Contents lists available at ScienceDirect Journal of Materials Processing Tech. journal homepage: www.elsevier.com/locate/jmatprotec Rapid sintering of nano-Ag paste at low current to bond large area (> 100 mm 2 ) power chips for electronics packaging Yijing Xie a,b , Yanjie Wang a,b , Yunhui Mei a,b, ⁎ , Haining Xie c , Kun Zhang c , Shuangtao Feng a,b , Kim S Siow d , Xin Li a,b , Guo-Quan Lu e a Key Laboratory of Advanced Ceramics and Machining Technology of Ministry of Education, Tianjin University, Tianjin, 300350, China b School of Materials Science and Engineering, Tianjin University, Tianjin, 300350, China c State Key Lab of Advanced Power Transmission Technology, Global Energy Interconnection Research Institute, Beijing, 102209, China d Institute of Micro-Engineering and Nanoelectronics, Universiti Kebangsaan Malaysia, UKM Bangi 43600, Selangor D.E., Malaysia e Department of Materials Science and Engineering, Virginia Tech, Blacksburg, 24061, USA ARTICLE INFO Keywords: Nano-Ag Die-attach Current-assisted sintering IGBT Twin ECAS ABSTRACT We achieved robust bonding of a large area power chip (> 100 mm 2 ) with sintered Ag joint produced by the electrical current assisted sintering (ECAS) technique operating at low current (1.1 kA) and short sintering time (10 s). Our ECAS-ed Ag joint possessed low thermal resistance (∼0.18 °C/W), high density (89.6%), as well as good static and dynamic electrical properties during switching on and off of the power chip. Our TEM analysis explained that the good electrical and thermal performances of the power chip were attributed to the high density of twins formed in the ECAS-ed nano-Ag joint. 1. Introduction Power semiconductor, such as, insulated gate bipolar transistors (IGBTs), diodes, and inverters, are widely used in various power ap- plications in renewable energies and lamp circuit. Li et al. (2014) in- troduced eddy current pulsed thermography to characterize peel-off of bond wire in the IGBT modules. This development and others extended the investigation and application of power semiconductor and elec- tronic devices. Others like Ji et al. (2014) studied the mechanism of high thermal conductivity by pressureless sintering of a paste con- taining silver nanoparticles. The industry key trends show an increase in power density, use of wide-band gap semiconductor (e.g., gallium nitride (GaN) and silicon carbide (SiC)) and junction temperatures, in some instance to more than 125 °C, for these power devices. In these demanding condition, traditional die-bonding materials like high lead solders suffered from thermal fatigue-creep failure because of their low homologous temperature. At the same time, there is an on-going in- dustry-wide initiative to search for an alternative Pb-free bonding material to operate reliably at temperature higher than 200 °C for die- bonding applications. Lim Sze Pei et al. (2017) and Shen et al. (2016) reviewed the different alternatives of die-bonding and claimed that the pressure-less sintered Ag joint, ranging from 200 °C to 250 °C, is the most popular choice. Such bonding with metallic or metallo-organic nanoparticles has already been demonstrated much earlier by Ide et al. (2005), albeit on copper substrates. Since then, much progress has been made in (Scheuermann, 2009) and (Göbl and Faltenbacher, 2011) in- cluding manufacturing of power module with pressure-assisted sintered silver as bonding materials and evaluating the reliability of the power electronic module. Here, we can generalize that the main bonding techniques for sin- tered Ag are pressure assisted sintering (also known as hot-pressing) and pressure-less sintering, which has cycle time ranging from 5 min for pressure sintering (5–10 MPa) to an hour for a completely pressureless sintering process (Siow and Lin, 2016). In terms of reliability, Yu et al. (2017) and Chua and Siow (2016)) compared the mechanical properties and microstructure of the pressureless and pressure sintered nano-Ag joints, results show that the pressure assisted sintering has higher mi- crostructural stability and density than the pressureless sintered Ag joints. Due to this long cycle time in pressureless sintering and relia- bility issue, there is a continuous interest to formulate new Ag pastes with better bonding quality or alternative bonding methods that elim- inate the pressure and reduce the sintering time during the bonding process. One such rapid sintering technology is known as electrical current assisted sintering (ECAS) which is widely used in other in- dustries. Grasso et al. (2008) reviewed the evolution and optimization of ECAS devices and processes. Mei et al. (2013) explored the feasibility of ECAS by applying alternating pulse current with nano-Ag paste to achieve this strong bonding with copper substrate. https://doi.org/10.1016/j.jmatprotec.2018.01.017 Received 7 July 2017; Received in revised form 22 November 2017; Accepted 16 January 2018 ⁎ Corresponding author. E-mail address: yunhui@tju.edu.cn (Y. Mei). Journal of Materials Processing Tech. 255 (2018) 644–649 0924-0136/ © 2018 Elsevier B.V. All rights reserved. T