13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Fatigue and dwell-fatigue behavior of nano-silver sintered lap-shear joint at elevated temperature Yansong Tan1, Xin Li2, Chengjun Li1, Xu Chen1,* 1 School of Chemical Engineering & Technology, Tianjin University, Tianjin 300072, China 2 School of Material Science and Engineering, Tianjin University, Tianjin 300072, China * Corresponding author: xchen@tju.edu.cn Abstract Load-controlled fatigue and dwell-fatigue tests were conducted at elevated temperature to describe the high temperature behavior of nano-silver sintered lap-shear joints. The results show that the shear strength of nano-silver sintered lap-shear joints are strongly temperature dependent, and almost halved at the temperature of 325℃. To describe the temperature effect on fatigue life under fully-reversed loading, Basquin’s equation is developed by introducing temperature factor, and shows a good agreement with experiment results. In dwell-fatigue tests, creep is found the main factor resulted in failure acceleration and cyclic life reduction. Keywords lap-shear, fatigue, dwell-fatigue, Basquin’ equation, temperature dependent 1. Introduction Nowadays, the use of tin-lead solder in certain application has been banned for its damage on healthy. However, there still are some fields such as power electronics packaging using high lead solder as interconnected material [1], which can be mainly attributed to the absence of appropriate substitution. Therefore, the introducing of environmental friendly die-attaching material becomes more and more important due to increasing stringent requirements of weight reduction, size miniaturization, high thermal dissipation, etc. [2]. In the 1970s, the view of diffusion welding silver film had been introduced by O'brien et al.[3], and thus a new die-attaching technology named low-temperature joining technology was remarkably promoted. With the assistance of mechanical pressure of about 40MPa, micro-sized silver powder could be sintered at temperature below 300℃ [4]. From then on, silver is used widely in microelectronic packages as a promising interconnection material between substrates and chips because of its superior electrical/thermal conductivity, high melting temperature (1,233 K), and good reliability. Though, for brittle silicon chips and ceramic substrates, the aided pressure might be destructive even slightest irregularities [5]. To raise the sintering driving force of this interconnection material, the paste formed by nano-sized silver powder, which gained the close attention of both scientists and power electronics engineers, was introduced by Lu et al [6]. Before the sintering technology coming into practical application, the processing profile and the property of nano-silver paste had been studied. In recent years, A low-temperature sintering profile with sintering temperature of 285℃, heating rate of 10℃/min, and holding time of 60 min was introduced by Wang et al [7]. Yu et al. studied the tensile behaviors of low-temperature sintered nano-silver films and proved that accumulation of plastic strain took place in silver-bonding layer during thermal cycling, which might lead to the final failure of the chip-attachment [8]. Chen et al. stated that the process of damage evolution of the nano-silver films was temperature independent by
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