I did several years in production engineering. We never used flux. Not once. It’s a crutch for people who don’t know how to solder.
What we did was use solder that wasn’t shitty. Big fan of felder 62/36/2 but it ain’t cheap.
We also cleaned stuff properly before soldering it. The reason people tend to flux things to death is that they didn’t clean the oxide layer off before soldering. Or used shitty solder.
felder 62/36/2 [0] is a flux-cored solder. So you were using flux every time.
It's also a leaded solder, which is much easier to get nice joints from than lead-free.
Flux is great, adding some before you solder is a good tip, and will likely help you make better joints if as you said, you haven't perfectly cleaned everything. The only downside is perhaps some more cleanup afterwards. There's no reason to disparage it's use.
So flux is 'a crutch for people who don't know how to solder', because that knowledge would lead you to use 'expensive' flux-cored solder instead of 'shitty solder' plus flux?
I really don't think either's wrong, and anyway I assume 'production engineering' is not using how-to-solder tutorials.
Ding ding ding. Production soldering isn't easy, but it's much easier to dial in than rework jobs. It's definitely a desirable goal to not need flux for production work.
I most certainly do not use flux in my rework. I am in a zero-clean facility, the only flux allowed is that which comes with the solder paste for stencil and SMT placement - on initial production work.
Fluxless rework isn't difficult at all. I do it dozens of times a day.
I'm having a little trouble believing you unless by "rework" you meant "reflow".
Production reflow without extra added flux is normal. It's the goal for every assembly line anywhere and is almost always achieved.
Rework of existing joints after assembly without flux is just about impossible. The oxidation of the joints guarantees it. Many times the flux in the paste or wire is sufficient, but this is more true for through-hole than for surface-mount, mainly due to joint geometry and available volumes. If you are regularly reworking old fine-pitch surface mount joints previously assembled with no-clean flux, without flux of your own... then I'd like to know what materials you're using, because that is not possible in general. The "no-clean" fluxes are notorious for causing rework trouble, and they are difficult to clean off once reflow temperatures have been achieved (that's why we call them "can't-clean"). They are never active twice, so they must be removed and replaced once heated the first time. We have to use special solvent flux removers around here (based on DuPont's hellish Vertrel XF) to get the crap off just to be able to access joints again. (This is on assembly work done out-of-house or on COTS devices, made with who-knows-what.)
"I'm having a little trouble believing you unless by "rework" you meant "reflow"."
Nope, we don't use flux at all for rework. As the majority of our boards are solid metal, we just slap them on a heater and poke the components down or slide them into place. Flux isn't needed. Even with crappy RoHS tin solder. If you're getting significant-enough oxidation that interferes with rework with the product fresh out of the oven, or even a day or two later, you're doing something extremely wrong. Check and make sure your production paste isn't contaminated.
"It’s a crutch for people who don’t know how to solder."
This needs shouting from the rooftops.
So many people get sucked into the groupthink on this; yes it helps with less-than-perfect beginner's soldering skills, but it should not be normalized.
Flooding every joint with extra flux is unnecessary and a waste of money.
We all don’t get to work on nice, new, shiny PCBs. Sometimes other things get in the way. I have three different kinds of flux, two types of solder, copper wick, three solder suckers, two guns, and a scratch pen. I’m not out to practice the art, I just want to be effective.
Most soldering that relies on effects from solder surface tension simply will not work without quite a bit more flux than you can get from the core of a solder wire. Drag soldering, for example, won't work on quad flat pack chips without quite a bit of flux.
And while my techs will absolutely back you up that my soldering skill sucks, to a person they ALL use solder flux for their soldering. Not even a single exception. And they're all trained to NASA aerospace standards.
Now, maybe you can be more skilled than they are and get away without using solder; however, back down here in reality, the rest of us punters will just add flux when soldering stuff, thanks.
I agree up to... new parts shouldn't need cleaning. And cheapo hobbyist-grade RF and audio connectors often have a weird chrome + some kind of oil or varnish surface finish that just won't clean off or solder and flux is a godsend for those.
That said, I let someone borrow my bottle of liquid flux about a decade ago and have never bothered to replace it.
What we did was use solder that wasn’t shitty. Big fan of felder 62/36/2 but it ain’t cheap.
We also cleaned stuff properly before soldering it. The reason people tend to flux things to death is that they didn’t clean the oxide layer off before soldering. Or used shitty solder.