Wirebonding is the electrical connection between the silicon chip and the external leads of the semiconductor device using very fine bonding wires. There are two common wirebonding processes: Au ball bonding and Al wedge bonding; HTS is able to perform both of them.
Thermosonic Gold - 0.7 to 3 mils
Ultrasonic Aluminum – 1 to 25 mils
During Au ball wire bonding, a gold ball, with a diameter ranging from 1.5 to 2.5 times the wire diameter, is first formed by melting the end of the wire utilizing an electronic flame-off (EFO). The gold ball is then brought into contact with the bond pad. Adequate pressure, heat, and ultrasonic forces are then applied to the ball for a specific amount of time, forming the initial metallurgical weld between the ball and the bond pad, as well as deforming the ball bond itself into its final shape. The wire is then run to the corresponding finger of the package or substrate forming a "loop" between the bond pad and the package lead. Pressure and ultrasonic forces are then applied to the wire to form the second bond (known as a wedge bond, stitch bond, or fishtail bond). The wirebonding machine or wirebonder breaks the wire in preparation for the next wirebonding cycle by clamping the wire and raising the capillary.
During Al wedge wire bonding, ultrasonic energy is applied to the wire for a specific duration while being held down by a specific amount of force, forming the first wedge bond between a clamped aluminium wire and the Aluminium bond pad. The wire is then run to the corresponding finger of the package or substrate, against which it is again pressed. The second bond is then formed by applying ultrasonic energy to the wire, which is then broken off by its clamping and movement.
Because it is non-directional, gold ball bonding is much faster than aluminum wedge bonding, which is why it is extensively used in plastic packaging. Unfortunately, Au ball bonding on Al bond pads cannot be used in hermetic packages, primarily beacuase the high sealing temperatures (400-450 deg C) used for these packages tremendously accelerate the formation of Au-Al intermetallics that can lead to early life failures. Gold ball bonding on gold bond pads, however, may be employed in hermetic packages.