The role of bonding duration in wire bond formation: a study of footprints of thermosonic gold wire on aluminium pad

Abstract

Purpose

Optimization of the process parameters remains a challenging task in thermosonic wire bonding due to relatively poor understanding of the bonding mechanism. The purpose of this paper is to understand initial bond formation in thermosonic gold wire bonding on aluminium metallization pads and the effect of bonding time on the initiation of bonding.

Design/methodology/approach

A gold wire (20 μm diameter/99.99 per cent wt%) was bonded to aluminium metallization pads (1 μm thick) on a silicon chip using a commercial ball/wedge automatic bonder. Bonding parameters were selected specifically to produce underdeveloped ball bonds so that ball lift‐off occurred during looping process. The lift‐off footprints on the aluminium metallization pads and their evolution were carried out using optical microscopy and scanning electron microscopy. A model is proposed to elaborate the effect of bonding time on initiation of bonding.

Findings

The obtained results showed that metallurgical bonding initiated at the peripheral areas of the contact area situated along the direction of ultrasonic vibration. Those areas extended inwards with bonding time, eventually covering the entire contact area.

Originality/value

This paper describes how bond initiation and its evolution in thermosonic gold wire bonding on aluminium metallization is ascertained by observing lift‐off footprints. The understanding of bonding mechanism benefits the optimization of process parameters and improvement of bondability in thermosonic wire bonding.

Citation

Xu, H., Liu, C., Silberschmidt, V.V., Chen, Z. and Wei, J. (2010), "The role of bonding duration in wire bond formation: a study of footprints of thermosonic gold wire on aluminium pad", Microelectronics International, Vol. 27 No. 1, pp. 11-16. https://doi.org/10.1108/13565361011009469