The atomic behavior during heating in the amorphous diffusion nanolayer between Cu and solder

The formation of an amorphous solid has been generally investigated through simulations due to the difficulties related to experimental observation. There has been little experimental observation of the dynamic behavior of atoms in amorphous solids especially in the case of the amorphous interfacial diffusion region, which governs the interaction between two contact metals. Here, we presented an in situ observation of the dynamic behavior of atoms in an amorphous interfacial region existing between solder and Cu. The layer was produced via rapid quenching in liquid nitrogen with a Cu specimen soldered with Sn3.0Ag0.5Cu at above the melting temperature of the solder. The investigation of the diffusion layer of the solidified specimen was conducted in situ with a high resolution transmission electron microscope (HRTEM) under heating at 100°C. The atoms aggregated in the amorphous layer in terms of different unit structures, which gave rise to an entirely disordered structure. The study showed that the heating caused dynamic interactions among atoms that resulted in the transformation of these unit structures in the amorphous nanolayer.