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Philips LUXEON Rebel platform

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					Design for Reliability

LUXEON Rebel platform




                          Mark Hodapp
                          July 15, 2009
Design for reliability – key points

• All LEDs do not behave the same!!!
    – Do not fall into the trap of assuming that one manufacturer’s data
       applies to any LED

• White LUXEON Rebel data
   – Lumen maintenance
   – Catastrophic failures
   – Combined L70 and catastrophic failures

• Need to get similar data from your LED manufacturer

• System aspects of reliability


                                                                           2
Design for reliability – LUXEON Rebel





• Lumen maintenance
• Catastrophic failures
• Combined L70 and catastrophic failures




                                           3
Lumen maintenance and catastrophic failures

•	 Philips Lumileds Reliability Datasheet RD07 “LUXEON Rebel Reliability
   Data”, available on the Philips Lumileds website, combines catastrophic
   and L70 lumen maintenance failures together.


• Whats New:

•	 System impacts of catastrophic and L70 lumen maintenance failures are
   different.
    –	 Catastrophic failures generate no light, and may have consequences on drive
       currents and light output of remaining LEDs.
    –	 L70 Lumen Maintenance failures still generate light (< 70% of initial) and have no
       impact on drive currents and light output of remaining LEDs.


•	 Reliability modeling from Philips Lumileds can separate catastrophic and
   L70 lumen maintenance failures.
                                                                                            4
LUXEON Rebel Reliability Update

(utilizing TFFC Die technology) B50, L70

                   Power LED Reliability



 BYY, L70                                                   BXX


        Long-Term
                                     Catastrophic Failure
     Lumen Maintenance



                                            BXX+YY, L70

                   Combined (Bxx, Lyy)

                       Reliability


                                                                  5
Philips Lumileds
Lumen maintenance extrapolations
• Approach has been modified to conform with ENERGY STAR


• Lumen maintenance of each unit is normalized to 1 after 24 hours
  stress.
• Any failures are excluded from the data set.
• Units are averaged together
• Least-squares exponential extrapolation is done for all points from
  1,000 to 9,000 hours.
                                N o t e : g e n e r a ll y      0 .
        (             (
       φ
 t ) =
 b exp
 α t )            
                 α <
 
 





                                                                        6
Cool-white LUXEON Rebel at 55C, 0.35A

                                                        Cool-White LUXEON Rebel stressed at 55°C, 0.35A

                                                                      (Tjunction ≅ 68°C)

                                                                             Normalized to 1 at 24 hours

                            1.2

                                                                                                    Actual data = -1.4% at 10,000 hours

                            1.1
  Normalized Light Output




                            1.0

                                                            35,000 hour
                                                            25,000 hour
                            0.9
                                                                                 ENERGY STAR 25,000 and 35,000
                                                                                 limits after 6,000 hours of stress

                            0.8



                            0.7
                                      Ta within -5C of Ts, in accordance with LM80.
                                      Sample size = 77 units, y-axis error bar = +/- 3 standard deviations.
                            0.6
                                  0               2,000              4,000             6,000              8,000           10,000          12,000

                                                                             Hours

                                                                                                                                                   7
Cool-white LUXEON Rebel at 55C, 0.35A

                                                       Cool-White LUXEON Rebel stressed at 55°C, 0.35A

                                                                     (Tjunction ≅ 68°C)

                                                                         Normalized to 1 at 24 hours

                           1.2
                                             ⎡ 0.7 ⎤                    a = -1.6640e-6                   *Philips Lumileds
                                           ln ⎢    ⎥                    b = 1.0023                       recommends extrapolations
                                             ⎣ b ⎦
                                 L70 =                                                                   of ≤ 6x the test time
                                                  a
                           1.1
 Normalized Light Output




                           1.0
                                                                                    Extrapolated data = -1.4% at 10,000 hours
                                     35,000 hour
                                     25,000 hour
                           0.9
                                     ENERGY STAR 25,000 and 35,000 hour        6x test time*
                                     limits after 6,000 hours of stress
                           0.8



                           0.7
                                                                                                            L70 = 216,000 hours
                                 Ta within -5C of Ts, in accordance with LM80.
                                 Sample size = 77 units, y-axis error bar = +/- 3 standard deviations.
                           0.6
                             1,000                             10,000                             100,000                         1,000,000

                                                                        Hours

                                                                                                                                              8
Cool-white LUXEON Rebel at 85C, 0.35A

                                                       Cool-White LUXEON Rebel stressed at 85°C, 0.35A

                                                                     (Tjunction ≅ 98°C)

                                                                             Normalized to 1 at 24 hours

                            1.2



                            1.1
                                                                                                   Actual Data = -1.5% at 10,000 hours
  Normalized Light Output




                            1.0

                                                              35,000 hour
                                                              25,000 hour
                            0.9
                                                             ENERGY STAR 35,000 and 25,000 hour limits
                                                             after 6,000 hours of stress

                            0.8



                            0.7
                                      Ta within -5C of Ts, in accordance with LM80.
                                      Sample size = 78 units, y-axis error bar = +/- 3 standard deviations.

