When a controller goes up in smoke, engineers learn never
to assume the other guy has done his job
Several years ago I managed a group in a fab-less company which did audio product IC design. At the time we were designing an AC-97 controller and an AC-97 codec. The controller design and chip floor plan layout was completed and went into DRC (design rule check). Everything passed all the checks required for the design tool being used, and for the CMOS design process being used at the selected fab.
A few weeks later, the part came back from the fab late one afternoon. We stayed late, wanting to know if we had a live and kicking part. We applied power, and watched in horror as the part rapidly overheated and went up in smoke. Thinking something was wrong with the setup, and assuring ourselves nothing was, power was applied to another part. Poof ! The same result. Basically we had one great big diode conducting lots of current..and getting hot very fast.
So everyone trudged home quite mystified as to the problem.
Soon thereafter we began a microscopic view of the die from a de-capped package. What we found was massive amounts of signal lines tied together at different areas of the die. No way was the part designed that way, and any tests we had done prior to sending out to the fab would have caught such a major mess.
Without going into the days of effort that followed, we finally found out that all the connections that were tied together had identical first 16 characters of the 32 character node names used in the design.
Turns out we had upgraded our design tools to match the fab, but the mask maker contractor had not caught up at the time. They were still using 16 character node names. So, when 16 characters matched, the mask maker connected the nodes in the mask layers together.
Once the mask was corrected using 32 character node names....we had a good part.
Lesson: Double check anyone and anything in all the steps from design to fab. Don't assume the other guy has done his job.
KD Boyce has nearly 40 years experience in electronic systems design and semiconductor technical marketing. Further info may be found here.