Development and reliability analysis of novel die attach material for light emitting diodes

• Main Authors: Po-Hung Liu, 劉柏宏
• Other Authors: 陳志銘
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/12399072476481250359

碩士 === 國立中興大學 === 化學工程學系所 === 99 === In recent years, the light emitting diode is a crucial breakthrough in the technology of illumination development. However, there are only 40~50% of the input power converting to light and the rest convert to heat. The heat is a great defect for electronic product because it might make LEDs not work efficiently and shorten the lifespan of LEDs. Hence, how to dissipate the heat from LED is an important lesson. In the market, the sliver paste which thermal conductivity coefficient is only 10~20 W/mK is commonly used as die attach material, but it may be not suitable for the high power LED. For high power LEDs, we use Sn-3wt.%Ag-0.5wt.%Cu (SAC305) which thermal conductivity coefficient is about 60 W/mK for die attach material in LED fabrication. Although the thermal conductivity coefficient of SAC305 is higher than silver paste, there are only limiting ability for lowering the temperature on LED surface. To overcome this problem, we try to mix SAC305 with different ratio of carbon nanotubes (3000~3500W/mK), and then screen-print it on heat sink. Based on the infrared image and thermal resistance analysis, this composite solder can lower the surface temperature and the total thermal resistance of LED, which confirm that the composite solder is useful in dissipating heat. We separated the total thermal resistance into three parts, LED, die attach material, and heat sink, respectively, to understand the partial thermal resistance of the LED device. In the fabrication of LED, there might exist voids at the interfaces of LED/die attach material and die attach material/heat sink, which would cause the contact thermal resistance. In the fabrication of LED, the mechanic strength decides the life of LED device. In our research, we tested the mechanic strength of different die attach materials. And then, we made the cross sections of the die attach layers to observe the cross-sectioned microstructure using the scanning electron microscopy(SEM).