snag

SnAg refers to a tin-silver binary alloy used as a lead-free solder in electronics. The most widely cited composition is Sn-3.5Ag, a eutectic alloy with a melting point around 221°C, which provides a single, sharp melt and good wettability. Other Sn-Ag compositions near the 3–4 wt% Ag range are also used, typically without copper in the alloy itself.

During solidification, the Sn-rich matrix contains silver-rich intermetallics, primarily Ag3Sn. When solder joints are formed on copper or copper alloys, a Cu6Sn5 intermetallic layer often grows at the solder–substrate interface; further diffusion can produce Cu3Sn. The intermetallics influence the joint’s mechanical behavior, contributing hardness and brittleness, and they affect long-term reliability under thermal cycling.

Sn-Ag solders generally offer higher melting temperatures and corrosion resistance compared with tin–lead solders, along with strong electrical conductivity. However, they tend to be harder and more brittle than Sn-Pb solders, and their reliability can be sensitive to intermetallic growth and processing conditions. Reflow profiles are typically adjusted to minimize excessive intermetallic formation and to achieve proper wetting.

Applications and limitations: Sn-Ag solders are used in many electronics assemblies as part of lead-free soldering practices. While the common SAC (Sn-Ag-Cu) alloys dominate commercial use, binary Sn-Ag solders like Sn-3.5Ag are employed in specialized applications and research. Cost is higher than tin-lead, and care is required to manage brittleness and intermetallic development through proper fluxing, surface finish, and thermal cycling considerations.