M. WONG PIXEL MECHANICAL GROUP MEETING 14 JAN 2002

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10% Model Outgassing Rate Measurement

• Model building status• Setup• Method explanation

– Throughput method w/ variable conductance

– Rate-of-rise method

M. WONG PIXEL MECHANICAL GROUP MEETING 14 JAN 2002

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Assembly Status – Shingled Substrate

M. WONG PIXEL MECHANICAL GROUP MEETING 14 JAN 2002

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Assembly Status – Dummy Silicon

• Silicon assembly– ROC– Sensor– HDI

• Almost complete

M. WONG PIXEL MECHANICAL GROUP MEETING 14 JAN 2002

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Assembly Status

• Substrate to be modified to fit dummy silicon assemblies

M. WONG PIXEL MECHANICAL GROUP MEETING 14 JAN 2002

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Test Setup - Chamber

• Stainless steel• 19.5 inches ID• 66 inches length

M. WONG PIXEL MECHANICAL GROUP MEETING 14 JAN 2002

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Test Setup – Vacuum Vessel

• 3 turbo pumps in parallel

• Total pumping speed 2550 L/sec

• Fixed & rotating disk dividing chamber into 2 volumes

• Rotating disk with different sized holes

M. WONG PIXEL MECHANICAL GROUP MEETING 14 JAN 2002

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Test Setup – Vacuum Vessel

• Volume 1 (w/ sample) = 50” length• Volume 2 = 16” length• RGA

M. WONG PIXEL MECHANICAL GROUP MEETING 14 JAN 2002

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Test Setup – Variable Conductance

• Rotate disk to different pumping speeds between volumes

• 2”, 2”+3”, 6”• Largest A~500

cm2

• Blank (no seals between disks)

M. WONG PIXEL MECHANICAL GROUP MEETING 14 JAN 2002

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Methods to measure gas load

• Throughput method with variable conductance– Measurements at

pressures between 10-3 & 10-

6 torr– Extrapolate to 10-7

torr (test can’t reach this)

• Rate-of-rise method– Cross-check

measurements from throughput method

M. WONG PIXEL MECHANICAL GROUP MEETING 14 JAN 2002

10

Throughput method w/ variable conductance

• For a given orifice size:Q=P1S=P2Spump

&

pumpS1

C1

S1

M. WONG PIXEL MECHANICAL GROUP MEETING 14 JAN 2002

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Assumptions• Q = nd – na

where Q = outgassing rate

nd = desorption rate

na = adsorption rate

• Outgassing rate is dependent on chamber pressure

• Decrease pressure, decrease na, more accurate measure of Q

M. WONG PIXEL MECHANICAL GROUP MEETING 14 JAN 2002

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Capability of Test Setup

• When the orifice size changes, what happens to:– P1

– ratio of sample surface area (~3 m2) to effective area of pumping orifice (S/11.6 L/sec-cm2)

M. WONG PIXEL MECHANICAL GROUP MEETING 14 JAN 2002

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Assumptions in Test Design

• Constant gas load of 0.01 torr-L/sec (Q is independent of P1)

• Outgassing rate of test chamber is negligible

• Flow through orifice is air @ room temperature

M. WONG PIXEL MECHANICAL GROUP MEETING 14 JAN 2002

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Varying pumping speedd

(in)d (cm) A

(cm2)C

(L/s)S

(L/s)P1

(torr)

Ratio

Blank Blank ~10 ~10 1.0e-3 30,000

2 5.08 20.3 235 215 4.7e-5 1600

2+3 65.9 760 600 1.7e-5 580

6 15.2 182.0 2120 1200 8.3e-6 290

Large ~500 ~5000 ~1800 5.6e-6 190

Ratio = sample surface area (3m2) : effective area of pumping orifice

M. WONG PIXEL MECHANICAL GROUP MEETING 14 JAN 2002

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Rate-of-Rise Method

• Different than previous rate-of-rise test• Use same test chamber • Use largest orifice

– P1 settles at steady-state condition

• Then, change to blank position– Long settling time– Measure outgassing rate at beginning of transient– Use as a cross-check for throughput method