Study on Low-Temperature Bonding and Reliability of Nano-Twin Copper Micro-Cone Array

nano-twin copper (nt-Cu) has been a promising bonding material for its capability to control the unidirectional growth of intermetallic compounds (IMCs) and suppress the formation of Kirkendall voids at bonding interface. Furthermore, copper nano/micro cones have been applied in the field of low-temperature solid-state bonding, where mechanical interlocking effects improve bonding strength. In this paper, nano-twin copper micro-cone array (MCA) with twin boundaries (111-orientation) nearly perpendicular to the substrate prepared by pulse deposition was used to bond with SAC305 solder ball. Shearing test results show that the bonding strength between nt-Cu MCA substrate and solder ball is about 50% higher than that of twin-free Cu MCA and ten times of flat Cu. Reliability tests results show that nt-Cu MCA will generate thicker IMCs with electroplated Sn than other two substrates after reflow, which promotes bonding. In addition, nt-Cu MCA can promote the unidirectional diffusion of Cu atoms along the twinning plane, facilitating unidirectional growth of IMCs, which improves bonding reliability.