Hi guys,
I'm having a strange issue with some ATtiny25 SOIC chips programmed with Arduino IDE and flashed with a USBasp. I made a few kits, each kit involving 4 mcus.
These kits were designed for a specific car application (LED lightning) and I tested every circuit after assembly. Everything was OK on my side, on the bench.
Design is kinda simple... 4 boards per kit, one LM1117-5 and ATtiny25 on each board, transistors, LEDs etc... They are designed to work "in pair" (2 boards sandwiched together") sharing a common ground and having their own +12v input.
A while ago I sent the first kit from France to Germany. The other kits leaved for the US. Once arrived in Germany the guy there tested the boards before installing them in his car, and all boards were defective. He assured me he did respect polarities, and I'd like to trust him.
He sent the boards back to me and this is what I discovered:
Pair 1 :
PCB 1: ATtiny KO - not responding to USBasp/Arduino as ISP programmers
PCB 2: ATtiny KO - not responding to USBasp/Arduino as ISP programmers
Pair 2 :
PCB 3: ATtiny KO - not responding to USBasp/Arduino as ISP programmers
PCB 4: ATtiny KO - overheating and shorted (didn't got on fire I guess thanks to the LM1117 overcurrent protection)
On PCB 4 a high power LED was also fried and I had to replace it. That leads me to say that particular board was shorted or polarity was reversed one way or another.
So I sent my own boards to that guy, and started repairing his boards for myself.
Then he received the 2nd kit and again... They are defective:
Pair 1
PCB 1 - Working
PCB 2 - KO
Pair 2
PCB 3 - KO
PCB 4 - Working
What the hell could fry an ATtiny like this? The LM1117-5 have their decoupling capacitors on the input and output. Also I tested my own board on my own car and it works, being the same car I doubt the car itself could be the root cause.
I also doubt French or German posts use gamma rays on parcels. X-rays maybe but would this be a problem anyway? We all order stuff from China and items usually work OK
All boards were sealed in antistatic bags and protected with paper towel for shipping and they don't look physically damaged.
Did anyone here have a similar issue while shipping programmed chips by mail?