Name two primary families of solders used in electronics and describe their melting characteristics.

• A. Tin-solder alloys with very high melting points and copper-solder alloys with moderate melting points.
• B. Tin-lead solders (lower melting point) and lead-free SAC alloys (higher melting point).
• C. Silver-tin solders (high melting) and gold-nickel solders (low melting).
• D. Bismuth-based solders (low melting) and aluminum-based solders (high melting).

Answer: (B)

Solder choices in electronics are commonly grouped by how they melt: tin-lead solders, which have a relatively low melting point, and lead-free SAC (tin-silver-copper) alloys, which melt at higher temperatures. Tin-lead solders have long been the standard because they melt around 183°C for the common Sn63Pb37 eutectic and wet well on copper pads, giving a forgiving and easy-to-control process. Lead-free SAC alloys, such as SAC305, melt in the ~217–221°C range, so they require higher reflow temperatures and can behave differently in terms of wetting and solder joint stress; they’re used to meet RoHS and other environmental requirements. The other options pair incorrect melting characteristics or nonstandard alloy families for electronics soldering, so they don’t describe the typical two primary families.