Flip chip interconnects based on carbon nanofibers-solder composites

In this paper, we propose the introduction of vertically aligned carbon nanofibers (CNF) directly grown on the bonding pad by chemical vapor deposition at CMOS compatible temperatures as a solution to reinforce and confine the solder joint between two chips bonded by solder. This concept potentially enables the reduction of pitches and size of the solder interconnects. The solder joints are realized by thermal compression bonding technique and the assemblies are characterized by means of electrical measurements of daisy chains and kelvin structures formed by the connection of the two chips. Flip chip interconnects based on two solder composite solutions (CNFs/SnAg and CNFs/SAC305) are analyzed in terms of electrical resistance, and different growth conditions for the CNFs and a post-growth treatment have been tested. The addition of the carbon nanofibers to the solder led to an additional resistance lower than 10% of the total resistance, while possibly improving the reliability of the joint.