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Materials 2017, 10(10), 1181; doi:10.3390/ma10101181

Photometric and Colorimetric Assessment of LED Chip Scale Packages by Using a Step-Stress Accelerated Degradation Test (SSADT) Method

1
School of Reliability and Systems Engineering, Beihang University, Beijing 100191, China
2
College of Mechanical and Electrical Engineering, Hohai University, Changzhou 213022, China
3
Changzhou Institute of Technology Research for Solid State Lighting, Changzhou 213161, China
4
College of Mathematics and Physics, Changzhou University, Changzhou 213164, China
5
Department of Mechanical Engineering, Lamar University, Beaumont, TX 77710, USA
6
EEMCS Faculty, Delft University of Technology, Delft 2628, The Netherlands
*
Author to whom correspondence should be addressed.
Received: 17 September 2017 / Revised: 8 October 2017 / Accepted: 10 October 2017 / Published: 16 October 2017
(This article belongs to the Special Issue Light Emitting Diodes and Laser Diodes: Materials and Devices)
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Abstract

By solving the problem of very long test time on reliability qualification for Light-emitting Diode (LED) products, the accelerated degradation test with a thermal overstress at a proper range is regarded as a promising and effective approach. For a comprehensive survey of the application of step-stress accelerated degradation test (SSADT) in LEDs, the thermal, photometric, and colorimetric properties of two types of LED chip scale packages (CSPs), i.e., 4000 °K and 5000 °K samples each of which was driven by two different levels of currents (i.e., 120 mA and 350 mA, respectively), were investigated under an increasing temperature from 55 °C to 150 °C and a systemic study of driving current effect on the SSADT results were also reported in this paper. During SSADT, junction temperatures of the test samples have a positive relationship with their driving currents. However, the temperature-voltage curve, which represents the thermal resistance property of the test samples, does not show significant variance as long as the driving current is no more than the sample’s rated current. But when the test sample is tested under an overdrive current, its temperature-voltage curve is observed as obviously shifted to the left when compared to that before SSADT. Similar overdrive current affected the degradation scenario is also found in the attenuation of Spectral Power Distributions (SPDs) of the test samples. As used in the reliability qualification, SSADT provides explicit scenes on color shift and correlated color temperature (CCT) depreciation of the test samples, but not on lumen maintenance depreciation. It is also proved that the varying rates of the color shift and CCT depreciation failures can be effectively accelerated with an increase of the driving current, for instance, from 120 mA to 350 mA. For these reasons, SSADT is considered as a suitable accelerated test method for qualifying these two failure modes of LED CSPs. View Full-Text
Keywords: light-emitting diode; chip scale package; accelerated aging; step stress test; reliability qualification light-emitting diode; chip scale package; accelerated aging; step stress test; reliability qualification
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Qian, C.; Fan, J.; Fang, J.; Yu, C.; Ren, Y.; Fan, X.; Zhang, G. Photometric and Colorimetric Assessment of LED Chip Scale Packages by Using a Step-Stress Accelerated Degradation Test (SSADT) Method. Materials 2017, 10, 1181.

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