and troubleshooting rough vacuum specifically, … educational seminar discusses creating,...
TRANSCRIPT
This educational seminar discusses creating, measuring, and troubleshooting Rough Vacuum.
Specifically, today’s talk will cover:• Brief review of Vacuum Fundamentals• Applications Using Rough Vacuum• Rough Vacuum Pumps• Rough Vacuum Gauges• Troubleshooting Rough Vacuum Applications• Summary and Preview of High Vacuum Webinar
Previous Webinar (Vacuum Fundamentals) is available for download at:http://www.agilent.com/en-us/training-events/eseminars/vacuum
Vacuum History Review
• Credited with first Vacuum Pump• Magdeburg Experiment (1657)
Von Guericke(1602-1686)
Varian Brothers (1898-1961)
• Vacuum Tubes for Radio & Radar applications (Klystron linear vacuum-tube amp)
• Invented ‘sputter-ion’ pump to improve tube life (1956)• Inventors of Nuclear Magnetic Resonance (NMR)
2010
Pressure: Molecular Collisions
Momentum transfer from a particle hitting a fixed surface creates a Force on the wall.
P = F/A
P1F1
F1 F2
PT
MOLECULAR FLOW VISCOUS FLOW (P < 1 mTorr) (P > 100 mTorr)
Flow Regimes: Viscous vs Molecular
Conductance in Viscous Flow (> 100 mTorr)
In Viscous Flow, the Conductance of a TUBE can be calculated using the formula:
C = 180 D4 x P/L (l/sec)D = Diameter of tube in cmL = Length in cmP = Pressure in Torr
L (cm)
D (cm)
Diameter Conductance (m3/hr)
¼” 0.151” (NW25) 37
1.5” (NW40) 1902” (NW50) 600
Snet = (C x S) (C + S)
Conductance of 1m (100 cm) tubing sizes at 500 mTorr
In Viscous Flow, the Conductance of a TUBE can be calculated using the formula:
L (cm)
D (cm)
Diameter Conductance (cfm)
¼” 0.11” (NW25) 22
1.5” (NW40) 1122” (NW50) 353
Conductance of 1m (100 cm) tubing sizes at 500 mTorr
Snet = (C x S) (C + S)
C = 180 D4 x P/L (l/sec)D = Diameter of tube in cmL = Length in cmP = Pressure in Torr
Conductance in Viscous Flow (> 100 mTorr)
Pressure Regions: Rough Vacuum UHV
Pressure (Torr)
Vacuum Pressure Regions
Rough Vacuum
UltraHigh
Vacuum
High Vacuum
Tran
sitio
n
Rough Vacuum Applications
Instrumentation & Mass Spec- ‘Backing’ High Vacuum Pumps- ‘Interface’ Pumping (Differential
Vacuum)
Vacuum Coating- Surface coatings for
decorative or structural properties
Detector
Rough Vacuum PumpEvacuates ‘Interface’ region to a few Torr AND acts as ‘Backing’ pump for the Turbo
1 x 10-3 Torr 1 x 10-5 Torr
1 – 3 Torr DUAL-INLET Turbo PumpsSingle Pump evacuates multiple vacuum regions at different pressures
Rough Vacuum Applications
Automotive- Leak Detection (AC & Engine)- Brake line filling
Water Removal- Insulation for Electrical
Transformers- Freeze Drying food and
pharmaceuticals
Rough Vacuum Applications
Heat Treatment (Furnaces)- Heating components under vacuum
to change mechanical properties
Vacuum Forming & Conveyance
Rough Vacuum ApplicationsSemiconductor Manufacturing
- Rough vacuum pumps are used for:• Initial pump down from atmosphere• Backing HV or UHV pumps• Wafer transfer and loadlock chambers.
