Integrated temperature microsensors for characterization and optimization of thermosonic ball bonding process

Abstract

A novel ball bond process optimization method based on a thermal signal from an integrated aluminum microsensor is reported. The in-situ temperature during the ball bonding is measured and analyzed. The ultrasonic period shows distinct features corresponding to the scrubbing of the ball on the pad and the intermetallic bond growth, and the ball deformation by ultrasonic softening. A peak of the signal indicates the end of interconnection growth. This can be used for bond time optimization. When optimizing bonding force, the sensor signal correlates with ball shear strength. Using this method, bonding force process windows can be determined by on-line measurements. Maximum shear strength and maximum microsensor signal were within 20 mN at 34/spl deg/C. In summary, the method produces a wealth of new insights in transient thermal phenomena of the ball bonding process and promises to simplify the evaluation of ball bonding process windows.