Neutron diffraction study of stability and phase transitions in Cu-Sn-In alloys as alternative Pb-free solders

Abstract

In this work we present an experimental study of structure and phase stability in ternary Cu-Sn-In alloys around 55 at.% Cu in the temperature range 100 • C ≤ T ≤ 550 • C. We have followed in real-time the sequence of phase transformations in succesive heating and cooling ramps, using state-of-the-art neutron powder thermodiffractometry. These experiments were complemented with calorimetric studies of the same alloys. Our results give experimental support to the current assessment of the ternary phase diagram in this composition and temperature range, yielding the sequence of transitions η → (η + L) → (ε + L) with transformation temperatures of 210 • C and 445 • C, respectively. The use of neutrons allowed to overcome common difficulties in phase identification with powder XRD due to absorption and preferred orientation issues. Even the transitions to liquid phases could be successfully identified and monitored in situ, turning this technique into a valuable tool for phase diagram studies of emerging lead-free solder candidates. PACS numbers:arXiv:1205.0965v1 [cond-mat.mtrl-sci]

Crystal structure of Cu-Sn-In alloys around the η phase field studied by neutron diffraction

“…When In atoms are added to the alloys, we can see from the diffraction data that no further reflections appear, indicating that In is indeed being incorporated in the crystal structure of Cu 6 Sn 5 . However, a further set of samples with increasing In content along the pro- posed η-phase field, which will be reported in a separate paper, already show the presence of additional reflections for 27 at.% In [23]. In the remaining we shall focus on samples with less than 25 at.% In.…”

“…There is also a weak evidence of some LT-η-phase in very small amounts. A deeper discussion of these issues is presented in a separate report dealing with in situ high-temperature measurements [23]. For this reason, the Rietveld refinements present rather high values of χ 2 and the data backgrounds are not perfectly accounted for.…”

Multiphase Characterization of Cu-In-Sn Alloys with 17 at.% Cu and Comparison with Calculated Phase Equilibria

“…Neutron diffraction technique applied to the ternary g field proved to be suitable for Cu-In-Sn structure investigations. [15,16] More investigations are needed in the In-Sn-rich side of the Cu-In-Sn to elucidate inconsistencies; combining experimental and semi-empirical approaches is adequate to limit the amount of experimental work and for a more accurate interpretation of the results. In this work we investigate the solidification of Cu-In-Sn alloys with 17 at.% Cu (10 wt.%) by heat-flux differential scanning calorimetry and we compare our results with simulated responses based on equilibrium calculated data using the thermodynamic description of Liu et al [2] available in the literature.…”

Phase stability and thermal expansion behavior of Cu6Sn5 intermetallics doped with Zn, Au and In

“…However, as electronic devices usually experience thermal cycling or thermal shock during operation, the interfacial layers of solder joints, which are commonly dominated by Cu 6 Sn 5 intermetallics, require sufficient chemical and thermal stability [6,10,11,14,15,18,19,23,25,26,27,28,29,30,31]. Therefore the thermal expansion behavior of Cu 6 Sn 5 over the service temperature range is of great importance with respect to the integrity of solder joints.…”

“…It has been proposed that stabilizing the crystal structure of Cu 6 Sn 5 could improve the joint strength and reliability [17] although the effect of composition on the crystal structure and stability of Cu 6 Sn 5 is not fully understood. The elements Ni, Zn, Au and In, which all are common elements in lead-free soldering systems exhibiting marked solubility in Cu 6 Sn 5 [18,19,20] are of significant practical importance in soldering, since the properties of the Cu 6 Sn 5 layer influence the reliability of the solder joints [18,19,21]. As discovered by Nogita et al [11,17,22,23,24,25] using synchrotron PXRD, transmission electron microscopy (TEM) and differential scanning calorimetry (DSC), the hexagonal structure of Cu 6 Sn 5 in lead-free solder alloys and joints containing trace Ni additions is very stable down to room temperature.…”