TOPOLOGY ANALYSIS OF THE CU3SN PHASE IN ELECTRONIC INTERCONNECTIONS

The topology of the Cu3Sn phase during liquid soldering and isothermal aging was characterized to explore the close correlation with the Kirkendall void formation. For Sn3.5Ag/Cu during the liquid soldering, the growth of the Cu3Sn phase is closely dependent on the geometry of Cu6Sn5 phase. That is, at the grain boundary domain of Cu6Sn5 phase, the growth rate of Cu3Sn phase is slower than that within the Cu6Sn5 grain region. The undulation behavior of the Cu3Sn phase is perfectly consistent with that of Cu6Sn5 phase. This phenomenon persists even after the aging at 150 degrees C for 504h, although both Cu6Sn5 and Cu3Sn phases tended to be flat. This indicates that the Cu migration through the grain boundary from the base substrate mainly contributes to the growth of Cu6Sn5 and Cu3Sn phases near the solder, while volume diffusion of Cu enhances the growth of the Cu3Sn phase. It is interesting that the minor addition of (Co, Ni) into Sn-3.5Ag eutectic solder altered this undulation correlation, and suppressed the growth of the Cu3Sn phase remarkably, in particular during the aging process, which definitely impacted Kirkendall void formation.