Analysis of the wire/substrate interface during ultrasonic bonding process

Abstract

The ultrasonic wire bonding has been applied in the semiconductor packaging industry ever since its innovation in the 1960s. The mechanisms of the bonding process, however, are still unclear. According to state-of-the-art, the extremely short bonding process can be divided into four phases. These phases at the bonding interface were analyzed either from a side view or from a 2-D view but only after the bonding process when the wire was removed or cut. A 2-D real-time observation at the bonding interface, which is beneficial to a deeper understanding on these phases, has not been conducted. In this work, a transparent glass was used as the substrate and a high-speed observation system was installed underneath the glass to real-time observe the different phases from a 2-D view. The wire/substrate contact area and the friction area as well as their expansion over time were first observed. During this period, the oxide scale breakage area can be detected. A static dark area related to the formation of microwelds then appeared from the central region. During the expansion of this area, some oxides retained within this static area while most oxides were carried to the peripheral contact area. Friction continued during the extension of the contact area and the static area. These findings provide a deeper insight into the wire bonding process.