Sophisticated PCBA, with a DM6446 using two 16 bits DDR2 devices to implement a 32 bit memory space. On some boards, we see a stuck bit on either bit 24 or bit 8, which map to the same BGA ball (C8) on the two different devices. Of the known-bad boards, 12/12 have this failure mode (either bit 8 or bit 24 stuck).
Sent one board out for cross-section & SEM. Reliability lab says the solder ball did not wet the pad, so electrically open.
Did a die and pry on a second board with the same failure mode. All balls on the two devices are good, except for ball C8 on both devices. On one device, the joint is half failed; on the other device, full failure.
Anyone ever see anything like this?
Best Answer
Perhaps a long shot, but maybe inspect a few dozen of the RAM chips under scope for any sign of C8 pad defect?