TinSilverCopper

Tin-silver-copper, commonly abbreviated SAC, refers to a family of lead-free solder alloys based on tin (Sn) with small additions of silver (Ag) and copper (Cu). The most widely used compositions are SAC105 (Sn-1.0% Ag-0.5% Cu), SAC305 (Sn-3.0% Ag-0.5% Cu), and SAC405 (Sn-4.0% Ag-0.5% Cu). In all cases, the balance is tin, with trace impurities within industry standards.

These alloys have a melting range typically around 217–221 °C, higher than traditional Sn-Pb solders, which provides temperature tolerance for solder joints. They wet copper surfaces and many PCB finishes well and offer good mechanical strength and fatigue resistance, making them suitable for reflow soldering in mass production. The silver content improves strength and joint reliability, while copper helps form intermetallic compounds that contribute to bond integrity.

During soldering, intermetallic compounds such as Cu6Sn5 form at the Sn/Cu interfaces, and Ag3Sn can appear as dispersed phases within the Sn matrix. Over time, aging and microstructural changes can influence joint properties, so process control and appropriate storage are important to maintain reliability.

Applications for SAC alloys are widespread in electronics manufacturing, including consumer devices, computing equipment, automotive electronics, and aerospace applications. They are preferred for RoHS-compliant, lead-free assembly and are compatible with standard reflow and wave soldering techniques.

Safety and handling follow standard metallurgical practices for tin-based solders. As with many Sn-based systems, care is taken to manage tin whisker formation and to protect solder joints with proper finishes and encapsulation where appropriate.