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research-article

PREDICTION AND MITIGATION OF VERTICAL CRACKING IN HIGH-TEMPERATURE TRANSIENT LIQUID PHASE SINTERED JOINTS BY THERMO-MECHANICAL SIMULATION

[+] Author and Article Information
Hannes Greve

Department of Mechanical Engineering, Center for Advanced Life Cycle Engineering (CALCE), University of Maryland, College Park, MD 20742
hgreve@umd.edu

S. Ali Moeini

Department of Mechanical Engineering, Center for Advanced Life Cycle Engineering (CALCE), University of Maryland, College Park, MD 20742
moeini@umd.edu

Patrick McCluskey

Department of Mechanical Engineering, Center for Advanced Life Cycle Engineering (CALCE), University of Maryland, College Park, MD 20742
mcclupa@umd.edu

Shailesh Joshi

Toyota Research Institute of North America, Toyota Technical Center, 1555 Woodridge Avenue, Ann Arbor, MI 48105
hgreve@umd.edu

1Corresponding author.

ASME doi:10.1115/1.4039265 History: Received September 27, 2017; Revised January 13, 2018

Abstract

Transient Liquid Phase Sintering (TLPS) is a novel high temperature attach technology of particular interest for application as a die attach in power electronic. TLPS joints are comprised of metallic particles embedded in matrices of brittle Intermetallic Compounds (IMCs). This raises the concern that TLPS joints are susceptible to brittle failure. In this paper we analyze the cooling-induced formation of vertical cracks as a newly detected failure mechanism unique to TLPS joints. In a power module with a TLPS attach between a power device and a Direct Bond Copper (DBC) substrate, cracks can form between the interface of the DBC and the TLPS joint when large voids are located near the DBC. These cracks do not appear near small voids. A method has been developed for the modelling of paste-based TLPS sinter joints that possess complex microstructures. Thermo-mechanical simulations of post-sintering cooling have been performed and the influence of microstructure on the stress-responses has been characterized for three different material systems (Cu+Cu6Sn5, Cu+Cu3Sn, Ni+Ni3Sn4). The principal stress within the assembly was found to be a poor indicator for prediction of vertical crack formation. In contrast, stress levels at the interface between the TLPS joint and the power substrate metallization are good indicators for this failure mechanism. Small voids lead to higher joint maximum principal stresses, but large voids induce higher interfacial stresses, which explains why vertical cracking failure was only observed in joints with large voids.

Copyright (c) 2018 by ASME
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