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TRT ROD Update

TRT ROD Update. Colin Gay. Spares. 8 Spares are mostly working The issue that keeps them from being usable is that typically 1 of the NSEs is not functioning correctly Rest of the board looks good Tried some local investigation, but haven’t isolated the cause

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TRT ROD Update

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  1. TRT ROD Update Colin Gay

  2. Spares • 8 Spares are mostly working • The issue that keeps them from being usable is that typically 1 of the NSEs is not functioning correctly • Rest of the board looks good • Tried some local investigation, but haven’t isolated the cause • We’ve spent some time xraying the NSEs (working and not) as well as some other chips to evaluate the quality of the solder joints • Recall – for the spares, we moved to an all lead-free solder process, consistent with requirements at the fabrication time of the second set of boards Colin Gay

  3. Spares • However, the only part that was not available in a lead-free version was the NSE • We took the approach of removing the leaded solder balls and reballing the chips with lead-free solder • (Recall lead-free solder melts at a higher temperature than leaded) • Not entirely surprising that any issues would be with the parts that have been through the most heating cycles .... Colin Gay

  4. Spares Colin Gay

  5. Colin Gay

  6. Middle region (no balls for our size NSE) Colin Gay

  7. Spares • Focus of xray is in centre of image, so there is some parallax at edges • However, some balls near corners seem a bit elongated • Not sure if this is an issue or not • Some strange effects in middle section – see images • The 128k NSE chip we use does not have the balls in the middle square filled – only the outer 3 rows are needed • The larger sized 256k uses those balls for extra power. We added pads to the board in case we decided we needed the larger size chip. • However, there are some odd blobs in that area that we don’t understand Colin Gay

  8. Spares Will remove a few (non working!) chips and visually inspect Plan to reball NSE and try to replace. If successful, will try to recover all the 8 boards. Colin Gay

  9. Clock Sync studies Have not been able to reproduce the rare loss-of-sync that happens on a few boards at high occupancy Tried playing with power to board, but no success in creating a similar effect yet Have new function generator arriving next week (delivery is about 6 weeks late) that will let us play with input clocks in a more controlled manner to try to reproduce the effect If we get the last spares working, this will help in testing statistics – one board may be more stable than ones on a timing edge, etc … Colin Gay

  10. Firmware modifications • 23-bit firmware ready for large-scale testing • Passes all local tests • If works in full system, should be able to make a version that can be configured to run either 27 bit or 23 bit, selectable at runtime (I think the extra logic needed to switch at runtime should not affect the data unpacking path enough to throw off the timing margins) • Hardcoding of top 20 or so patterns, to avoid NSE lookup not yet implemented • Clock speedup for NSE to increase bandwidth needed at highest occupancy • Sometimes reduced timing margins need creative solutions to eliminate logic layers and help optimize the place/routing Colin Gay

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