Novel ultrasonic transducer design for fine-pitch wire bonding

Today's high speed, ball-wedge wire bonder technology puts stringent requirements on its bond process modules. The intermetallic joint between the wire and chip/substrate must grow reliably at a high speed. Most bond processes utilize ultrasonic energy for bond formation in addition to heat and force. This energy is transferred from an ultrasonic transducer via a capillary tip to the bond. A reliable bond requires that several conditions be met. First, the capillary tip must oscillate parallel to the surface. Any movement of the capillary perpendicular to the bond surface should be small. Excessive movement can deform the ball without building up any bond strength and make the bond formation model more complex. Thus, the bond quality deteriorates. Second, ultrasonic acceleration of the capillary causes strong dynamic forces between capillary and transducer. The capillary mounting method must ensure a reliable clamping of the capillary under these forces. Third, the electrical drive of the transducer must be straight forward. We propose a transducer design that (1) reduces the movement components perpendicular to the bond surface, (2) enables a reliable clamping of the capillary under strong forces and (3) has no side resonances that complicate the electrical drive.