Using a water brush pen to dispense liquid flux

[WildCamper]

Hi everyone! I have a bottle of liquid flux that has a brush thats included but I would like more control over how much it puts down.
My question is, has anyone successfully used a "water brush pen" as a flux pen? The reason i'm curious is that they are very cheap, the nibs come in multiple sizes and I can buy them locally so no need to wait for the postie (wouldn't mind supporting a local business too with whats going on)

If I need to get a proper flux pen that's fine but if I can save some money and time, I can spend it on my projects instead 

Thanks for any advice/opinions offered

[Ian.M]

Give it a try and post the results.  However I'm skeptical whether an artist's waterbrush pen can withstand the solvents in the flux.  You almost certainly need a refillable paint marker of a brand that's compatible with solvent inks.

Personally I made my own flux pen from a dollar store hiliter.  I disassembled it and washed its nib and core in water till no more color came off them, dried them on kitchen towel, washed them again in denatured alcohol (Methylated Spirits), dried them again and finally rinsed them with a little IPA and dried them thoroughly overnight.  I then reassembled it and soaked the core and nib in flux, drained off excess, capped it and let it settle overnight then wiped the cap interior and nib.  The result works as well as any commercial flux pen with similar flux.

[wizard69]

It might help to better explain what a "water Brush pen" is and where you get them.   As the poster above has stated give it a try and report back.    Many of us appreciate new ideas that lower costs.

[WildCamper]

Thats a very good point Ian, i didnt consider the solvent so i'll bear that in mind.

I may very well experiment with a highlighter too as I have tons of them and no doubt at least one has dried out by now...

Wizard69 here is the wikihow explaining how artists use them; https://www.wikihow.com/Use-Watercolor-Brush-Pens and here is a link to some premium brand pens; https://www.amazon.co.uk/Pentel-Aquash-Water-Brush-Assorted/dp/B002JIN2Q0
(sorry mods if this breaks any rules...)
You can get them a lot cheaper on places like ebay or just go no-name from a hobby/art supplier to save a bit

I'll go grab some today/tomorrow and report back

[Ian.M]

Why would it break any rules? You didn't post an Amazon affiliate link with you as the affiliate, so you aren't making money on it, so the mods wont have a beef with you.

[RoadRunner]

I have tried all sort of Flux dispensing  methods, I have tried these Brush pens as well.  Result may differ depending on what type flux you are dealing with and how you apply flux. I have been using rosin flux. and i sometime need to apply flux even when joint is still hot.

First problem with Brush pens, Rosin dry up jamming the opening, so you have to apply more force, which will cause pen threads to leak and take too much time to apply flux.

Second problem depending on usage, pen brush is made of a material which will not bear heat, so if you need to add additional flux joint/target still hot brush will melt, only after few days of use brush will become useless.

I have hand soldered hundreds of board from 0402 to BGA , anything that non metal tip will not work long term.
Small 50ml bottle with metal needle tip works best, I have never found them made of high quality plastic so bottle itself also wear out but one ever 6 months or so. bottle from ebay or amazon comes with different size of needle by which you can control amount of force needed for flux application. And if needle jams up, heat from soldering iron can easily open up without damage.

[Ian.M]

RoadRunner's got a good point - a metal needle accordion bottle is good for applying flux as you are working, but I'm not giving up my flux pen as its much handier for pre-fluxing pads.   If you find a needle bottle is too uncontrollable, pack the needle with linen thread pulled through it with a fine doubled over wire.

[tooki]

I tried a few water brush pens with flux (both Chinese no-name and Caran d’Ache) and I cannot recommend it. They end up leaking. Bear in mind, even my genuine bon-kote brush pen has started leaking with age.

What I may try is Molotov brand empty markers; they’re expressly made to work with alcohol based inks.

[Mechatrommer]

a picture worth many words, probably not worth a dime to you... i repurpose my china brush pen, refill flux inside the upside down cover, dilute with alcohol, open and dab the brush somewhere (pcb and components) the flux marker dried up useless, my less favorable since its hard and difficult to reach corners, unlike brush. so even though its agreeable leaky, my brush pen still have its purpose. but my mostly used are the containers at the front (esp the bga flux marked as kingbo), just take a little bit on a paper knife's tip and dab on components, save a lot unlike louis rossman's way that waste a lot. ymmv.

[WildCamper]

Thanks for the replies everyone! So, to move forward i'm going to make a needle bottle as i have blunt needles already and sadly none of the local hobby shops have re-opened so i can't get a water brush pen without mail-order anyway.

You guys raised some good points I hadn't considered like the solvent & working temps ruining the tips. I actually think these problems are overcomable using DIY stuff but there doesnt seem to be a cost saving in pursuing it

Thanks for all the advice, I appreciate it

[tkamiya]

I guess it'll depend on what you are really doing....  but why would you need to "paint" flux?  Won't you end up wasting awful a lot of flux that way and need to clean every time?  I use blunt end hypodermic needles and squeeze bottles.  Just a drop or two will do.  If you are soldering really big wires, that's a different story though.

[Ian.M]

Its mostly an assembly thing or at the component replacement phase of SMD rework/repair, if you've got more time and patience that Louis R, so can let the liquid flux dry a bit.  Also, maybe not so much now in the days of cheap Chinese ENIG pcbs, but back in the days of home etching, if you weren't also set up to do electroless tin, painting on Rosin R flux preserved solderability, crucially important if you knew it was going to a slow build, maybe put on the shelf and come back to.

You actually use less flux vs flooding it on with the joint already hot, as ideally you paint the pads with a very thin coat of flux before placing the component.  Be selective *where* you paint and use Rosin R (or RMA with a non-corrosive activator, so you don't have to worry about corrosion from unactivated flux), and cleanup is minimal.

[helius]

The electronics industry uses flux pens from Bonkote, which are industrially priced. The main reasons for this are the special double chamber that reduces solvent evaporation, and the brush fibers which are both optimized for use with alcohol thinned rosin fluxes. Other brushes may suffer from clogging since this fluid is much stickier than normal paint or ink.

[tooki]

I guess it'll depend on what you are really doing....  but why would you need to "paint" flux?  Won't you end up wasting awful a lot of flux that way and need to clean every time?  I use blunt end hypodermic needles and squeeze bottles.  Just a drop or two will do.  If you are soldering really big wires, that's a different story though.

Huh?!? You apply WAY less flux by brushing it on than with a needle.