Analysis of Sn-Bi Solders: X-ray Micro Computed Tomography Imaging and Microstructure Characterization in Relation to Properties and Liquid Phase Healing Potential

Abstract

This work provides an analysis of X-ray micro computed tomography data of Sn-xBi solders with x = 20, 30, 35, 47, 58 wt.% Bi. The eutectic thickness, fraction of eutectic and primary phase are analyzed. Furthermore, the 3D data is evaluated by means of morphology parameters, such as, shape complexity, flatness, elongation and mean intercept length tensor. The investigated alloys are categorized in three groups based on their morphology, which are described as “complex dominant”, “complex- equiaxed” and “mixed”. The mechanical behavior of Sn-Bi alloys in the semi-solid configuration and the correlation with microstructural parameters are discussed. A varying degree of geometric anisotropy of the investigated alloys is found through the mean intercept length tensor. Representative volume element models for finite element simulations (RVE-FEM) are created from tomography data of each alloy to analyze a correlation of geometric and elastic anisotropy. The simulations reveal an elastic isotropic behavior due to the small difference of elastic constants of primary and eutectic phase. A discussion of properties in the semi-solid state and liquid phase healing is provided.

Long-Term Microstructural Stability of Sn-40Bi and Sn-40Bi-10In Alloys

“…5 Using temperature variation to heal solder material, particularly in Sn-Bi alloys, is a novel approach recently explored to enhance solder joint reliability under thermomechanical stresses. [6][7][8] Sn-Bi alloys have been shown to exhibit a liquid-assisted healing phenomenon when subjected to compressive forces and elevated temperatures. This self-healing process involves localized melting 6,7 ; an alloy must possess a two-phase region where both the solid and liquid phases can coexist to enable this healing mechanism.…”

“…[6][7][8] Sn-Bi alloys have been shown to exhibit a liquid-assisted healing phenomenon when subjected to compressive forces and elevated temperatures. This self-healing process involves localized melting 6,7 ; an alloy must possess a two-phase region where both the solid and liquid phases can coexist to enable this healing mechanism. The effectiveness of damage repair hinges on the presence and morphology of the liquid phase.…”

Study on the Influence of Defects on Fracture Mechanical Behavior of Cu/SAC305/Cu Solder Joint

“…Currently, many related studies have been carried out in the fields of electronics and microelectronics. For example, X-ray μ-CT has been used to quantitatively characterize the number and volumes of pores [ 27 , 28 ], the crack length [ 29 , 30 ], and their distribution in solder joints [ 31 ]. This non-destructive method enables us to investigate the damage evolution of internal defects in solder joints under external loading, so as to elucidate the role of the microstructural characteristics in the damage process.…”