Effects of β-Sn grain c-axis on electromigration behavior in BGA Sn3.0Ag0.5Cu solder interconnects

Abstract

The anisotropy of β-Sn grain can significantly affect the electromigration (EM) behavior in Sn3.0Ag0.5Cu (SAC305) solder interconnects. A real ball grid array (BGA) specimen with a cross sectioned edge row suffered electromigration for 600 h to investigate the effects of β-Sn c-axis on the behavior of electromigration in SAC305 solder interconnects. Scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD) were used to obtain the microstructure and orientation of β-Sn grains in as-reflowed and low current density conditions. Besides, the orientation of c-axis had a great effect on the growth direction of IMCs in solder matrix. The solder interconnect with the Sn grain c-axis pointing the positive direction of ND would emerge serious electromigration phenomena. The density of Cu6Sn5 IMCs distributing at the surface of solder matrix increased obviously. However, when Sn grain c-axis was in the same direction with the opposite direction of ND, the original Cu6Sn5 IMCs in as-reflowed solder interconnect disappeared. Therefore, the results show that the solder interconnects will performance a different electromigration behavior due to the direction of c-axis in Sn grain: the growth direction of Cu6Sn5 IMCs in solder matrix will along the c-axis accompanied growing into solder matrix or gathering at the surface of the cross section.