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How do the pros clean PCBs? How about while in place?

Discussion in 'General Electronics Chat' started by fastline, Sep 26, 2017.

  1. fastline

    fastline Member

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    Sort of a 2 part question. We have some industrial equipment that has become unreliable with some indication that the boards are dirty, causing erroneous shorts. In the past I have used isopropyl and a brush but this seems problematic as under the microscope, it is obvious that areas around multi-pin components tend not to get very clean.

    I have used compressed air as well, but I am left wondering how to pros actually do this in a repair facility? One thing I am thinking is air airbrush loaded with alcohol and run at higher pressures? Or do you really need a mode of physical contact to break stuff loose?


    Also, in another machine, it has been sitting for some time until a reasonable process can be decided to clean some boards that will otherwise take countless hours to remove and clean. This machine cannot be afforded much capital investment for this work, so we are trying to find a slick way to clean them.
    For instance, a VFD shut down in this machine and was sent out for repairs. It was returned as "no defects other than cleaned the boards".

    Now, this machine was NOT in our facility and we know better than to disregard cooling air filters so if we can get it clean, we can keep it that way.
     
  2. dknguyen

    dknguyen Well-Known Member

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    Have you tried MG chemicals Superwash aerosol?

    My understanding was that the only thing better than a brush for those tiny areas was ultrasonic cleaning...but obviously that can't be done in place.

    However, I am reminded of the way ultrasonic tartar scalers work...the ones that dentists use that obviously allow cleaning things in place.
    Try going out to buy a consumer dental water pick and filling it with either distilled water or isopropyl alcohol and test it starting at low to to maximum setting. Make sure to wear goggles and a mask especially if you use the alcohol. The water pick that I have when turned to maximum actually hurts external flesh at close range so I don't know why it can be turned up that high to begin with since it's meant to be used inside your mouth. Test on a deadboard on tiny components to see if it might damage things at close range (might sound silly since it's an oral device but those things shoot water real hard).
     
    Last edited: Sep 26, 2017
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  3. fastline

    fastline Member

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    I think my concern is making things worse by cleaning, or not cleaning properly.

    I might take a look at some aerosols but I do like the ability to tune the air pressure and delivery with basic compressed air. Just figured if I could get some droplets delivered with the air, it might offer enough energy to break some stuff loose.

    I don;t think we are after surgery clean here, but realized on the machine in situ, they used it around Cast Iron dust!!!! Basically in machining, most metals form a chip, but cast iron like to create a powder that can become airborne! For that reason, we have not run the machine until we can make a plan to clean some electronics.

    may I also ask what you guys recommend for economical head gear for magnification? We have the scope on the bench, but I can;t wear that.
     
  4. dave

    Dave New Member

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  5. dknguyen

    dknguyen Well-Known Member

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    I was updating my response as you were replying. Did you catch the water pick part? $20 to buy one and test.
     
  6. tomizett

    tomizett Active Member

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    This is an interesting topic, and one that I've asked about before. For heavily contaminated boards I tend to use water (maybe a little detergent to start, then rinse) and then finish with isopropanol, scrubbing with a brush to loosen harder debris. Often I'll use an air line or canned air to blast the fluid from under and around components - this has the effect of carying away solids with the fliud and also helps the drying process.

    As you've spotted though, it's a labour-intensive process and I've been on the lookout myself for more efficient (both quicker and more effective) methods.

    I'm interested in ultrasonic cleaning, but have not tried it yet. I've got an ongoing project to build a vacuum over for drying after cleaning with water (this being the hardest part) - I'll be updating here with how that goes as (if) it progresses.

    I'd never heard of these "water picks", but they sound like they could be very useful, so thanks dknguyen for briging these to our attention.

    None of these really adress fastline's need to clean in-situ though... I'd imagine that if your contamination is dry then you should get pretty good results with compressed air. Maybe with a little help from a brush (preferably a cardon-fibre anti-static one).

    Would also be interested in hearing others' experiences.
     
  7. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    There is a large difference in solvent potency between 99% isopropyl alcohol (IPA) and 100%. Similarly, absolute ethanol (100%) is quite a different solvent than 95%. One of the big differences is its ability to dissolve fats and lipids. I have used 99% IPA and was not satisfied with the small amount of white, chalky deposits it left. My solder is 63/37 tin/lead and flux is Kesters #44. Different fluxes may make a difference.

    My preferred flux remover is absolute ethanol with a little acetone. I use two washes (first wash and clean wash) and blow off in between. Boards come out shiny. I do minimal scrubbing with a toothbrush.

