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Method for removing flux? — Parallax Forums

Method for removing flux?

Oldbitcollector (Jeff)Oldbitcollector (Jeff) Posts: 8,091
edited 2009-05-11 03:15 in General Discussion
What is the best way to remove the flux (from solder) from the board itself when finished with my project? I've learned from experience not to ignore
this problem. What's the preferred removal method without damage?

Thanks
OBC

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Comments

  • kwinnkwinn Posts: 8,697
    edited 2009-05-04 12:35
    I use a flux remover/solvent and a tooth brush.
  • parts-man73parts-man73 Posts: 830
    edited 2009-05-04 12:45
    Same. A local Electronics store sells "Flux remover" I fill a container and soak the boards for a few minutes and lightly agitate the containers whilst they soak. Remove, shake and set to dry on paper towels. I can then carefully pour back into the can that it came in for safe storage, can be reused numerous times before it has to be disposed of. (dispose of properly of course)

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    Post Edited (parts-man73) : 5/4/2009 12:51:56 PM GMT
  • Oldbitcollector (Jeff)Oldbitcollector (Jeff) Posts: 8,091
    edited 2009-05-04 13:57
    I was hoping for a more "household" solution. Looks like I need to place an order!

    OBC

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  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2009-05-04 15:08
    Isopropyl alcohol — the hi-test (99%) kind, not rubbing alcohol — from the drugstore. I dip a toothbrush in it and scrub the board until the flux is gone. 'Works for me.

    -Phil
  • davejamesdavejames Posts: 4,047
    edited 2009-05-04 15:19
    Ditto Phil's response. It's cheap and works great.

    Then the "used" alcohol can light the lamps you'll need after that kid in your avatar gets done blowing out your electrical service!

    (smiles)

    DJ

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  • ElectricAyeElectricAye Posts: 4,561
    edited 2009-05-04 15:26
    Phil Pilgrim (PhiPi) said...
    Isopropyl alcohol — the hi-test (99%) kind, not rubbing alcohol — from the drugstore.....

    Yes, I agree. I got my 99% isopropyl from Walmart, very cheap. I use a Q-tip and scrub it off. Make sure nobody in the house uses the alcohol for anything else, though, since solder flux and possibly solder lead, etc. could get into the bottle if you are re-using the same Q-tip or whatever.

    One hazard of using a toothbrush is that the flick of the bristles might flick some of the alcohol into your face.


    cool.gif

    Post Edited (ElectricAye) : 5/4/2009 3:32:41 PM GMT
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2009-05-04 15:44
    I tried Q-Tips once, but found that the clipped leads on the through-hole parts snagged bits of cotton, which I'd then have to remove with a toothbrush. smile.gif

    -Phil
  • StarManStarMan Posts: 306
    edited 2009-05-04 16:56
    I use a "no-clean" solder.· It leaves a residue that I don't clean off.· Should I be cleaning it?· What are the harmful effects?
  • RobotWorkshopRobotWorkshop Posts: 2,307
    edited 2009-05-04 17:32
    I'd like to hear more about this topic and what other use. Cleaning the boards is a pain in the rear and one of my least favorite chores. I've often had to clean up boards that had old flux still on them and also others that are dirty from use and/or poor storage. One of the ones I just rebuilt was a PS board for an old robot. That was a particularly nasty one since it at one time has been in a dusty environment and appeared also to have an oily residue from hydraulic oil. In order to clean that I ended up removing many of the parts to get at the board itself.

    Depending upon the flux you may have to try different cleaners. From past experience there doesn't seem to be a one size fits all cleaner. I usually start out with the cheapest solution and use the inexpensive isopropyl alcohol from the local drug store (not a fan of WalMart) with a tooth brush to help loosen stubborn flux, etc. From there I'll try some of the electronic cleaners and the flux sprays. Recently I tend to avoid the flux sprays since it seems the formulas have changed and don't seem to work nearly as well as they used to. Whatever cleaner you try be careful where you spray it. Most of the parts seem fine but one notable example are older relays with clear plastic covers. Some of the flux sprays can react with the plastic and melt them. Not to mention what it may do to the person using it.

    If the boards are dusty, etc there are some instances where I have actually washed them off (yes, with water) and used a dish soap to act as a degreaser and cleaner. The results can be fantastic. I don't submerge the board but rinse and scrub them with a soft brush. Once done I make sure they are thoroughly dry and use compressed air to blow them off and get any water out from under parts and out of sockets. A hair dryer on warm helps finish the job. The key is to make sure you dry them right after they are cleaned to remove the excess moisture. After that I let them sit for a while before even thinking of powering them back up.

    Anyone else have good methods for cleaning boards?
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2009-05-04 18:01
    The old flux sprays used chlorinated hydrocarbons, which are highly carcinogenic. They were effective, but it's a good thing they've been banned.

