I have a several chips (microcontroller, PIC16F1939) some of which have weird behavior (random resets, some pins pulled high some of the time). All of them are running the same software. I suspect that those chips have ESD damage (or some other internal damage). How can I be sure? X-ray? Any other method available?
Electronic – How to tell if a chip has ESD damage
esd
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I think #2 is quite plausible, especially since you mentioned plastic case. You probably generated some static electricity while handling the plastic case, and that got discharged thru the switch line. The switch is probably sticking out more than other things, so would be more likely to get zapped.
If this only happens when you first install the board in the case, then you can just ignore if necessary. However, something is marginal, and I'd want to make the system more robust. There are various options:
- Make the pulldown stiffer. If this unit is not battery powered, then changing the 10 kΩ to 1 kΩ is a easy thing to do. That will use 25 mW when the switch is pressed. If this is line powered, than that's irrelevant.
- Put a capacitor to ground on the switch line. This will require more charge on the line before it gets to a logic high level. A 1 uF ceramic is cheap and small. Even with the 10 kΩ pulldown, that's still only 10 ms time constant, so is irrelevant in human time.
- Put a R-C low pass filter after the switch and pulldown. For example, another 10 kΩ in series followed by 1 µF to ground. The extra delay is still irrelevant in human time since you have 10 ms time constant towards the switch on state and 20 ms towards the switch off state. This will definitely filter out short spikes, and provides additional impedance for the pin protection circuitry to work against.
If you measured in-circuit, chances are you measured something else. Gates must never be exposed externally as a high impedance and often the driver RdsOn is only 10 to 100x RdsOn of output stage depending on desired risetime and current levels for high power PWM switches.
For ESD protection, read this.
Best Answer
I don't know of an "easy" way to confirm ESD damage - there appear to be quite a few methods used to detect failure in ICs, all of them pretty expensive. They include X-ray, Microscopy, IR Thermal Analysis, Curve tracer, TDR, etc.
This sample report of failure analysis is quite informative, detailing several different methods used to (eventually) find a fault.
However, I would check the code carefully to make sure there isn't an intermittent bug responsible for what you are seeing, or a problem with your circuit (e.g. EMI, power supply problems, etc)
Maybe try a few simple test programs which replicates various parts of the full firmware and see if the problem is specific to one part (or is present all the time)
Also check on Microchips site for any known silicon issues, I have been caught by this a couple of times in the past.