VELO HYBRID STATUS

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VELO HYBRID STATUS
SUBSTRATES
CONSTRUCTION of composite SUBSTRATE best
flatness obtained with TPG central core 400um
woven layer of CF prepreg each side oriented -45
degrees 125um nominal woven layer of CF prepreg
each side oriented 0,90 degrees 125um
nominal Total thickness 900um Two Lamination
methods tried in vac bag and autoclave
at Liverpool - some voids and Flat to 200um
Thickness 900um - 30um
randomly distributed in PCB press at
Stevenage Circuits very flat, still some very
small voids Thickness
870um at centre 40um at edges but smooth taper
Obvious loss of epoxy at
the edges not considered a problem
small voids could be filled with epoxy
flat to the extent that it
floats on air when placed on a flat surface
on either side. .
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VELO HYBRID STATUS
SUBSTRATES 2
LAMINATION of circuits Two Adhesives tried
STAYSTIK 672 75um 130 degs BONDPLY (polyimide
used for PCB lamination) 35um 160degs Staystik
sample dished 500um but good surface finish
good adhesion but circuit peels
easily at the edges
Thickness 1.38 1.47 It is not known if
substrate contributed to dishing. Bondply sample
good flatness but surface finish shows voids in
substrate - good adhesion Thickness 1.35
1.36 BUT the sample
showed delamination of the TPG
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VELO HYBRID STATUS
SUBSTRATES 3
DELAMINATION of TPG considered a serious
problem Note that the failures at the edges all
appeared to be due to laminar cracks in the TPG
rather than a failure of the bond between the tpg
and the CF facings New substrates made with a
CF frame approx 4mm wide around TPG TPG is
cut to a smaller size and CF prepreg strips
placed around the edges This bonds the CF
facings at the edges and relieves the outward
stress on the TPG. Lamination was done in vac
bag and autoclave at Liverpool Circuits were
bonded using Bondply and there were no signs of
delamination at the edges. Unfortunately the
cutouts in the side were not machined out so the
lamination pressure would not have been
even. There is a small area on one side where the
circuit has obviously been pressed hard, as seen
from its taking up the pattern of the holes in
the substrate however there is a failure of the
adhesive at this point. Given that this is a
localised problem and all other areas seem to be
bonded very well it is thought that it is
possible that there was some contamination from
the profiling process. Substrates will be
thoroughly cleaned before lamination in future

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VELO HYBRID STATUS
Population
The two substrates laminated at Stevenage will
be sent back to them and laser cut rather than
using CNC milling. One will have holes filled
with BN loaded Epoxy to planarise it. Need to
create CAD data for profiling Monday 2nd
August These will be laminated with good K04
circuits on one side and failed circuits on the
other side. 4 more prepared for lamination by
wed 11 August INVENTORY of parts 2 laminated
substrates 4 TPG cores in stock, 100 On order
for delivery by end October Sufficient CF
prepreg for many Substrates but will be past use
date for main build 9 good K04 circuits and 3
failed ones at Stevenage
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VELO HYBRID STATUS
Population
Population of circuits Final pop will be
done using solder paste stencilled onto circuit
and reflowed setup for this will take too long
to use this method for beamtest (Will need some
iteration with the company to get jigging
right they normally silk screen full panels
populate them and then cut/ break
out individual boards. ) For October beamtest
components will be soldered in house.
Standard solder paste and indium solder
paste will be tried. Components available for
population of 4 single sided modules
(connector limited
lots of other comps) One more set of short
tails available.
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VELO HYBRID STATUS
Fanouts
Fanout designs for Phi and R both completed All
locations are different, drawn in sets of 4
One complete set of Phi and R on one sheet Will
make 6 sheets by 20th August Gold on copper on
upilex 22um min TG
Rfanout detector end
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VELO HYBRID STATUS
HT TEST
Hybrid short cable tested together in Vac
Tank Hybrid populated with decoupling caps
(2500v 10nf to Gnd) Guard and HT shorted
together All lines except HT and Guard on HT
connector shorted to ground (includes Power) 1meg
ohms in both HT and return lines 0- 420 volts
leakage current steady at 0.2nA (temporary 0.3 at
90V) Discharges observed at 430V (2.3nA typical
several seconds period) Baseline 0.2nA 440V
500V discharges of up to 15nA almost every
reading above 460V Back down to 430 then up onset
of discharges at 480V Regular discharges at 520V
and baseline 0.5nA Down to 510 no discharges,
baseline back to 0.2nA Up to 550 discharges of
6nA down to 530 no discharges Baseline 0.3nA Left
at 500V and after 1 hour baseline 4nA no
discharges Up to 510V (discharges) and back down
baseline returns to 0.2nA
SEEMS TO RESPOND TO TRAINING NEED LONGER
TESTS