Understanding the transport phenomena leading to tarnishing of the reflecting silver layer causing reduced light output of LEDs

Herrmann, Annemarie; Erich, Sjf Sebastiaan; Ven, L.G.J. van der; Driel, W.D. van; Soestbergen, M. van; Mavinkurve, A.; Buyl, François de; Adan, O.C.G.

doi:10.1109/eurosime.2017.7926238

Cited by 3 publications

(4 citation statements)

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“…As the silver tarnishes, the reflective behavior changes, especially in the blue and green spectral range, causing short-wave radiation to be absorbed more strongly [24]. The oxidation reaction can be accelerated by sulfur, halogens, chlorines, iodines, or bromides in the region of the silver reflector [25], [26].…”

Section: Discussionmentioning

confidence: 99%

Long-Term Temperature-Dependent Degradation of 175 W Chip-on-Board LED Modules

Herzog

Wagner

Benkner

et al. 2022

IEEE Trans. Electron Devices

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We report on the degradation dynamics and mechanisms of the commercially available chip-on-board (COB) high-power light-emitting diode (LED) modules with an electrical power of 175 W. Due to the associated thermal load, the temperature dependence of the aging processes is additionally analyzed within the scope of this work. The aging tests were performed for a period of 6000 h at four different case temperatures between 55 • C and 120 • C. The results of the accelerated stress tests indicate a temperature-activated aging process, which severely limits the lifetime of the modules. In addition, the following key findings can be reported: 1) a significant decrease in optical power occurs within 6000 h of operation; 2) depending on the stress test condition the accompanying color shifts exceed a limit of u v = 0.007; and 3) the limiting degradation mechanism can be attributed to the package of the device and can be accelerated with temperature, current, and chemicals. Reported findings can be manifested by additional optical material inspections, allowing to use the results for optimizations of future module generations.

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Section: Discussionmentioning

confidence: 99%

Long-Term Temperature-Dependent Degradation of 175 W Chip-on-Board LED Modules

Herzog

Wagner

Benkner

et al. 2022

IEEE Trans. Electron Devices

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“…A commercially available optical grade silicone resins (OE-6650, Part A &B 1:3 ratio; supplied by Dow Corning*) with a high refractive index of 1.54 were used. In contrast to low refractive index silicones, which are made up of pure poly-dimethyl-siloxane (PDMS), this resin contains a higher amount of phenyl-siloxane, which increase the refractive index of the silicone (1.41 in pure PDMS vs. 1.55 in poly-methyl-phenyl siloxane polymer) [7,36]. Now, a thin layer of silicone resin (40 m) was manually casted on the substrate using bar coater and cured at 150 • C for 2 h. Another set of copper alloy (C581) sheet is used as deposition target and deposited on a ZnSe internal reflection element (IRE) crystal (and on glass substrate to characterize the surface of metallic film) using high vacuum evaporating system in order to mimic similar chemical composition of the metallic substrate on the crystal.…”

Section: Sample Preparationmentioning

confidence: 99%

“…Upon diffusion through the polymer, the contaminants will reach the packaging/metallic circuitry interface and initiate an interfacial corrosion process. Reports devoted to the basic understanding of the transport phenomena involved are limited [3][4][5][6][7]. Two main transport pathways are identified in the microelectronics and LED packaging systems.…”

Section: Introductionmentioning

confidence: 99%

“…As the water uptake in polymers is a root cause for the initiation of the corrosion process, researchers worldwide investigated water transport behaviour using electrochemical impedance spectroscopy (EIS), gravimetry, infrared spectroscopy, differential scanning calorimetry, dynamic vapour absorption, finite element analysis and molecular dynamics study [7][8][9][10][11][12]. Studies have shown that the water and ions penetrate through micropores and free volume of the polymer coatings and surface inhomogeneities or inherent defects may influence their ionic conduction [13,14].…”

Section: Introductionmentioning

confidence: 99%

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Exploring water and ion transport process at silicone/copper interfaces using in-situ electrochemical and Kelvin probe approaches

Munirathinam

Dam

Herrmann

et al. 2021

Journal of Materials Science & Technology

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In general, packaging materials which encapsulate light emitting diodes (LEDs) and microelectronic devices offer barrier protection against several environmental hazards such as water and ionic contaminants. However, these encapsulants may provide pathways for water and ionic contaminants to reach the metal/polymer interfaces and provoke local corrosion of electronics, which is a major reliability concern for polymer encapsulated LEDs and microelectronics. As the water and corrosive constituents play a crucial role in their reliability, water uptake kinetics, interfacial ion transport and delamination behaviour of silicone coated copper model system, mimicking a typical microelectronics packaging system, is explored in the present work. Electrochemical impedance spectroscopy (EIS) integrated with attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy studies revealed that water diffusion inside the silicone network is Fickian in nature and the evolution of the observed time constants are related to the diffusion and interfacial reactions. A decrease of impedance magnitude with time was observed in EIS measurements concurrently with water absorption bands shifting towards lower wavenumber in ATR-FTIR measurements, implying the growth of strong hydrogen bonding between water molecules and the silicone network. The estimated diffusion constant of water using the capacitance method was in the order of 7 × 10 -12 m 2 s −1 and the water absorption volume fraction was in the range of 0% to 0.30%. Scanning Kelvin probe studies elucidated the ion transport process occurring at the silicone/copper interface in a humid atmosphere. The interfacial ion transport process is controlled by the interfacial electrochemical reactions at the cathodic delamination front and the estimated average delamination rate is 0.43 mm h -1/2 . This work demonstrates that exploring ion and water transport in the silicone coating and along the silicone/copper interface is of pivotal importance as part of a detailed reliability assessment of the polymer encapsulated LEDs and microelectronics.

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