DETERMINATION OF THE MELTING AND SOLIDIFICATION CHARACTERISTICS OF SOLDERS USING DIFFERENTIAL SCANNING CALORIMETRY

Differential scanning calorimetry (DSC) is used in the present study t o determine the onset temperature of phase transformation and the enth alpy of fusion of various solder alloys. The solders studied are Sn-Pb , Sn-Bi, Ag-Sn, In-Ag, and Sn-Pb-Bi alloys. Very notable undercooling, such as 35 degrees C, is observed in the solidification process; howe ver, a superheating effect is not as significant in the heating proces s. Besides the direct measurements of reaction temperature and heat of fusion, the fraction solid vs temperature has also been determined us ing a DSC coupled with a mathematical-model method. The heating and co oling curves of the solders are first determined using DSC. By mathema tically modeling the heat transfer of the DSC cells, the heat evolutio n and absorption can be calculated, and then the melting and solidific ation curves of the solder alloys are determined. The three ternary al loys, Sn-35 wt pct Pb-10 wt pct Bi, Sn-45 wt pct Pb-10 wt pct Bi, and Sn-55 wt pct Pb-10 wt pct Bi, displayed similar DSC cooling curves, wh ich had three reaction peaks. However, the solid fractions of the thre e alloys at the same temperature in the semisolid state, which had bee n determined quantitatively using the DSC coupled with a mathematical method, were different, and their primary solidification phases were a lso different.