In welding, the parent metal, that is the pieces to be joined are actually melted along with the filler metal, if any. The filler metal is the same material as the parent metal. In brazing, the pieces to be joined are heated, but do not melt. Only the filler metal is melted. The filler is a brazing alloy, usually an alloy containing brass, silver, or other metals. The filler metal is not the same as the parent metal. Since brazing does not melt the parent metal, less heat is required, but the resulting joint is not as strong as a welded joint. The brazing alloy is usually a different color than the parent metal, so the joint will stand out and be visible, which can be an issue where appearance is important.

When Brazing copper to copper flux is normally not needed When brazing steel or copper based alloys then the flux is used to help the wetting action (Better flow of the brazing alloy) and to prevent oxidation A typical rod would be Union Carbide 25 M or check out the AWS booklet

I have just posted one answer but cannot see it, so here goes. Try typical brass brazing rod, which is a brass alloy composition, normally 2mm dia.

Has for brazing flux use propriety brazing flux powder mixed with a little H2o to make a paste. Or sodium bicarbonate. ( Bicarb of soda ).

Yes, its a requirement of all manufacturers, that i know of, to braze 410a connections with a brazing alloy containing a minimum of 15%

yes there is brazing is done w silver alloy

Brazing has a tensile strenght of 87,000 PSI and soldering around 16,000

Brazing filler metals require a melting point of 1,100 DEG Fsoldering around 600 Def F

Using the correct type of brazing rod they are self fluxing on copper alloys and thus great for Oxygen and other medical gases and HVAC work