In wire bonding, a gold ball is forced down and thermosonically bonded to a die-bond pad forming the first connection of an integrated circuit (IC) and substrate. With the ball connected, the wire is fed out and attached to a second surface, and then torn off to complete the connection.
In the ball-bumping process, instead of making the second connection with a wire loop and stitch, the wire is removed after the ball is connected to the die. A new ball is formed and the process repeats as necessary on all the die bond pads.Gold-ball bumping can be a one-step process, but can involve two steps if a coining process is needed to planarize the ball bumps.
Once the die is completely bumped, it is flipped and attached to the substrate, providing the first-level interconnect as well as protection for the active die surface.