VACUUM PUMP SELECTION
RANGE PUMP TYPE EXAMPLES
Rough Vacuum Atm - 10-3 Displacement
Pumps
Diaphragm PumpsRotary Vane PumpsOil-Free Scroll PumpsPiston PumpsScrew Pumps
High Vacuum 10-3 - 10-9 Displacement Pumps Capture Pumps
Diffusion PumpsTurbo Molecular PumpsCryo Pumps
Ultra High Vacuum < 10-10 Capture Pumps
Cryo Pumps, Ion PumpsSublimation Pumps
• ROUGH VACUUM pumps are most effective when gas is moving in VISCOUS FLOW
Displacement Pumps: Rough Vacuum
ROUGH VACUUM PUMPS
DIAPHRAGM PUMPS• Pressure differential created by deformation of elastic membrane allows gas
to enter the space above the piston• Inlet valve closes & exhaust valve opens (discharge to atmosphere or to inlet
of a second chamber)• Single and multi-stage models available
Limited base pressure Frequent replacement of
diaphragms (annual) Maintenance can be
complicated
Rough Vacuum: Oil-Sealed RVP
OIL-SEALED ROTARY VANE PUMPS• 1.5 m3/hr – 600 m3/hr• Molecules in VISCOUS FLOW enter the pump inlet• Gas is Isolated, Compressed (to above 760 Torr),
then Exhausted (or to 2nd stage)
Inlet Isolation Compression/Exhaust
Rough Vacuum: Oil-Free Scroll Pump
DRY SCROLL PUMPS (3 m3/hr – 35 m3/hr)• Compact, Oil-free pumps with high pump speed and low mTorr base pressure• Without OIL to achieve sealing, SCROLL PUMPS rely on (field replaceable)
TIP SEALS to achieve vacuum• Single and Dual Stage Versions available:
- Maintenance Simplicity vs Base Pressure!
15m3/hr • <50 dB15m3/hr• Hermetically Sealed
ROUGH VACUUM PUMPS
PISTON PUMPS • Piston pumps use coated PISTONS (eg.Teflon) and
CYLINDERS, and valving to achieve compression:- Inline, V-Twin, and Opposed Piston designs
Oil Free Initial Cost– Ultimate Vacuum– Maintenance
Oil Free Initial Cost Ultimate Vacuum– Maintenance
Displacement Pump Comparison
Diaphragm Pump
Oil-Sealed Rotary VanePump (RVP)
Oil-Free Scroll Pump
Oil FreePiston Pump
Oil Free Ultimate Vacuum Maintenance– Initial Cost
Initial Cost Ultimate Vacuum Oil
Oil Free Light Gases Audible Noise– Maintenance
RANGE GAUGE TYPE EXAMPLES
Rough Vacuum Atm - 10-3
Mechanical Deflection & Thermal Transfer Gauges
Capacitance ManometerThermocouple ConvectionPirani
High Vacuum 10-3 - 10-9 Mechanical Deflection
& Ionization Gauges
Capacitance ManometerHot Ion Gauge (BAG)Cold Cathode
Ultra High Vacuum < 10-10 Ionization Gauges &
Gas Analyzers
UHV Ionization GaugesIon Pump CurrentResidual Gas Analyzer (RGA)
Vacuum Measurement Technologies
- Different technologies are required to measure the vacuum pressure in different vacuum regions
Vacuum Measurement Technologies
GAUGE TECHNOLOGIES OVERLAP VACUUM REGIONS
Ultra High Vacuum High Vacuum Rough Vacuum
Mechanical Deflection Gauges
CAPACITANCE MANOMETER- DIAPHRAGM (between reference
and ‘test’ pressures) forms part of a capacitor circuit
- PRESSURE causes deflection which alters the capacitance) P C
- MOST ACCURATE and FASTEST RESPONSE gas independent gauge; Dynamic range ≈ 3.5
decades/gauge
Directly measure the physical force of gas molecules striking a surface
F1 F2
PT
Thermal Transfer Gauges
CONVECTION GAUGE- Maintain filament at constant T (above ambient): (P I)- Enhanced response time in viscous flow- Atm – < 1 x 10-3 Torr
THERMOCOUPLE GAUGE- Temperature of wire filament monitored at constant
Current (P T)- Slow response time; non linear above 2 - 5 Torr
Exploit the relationship between heat loss (through convection) and pressure
Thermal Transfer: Pirani Gauge
PIRANI GAUGEFilament (exposed to vacuum) forms one leg of a Wheatstone Bridge circuit;
• Loss of heat changes the resistance of the filament, unbalancing the bridge