                            0.6
                                  0              2,000             4,000             6,000            8,000           10,000             12,000
                                                                                    Hours

                                                                                                                                                  9
Cool-white LUXEON Rebel at 85C, 0.35A

                                                         Cool-White LUXEON Rebel stressed at 85°C, 0.35A

                                                                       (Tjunction ≅ 98°C)

                                                                          Normalized to 1 at 24 hours

                            1.2
                                                ⎡ 0.7 ⎤                 a = -2.2816e-6                 *Philips Lumileds
                                              ln ⎢    ⎥
                                                ⎣ b ⎦                   b = 1.0054                     recommends extrapolations
                                      L70 =                                                            of ≤ 6x the test time
                                                     a
                            1.1
  Normalized Light Output




                            1.0
                                                                                       Extrapolated Data = -1.7% at 10,000 hours

                                      35,000 hour
                                      25,000 hour
                            0.9
                                  ENERGY STAR 35,000 and 25,000 hour limits
                                  after 6,000 hours of stress               6x test time*
                            0.8



                            0.7
                                                                                                        L70 = 159,000 hours
                                  Ta within -5C of Ts, in accordance with LM80.
                                  Sample size = 78 units, y-axis error bar = +/- 3 standard
                                  d i ti
                            0.6
                              1,000                            10,000                           100,000                            1,000,000
                                                                                Hours
                                                                                                                                               10
Cool-white LUXEON Rebel
Summary test data
         Estimated Junction Temperatures
                       Current
             Board Temp 0.35A        0.7A      1A
                 110C    123C
                  85C    98C         112C
                  55C    68C         82C       95C



         Modeled median L70 Lifetime
                         Current
             Board Temp 0.35A         0.7A       1A
                 110C     156,000
                  85C     170,000    92,000
                  55C     182,000    99,000    71,000
               Philips Lumileds lumen maintenance model




                                                          11
Cool-white LUXEON Rebel
Lumen Maintenance Conclusions
•	 Philips Lumileds has lumen maintenance data to 9,000+ hours

•	 Results for Cool-white LUXEON Rebel
    –	 Some units have so little degradation that the extrapolation predicts increasing flux
       with time!! (This means that the L70 time is less than 0 hours).

    –	 All stress conditions shown easily pass ENERGY STAR 35,000 hour average lumen
       maintenance requirement.

    –	 Drive current has a very strong effect on lumen maintenance.

    –	 Temperature has a very weak effect on lumen maintenance.


•	 Should not assume that all LEDs behave the same way!! You should request
   similar data from your LED manufacturer.


                                                                                               12
Catastrophic failures for LEDs

•	 LEDs can fail catastrophically, especially when driven at very high
   junction temperatures and drive currents!
    –	 InGaN technology from Philips Lumileds generally fails short.
    –	 Recommendation would be to consult with your LED supplier.


•	 Catastrophic failures can be reduced with lower stress conditions.


•	 Large array of LEDs can benefit from redundant design concepts, so that
   single failure does not result in a cascade effect.




                                                                             13
Cool-white LUXEON Rebel
Catastrophic failure rate modeling
•	 Philips Lumileds has made considerable advances in understanding the
   causes of catastrophic failures.


•	 In the event of a catastrophic failure, InGaN-based LUXEON Rebel LEDs
   generally fail short.


•	 LED catastrophic failure rates can be modeled using the same general
   principles as silicon-based semiconductors.
    –	 Failure rate versus operating time can be determined for several different stress
       conditions [i.e. different combinations of TJ and IF].
    –	 Results can be used with commercial reliability software packages to develop a
       model.


• Results for TFFC-based LUXEON Rebel.
    – Catastrophic failures are described with Weibull failure rate model.

                                                                                           14
Cool-white LUXEON Rebel
                                                                    Catastrophic failure rates
                                                                   LUXEON Rebel using TFFC

                             1
                                     Temperature1 > Temperature2 > Temperature3



                            0.1
                                                            Temperature1
Probability of Failure




                           0.01
                                                               Temperature2




                          0.001
                                                                  Temperature3




                         0.0001
                               100                  1,000                  10,000         100,000   1,000,000
                                                                           Hours
Curves are 90% LCL worst case. Curve shape is approximately the same at any
temperature. Curve shifts to the left at higher temperatures.
                                                                                                                15
Cool-white LUXEON Rebel
Catastrophic failure rate conclusions
•	 Results for LUXEON Rebel using TFFC technology
   –	 Devices tend to fail short.


