Title

Isothermal Aging Effect on Sn-58bi Solder Interconnect Mechanical Shear Stability

Published In

Journal of Electronic Materials

Document Type

Article

Publication Date

1-2-2022

Subjects

Isothermal Aging Effect

Abstract

Use of low melting temperature solder (LTS) materials in interconnect devices is a recent application as they lower the challenges of high reflow peak temperature-induced package warpage during assembly. A good candidate to overcome this challenge is a eutectic Sn-Bi system solder, with a melting temperature of 138°C and a reflow peak assembly temperature of around 185°C. However, Bi causes joint hardening and is prone to brittle fractures under mechanical bend and shock. Therefore, it is critical to understand mechanical properties of Sn-58Bi solder joints under conditions of end-use condition and applications. In this study, a series of isothermally aged 300-μm-diameter solder balls attached to a NiAu pad surface finish, are subject to single-ball shear tests after up to 500 h aging at room temperature, 100°C and −25°C. Single-ball shear tests were performed using a multi-bond tester with 10-μm shear height and two shear speed condition, 10 μm/s and 100 μm/s. The maximum shear load and the distance to the peak shear load were measured to observe the deformation behavior change. Comparative testing was also conducted for Sn-1.0Ag-0.5Cu (wt.%) aged samples for comparison. A decrease in maximum shear strength and loss of ductility with 100°C isothermal aging, opposite to an increase in ductility with room temperature isothermal aging were observed. Isothermally aged Sn-58Bi samples reveal further loss of ductility compared to SAC105 which show increase in ductility. This phenomenon is due to the increased Bi solubility into Sn at a higher temperature range. The deformation behavior for both Sn-58Bi and SAC105 were observed and discussed on partially sheared solder joints using EBSD analysis.

Rights

© The Minerals, Metals & Materials Society 2021

Description

The authors want to thank the Center of Electron Microscopy and Nanofabrication (CEMN) at Portland State University for their technical support on EBSD imaging and analysis.

DOI

10.1007/s11664-021-09379-5

Persistent Identifier

https://archives.pdx.edu/ds/psu/37020

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