Thermodynamic description of the Cu–Sn system

Abstract

The Cu–Sn binary system is important for various applications, especially for recent developments in the electronics packaging industry. The ϵ-Cu3Sn and η-Cu6Sn5 (η′ phases) phases are frequently encountered in electronics products. However, the two phases have been described as line compounds in previous thermodynamic modeling, and their compositional homogeneities were not considered. In this study, the thermodynamic properties of the Cu–Sn binary system are modeled and the phase diagram is calculated by the CALPHAD method, using experimental information reported in the literature. The ϵ and η (η′) phases are described using compound energy models with two and three sublattices, respectively, so that their compositional homogeneities could be calculated. Good agreement was observed between the calculated result and the existing experimental data.

Phase Diagrams and Their Applications in Pb‐Free Soldering

“…Figure 2.27 shows the microstructure of the Sn-3.5 wt%Ag/Cu couple reacted at 450 C for one hour [27]. Three IMCs, d (Cu 4 Sn), e 1 (Cu 3 Sn) and Z (Cu 6 Sn 5 ), are observed at the interface and similar results can be found with longer reaction time; however, according to the Sn-Cu binary diagram [15], there are only two stable phases, d (Cu 4 Sn) and e 1 (Cu 3 Sn), at 450 C. With careful analysis, it is confirmed that the Z (Cu 6 Sn 5 ) phase is formed during solidification and not as a result from interfacial reaction. If only the reaction couple results were analyzed without referring to the phase diagram, the Z (Cu 6 Sn 5 ) at the interfaces could be concluded as a reaction product by mistake.…”

“…The most important ones include Sn-Ag [12], Sn-Au [13], Sn-Bi [14], Sn-Cu [15], Sn-In [16], Sn-Sb [12], Sn-Zn [14], Cu-In [16] and Ag-In [17]. show the phase diagrams of the systems mentioned above.…”

“…In addition, solders typically possess relative low melting temperatures, and solder joints are processed and operated in relative medium to high homologous temperatures. The local phase equilibrium approximation is thus generally valid for soldering systems [9][10][11][12][13][14][15]. This local phase equilibrium approximation further extends the applications of equilibrium phase diagrams in Pb-free soldering.…”

Transient Liquid Phase Behavior of Sn-Coated Cu Particles and Chip Bonding using Paste Containing the Particles

“…The first minor exothermic peak formed at 98°C is thought to arise due to the reaction between the Sn coating and the Cu core. The reaction between Sn and Cu preferentially forms the intermetallic Cu 6 Sn 5 and releases the exothermic enthalpy of formation [7,8]. These peaks were observed at 98°C irrespective of the thickness of Sn coating.…”

“…Significantly, when compared to earlier TLP bonding methods [7], the inclusion of particles results in the formation of a relatively uniform bondline structure at low magnification. Moreover, the core/shell particles will remarkably decrease the TLP bonding time at relatively low temperature because particles with this structure can reduce the time required for the completion of the reaction between molten Sn and Cu.…”