In situ quantitative study of microstructural evolution at the interface of Sn3.0Ag0.5Cu/Cu solder joint during solid state aging

Abstract

In situ microstructural evolution at the interface of Sn3.0Ag0.5Cu/Cu solder joint during solid state aging was quantitatively studied by nanoindentation. The morphology of Cu6Sn5 gradually altered from scallop type to layer type. Though the growth of IMCs was diffusion-controlled, the consumption of Cu substrate was not linear with the square root of aging time. At the initial stage of solid state aging, the Cu atoms essential to the growth of IMCs were mainly from the supersaturated solder matrix. When the Cu atoms from supersaturated solder matrix were exhausted, the Cu atoms for the growth of IMCs were primarily from the Cu substrate. In addition, the IMCs formed at this state were principally used to fill up the gaps between scallops. After the gaps disappeared, the consumption of Cu substrate slowed down. Furthermore, the growth of Cu3Sn layer in Sn3.0Ag0.5Cu/Cu solder joint was on the both sides with layer type. Since the Sn atoms were inhibited to diffuse into the Cu substrate by the alloying elements of Ag and Cu, the thickness of Cu3Sn layer in SnAgCu/Cu solder joint was much thinner than that in pure Sn/Cu solder joint.