Lead-free alternatives for interconnects in high-temperature electronics

[+] Author and Article Information
Sandeep Mallampati


Liang Yin

GE Global Research, Niskayuna, NY, USA

David Shaddock

GE Global Research, Niskayuna, NY, USA

Harry Schoeller

Germanna Community College, Fredericksburg, VA, USA

Junghyun Cho

Binghamton University (State University of New York), Mech Eng & MSE, Binghamton, NY, USA

1Corresponding author.

ASME doi:10.1115/1.4039027 History: Received September 28, 2017; Revised January 04, 2018


Predominant high melting point solders for high temperature and harsh environment electronics are Pb-based systems, which are being subjected to RoHS regulations because of their toxic nature. In this study, high bismuth (Bi) alloy compositions with Bi-XSb-10Cu (X from 10 wt.% to 20 wt.%) were designed and developed to evaluate their potential as high-temperature, Pb-free replacements. The die-attach joints made out of Bi-15Sb-10Cu alloy exhibited an average shear strength of 24 MPa, which is comparable to that of commercially available high Pb solders. In addition, heat dissipation capabilities, using flash diffusivity, were measured on the die-attach assembly, compared to the corresponding bulk alloys. The thermal conductivity of all the Bi-Sb alloys was higher than that of pure Bi. By creating high volume fraction of precipitates in a die-attach joint microstructure, it was feasible to further increase thermal conductivity of this joint to 24 W/m·K, which is three times higher than that of pure Bi (8 W/m·K). Bi-15Sb-10Cu alloy has shown limited plastic deformation in room temperature tensile testing, in which premature fracture occurred via the cracks propagated on the (111) cleavage planes of rhombohedral crystal structure of the Bi(Sb) matrix. The same alloy has, however, shown up to 7% plastic strain under tension when tested at 175°C. The cleavage planes, which became oriented at smaller angles to the tensile stress, contributed to improved plasticity in the high temperature test.

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