    -Phil
  • LeonLeon Posts: 7,620
    edited 2009-05-04 18:24
    StarMan said...
    I use a "no-clean" solder. It leaves a residue that I don't clean off. Should I be cleaning it? What are the harmful effects?

    It can cause problems with high-impedance circuits as it can absorb moisture and become conducting. Normally, it doesn't matter.

    Leon

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  • RobotWorkshopRobotWorkshop Posts: 2,307
    edited 2009-05-04 18:42
    Phil Pilgrim (PhiPi) said...
    The old flux sprays used chlorinated hydrocarbons, which are highly carcinogenic. They were effective, but it's a good thing they've been banned.
    -Phil

    Yes, that is one of the reasons I prefer to avoid all the Flux sprays. I'd like to stay around long enough to watch the kids grow up and take care of some more projects on my wish list!

    Finding alternate methods for cleaning boards is definitely an interesting topic and I hope others will chime in with what they have been successful with.

    On that note I have heard of one method that I have seen used but am not a fan of. One particular repair shop used to clean the back of their boards with lighter fluid. This removed the flux but ends up leaving a shinny coating over the back of the board once it evaporates. I have seen boards that this was done to and wondered what had happened to them. Didn't seem to cause any problems but I don't ever plan on trying it. Whenever I have repaired one I try to clean them again to get rid of it.

    Robert
  • LeonLeon Posts: 7,620
    edited 2009-05-04 19:16
    IPA is quite safe.

    That residue was probably the flux left after the solvent has evaporated.

    Leon

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  • ElectricAyeElectricAye Posts: 4,561
    edited 2009-05-04 19:28
    Phil Pilgrim (PhiPi) said...
    I tried Q-Tips once, but found that the clipped leads on the through-hole parts snagged bits of cotton, which I'd then have to remove with a toothbrush. smile.gif

    -Phil

    That's why no serious master of soldering ever goes anywhere without his or her boll weevil. nono.gif


    en.wikipedia.org/wiki/Boll_weevil

    Get with the times, Phil.
  • Bill DrummondBill Drummond Posts: 54
    edited 2009-05-04 19:48
    I use Isopropyl alcohol and an acid brush with the bristles cut down to 1/4 inch. For a large board put it the dishwasher.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2009-05-04 20:02
    ElectricAye said...
    That's why no serious master of soldering ever goes anywhere without his or her boll weevil.
    LOL! But, you know, you might be on to something. Museums employ beetles to clean skeletal specimens. Maybe there's an insect that likes solder flux. Or else a flux could be developed that insects would like. It might take a week to clean a board, but I understand the bone-cleaners do a spectacular job!

    -Phil
  • ElectricAyeElectricAye Posts: 4,561
    edited 2009-05-04 20:15
    Phil Pilgrim (PhiPi) said...
    ...Maybe there's an insect that likes solder flux....

    Now you've got me thinking along the lines of engineering a bacterium to do the job. It might eat your face, though.


    skull.gif
  • WBA ConsultingWBA Consulting Posts: 2,935
    edited 2009-05-05 00:07
    If you are using an organic flux, it will need to be removed as it will be corrosive if left on the board. Use a readily available flux remover from Fry's, etc. Techspray makes very good flux removers that are environmentally friendly. Check Mouser or Techni-tool for the G3 series of cleaners (http://www.techspray.com/pindex.htm#1600).
    If that's too difficult to source, just use 91% Isopropyl Alcohol (available at every walmart). Typically used with a plain old acid flux brush with shortened bristles for stiffness (already mentioned). The ideal brush is one made of hog bristle as they clean better with less force. Also, they last much longer because it is easier to clean the residue out of the bristles.

    If you are using no-clean flux, removal is dependent on your circuit, but typically only "excessive" flux residue is removed and usually only for cosmetic reasons. Removal of no-clean flux is performed with IPA or flux remover.
    RF and high speed circuitry can be affected by no clean flux residue, but it is not a common problem for most circuits discussed on these forums. Most of the electronics in your house probably have no-clean flux residue on their PCBs.

    In volume manufacturing, organic flux (commonly referred to as "water soluble" or "aqueous" flux) is usually removed by an inline cleaner. Hot (140F), treated, de-ionized water is sprayed at high pressure on the PCB to remove the flux. Basically the machine is a large dishwasher with a conveyor running through it.

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  • ForrestForrest Posts: 1,341
    edited 2009-05-05 00:37
    No-clean flux can be left on the board, but don't use an excessive amount. No no-clean flux is only safe to leave on the board if it's been heated. Non heated no-clean flux IS harmful - it's a weak acid and it is a weak electrical conductor! If in doubt, you can remove no-clean flux with a brush and IPA - it just takes a bit more scrubbing to remove than aqueous flux.
  • Bill DrummondBill Drummond Posts: 54
    edited 2009-05-05 01:16
    It's a common practice for small electronic manufacturers to use an ordinary dishwasher to clean boards, the spot free agent in dishwasher powder probably de-ionizes the water. I worked for a nuclear imaging company that did this.
  • $WMc%$WMc% Posts: 1,884
    edited 2009-05-05 01:40
    I shorted an electrolytic cap using the soak in isopropyl method. This could have just been a fluke, but now I use 409 with a hot water rinse. I then blow dry the board (with compressed air). I then spray on a lite film of WD-40.

