Abstract
This study investigates the power cycling reliability of nanosilver sintered joints formed by a time-reduced sintering process, designed for use on a die bonder. A range of sintering parameters, reflecting different levels of manufacturability, were used to produce sintered joints in respect of shear strength and porosity, within a process cycle time of a few seconds. The reliability of the sintered attachments were evaluated against Pb5Sn solder joints under constant temperature swing power cycling conditions over the range 50 to 200 °C. The thermal performance and microstructural changes of the sintered joints were monitored and evaluated non-destructively at regular intervals using transient thermal impedance and X-ray computed tomography. The results show that sintered joints with higher shear strengths (>50 MPa) and lower porosities (<25 %) tend to maintain their thermal performance up to ~100k power cycles before gradual degradation occurs. Sintered joints with intermediate shear strengths (20 to 40 MPa) and with corresponding analogous porosities (35 to 51 %) also demonstrated comparable power cycling behavior; exhibiting a progressive decrease in effective thermal conductivity with increasing cycles. The evaluated lifetime of sintered joints with the highest shear strengths were found to be at least double those for the lower shear strength joints, and up to fourteen times those of a Pb5Sn solder die attachment. Even the most porous sintered joints exhibited lifetimes appreciably longer than a Pb5Sn die attachment. Degradation in thermal resistance was seen to correlate with observed microstructural changes, with a dependence on initial sintering parameters.
Highlights
WIDE band gap (WBG) devices have higher switching speeds and lower on-state losses than ratedManuscript received October 21, 2020
The effective thermal conductivity of sample W4 remained relatively constant until ~100k power cycles, before gradually decreasing to 88 W/(m K) at 260k power cycles and further to 72 W/(m K) at 303k power cycles, at which point the test was terminated due to the instability of the device. This slow rate of change of thermal conductivity under power cycling agrees with our previous studies on sintered attachments [29, 30]
The effective thermal conductivity of the Pb5Sn solder attachment decreased sharply, from 43.7 W/(m K) in the as-soldered condition to 12.5 W/(m K) after 63k power cycles
Summary
WIDE band gap (WBG) devices have higher switching speeds and lower on-state losses than ratedManuscript received October 21, 2020. Li, was with University of Nottingham, Nottingham NG7 2RD, UK He is with with the Times Electric Innovation Centre of CRRC, Birmingham, Si-based power semiconductors, and have significant advantages for the development of generation power conversion systems [1,2,3,4]. Die-attach materials for packaging SiC or GaN dies are nominally required to operate at temperatures higher than 175 °C, while maintaining high reliability throughout their service lifetime. Silver sintering is widely accepted as a promising packaging technology to fulfil the reliability requirements of higher density/high temperature power electronic applications. Unlike solder attachments produced via melting and solidification, sintered Ag attachments have the key advantage of low processing temperatures yet high operation temperatures, together with higher electrical and thermal conductivity
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callMore From: IEEE Transactions on Device and Materials Reliability
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
