The process of wire bonding, particularly when utilizing gold and copper wires, represents a pivotal step in the field of microelectronics packaging. As devices continue to become increasingly miniaturized, it is imperative to gain a deeper understanding of the effects of materials and bonding parameters to ensure the reliability of these interconnects. The research is driven by the challenges posed by fine-pitch bonding, smaller bond pad sizes, and the increased use of Cu wire. Despite its cost benefits and mechanical strength, Cu wire. Despite its cost benefits and mechanical strength, Cu wire presents reliability challenges due to its tendency to oxidize and form brittle intermetallics with Al bond pads. The objective of this study is to address these issues by investigating the factors that influence the quality and longevity of Au and Cu ball bonds on Al alloy pads. These factors include ultrasonic energy, bond force, and wire metallization.

The research employs a combination of experimental and theoretical approaches to analyze the ball bonding process, employing a methodology that is both empirical and theoretical in nature. The principal methodologies employed are as follows:

• Tensile Stress-Strain Analysis: An evaluation of the mechanical properties of Au and Cu wires was conducted, including an assessment of work hardening and strain rate sensitivity.
• High-temperature storage (HTS) is a process whereby materials are stored at elevated temperatures. Ball bonds are subjected to elevated temperatures (up to 175°C) to facilitate the study of intermetallic growth and bond degradation over time.
• (PCT), Temperature Cycling (TCL), and Thermal Humidity Bias (THB) tests were conducted.
• Ultrasonic Power Modulation: Bonding experiments were conducted at varying levels of ultrasonic power to study the effect of this variable on bond quality, deformation, and intermetallic phase growth.
• Scanning electron microscopy (SEM) is employed for: This method is employed to evaluate the microstructure, intermetallic phase formation, and void/crack propagation at the bond interface.
• Finite Element Modeling (FEM): The simulation of stress-strain distributions and deformation patterns in ball bonds under varying ultrasonic power and bonding forces is a key application of this technique.
• Environmental stress tests were conducted. To assess the reliability of the bond in harsh environmental conditions, Pressure Cooker Tests (PCT), Temperature Cycling (TCL), and Thermal Humidity Bias (THB) tests were conducted.
• Ultrasonic Power Modulation: Bonding experiments were conducted at varying levels of ultrasonic power to study the effect of this variable on bond quality, deformation, and intermetallic phase growth.

• Intermetallic growth in Au and Cu bonds: At elevated temperatures, intermetallics such as Au8Al3 form rapidly, increasing in thickness over time. While this can enhance bond reliability, it can also result in void formation. In comparison to Au–Al phases, Cu–Al intermetallics, such as CuAl₂ are thinner and more brittle, which results in a higher susceptibility to crack formation and reliability issues during stress tests.
• Impact of Ultrasonic Power: The application of elevated ultrasonic power has been observed to enhance the extent of plastic deformation and intermetallic coverage. However, the utilization of excessive power has been shown to result in the over-deformation of the material, the formation of voids, and a reduction in bond strength. This is attributed to the damage caused to the neck region of both Au and Cu bonds. The deformation patterns observed in Cu bonds were less uniform than those in Au bonds, likely due to the coarser grain structure of the Cu wire. This resulted in inconsistent bond dimensions and lower pull strength in reliability tests.
• Mechanical Properties and Plastic Deformation: The deformation of Au wires was observed to be more uniform, which was attributed to their finer grain structure and higher strain rate sensitivity. This resulted in more consistent bond dimensions and a reduction in the variance in pull strength. In contrast, Cu wires, with their larger grain sizes, demonstrated greater variability in deformation behavior, which led to higher inconsistencies in bond quality, particularly in the formation of the second bond.

• Optimization of Process Parameters for Cu Bonding: The research findings suggest the necessity for precise adjustment of ultrasonic power and bonding force, particularly in Cu bonding, to prevent excessive deformation and void formation. One potential avenue for future research is the development of novel capillary designs that reduce stress concentration at the bond interface and minimize void formation during Cu bonding.
• Exploration of Alternative Wire Materials: Palladium-coated Cu wires (PdCu) and other metal alloys may be considered as potential alternatives to pure Cu wires due to their enhanced resistance to oxidation and superior performance in environmental stress tests.
• Intermetallic Growth Management: Further research is necessary to ascertain the long-term stability of Cu–Al intermetallic phases and their role in bond reliability. A more comprehensive examination of the manner in which these phases evolve over time at varying temperature ranges could prove instrumental in the development of more robust bonding processes.

One of the principal constraints of the study is the considerable variability observed in Cu wire bonding, which can be attributed to the inconsistent plastic deformation of its larger grains. This renders the implementation of a uniform bonding process across disparate devices a challenging endeavor. Although the study employed a variety of stress tests, additional long-term reliability tests under extreme environmental conditions (e.g., extended temperature cycling or humidity exposure) could provide a more comprehensive understanding of the failure mechanisms in Cu bonds.
Further research is required to elucidate the precise mechanisms underlying void formation in Cu–Al bonds, particularly to distinguish the influence of ultrasonic power from other process variables such as bond force and temperature. The present study concentrated predominantly on Au and Cu bonding with Al alloy bond pads. Future research could investigate alternative metallizations, including nickel or silver, which may exhibit disparate intermetallic growth behaviors and bonding characteristics.