• Voltage is applied to re-establish the balance: P Vapplied- Response is Gas Type Dependent (Gas
Correction factors required)- Extremely ‘non-linear’ above 1 Torr
Typical Pirani Gauge Response
Troubleshooting Rough Vacuum Systems
Time
Desorption
Pres
sure
(Tor
r) Volume
Diffusion
Pressure Decay
10+3
10-0
10-3
Troubleshooting Rough Vacuum Pumpdown
Monitoring the CHANGE in Pressure over Time can help to determine if there is a leak in the vacuum system
• A leak-tight system will display steadily decreasing slope until we reach the limits of the ROUGH VACUUM pumps
The slope of this line is proportional to the pumping speed
Time (min)0 5 15 2510 20 30
Pre
ssur
e (T
orr)
10+3
10+1
10-1
10-3
P
T Base Pressure
Troubleshooting Rough Vacuum Pumpdown
Time (min)0 5 15 2510 20 30
Pre
ssur
e (T
orr)
10+3
10+1
10-1
10-3
P
T
Monitoring the CHANGE in Pressure over Time can help to determine if there is a leak in the vacuum system
• A vacuum system with OUTGASSING issues will display a fairly constant rate of decrease in pressure over time
Base PressureOutgassing
Troubleshooting Rough Vacuum Pumpdown
Base Pressure
Time (min)0 5 15 2510 20 30
Pre
ssur
e (T
orr)
10+3
10+1
10-1
10-3
Real leak
Outgassing
Monitoring the CHANGE in Pressure over Time can help to determine if there is a leak in the vacuum system
• A vacuum system with a REAL LEAK will show a pressure change that drops, then flattens at the level of the leak
Rough Vacuum Troubleshooting: Rate of Rise TEST
Pres
sure
Time
TP
TP
Pre
ssur
e
Time
T
P
TPOutgassing/Virtual Leak:
- Rate of Rise (P/ T) DECREASES over time
Real Leak:- Rate of Rise (P/ T) remains
STEADY over time
Summary: Rough Vacuum Rough Vacuum Pumps (displacement pumps) require gas to be in
Viscous Flow to be effective. EFFECTIVE pumping speed approaches ZERO around 1 x 10-3 Torr.
Vacuum Pump choice depends on the importance to the user of:• Oil vs Oil-free Process• Base Pressure Requirements• Initial cost vs Lifetime Cost• Process Gas Limitations
Vacuum gauge selection depends on the accuracy required vs the cost. Gas dependent gauges require correction factor.
When approaching the lower limits of Rough Vacuum, OUTGASSING (Desorption and Diffusion) is the dominant factor (vs chamber volume)
Techniques for troubleshooting ROUGH VACUUM applications include Pumpdown Curves (P/T) and Rate-of-Rise or ‘Leak-Up’ Tests.
• Pump Speed at Operating Pressure• Maintenance Simplicity• Audible Noise
Vacuum Education Programs
For Information on Agilent’s Vacuum Technology Products and Services, please e-mail [email protected] or call 800-882 7426, and select option 3.
To learn about more Agilent Vacuum Technology Education programs, including• UHV Seminars at your institution• Scheduled multi-day classes in Vacuum Practice and Leak Detection• Custom multi-day classes at your site• Other custom training classes to fit your needs
Please e-mail Robin Arons ([email protected]), or call Customer Care at 800-882-7426 (Option 3) for more details on these programs
December 12, 2016
Confidentiality Label
29
Next Live Webinar: High Vacuum (Feb-7)
High Vacuum Webinar deals with the process of generating, measuring, and maintaining High Vacuum Pressure (10^-3 Torr to approx. 10^-8 Torr). ‘Roots’ type pumps (covering ‘Transition’ vacuum region) will also be discussed.Participants will learn about the benefits and drawbacks of different High Vacuum pump and Gauge technologies, and what to consider when constructing a vacuum system or troubleshooting leaks in the High Vacuum regime.
http://www.agilent.com/en-us/training-events/eseminars/vacuum
To Register, Visit: