物理学报2017，Vol.66Issue(4)：315-323,9.DOI:10.7498/aps.66.048501
GaN基通孔垂直结构的发光二极管失效分析
Failure analysis of GaN-based Light-emitting diode with hole vertical structure
摘要
Abstract
Light-emitting diode (LED) failure mechanism plays an important role in studying and manufacturing LEDs. In this paper, X-ray perspective instrument is used to carry out the non-invasive and real-time X-ray imaging detection of the representative LED packaging products purchased from 5 Chinese companies. A large number of the welded voids are founded in the thermal pad and the void ratio of thermal pad, which represents the ratio of void area to pad area, is more than 30% for all samples. 1 W warm white light LED of GaN-based vertical via structure is selected to study the mechanism of short-circuit invalidation. The method is carried out by the following steps. Firstly, the surface morphologies of failure samples are compared with those of normal samples by visual observation. Secondly, antistatic electric capacity testing instrument is used to detect the existences of the electrical parameter abnormalities of the failure of non-short-circuit samples. Thirdly, decapsulations are operated on samples by using Silica gel dissolving agent. And the microtopographies of the samples are characterized by optical microscope, energy dispersive spectrometer and scanning electron microscopy. Then the cross-sectional morphologies of failure samples are observed. The failure mechanism can be drawn from the characterizations mentioned above. The study shows that the failure mechanism of the vertical structure of GaN-based vias is that the existences of voids in the Ni-Sn alloy back gold layer and solid-crystal layer reduce the interface bonding strength and thermal conductivity of the LED chip. The heat building-up leads to thermal expansion of the air inside the voids, which increases the electrical stress and thermal stress distribution at the LED chip vias. Long-term heat accumulation and higher electrical stress in the through-hole region, where the chip current density is greatest, lead to the crack and break of GaN epitaxial layer, which is so brittle and fragile, around the through-hole region. It can eventually lead to short-circuit of PN junction and then failure of LED. Back gold layer is the heat-conductive and electric-conductive channel of LED. The concentrations of thermal stress and electrical stress caused by voids in the back gold layer further lead to the uneven current distribution on the chip. This is the main reason why GaN epitaxial layer cracks and breaks. Voids in the back gold layer and solid-crystal layer are the direct and indirect causes of LED short-circuit failure, respectively. Therefore, the packaging process should be standardized to avoid the void occurrence, based on the reasons why voids exist. It can finally improve reliability of LED.关键词
发光二级管/失效分析/空洞/可靠性Key words
light-emitting diode/failure analysis/void/reliability引用本文复制引用
符民,文尚胜,夏云云,向昌明,马丙戌,方方..GaN基通孔垂直结构的发光二极管失效分析[J].物理学报,2017,66(4):315-323,9.基金项目
Project supported by the Guangdong Province Applied Science and Technology Development, China (Grant No. 2015B010134001), the Guangdong Province Sail Plans to Introduce a Special Team of Innovation and Entrepreneurship, China (Grant No. 2015YT02C093), and the Guangzhou City Collaborative Innovation Major Projects, China (Grant No. 201604010006). 广东省应用型科技研发专项(批准号: 2015B010134001)、广东省扬帆计划引进创新创业团队专项(批准号: 2015YT02C093) 和广州市产学研协同创新重大专项(批准号: 201604010006)资助的课题. （Grant No. 2015B010134001）
