SAC305 Solder Alloy

SAC305 is the most widely used lead-free solder alloy in modern electronics, and the one you will most often encounter when reworking factory-assembled mining hardware. Its name encodes its composition: Sn, Ag, Cu at 3.0% silver and 0.5% copper, with the balance (96.5%) tin. It became the de-facto standard after RoHS restricted lead in consumer electronics, prized for strong joints and good resistance to thermal-fatigue cracking.

Working temperatures

SAC305 is not eutectic, so it does not melt at a single sharp point. It has a solidus around 217°C and a liquidus near 220°C, meaning there is a narrow pasty range between fully solid and fully liquid. That is roughly 35°C hotter than classic Sn63Pb37, which is exactly why lead-free rework demands more aggressive preheating and higher iron or hot-air temperatures, and why mixing leaded and lead-free solder on the same joint can yield unpredictable, weakened results.

Practical implications for repair

The higher melt point means more heat soaks into surrounding components and copper planes, raising the risk of collateral damage without a preheater. SAC305 also tends to look duller and grainier than leaded solder when solidified; that matte appearance is normal and should not be mistaken for a cold joint. Its silver content improves wetting and fatigue life but makes the alloy and the resulting joints harder and less forgiving of mechanical flex.

To understand why a single-temperature melt behaves differently, see eutectic solder; for what forms at the copper boundary, see intermetallic compound.