Liquidus Projection

The liquidus projection at Sn-rich corner of other promising lead-free solder materials, such as Sn-Ag-Bi and Sn-Ag-In are shown using the TCS Solder Alloy Solutions Database (TCSLD). Comparison between the reported melting temperatures and the calculated melting temperatures are included.

Sn-Ag-Cu

SnAgCu (SAC) alloys are one of the most commonly used Pb-free solders and are also the leading alloys in replacing Sn-Pb solder for electronic assembly applications. Typical compositions are 3-4 wt.% Ag, 0.5-0.7 wt.% Cu with balanced Sn, for example, SAC305, SAC 307, and so forth.

The calculated Sn-Ag-Cu liquidus projection at an Sn-rich corner is shown in Figure 1. The green curves in the diagram are calculated constant temperature contours with the temperature indicated next to it. The compositions of commercial alloys are shown as circles and the corresponding melting points reported by different solder companies are marked next to the circles. The temperature difference between the calculated and the reported melting points is within 1 to 2 degrees in most cases. E represents the calculated ternary eutectic point for the invariant reaction L <-> Ag3Sn+(Sn)+Cu6Sn5_HT. Figure 2 demonstrates the validation of the density of liquid SnAgCu solder alloys.

Calculated Sn-Ag-Cu liquidus projection at Sn-rich corner.

Figure 1: Calculated Sn-Ag-Cu liquidus projection at Sn-rich corner. The reported liquidus temperatures of SnAgCu (SAC) solder alloys are shown for comparison. The difference is less than 2 °C. E: Tcal.=216 °C, Texp.=217 °C.

Calculated density of liquid Sn-Ag-Cu alloys. Symbols are the experimental values from Kaban et al.

Figure 2: Calculated density of liquid Sn-Ag-Cu alloys compared to experimental data.

Sn-Ag-Bi

Calculated Sn-Ag-Bi liquidus projection at Sn-rich corner.

Figure 3: Calculated Sn-Ag-Bi liquidus projection at Sn-rich corner. The reported liquidus temperatures of SnAgBi solder alloys are shown for comparison. Ternary eutectic reaction E: Tcal.=137.5 ºC, Texp.=138.4 ºC.

Sn-Ag-In

Calculated Sn-Ag-In liquidus projection at Sn-rich corner.

Figure 4: Calculated Sn-Ag-In liquidus projection at Sn-rich corner. The reported liquidus temperatures of SnAgIn solder alloys are shown for comparison. The difference is less than 2 °C. U1: Tcal=214 °C, Texp=215 °C ; U2: Tcal=207.5 °C, Texp=206 °C.