And that is exactly what flux is for. Cleaning and allowing a better flow of the solder onto the part. 63/37 goes through the eutectic stage faster, (it doesn't stay plastic for as long) so when your hands are burning and you let off the iron it will harden faster. It does very well with wire soldering.
Jeff
The Warnings & Cautions discussed in this manual cant cover all possible conditions/situations. It must be understood that common sense and caution are factors which cant be built into this product.