In-situ observations on fracture behaviors of Cu–Sn IMC layers induced by deformation of Cu substrates

The fracture behaviors of the interfacial Cu–Sn intermetallic compound (IMC) layers induced by deformation of the Cu substrates were investigated in this study. The IMC layers at the Sn–Ag/Cu single crystal and the Sn–Ag/cold-drawn Cu interfaces were driven to deform synchronously with the Cu substrates, and their fracture morphologies were in situ observed. The results show that fractures in the IMC layers at both of the two interfaces occur shortly after the Cu yields, and the cracks correlate well with the slip bands in the Cu substrates. In micro-scale, the fractures are predicated to be induced by dislocation pile-up. After the Cu substrates yield, the dislocations in them slip toward their surfaces. Since the dislocations cannot get across the IMC/Cu interface, they pile-up at the interface and generate a high cumulative stress ahead the pile-up group. When the cumulative stress reaches the fracture strength of the IMC, fractures inside the IMC layer occur. Before yielding of the Cu substrates, the IMC layer can withstand a high strain without fracture, because there are thin gaps between the IMC grains that can be opened to accommodate deformation. The yield behavior of the Cu substrate is the major influencing factor on the fracture behaviors of the interfacial IMC layers. Thermal aging makes the IMC layers thicker, more compact and easier to fracture.

► Fracture behaviors of the IMC layer at the Sn–Ag/Cu interface were investigated.
► In-situ observation by SEM is employed to reveal the fracture behaviors.
► Fracture in the interfacial IMC layers are induced by dislocation pile-up.
► The fracture behaviors are affected by the yield strength of the Cu substrates.