Effect of Direction of Ultrasonic Vibration on Flip-Chip Bonding

Abstract

Flip-chip bonding has several advantages, such as high precision, high density, short interconnections, and small parasitic elements. However, creating reliable interconnections between chips and substrates is the key issue in flip-chip bonding. In this work, bonding states are investigated using test element group (TEG) dies with gold stud bumps. Ultrasonic bonding is applied to a substrate with longitudinal and lateral leads, and the die-pull mode is investigated systematically. For conventional flip-chip bonding equipment, the die-pull test shows different bonding states for longitudinal and lateral leads. However, we have developed a flip-chip bonder with a rotational vibration head, where the direction of the angle of the vibration with respect to the die configuration can be changed. For a head rotated to 45 degrees, uniform bonding is established on both the longitudinal and the lateral leads. A wide process margin for flip-chip bonding is obtained, with a high yield.