Abstract
Ultrasonic ball-bonding technology using high-frequency vibration was investigated in order to obtain high strength bonds with small deformation under low bonding temperature condition. A novel bonding machine with resonance frequencies of 130 and 172 kHz was developed. Vibration characteristics at the tip of the capillary tool in the machine were measured and compared with that of a conventional 60 kHz bonding machine. Vibration amplitude at each frequency of the developed machine was smaller than that of the conventional machine, which was 1/10 to 1/50. Using the developed machine, Au wire was ball-bonded to Al pads on Si chip at the three frequencies under different conditions of vibration amplitude, bonding static force and bonding temperature. The bondability at each frequency was evaluated by measuring deformed ball diameter and shear strength after bonding. Main results are as followed:(1) Minimum vibration amplitude at the tip of a bonding tool decreases, which is required for obtaining higher bond-strength than wire-strength, as vibration frequency increases.(2) The smallest ball deformation ratio that guarantees more than 0.3 N bond-strength decreases as vibration frequency increases, that is, increasing the frequency elevates ultrasonic ball-bondability of Au wire to Al pads.
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