We have a series of 5mm LED display boards that use the ATTINY87. This series of boards has been in production for about 1.5 years. In the past 3 days, we have had a roughly 25% failure rate of what appear to be nonfunctional/corrupt MCU’s. The series uses the internal 8MHz clock. To keep things simple, the focus will be on 2 failures I found:
Here is a photo of one of the failures: (the 6 pin ISP header is on the right, C11 is a bypass cap)
We have 5 stations in production where the MCU’s are programmed. At one of these stations, I looked at 6 boards with Atmel studio. (these boards had not been programmed before) The programmer is a MK-II programmer modified to supply 5V to the MCU. On two of the boards, I could not read the device ID. After some probing with the oscilloscope, I could see the clock and data going to the MCU from the MK-II, but no data was coming back to the MK-II. Here are some things I have tried:
-The 5V to the MCU seems stable. I added a 0.47uF cap across the 5V lines, no change.
-In case the fuse settings had been changed to an external clock, I added a 1MHz, 5V square wave signal to pin 14, no change.
-A debug wire connection (using the AVR dragon) was tried. No connection could be made.
-The reset pin of the MCU seems to be stable at 5V.
-I asked the tech to replace the MCUs and once that was done, the boards could be programmed and were testing normal.
Some of the other failures from production are rather interesting. (Production uses a batch file on the network to program hex file and fuses in one step) Several boards had the fuses set to an external clock. Once I set the clock back to the internal RC oscillator, the flash data had the repeating pattern of “FFFF0000”. Others had a hex file or parts of a hex file I could not identify. (all of the hex files we have are on the network, so they are easily searchable)
The only thing I can think of is bad parts from manufacturer or that we some got counterfeit parts. (The parts and reel do not appear to counterfeit)
This is an image of the reel sticker:
Right now, I’m out of ideas on the possible cause of failures. Any thoughts would be helpful.