EEVblog Electronics Community Forum
Electronics => Manufacturing & Assembly => Topic started by: jmelson on October 05, 2017, 08:31:37 pm
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I got some ChipQuik leaded solder for a project that required leaded solder. The soldering looked great, but there was a lot of flux residue left after reflow.
We have to clean these boards thoroughly anyway, as they have 400 V across 34 SMT capacitors, and need leakage to be around 10 nA total for all the caps.
Well, I've been having a HORRIBLE time getting them to pass the leakage test. I have cleaned most of these board 5+ cycles in ethanol with an ultrasonic cleaner.
I still have bad leakage, and it gets 10X worse when it is humid here.
I'm now cleaning with methanol, just to see if that performs better.
Anybody have suggestions on how to do better?
Thanks,
Jon
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I just thinner with alcohol mixed and brush it with a tooth brush. Then use pcb spray or something similar to do a last lean and let drip down dry.
Works for me.
Www.Georgehobby.wordpress.com
Equipments: DSO104z, Hakko FX888D
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Use the part number to look up the datasheet. Chip Quick makes several kinds of solder with several kinds of fluxes.
What you have there could be no clean, no clean water soluble (which as you might guess must be washed with water), or rosin.
If the board MUST be washed after assembly, try to choose a flux that is designed to be washed off. Some of the no clean residues are optimized for not being cleaned and will not as easily be removed.
Rosin and many synthetic flux resins are soluble in ethanol, but the tiny bits of salts leftover from flux turning copper/tin oxides into ions and/or from many inorganic acids which may be added will not be soluble in ethanol. It may be sufficient to add small ratio of water to the ethanol. If your standards are high enough, you might need to do multiple baths... ethanol, then deionized water (plus maybe degreaser/detergent). And maybe finish with alcohol, again, just for drying.
I still have bad leakage, and it gets 10X worse when it is humid here.
Any bare salt left on the board will increase in conductivity with humidity, which can happen with improper cleaning of any flux residue. With enough water, salt dissolves into conductive ions. But this is esp noticeable if you are using a flux with a water soluble residue (which you have not completely removed). Depending on the application, improper/incomplete cleaning is often worse than not cleaning. Taking a close look around component leads under the microscope can give you another clue as to what you're dealing with. Dry tin/copper salts are white.
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What is the key content of the course?
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Thanks, KL27x, I did an ultrasonic wash in ethanol/water/detergent mixture. This left leakage higher due to absorbed water. Then, I did several cleaning cycles with pure ethanol, some ultrasonic and then brushing with a toothbrush and spritzing with ethanol, Finally, dry at 50 C for a couple hours in an oven, and it seems to have solved the problem.
Thanks a bunch!
Jon