During the soldering process the eutectic melt
dissolves gold and forms z-phase. This phase is stable up
to 519°C, has good mechanical properties, a decreased
thermal resistance and excellent reliability. It is
possible to achieve pure z-phase interconnections.
Tests performed with the other eutectic composition
Au10Sn90 are described in Aschenbrenner et al6. He
reports bad results with this composition. It is brittle and
often cracks appear directly after the reflow. Shear values
are lower compared to dice bonded with Au80Sn20.
Further, he found a strong degradation of an LED
soldered with the Au10Sn90 eutectic during aging.