Originally Posted by
Imbuter2000
Afterall in the video of the Tekin RX8 he solders easiliy without added flux.
I know that some rosin evaporates with the heat of soldering but what about the residue that remain mixed in the alloy or, even worse, between the alloy and the connector, that cannot be cleaned
Flux is acidic, (this is where the RMA comes in, it is mildy/medium acidic) and it removes the impuritys and oxide layers from metal when heated. That helps the solder flow better and stick to (wet) the joint. Solder actually forms a metallurgical bond with the metal, so flux can not "mix" in the solder. This means that there will be less resistance in the connection due to a better bond.
I have seen people try to solder on old equipment and the corrosion being really bad and the solder not sticking well if at all. The solder would stick to the wire but not the contact area. In that case there is a layer of flux between components, but its not the fault of the flux. It just means that the connection is very dirty/corroded and this is unlikely to happen on new components. The components I seen this happen on were off of helicopters built in the 70's.
If you glob on a big glob of solder, and make that a habit, that big blob can hide the bad connection underneath because you can not see it. That is why I said in the post that you only need a good fillet of solder flowing between the components. A good fillet also reduces resistance. I have seen many pics of guys cars on this forum where they do not glob on too much or use too little, but they do not have a good even solder fillet, or the wires look bird-caged (the wire stands are separating from each other like the bars of a cage) and that causes resistance as well.
In the video, he did not use flux, but he did pre-tin the wire and post, so the fresh solder on them helped the solder flow pretty well without flux. Pre-tinning helps prevent "bird-caging" as well. the strands of wire should be running smoothly just like they are in the un-stripped areas for the best connection. Also, high quality multi-core solder has quite a good bit of flux inside, and larger diameter solders have a good amount of flux as well.
You can buy a "flux pen" which is a felt tip pen that applies flux like an ink marker. They are far less messy, and work great on new components or well maintained/clean components. Just be careful not to bird-cage the wire when applying the flux for pre-tinning. You still must clean up after though.
