183Nanosensor Laboratory
a very thin wire, usually 25–75 m in diameter, from one connection pad
to another, completing the electrical connection in the electronic device.
The most frequently used method of joining the wires is ultrasonic welding,
a high-frequency ultrasonic acoustic vibration is locally applied to work-
pieces being held together. Thermocompression wire bonding requires the
application of a high force on the surface along with a high temperature,
around 300°C. It provides excellent, reliable Al–Au bonds with exibil-
ity in the bonding direction allowed. The wire material is Au but the pad
can be either Au or aluminum. Depending on their shapes, there are two
basic types of wire bonds: ball/wedge and wedge ...