   –	 Temperature has a very strong effect on catastrophic failure rates.


   –	 Drive current has a weak effect on catastrophic failure rates.


   –	 Note that lumen maintenance and catastrophic failure rate models are very
      different:
        •	 Lumen maintenance – strong forward current and weak temperature effect
        •	 Catastrophic – strong temperature and weak forward current effect


•	 Should not assume that all LEDs behave the same way!! You should
   request similar data from your LED manufacturer.


                                                                                    16
Combined effects

• Can combine LM-80 lumen maintenance extrapolations and estimated
  catastrophic failure rate models together to show combined failure rates
  (and ratio of L70 lumen maintenance failures to catastrophic failures).




                                                                             17
Impact of driving at higher temperatures

                                                         Estimated failure rates at 50,000 hours
                                                                        50% CL calculations
                          150

                                   Area of circles proportional to total FR
                                                                                                        Maximum TJ

                                                                                               (B50, L70)
                          130
                                          Operating
                                                                        Conditions
   Junction Temperature




                                                                        Specified for
                                                                        Lumen
                          110
                                          Maintenance
                                                                        Statement in
                                                                        Data Sheet

                           90


                                                                                                            Maximum I F


                           70





                           50

                             0.2          0.3         0.4        0.5          0.6        0.7          0.8      0.9        1.0
                                                                       Forward Current
                                                                                                                                18
Impact of driving at higher temperatures

                                                        Estimated failure rates at 50,000 hours
                                                                        50% CL calculations
                          150

                                   Area of circles proportional to total FR
                                                                                                  Maximum TJ
                                                                                         (B50, L70)
                          130

   Junction Temperature




                                      Predominantly cat failures at 50,000 hours

                          110
                                         Operating
                                                                       Conditions
                                                                       Specified for
                                                                       Lumen
                           90
                                         Maintenance
                                                                       Statement in
                                                                       Data Sheet                      Maximum IF

                           70


                                     Predominantly L70 failures at 50,000 hours

                           50

                             0.2          0.3        0.4         0.5          0.6      0.7      0.8      0.9        1.0
                                                                    Forward Current

                                                                                                                          19
Impact of driving at higher forward current

                                                       Estimated failure rates at 50,000 hours
                                                                       50% CL calculations
                         150

                                  Area of circles proportional to total FR
                                                                                                      Maximum TJ

                                                                                              (B50, L70)
                         130

                                                                       Operating
                                                                       Conditions
  Junction Temperature




                                                                       Specified for
                         110

                                                                       Lumen
                                                                       Maintenance
                                                                       Statement in
                                                                       Data Sheet
                          90



                                                                                                           Maximum I F

                          70





                          50

                            0.2          0.3        0.4         0.5          0.6        0.7         0.8      0.9         1.0
                                                                      Forward Current
                                                                                                                               20
Combined forward current and temperature

                                                        Estimated failure rates at 50,000 hours
                                                                        50% CL calculations
                          150

                                   Area of circles proportional to total FR
                                                                                                     Maximum TJ

                                                                                               (B50, L70)
                          130

   Junction Temperature




                                    Predominantly cat failures at 50,000 hours

                          110


                                   Operating Conditions Specified for Lumen
                                   Maintenance Statement in Data Sheet
                           90



                                                                                                            Maximum I F

                           70


                                    Predominantly L70 failures at 50,000 hours


                           50

                             0.2          0.3        0.4         0.5          0.6        0.7       0.8         0.9        1.0
                                                                       Forward Current

                                                                                                                                21
System aspects of reliability for LED-based
luminaires
•	 In general, the reliability of the LED is a function of drive current, and LED
   case temperature.

•	 The impact of a single LED failure on the system reliability depends on
   how the LEDs are wired together.
    –	 Opens versus shorts
    –	 LED interconnection scheme
    –	 Failure of one LED may cause forward current of remaining LEDs to change

•	 There are other causes of failures besides the LEDs.
    –	 Solder joints
    –	 Electrical drivers
    –	 Deterioration of external lens/optics

•	 Overall system reliability is only as good as the weakest link. While we
   can quantify the reliability impact of the LED, the customer also needs to
   quantify the probability of failure of the rest of the LED system.

                                                                                    22
End


Thank you for your valuable time.

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