    For old boards that were originally clean, I suspect you need to cut through accumulated aerosol grime. Detergents might help, if heated. I have read that Tektronics just used to put dirty boards in a household dishwasher. I would still consider my alcohol/acetone mixture after the dishwasher. Absolute ethanol may be hard for you to get. Denatured alcohol may be a suitable substitute.

    Chloroform is a great solvent for lipids and grease. It is non-flammable, but can attack paints and plastics. It is less aggressive than methylene chloride that is in many paint removers. If your components are not a concern, a little chloroform or perchloroethylene (PERC) to your IPA or ethanol will enhance their potency.
     
    Last edited: Sep 26, 2017
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  8. tomizett

    tomizett Active Member

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    As ever, a fascinating insight into the chemistry - thank you. I wish I understood it better!

    Without wanting to take us off-topic, you mention:
    I have noticed similar deposits (and other people here have mentioned the same) but could never work out where they originated. Is your implication that these are some component of the flux that is not desloved by the slightly impure isopropanol?
     
  9. dknguyen

    dknguyen Well-Known Member

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    Yeah, there are two steps to washing flux off a board. You have to first dissolve the flux in something and then you need something else to displace the solvent in which the flux has dissolved. This could either be a separate washing agent that is sprayed or just by bathing it an ample amount of the original solvent so that clean solvent displaces the dirty solvent. It's the difference between showering vs taking a bath and soaking in your own filth.
     
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  10. Little Ghostman

    Little Ghostman Well-Known Member Most Helpful Member

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    99.9% IPA is what I use, as pointed out stay away from DCM (Meth chloride/ dichloromethane), I have access to chloroform but on a board for grease i would opt for IPA (75%) and detergent. unless you got alot of boards then maybe Chloroform is worth a look. We dont get 100% ethanol here unless we make it or pay a vast amount for it, but I find IPA much better.
    DO NOT USE Acetone!!! It will strip the lettering off components and some solder masks dissolve in it.

    Oddly with pure IPA I have never had white deposits, but I am in the UK, so solders and fluxs will differ as will purity of solvents. The other thing I have used with effect is the dishwasher.....mild dishwashing tablets 40C temp on quick and eco wash. But I dried them with compressed air. For switches and contacts etc, and card edges I dont think you can beat switch cleaner! Yeah costs alot per can but worth it.

    No point saying which solvents are in it, apparently it depends which country you are in! Trichloro etc should not be used, infact treat all solvents with care. I use one of those glass fiber pens carefully when cleaning. If the boards are pro standard then ultra sonic with IPA is excellent, but any dry joints will show up :D, not saying much on how i know this ;)
     
  11. JLNY

    JLNY Active Member

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    One aerosol-type cleaner that I use at work is a heavy-duty cleaner called "Lectra Sol TC" made by Tri-Chem. It sounds to be similar to the MG superwash. It cuts through oils and flux very easily without having to brush off, and evaporates quickly and without residue.

    However, I will warn that it dissolves certain types of plastics and can strip paint, so use with caution depending on what's near the boards-- I and the rest of our EE department found out the hard way that it is capable of melting the polystyrene dielectric beads used in expensive precision RF adapters. In spite of the risks, I swear by the stuff and I sometimes bring boards from home into work to clean them off with it.

    http://www.tri-chem.com/product-catalog/Cleaners & Degreasers/Aerosol/AERLSTC/Lectra Sol TC Aerosol/

    One type of magnifier that I use when assembling and inspecting SMD components on my PCBs at home is a "Donegan Optivisor." They come with lenses in differing levels of magnification and focal distances, so you might trying looking for one that suits your application. They work well, but bear in mind that the higher magnification levels will also have a pretty short focal distance.

    http://www.doneganoptical.com/products/optivisor
     
  12. ClydeCrashKop

    ClydeCrashKop Well-Known Member

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    This works well. Like a solvent pressure washer.
    There are more expensive ones but I don't know if they are better.
    Air Engine Cleaning Gun W/6 Ft Hose $15.00
    High speed, 2 way action removes dirt, grease and oil quickly from engines and machinery. Sprays, kerosene, soap and other solvents under high pressure. Pressure trigger for maximum efficiency. Includes a 6' hose siphon hose w/screen for combining solvents and water. 1/4" NPT fitting.

    My first choice for cleaning anything is Spray Nine but it etches glass & ceramics.
    https://www.amazon.com/Spray-Nine-26832-Degreaser-Disinfectant/dp/B0014COKYU
     

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