Sn30Ag05Cu

Sn30Ag05Cu (commonly written Sn-3.0Ag-0.5Cu and marketed as SAC305) is a lead-free tin–silver–copper solder alloy widely used in electronic assembly. Its nominal composition is about 96.5% tin, 3.0% silver and 0.5% copper by mass. The alloy was developed as a RoHS-compliant replacement for traditional tin–lead solders.

The alloy has a melting range rather than a single eutectic point, with liquidus temperatures typically around 217–220 °C. Solidification produces a tin-rich matrix containing intermetallic compounds, principally Ag3Sn and Cu6Sn5, which influence mechanical strength and thermal fatigue behavior. Compared with Sn–Pb solders, SAC305 offers improved high-temperature strength and better performance under cyclic thermal loading, but it requires higher reflow temperatures and can be less ductile.

SAC305 is commonly used in surface-mount and mixed-technology assemblies in consumer, automotive and industrial electronics. Typical reflow processing uses peak temperatures above the alloy’s liquidus, with controlled time above liquidus to manage wetting and microstructure. Flux selection and process control are important to avoid defects such as poor wetting, voiding or brittle intermetallic layers.

Standards and industry guidelines for lead-free soldering, such as IPC specifications and RoHS directives, include SAC305 among commonly accepted alloys. Variants with slightly different Ag/Cu levels are available to tailor properties such as melting behavior, cost and reliability for specific applications.