Microstructural Change Due to Aging and Its Effect on Fatigue Properties in Sn-Sb-Ag-Ni-Ge Alloy

Area of Science:

• Materials Science
• Metallurgy
• Physical Chemistry

Background:

• The Sn-Ag-Cu alloy system is widely used in electronics packaging.
• Understanding microstructural evolution and fatigue behavior is crucial for reliability.
• The role of alloying elements like Sb, Ni, and Ge in Sn-based solders requires further investigation.

Purpose of the Study:

• To investigate the microstructural changes and coarsening behavior of Ag3Sn in Sn-6.4Sb-3.9Ag-0.25Ni-0.003Ge during high-temperature aging.
• To compare the low-cycle fatigue behavior of Sn-6.4Sb-3.9Ag-0.25Ni-0.003Ge with Sn-3.0Ag-0.5Cu.
• To elucidate the influence of Sb on Ag3Sn coarsening and the subsequent impact on fatigue properties.

Main Methods:

• High-temperature aging experiments to observe microstructural evolution.
• Differential Scanning Calorimetry (DSC) to determine phase transformations and activation energy.
• Low-cycle fatigue (LCF) testing at room temperature and 175 °C.
• Microstructural analysis using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS).

Main Results:

• SbSn phases dispersed in the β-Sn matrix at room temperature disappeared upon heating as Sb dissolved into the β-Sn phase.
• The activation energy for Ag3Sn coarsening was determined to be 45 kJ/mol, controlled by Ag lattice diffusion in β-Sn.
• Solid solution Sb in β-Sn reduced the Ag solubility limit, significantly delaying Ag3Sn coarsening.
• The Sn-6.4Sb-3.9Ag-0.25Ni-0.003Ge alloy showed suppressed increase in fatigue ductility exponent at 175 °C compared to Sn-3.0Ag-0.5Cu.
• Delayed Ag3Sn coarsening in the Sn-Sb-Ag-Ni-Ge alloy helped maintain the cyclic strain-hardening exponent at elevated temperatures.

Conclusions:

• Antimony in the Sn-Sb-Ag-Ni-Ge solder alloy effectively hinders Ag3Sn coarsening by reducing silver solubility.
• This delayed coarsening mechanism enhances the high-temperature fatigue resistance of the Sn-Sb-Ag-Ni-Ge alloy.
• The findings suggest potential for developing advanced lead-free solders with improved reliability at elevated temperatures.