Effect of Temperature and Solder Thickness on Interfacial Reaction in Cu/Sn/Ni Solder Joints Formed by TLP Bonding

With the continuous development of electronic packaging technology in the direction of miniaturization, the performance requirements for chips and electronic products continue to increase, the size of the solder joints in the 3D package must be continuously reduced. The reduction of the bump size will significantly affect the interfacial reaction, in which Ni and Cu atoms diffuse into the solder and the opposite interface and strongly influence the growth of the interfacial IMCs. In this paper, the effects of Cu-Ni cross-interaction on the type and morphology of the interfacial IMCs during the interfacial reaction of Cu/Sn/Ni solder joints with two pitch sizes of 50 μm and 100 μm at 250°C and 300°C were observed. During the liquid-solid interfacial reaction, (Cu,Ni)
6
Sn
5
with different morphologies was observed on both UBMs, and Cu
3
Sn was only formed on the Cu UBM at 300°C. The morphologies of (Cu,Ni)
6
Sn
5
changed from long rods to a mixture of long and short rods at 250 °C, while their morphologies changed from short rods to scallops at 300 °C. As the reaction time increases, regardless of whether the size of the solder joint is 50 μm or 100 μm, the interfacial IMCs were (Cu,Ni)
6
Sn
5
, but the interfacial IMCs on both UBMs grow asymmetrically. The thickness of the interfacial IMCs on both UBMs increases with the prolongation of the liquid-solid reaction time. And the thickness of the interfacial IMCs formed on the Cu UBM is always thinner than that on the Ni UBM. Moreover, the growth velocity of (Cu,Ni)
6
Sn
5
IMC developed on the Ni UBM at 250 °C is faster than that at 300 °C, and conversely, the growth velocity of (Cu,Ni)
6
Sn
5
IMC formed on the Cu UBM at 250 °C is slower than that at 300 °C. The different morphologies of (Cu,Ni)
6
Sn
5
IMC could be ascribed to the consistency of Ni in the interfacial IMCs.