Characteristics of interfacial microstructure of PBGA solder bump during multi-reflow and aging processes

Abstract

Characteristics of intermetallic compounds at the interface of PBGA solder ball and Au/Ni/Cu metallization on BT substrate during multi-reflow and aging processes was presented. The eutectic SnPb solder bump was formed by laser reflow first, followed by a secondary infrared reflow process to form solder joint, and then the solder joint was aged at 160/spl deg/C for various numbers of days; finally, the aged solder joint was reflowed once again. During first laser reflow, the morphology and distribution of AuSn/sub 4/ 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. After the aging process, AuSn/sub 4/ IMC converted into Au-Ni-Sn ternary compounds, and a continuous Ni/sub 3/Sn/sub 4/ layer grew out under the Au-Ni-Sn IMC layer. The thickness of Au-Ni-Sn and the Ni/sub 3/Sn/sub 4/ IMC layer increased as the aging time increased. When the aged solder joint was reflowed again, the Au-Ni-Sn IMC disappeared at the interface, and continuous Ni/sub 3/Sn/sub 4/ IMC transformed to scallop-type morphology.