A single-wire contacting method, called bonding, is known for establishing an electrical connection between at least two contact surfaces. In doing this, individual wires, in particular, gold or aluminum wires, are positioned between the contact surfaces to be bonded, using a wire-bonding tool. In bonding, the contact wire is bonded to the contact surfaces by applying ultrasonic pressure and heat. The free end of the bonding wire is first melted to form a ball, by applying thermal energy, and subsequently pressed onto the first contact surface, using a bonding capillary. The contact wire bonds to the contact surface as a result of atomic bonding forces (material fusion) arising at the boundary between the contact surface and the contact wire. During bonding to the first contact surface, the ball that was previously melted on is deformed into a nail head. The contact wire is then led to the second contact surface, using the wire-bonding tool. To prevent the contact wire from breaking away at the first contact point, the contact wire is formed into a loop. The contact wire is then pressed onto the second contact surface with the wire-bonding tool by again applying ultrasonic pressure and heat. This produces necking of the contact wire, causing the latter to form a rupture joint at which the contact wire breaks away from the second contact surface as the wire-bonding tool moves on. The contact wire is bonded to the second contact surface by a “stitch,” with atomic bonding forces again arising at the boundary between the contact wire and the second contact surface.
This known ball-wedge bonding method (ball bonding with the first contact surface, and stitch bonding with the second contact surface) produces a strong dependency between the materials of the contact wire and the contact surface, thus forming strong atomic bonding forces at the boundaries. Particularly when contacting the second contact surface, a relatively weak surface bonding forms between the stitch and the contact surface, resulting in contacting errors, particularly in the case of contact surfaces made of hard-to-bond materials.
USPTO Backgrounds
USPTO Backgrounds