Issue link: https://iconnect007.uberflip.com/i/1137649
104 SMT007 MAGAZINE I JULY 2019 Figures 8 and 9 show examples of scratches on the wire-bonding surface on rejected PCBs of Product I from the manufacturer. Those scratches seem to be made after the final sur- face finish step since the gold layer looks dam- aged due to the scratch. The widths of the scratches were about 9 mm and 20 mm (Fig- ures 8 and 9). The wire-bonding process used in this study is a specialized gold ball bonding process called either stand-off-stitch bonding (SSB) or ball-stitch-on-ball (BSOB) in the industry. The diameter of the bonding wire used was 25 mm. Figures 10 and 11 show an example of the SSB process in which ball bonds (or bump bonds) Figure 8: Scratches observed on wire-bonding track on rejected PCBs at low magnification (L) and high magnification on the (R). Figure 9: Scratch observed on individually defined wire-bonding pad on rejected PCB. Figure 10: Bonds on die for SSB process. Figure 11: Bonds on PCB for SSB process.