Ultraviolet radiation curable epoxy resin encapsulant for light emitting diodes

Kumar, R. N.; Keem, Lim Yoke; Mang, Ng Chee; Abubakar, A.

doi:10.1002/app.23189

Cited by 31 publications

(19 citation statements)

References 39 publications

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“…Epoxy resin, or even optical grade epoxy resins, has been used as encapsulant for several years due to its high transmittance, high refractive index (1,5 to 1,6), high glass transition temperature (T g ), good thermal stability and mechanical properties [18][19]. However, several problems have been identified in GaN-based LEDs.…”

Section: Light Extraction From the Packagingmentioning

confidence: 99%

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Optical performances degradation of InGaN/GaN MQW LEDs related to fluorescence shift of copolymer-based silicone coating

et al. 2011

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Accelerated ageing tests (1500h/85°C/30mA) performed on packaged InGaN/GaN MQW LEDs have reported a fluorescence shift of silicone oil responsible for optical losses. Electrical and optical characteristics highlight a 65% loss of optical power. Through measurements of the copolymer silicone coating fluorescence emission spectra, we demonstrate that the polymer fluorescence (induced from the blue light emitted from the chip) enlarges the LED emission spectrum (7%) and shifts central wavelength (5 to 7 nm). To understand such a fluorescence shift, Attenuated Total Reflection, Nuclear Magnetic Resonance (NMR), mass spectrometry and Differential Scanning Calorimetry (DSC) have been performed. The copolymer molecular structure has been affected after ageing. Actually, NMR and Mass spectrometry evidences the disappearance of low molecular weight molecules and the presence of high molecular weight molecules after ageing. Such a mechanism is associated with the polymerization of the silicone oil after ageing. Indeed, DSC has confirmed that silicone oil polymerization process is activated by temperature. Finally, both polymerization of the silicone oil due to temperature and fluorescence shift activated by photothermal process have been identified as the main failure mechanisms responsible for optical power degradation. CONTEXT AND OBJECTIVESGaN-based LEDs are currently used in a wide range of applications such as solid-state lighting, backlighting or full-color displays. It is well-known that polymer-based packaging degradation impacts operational reliability of InGaN/GaN Multiple Quantum Well (MQW) LEDs thus limiting their performances. Up to date, the polymer degradation mechanisms are not fully understood. To analyze such limitation, ageing tests have been delimited from both operating conditions and environment. Temperature, current or thermal cycling are the most predominant environmental stresses for the previous quoted applications. This paper mainly focuses on active storage as it is the most destructive one. Thus, primary challenge is to work out failure mechanisms responsible for the optical power decrease when the device is submitted to active storage (1500h/T max /I nominal ). Among the different parts of the packaging, the co-polymer silicone coating is pointed out to be the most sensitive part of the studied GaN-based technology. *raphael.baillot@ims-bordeaux.fr; phone +33 540 002-470; fax +33 556 371-545; www.ims-bordeaux.fr

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Section: Light Extraction From the Packagingmentioning

confidence: 99%

“…Moreover, such mechanism tends to amplify as temperature increases. Despite this fact, solutions have been proposed by Kumar et al using a UV curable epoxy resin [19]. A new chemical formulation of epoxy mixture has been reported resulting in higher optical performances and durability.…”

Section: Light Extraction From the Packagingmentioning

confidence: 99%

Optical performances degradation of InGaN/GaN MQW LEDs related to fluorescence shift of copolymer-based silicone coating

et al. 2011

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“…Light emitting diodes (LEDs) have been widely applied in many areas, including displaying, lighting, communications, medical services, signage, and general illuminations in recent years, owing to their favorable characteristics, such as higher luminosity at low currents and voltages, longer service life, versatility in a variety of colors, environmental friendliness, higher resistance to vibration, and higher tolerance to repeated power switching …”

Section: Introductionmentioning

confidence: 99%

Synthesis of an adhesion‐enhancing polysiloxane containing epoxy groups for addition‐cure silicone light emitting diodes encapsulant

