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Tin-silver-copper (Sn-Ag-Cu, also known as SAC), is a lead-free alloy commonly used for electronic solder.It is the main choice for lead-free surface-mount technology (SMT) assembly in the industry, [1] as it is near eutectic, with adequate thermal fatigue properties, strength, and wettability. [2]
Cd70, thermal-free solder. Produces low thermal EMF joints in copper, does not form parasitic thermocouples. Used in low-temperature physics. [2] Sn 40 Pb 42 Cd 18: 145: Cd, Pb: Low melting temperature allows repairing pewter and zinc objects, including die-cast toys. Sn 50 Pb 32 Cd 18: 145 [16] Cd, Pb: Cd18: Cd 82.5 Zn 17.5: 265 [27] Cd: Yes
Most lead-free replacements for conventional 60/40 and 63/37 Sn-Pb solder have melting points from 50 to 200 °C higher, [17] though there are also solders with much lower melting points. Lead-free solder typically requires around 2% flux by mass for adequate wetting ability. [18]
Common solder alloys include tin-lead, tin-silver, and tin-copper, among others. Lead-free solder has also become more widely used in recent years due to health and environmental concerns associated with the use of lead. In addition to the type of solder used, the temperature and method of heating also play a crucial role in the soldering process.
The more common lead-free solder systems have a higher melting point, e.g. a 30 °C typical difference for tin-silver-copper alloys, but wave soldering temperatures are approximately the same at ~255 °C; [47] however at this temperature most typical lead-free solders have longer wetting times than eutectic Pb/Sn 37:63 solder. [49]
Solder paste must be refrigerated when transported and stored in an airtight container at a temperature between 0-10 °C. It should be warmed to room temperature for use. Recently, new solder pastes have been introduced that remain stable at 26.5 °C for one year and at 40 °C for one month. [8]
Most solders experience temperature exposures near their melting temperature (high homologous temperature) throughout their operational lifetime which makes them susceptible to significant creep. Several constitutive models have been developed to capture the creep characteristics of lead and lead-free solders.
Solderability when using lead-free alloys can differ significantly from solderability when using lead based alloys. Noble metals may be easy to solder but they have brittle joints. The metals in the good category require a large amount of heat therefore oxidation is an issue. To overcome this a flux is required.
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