Soft Solder Flux No.3S™ Flux Paste is a predominantly designed for industrial soldering applications. It is recommended for use on all common engineering materials except aluminum. It is particularly suitable for use on carbon steel and stainless steel as well as being effective on copper and copper alloys such as brass. Soft Solder Flux No.3S™ Flux Paste has an active or working range which goes up to 350°C. It can therefore be used with tin-copper solders and tin-silver solders. It is also suitable for use with specialized high temperature solders. Soft Solder Flux No.3S™ Flux Paste is a semi-fluid light grey colored flux paste that can be readily applied by brushing onto components prior to heating. Information provided by Johnson Matthey Metal Joining |