Zhao

Feng

et al. 2014

Polymers for Advanced Techs

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Addition-cure silicone resin is considered as a good choice for light emitting diodes (LEDs); however, it has very poor adhesion to the substrate, which limits its practical application. A novel polysiloxane with self-adhesion ability and higher refractive index for the encapsulating of high-power LEDs is prepared and characterized. This polysiloxane containing vinyl groups, phenyl groups, and epoxy groups was synthesized by a sol-gel condensation process from methacryloxy propyl trimethoxyl silane, γ-(2,3-epoxypropoxy)propytrimethoxysilane, and diphenylsilanediol under the catalysis of an anion exchange resin. Then, the resin-type encapsulation material was prepared by hydrosilylation of methylphenyl hydrogen-containing silicone resin and the newly synthesized polysiloxane material. The novel polysiloxane was characterized by 1 H-NMR and Fourier transform infrared spectroscopy. On the basis of higher refractive index, higher transparency, excellent thermal stability, and appropriate hardness, as well as good adhesive strength between the encapsulating material and the LED lead frame (polyphthalamide), the curable silicone resin-type encapsulation material can be used as an encapsulant for LEDs.

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“…Epoxy monomers employed for LEDs encapsulation are either aromatic diglycidyl ether of bisphenol‐A (DGEBA) or cycloaliphatic epoxides cationically cured using thermal cationic initiator or cured thermally by an anhydride . However, there are several disadvantages associated with the thermal cure of epoxy formulations such as high cure temperature (>120 °C), long period of curing schedules requiring stringent process control to avoid failure of the devices, and high consumption of energy . A typical curing schedule reported by Lee et al .…”

Section: Introductionmentioning

confidence: 99%

Encapsulants for light‐emitting diodes from visible light‐cured epoxy monomers

Schroeder

Erba

Arenas

et al. 2013

Polymers for Advanced Techs

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During the last decade, light‐emitting diodes (LEDs) have replaced incandescent, fluorescent, and neon lamps due to their ability to produce high luminosity at low currents and voltages. LEDs are currently encapsulated by thermally curable epoxy resins. However, long periods of curing at high temperature result in high consumption of energy and require stringent process control to avoid failure of the devices. In addition, the thermal cure results in yellowing of the encapsulant, which decreases the efficiency of the LED. In recent years, photoinitiated polymerization has received much interest as it congregates a wide range of economic and ecological benefits. Cationic photoinitiators, such as diaryliodonium salts, generate Brønsted acid in situ, which initiates polymerization. The process can be triggered on demand by irradiating the mixture with light. Results from the present research reveal that cycloaliphatic epoxy monomers, photoactivated with an iodonium salt and Camphorquinone, polymerize readily under visible light irradiation (470 nm) in the absence of external heating. The partial replacement of cycloaliphatic epoxy with aromatic diglycidyl ether of bisphenol‐A (DGEBA) is an effective means of improving the refractive index of the material and consequently the efficiency of the photoemission. Visible light polymerization of DGEBA pure proceeds at a slow rate; however, it is enhanced by the increase in temperature during the polymerization of the highly reactive cycloaliphatic monomer. From results obtained in the present research, it may be concluded that visible light polymerization of epoxy monomers is a promising route for the processing of LED encapsulants. Copyright © 2013 John Wiley & Sons, Ltd.

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Ultraviolet radiation curable epoxy resin encapsulant for light emitting diodes

Cited by 31 publications

References 39 publications

Optical performances degradation of InGaN/GaN MQW LEDs related to fluorescence shift of copolymer-based silicone coating

Optical performances degradation of InGaN/GaN MQW LEDs related to fluorescence shift of copolymer-based silicone coating

Synthesis of an adhesion‐enhancing polysiloxane containing epoxy groups for addition‐cure silicone light emitting diodes encapsulant

Encapsulants for light‐emitting diodes from visible light‐cured epoxy monomers

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