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Need help finding high current drain on my PCB

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Kasper:
Just came across this IP68 waterproof LoRa sensor that reminded me of your product.  I wouldn't expect seeed to be great quality but it could help you get some ideas for waterproof antennas.

https://www.seeedstudio.com/Dragino-LSN50-V2-Waterproof-Long-Range-Wireless-LoRa-Sensor-Node-Support-868MHz-Frequency-p-4474.html

jmelson:
Interesting paper, thanks!
I am just wondering, what the HECK I have stumbled into doing right, so that I have almost NEVER run into this.
Now, I do my own reflow here, using a toaster oven with ramp-and-soak thermocouple controller, and reflow at the lowest temp I can get reliable melting at.  So, maybe the whole issue is crazy reflow profiles and very rapid heat-cool delta-T ramps.  And, maybe I'd never notice a capacitor leaking a few microamps, as I don't usually do battery-powered stuff.  But, I am just mystified as to why I have not run across this issue.  I have had exactly ONE capacitor that clearly was bad, and split into two pieces when replaced.

Jon

Kasper:

--- Quote from: jmelson on October 28, 2021, 06:45:31 pm ---Interesting paper, thanks!
I am just wondering, what the HECK I have stumbled into doing right, so that I have almost NEVER run into this.
Now, I do my own reflow here, using a toaster oven with ramp-and-soak thermocouple controller, and reflow at the lowest temp I can get reliable melting at.  So, maybe the whole issue is crazy reflow profiles and very rapid heat-cool delta-T ramps.  And, maybe I'd never notice a capacitor leaking a few microamps, as I don't usually do battery-powered stuff.  But, I am just mystified as to why I have not run across this issue.  I have had exactly ONE capacitor that clearly was bad, and split into two pieces when replaced.

Jon

--- End quote ---


I too am surprised how supposedly fragile ceramic caps are.  I used to solder avionics comms equipment.  We would hand solder lots of ceramic caps. We'd put them between legs on ICs, solder 0805s ontop of 0603s, etc. We'd do all sorts of mods because it was easier to certify and perform mods than it was to update a PCB and certify it.

sailah:

--- Quote from: mikeselectricstuff on October 25, 2021, 08:22:40 pm ---For production test, would it be easier to not connect the battery, charge the supercap and check that voltage was still above a certain value after a fixed tim, with the mcu in a test sleep mode?

--- End quote ---

Possible but that's not how we flash the firmware, not sure how we could calibrate that.  I'm sure that there's a calculation to figure out the voltage drop on a 0.47F cap over time given anything about say 10µA.  I suspect that 2.4mA is pretty simple to figure out, but what about 67µA?  Our cycle time on programming is about 20 secs.  Clearly the Keysight is the right tool for this job but I would need to get someone to program it to turn it on for a set amount of time and then switch off the outputs, measure.  Maybe not as big a deal but just one more thing...I need an easy button here :-DD


--- Quote from: Kasper on October 28, 2021, 05:22:56 pm ---Just came across this IP68 waterproof LoRa sensor that reminded me of your product.  I wouldn't expect seeed to be great quality but it could help you get some ideas for waterproof antennas.

https://www.seeedstudio.com/Dragino-LSN50-V2-Waterproof-Long-Range-Wireless-LoRa-Sensor-Node-Support-868MHz-Frequency-p-4474.html


--- End quote ---

Thanks, we have our device certified to IP67, although generally speaking we are strictly in an industrial environment or maybe outside in a pipe rack.  I have had instances where customers broke the antenna but usually it was from a ham-fisted installer.  In thousands of deployed devices maybe only a couple have broken.

Here's the latest in this saga, again, massive thanks to mystery EEVblog member who walked me through numerous debug steps.  Thanks and thanks to everyone else for their kindness and interest with a complete stranger.

I spoke to my CM, who was also a bit mystified at this issue.  They place millions and millions of caps every year and never had an issue.  I sent them the faulty device with the traces cut to the bad cap but no other modifications were performed.

I had approx 55 devices left from that production run so rather than test them all by unsoldering the supercap, I decided to swap out C13 to a comparable soft termination X7R cap from TDK.  I also sent CM a reel of these for our run.  Probably not necessary but I also switched C14 and C15 to soft caps as well, belt and suspenders.  I had to upgrade my soldering situation and got a soldering smoke collector from Weller, nice 10" microscope to verify solder joins, new flux from Chipquik.  I don't do a lot of soldering so it was helpful practice.  Most of my joints were pretty good and if they weren't I did them again.

The CM is going to make 50 devices with no supercap and ship them to me.  I will test all 50, flashed, on Keysight to verify sleep current.  If all 50 pass, I'll greenlight the rest of the run and send them back to be finished.

Thanks, Peter

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