Ball bonding

However copper is cheaper than gold and has superior electrical properties,[1] and so remains a compelling choice.

Almost all modern ball bonding processes use a combination of heat, pressure, and ultrasonic energy to make a weld at each end of the wire.

The tip of the wire forms into a ball because of the surface tension of the molten metal.

The ball quickly solidifies, and the capillary is lowered to the surface of the chip, which is typically heated to at least 125 °C.

[2] (All-aluminum systems in semiconductor fabrication eliminate the "purple plague"—a brittle gold-aluminum intermetallic compound—sometimes associated with pure gold bonding wire.

The machine again descends to the surface, this time without making a ball so that the wire is crushed between the leadframe and the tip of the capillary.

The process where wire is cut right after ball is formed is also called stud bumping.

At the same time, in order to minimize energy loss to the surroundings, the transducer is held at an antinode (no displacement).

The horn's taper reduces the cross-sectional area, causing a larger ultrasonic energy density, then leading to more displacement near the tip.