Solid state diffusion between Sn and Cu microcones on Cu microcones

• Solid state diffusion in low-temperature bonding based on Cu microcone is reported.
• Cu6Sn5 crystal orientation in Sn/Cu-microcone and Sn/flat-Cu samples are different.
• Special morphology of Cu microcone is beneficial for the growth of IMC.
• IMC of Sn/Cu-microcone samples grow with fine and uniform grain size.
• The diffusion mechanism is dominated by grain boundary diffusion.

Theoretical study of solid state diffusion mechanism in low-temperature bonding method based on Cu microcones is reported. A Sn layer was electrodeposited on Cu microcones as well as flat Cu substrate then annealed at bonding temperature 463 K. IMC grains of Sn/Cu-microcones diffusion samples grew with a relatively fine and uniform size. Cu6Sn5 crystal orientation in Sn/Cu-microcones and Sn/flat-Cu diffusion samples were different according to X-ray diffusion patterns. Nucleation was more likely to occur near the pinpoints of the Cu microcones. The kinetic factors showed that the special morphology of Cu microcones was beneficial for the growth of intermetallic layer (Cu6Sn5) in short annealing time and the grain boundary diffusion partially contributes to the rate-controlling process.