Interfacial reactions and compound formation in the edge of PbSn flip-chip solder bumps on Ni/Cu under-bump metallization

Abstract

Flip-chip technology with the layout of ball grid array has been widely used in today’s microelectronics industry. The elemental distribution in the edge of the solder bump is crucial for its correlation with the bump strength. In this study, Ni/Cu under-bump metallization (UBM) was used to evaluate the intermetallic compound (IMC) formation in the edge of the solder bump between the UBM and eutectic Sn-Pb solder in the 63Sn-37Pb/Ni/Cu/Ti/Si3N4/Si multilayer structure. During reflows, layered-type (Ni1−xCux)3Sn4 and island-like (Cu1−yNiy)6Sn5 IMCs formed in the interface between the solder and UMB, while only the (Cu1−yNiy)6Sn5 IMC was observed in the sideway of the Ni/Cu UBM. After high-temperature storage (HTS) at 150°C for 1,000 h, both (Cu1−yNiy)6Sn5 and (Cu1−zNiz)3Sn were found in the sideway of the Ni/Cu UBM. Two other IMCs, (Ni1−xCux)3Sn4 and (Cu1−yNiy)6Sn5, formed in the interface between the solder and UBM. The growth of the (Cu1−yNiy)6Sn5 IMC was relatively fast during HTS.