Study on the formation mechanism of liquid film on the Au/Cu bilayered film

Solder wetting and dewetting have attracted much more attention in the past years because solder joint is widely used in modern microelectronic technology. In this study, by using a photolithography process, the Au/Cu bilayered film was prepared into a wheel pattern. Wetting experiments of liquid solder on the wheel pattern were carried out on a home-made hot-stage optical microscope in a flow of reducing atmosphere. Far different from the classical spreading cap, liquid film was observed ahead of the main liquid flow. More experiments were designed to confirm that gold element played a key role in the formation of liquid film. Moreover, the gold film thickness, temperature and liquid quantity had great effect on the sprading of liquid film. The formation mechanism of precursor film was discussed in great details.