Thermal management and humidity based prognostics of high-power LED packages

Law, Thong Kok (2019) Thermal management and humidity based prognostics of high-power LED packages. PhD thesis, University of Glasgow.

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While Light Emitting Diodes (LEDs) hold much potential as the future of lighting, the high junction temperatures generated during usage result in higher than expected degradation rates and premature failures ahead of the expected lifetime. This problem is especially under-addressed under conditions of high humidity, where there has been limited studies and standards to manage humidity based usage. This research provides an analysis of the factors that contribute to high junction temperatures and suggests prognostic techniques to aid in LED thermal management, specifically under humidity stress.
First, this research investigates the effects of current, temperature and humidity on the electrical-optical-thermal (EOT) properties. Temperature rises within an LED because of input stressors which cause heat to build up: the input current, the operating and ambient temperature, and the relative humidity of the environment. Not only is there an accumulation of heat due to these factors that alter the thermal properties, but the electrical and optical characteristics are changed as well. By uncovering specific configurations causing the EOT performance to degrade under stress, better thermal management techniques can be employed.
Second, this research proceeds to quantitatively link the EOT performance degradation to the humidity causal factor. The recent proliferation of LED usage in regions with high humidity has not corresponded with sufficient studies and standards governing LED test and usage under the humidity stressor. This has led to indeterminate use and consequentially, a lack of understanding of humidity based failures. A novel humidity based degradation model (HBDM) is successfully developed to gauge the impact of the humidity stressor by means of an index which is shown to be an effective predictor of colour degradation. This prognostication of the colour shift by the HBDM provides both academia and industry not only with an indicator of the physical degradation but also an assessment of the LED yellow-blue colour rendering stability, a critical application criterion. Using the HBDM parameters as indicators of the state of the LED, the degradation study is expanded in the development of a Distance Measure approach to isolate degraded samples exceeding a specified multivariate boundary. The HBDM and Distance Measure approach serve as powerful prognostic techniques in overall LED thermal management.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: List of publications: [1] T. K. Law and F. Lim, "A Practical Degradation Based Method to Predict Long-Term Moisture Incursion and Color Change in High Power LEDs," IEEE Photonics Journal, vol. 10, pp. 1-14, 2018. [2] T. K. Law, F. Lim, Y. Li, X. Puan, G. K. E. Sng, and J. W. Ronnie Teo, "Effect of Packaging Architecture on the Optical and Thermal Performances of High-Power Light Emitting Diodes," ASME Journal of Electronic Packaging, vol. 139, pp. 0310031-0310035, 2017. [3] T. K. Law, F. Lim, Y. Li, K. K. G. Yeong, G. K. E. Sng, M. V. Uvarajan, et al., "Implications of Phosphor Coating on the Thermal Characteristics of Phosphor-Converted White LEDs," IEEE Transactions on Device and Materials Reliability, vol. 16, pp. 576-582, 2016. [4] T. Law, F. Lim, Y. Li, J. R. Teo, and S. Wei, "Effects of Humidity on the Electro-Optical-Thermal Characteristics of High-power LEDs," in IEEE 18th Electronics Packaging Technology Conference, 2016, pp. 718-723. [5] T. K. Law, F. Lim, Y. Li, J. W. R. Teo, and Z. M. Tai, "Achieving Accurate Electro-Optical-Thermal Measurements of High-power LEDs," in IEEE 17th Electronics Packaging and Technology Conference, 2015, pp. 1-7.
Keywords: Light emitting diodes, photonics, reliability engineering, thermal sciences.
Subjects: T Technology > TK Electrical engineering. Electronics Nuclear engineering
Colleges/Schools: College of Science and Engineering > School of Engineering
Supervisor's Name: Lim, Dr. Fannon
Date of Award: 2019
Depositing User: Mr Thong K Law
Unique ID: glathesis:2019-74278
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 20 Aug 2019 13:14
Last Modified: 10 Dec 2019 10:59
Thesis DOI: 10.5525/gla.thesis.74278
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