Solder can be Lead/Tin, Antimony/Tin (95/5), or
Silver bearing. All require Zinc Chloride flux to prevent
surface oxide formation on the heated copper.
Copper can be joined to Copper, Zinc, Steel, Brass,
and a few other elements and compounds; but not
Aluminum or a number of others.
The working temperature required is about 450°F.
"Filler metal" is not used in soldering.
Solder is intended to fill joints nor exceeding .1mm.
(1) What are you joining?
Copper to Copper?
(2) Can you provide any additional detail?
Yes, you MUST use a flux.
You must use a soldering iron of sufficient heat input to suit the size of the wire and whatever you are soldering it to. If this is electrical/ electronic work, you should use resin cored wire solder.
If not electrical/ electronic, you have a choice of many fluxes ranging from muriatic acid to candle wax, the choice depending on what metals you are soldering.
If using a flux, you apply it to the join area. You then apply the hot iron to heat the metals, before applying the solder to the junction between the metals and the iron. If using cored solder, you apply the iron to the metals, then feed the solder wire to the junction of the iron and the metals. The flux core will keep the metals from oxidising.
I think you need some resin, if not just use some silver paste if it's a big deal.
It depends on what the "filler material" is. Fluxes (there are different types) work by chemically cleaning the surface of oxides. It is the presence of surface layers of oxides (or most any other contaminant) which prevent solder alloy from "wetting" to the surface.
What are the possible mistakes I'm making? The filler material just will not stay stuck to the copper wire. Should i be using flux?
