Experimental characterization of the mechanical behavior of two solder alloys for high temperature power electronics applications S. Msolli ⇑ , J. Alexis, O. Dalverny, M. Karama Université de Toulouse, INP/ENIT, LGP, 47, avenue d’Azereix, F-65013 Tarbes, France article info Article history: Received 20 August 2014 Accepted 16 September 2014 Available online 30 September 2014 Keywords: Power electronics High temperature Shear Creep Nano-indentation Hardening abstract An experimental investigation of two potential candidate materials for the diamond die attachment is presented in this framework. These efforts are motivated by the need of developing a power electronic packaging for the diamond chip. The performance of the designed packaging relies particularly on the specific choice of the solder alloys for the die/substrate junction. To implement a high temperature junction, AuGe and AlSi eutectic alloys were chosen as die attachment and characterized experimentally. The choice of the AlSi alloy is motivated by its high melting temperature T m (577 °C), its practical elaboration process and the restrictions of hazardous substances (RoHS) inter alia. The AuGe eutectic solder alloy has a melting temperature (356 °C) and it is investigated here for comparison purposes with AlSi. The paper presents experimental results such as SEM observations of failure facies which are obtained from mechanical shear as well as cyclic nano-indentation results for the mechanical harden- ing/softening evaluation under cyclic loading paths. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Nowadays, high-temperature power electronics packaging designed for the power electronics systems are paramount compo- nents of the electrical inverters in the hybrid electrical vehicles as well as the aeronautical and military engines. Mainly, a power electronic packaging is subjected to a high thermomechanical and power cycling as well as external environmental conditions such as moisture and corrosion. At the end of the packaging life- time, the failure happens very often due to the voids growth and microcracks propagation in the solder alloy. The last constitutes the major cause of the lifetime reduction. To take up the wide temperature ranges and the high current densities, a new high temperature packaging generation is currently investigated. In power electronic applications, diamond based semi-conductors appear to be the solution in order to widely increase the capabili- ties of the power electronic converters [1]. Diamond is known to have exceptional thermal, electrical and mechanical properties. In order to make use of the exceptional characteristics of the dia- mond and increase the packaging reliability at high temperatures, a good choice of the die attachment is primordial to improve the thermomechanical behavior of the electronic device. Many technologies have been proposed in the literature [4,5]. The first technology is concerning solders with a high melting temperature. Inspite of the availability of high temperature solders in power electronics, researches involving this kind of materials are scarce. The implementation cost of these alloys remains the major obsta- cle to their use. It should be also denoted that most solders which operate at temperatures higher than 500 °C are ternary alloys that may potentially cause the formation of unfavorable intermetallic phases in the interfaces. But this was not the rule. For example, studies were conducted on some ternary alloys such as the ternary systems AuAgGe and AgCuSb. It has been shown that for an AgCuSb system, the wettability, the temperature melting, the qual- ity of the interface as well as the microstructure, are favorable for operating between 400 °C and 500 °C. This system is also compat- ible with a Ni/Au metallization deposited on an AlSiC substrate. No cracks or brittle intermetallic phases are formed [15]. However, Sb is an element classified as toxic although it is not affected by the RoHS and WEEE directives. Works are underway to test AuAgSi alloy with the same kind of metallization [11]. A second technology proposed to solve the problem of solder fatigue is to replace soldering by another technique compatible with the power module service conditions. This is achieved by replacing the junction chip/substrate and wire bonding connection by a low temperature sintering technique involving more resistant materials and thereby, minimizes the residual stresses produced at the elaboration process. Sintering consists on a powder form alloy which is subjected to a thermomechanical process (temperature http://dx.doi.org/10.1016/j.microrel.2014.09.021 0026-2714/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +33 5 62 44 27 16; fax: +33 5 62 44 27 08. E-mail address: sabeur.msolli@univ-lorraine.fr (S. Msolli). Microelectronics Reliability 55 (2015) 164–171 Contents lists available at ScienceDirect Microelectronics Reliability journal homepage: www.elsevier.com/locate/microrel