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

Abstract

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 AuSn/sub 4/ and Cu/sub 3/Sn 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 AuSn/sub 4/ and Cu/sub 3/Sn IMC were strongly dependent on the laser reflow power and heating time applied, and both changed after the secondary infrared reflow process. The AuSn/sub 4/ layer formed at the interface in the first laser reflow process dissolved partially after the secondary infrared reflow process, and AuSn/sub 4/ particles precipitated out at the eutectic cell boundary of the solder. The Cu/sub 3/Sn IMC converted into a Cu/sub 6/Sn/sub 5/ layer at the interface after the secondary infrared reflow process, and Cu/sub 6/Sn/sub 5/ particles distributed randomly within the bulk solder.