I have been told that to solder properly the source of heat is to be directed at the bottom of object to be soldered (6 o'clock), Particularly, During a soldering operation to join two copper pipes.When I asked why that is, I was told it was due to convection distributing the heat around the pipe or object. I don't understand the need for convective heat distribution in this application given the more than adequate thermal conductive properties of copper. Does it really make a difference where the heat is directed? the convective heat transfer (and I assume by convective they are referring to heat transfer in the gas phase on the surface of the pipe) should be negligible given coppers ability to transfer heat. What do you think about this? Thanks so much.