Flux residue can be a good conductor. I clean boards with soapy water and a fine toothbrush
But what type of flux do you use, is it rosin type?
Just the normal solder reel and solder paste types.
Nice fireworks.
I’m pleased we don’t have to blame Kicad 
Maybe those chips aren’t all dead.
Maybe they didn’t respond because their power was shorted.
You will have to lift them all to get rid of all the flux.
Can’t electronics be an enjoyable pastime 
They have an internal voltage regulator for a low voltage core. This core cannot tolerate 5V
Difficult for me to see but, looking at the screenshot suggests checking:
Gap between Pads:
• Solder bridging (though seeing no resistance on meter)
• ‘Gap Width’ and possible arching at 1A
• Pads/solder looks fairly consistent except for the two in question (screenshot).
Quality of the PCB:
• Deformed/distorted traces (resulting in gap issue)
• Expansion of trace under (thermal) load, causing gap issue)
And, for sure, consider @davidsrsb recent post (re voltage regulator)
The list can go on and on and I’ve seen too many issues to list here and it happens in production with Pick&Place and Wave/flow soldering. Lessons learned keeps me from having anything to do with hand-soldered SMD.
No guarantee I’ll get to it but, if you post your files, I’ll consider doing a Thermal FEA (see my post )
I posted this earlier I’m the thread but it probably got lost in the weeds. My project zip file is located here:
https://drive.google.com/drive/folders/1rH_9bEHngeySth9yQ-QKCI5J5p1dckLf
By the way, are the traces too skimpy for 1A/5V? Use the Calculator tool as an aid.
How many layers on PCB?..
[EDIT] got the zip file…
Now I need to clean all three PCBs very well. 91% IPA doesn’t seem to work too well on this flux. Can somebody suggest a different method? I did a search online and people were suggesting things like paint thinner and other harsh chemicals.
Also, I need suggestions on how to remove these SSOPs. I ruined the pins on the one I took off the board in the video. I’m afraid the uC on the first board is probably dead since I wasn’t limiting current on that one. I saw a video of somebody using something called “Chip Quik” low temperature solder. Can I purchase this product at a local store? I’d like to get working on these boards this weekend so I don’t want to order online and wait around…
By the way, I processed the return on Amazon for my flux. Today was the last day of the return period, so I just barely beat it.
You first have to figure out which type of flux you have.
Some flux types are water soluble
I used the calculator during my layout design. I think they’re ok. I don’t think I’ll be drawing a full Amp anyway though
The flux I used is Rosin Activated.
I started the Thermal FEA and while waiting for an almost endless time, what caught my attention (relating to my question about trace widths):
• I think the trace width is too narrow (marginal, at best).
• Proximity of trace to pad is narrower than trace width, suggesting too close.
Using the calculator (assuming Cu is 18um) and estimating a Max Temp rise of 65º C (150ºF, adding the Ambient of 70ºF = 220ºF). Is perhaps too much for the PCB, and calculated widths of 7.4mil.
And, that’s for External traces. But, with conformal coating, I’m thinking you should reconsider the trace widths and proximity, mentioned above.
Might be a fun test, if you have a Temperature Measurement tool and measure Temp when it smokes…
Thanks for running this analysis on my PCB. I’ll keep the spacing between traces in mind when I’m designing version 2 of this board.
Just want to point out though that this spacing wasn’t what caused the shorting, it was most definitely the flux. Remember, I had the same short problem on an SSOP protoboard.
Thanks everyone for your help with this. I now have a working, populated board.
I don’t see a way to mark a reply as the “solution”, but it would be jmk’s post from 9/3.
This one:
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I would put something like a LED across the core voltage capacitor to prevent the voltage exceeding the absolute maximum
edit you want to prevent Vcap exceeding 2V, so a green LED is about right
Congratulations and well done!
Hmm, if you look at https://www.lifewire.com/types-of-solder-flux-818849 there is a caution for organic acid flux. Then if you look at the back label of the product you have https://www.amazon.com/MG-Chemicals-Rosin-Paste-8342-50G/dp/B01MS04SO4/ it says it contains succinic acid and suberic acid in addition to rosin.
It would be interesting if you could experiment with a dab of your flux on a pair of adjacent pads that are powered on a sacrificial board. I find it surprising that such a low voltage can cause arcing through this kind of flux, but I can believe it.
One more thing,
Superglue (cyanoacrylate adhesive) will cause the same problem even at 5v. The smoke just smells far worse. Don’t even keep it in the same room as your electronics.
Another lesson I learnt many years ago along with soldering irons and flux and … oh!, the list is far too long to continue.
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Long time ago I read a story about someone who made his own flux from kitchen ingredients. Main ingredient was citric acid and water, combined with something that made it a bit less runny. Part of the goal was to only use ingredients which dreadily dissove in water, so it’s easy to clean by washing with water.
There is nothing wrong with cleaning PCB’s with water, soap and a brush, if you do it right.
Most important is to let it dry thoroughly before applying voltage.
Another thing that may help is to make the water a bit more conductive to prevent ESD buildup, although this is probably not very important, but don’t hurt either. Just a bit of regular table salt will do for this.
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