Microstructure Control in Sn–0.7 mass%Cu Alloys

Abstract

Soldering alloys based on the Sn-Cu alloy system are amongst the most favourable lead-free alternatives due to a range of attractive properties. Trace additions of Ni have been found to significantly improve the soldering characteristics of these alloys (reduced bridging etc.). This paper examines the mechanisms underlying the improvement in soldering properties of Sn-0.7 mass%Cu eutectic alloys modified with concentrations of Ni ranging from 0 to 1000 ppm. The alloys were investigated by thermal analysis during solidification, as well as optical/SEM microanalyses of fully solidified samples and samples quenched during solidification. It is concluded that Ni additions dramatically alter the nucleation patterns and solidification behaviour of the Sn-Cu 6 Sn 5 eutectic and that these changes are related to the superior soldering characteristics of the Ni-modified Sn-0.7 mass%Cu alloys.

Effects of Phosphorus on Microstructure and Fluidity of Sn-0.7Cu-0.05Ni Lead-Free Solder

“…At the higher measured levels of 0.021 and 0.025 mass% P, however, the microstructure is clearly hypoeutectic, containing a significant volume fraction of Sn dendrites. Previous research by the authors 5,14) has shown that, as the Ni content in Sn-0.7Cu-xNi decreases from 0.05 mass%, the volume fraction of primary Sn dendrites in the microstructure increases. This result was shown to be consistent with the phase equilibria of the Sn-Cu-Ni system, 15) where Sn-0.7Cu-0.05Ni is closer to a eutectic valley than Sn-0.7Cu.…”

Inhibiting Cracking of Interfacial Cu6Sn5 by Ni Additions to Sn-based Lead-free Solders

“…[1] One attractive group of lead-free solder alloys are those based on the Sn-Cu-Ni system which have found applications in wave-, dip-, and iron-soldering processes and are cheaper than most other candidate alloys due to the omission of expensive elements such as silver or rare earths. [2][3][4][5] The intermetallic compound (IMC) of Cu 6 Sn 5 that forms between Sn-based lead-free solder alloys and Cu substrates influences the soldering process and the subsequent joint properties. Figure 1 shows the Sn-Cu binary phase diagram.…”

Microstructure and mechanical properties of lead-free Sn-Cu-Ni composite solder paste reinforced with silicon (Si) particles

“…The Ni has a strong influence on the microstructure of Sn-Cu-Ni alloys which result in fully eutectic morphology and reduce the fraction of Sn dendrites that form during solidification of Sn-0.7Cu solder alloys [5]. Recently, in order to improve the Sn-0.7Cu-0.05Ni lead-free solder, researchers added small amount of alloying elements such as transition metals, rare earth elements and also addition of micron or nanoparticles into Sn-0.7Cu-0.05Ni lead-free solder to form composite solder to improve the microstructural stability and mechanical properties of solders [6]. Tsao et al [7] found that addition of TiO 2 nano-particles evidently improved the microstructure and mechanical properties of low-Ag Sn-1.5Sb-1Ag solders.…”