Felder Solder Solder, lead-free 627229 - Felder 18940770, Felder's ISO-Core "RA" Sn99Cu1 is a lead-free solder wire featuring 99.3% tin and 0.7% copper composition, with a diameter of 0.75 mm. This solder is ideal for various soldering applications, especially where lead-free compliance is required. It is typically used in electronics assembly and repair. Felder 18940770 ISO-Core Solder Lead-Free 0.75mm Sn99.3Cu0.7 Rosin Flux