Shear strength and fracture behavior of solder/Kovar joints with electroplated Cu film.

In this study, the effects of isothermal aging on the interfacial reactions, shear strength and failure mode of Sn37Pb/electroplated Cu (EPC)/Kovar solder joints were investigated in detail. Various interfacial intermetallic compound (IMC) layers were formed in all as-reflowed solder joints. The as-reflowed solder joints were aged up to 360 h at 150 °C before single-lap shear tests. The microstructure of interfacial IMCs layers was affected by the isothermal aging, as well as deposited thickness of Cu film on Kovar substrate. Single-lap shear tests results revealed that the introduction of Cu film on Kovar significantly improved the shear strength of Sn37Pb/EPC/Kovar solder joints. This is because the Cu film could act as a sacrificial layer and react with molten solder to form a thin Cu-Sn IMCs layer, which was expected to protect Au/Ni films from further reaction with solder, rendering a enhanced bonding strength of joints. The shear strength of Sn37Pb/EPC/Kovar solder joints with same aging time increased first and then decreased with the increase of deposited Cu film thickness. The shear strength of aged solder joints decreased with increasing aging time, which could be ascribed to the thicker IMC layer generated at the joint interface. • The surface morphologies of deposited Cu films were analyzed by AFM tests. • Various interfacial IMCs layers were formed in all as-reflowed solder joints. • A novel method to improve the shear properties by introducing a Cu film is proposed. • The failure modes of aged solder joints changed during long-term aging treatment. [ABSTRACT FROM AUTHOR]