Intrinsic and Interdiffusion in Cu-Sn System

Abstract

Solid-solid diffusion couples assembled with disks of copper, tin and intermetallics (Cu 3 Sn and Cu 6 Sn 5 ) were employed to investigate the Kirkendall effect in the copper-tin system at the temperature of 200°C. In the Cu(99.9%)/Sn diffusion couple, inert alumina particles used as markers were identified in the Cu 6 Sn 5 phase, while microvoids were observed at the Cu/Cu 3 Sn interface. The Cu(99.9%)/Sn and Cu(99.9%)/Cu 6 Sn 5 diffusion couples annealed at 200°C for 10 days were analyzed for intrinsic diffusion coefficients of Cu and Sn in the Cu 6 Sn 5 and Cu 3 Sn phases, respectively with due consideration of changes in molar volume. Interdiffusion, integrated and effective interdiffusion coefficients were also calculated for the intermetallic phases. Diffusion couples annealed at 125-400°C for various times were analyzed for the kinetic parameters such as growth rate constants and activation energies for the formation of Cu 3 Sn and Cu 6 Sn 5 phases. Uncertainties in the calculated intrinsic diffusivities of Cu and Sn arise mainly from the non-planar morphologies of the interfaces and the non-planar distribution of the markers. Intrinsic diffusion coefficients based on average locations of the marker plane indicate that Cu is the faster diffusing component than Sn in both the Cu 3 Sn and Cu 6 Sn 5 phases.

Numerical modeling of bronze coating formation using concentration-dependent diffusivity

“…During the heat treatment of Cu-Sn couples (~200°C), a layered system of the Cu/ε/η/Sn form is reported, where the ε-phase is the last to form but grows quickly by consuming the η-phase. Similar to what has been observed in η, ε retains a planar geometry on the Cu interface but is dissimilar on its interface with η [12]- [14], [16].…”

“…This intermetallic has been reported to form between Cu-Sn couples at temperatures as low as -2°C [12], [13]. When formed in a Cu-Sn couple, its interface with Sn is highly non-planar, but remains uniform on the Cu side [14]. Gagliano et al [15] analyzed the nucleation kinetics of η by dipping Cu coupons into molten Sn, and demonstrated the quick formation of η crystallites, which appeared even when the dipping was carried out for a single second.…”

Response to comments on “A numerical method to determine interdiffusion coefficients of Cu6Sn5 and Cu3Sn intermetallic compounds”

“…For example, as reported in Ref. [7], the thickness of Cu 3 Sn IMC was approximately 15 µm, and those of the interface zones were 2 to 3 µm for the growth of Cu 3 Sn IMC in the Cu/Cu 6 Sn 5 diffusion couple. Therefore, it cannot be justified to simply ignore the contribution from the integral part in Eq.…”

“…However, given the fact that the thicknesses of the phase layers reported in the literature [4][5][6][7] were in the range of a few to tens of micrometres, it is hard to say that the micro-scaled thicknesses of the interface zones are several orders of magnitude thinner than the length of the phase layer in the diffusion zone. For example, as reported in Ref.…”

Corrosion Resistance of Multilayered Sn/Ag3Sn Films Electroplated on Cu Alloys for Highly Reliable Automotive Connectors

“…This can be attributed to the reactive diffusion between Cu base materials and the Sn or Ag films at high temperature, of which the outward Cu diffusion occurred preferentially to the inward Sn or Ag diffusion, thus leading to the formation of thick Cu oxide films. [28][29][30] In contrast, only small Kirkendall voids can be observed at the Cu 3 Sn/Cu interface for the multilayered Sn/Ag 3 Sn specimen, which may be ascribed to the volume reduction of phase transformation from η-Cu 6 Sn 5 (ρ = 8.31 g cm −3 ) to ε-Cu 3 Sn (ρ = 11.3 g cm −3 ) during aging. 31 Noticeably, the Ag 3 Sn grains were retained on the top of the coating film, irrespectively of the disappearance of Sn layer and the progress of Sn-Cu alloying with the outward Cu diffusion at prolonged high temperature.…”