    This might sound wierd, But it works for Me.

    ____________$WMc%____________

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  • ElectricAyeElectricAye Posts: 4,561
    edited 2009-05-05 02:00
    Bill Drummond said...
    It's a common practice for small electronic manufacturers to use an ordinary dishwasher to clean boards, the spot free agent in dishwasher powder probably de-ionizes the water. I worked for a nuclear imaging company that did this.

    I don't suppose they used the same dishwasher to wash the company coffee pot.
    "Sugar? Cream? Splenda? How about a little Lead Oxide?" skull.gifskull.gifskull.gif
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2009-05-05 02:49
    $WMc%,

    I doubt that isopropyl alcohol alone could cause a short. Even though it's conductive as a liquid, the pure form evaporates vey quickly. There may have been other contaminants that got moved around but not eliminated during the cleaning process. Or you didn't wait long enough before powering up the board.

    BTW, there are much better protectants than WD40, which can get gummy with age. I sometimes use a polystyrene conformal coat, which seals a PCB against moisture, salt, and other environmental nasties.

    -Phil
  • TeslaTesla Posts: 55
    edited 2009-05-05 03:03
    I add a vote for the IPA. I have always used it. Works great. I had a can of flux remover and it was mostly IPA.
  • StarManStarMan Posts: 306
    edited 2009-05-05 04:09
    What about methanol?· It seems to me that it should be no different than IPA as a cleaner/solvent.· Maybe a little more aggressive.· I buy it at Home Depot under the name "Denatured Alcohol".

    Also, as a note, a while back I was having trouble with SMT resonators (the 20MHz ones that Parallax sells) on boards I was having reflow soldered.· The conclusion was that they were affected by the wash.· Since then, I solder them on the boards myself with the no-clean solder and have had no further problems.

    Chris I.
  • Oldbitcollector (Jeff)Oldbitcollector (Jeff) Posts: 8,091
    edited 2009-05-05 13:39
    Had the wife pick up alcohol from Walmart. She called and gave me the choice of 91% alcohol or vodka. [noparse]:)[/noparse] Looks like I'll be trying the local pharmacy today.

    91% strikes me as not being pure enough for this use?

    OBC

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  • WhitWhit Posts: 4,191
    edited 2009-05-05 14:42
    If you drink enough of the vodka, your board will look clean.

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  • LeonLeon Posts: 7,620
    edited 2009-05-05 14:47
    OBC:

    You need 99% IPA.

    Starman:

    Denatured alcohol is mainly ethanol with some methanol and other stuff to make it undrinkable. It isn't much use for removing flux. Cellulose paint thinners (xylene) works quite well and is easy to obtain, but isn't very pleasant to use.

    Leon

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    Post Edited (Leon) : 5/5/2009 2:52:56 PM GMT
  • uxoriousuxorious Posts: 126
    edited 2009-05-05 17:10
    Anything over 91% will work fine. The only thing I have ever used for cleaning flux residue off boards at home is 91% from Walgreens and I've been happy with the results. You can use 70% (plain rubbing alcohol) depending on your flux composition. If you are using a very active flux, 70% may not be able to dissolve the residue.

    At all of my jobs in electronics manufacturing, we use >99% in 1 gallon jugs from typical distributors. My current company uses "Techspray 1610" which is "Isopropanol (67-63-0) 100%". Data sheet states: "99.8+% pure, anhydrous isopropanol for all-purpose cleaning. Excellent for tape head cleaning, removal of fluxes, light oils, polar soils, and white mineral residue. Can be used as a thinner for most fluxes."

    The lower percentage of alcohol just means there is a higher percentage of water. The greater the dilution, the lower the ability of the alcohol to dissolve the flux. So, the alcohol will still remove the flux, just at a slower rate and more may have to be used.

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  • ElectricAyeElectricAye Posts: 4,561
    edited 2009-05-06 05:19
    Phil Pilgrim (PhiPi) said...
    I tried Q-Tips once, but found that the clipped leads on the through-hole parts snagged bits of cotton, which I'd then have to remove with a toothbrush. smile.gif

    -Phil

    Okay, I'm bowing down in respect for Phil, here. My Q-tip suggestion sucks in light of the toothbrush method. I just got through soldering a VGA connection, and I had forgotten what a mess all that loose cotton creates.

    That, and my boll weevil just up and died.


    cry.gif
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