Author Topic: Can flux cause shorts?  (Read 8775 times)

catfud

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Can flux cause shorts?
« on: October 25, 2013, 12:12:38 PM »
Probably a really silly question, but can excess flux cause a short circuit? Just trying to figure out the cause of a temporary short circuit...

Mike B.

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Re: Can flux cause shorts?
« Reply #1 on: October 25, 2013, 12:17:46 PM »
Flux is non-conductive - at least at the supply voltages of a pedal.

catfud

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Re: Can flux cause shorts?
« Reply #2 on: October 25, 2013, 12:42:38 PM »
Flux is non-conductive - at least at the supply voltages of a pedal.

Thanks Mike, that makes sense. If there's loads of flux left on the board after soldering that I haven't cleaned off, small bits of cut-off metal from my work surface could stick more easily to it. That could explain the short.

What's the right thing to use for cleaning flux off a board? Would isopropanol do the trick?

Mike B.

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Re: Can flux cause shorts?
« Reply #3 on: October 25, 2013, 01:42:52 PM »
Isopropyl alcohol works great, but try to get the 90% not the 70%. Also, I use an old toothbrush with the alcohol and scrub lightly on the board to make sure there aren't any tiny droplets of solder between the traces.

pickdropper

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Re: Can flux cause shorts?
« Reply #4 on: October 25, 2013, 02:06:00 PM »
Yep, 90%+ purity isopropyl alcohol works well.  It may take a few passes with it as it tends to leave the board a bit sticky.

Flux remover works better but is more expensive.  I often use both.  I start with flux remover to get most of it off and then do a second pass with alcohol.
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catfud

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Re: Can flux cause shorts?
« Reply #5 on: October 25, 2013, 02:25:58 PM »
I've got some 99.7% isopropyl alcohol and come to think of it I probably need a new toothbrush, so will clean my boards after soldering now. I'll look up flux cleaner (first time I heard of it!)

If it saves some time in the test stage it'll be well worth it, thanks guys!

alanp

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Re: Can flux cause shorts?
« Reply #6 on: October 25, 2013, 02:39:14 PM »
If flux did short, I'd be in huge trouble!
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Re: Can flux cause shorts?
« Reply #7 on: October 30, 2013, 07:56:13 PM »
Flux isn't really a big deal for operation unless you are doing RF/Microwave circuits and you are either using water/alcohol/rosin flux.  You shouldn't be using Acid flux (as used for plumbing) because that stuff WILL eat your board and you will have a bad day. 

Alcohol and a toothbrush is a popular way to remove flux.  Bonus points for rinsing and then blowing off with compressed air.

I also find that Simple Green as a solution works awesome for removing flux.  I have a cheap-o (Harbor Freight store) Ultrasonic cleaner which I use to clean PCB's along with Isopropyl or Simple Green diluted.  Just make sure what you are putting in there is sealed.  I try to take out ICs and any switches but most discrete components and transistors are fine in a bath.  I make a solution, get the water heated, and toss the board in for a few minutes.  Works great!

If you leave it on, no biggie.  It just looks horrid. 



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pickdropper

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Re: Can flux cause shorts?
« Reply #8 on: October 31, 2013, 10:34:33 PM »
Flux isn't really a big deal for operation unless you are doing RF/Microwave circuits and you are either using water/alcohol/rosin flux.  You shouldn't be using Acid flux (as used for plumbing) because that stuff WILL eat your board and you will have a bad day. 

Alcohol and a toothbrush is a popular way to remove flux.  Bonus points for rinsing and then blowing off with compressed air.

I also find that Simple Green as a solution works awesome for removing flux.  I have a cheap-o (Harbor Freight store) Ultrasonic cleaner which I use to clean PCB's along with Isopropyl or Simple Green diluted.  Just make sure what you are putting in there is sealed.  I try to take out ICs and any switches but most discrete components and transistors are fine in a bath.  I make a solution, get the water heated, and toss the board in for a few minutes.  Works great!

If you leave it on, no biggie.  It just looks horrid.

Yeah, flux can cause nightmares on RF boards.  I have one at work that goes to the board house with strict No Clean / No Wash instructions.  They want to wash everything because it looks better, so we have to make sure they don't forget that.
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Bret608

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Re: Can flux cause shorts?
« Reply #9 on: November 01, 2013, 07:52:25 AM »
One of the electronics instructors where I work told me that although flux is non-conductive, over time it can pick up a bit of dust as it's just a tiny bit sticky. That can cause some slight noisiness. I just gently scrape it out anywhere it's touching two adjacent pads. I did not know about the bath idea! May have to try it at some point.

muddyfox

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Re: Can flux cause shorts?
« Reply #10 on: December 22, 2013, 05:31:36 AM »

I'm just gonna piggyback here...
So what do you guys do after cleaning with IPA? Just dry it off or run it under some tap/distilled water as well?

pickdropper

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Re: Can flux cause shorts?
« Reply #11 on: December 22, 2013, 08:00:43 AM »
I take a can of compressed air and blow out underneath all of the chips so that the flux that's been washed away doesn't stay trapped underneath.

Other than that, I usually just let it dry.  If you do wash it with water, it's probably safer to use distilled.
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davent

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Re: Can flux cause shorts?
« Reply #12 on: December 22, 2013, 10:35:44 AM »
For the little bit of flux i find, i pop it off with a dental pick, always found i was chasing my tail with the alcohol, keep needing more and more, the flux spreading further and further, sticky sticky sticky. Pop it free, brush it off with a cutoff little paint brush or compressed air, done.  Works really well on solder lugs, eyelet and turrets.
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jimilee

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Re: Can flux cause shorts?
« Reply #13 on: December 22, 2013, 01:08:12 PM »


I'm just gonna piggyback here...
So what do you guys do after cleaning with IPA? Just dry it off or run it under some tap/distilled water as well?
Dishwasher works great! No no no I'm joking I just let it air dry, doesn't take that long. I wouldn't run any water on it. Honestly I'd your solder contains flux, there's no real reason to worry about it.
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