The nucleation of Ag3Sn and the growth orientation relationships with Cu6Sn5

By virtue of the synchrotron radiation imaging combing the analysis of the actual soldering morphology data in lab, we have a more specific understanding of the characteristic of nucleation and growth of Ag₃Sn. In furnace cooling conditions, inside the pure Sn3.0Ag solder, there is no sheet Ag₃Sn formed. The IMC at the soldering interface is a priority site for the nucleation of the Ag₃Sn in the soldering interface reaction for the surface of Cu₆Sn₅ formed in soldering reaction providing the surface energy of nucleation and decreasing the energy needed for nucleation and growth. Ag₃Sn grew around Cu₆Sn₅ inside the Sn3.5Ag solder in furnace cooling process. Ag₃Sn embedded itself in Cu₆Sn₅, suppressing the growth of Cu₆Sn₅, and finally affecting the morphology of Cu₆Sn₅. With the decrease of cooling rate, the size of Ag₃Sn increases and the morphology transforms from nano particles to linear distribution with continuous structure, then to sheet morphology. The fast cooling rate provides large degree of supercooling for the nucleation of Ag₃Sn; however the slow cooling rate offers abundant time for the diffusion of elements.