Microstructure development during directional solidification of a Sn-Ag-Cu ternary alloy

OSVALDO FORNARO AND CARINA MORANDO

INTERNATIONAL JOURNAL OF CAST METALS RESEARCH

MANEY PUBLISHING

Lugar: London; Año: 2017 p. 1 - 7

1364-0461

The alloys of Sn-Ag-Cu family (SAC) are candidates for lead-free replacement of Sn-Pb eutectic used in the solder processes of electronic devices. These al-loys, with eventual adding of trace elements like Zn, In and Bi highly improve the morphological stability and the corrosion resistance. Close to the eutectic ternary composition, the solidification occurs through the simultaneous growth of three distinctive phases: Sn-rich dendritic primary phase, and the intermetallic phases Ag3Sn and Cu6Sn5. These intermetallic phases have a limited solubility into the Sn-rich phase and for this reason some authors consider these alloys as compounds of Sn with the mentioned phases. The solidification process is a fundamental aspect of the microstructure development during the solder and the freezing of the alloy.In this aspect, the directional solidification is a suitable tool to study the solidification under strictly controlled conditions. In this work, samples of Sn-Ag-Cu with a composition close to the ternary eutectic were directionally grown to analyze the mechanisms involved in the solidification of these alloys.The typical microstructure was developed in a similar fashion with the description above, but showing at least two different mechanisms, depending on the advance velocity, resulting on different distribution of the intermetallic phases.