GOALI: Understanding the Mechanisms of Ultrasonic Bonding at Atomic Scale

Santa Clara University, Santa Clara CA

Investigators

Abstract

Ultrasonic vibration is essential for various solid-state bonding techniques, such as ultrasonic wedge and ball bonding, flip-chip bonding, battery welding, and ultrasonic additive manufacturing. These processes are essential in the consumer electronics, defense, automotive and aerospace industries. Although the essential role of ultrasonic vibration in bond formation is well recognized, the underlying mechanisms are still largely unknown. Development of a fundamental understanding of bond formation mechanisms would result in an improved ability to tailor and optimize bonding processes for new materials and improved properties. This would specifically address the goal of improved current-carrying capabilities in battery and automotive power applications, thereby improving efficiency and reducing energy demand. Given this important focus, and the partnership with the electronics industry, this Grant Opportunities for Academic Liaison with Industry (GOALI) project has significant industry impact while simultaneously offering a rich environment for graduate student training and exposure of undergraduates to engineering research. The multi-level complexity of the project enables involvement of students at different levels, including undergraduate and graduate students. The close collaboration between the PIs and the industrial partner provides a unique learning environment for the students, preparing them with very relevant experience closely aligned with the needs of local Silicon Valley's microelectronic industry. Based on the combination of modeling results and experimental analysis, the PIs will establish a new workshop for university outreach activities targeting promotion of STEM field among K-12 and underrepresented students. The objective of this GOALI project is to provide fundamental understanding on the atomic-scale mechanisms that govern bond formation during ultrasonic bonding. The research focuses on the central hypothesis that bonding occurs through growth of the microwelds that form by an atomic avalanche between clean, oxide-free surfaces. Two specific objectives are followed: 1) Investigating the nature of oxide film breakage during ultrasonic vibration through a combination of experimental, analytical and finite element analysis. 2) Investigating mechanism of atomic movement that leads to microwelds formation and growth through a combination of molecular dynamics and experimental analysis. Employing a combination of computational modeling and experimental approaches enables analysis of the phenomena during a very short period of bonding time. The successful completion of the research will lead to new insights into the fundamental atomic interactions that govern bond formation mechanisms during ultrasonic bonding. The application of the newly developed theoretical and experimental techniques to these problems enhances the understanding of the role of surface forces in the formation of micro-contacts and the fundamental issues pertaining to interfacial adhesion.