Cleaning Flux and other dust residues.

Discussion in 'General Electronics Chat' started by R!f@@, Feb 20, 2011.

  1. R!f@@

    Thread Starter AAC Fanatic!

    Apr 2, 2009
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    What is the best chemical that I could use to clean the PCB's after a thorough reflow.

    I am using thinner and Acetone, since this is what I can easily get here.
    But it does not do a good job. I am using a paint gun to spray it and clean the board.
    Thinner leaves an oily residue and sometimes it gives me trouble.
    Acetone is clean but it does not dissolve flux too easily.

    What are the chemicals used in PCB industries to clean the PCB after soldering?
     
  2. SgtWookie

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    Jul 17, 2007
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    Pure Isopropyl alcohol is the most commonly used solvent. The kind typically available in drugstores really isn't suitable because the water content is too high (30%). Sometimes you can find 90% or better in drugstores. Hardware supply stores frequently carry 99% pure isopropyl alcohol. It will dry your skin very quickly, so avoid getting it on your skin/clothing.

    Isopropyl alcohol is hygroscopic, which means that it absorbs moisture out of the atmosphere - so you really need to keep it covered when not in use, particularly in your humid environment. It's also flammable; burns with a nearly invisible blue flame.

    However, even with the skin dryness and the flammability, it's one of the more benign and readily available solvents that you can use. Soaking the parts for a period of time before light scrubbing with a brush will help to loosen the flux. Pure isopropyl alcohol will evaporate and leave no residue, and I've never had it damage a component.

    Some of the harsher solvents I've used will damage components in strange ways. I've had a solvent change the AL value of powdered iron toroids, which wreaked havoc on certain bandpass filter designs. It took a good while to figure out just what the heck was happening to cause the filters to shift frequency so badly.
     
  3. jpanhalt

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    If you can't get pure isopropyl alcohol, can you get denatured alcohol (ethanol)? That also works well and usually does not contain water. As you may have found out, acetone can damage many plastics. Some denatured alcohol can do likewise, depending on what is added to denature it. John
     
  4. shortbus

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    Many of the fluxes used are a water base type. And water is used to clean it off of the board. I know water and component/electronics don't mix :) But after washing a board with warm water they are then dried in a low heat oven and are not harmed by the water. It's done all the time in manufacturing.
     
  5. jpanhalt

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    Good point. My comment applies to the non-water soluble fluxes, like Kester #44 Rosin.

    John
     
  6. marshallf3

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    Jul 26, 2010
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    You can get 91% in any drugstore or even Wal-Mart.
     
  7. creakndale

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    Mar 13, 2009
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    I have tried all the over-the-counter flux removal remedies discussed above plus some others and wasn't happy with the results from any of them. I finally broke down and bought a spray can of Techspray Flux Remover. What a huge difference. Even though it's more expensive than the over-the-counter chemicals, it is so superior that it's not even funny.

    creakndale
     
  8. R!f@@

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    I don't think I can buy anything with alcohol in it. Here it is prohibited.

    So I have to rely on water jet and oven ways I guess.
    I can use a stream of water jet to blast of debris and use an oven to heat the board.

    What is the temperature setting for this purpose that u guys use. any DIY kit that I can make to build a good oven to heat the boards.

    Problem with alcohol here is the drug addicts will steal them..and any chemical containing alcohol is controlled here. It is very recently I am able to buy acetone, u know.

    How do I identify "Pure Isopropyl alcohol"
     
  9. spinnaker

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    Oct 29, 2009
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    Isopropyl alcohol is banned??? If you drink it you will go blind. Why would they ban it?

    Look at the percentage on the bottle. I doubt you will find "pure" alcohol. Maybe 99% at best.
     
  10. jpanhalt

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    I don't understand. Alcohol is both a class of chemicals ranging from methanol (CH3OH) to large and very complex alcohols, and a single compound ethanol (aka ethyl alcohol). In a sense, your own RNA, DNA, liver, fats, etc. contain alcohols. Ethanol is what humans drink, and I understand that it is regulated. It is hard to imagine that it is actually prohibited on the island, as it has so many non-intoxicant uses. Pathology labs, for example, would be lost without it for tissue preparations.

    Water will not work for the non-water-soluble fluxes, unless it is very hot and/or has detergents in it. As for alcohols, if you cannot get denatured ethanol or essentially water-free isopropyl alcohol, you can try methanol (aka wood alcohol). The commercial cleaner(s) recommended above contain, based on their MSDS's: 1) methanol + nitromethane + 1,2-dichloroethylene + dichloropentafluoropropanes; 2) pure isopropyl alcohol; or 3) pure ethanol. I suspect you cannot buy nitromethane easily.

    From a chemical standpoint (just guessing), the components of rosin flux need something that is both polar (water, alcohols, and nitromethane are polar) AND has a non-polar end so they can dissolve the hydrophobic part of the resinous carboxylic acids. That is why water alone doesn't work and water-containing alcohols probably work less well than purer alcohols, depending on the amount of water present. Nitromethane is a great solvent and is relatively non-toxic, but it is explosive, particularly if made alkaline or subjected to pressure. It is used with methanol as a high-power fuel for dragsters and model engines.

    Acetone has a lot of desirable qualities, but it is not quite as polar as alcohols. (I actually use histologic-grade absolute ethanol with a little acetone, but leave the acetone out, if there are soft plastics on the board. I do not use nitromethane as there are better uses for it in my pulse jet engines, etc.)

    Bottom line, you will either need to buy a commercial cleaner, go to water soluble flux, or find some alcohols that are relatively pure. Have you tried acetone alone? Can you get anti-freeze (ha, ha) without water in it? Ethylene glycol or propylene glycol plus acetone (no water!) might work. The glycols will be slow to evaporate, so you will probably have to rinse with water, if you go that way.

    John
     
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  11. shortbus

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    R!f@@, do they use shellac in Maldives? The most common thinner - clean-up product for shellac(not lacquer) is alcohol. Also it is used as a camp stove fuel, it will say methanol on the label.
     
  12. R!f@@

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    Shellac? aren't that the liquid used to hold the coils in transformers after field windings.

    We have something like that. U said shellac but here most of em says "selac". I have seen 'em pouring selac on to the windings of dynamo's , motors, and transformers as such.
    then they put the thing into a n oven and heat the windings and It hardens. Something like varnish, I think
     
  13. jpanhalt

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    Varnish and shellac are fundamentally different. Varnish cures chemically and cannot be removed simply by using the same solvent with which it was applied. Shellac cures (mostly) by solvent evaporation. It can be redissolved in its original solvent, like lacquer can be.

    Varnishes will typically have mineral spirits/paint thinner as a solvent that you know doesn't work.

    Alcohol will have a sharper, distinctive odor. If you compare mineral spirits to acetone, alcohols will have an odor more like acetone or acetone + water. That applies to isopropyl, propyl, ethyl, and methyl alcohols.

    John
     
  14. shortbus

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    Shellac is a type of wood finish. similar to varnish but not the same thing.
     
  15. SSgtKirby

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    Jan 20, 2011
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  16. bob332

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    Feb 14, 2011
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    cvs has 91% isopropryl in 32oz bottles for a couple $$
     
  17. R!f@@

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    Do you want me to get arrested at the post office buddy? :eek:
     
  18. debjit625

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    Apr 17, 2010
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    What about alcoholic beverages (atleast BEER) in Maldives????????
     
  19. R!f@@

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    Locally never anywhere in Maldives
    But with permission u can have it in the capital in a Hotel room. Never in the public, If outside, you will end up in jail.

    But in resorts, you can.
     
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