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The preparation and evaluation of a zirconia/ oligosiloxane nanocomposite for LED encapsulation Pao-Tang Chung, Shian-Hau Chiou, Chin-Yao Tseng, and Anthony Shiaw Tseh Chiang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b02082 • Publication Date (Web): 31 Mar 2016 Downloaded from http://pubs.acs.org on April 10, 2016

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ACS Applied Materials & Interfaces

The preparation and evaluation of a zirconia/oligosiloxane nanocomposite for LED encapsulation Pao-Tang Chung, Shian-Hau Chiou, Chin-Yao Tseng, Anthony Shiaw-Tseh Chiang* Department of Chemical & Materials Engineering, National Central University, JungLi, TaoYuan, Taiwan, ROC 32054 KEYWORDS: LED, encapsulation, nanocomposite, oligosiloxane, zirconia

ACS Paragon Plus Environment

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ABSTRACT

A zirconia/oligosiloxane nanocomposite encapsulant has been developed and tested in a highpower LED package against commercial silicone resins. The composite was a marriage of zirconia nanocrystals modified with BA (butyric acid) and MPTMS (3-methacryloxy propyl trimethoxysilane) and a high index methacryloxy-oligosiloxanes resin made from MPTMS plus dimethyl, diphenyl, and triphenyl silanes. The modified zirconia had an index of 1.762 (@589nm) and was dispersible in many solvents. The oligosiloxane resin, on the other hand, had an index of 1.5413 with good encapsulation properties and low viscosity allowing the incorporation of more zirconia. The final nanocomposite showed a refractive index of 1.625 with high transparency and a wavelength-independent scattering, both desirable for the light extraction from LED. When tested in a high-power LED package, the composite encapsulant resulted in 13% more light output compared to the commercial encapsulant (OE-6630, Dow Corning Corp.) and showed longer than 1000 hours of lifetime (L70) under the steady state Temperature Humidity Bias (THB) test.


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INTRODUCTION

The internal quantum efficiency of solid-state lighting, or light emitting diodes (LEDs), has dramatically improved over the past decades, thus enabled the production of high-quality lighting in versatile applications. However, to take full advantage of the quantum efficiency, continuous studies on improving the external efficiency of an LED package are still needed. Among the many aspects affecting the external efficiency, the development of a better encapsulation material with high transparency, long-term thermal and moisture stability, good heat conductivity and high refractive index (RI) is essential. High-RI encapsulant is needed to alleviate the interface index mismatch and to improve the extraction of light. Good heat conductivity helps to dissipate the heat and reduces the junction temperature of the LED chip, thus promotes the quantum yield.

The epoxy resin has been the popular LED encapsulant for its good insulation to moisture, strong adhesion to metal, mechanical robustness and, most importantly, low cost. There are several ways to increase the RI of an epoxy encapsulant, such as the curing with a cationic initiator1, the inclusion of thiol compounds2 as well as TiO2 or ZrO2 nanocrystals3-5. The incorporation of ZrO2 nanocrystal also increases the thermal conductivity and brings a lower junction temperature4. However, the long-term thermal and moisture stability of epoxy-based encapsulant is only suitable for LED operated at 1000

C-2

0.992/1

39.5

52.3

55.0

24.4

1.5950

1.5941 1.5936 424

C-3

1.491/1

47.5

58.5

61.6

32.6

1.6146

1.6131 1.6127 322

C-4

1.866/1

51.7

61.8

64.4

37.7

-

1.6248 -

-

79.4

83.5

83.5

100

1.7620 c -

-

Filler 1/0

a: Calculated based on the TGA residue of filler (83.5%) and S-3(21.3%). b: Calculated based on the density of filler (3.11 g/mL) and that of cured silicone (1.01 g/mL). c: Estimated from the zirconia contents in the filler and confirmed with index measured on 2Phenoxy ethyl acrylate dispersions at various filler loadings.


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ASSOCIATED CONTENT

Supporting Information. The specifications of the LED packages, the characteristics of the modified zirconia (1H NMR spectrum, RI, DLS), the

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Si NMR spectra of the oligosiloxane resins, pictures of the

encapsulations, TGA analysis results of the composites and the view angle of the packages. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author *Email: [email protected]. ACKNOWLEDGMENT This work was supported by the National Science council (NSC) of ROC through grant NSC 102-2622-E-008 -003.


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TOC graphic

Light Output power (mW)

500 400 300 200 100 0 0

100 200 300 Injection current (mA)

100 Relative output power(%)

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95 90 85 80 OE-6336 OE-6630 ZrO2/oligosiloxane

75 70 65 60 0

200

400 600 Time(hr)

800 1000


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Preparation and Evaluation of a Zirconia ... - ACS Publications

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