Melting temperatures of solder alloys: the complete chart
At what temperature does tin melt? And a 60/40 alloy, SAC305 or Sn97Cu3? This guide brings together in a single table the solidus and liquidus of the most widely used solder alloys, explains the difference between eutectic alloys and alloys with a melting range, and shows how to go from the melting temperature to the working temperature.
Dickmann Srl · updated
Melting temperature chart
The solidus is the temperature at which the alloy begins to melt, the liquidus the temperature at which it is completely liquid. For eutectic alloys the two values coincide. The values are typical: for each lot, the technical data sheet and the certificate of analysis are authoritative.
| Alloy | Composition | Solidus | Liquidus | Type |
|---|---|---|---|---|
| Pure tin | Sn 99.9 % | 232 °C | 232 °C | Pure metal |
| Sn63Pb37 | Sn63/Pb37 | 183 °C | 183 °C | Eutectic tin-lead |
| Sn60Pb40 | Sn60/Pb40 | 183 °C | 190 °C | Tin-lead |
| Sn50Pb50 (50/50) | Sn50/Pb50 | 183 °C | 215 °C | Tin-lead |
| SAC305 | Sn96.5/Ag3/Cu0.5 | 217 °C | 220 °C | Lead-free, near-eutectic |
| SAC405 | Sn95.5/Ag4/Cu0.5 | 217 °C | 219 °C | Lead-free |
| SAC0307 | Sn99/Ag0.3/Cu0.7 | 217 °C | 227 °C | Lead-free, low silver |
| Sn96.5Ag3.5 | Sn96.5/Ag3.5 | 221 °C | 221 °C | Lead-free, eutectic |
| Sn97Ag3 | Sn97/Ag3 | 221 °C | 224 °C | Lead-free |
| Sn99.3Cu0.7 | Sn99.3/Cu0.7 | 227 °C | 227 °C | Lead-free, eutectic |
| 99SnCuNiGe (SN100C equivalent) | Sn/Cu0.7/Ni0.05/Ge | 227 °C | 227 °C | Lead-free, eutectic |
| Sn97Cu3 | Sn97/Cu3 | 227 °C | 310 °C | Lead-free, wide melting range |
| Sn95Sb5 | Sn95/Sb5 | 235 °C | 240 °C | Lead-free, high temperature |
| Sn95Ag5 | Sn95/Ag5 | 221 °C | 240 °C | Lead-free, high temperature |
| Pure lead | Pb | 327 °C | 327 °C | Pure metal |
Alloy designation and purity according to EN ISO 9453 and IPC J-STD-006.
Eutectic alloys and melting range
A eutectic alloy changes from solid to liquid at a single temperature: Sn63Pb37 at 183 °C, Sn99.3Cu0.7 and 99SnCuNiGe at 227 °C. It solidifies quickly and uniformly, without a pasty phase: it is the preferred choice in electronics, where the joint must not move while it cools.
Alloys with a melting range remain pasty between solidus and liquidus. A wide range, such as the 183–215 °C of 50/50 or the 227–310 °C of Sn97Cu3, is useful when the bead has to be shaped or wide joints filled, for example in sheet-metal work and in sealing zinc coffin liners. In electronics, on the other hand, a joint disturbed during the pasty phase risks becoming porous or cracked.
From melting temperature to working temperature
The working temperature is always higher than the liquidus: the alloy must wet the surfaces and the thermal mass of the joint absorbs heat. These are the typical values we use in our pages; the technical data sheets of the alloy, flux and machine are authoritative.
| Process | Lead-free alloys | Tin-lead alloys |
|---|---|---|
| Soldering iron (tip) | 330–370 °C | 300–340 °C |
| Wave solder bath | 255–265 °C for SAC305 and SAC0307, 260–270 °C for Sn99.3Cu0.7 and 99SnCuNiGe | Lower, depending on the alloy |
| Selective soldering pot | 280–320 °C, depending on nozzle and thermal mass | Lower, depending on the alloy |
| Reflow (peak) | 240–250 °C for SAC305 | Profile according to the solder paste technical data sheet |
Why lead-free alloys melt at higher temperatures
Lead lowers the melting temperature of tin down to the 183 °C of the Sn63Pb37 eutectic. Without lead, tin-based alloys with silver and copper melt between 217 and 227 °C: the switch to lead-free, mandatory for equipment covered by the RoHS Directive, raised the melting temperature by 34–44 °C and, to a lesser extent, the process temperatures, with narrower process windows. To choose the alloy, see the guide to lead-free alloys and the comparison of SAC305, SAC0307 and 99SnCuNiGe.