For boards you are cleaning for rework and repair…
I was told by a solder manufacturer that if you dissolved Ascorbic Acid (the active ingredient in the cheap Vitamin C tablets) in your Isopropyl Alcohol, it dealt with any oxidation of the copper, tin, zinc etc and vastly improved solderability. I tried it a number of times and got very good results.
You need to wash the board again in 99% IPA to remove the acidity and flux after the rework.
If your board doesn’t mind being immersed, just fill a bath with pure IPA and leave the board in this for 20 minutes. Cleaning is then much easier, often even unnecessary.
My experience of no clean fluxes is that YOU DON’T NEED TO CLEAN THEM, even on high frequency products or where you need high PCB isolation. 42 Deg C daytime temperature up to 100% humidity (our weather station sometimes says 105% but this is Africa!!) and 6 million units manufactured. “No clean” fluxes are fussy when soldering and dont like oxidised leads or pads. I prefer Eutectic solder with old fashioned rosin and a Weller No 7 for my hobby work.
During the monsoon in Phoenix the humidity went high enough to make the flux on my project conduct. I cleaned it with 77% IPA initially but the water they used was not DI water and you could see a residue (like the "new and improved" Windex). A lot of the cleaning agent companies have cheaped out, hoping we wouldn't notice, on process water the last few years. When I switched to 99.97% IPA my projects started coming out looking good. I let them dry out in the sun for 8 hours before trying to power anything up. If you put them in a glass box here they get to 150 degrees F during the day and right now the relative humidity is 7%. Its not a vacuum oven but close enough for my projects.
guys, i took Bean's advice long ago and bought a cheap ultrasonic jewelery cleaner. I put 99% ipa in it and submerge the boards and run till clean. This is how i clean all the boards i was assembling for him and others.
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It's Only A Stupid Question If You Have Not Googled It First!!
As tempting as it may be, you should never use flammable liquids in an ultrasonic cleaner! Every cleaner I've seen warns against it, due to the fire hazard.
Brian Carpenter said...
guys, i took Bean's advice long ago and bought a cheap ultrasonic jewelery cleaner. I put 99% ipa in it and submerge the boards and run till clean. This is how i clean all the boards i was assembling for him and others.
There should be a disclaimer in your statement. "Cleaning a board with a crystal on it, in a ultrasonic cleaner is not recommended."
Best bet is put it in an enclosure, if you can't see it it want bother you. That'll free you mind to worry about something serous like toe nail fungus.
SRLM said...
On a related note, are there any recommendations for conformative coating? After I clean my board I'd like it to stay that way [noparse]:)[/noparse]
Others may feel differently but if you think you'll ever need to to any repairs or rework in the future I would stay away from any coatings unless you absolutely have to use it because of moisture problems or other issues.· Any boards coated with that can be a PITA to work on.· Just because the board has a coating on it doesn't mean that it still won't be a magnet for dust, etc and it will probably still get dirty too.· As someone else mentioned try to use an enclosure or at least use some compressed air to blow off the dust every once in a while.
Industry practice is NOT to use an ultrasonic to clean ANY board with an active device - transistors, IC's, etc. They may damage the sensitive wirebonds used to package the active device.
I've done rework on boards that were conformal coated and didn't have much trouble with it. In my experience, you can pretty much just pretend that it's not there. Some conformal coats are a magnet for dust, though, especially the ones that stay soft. I've switched to a harder polystyrene coating that doesn't seem to have this issue. For marine and industrial environments, conformal coatings are de rigueur, but for indoor home or office environments, they have little extra benefit to offer.
BTW, before spraying a conformal coat, tape over any connectors, switches, and other components that you don't want coated or which the spray could seep into. I use blue or green masking tape for this. There are also liquid latex formulations that can be brushed on or applied from a squeeze bottle. When spraying, be generous with the application, spraying from all directions to reach every nook and cranny on the board. Follow the directions on the can for application temperature and for timing second and subsequent coats. And by all means clean the nozzle when you're done, else you'll end up tossing a partly-used can. BUT MOST IMPORTANT OF ALL, USE ADEQUATE VENTILATION! The volatiles in these products are truly nasty!
Comments
I was told by a solder manufacturer that if you dissolved Ascorbic Acid (the active ingredient in the cheap Vitamin C tablets) in your Isopropyl Alcohol, it dealt with any oxidation of the copper, tin, zinc etc and vastly improved solderability. I tried it a number of times and got very good results.
You need to wash the board again in 99% IPA to remove the acidity and flux after the rework.
If your board doesn’t mind being immersed, just fill a bath with pure IPA and leave the board in this for 20 minutes. Cleaning is then much easier, often even unnecessary.
My experience of no clean fluxes is that YOU DON’T NEED TO CLEAN THEM, even on high frequency products or where you need high PCB isolation. 42 Deg C daytime temperature up to 100% humidity (our weather station sometimes says 105% but this is Africa!!) and 6 million units manufactured. “No clean” fluxes are fussy when soldering and dont like oxidised leads or pads. I prefer Eutectic solder with old fashioned rosin and a Weller No 7 for my hobby work.
You can tell how old fashioned I am.
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It's Only A Stupid Question If You Have Not Googled It First!!
-Phil
91% -- Cheap, does remove flux, leaves greasy film (possibly conductive)
99% -- Expensive and works better, still seeing slight film.
both burn cuts on hands. [noparse]:)[/noparse]
OBC
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Post Edited (Oldbitcollector) : 5/8/2009 2:52:07 AM GMT
There should be a disclaimer in your statement. "Cleaning a board with a crystal on it, in a ultrasonic cleaner is not recommended."
It can kill some crystals. So readers be aware.
James L
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James L
Partner/Designer
Lil Brother SMT Assembly Services
Robert
BTW, before spraying a conformal coat, tape over any connectors, switches, and other components that you don't want coated or which the spray could seep into. I use blue or green masking tape for this. There are also liquid latex formulations that can be brushed on or applied from a squeeze bottle. When spraying, be generous with the application, spraying from all directions to reach every nook and cranny on the board. Follow the directions on the can for application temperature and for timing second and subsequent coats. And by all means clean the nozzle when you're done, else you'll end up tossing a partly-used can. BUT MOST IMPORTANT OF ALL, USE ADEQUATE VENTILATION! The volatiles in these products are truly nasty!
-Phil