Light Output, Thermal Properties, and Reliability of Using Glass Phosphors in WLED Packages

Chin-Chuan Huang,Chun-Liang Lin,Tsung-Han Weng,Yan-Kuin Su

doi:10.3390/coatings11020239

Chin-Chuan Huang, Chun-Liang Lin + Show 2 more

Open Access

https://doi.org/10.3390/coatings11020239

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Journal: Coatings	Publication Date: Feb 17, 2021
Citations: 6	License type: CC BY 4.0

Affiliation: Kun Shan University, National Cheng Kung University

Abstract

White-light-emitting diodes (WLED) based on yttrium aluminum garnet (YAG) phosphors sintered with glass (PiG) and with silicone (PiS) are compared in terms of their light properties, temperature properties and reliability.The complete YAG phosphor was doped with an encapsulant traditional WLED (PiS WLED), and the WLED was covered with PiG (PiG WLED). PiG was made by sintering glass powder and YAG phosphor at the ratio of 87:13 (%), and the correlated color temperature (CCT) was 5564 K. The CCT of the PiG WLED with the YAG doping concentration of 8.5 wt.% approximated 5649 K. The initial light output of the PiG WLED was 6.4% lower than that of the PiS WLED. Under 1008 h and 350 mA aging, PiG WLED and PiS WLED’ light output, CCT and color rendering index variation rates were all within 1%. In the saturated vapor-pressure test, no sample exhibited red ink infiltration, light nor peeling between the encapsulant and the lead-frame. Compared with that of the PiS WLED, the junction temperature of the PiG WLED reduced from 88.4 °C to 81.3 °C. Thermal resistance dropped from 37.4 °C/W to 35.6 °C/W. The PiG WLED presented a better CIE (Commission Internationale de l’Eclairage) 1931 chromaticity coordinate (x,y) concentration and thermal properties than the PiS WLED.

Highlights

The application of light-emitting diodes (LEDs) has become widespread, the amounts of light and power used have increased, and the accompanying thermal problems have been relatively addressed and studied [1,2,3]
A small portion of the heat is transferred by heat convection and heat radiation through the packaging adhesive. This study investigated this part by using phosphor in glass (PiG) instead of phosphor in silicone (PiS)
Conventional white LED (WLED) packaging is made by using yttrium aluminum garnet (YAG) phosphors mixed in an encapsulant with blue LED excitation

Summary

Introduction

The application of light-emitting diodes (LEDs) has become widespread, the amounts of light and power used have increased, and the accompanying thermal problems have been relatively addressed and studied [1,2,3]. The lower the amount of phosphor doping concentration, the less heat accumulates inside the LED during operation, and the higher the efficiency of external heat transfer will be [5]. This problem cannot be solved by the adjustment of the phosphor concentration because phosphor concentration directly affects the CIE coordinates and correlated color temperature (CCT) of WLEDs. The precipitation problem of encapsulant mixed with phosphors [6,7] can be solved by sintering the phosphors in glass. Two different packaging structures, namely PiS and PiS, were compared, and the light output flux and thermal properties were discussed [17,18,19]

Materials

Experimental Procedure

Findings

Conclusions