In situ study on interfacial reactions of Cu/Sn-9Zn/Cu solder joints under temperature gradient

Synchrotron radiation real-time imaging technology was used to in situ study the interfacial reactions of Cu/Sn-9Zn/Cu solder joints during reflow under a temperature gradient. It was clarified that both Zn and Cu atoms were driven to migrate towards the cold end by the temperature gradient, which enhanced the intermetallic compounds (IMCs) growth locally and the Cu consumption at the hot end. A Cu5Zn8 layer adhered to the hot end interface could drastically restrict the consumption of the neighboring Cu substrate till it spalled from the interface. Additionally, the crystallization of β-Sn grains was observed to follow a highly preferred orientation with the c-axis of β-Sn grains departing from the direction of temperature gradient by about 30°-40°. These peculiar phenomena may inspire future exploration of interfacial reaction and grain orientation control by temperature gradient in 3D IC packaging technology.