The proper way to clean PCBs...before & after soldering

BRBR Posts: 92
What is the "best practice" for cleaning PCBs? I've caught snippets of information here and there on the forums, but would like to be sure I've got it right.

I believe the following to be true:
1) I should clean my PCB with isopropyl alcohol both before and after soldering. The before is to be sure the pads are clean of any oils or films. The after is to remove the flux, which is mildly acidic (?) and, over time, will attack the solder joint.

2) I should use the type of isopropyl alcohol that you get in the paint section of Lowes or Home Depot (which is ~95% alcohol), and NOT rubbing alcohol (which is 50% alcohol, 50% water).

3) I should clean the PCB by dipping a q-tip or small brush in alcohol and wiping it across the PCB surface, following that with a wipe from a clean cloth or q-tip to dry it a bit.

Should I clean both top and bottom of the PCB after soldering is complete? If so, how do I ensure that I've thoroughly cleaned the front, as the many nooks and crannys of the components seem like they'd be tough to clean. I assume, but do not know, that it would NOT be a good idea to simply drop the populated PCB into a pan of alcohol, swish it around a bit, and tamp dry with a cloth.

Any advice on tools, techniques, and procedures would be appreciated.

Comments

  • 27 Comments sorted by Date Added Votes
  • James LongJames Long Posts: 1,181
    edited December 2009 Vote Up0Vote Down
    BR said...
    What is the "best practice" for cleaning PCBs? I've caught snippets of information here and there on the forums, but would like to be sure I've got it right.

    I believe the following to be true:
    1) I should clean my PCB with isopropyl alcohol both before and after soldering. The before is to be sure the pads are clean of any oils or films. The after is to remove the flux, which is mildly acidic (?) and, over time, will attack the solder joint.

    2) I should use the type of isopropyl alcohol that you get in the paint section of Lowes or Home Depot (which is ~95% alcohol), and NOT rubbing alcohol (which is 50% alcohol, 50% water).

    3) I should clean the PCB by dipping a q-tip or small brush in alcohol and wiping it across the PCB surface, following that with a wipe from a clean cloth or q-tip to dry it a bit.

    Should I clean both top and bottom of the PCB after soldering is complete? If so, how do I ensure that I've thoroughly cleaned the front, as the many nooks and crannys of the components seem like they'd be tough to clean. I assume, but do not know, that it would NOT be a good idea to simply drop the populated PCB into a pan of alcohol, swish it around a bit, and tamp dry with a cloth.

    Any advice on tools, techniques, and procedures would be appreciated.

    You are pretty close to the whole idea.....

    I sometimes use an old toothbrush (should be teethbrush) on the boards to get into the nooks and crannys. We also do drop boards into a ultrasonic cleaner with IPA (isopropyl Alcohol). There is a caveat to this. If you have any parts which are not to be washed, this is not a good idea. Usually these parts are buttons or dip switches. The Datasheet will say. Also......there are possibilities you may break a chip with ultrasonic. Most of the time I do not have problems, but when I do it's typically a crystal which dies.

    James L

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  • LeonLeon Posts: 7,619
    edited December 2009 Vote Up0Vote Down
    PCBs don't need cleaning before soldering if they have been made properly.

    I remove flux after soldering by brushing with 99% IPA. The diluted stuff is useless.

    Leon

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  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 22,041
    edited December 2009 Vote Up0Vote Down
    James Long said...
    We also do drop boards into a ultrasonic cleaner with IPA (isopropyl Alcohol).
    I'm glad I'm not carrying your fire insurance! smile.gif Seriously, flammable liquids used in an ultrasonic cleaner constitute a rather serious fire hazard.

    -Phil
    “Perfection is achieved not when there is nothing more to add, but when there is nothing left to take away. -Antoine de Saint-Exupery
  • James LongJames Long Posts: 1,181
    edited December 2009 Vote Up0Vote Down
    Phil Pilgrim (PhiPi) said...
    James Long said...
    We also do drop boards into a ultrasonic cleaner with IPA (isopropyl Alcohol).
    I'm glad I'm not carrying your fire insurance! smile.gif Seriously, flammable liquids used in an ultrasonic cleaner constitute a rather serious fire hazard.

    -Phil

    Phil,

    We have a fire suppression system in the enclosure that the ultrasonic cleaner sits in (Halon). It also has a lid on at all times in operation. We thought of the possibility of fire when using ultrasonic with IPA.

    It does create a serious fire hazard. The ultrasonic cleaner creates a huge amount of alcohol vapor when in operation. That is why we enclosed it and vented it with a sealed fan. We were going to seal the tank it but wasn't ever successful making a lid which would seal during operation.

    It should be noted that anyone who places a flammable liquid in an ultrasonic cleaner should be aware of the risks. This is inherently dangerous unless serious safety provisions are used. Even then, a possibility of a fire or explosion is possible. We do not take responsibility of anyone who tries this on their own!

