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Old 12th August 2006, 03:32 AM   #1
Clipped is offline Clipped  Thailand
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Default cleaning off after assembly flux?

how do the pcba manufacturers clean off the flux after they solder together a board?

is there a way to do it that doesnt require big machinery? sprays that are effective, and that can be used with a populated board?

i have a magazine with a list of chemical sprays to clean the flux off, but not quite sure how to use it properly or the right type that i need...any help appreciated!

thanx

oh and how much can one can clean off?
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Old 12th August 2006, 03:45 AM   #2
anatech is offline anatech  Canada
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Hi Clipped,
You can clean it all off. I use Electrowash 2000 and a toothbrush on the foil side only. Components like electrolytic caps do not like cleaners in general. Trim pots and other parts are similar.

You can use lacquer thinner and a tooth brush or cotton swab also.

-Chris
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Old 12th August 2006, 11:12 AM   #3
Clipped is offline Clipped  Thailand
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thanks

after cleaning the board, would i just hang them vertically to dry?

or should i fan dry them too?

thanx again!
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Old 12th August 2006, 12:43 PM   #4
tade is offline tade  United States
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I found that acetone works well, and very quickly which may allow you to reduce the exposure of components.
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Old 12th August 2006, 02:28 PM   #5
poobah is offline poobah  United States
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The PCB manufacturers use water based flux... then the boards are cleaned in hot water.

Lacquer thinner and especially acetone are pretty "hot", OK for a quick wipe, but no soaking. They attack plastics, especially PVC (vinyl).

Denatured alcohol can be used any ole way... soaking etc...

Actually tetrachoroethylene (dry cleaning fluid... brake cleaner from the local auto parts store) works great for removing rosin based flux. You can't use it near polycarbonate plastics (Lexan) but these are fairly rare (except some caps) in electronic parts. Like Chris says, watch out for electrolytics, chlorine and lytics don't mix.

Most pots these days are sealed for cleaning, but certainly not all. Switches, pots, caps, and transformers all need special consideration.

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Old 12th August 2006, 02:59 PM   #6
BrianL is offline BrianL  United States
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Assuming nothing like potentiometers or switches to worry about, I soak mine in alcohol (not rubbing alcohol as it has glycerin in it). Denatured alcohol from the paint department of your local home store will work. Soak and scrubb with something like a toothbrush:

VERY IMPORTANT: a partial cleaning is worse than no cleaning as the first material to be removed is the rosin carrier, leaving the corrosive components which will eat away at your metal. So either make it squeaky clean or do nothing.
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Old 12th August 2006, 03:20 PM   #7
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It appears as if many of the pcbs in modern mobile devices (cell phones, wifi cards, gps antennas, etc) are clear coated with some form of protectant against humidity and other abuse/contamination. Perhaps a clear lacquer or epoxy? Most of the benefits of potting, without the heat xfer problems, shrink rates, weight, and cost of a full potting.

Any reason why this couldn't be accomplished by a diy'er? Would there be any benefit?
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Old 12th August 2006, 03:34 PM   #8
poobah is offline poobah  United States
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Excellent point BrianL... cleaning is ALL OR NOTHING.

Bluebeard,

No reason why DIYers can't coat their boards. It will make a mess for the guys that are always changing their resistors for faster bass or open midrange.

Coating is good in tropical climates especially... stops rot. In certain circuits, it is a must to control drift. BTW... you don't have to spend a fistful of cash for a good coating. Krylon clear works just dandy. I use it here for products that go in industrial apps. The choice was simple, $14 per can for "electronic" coating, or $4 per can for the same stuff minus the UV tracking dye.


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Old 12th August 2006, 04:04 PM   #9
anatech is offline anatech  Canada
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Hi,
Anything I have suggested evaporates quickly. Therefore they are a fire hazard. Do not use in enclosed spaces (ventilate!!).

I have spot cleaned flux from boards many times with no trouble. You will find that a cotton swab tends to take the flux with it. More than one treatment may be required.

I don't soak my boards, I just clean the solder side and use cotton swabs near components that don't like cleaners. I can't agree with the statement that you clean all or nothing. 'Tan't true folks!

Having said that, I approach cleaning test equipment completely differently. What I've said is valid for consumer audio.

Coating boards is valuable for items in environments in corrosive atmospheres and areas that reach or exceed the dew point. It is a pain to work on afterwards, so normally you don't want to do this. I have lots of stuff I built in the 70's that still works fine. The boards look good too.

-Chris
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Old 12th August 2006, 04:18 PM   #10
poobah is offline poobah  United States
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Chris,

You've never had problems with partially removed flux becoming conductive?

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