Automatic wire bonders make electrical connections from semiconductor chips to other parts of the semiconductor. It is highly cost-effective and flexible. It is also used to manufacture a large majority of semiconductor packages.
The wire used in wire bonding is called bonding wire, coincidentally. They are fine wires made of gold, aluminum, or copper. Their diameter ranges from usually about 15 micrometers to several hundred micrometers. The type of wire used in the machine is greatly dependant upon the technology being used. For example advanced packaging technology requires special loop profiles and fine-pitch bonding, and thus cannot use just any wire.
Wire bonding can be placed into two categories: ball bonding and wedge bonding. Ball bonding is restricted mostly to copper and gold wire. A ball is formed by melting the end of the wire by electronic flame-off. It is then called a free air ball and is necessary for proper bonding. It is brought into contact with the bond pad where pressure, heat, and ultrasonic energy is applied to the ball, creating a metallurgical weld between the bond pad and the ball, creating the ball bond’s final shape. The wire is then run through the corresponding lead frame to produce a loop and more bonds are formed. The wire bonder breaks the wire in preparation for the next cycle.
Wedge bonding is similar, capable of using gold wire but can also be performed using aluminum wire. Gold wire is the only type that requires heat. The wire is brought in contact with the bond pad, where ultrasonic energy is applied to the wire and forms the initial wedge bond. The wire is then run through its corresponding lead frame. The process then cycles again. It then uses the same welding technique as ball bonding to attach the wire, though using different kinds and amounts of pressure, heat, energy and element.