My $0.02 is to choose name-brand solder wire (e.g. Kester/Multicore/ChipQuik) with "RA" or "RMA" flux core. That will flow well and be gentle on your tips. The

My $0.02 is to choose name-brand solder wire (e.g. Kester/Multicore/ChipQuik) with "RA" or "RMA" flux core. That will flow well and be gentle on your tips. The "not right" flux is often a nasty no-clean flux core in solder wire. Many don't flow well and leave a horrid residue on your tips that's hard to remove. (The bad reputation of lead-free solder seems to come not from the alloy but from solder wire with lousy choice of flux core.) The "not enough" flux is often reworking something where the flux has been vaporized leaving only the solder. Then you need to add some new flux like in the video. The gold standard seems to be Amtech tacky fluxes like https://www.amazon.com/Amtech-Solder-Flux-NC-559-V2-TF-16150 https://www.amazon.com/Amtech-Solder-Flux-NC-559-V2-TF-16150