Another soldering question: cleaning flux

On3s&Z3r0s
On3s&Z3r0s Posts: 1,013
edited April 2011 in DIY, Mods & Tweaks
I'm working on some crossover mods and wondering how important it is to clean the flux off the PCB's after soldering. I did some Monitor 5Jr's this last weekend, and before I started I noticed there was already quite a bit of flux in places on the boards. After desoldering and re-soldering most of the connections on the boards (using Cardas Quad) there was even more. I didn't clean it figuring if it was there before it couldn't hurt much.

So, before I do more of these... should I be cleaning around the solder joints, and if so is there something in particular that works well? I know Parts Express sells some special solvent, and I've heard isopropyl can be used. Should I go back and clean the boards for the 5Jr crossovers?
Post edited by On3s&Z3r0s on
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Comments

  • heiney9
    heiney9 Posts: 25,197
    edited March 2011
    Rubbing alcohol and an old tooth brush work great for removing flux from pcb's. Cheap and effective.

    Yes, go back and clean the boards.
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass Pass Labs XA25 | EE Avant Pre | EE Mini Max Supreme DAC | MIT Shotgun S1 | Pangea AC14SE MKII | Legend L600 | BlueSound Node 3 - Tubes add soul!
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  • mhardy6647
    mhardy6647 Posts: 33,909
    edited March 2011
    as long as you're using good rosin core solder, the flux is a non-issue. Feel free, but not obligated, to clean it off if you wish.
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  • TECHNOKID
    TECHNOKID Posts: 4,298
    edited March 2011
    heiney9 wrote: »
    Rubbing alcohol and an old tooth brush work great for removing flux from pcb's. Cheap and effective.

    Yes, go back and clean the boards.
    +1, innexpensive and does a perfect job. :cool:
    mhardy6647 wrote: »
    as long as you're using good rosin core solder, the flux is a non-issue. Feel free, but not obligated, to clean it off if you wish.
    You would be surprised how many problems I have solved on PCBs by simply cleaning the flux residues. BTW, I would have failed my HRS course if any of the instructers had found flux residues on any of my exams soldered boards :wink:
    After you have made all the solder joints, it is good practice to clean all the excess flux residue from the board. Some fluxes are hydroscopic (they absorb water) and can slowly absorb enough water to become slightly conductive. This can be a significant issue in a hostile environment such as an automotive application. Most fluxes will clean up easily using methyl hydrate and a rag but some will require a stronger solvent. Use the appropriate solvent to remove the flux, then blow the board dry with compressed air.
    http://www.aaroncake.net/electronics/solder.htm
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  • On3s&Z3r0s
    On3s&Z3r0s Posts: 1,013
    edited March 2011
    Methyl hydrate?!? Just googled it and it sounds like it's either paint thinner or camp stove fuel! :eek: I do have some rubbing alcohol around somewhere. Unfortunately, I already put them back in the cabinets. I finished them up at 1am last night and was impatient to get them back together and see if they still worked. After the first day of burn-in they're sounding pretty good already. But if I get some time tonight I'll pull them out again and do it right. Thanks for the input!
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  • TECHNOKID
    TECHNOKID Posts: 4,298
    edited March 2011
    Actually, what I was buying is isopropyl alcohol which basically the same as the rubbing alcohol but 99% versus the 70% you usally find in most pharmacies. I would be worried about methyl hidrate too (a little too flammable for my taste I would believe. Not counting I'd be worried about the PCB varnish coating too ;) )
    DARE TO SOAR:
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  • Jack A
    Jack A Posts: 77
    edited April 2011
    Check out www.hardwaresecrets.com How To Desolder Components.Use Isopropyl alcohol only... do not use regular alcohol.
    Clarajack
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  • maxima
    maxima Posts: 143
    edited April 2011
    Definitely clean the flux off. It is corrosive and can eat away at the connections. Ethyl alcohol is the best (it is what the military and Nasa require) followed by isopropyl.
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  • Outfitter03
    Outfitter03 Posts: 563
    edited April 2011
    Nothing like a little Everclear to get that flux off. Makes a pretty wicked punch too.
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