CERN 15.02.2013ATLAS ID Week: TRT ROD Update

Colin Gay

University of British Columbia

TRT ROD Update

Colin Gay

CERN 15.02.2013ATLAS ID Week: TRT ROD Update

Colin Gay

University of British Columbia 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• 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

CERN 15.02.2013ATLAS ID Week: TRT ROD Update

Colin Gay

University of British Columbia Colin Gay

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 ....

CERN 15.02.2013ATLAS ID Week: TRT ROD Update

Colin Gay

University of British Columbia Colin Gay

Spares

CERN 15.02.2013ATLAS ID Week: TRT ROD Update

Colin Gay

University of British Columbia Colin Gay

CERN 15.02.2013ATLAS ID Week: TRT ROD Update

Colin Gay

University of British Columbia Colin Gay

Middle region (no balls for our size NSE)

CERN 15.02.2013ATLAS ID Week: TRT ROD Update

Colin Gay

University of British Columbia Colin Gay

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

CERN 15.02.2013ATLAS ID Week: TRT ROD Update

Colin Gay

University of British Columbia Colin Gay

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.

CERN 15.02.2013ATLAS ID Week: TRT ROD Update

Colin Gay

University of British Columbia Colin Gay

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 …

CERN 15.02.2013ATLAS ID Week: TRT ROD Update

Colin Gay

University of British Columbia Colin Gay

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