Growth behavior of Cu6Sn5 Grains at Sn3.0Ag/(001)Cu Soldering Interface

With the continually increasing of integration level in electronic devices, connecting bumps in electronic packaging are downsizing accordingly. Even in some micro- electronic components, the size of solder joints belongs to a range of a few microns. In this condition, the under bump metal (UBM) may only contain several grains and the effect of crystal orientation on growth of interfacial intermetallic compounds (IMCs) becomes extremely distinct. For a limit case, the grains of IMCs on a single crystal substrate tend to grow regularly and consequently resulting in a performance anisotropy of solder joints which is closely related to the service reliability of micro devices. Therefore, the IMC growth behavior on single crystal substrate has attracted a great of attention in electronic industry. Growth behavior of IMC grains at Sn3.0Ag/(001)Cu interface were respectively observed in isothermal heating and cooling stages of soldering in this article. Results showed that the IMC grains on (001)Cu present scallop type in isothermal heating and were inclined to turn into prism type in cooling. Except for environmental reasons, inherent orientation of interfacial IMC grains is also an effective factor for the formation of their final morphologies. Furthermore, the existence of Cu
₃
Sn phase under IMC grains was found in a soldering time of only 30s at 300°C. Obviously, cooling is a stage that IMC grains grow to facet type and cannot be ignored in the analysis of interfacial reaction.