Bond wire

A bond wire is an extremely fine wire that carries signals and power from a chip's tiny pads out to its package. Typical bond wires are about 15 to 50 micrometers across, thinner than a human hair, and one chip may have hundreds of them.

They start as very pure gold, often 99.99%, sometimes with traces of other elements for strength. A gold rod is pulled through a series of diamond dies, each hole slightly smaller than the last, until it's finer than a hair. It's then heat-treated to soften it and wound onto spools.

A wire bonder stitches each connection at high speed. A spark melts the tip of the wire into a tiny ball. The machine presses the ball onto a pad on the die with heat and ultrasonic vibration, which welds it on. It then loops the wire over to the lead frame or package substrate, presses it down to make a second weld and snips it.

Bond wires connect the dies in integrated circuits, memory and storage chips, power transistors, and the chips in white LEDs and infrared LEDs. Gold resists corrosion and bonds easily, but to save money many makers now use copper wire.