SB²-WB: A New Process Solution for Advanced Wire-Bonding

This paper describes a novel and innovative wire-bonding method which combines standard wire feeding application with the unique solder-jetting process; i.e. SB²-Jet. In contrast to conventional ultrasonic, thermosonic or thermocompression bonding, the laser-wire-bond connection, SB²-WB, is not welded but soldered. Neither pressure, ultrasonic vibration nor high temperatures are utilized. These technical advancements broaden the spectrum of wire-bonding applications. Besides the fundamental process explanation and the comparison to conventional wire-bonding methods, the results of initial reliability and stability tests on 50µm Au wire contacts bonded in wedge-wedge configuration are presented and discussed. For this comparison, the bonds were thermally, mechanically and electrically stressed. The impact on the bonds after thermal cycling (250TW) and vibration tests were microscopically inspected and metallurgically studied through cross-sectional polishing and FIB-SEM characterization. The mechanical load-capacity was quantified using a pull and shear test measurement system. The failure characteristics of the bonds during an ampacity test were analyzed by thermal imaging. Moreover, the fabrication of laser-wire-bond connections on a piezoceramic element as part of a PDC-ultrasonic sensor using 80µm insulated Cu wire and SAC_305 (760µm sphere diameter) solder alloy is described and qualified as an example of potential application. The mechanical strengths of the interconnections were measured using a shear tester, while the concomitant metallurgical properties were analyzed by X-ray and FIB-SEM. The opportunity to remove surrounding insulation material of a wire during the bonding process will be an additional topic of discussion. Finally, a roadmap for this new technology and future prospects involving intended reliability and comparative stability studies are elucidated.