Abstract
Sn-0.7 wt% Cu alloy is an important Pb-free solder, and Ni-7 wt% V is the major diffusion barrier layer material of flip chip technology. Reactions at the Sn-0.7 wt% Cu/Ni-7 wt% V interface are examined at 160, 180, and 210 °C. Only the CU6Sn5 phase is formed in the Sn-0.7 wt% Cu/Ni-7 wt% V couple reacted at 160 and 180 °C; however, in addition to the CU 6 Sn 5 and Ni 3 Sn 4 phases, a quaternary Q phase is formed in the Sn-0.7 wt% Cu/Ni-7 wt% V couple reacted at 210 °C. The Q phase is a mixture of nanocrystalline N 3 Sn 4 , phase and an amorphous phase. With longer reaction time at 210 °C in the Ni-V/Q/Sn-Cu couple where the Q phase is in direct contact with solder, the N 3 Sn 4 phase nucleates inside the preformed Q phase, and the alternating layer phenomenon Ni-V/ Q/Ni 3 Sn 4 /Q/Ni 3 Sn 4 / CU6 S n 5 /Sn-Cu is observed. The interesting solid state amorphization and alternating layer phenomena at 210 °C are primarily caused by the fact that Sn and Cu are fast diffusing species, while V is relatively immobile. © 2008 Materials Research Society.