Abstract: An improved method is described for ball bonding an aluminum wire to a contact pad of a microelectric device. In ball bonding, the wire is fed through and protrudes from a capillary hole in a bonding head, an electric arc melts the protruding wire into a ball, the solid ball thus formed is pressed and flattened onto the contact pad by the bonding head and the ball-contact surface interface is subjected to ultrasonic vibrations to form a bond between the flattened ball and the contact pad. Aluminum wire has presented a problem in forming asymmetric, porous, faceted balls that ball-bond very poorly. By using an aluminum wire coated with an electrically insulating layer that melts above the melting temperature of aluminum and has an electrical resistance sufficient to prevent the electric arc from shifting up the wire and away from the tip, the problem of poor quality balls is solved and a round, axisymmetric ball is formed which ball-bonds consistently well.