General question about failure analysis

[Christopher4187]

Melanie,

Thanks for the reply. I currently don't use a protective coating over the PCB when it's finished being soldered. Do you think this may have contributed to the failure? I am guessing it would be a good idea to spray a coating over the board before it is shipped. What do you think?

Thanks,

Chris

[Melanie]

Most of our boards don't have any conformal coating, so that should not have any effect on reliability.

This really is a wide-open question... namely "What caused the PIC to fail"?

1. Was it a Microchip manufacturing defect? Most Unlikely but still could be...
2. Was it a poor hardware design? Only you can answer that.
3. Was it a software conflicting with the Hardware design (eg pin set to Output when it should be an input)? Again only you can answer that one.
4. Was it mishandled in shipping? Probably unlikely, these things would tend to blow an input port, rather than cause an output short.
5. Was it the customer poking test probes or screwdrivers around the board? Well was it?
6. Was it a customer miss-wire that he's denying? Most of mine fell into this category!
7. Was there some ambient condition that caused the failure? By ambient, static or EMP or high levels of localised high-power RF or excessive damp... But those again tend to blow-up input ports and not short outputs...
8. Has the customer taken out the PIC, tried to read the program and put it back in the socket initially the wrong-way round so Power Supply pins now don't line up and destroy the pins they are now connected to... Yes, I've had this happen too... if it's on a socket, someone, somewhere will unplug it sometime...

Well, there's the list... it's probably one of those... but which one?

[Christopher4187]

Melanie,

Thanks for the reply. Since it's my first failure, I am not too worried about it but I am concerned. To replace it, it costs $1.25 plus my labor of 5 minutes. I'll just keep an eye on the problem to see if it happens again. As a side note, they have miswired the positive and negative leads but I have protection for that. The unit works fine after this happens. I'll chalk this one up to the customer damaging it because it worked fine when it l tested it.

Chris