Evolution of intermetallic compounds at interface between PBGA solder ball and pads during laser reflow soldering

This paper presents the evolution of Au-Sn and Cu-Sn intermetallic compounds at the interface between the PBGA solder ball and the PBGA metallization (Au/Ni/Cu and Cu pad) substrate during a first laser reflow followed by a second infrared reflow processes. A thin layer of AuSn₄ and Cu₃Sn intermetallic compounds were observed at the solder bump interface reflowed by laser when the metallization was Au/Ni/Cu and Cu respectively. The morphology of AuSn₄ and Cu₃Sn IMC were strongly dependent on the laser reflow power and heating time applied, and both changed after the secondary infrared reflow process. The AuSn₄ layer formed at the interface in the first laser reflow process dissolved partially after the secondary infrared reflow process, and AuSn₄ particles precipitated out at the eutectic cell boundary of the solder. The Cu₃Sn IMC converted into a Cu₆Sn₅ layer at the interface after the secondary infrared reflow process, and Cu₆Sn₅ particles distributed randomly within the bulk solder.