Mechanisms of beta-Sn nucleation and microstructure evolution in Sn-Ag-Cu solders containing titanium

Abstract

The mechanisms by which Ti additions catalyse the nucleation of β-Sn are studied in 550 µm Sn-3Ag-0.5Cu (wt%) solder balls and joints on Cu and Ni substrates. It is shown that at least two new intermetallic compounds (IMCs), Ti 2 Sn 3 and (Ti,Fe,Cu)Sn 2 , form as a result of a 0.2wt% Ti addition. The nucleation potential of each IMC was studied by electron backscatter diffraction (EBSD) of tin droplets solidified on the cross sectioned facets of each IMC. It is found that reproducible orientation relationships (ORs) form only between β-Sn and Ti 2 Sn 3 and that the two ORs generate good atomic matching between the Sn atoms in Ti 2 Sn 3 and the closest packed plane in β-Sn, {100}. β-Sn cyclic twinning occurred in droplets on Ti 2 Sn 3 where the twinning axis <100>Sn was always parallel with the lowest disregistry direction in the ORs. In solder balls and joints, the Ti 2 Sn 3 addition triggered up to 12 independent β-Sn grains, whereas Ti-free SAC305 always solidified with one independent grain.

Effect of kaolin geopolymer ceramic addition on the properties of Sn-3.0Ag-0.5Cu solder joint

“…On top of that, other major concerns related with SAC are the formation of large and brittle intermetallic compounds (IMC) which can reduce the mechanical strength and solder reliability [6]. In typical SAC solder joint, the large and brittle IMC arise at higher undercooling of β-Sn (~10-40 K) which promotes the formation of large primary IMCs Cu6Sn5 rods and Ag3Sn plates [8]. Since IMCs are brittle, controlling its growth is necessary in obtaining a strong solder joint.…”

On the 3-D Shape of Interlaced Regions in Sn-3Ag-0.5Cu Solder Balls

“…9,12 Electron backscatter diffraction (EBSD) techniques have been successfully used to identify crystal orientations and relationships between bSn grains, such as the common twinning axis. 1,7,13,14 A SAC solder joint with an interlaced microstructure, composed of many small bSn grains, shows increased mechanical properties, such as hardness and creep, 15 as well as better reliability compared to a beach-ball microstructure, by delaying crack initiation. 16 Furthermore, a solder joint of a single grain will have anisotropic mechanical properties, corresponding to bSn anisotropy, 17 and can result in early joint failure for certain grain orientations.…”

Combined powder metallurgy routes to improve thermal and mechanical response of Al−Sn composite phase change materials

“…Moreover, it is not possible to identify a relationship between Al grains and Sn particles, because Sn has a preferential orientation everywhere and Al grains in contact with it are randomly oriented. As reported by Ma et al [24], the anisotropy of Sn could affect thermal expansion and mechanical properties. However, in the tests performed up to now, clear effects of this feature were not observed.…”