High Moisture Accelerated Mechanical Behavior Degradation of Phosphor/Silicone Composites Used in White Light-Emitting Diodes

Jiajie Fan; Zhen Wang; Zhentao Deng; Xuejun Fan; Guoqi Zhang

doi:10.3390/polym11081277

High Moisture Accelerated Mechanical Behavior Degradation of Phosphor/Silicone Composites Used in White Light-Emitting Diodes

Polymers (Basel). 2019 Jul 31;11(8):1277. doi: 10.3390/polym11081277.

Authors

Jiajie Fan^{1

2

3}, Zhen Wang^{4

5}, Zhentao Deng⁶, Xuejun Fan⁷, Guoqi Zhang⁸

Affiliations

¹ College of Mechanical and Electrical Engineering, Hohai University, Changzhou 213022, China. jay.fan@connect.polyu.hk.
² State Key Lab of Solid State Lighting, Changzhou Institute of Technology Research for Solid State Lighting, Changzhou 213164, China. jay.fan@connect.polyu.hk.
³ Department of Microelectronics, EEMCS Faculty, Delft University of Technology, 2628 Delft, The Netherlands. jay.fan@connect.polyu.hk.
⁴ College of Mechanical and Electrical Engineering, Hohai University, Changzhou 213022, China.
⁵ State Key Lab of Solid State Lighting, Changzhou Institute of Technology Research for Solid State Lighting, Changzhou 213164, China.
⁶ College of Chemistry and Environmental Engineering, Shenzhen University, Shenzhen 518061, China.
⁷ Department of Mechanical Engineering, Lamar University, Beaumont, TX 77710, USA.
⁸ Department of Microelectronics, EEMCS Faculty, Delft University of Technology, 2628 Delft, The Netherlands.

Abstract

In a high-power white light emitting diode (LED) package, the phosphor/silicone composite is typically used for photometric and colorimetric conversions, ultimately producing the white light. However, the phosphor/silicone composite is always exposed under harsh environments with high temperature, high blue light irradiation and high moisture when the LED operates. Therefore, its reliability issue has become one of the critical bottlenecks to improve the lifetime of a high-power white LED package. As the curing process and mechanical behavior of phosphor/silicone composite essentially determine its reliability, this paper firstly uses an in situ viscosity monitoring approach combined with Differential Scanning Calorimetry (DSC) and Fourier Transform Infrared Spectroscopy (FTIR) analysis to explain the curing mechanism of a phosphor/silicone composite by taking the effects of temperature and phosphor mass fraction into consideration. Then, the mechanical properties of phosphor/silicone composites aged under a long-term high moisture condition are evaluated by using the tensile test. Meanwhile, the finite element (FE) simulations, the Mori-Tanaka theoretical estimations and the microstructure analysis are applied to investigate the high moisture induced degradation mechanisms. The results show that: (1) the in situ measured isothermal viscosity curves of both pristine silicone and phosphor/silicone composites follow the Arrhenius empirical model, and high temperature and high phosphor mass fraction can increase the curing rate; (2) the hydrosilylation reaction between silicones determines the curing mechanism of phosphor/silicone composite; (3) the tensile test, FE simulation and Mori-Tanaka theoretical prediction results confirm that the Young's modulus of phosphor/silicone composite increases by gradually adding phosphors; and (4) the Young's modulus of phosphor/silicone composite increases after the high moisture ageing test, which can be attributed to the oxidation and cross-linking reaction of silicone and the hydrolysis of phosphor powders.

Keywords: curing mechanism; light-emitting diode; mechanical properties; moisture; phosphor/silicone composite.

Abstract

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