Solder will not bond to all materials, just the ones that the solder is designed for, usually conductive materials such as brass, copper or tin. Solder flux paste does a couple things, it helps keep the guns element clean and it helps the solder bond to the part in question. Moreover, it can keelp the components temperature down.

Specification:

• Good immersion
• PH7 +/- 0.3
• No poision, no corrosion
• Good insulation
• Smooth welding surface
• No deterioration
• No dry
• 150g