 2010 G. Marosy, Z. Kovács, A. Poppe: Diagnostics of LED-based streetlighting luminaires ... 7
Data from thermal transient tests of LEDs
1e-5 1e-4 0.001 0.01 0.1 1 10 100
0.5
1
1.5
2
2.5
3
3.5
Time [s]
Pu
lse
th
erm
al re
sis
tan
ce
[K
/W]
T3Ster Master: Pulse Rth Diagram
CREE_MCE_AL_2_25_MY_F1_T25_I0350 - 0.50
CREE_MCE_AL_2_25_MY_F1_T25_I0350 - 0.25
CREE_MCE_AL_2_25_MY_F1_T25_I0350 - 0.10
CREE_MCE_AL_2_25_MY_F1_T25_I0350 - 0.05
h(t) a(t)
Junction temperature
time
time
Power
0.5 1 1.5 2 2.5 3 3.5 4
0.001
0.01
0.1
1
10
100
Rth [K/W]
Cth
[W
s/K
]
T3Ster Master: cumulative structure function(s)
CREE_MCE_AL_2_25_MY_F1_T25_I0350 - Ch. 0
Pulse thermal resistance diagram
Structure function
Package dynamic model
► The h(t) step-wise change in heating is applied at the junction (abrupt switching)
► The a(t) temperature response at the junction is being measured (unit-step response function) while linearity is assumed
► All available information is extracted from a(t) using sophisticated mathematical procedures structure functions – ideal to characterize TIM compact dynamic thermal models pulsed thermal resistance / complex locus (frequency domain representation)
6 October 2010 G. Marosy, Z. Kovács, A. Poppe: Diagnostics of LED-based streetlighting luminaires ... 17
►Considering a constant sensitivity value (-2mV/K) the aging of TIM is screened:
Results from LM80 tests: without real dVF/dT
1e-6 1e-5 1e-4 0.001 0.01 0.1 1 10 t [s] 0
2
4
6
8
10
12
14
16
T
J [
°C] T3Ster Master: Smoothed response
Vendor O, sample #44, 0h
Vendor O, sample #44, 3000h
Vendor O, sample #44, 2000h
Vendor O, sample #44, 500h
dVF/dT = -2mV/K
0 2 4 6 8 10 12 14 16
1e-5
1e-4
0.001
0.01
0.1
1
10
100
1000
Rth [K/W]
Cth
[W
s/K
]
T3Ster Master: cumulative structure function(s)
GoldenD_44_0h - Ch. 0
44_54_64_500h - Ch. 0
14-24-34-44_2000h - Ch. 3
14_24_34_44_3000h - Ch. 3
With an assumed constant sensitivity even structure functions appear to be identical, though in a quick diagnostic system in the field probably there will be no possibility to implement structure function calculations.
6 October 2010 G. Marosy, Z. Kovács, A. Poppe: Diagnostics of LED-based streetlighting luminaires ... 20
Conclusions ►We made an analysis of possible structural integrity issues
in the junction to ambient heat-flow paths of LEDs to be used in streetlighting luminaires.
►Preliminary results of long term stability studies of LEDs suggest that in harsh environment we should expect degradation of the different thermal interfaces.
► If the degradation exceeds a given limit (resulting thermal resistance change bigger then variation of temperature sensitivity of the forward woltage), with built-in thermal transient measurement based diagnosis early warnings can be provided and maintenance of luminaires can be scheduled to avoid fatal breakdown. Requirements for such testing circuitry are not too high, ~1ms time
resolution seems to be sufficient ti detect LED/MCPCB or TIM2 delamination/ageing
No sophisticated data processing is required for such tests, it seems, raw forward voltage transients are sufficient
6 October 2010 G. Marosy, Z. Kovács, A. Poppe: Diagnostics of LED-based streetlighting luminaires ... 21
Acknowledgements ►This work was partially supported by the KÖZLED
TECH_08-A4/2-2008-0168 project of the Hungarian National Technology Research and Development Office.
►Further support of the Hungarian Government through the TÁMOP-4.2.1/B-09/1/KMR-2010-0002 project at the Budapest University of Technology and Economics is also acknowledged.
►We are grateful for the help of KÖZLED partners: University of Pannonia (Veszprém, Hungary) for sharing their LM80
test facility and test results with us.
OptimalOptic Ltd. for LED samples with different thermal management solutions and their CAD images
Hungarolux Ltd. for CAD images of their luminaires
►Help of Mentor Graphics MicReD Division is also acknowledged for some CFD simulations as well as helping us perform some of our measurements