Newbie to flux purchasing (for desoldering and SMD drag-soldering)

[analogix]

Throughout all the years I've been into electronics I've never known about or used flux   

Forum threads and Youtube videos on the subject has however convinced me that this is something even the occasional hobbyist with a cheapo soldering iron needs to consider essential to have in their toolbox, so I have a few questions prior to ordering the right type(s) of flux. My specific need for flux is twofold:

a) Desoldering through-hole components from PCBs with the aid of flux and desoldering braid.
These will be mostly from 80's circuit boards, but I also have some recent PCBs where I need to desolder a couple of multiple pin through hole pin-headers. The 80's boards will surely have leaded solder while I assume the recent ones are lead-free.
I've used desoldering pumps with highly varied results, which is why I'm looking for ways on getting better and more consistent results.

b) Drag soldering SMD ICs with flux and a suitable soldering iron tip.
I've never done this before, and am just about to start out with SMD components, but have recently purchased an Ersa iCon Nano soldering station with several different tips as recommended in these forums.
According to videos I've seen, soldering SMD ICs should be a breeze with the correct tip, flux and technique.

I'm the occasional hobbyist who works on a few projects now and then, meaning that I don't need huge amounts of flux, it has to last (i.e. not expire in a short time). I also don't want to get in a nitpicky discussion on what's the best, but rather what will do the job.
I have some questions:

1) For desoldering, are there specific flux types intended for leaded or unleaded solder that you want removed?
Similarly, for soldering (drag soldering), when applying flux, are there specific types for leaded or unleaded solder?
(I currently have a large roll of leaded solder to use up, and as of yet don't have any prior experience using unleaded solder, so leaded soldering it'll be for a while. But it's nice to know what kind of flux I need to get later when buying more (and unleaded as I've heard that's the only solder you can (legally) buy these days, at least through the usual big electronic component outlets such as Mouser, Farnell, Digikey etc.)

2) again, for desoldering: is it a good idea to get desoldering braid without flux (then add flux separately to the PCB), or desoldering braid with flux included? I already found a couple of rolls with desoldering braid in my toolbox, but there was no mention of lfux on the label, so I assume they're un-fluxed.

3) should I get flux in liquid form or paste, or both?
Do they have different uses, or is this just up to personal preference as they both do the same thing?
I read that flux pens often flood PCBs while syringes are more "tacky" which sounds to me like I should choose the latter as they appear to be controllable.
Does this also mean that flux pens always contain liquid while syringes contain paste?

4) are there specific flux types meant for soldering SMD ICs using the drag-soldering technique?


In these (and other) forums I've noted what people like to use. I conclude that "no clean" types are the way to go, and most of them can be stored at room temperature (no refridgeration needed).
Chip Quik's SMD291 comes up a lot in forum threads as something that generally works well, is easy to use (no clean) and lasts for a long time, so it appears to be good for the occasional hobbyist such as myself.
I read somewhere that the "NL" version (SMD291NL) is for lead free ("NL"=No Lead?) soldering, so should I assume that SMD291 should be for use with leaded solder?
Chip Quik comes a lot in forum discussions, and many people seem to be happy with this brand, but then there are contradicting reports, and all the different model numbers are confusing )the Chip Quik website isn't very helpful in explaining things to newbies either).
For desoldering braid, Chemtronics and MG chemicals comes up as recommendations.

So what should I go for?

[Psi]

1) For desoldering, are there specific flux types intended for leaded or unleaded solder that you want removed?
Similarly, for soldering (drag soldering), when applying flux, are there specific types for leaded or unleaded solder?
(I currently have a large roll of leaded solder to use up, and as of yet don't have any prior experience using unleaded solder, so leaded soldering it'll be for a while. But it's nice to know what kind of flux I need to get later when buying more (and unleaded as I've heard that's the only solder you can (legally) buy these days, at least through the usual big electronic component outlets such as Mouser, Farnell, Digikey etc.)

Just stick with a well known brand of flux Chemtronics, Kester, MG Chemicals  are all good.
Stay away from some random brand or from ebay/aliexpress/etc. where you might get fake stuff.
I don't particularly like chipquik brand myself, mainly ive found it inconstant. Mostly in their solder paste quallity, but it put me off the brand.
If soldering brand new parts I would recommend RMA flux, (Rosin Midly Activated) over RA or Water-Soluble.
Sometimes RA is better if you're using older oxidized parts, but it can be more corrosive so best to stick with RMA if you can.
AFAIK it doesnt matter for lead vs lead free

2) again, for desoldering: is it a good idea to get desoldering braid without flux (then add flux separately to the PCB), or desoldering braid with flux included? I already found a couple of rolls with desoldering braid in my toolbox, but there was no mention of lfux on the label, so I assume they're un-fluxed.

Desoldering braid is one of those things where you want to get the good stuff.  Crap stuff can sometimes work if you flood it with flux but the goods stuff is worth it.
Can't go wrong with Chemtronics brand solder braid. Just make sure it's the kind with flux.
The main thing I use it for is getting solder out of through-holes.

3) should I get flux in liquid form or paste, or both?
Do they have different uses, or is this just up to personal preference as they both do the same thing?
I read that flux pens often flood PCBs while syringes are more "tacky" which sounds to me like I should choose the latter as they appear to be controllable.
Does this also mean that flux pens always contain liquid while syringes contain paste?

Get gel flux for SMT stuff. The stuff the comes in a syringe. Ideally get one that comes with the plunger for the syringe and some sort of a dispensing needle.

are there specific flux types meant for soldering SMD ICs using the drag-soldering technique?

AFAIK no, no flux especially for drag soldering.
You can get special iron tips for drag soldering that have a recessed cup shape within the tip area to hold solder inside the tip, but i don't bother using the one i have.
I just use a small chisel tip.

Drag soldering is pretty easy once you have the pins all fluxed up. The key is getting the right amount of solder on the tip so you don't end up with a bridge when you get to the last pin.
But you can usually just moved it back and remove the bridge unless there is way too much solder.
It often helps if you put a little flux on to the PCB pads first, before you put the chip on top. It makes the solder 'want' to flow onto and under the pads more.

[thm_w]

https://www.eevblog.com/forum/other-blog-specific/nanofix-youtube-flux-comparison/

All you really need is paste flux in a syringe. I use Amaoe M50 for smd rework, but there are a variety of fluxes available that have different properties.

For the 80's stuff you'll likely want something more aggressive, and you may need to clean it off after you finish soldering.