A fluxless Au-Sn bonding process of tin-rich compositions achieved in ambient air

A new alternative fluxless bonding process conducted in ambient air is reported based on two different Au-Sn multilayer composite designs that are substantially tin-rich; namely, one with composition of 80 at.% Sn (70.54 wt.% Sn) and 20 at.% Au (29.46 wt.% Au), and another with 95 at.% Sn (91.82 wt.% Sn) and 5 at.% Au. (8.18 wt.% Au). We believe that this is the first time that Au-Sn bonding is achieved in air without the use of flux. The bonding process temperatures chosen for constructing 80 Sn-20 Au and 95 Sn-5 Au joints are 285°C and 225°C, respectively. Once produced, both types of joints were examined using the scanning acoustic microscopy (SAM) to confirm the bonding quality and the results obtained are nearly void-free. To study the microstructure and composition of the samples the scanning electron microscopy (SEM) equipped with energy dispersive X-ray (EDX) detector were conducted across the 95 Sn-5 Au joint cross-section.