On the other hand, the solder ball supply method is a method in which contaminants such as oxides, moisture, oils and fats, etc., deposited on the surfaces of the Al electrodes are removed completely by ion impacts and then spherical solder balls are superposed on the cleaned surfaces in an ultra high vacuum, followed by bonding, as for instance described on pages 88-91 of Yosetsu Gijutsu (Weldin