Mechanism on preferred orientation roof-type Cu6Sn5 grain formation in micro-bump with (111) nanotwinned copper UBM

Abstract

The (111) nanotwinned copper films used as a novel under bump metallization (UBM) were applied in micro-bump solder technology for 3D packaging. The orientation and morphology of interfacial Cu 6 Sn 5 grains on (111) nanotwinned copper UBMs were investigated by soldering at different temperatures (250 °C and 300 °C). The (11−20) preferred orientation roof-type Cu 6 Sn 5 intermetallic compound (IMC) formed on Sn/(111) nanotwinned copper interface at a higher soldering temperature of 300 °C; while random orientation scallop-type Cu 6 Sn 5 grains formed on Sn/(111) nanotwinned copper interface at lower soldering temperature of 250 °C. The preferred orientation relationships between and interfacial roof-type Cu 6 Sn 5 grains and (111) nanotwinned copper UBMs are {11−20} Cu6Sn5 ||{111} copper in 〈0001〉 Cu6Sn5 ||〈011〉 copper and {11–20} Cu6Sn5 ||{111} copper in 〈10−10〉 Cu6Sn5 ||〈112〉 copper . Moreover, the average shear strength of the (111) nanotwinned copper/Sn/(111) nanotwinned copper solder interconnects soldered at 300 °C (40.19 MPa) is 30% higher than that soldered at 250 °C (31.09 MPa). This study provides an insight in controlling the morphology and orientation of interfacial Cu 6 Sn 5 grains on the (111) nanotwinned copper used as UBMs for the 3D packaging application. • Random intersecting angles of roof-type Cu 6 Sn 5 grains formed on (111) nt-Cu UBM. • ORs: {11–20} η ||{111} Cu in <0001> η ||<011 > Cu , {11–20} η ||{111} Cu in<10–10 > η||<112 > Cu . • Average shear strength of the solder interconnects soldered at 300 °C is 40.19 MPa.