Microstructure evolution of the Sn–Ag– y%Cu interconnect

Abstract

The lead free Sn–Ag– y%Cu ( y = 0.0, 0.5, 1.0 and 2.0) interconnect interfacial microstructures and the microstructure evolution under thermal treatment (isothermal aging, 150 °C/1000 h) were studied in detail by using surface microetching microscopy and cross section microscopy. The corresponding mechanical and reliability behaviors were evaluated by performing shear test and fracture mode analysis before and after the thermal treatment. The results indicate: (i) The interconnects could have different microstructures and intermetallic compound (IMC), depending on the Cu content. The Cu–Sn IMC could have microstructures that were clusters or protrusion-like, Augustine grass leaf-like, scissor-like, tweezers-like, etc. (ii) Ag 3Sn IMCs were not observed at time zero for any interconnect groups, but they occurred after the aging for all groups. The Ag 3Sn IMC could have different microstructures, again depending on Cu content. For low Cu content, the Ag 3Sn IMCs were granules or nodules; for higher Cu content, Ag 3Sn IMCs were plate-like. (iii) The growth of Ag 3Sn plates was promoted by the growth of Cu–Sn IMCs, but indirectly linked to the Cu content. (iv) High Cu content (1.0 wt% and higher) could degrade the mechanical and reliability performances of the LF interconnect by providing a brittle joint, which was mainly achieved through the substantial growth of Cu–Sn IMCs and Ag 3Sn plates.