Ultrasonic Bonding of Cone Bump for Integration of Large-Scale Integrated Circuits in Flexible Electronics

This paper reports that room-temperature bonding of LSI chips to metalization on a plastic film made of poly(ethylene naphthalate) (PEN) can be realized by ultrasonic bonding of a cone-shaped microbump made of Au. A 20-μm-pitch area array of cone-shaped Au microbumps was fabricated on a Si wafer by photolithography and electroplating. The counter electrode on the PEN film was composed of a Au (top)/Ni/Al (bottom) layered structure, where Ni and Au layers were deposited by electroless plating on Al interconnection. Bonding of 8,800 bump connections with 83.4 m$\Omega$/bump has been achieved at room temperature.