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Soldering and replacing SMD LEDS

john.r2

Mar 27, 2023
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I want to replace some SMD led's on a PCB. Last time I did it, some sort of residue builds up around the area that becomes very crusty and i'm not sure if that residue is bad to keep on the board and maybe it causes the board to detoriate? Question, how can I prevent his? I've tried cleaning with rubbing alcohol wipes but didn't seem to help. can the surround area not be masked or covered with something to prevent this?
 

kellys_eye

Jun 25, 2010
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Residue? Do you mean solder FLUX perhaps? This is usually easily removed using IPA (isopropylalcohol). It's corrosive by nature so should be removed.
 

john.r2

Mar 27, 2023
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Residue? Do you mean solder FLUX perhaps? This is usually easily removed using IPA (isopropylalcohol). It's corrosive by nature so should be removed.
Yes it may be flux, but i dont actually put any flux, i just de-solder and put new LED in but the surrounding area gets like a glaze around it and after a while it kind of turns into a cloudy white layer that you can scrape off.

If i need isopropylalcohol, how do I apply and clan it? considering the residue isn't always visible straight away until it becomes cloudy. I'd have to buy some IPA. By any chance does electronic sensor cleaning spray help? I have Mass Air Flow sensor cleaning spray and wondering if squirty some of that on the board can help?
 
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kellys_eye

Jun 25, 2010
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If you use solder and/or flux when replacing the LEDs (you should) then it will have a flux core (presumably, some use liquid flux too) otherwise the stuff you're seeing is possibly 'glue' that they use to stick the LEDs to the board before they solder-reflow (or IR heat) the board to fix/solder them in place.

Not sure what's in those other cleaning items you state - check the contents label - but IPA is, or should be, standard stuff in any well equipped workshop.
 

john.r2

Mar 27, 2023
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If you use solder and/or flux when replacing the LEDs (you should) then it will have a flux core (presumably, some use liquid flux too) otherwise the stuff you're seeing is possibly 'glue' that they use to stick the LEDs to the board before they solder-reflow (or IR heat) the board to fix/solder them in place.

Not sure what's in those other cleaning items you state - check the contents label - but IPA is, or should be, standard stuff in any well equipped workshop.

Yes I use solder wire on the two points to mount the LED. So the solder possibly contains flux? I've ordered some IPA. Is there a way to use this? can I just wipe down the entire area? do i have to avoid touching the LED and other SMD components?
 

kellys_eye

Jun 25, 2010
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do i have to avoid touching the LED and other SMD components?
No, IPA is no threat to components and should evaporate quite quickly after application anyway. I use a cotton bud stick to apply/wipe the stuff on.
 

Delta Prime

Jul 29, 2020
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After populating my board both surface mount and through hole components I always use a Ultra Sonic, Sonicator with variable frequency & heater just put the PCB in the sonicator cover components special Care should be taken if you're using electrolytics capacitors,you can immerse them,just don't cover the vents on top.
I use99.9%ethyl alcohol EtOH. After about a hundred runs I usually pause just because the unused ethyl alcohol makes very good punch to share with colleagues. ;)
 
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