the flux makes the solder flow exactly to the metal.. its like crazy when you try it… the liquid just goes where its supposed to go like it has a mind or something… if you get the paste, it is like paste till you touch the heat and it turns to liquid… it is like a pathway for the solder and it just flows
https://www.amazon.com/Solder-Wire-Rosin-Paste-Flux/dp/B08BLSJHW1
Yeah, flux is good. Lots of it. When I worked at a medical company, hand soldering the boards, they would actually paint the flux on the boards using a paint roller. Thin coat, but still lots of flux.
I have taken to making my own. Find an old damaged pine tree, where the sap has run out and dried up over time. Break off some bigger pieces, and add that to a jar of denatured alcohol. Heat it up a bit (LOW temps, and carefully, you don’t need nor want this stuff catching fire!). Get it all melted and dissolved. Then filter it real well, and reduce it down (like cooking or evaporating) until it’s just a bit thicker than alcohol by itself. Should be a nice amber color too.
Then apply it to you board/joints and solder.
I made some a couple years ago, and I may never have to buy flux again.
try Northridge Fix… Not a sponsor
Here is also a good write up on Solder flux. It discusses types of solder flux and considerations for Effective Soldering with Solder Flux. It also says in what Cases It is possible to solder without using flux. While solder flux is generally recommended to achieve a successful solder joint, there are cases where it may not be necessary.