PCB solder joints blackening after two week's use - pic attached - diyAudio
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Old 16th May 2011, 07:31 PM   #1
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Default PCB solder joints blackening after two week's use - pic attached

Hello again,

My last query for a while - I shall attempt to resist the urge to tinker further until the winter - thanks for all your help.

My SSE has been in service for just over two weeks now and has been running without problems. The PCB now has quite a bit of blackening at the solder joints, and it's particularly bad around the valve sockets (see picture). These solder joints were completely blemish free after soldering and before power-up (honest!).

Anybody else have the same thing, or know what the cause might be? I'm a bit worried that it'll get worse until something goes pop.

Cheers!
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Old 16th May 2011, 07:40 PM   #2
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Quote:
Originally Posted by Horsebox View Post
Anybody... know what the cause might be?
You didn't clean off the solder flux before you powered up the amp. Now the flux is baked dry from the heat of the tubes, and probably won't ever come off.

Don't worry, it should be pretty much harmless. I did the same thing on mine, and it looks like yours. I wish I had cleaned it before I played it, but I was impatient.

Click the image to open in full size. Click the image to open in full size.

http://i69.photobucket.com/albums/i4...E/P1140548.jpg
http://i69.photobucket.com/albums/i4...E/P1100584.jpg
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Old 16th May 2011, 09:25 PM   #3
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Ah, I wondered if that might be the cause! I applied flux separately to the solder and it was difficult not to overdo it. I made a half-hearted attempt to remove obvious excess after soldering but the sharp edges made access hard. No doubt impatient too.

Will use the wife's toothbrush and a soapy solution next time.
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Old 17th May 2011, 01:04 AM   #4
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You may be able to scrape off the stubborn ones with toothpick or metal tweezers. Then use isopropyl (rubbing alcohol) on "Q" tips to remove the remaining.
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Old 17th May 2011, 01:15 AM   #5
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Yes, it's crispy fried flux. It's harmless and I don't bother to clean it off unless I am taking pictures of the board. There are commercial products that will remove it. I got one called "Flux Off" to clean up the boards for pictures. Laquer thinner will remove the green stuff, don't use it.

After the flux has hardened to the dark brown color, it is very brittle and much of it will crumble away with a little persuasion from an Xacto knife or small screwdriver.
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Old 17th May 2011, 01:21 AM   #6
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Hello Horsebox - take at look at this link for a look at how I have done this when slaughtering stuff together. Alcohol Dispensing Pump Bottle

The pump bottles are very handy but can get expensive. Take a look at beauty supply shops as the ladies use them to dispense acetone when doing finger nail jobs and they have the bottles for reasonable. Also - I prefer to use acetone for flux removal - if using alcohol use the denatured type rather than the isopropyl (however you Brit's might spell "isopropyl") i-so-pro-pall??? Isopropyl alcohol is commonly known as "rubbing alcohol" and contains water (H2O) which will cause corrosion to form down the road.

Hope this helps!!!
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Old 17th May 2011, 03:35 AM   #7
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wrong - acetone, other ketones can eat some common plastics, especially polycarbonate and polystyrene caps

isopropyl is safer, the 90% grade should be good for dissolving most organic residue

at worst I would carefully spot apply acetone only if and where the isopropyl wasn't working

water is perfectly fine on most assembed pcb - a 1st pass is a simple tap water/detergent cleaning with a toothbrush

distilled water, isopropyl rinses

the alcohol as a final rinse actually helps dry the board, parts, crevices by diluting the retained water and flows away more freely

still air blast, gentle heat or just leaving overnite to dry out any moisture can help

anyway distilled water is not a very good conductor if the board is properly clean

corrosion is only an issue if you still have conductive residue on the board

Last edited by jcx; 17th May 2011 at 03:43 AM.
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Old 17th May 2011, 03:43 AM   #8
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Quote:
Originally Posted by jcx View Post
wrong - acetone, other ketones can eat some common plastics, especially polycarbonate and polystyrene caps

isopropyl is safer, the 90% grade should be good for dissolving most organic residue

at worst I would carefully spot apply acetone only if and where the isopropyl wasn't working

water is perfectly fine on most assembed pcb - a 1st pass is a simple tap water/detergent cleaning with a toothbrush

distilled water, isopropyl rinses

the alcohol as a final rinse actually helps dry the board

still air blast, gentle heat or just leaving overnite to dry out any moisture can help

anyway distilled water is not a very good conductor if the board is properly clean

corrosion is only an issue if you still have conductive residue on the board
This is all true - usually not a problem around tube amps tho. Still - I would go with the alcohol too.
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Old 17th May 2011, 03:54 AM   #9
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I've heard some electronics fluxes can turn corrosive, but I've never experienced that myself. I've always used an old toothbrush and IPA. Running water for water-soluble flux. Followed by a compressed air blast. The OP's baked flux can probably be mostly rid of using a dental pick and the alcohol-toothbrush treatment.
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Old 17th May 2011, 04:07 AM   #10
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If acetone is used carefully, especialy BEFORE adding plastic components that are sensitive, it is superior to alcohol for this purpose.

Getting a good resin to coat your boards will seal in the clean!
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