Effect of Ni content on the diffusion-controlled growth of the product phases in the Cu(Ni)–Sn system

Liquid-phase diffusion bonding and the development of a Cu-Ni/Sn composite solder paste for high temperature lead-free electrical connections

“…The absence of (Cu, Ni)3Sn has been reported previously for similar diffusion couples annealed at 240°C by Vuorinen et al and at 200°C by Baheti et al [74], [75] . Baheti et al…”

“…% Ni, (Cu, Ni)3Sn was not present even though it was thermodynamically stable. This was attributed to the increase in the growth rate of (Cu, Ni)6Sn5 with increasing Ni concentrations, due to both the change in the relative diffusivities of Sn and Cu in the (Cu, Ni)6Sn5 phase and the increasing contribution of grain boundary diffusion to growth as the (Cu, Ni)6Sn5 grain size decreased with increasing Ni concentration [75] . [77] .…”

“…presented evidence that (Cu, Ni)3Sn is not thermodynamically stable at 200°C for Ni concentrations equal to or greater than 7.5 wt. % Ni, and suggested that the absence of the thermodynamically stable ternary intermetallic was due to difficulty in nucleation of the phase [75] . However, at 240°C, Vuorinen et al argued that the absence of the (Cu, Ni)3Sn was kinetic in origin, i.e., that (Cu, Ni)3Sn was thermodynamically stable, but did not form due to rapid growth of (Cu, Ni)6Sn5 [74] .…”

Advances in Pb-free Solder Microstructure Control and Interconnect Design

“…The absence of (Cu, Ni) 3 Sn has been reported previously for similar diffusion couples annealed at 240°C by Vuorinen et al and at 200°C by Baheti et al [74,75] Baheti et al presented evidence that (Cu, Ni) 3 Sn is not thermodynamically stable at 200°C for Ni concentrations equal to or greater than 7.5 wt.% Ni, and suggested that the absence of the thermodynamically stable ternary intermetallic was due to difficulty in nucleation of the phase. [75] However, at 240°C, Vuorinen et al argued that the absence of the (Cu, Ni) 3 Sn was kinetic in origin, i.e., that (Cu, Ni) 3 Sn was thermodynamically stable, but did not form due to rapid growth of (Cu, Ni) 6 Sn 5 . [74] This latter interpretation is supported by phase equilibrium experiments by Lin et al that showed (Cu, Ni) 3 Sn in equilibrium with Cu-Ni alloys at 240°C.…”

“…Experimental measurements of the specific reaction paths for different LTP compositions and the relative diffusivities of Sn and In in the IMCs still must be evaluated to determine what ranges can be used (Color figure available online) with increasing Ni concentrations, due to both the change in the relative diffusivities of Sn and Cu in the (Cu, Ni) 6 Sn 5 phase and the increasing contribution of grain boundary diffusion to growth as the (Cu, Ni) 6 Sn 5 grain size decreased with increasing Ni concentration. [75] Stable phases at operating temperatures must be considered as well. For instance, Chen et al found that Sn-20In wt.% reacts with Ag to form a ternary IMC phase over a wide range of compositions at 250°C, but aging at 125°C caused a AgIn 2 phase to form.…”