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

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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. .

Tony Smith LHCb Velo Hybrid Meeting CERN 29/07/04


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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

Tony Smith LHCb Velo Hybrid Meeting CERN 29/07/04


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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

Tony Smith LHCb Velo Hybrid Meeting CERN 29/07/04


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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

Tony Smith LHCb Velo Hybrid Meeting CERN 29/07/04


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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.

Tony Smith LHCb Velo Hybrid Meeting CERN 29/07/04


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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 T&G

Rfanout detector end

Tony Smith LHCb Velo Hybrid Meeting CERN 29/07/04


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VELO HYBRID STATUS

HT TEST

Hybrid + short cable tested together in Vac Tank

Hybrid populated with decoupling caps (2*500v 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

Tony Smith LHCb Velo Hybrid Meeting CERN 29/07/04


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