Vol:.(1234567890) Journal of Materials Science: Materials in Electronics (2018) 29:8854–8862 https://doi.org/10.1007/s10854-018-8903-9 1 3 High-temperature reliability of low-temperature and pressureless micron Ag sintered joints for die attachment in high-power device Hao Zhang 1,2  · Chuantong Chen 2  · Jinting Jiu 2,3  · Shijo Nagao 1,2  · Katsuaki Suganuma 1,2 Received: 23 September 2017 / Accepted: 12 March 2018 / Published online: 15 March 2018 © Springer Science+Business Media, LLC, part of Springer Nature 2018 Abstract Micron Ag paste had a more afordable price, feasible large-scale synthesis, and longer storage life compared to nano Ag paste, thus it attracts much industrial interest for die attachment of high-power devices. However, the previous studies of high- temperature reliability were mainly focused on nano Ag joints, the research about reliability of micron Ag joints, especially low-temperature and pressureless, was very limited. Therefore, we evaluated high-temperature stability of low-temperature and pressureless micron Ag joint, involving in the changes of mechanical behaviors, evolution of microstructure and interfa- cial reliability. The average joint strength of micron Ag joints was independent of aging time and kept approximately 35 MPa after aging for 1000 h. The fracture of the micron joint was dominated by the ductile deformation of Ag grains during the fracture process. On the other hand, the microstructure of porous structure evolved greatly during aging process. Ag grains were oriented randomly before and after aging process, but the Ag grains increased slightly from 827.2 nm initially to 1178.4 nm after 1000 h aging. Meanwhile, the pores size in porous structure increased, the number decreased signifcantly, and the porosity also decreased slightly. Moreover, the barrier layers at interfaces of micron Ag joint remained stable and reliable during aging at 250 °C. The results would promote the large-scale application of the commercially available micron Ag paste in high-power devices. 1 Introduction Emerging SiC-based power devices can operate at higher temperature of 200 °C or above with a higher voltage and efciency, thus they have received increasing attention in hybrid electric vehicles (HEVs), aerospace and power gen- eration applications [1, 2]. In respond, the higher operation temperature also raises new challenges to die attachment, which is required to have a higher melting point, superior thermal conductivity and excellent reliability [3, 4]. How- ever, these requirements are beyond the endurance of most traditional high-temperature solder alloys [5–7]. For exam- ple, the thermal conductivity of Bi-based alloys was very poor, below 10 W/m k [8], thus heat dissipation problem will degenerate the performance, reliability and lifespan of devices. Zn-based solders exhibit a good mechanical behav- ior and reliability, but Zn element is traditionally very prone to corrosion and oxidation in moisture and oceanic environ- ments due to the high-oxygen afnities [9]. Therefore, there is a strong motivation to fnd a good alternative in high- temperature application. In order to address these issues, sintered Ag joining, using nanoparticles or micron particles, has emerged as one of the promising choices [10–19]. The Ag particles are sintered to a pure metal joint, which possesses a much wider melting temperature of 961.8 °C [11, 16, 17] and high thermal con- ductivity of 200–300 W/m k [11, 20]. Normally, compared to nano Ag particles, micron Ag particles are much less expensive, more feasible to large-scale synthesis process in industry and also have a longer storage life due to the aggre- gation problem of nanoparticles [3, 20, 21]. Thus, micron Ag paste is more desirable and easier to be promoted in industrial application. However, one of the major problems for micron-Ag paste is harsh sintering conditions [22–24]. Sintering the micron Ag particles always requires high tem- perature above 300 °C and the assistance of high pressures of 5–10 MPa [22–24], which will increase the manufacture * Chuantong Chen chenchuantong@sanken.osaka-u.ac.jp 1 Department of Adaptive Machine Systems, Osaka University, Osaka 567-0571, Japan 2 Institute of Scientifc and Industrial Research, Osaka University, Osaka 567-0047, Japan 3 Senju Metal Industry Co. Ltd., Tokyo 120-8555, Japan