    James L

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  • BRBR Posts: 92
    edited December 2009 Vote Up0Vote Down
    OK, thanks guys. Sounds like I'm doing the right thing...I'll just use an old toothbrush and give it a mild scrub.

    @Leon: "PCBs don't need cleaning before soldering if they have been made properly."

    An interesting statement...could you elaborate a bit? What constitutes a "proper" PCB? Are you saying that the pads can be laid out in such a way that having a bit of oil or other contaminate does no harm to the joint? Or are you saying that if they've been manufactured to high standards, they should arrive in a clean and ready-to-solder condition? And if the latter, let's say that I've handled the PCB a few times and gotten my grubby fingerprints on it...in which case prudence suggests I ought to go ahead and clean it a bit before soldering. Or maybe it would be fine to just wipe it off and call it good?

    @James/Phil: no worries, I assure you that an ultrasonic cleaning machine is well beyond my means and needs at this point, but thanks for the info. Duly noted.
  • LeonLeon Posts: 7,619
    edited December 2009 Vote Up0Vote Down
    I've never had any problems soldering PCBs from my usual suppliers, without cleaning them first. The flux in the solder, or applied with a flux pen, ensures good solder joints, in conjunction with correct soldering temperatures and the correct tip.

    Leon

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    Post Edited (Leon) : 12/29/2009 10:11:45 PM GMT
    Leon Heller
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  • PrettybirdPrettybird Posts: 269
    edited December 2009 Vote Up0Vote Down
    Sometimes old boards tarnish. I have LIGTHLY used steel wool carefully. Also have used pencil erasors.The hardest part is cleaning off the resin. When working as a bench technician, we had some resin remover stuff (not cheap). That's how the pros do it if you planning to do alot.
  • ForrestForrest Posts: 1,341
    edited December 2009 Vote Up0Vote Down
    Typically the only boards you need to clean before soldering are home-made boards made from copper clad FR4 or perf boards sold by Radio Shack and others. These boards do not have any final finish over the copper - so the manufacturer applies lacquer over the copper to prevent it from oxidizing. I clean these boards with isopropyl alcohol and light scrubbing with a scotchbrite pad.

    I clean assembled boards with a toothbrush dipped in isopropyl alcohol. Most of my hand assembled boards need two cleanings - I use a lot of flux.
  • ercoerco Posts: 19,289
    edited December 2009 Vote Up0Vote Down
    Scotchbrite to clean new pcbs.

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  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 22,041
    edited December 2009 Vote Up0Vote Down
    If two cleanings are required, it's best to have two bottle of IPA on hand, a "dirty" one and a "clean" one, not to mention two toothbrushes. What you don't want to do is just spread out the flux contamination. You want to remove it.

    -Phil

    Addendum: But no Scotchbriting boards with soldermask! You could easily scrape it off.
    “Perfection is achieved not when there is nothing more to add, but when there is nothing left to take away. -Antoine de Saint-Exupery
  • davejamesdavejames Posts: 3,919
    edited December 2009 Vote Up0Vote Down
    I miss the hot freon vapor bath units. Man could they clean!

    DJ

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  • skylightskylight Posts: 1,915
    edited December 2009 Vote Up0Vote Down
    Colclene with flux remover (blue label) was brilliant at the job till they banned CFC's shakehead.gif
  • Lee HarkerLee Harker Posts: 104
    edited December 2009 Vote Up0Vote Down
    I'm surprised nobody has mentioned water soluble flux. That is my preference and it washes off with warm water. There are a couple of downsides though. It tends to cost more and the flux is slightly conductive so washing it off is not optional.
  • James LongJames Long Posts: 1,181
    edited December 2009 Vote Up0Vote Down
    Lee Harker said...
    I'm surprised nobody has mentioned water soluble flux. That is my preference and it washes off with warm water. There are a couple of downsides though. It tends to cost more and the flux is slightly conductive so washing it off is not optional.

    There are many more issues with water soluble paste. First open air time is much shorter. Humidity can be a definite problem (shortens the open air time further).

    The ramp to reflow needs to be very close to the needed profile, and doesn't deal well with much variation.

    James L

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    Are you addicted to technology or Micro-controllers..... then checkout the forums at Savage Circuits. Learn to build your own Gizmos!
  • mctriviamctrivia Posts: 3,772
    edited December 2009 Vote Up0Vote Down
    if you use gold plated pcb you will never need to clean before hand(assuming you don't spill something on the board). copper and silver plated pcb do need to be cleaned depending on how long ago the pcb was made.

    generally you only have to clean the pcb after you solder the board though if you find solder does not run easy to the pads they have probably oxidized and cleaning or strong flux is needed.

