Optimization and reliability of ultrasonic wedge bonding performance of copper wires on gold pads for MEMS devices

This work focuses on optimizing the bonding performance and enhancing the reliability of copper (Cu) wires on gold (Au) pads for MEMS devices, aiming to address the critical role of bonding wire reliability in ensuring overall device performance. Through orthogonal experiments combined with response surface regression analysis, the effects of four key process parameters (bonding force, ultrasonic power, ultrasonic time, and bonding temperature) on bonding quality were systematically investigated, with a specific focus on their coupling mechanisms. The results revealed that bonding force and ultrasonic power are the dominant factors determining the bonding pull force. A medium parameter combination (bonding force of 25 gf, ultrasonic power of 0.85 W, ultrasonic time of 180 ms, and bonding temperature of 50 °C) achieved the optimal bonding quality. This superiority arises from the balanced interplay between ultrasonic softening and grain refinement during bonding. Moderate plastic deformation of the Cu wire promotes uniform dislocation activation and annihilation at grain boundaries, avoids excessive stress concentration or material damage, and facilitates the formation of uniform (111) and (001) textures at the interface. Notably, Cu-Au intermetallic compounds (IMCs) were scarcely observed, eliminating the risk of brittleness caused by abnormal IMCs growth. Reliability tests, including high-temperature aging and thermal cycling, demonstrated that long-term thermal stress leads to performance degradation of bonding joints, primarily driven by interface cracks. After 25 days of aging at 150 °C, the bond pull force dropped below 6 gf. After 800 cycles, the pull force decreased to approximately 7.5 gf. This work clarifies the parameter coupling mechanisms and reliability rules of ultrasonic wire bonding of Cu wires on Au pads, practical theoretical and experimental support for improving the bonding reliability of MEMS devices.