Effect of Cu content in the Ni-Cu under-bump metallurgy on the interfacial reaction between Ni1-xCux and Sn solder

In this investigation, deposited Ni-Cu with varying Cu content were utilized as under-bump metallization (UBM) for solder joints, subjected to a temperature of 250℃ for varying durations. The study findings elucidated a notable influence of copper (Cu) content how to influence the nucleation and growth of intermetallic compounds (IMCs). The UBMs were fabricated with distinct Cu deposits by altering the quantity of the principal salt, Cu (CH 3 COO) 2 •H 2 O. In the case of the Ni-25Cu/Sn joint, it was observed that the 4.6 μm UBM layer was not entirely consumed by the Sn solder even after 10 minutes of reflow. The initial phase arising from the interaction between the Sn solder and the Ni-25Cu UBM was observed to exhibit a rod-shaped morphology, EDX results identified as (Ni,Cu) 3 Sn 4 . With an increase in the concentration of Cu and a lengthening of the reflow time, the Ni-35Cu and Ni-50Cu UBM/Sn joints exhibited the presence of an additional diamond-shaped phase, identified as (Cu,Ni) 6 Sn 5 , in addition to the previously observed rod-shaped (Ni,Cu) 3 Sn 4 phase. Moreover, an amalgamated layer of IMCs, consisting of (Ni,Cu) 3 Sn 4 and (Cu,Ni) 6 Sn 5 , was observed to coincide with a sudden surge in IMC thickness and rapid dissolution of the underlying UBM. To analyze and predict the growth behavior of IMCs between different UBMs and Sn solder, theoretical models based on growth kinetics can be effectively employed. The growth process of IMCs on the interface of Ni-25Cu and Sn is predominantly controlled by atomic diffusion. Conversely, in the case of Ni-35Cu/50Cu, the growth of IMCs is primarily governed by the reaction rate.