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-temp 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 |