Elemental composition optimization to achieve eutectic Au-Sn solder

The loss of some elements during the bonding process causes the overall composition to deviate from the eutectic point, affecting the adhesion's strength. Experiments were conducted to find suitable conditions via percentage of film thickness ratio (Au thickness/(Au + Sn) thickness) in the 48.72-60.13% range, which corresponds to %Sn in the range of 29-40at% on the binary Au-Sn (Au-rich side) phase diagram. The squeeze-out phenomenon of Sn occurs during heat and pressure between two workpieces that are being welded together and because this element has a lower melting temperature than Au, this results in the preparation of Sn equivalent to 33at%, corresponding to a percentage film thickness ratio of 56%, to obtain the eutectic condition at Sn 29at% when the bonding process is completed. Specimens were prepared with focus ion beam for analysis elements to indicate the phase formation of IMCs and their distribution. The workpiece was prepared with FIB-lamella to study the nanometer structure with the transmission electron microscopy technique and identify the type of crystals formed by the selected area electron diffraction analysis. The adhesion strength was evaluated with all experimental conditions using a shear tester. It was found that the conditions of eutectic provide the highest adhesion strength at 285.20 +/- 10.62 MPa.