Effects of humidity and phosphor on silicone/phosphor composite in white light-emitting diode package

Abstract

Silicone/phosphor composite, which serve as mechanical protection and light conversion material, is an integral part of white light-emitting diode (LED) package. In this paper, a comprehensive study is conducted to investigate the effect of humidity and phosphor on moisture absorption, hygroscopic swelling, mechanical behavior, as well as thermal properties of silicone/ phosphor composite in comparison with the pure silicone. SEM/EDAX and FTIR were performed to identify the phosphor and silicone compositions. Through moisture sorption test, it has been observed that the addition of phosphor significantly lowers the capacity of moisture absorption, but accelerates the diffusivity of moisture absorption. The hygroscopic swelling test showed that the phosphor has little effect on the swelling compared to the pure silicone sample. Both moisture absorption/desorption and hygroscopic swelling/de-swelling are reversible. Strain ramp test revealed that the phosphor enhances the stiffness of the composite. The moisture absorption, however, has negligible impact on mechanical stiffness for both pure and composite samples. Finally, thermal expansion test showed that the coefficient of thermal expansion does not change with the addition of phosphor into pure silicone.

Sulfur-Rich Ageing Mechanism of Silicone Encapsulant Used in LED Packaging: An Experimental and Molecular Dynamic Simulation Study

“…The increases in Young's modulus and tensile strength had occurred in the four groups of silicone samples. The Young's modulus and tensile strength of silicone under humidity stress ageing conditions were higher than those of the samples aged under dry conditions because the hydrolysis reaction occurred under high humidity conditions (Fan et al, 2019;Hoque et al, 2019). In addition, the Young's modulus and tensile strength of the silicone samples treated under the sulfurized environment were largely higher than those of the samples aged without sulfur, which indicated that sulfur could accelerate the mechanical degradation of silicone.…”

“…Luo et al, (2017), Fan et al, (2019) studied a long-term degradation mechanism of phosphor/silicone composites under the conditions of high temperature and humidity with comparing the optical and mechanical properties of the aged composites. Khalilullah et al (2017), Hoque et al (2019) investigated the influence of humidity on phosphor/silicone composites and reported the reversibility of the hygroscopic expansion process occurring in the absorption/desorption cycle. They also concluded that exposure to moisture will cause permanent damage to silicone materials.…”

Spinel-Based ZnAl2O4: 0.5%Cr3+ Red Phosphor Ceramics for WLED

“…In this context, chromium (Cr 3+ ) ions, as transition metal ions with abundant reserves and the potential to serve as red emitting centers, have garnered widespread attention as activators for LED phosphor materials [13][14][15][16][17]. Another major issue faced by pc-WLEDs is the poor thermal conductivity of the phosphor film due to the current packaging method, where transparent silicone gel and phosphors are mixed and encapsulated on LEDs [18]. In response to this challenge, high thermal conductivity fluorescent ceramics have emerged, especially suitable for high-power/high-brightness excitation [19][20][21].…”