    Generally I use IPA and a hog hair brush. I have a special dispensing container for the IPA that dispenses a small amount at a time and any excess not used rapidly evaporates. This way you can not contaminate the IPA.

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  • Nick McClickNick McClick Posts: 1,003
    edited January 2010 Vote Up0Vote Down
    I use this MG Chemical spray I got a Fry's. It's something like 50% acetone, 50% Isopropyl (rubbing) alcohol. The spray will dissolve the flux - once it's dissolved, continue to flush it with spray or rinse it off. Otherwise, the flux resolves(?) into a white-ish powder. A hogs hair brush works great.

    I've never needed to clean the board before soldering, but I guess if your board has been sitting out for a few months, you might need to.

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  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 22,041
    edited January 2010 Vote Up0Vote Down
    I'm surprised the acetone content doesn't attack the epoxy, soldermask, and other plastics on the board.

    -Phil
    “Perfection is achieved not when there is nothing more to add, but when there is nothing left to take away. -Antoine de Saint-Exupery
  • Nick McClickNick McClick Posts: 1,003
    edited January 2010 Vote Up0Vote Down
    Phil - you made me go ahead and learn something [noparse]:)[/noparse]

    The MG spray is actually 90% Ethanol, 5% ethyl acetate, 5% IPA.

    Acetone is reactive to some plastics (like DIP sockets), so you shouldn't spray it on the plastics side of the board. It's only effective in dissolving epoxies before they harden, (or so says wikipedia) so it doesn't attack the FR4 or soldermask.

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  • Peter KG6LSEPeter KG6LSE Posts: 1,383
    edited January 2010 Vote Up0Vote Down
    After I etch I use toothpaste with a makeup sponge .. or a" Mark 1 finger "..

    But I also use 5 core Rosin solder that eats oxidation for lunch and dinner , so I normality don't ever have a issue with pre cleaning ..

    As for post cleaning I use IPA for the " light stuff " and I use toothpaste with a hacked (needed new batts) soniccare brush for the hard to remove stuff.
    After I use DI to wash the PCB ....

    Works Wonders!

    Peter KG6LSE

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  • BradCBradC Posts: 2,601
    edited January 2010 Vote Up0Vote Down
    Nick McClick said...

    Acetone is reactive to some plastics (like DIP sockets)

    And as I found out recently, it also reacts nicely with the plastic lid on my washing machine, and the epoxy coating on my floor boards [noparse]:([/noparse]

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  • BRBR Posts: 92
    edited January 2010 Vote Up0Vote Down
    <sarcastic_voice>

    Well, that'll learn ya to wash your clothes and your car in acetone...

    </sarcastic_voice>
  • BR wrote: »
    1) I should clean my PCB with isopropyl alcohol both before and after soldering. The before is to be sure the pads are clean of any oils or films. The after is to remove the flux, which is mildly acidic (?) and, over time, will attack the solder joint.

    I don't think so that there is any need for cleaning PCB before soldering. But if you think that your board might have some dirt or other pollutants then cleaning board before soldering have no issues as well.
  • What happens to the board if you don't clean it after soldering?
    There is no such thing as bad news.
  • Wow, this is a good old thread!

    If you don't clean your flux off after soldering you have a boards that looks horrible, all covered in brown gunge. At least mine do.

    The only times I have had to clean boards before soldering was when using really old stock PCB from a surplus store that where all the copper had a good thick layer of oxide on it. A quick rub sown with a scouring pad made soldering those boards much easier.
  • Many years ago I refurbished and sold or leased quite a few instruments, and I would clean the boards, motherboards, and chassis by first washing them using tap water, dish detergent, and paint brushes with the bristles cut short. Then I would rinse them off with more tap water, followed by distilled water, and finally isopropyl alcohol, followed by drying overnight over a heating vent. After that they looked as good as the day they arrived from the factory. Did the same for the mechanical parts and housings followed by greasing/oiling the mechanics and painting the cabinets. That worked so well that the most common reaction from customers was "wow, that's used? It looks like it's brand new.". Amazing what a bit of detergent, elbow grease, and paint can make.
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  • frank freedmanfrank freedman Posts: 1,414
    edited October 27 Vote Up0Vote Down
    Here is a similar process.

    https://www.elektormagazine.com/news/saturday-afternoon-give-your-oscilloscope-a-good-wash-down


    Here is the recipe from the Tek service engineer mentioned in the article.


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  • Hal AlbachHal Albach Posts: 736
    edited October 27 Vote Up0Vote Down
    What happens to the board if you don't clean it after soldering?

    Besides looking extremely ugly, some fluxes become slightly conductive after being heated. The flux paste I use contains zinc chloride and absolutely becomes conductive. ISA and a toothbrush does remove it. ( I should get rid of that little can, it's about 40 years old! )
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