Formation and growth of intermetallic compound Cu 6Sn 5 at early stages in lead-free soldering

Abstract

In this work, the early stages of the formation and growth of the intermetallic compound Cu 6Sn 5 during soldering reactions between a Cu substrate and liquid Sn are examined through phase-field simulations. The liquid Sn-based solder (L phase) and the copper substrate (α phase) are considered to be under metastable equilibrium conditions that eventually lead to nucleation of the Cu 6Sn 5 intermetallic compound (IMC) (η phase) at the solid/liquid interface. Nucleation is incorporated into the model through a classical treatment considering that individual nucleation events follow a Poisson distribution function. The driving forces for the nucleation and phase transformations are obtained by coupling the phase-field simulations to CALPHAD models. In the phase-field simulations, physical properties such as liquid surface as well as IMC interfacial energies are treated parametrically to probe the behavior of the system under various growth conditions. The simulations are compared with previous works and are shown to have good (qualitative) agreement with recent detailed studies on the early stages of the interaction between Cu and liquid Sn. © 2010 TMS.