Most printed circuit boards and electronic components are soldered using standard melting point alloys. The Tin/Lead alloys most commonly used are Sn63/Pb37 and Sn60/Pb40 with melting points of 361°F (183°C) and 370°F (188°C) respectively.
The Lead-Free solder alloys SAC305 and Sn99.3/Cu0.7 have melting points of 430°F (221°C) and 441F (227°C) respectively. While higher than the Sn63 alloy, lead-free solders are not considered high-temperature solders.
HIGH-TEMPERATURE SOLDER
Since pure Tin melts at 450°F (232°C) and pure Lead at 621°F (327°C), high-temperature solders contain mostly Lead. For instance, the Sn10/Pb88/Ag2 alloy containing 88% Lead has a 570°F (299°C) melting point.
APPLICATIONS for HIGH-TEMP SOLDERS
Components that will operate in very hot environments, such as in avionics, automotive and downhole oil and gas wells can benefit from higher temperature solders.
LOW-TEMPERATURE SOLDER
Low temperature solders have melting points ranging from 117°F (47°C) to 320°F (160°C). These solder alloys contain Tin blended with a variety of metals such as Bismuth, Indium, Cadmium, etc.
APPLICATIONS for LOW-TEMP SOLDERS
Components or substrates like flex circuits that are heat sensitive are good candidates for lower temperature solders. Step soldering, or 2nd side soldering using low temperature solder can be accomplished without disturbing previously soldered components that were attached using standard lead-free alloys.
Soldering at lower temperatures also reduces the thermal energy needed, extending the equipment life, and reducing overall electrical usage.
SOLDER ALLOY MELTING POINTS (°F)
|
SOLDER ALLOY
|
SOLIDUS | LIQUIDUS |
| Sn10/Pb88/2Ag | 514 | 570 |
| Sn97/Cu3 | 441 | 590 |
| Sn100 (pure Tin) | 450 | 450 |
| SAC305 lead-free | 423 | 442 |
| Sn50/Pb50 | 361 | 413 |
| Sn60/Pb40 | 361 | 370 |
| Sn63/Pb37 | 361 | 361 |
| 281 Alloy (Sn/Bi) | 281 | 281 |
| 117 Fusible (Optical) | 117 | 117 |
