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PCB solder flux

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Hi there,

Some weeks ago when I did some PCBs, I sprayed them with a solder flux. The board got very messy, sticky and very ugly. Now I realise that I didn't clean them before, so grease and dirt where still on them. Now to the question: How do I clean the boards?

Should I apply the solder resist just after etching, or should they dry up for long time (then they'll need oxidation remover). I have a SENO Scrub Block, but can it be used after eching (removes tiny PCB traces?).
 
acetone, carbon tetrachloride, an alcohol blend, soap & water?

are there parts on the board? Copper and FR4 can be cleaned with almost anything, but if there are parts, you'll want to use a process that won't damage them.

avoid cleaners with oxidizers like chlorine, as it will damage the copper.
 
rubbing alcohol (isopropanol) is a common method, get the strongest stuff you can get, I think grocery stores often carry it at like 90% concentration. the main advantage is that it evaporates very quickly so you don't have to worry as much when you've already got components on the board.
 
I find that alcohol alone doesn't cut the petroleum base of the 20 year old flux I use (hey, i got half a tube left). I suppose I should upgrade to a water soluble flux, but this stuff works so well.

Using a can of pcb wash, the petroleum is temporarily suspended, and then deposited evenly over the surface of the board. Actually, other than it being slightly sticky for a little while, it's not so bad. Copper traces stay bright and shiny, so it's like a conformal coating I guess. I don't clean my boards before soldering, the resist coating (from my photo-lithographic process) is designed to work as a fluxing agent, and it keeps the copper clean until I'm ready to go.
 
justDIY said:
carbon tetrachloride
I didn't know you could still get hold of it, isn't it banned in most countries?

You could always try petrol if you don't mind the smell.
 
Hero999 said:
I didn't know you could still get hold of it, isn't it banned in most countries?

i suppose it could be hard to come by, I've just heard it works well ;)

I have used paint thinner (mineral spirits) before, when I wanted to paint the pcb for extra moisture protection. I was careful to limit contact with plastic parts however.
 
Carbon tetrachloride is a poison, it is absorbed through the skin and by inhaling the fumes.

I can't recall what it does to you but it is not pleasant.
 
I buy bottles of 99.9% pure isopropyl alcohol at my neighborhood drugstore and use that for cleaning flux. Unfortunately, while it does dissolve the flux you still have to flush the solution of alcohol and dissolved flux off the board. I do this by flushing the dirty stuff off using clean alcohol. This is fairly easy to do, but tends to use up more of the alcohol than you would like. Happily, it is not expensive. The nice thing is that it dries up very quickly and you can spot clean with a brush if you want.
 
Nigel Goodwin said:
I think isopropyl alcohol is also banned in the UK

That seems rather surprising, as I always thought of it as a pretty mundane chemical... Sure, it's flammable and somewhat toxic (about twice as toxic as ethanol, which doesn't seem too bad since people intentionally drink ethanol all the time ;) ), but probably much less so than a lot of other household chemicals, such as, for example, acetone, or just about any cleaning product...
 
evandude said:
That seems rather surprising, as I always thought of it as a pretty mundane chemical... Sure, it's flammable and somewhat toxic (about twice as toxic as ethanol, which doesn't seem too bad since people intentionally drink ethanol all the time ;) ), but probably much less so than a lot of other household chemicals, such as, for example, acetone, or just about any cleaning product...

Almost EVERYTHING is banned in the UK!.

Even cheese has just been reclassified as 'junk food' and can't be advertised on TV before a certain time in the evening!.
 
i remove flux with alcohol and brush and then rinse immediately with tap water, blow off with compressed air and then dry in an oven for a good while - i think its set at like 70 or 75C.
 
OutToLunch said:
i remove flux with alcohol and brush and then rinse immediately with tap water, blow off with compressed air and then dry in an oven for a good while - i think its set at like 70 or 75C.

wow, that is a LOT of work ... are these boards you make professionally?
 
Nigel Goodwin said:
I think isopropyl alcohol is also banned in the UK as well as carbon tet!.

I'm not sure on that. . . We use loads of the stuff at work, all we have to do is wear gloves and goggles when handling (to keep the HSE happy)
 
Nigel Goodwin said:
Almost EVERYTHING is banned in the UK!.

Even cheese has just been reclassified as 'junk food' and can't be advertised on TV before a certain time in the evening!.

You're not serious! are you? Cheese is junk food? All cheeses? I had no idea that the UK was now some bizarre psuedo-fascist police state. Sure couldn't tell by watching BBC's Bargain Hunt which is on telly in the other room right now.
 
Nigel Goodwin said:
Perhaps it was just removed from general use then?, everything we ever used that contained it all disappeared at the same time a few years back.

I thnk you're probably right. Isopropanol does seem hard to get hold of now (unless you work with it of course).

I worked as a painter and decorator for a number of years when I left school, and half of the solvents we used to use are now classified as 'hazardous' and you can't get or use them anymore. (which is kind of good since most of them are carcinogenic)
 
justDIY said:
wow, that is a LOT of work ... are these boards you make professionally?
yes - that is the procedure for boards that are sent to customers.

for my own use, i only clean off the flux once it gets to thick from repeated component changes and then i'll just wipe it down with alcohol.
 
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