Continuous growth and coarsening mechanism of the orientation-preferred Cu6Sn5 at Sn-3.0Ag/(001)Cu interface

Abstract

Orientation-preferred Cu6Sn5 usually offers solder interconnections superior mechanical and physical performances. In this work, morphology and orientation evolutions of Cu6Sn5 at Sn-3.0Ag/(001)Cu interface were investigated in the 300 °C–300 °C, 230 °C–230 °C and 300 °C–230 °C reflow processes. Results demonstrated that the continuous growth of orientation-preferred Cu6Sn5 was realized in the temperature-decreased reflow process of 300 °C–230 °C and the fraction of 0° boundaries in preferred Cu6Sn5 decreased from 0.81 to 0.60 with time while the fraction of 90° boundaries increased from 0.19 to 0.40; both curvature difference and misorientation angle of grain boundaries should be valued in the growth of preferred Cu6Sn5; the coarsening of preferred Cu6Sn5 includes two methods: coalescence and annexation, induced by the disappearance and migration of grain boundaries respectively. These results are of great significance in the orientation and size control of Cu6Sn5 crystals in 3D packaging.