NiSn4 formation during the solidification of Sn–Ni alloys

Gourlay

2015

Materials Letters

Self Cite

Abstract:Microstructure development in solder joints between Sn-3.5Ag and Ni-based substrates has been widely reported. However, in the present study we illustrate a new phenomenon: that during soldering of Sn-3.5Ag to Ni or ENIG (electroless nickel, immersion gold), the bulk solder solidifies to contain a metastable eutectic consisting of βSn+Ag3Sn+NiSn4 instead of the βSn+Ag3Sn+Ni3Sn4, expected of equilibrium solidification. It is shown that metastable NiSn4 coarsens and then decomposes into Ni3Sn4 and βSn during ageing at 150 and 200˚C and that coarsened NiSn4 deteriorate impact shear properties.

Section: Ag/enig Joints At 150°csupporting

confidence: 78%

Section: Resultsmentioning

confidence: 73%

Metastable eutectic in Pb-free joints between Sn–3.5Ag and Ni-based substrates

Gourlay

2015

Materials Letters

Self Cite

“…Note that, in Figure 6, the substrate is 99.9% pure Ni to make the point that metastable NiSn4 forms when only Sn, Ag and Ni are present. Further details of metastable NiSn4 in Sn-3.5Ag/Ni and more complex Ni(P)/Au/Sn3.5Ag joints including phase identification by combining EBSD and EDX are given in our past work [47,48]. We have also shown that a binary metastable SnNiSn4 eutectic grows over a wide range of solidification conditions in the Sn-Ni system which is discussed in refs [48,49].…”

Section: Tin Grain Structure In Solder Balls On Common Substratesmentioning

confidence: 74%

Nucleation and Growth of Tin in Pb-Free Solder Joints

Gourlay

et al. 2015

JOM

The solidification of Pb-free solder joints is overviewed with a focus on the formation of the Sn grain structure and grain orientations. Three solders commonly used in electronics manufacturing, Sn-3Ag-0.5Cu, Sn-3.5Ag and Sn-0.7Cu-0.05Ni, are used as case studies to demonstrate that growth competition between primary dendrites and eutectic fronts during growth in undercooled melts is important in Pb-free solders, and that a metastable eutectic containing NiSn4 forms in Sn-3.5Ag/Ni joints. Additionally, it is shown that the substrate (metallization) has a strong influence on the nucleation and growth of tin. We identify Co, Pd and Pt substrates as having potential to control solidification and microstructure formation. In the case of Pd and Pt substrates, Sn is shown to nucleate on the PtSn4 or PdSn4 IMC reaction layer at relatively low undercooling of ~4K, even for small solder ball diameters down to <200 m. IntroductionThe transition to Pb-free electronic interconnections has been underway for more than a decade and despite the exemptions to the RoHS Directive there are few applications where Pb-free solders are not being used. At the same time, electronic packaging technologies have been advancing and there is an ongoing need to develop next-generation Pb-free solders and substrates that are better suited to smaller joints that can operate at higher temperature and that are more reliable.The most commonly used Pb-free solders are hypoeutectic or near-eutectic compositions from the Sn-Ag-Cu (SAC), Sn-Ag or Sn-Cu-Ni alloy systems. These compositions solidify with significant differences to the near-eutectic Sn-Pb solders used previously. For example, where the Sn-37Pb

“…Further details of metastable NiSn4 in Sn-3.5Ag/Ni and more complex Ni(P)/Au/Sn3.5Ag joints including phase identification by combining EBSD and EDX are given in our past work. [14][15][16][17]. Fig.…”

Section: A B Cmentioning

confidence: 98%

Influence of Bi additions on the distinct βSn grain structure of Sn-0.7Cu-0.05Ni-xBi (x = 0–4wt%)

2016 International Conference on Electronics Packaging (ICEP)

Nishimura

Sweatman

et al. 2016

Self Cite

Abstract-Effects of Bi addition to the Ag-containing leadfree solders have been the focus of a considerable amount of past investigations, however, influence of Bi on Sn-Cu-Ni system has not been studied so extensively. In the present study we aimed to reveal the influence of Bi on microstructure formation of Sn-0.7Cu-0.05Ni/Cu solder joints both in the bulk and at the interface. It is shown that (i) Sn-0.7Cu-0.05Ni solidifies to produce a markedly different grain structure to Ag-containing lead-free alloys; (ii) Bi additions to Sn-0.7Cu-0.05Ni had no discernible effect neither on the βSn grain structure nor on (Cu,Ni)6Sn5 interfacial intermetallic layers or primary intermetallic crystals in solder joints.