In none of the posts did I see much discussion about the actual soldering process. Relative to that process, as part of manual hand soldering, is the heating of the materials to be soldered.
What I have not seen in most of the texts about how to solder, is the tecnique of heating the connection to be joined. My experience has shown that a very small amount of solder applied between the joint and the soldering tool will conduct heat much better than the point contact of the soldering tip with a point on the joint to be soldered. Probably it is mentioned somewhere, but I have not seen it. The texts always say, "heat the joint, NOT the solder." They ignore the heat transfer requirements.
PRobably many will take exception to this because they do not understand it correctly.

 

My experience has shown that a very small amount of solder applied between the joint and the soldering tool will conduct heat much better than the point contact of the soldering tip with a point on the joint to be soldered.

This has always been the case. A tinned iron will form a thermal bridge between the iron, the lead and the pad. Then applying fresh solder to the heated joint you'll get good results.

Probably it is mentioned somewhere, but I have not seen it.

No, I haven't seen it mentioned either.

The texts always say, "heat the joint, NOT the solder." They ignore the heat transfer requirements.

I've seen this too. Heating the joint with an un-tinned iron is much slower and causes oxidation on a minor level. Oxidation can make getting solder to flow more difficult because the solder can't make contact with the lead or the pad.

Many years ago I did a test using scrap boards from a board manufacturer. Some boards were soaked in water for three days, some baked in an oven for 3 days and the rest stayed in their packaging. The goal was to prove there was no need for pre-baking boards to drive out moisture. Back in Connecticut the climate was often humid. The test results showed that the boards that soldered the best were the ones that stayed in their packaging. Second best - and nearly as well - was the boards soaked in water. Yes - I said that right. Boards that spent 3 days submerged in water soldered better than the boards that stayed in the oven for 3 days. The reason why the baked boards did more poorly than the rest is because oxidation had begun to build up on the copper.

I share this because bringing a hot dry iron to the solder joint will make for a poor connection. Having added flux to the joint you get some thermal bridging and solder may flow better. But the best technique I've seen in some 45 years of experience is to bring a tinned iron to the joint to be made. To reflow a joint that has already been made but is of poor quality - best is to add a little flux to the joint then reheat it. If you don't have flux then use a very small amount of fresh solder. The flux in the core of the solder will clean up the joint nicely almost every time.