Effect of Zn addition in Sn-rich alloys on interfacial reaction with Au foils

To restrain the formation of AuSnx intermetallic components (IMCs) in solder joints, Zn was added into Sn-rich solders. The solder joints were fabricated by a laser reflow soldering method, and then they were aged at 125 ℃. The results show that the total thickness of AuSnx IMCs at the interface of pure Sn solder and Au foils reaches about 54 μm under the condition of 600 h aging. In Sn-1.5Zn solder joints, however, formation of AuSn4 IMCs is restrained greatly. As the content of Zn in the solder is increased to 3.5%(mass fraction), no AuSn4 IMC is observed at the interface. Au-Zn phases form beside AuSn2 and AuSn IMCs layers. As for Sn-9.0Zn solder joints, Au-Zn and Au-Zn-Sn phases and few AuSnx IMCs form at the interface. Moreover, total thickness of the phases and IMCs is far less than that of AuSnx IMCs in the pure Sn solder joints.

EFFECT OF LASER INPUT ENERGY ON AuSn_x INTERMETALLIC COMPOUNDS FORMATION IN SOLDER JOINTS WITH DIFFER-ENT THICKNESS OF Au SURFACE FINISH ON PADS

Formation of AuSnx intermetallic compounds （IMCs） in laser reflowed solder joints was investigated. The results showed that few IMCs formed at the solder/0. 1μm Au interface. Needlelike AuSn4 IMCs were observed at the solder/0.5μm Au interface. In Sn-2.0Ag-O,75Cu-3,0Bi and Sn-3.5Ag-O.75Cu solder joints, when the laser input energy was increased, AuSn4 IMCs changed .from a layer to needlelike or dendritic distribution at the solder/0.9μm Au interface. As for the solder joints with 4.0 μm thickness of Au surface finish on pads, AuSn4 , AuSnx, AuSn IMCs, and Au2Sn phases formed at the interface. Moreover, the content of AuSnx IMCs, such as, AuSn4 and AuSn2, which contained high Sn concentration, would become larger as the laser input energy increased. In the Sn-37Pb solder joints with 0.9 μm or 4.0 μm thickness of the Au surface finish on pads, AuSn4 IMCs were in netlike distribution. The interspaces between them were filled with Pb-rich phases.