An ambient temperature ultrasonic bonding technology based on Cu micro-cone arrays for 3D packaging

• An ambient temperature ultrasonic bonding technology is introduced.
• Successful bonding joints can be achieved under 8 Mpa and 1 s.
• Possible mechanisms of the bonding method have been proposed.

An ambient temperature ultrasonic bonding based on Cu micro-cone arrays (MCAs) plated with thin Sn for potential application in 3D packaging is introduced. The interfacial morphology is investigated in joints bonded by this method. As the thickness of Sn layer in bonding interface was about 300 nm, the best bonding quality was obtained under the condition of low pressure of 8 Mpa and short time of 1 s, meanwhile, the voids of interfaces vanished. Under the effect of ultrasound, the Cu MCAs embedded into each other effectively and a stable physical occlusion was formed. The thin Sn transformed into Cu3Sn in the bonding interface due to quick atom diffusion. The bonding materials of two sides are the same, which makes the preparation of bonding process easier. Without solder balls, ultrasonic bonding joints with smaller size can be directly achieved using Cu MCAs plated with a thin Sn layer.