Presentation on theme: "Stave Hybrid Status Ashley Greenall 1. Current Status Current build of hybrids (Version 3) distributed to 6(+1) sites: Cambridge, DESY, Freiburg, LBL,"— Presentation transcript:
Current Status Current build of hybrids (Version 3) distributed to 6(+1) sites: Cambridge, DESY, Freiburg, LBL, Liverpool and Santa Cruz Glasgow outstanding but pieces available once their jig sets made Used as Mechanicals (gluing studies, wire-bonding) Leading to electrical test fixtures (DAQ evaluation) Will ultimately lead to module assembly Recently received another 60 off circuits stuffed with passives 59 passed visual One single failure – solder splash on bond pad Quality of soldering very good Electrical performance of hybrids indicates no show stoppers BUT there are features Identified ‘break’ in Wshunt Disable line on hybrid (affects group of 9 asics in a single column) Affects operation of PPB slow control on stavelet – no other problems identified Fix is trivial – requires addition of a single wire bond on a hybrid Studies of shield-less hybrid show performance is not as expected See following slides 2
Dtnoise at 1fC L1A/COM Regular pattern seen in Occ. on shield-less hybrid Affects single (outer) column 0 of hybrid only Not present on neighbouring column 1 2-3 BCOs width Not seen on shielded type hybrid Test done using L1A sent down COM line of hybrid Shield-less Hybrid 3 Dtnoise at 1fC using L1A line L1A now sent down its own dedicated line on hybrid Now see a different Occ. profile (compared to above) Again only seen on column 0 Likewise not seen on shielded hybrid In both instances this noise profile is not seen when conducting 3PT Gain scans.
Detailed view of the Dtnoise plots shows discrete occupancy peaks at differing locations. For the COM line, 4 discrete peaks per asic location: Strip pitch is ~75µm, noise peaks are 375µm wide Corresponds to ~5 channels Via geometry is 380µm land Outlying occ. peaks are 20 channels apart, 1.5mm Outlying via separation is 1.43mm (c-to-c) Likewise for the L1A line, 3 peaks with similar geometry profile as above Outlying occ. peaks are 10 channels apart, 750µm Outlying via separation is 750µm (c-to-c) Points to noise injection from the vias No evidence of pickup from bus traces 20 channels ~5 channels 1.43mm ~10 channels L1A lineCOM line 750µm 4 Shield-less Hybrid source of the noise
Hybrids are glued onto sensor asymmetrically w.r.t. Sensor strips Simply done to ensure asic-to-sensor wire bonding geometry is correct COM & L1A vias are sited directly above the column 0 strips, not the case for column 1 strips Hence noise injection only seen on the one column of strips Column 1 strips terminate here (at asic edge) Column 0 strips terminate adjacent to opposite column readout asics Clearly passing under the vias 5 Shield-less Hybrid – why pickup on one column per hybrid
Shield-less Hybrid Performance – Why is it happening? Ground + Top layer Power and Ground layers of hybrids have voids around the signal trace vias Drill span is 1 to 4 i.e. plated-thru-holes through all four layers (done to keep the build simple & cost down) Vias are not blind – results in them ‘exposed’ on underside (up against sensor) with only glue layer separation Whereas for the shielded hybrid, bottom shield layer is not perforated – vias are blind up to layer 4 Shield layer does it’s job – no evidence of pick up with this flavour of hybrid Via patterning clearly seen through solder resist Patterning is due to asic vacuum holes on FR4 carrier leaving imprint 6 Shield + Top layer Via patterning not so obvious Solder resist removed to expose Cu of shield layer Shield-less Shielded Fix would be to simply make signal vias (top 2 layers) blind for shield-less hybrid Will result in a non-perforated ground (shield) layer
What next – near term Planning for a new submission of the hybrid early September Could go earlier BUT past experience of submitting during vacation time is not good Hope to get layout files finalised by beginning of August Will draw up a list of changes would like to take on board for this new submission and circulate Feedback from users would be useful about changes they would like to see Known changes are 1.‘Fix’ to Wshunt Disable line 2.Addressing minor issues regarding solder resist - in some cases makes wire-bonding difficult (Problem with BJ820 deep-access head) 3.Likewise relocate a small number of bond pads 4.Complete rethink of hybrid cut out tabs – after reflow cause the hybrid edges to rise Consider also extending the (sacrificial) tabs for module retainment within their frames i.e. glue these to frame 5.Will re-visit Shield-less hybrid – address signal vias on top 2 layers to make blind 6.Rigid FR4 former (flex circuit glued to) will revert back to be plated (was not for version 3) – issue with warping Plating should compensate for the warping Submission in September should result in hybrid availability late October Which will then need to go for passive stuffing - expect their availability November 7
What next – longer term Preparing for ABC130 – hybrid issues Proposal is for the topology of hybrid to change from 2 column asic readout to a single column Assume that this is the default What level of redundancy will be taken on board Duplicate CLK/COM buses etc. Sensor HV spec. Assume it is 500V + overhead – impacts on layout due to HV clearances Propose a first attempt at hybrid layout with best guess of uncertainties Use realistic number of lines (CLK. COM. Data distribution) ABC130, HCC, Powering asic footprints Useful exercise as it could be used to feedback optimal locating of asic pad locations Further material reductions Number of layers we can get away with and build detail (Kapton/Cu thicknesses etc.) Use of hatching Whilst maintaining yield/manufacturability 8