SAC305

SAC305 is a widely used lead-free solder alloy in the electronics industry. Its designation reflects its approximate composition: Sn96.5, Ag3.0, Cu0.5 by weight. This makes SAC305 a tin-silver-copper alloy that serves as a standard replacement for traditional Sn-Pb solders in many applications, and it is available as solder wire, bars, and solder paste.

The alloy has a melting temperature near 217–221°C and a very narrow solidification range, characteristics that place it near the eutectic point for Sn-based solders. This relatively sharp melting behavior supports predictable reflow profiles. In practice, reflow temperatures typically range from about 230–260°C, depending on flux systems and process requirements.

During soldering, SAC305 wets copper and other metallizations well and forms intermetallic compounds at the solder-pad interface. The primary intermetallics are Cu6Sn5 and Cu3Sn, whose growth can affect joint reliability over time. The solder matrix can also develop fine Ag3Sn particles, which influence the microstructure. The presence and growth of intermetallic layers are influenced by time, temperature, and material interfaces, and they play a role in joint brittleness and long-term performance.

Reliability considerations for SAC305 include its general good solderability and performance under thermal cycling, but its brittleness relative to tin-lead solders and the evolution of intermetallic compounds can impact joint robustness. Tin whisker formation, while reduced by the alloy composition, remains a consideration in some environments and storage conditions.

SAC305 is RoHS-compliant and widely used in consumer electronics, automotive, and industrial equipment. It is often the default choice for lead-free solder pastes and alloys in many electronics manufacturing settings.