This educational seminar discusses creating, measuring, and troubleshooting Rough Vacuum.

Transcription

1 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:

2 Vacuum History Review Von Guericke ( ) Varian Brothers ( ) Credited with first Vacuum Pump Magdeburg Experiment (1657) 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

3 Pressure: Molecular Collisions Momentum transfer from a particle hitting a fixed surface creates a Force on the wall. P = F/A P P T 1 F 1 F 1 F 2 Flow Regimes: Viscous vs Molecular MOLECULAR FLOW VISCOUS FLOW (P < 1 mtorr) (P > 100 mtorr)

4 Conductance in Viscous Flow (> 100 mtorr) D (cm) L (cm) In Viscous Flow, the Conductance of a TUBE can be calculated using the formula: C = 180 D 4 x P/L (l/sec) S net = (C x S) (C + S) D = Diameter of tube in cm L = Length in cm P = Pressure in Torr Conductance of 1m (100 cm) tubing sizes at 500 mtorr Diameter Conductance (m 3 /hr) ¼ (NW25) (NW40) (NW50) 600

5 Conductance in Viscous Flow (> 100 mtorr) D (cm) L (cm) In Viscous Flow, the Conductance of a TUBE can be calculated using the formula: S net = (C x S) (C + S) C = 180 D 4 x P/L (l/sec) D = Diameter of tube in cm L = Length in cm P = Pressure in Torr Conductance of 1m (100 cm) tubing sizes at 500 mtorr Diameter Conductance (cfm) ¼ (NW25) (NW40) (NW50) 353

6 Pressure Regions: Rough Vacuum UHV Vacuum Pressure Regions Ultra High Vacuum High Vacuum Transition Rough Vacuum Pressure (Torr)

7 Rough Vacuum Applications Instrumentation & Mass Spec - Backing High Vacuum Pumps - Interface Pumping (Differential Vacuum) Vacuum Coating - Surface coatings for decorative or structural properties 1 x 10-3 Torr 1 x 10-5 Torr Detector 1 3 Torr DUAL-INLET Turbo Pumps Single Pump evacuates multiple vacuum regions at different pressures Rough Vacuum Pump Evacuates Interface region to a few Torr AND acts as Backing pump for the Turbo

8 Rough Vacuum Applications Automotive - Leak Detection (AC & Engine) - Brake line filling Water Removal - Insulation for Electrical Transformers - Freeze Drying food and pharmaceuticals

9 Rough Vacuum Applications Heat Treatment (Furnaces) - Heating components under vacuum to change mechanical properties Vacuum Forming & Conveyance

10 Rough Vacuum Applications Semiconductor Manufacturing - Rough vacuum pumps are used for: Initial pump down from atmosphere Backing HV or UHV pumps Wafer transfer and loadlock chambers.

11 VACUUM PUMP SELECTION ROUGH VACUUM pumps are most effective when gas is moving in VISCOUS FLOW RANGE PUMP TYPE EXAMPLES Rough Vacuum Atm - Displacement 10-3 Pumps High Vacuum Displacement Pumps Capture Pumps Diaphragm Pumps Rotary Vane Pumps Oil-Free Scroll Pumps Piston Pumps Screw Pumps Diffusion Pumps Turbo Molecular Pumps Cryo Pumps Ultra High Vacuum < Capture Pumps Cryo Pumps, Ion Pumps Sublimation Pumps

12 Displacement Pumps: Rough Vacuum

13 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

14 Rough Vacuum: Oil-Sealed RVP OIL-SEALED ROTARY VANE PUMPS 1.5 m 3 /hr 600 m 3 /hr Molecules in VISCOUS FLOW enter the pump inlet Gas is Isolated, Compressed (to above 760 Torr), then Exhausted (or to 2 nd stage) Inlet Isolation Compression/Exhaust

15 Rough Vacuum: Oil-Free Scroll Pump DRY SCROLL PUMPS (3 m 3 /hr 35 m 3 /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! 15m 3 /hr <50 db15m3/hr Hermetically Sealed

16 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

17 Displacement Pump Comparison Diaphragm Pump Oil-Sealed Rotary Vane Pump (RVP) Oil-Free Scroll Pump Oil Free Piston Pump Oil Free Ultimate Vacuum Maintenance Initial Cost Initial Cost Ultimate Vacuum Oil Oil Free Initial Cost Ultimate Vacuum Maintenance Oil Free Light Gases Audible Noise Maintenance

18 Vacuum Measurement Technologies - Different technologies are required to measure the vacuum pressure in different vacuum regions RANGE GAUGE TYPE EXAMPLES Rough Vacuum Atm Mechanical Deflection & Thermal Transfer Gauges Capacitance Manometer Thermocouple Convection Pirani High Vacuum Ultra High Vacuum Mechanical Deflection & Ionization Gauges < Ionization Gauges & Gas Analyzers Capacitance Manometer Hot Ion Gauge (BAG) Cold Cathode UHV Ionization Gauges Ion Pump Current Residual Gas Analyzer (RGA)

19 Vacuum Measurement Technologies GAUGE TECHNOLOGIES OVERLAP VACUUM REGIONS Ultra High Vacuum High Vacuum Rough Vacuum

20 Mechanical Deflection Gauges Directly measure the physical force of gas molecules striking a surface P T F 1 F 2 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

21 Thermal Transfer Gauges Exploit the relationship between heat loss (through convection) and pressure 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

22 Thermal Transfer: Pirani Gauge PIRANI GAUGE Filament (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 V applied - Response is Gas Type Dependent (Gas Correction factors required) - Extremely non-linear above 1 Torr Typical Pirani Gauge Response

23 Troubleshooting Rough Vacuum Systems Pressure (Torr) Volume Desorption Diffusion Pressure Decay Time

24 Troubleshooting Rough Vacuum Pumpdown Pressure (Torr) P 10-3 T The slope of this line is proportional to the pumping speed Base Pressure Time (min) 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

25 Troubleshooting Rough Vacuum Pumpdown Pressure (Torr) P T Outgassing Base Pressure Time (min) 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

26 Troubleshooting Rough Vacuum Pumpdown Pressure (Torr) Real leak Outgassing Base Pressure Time (min) 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

27 Rough Vacuum Troubleshooting: Rate of Rise TEST Outgassing/Virtual Leak: - Rate of Rise ( P/ T) DECREASES over time Pressure T P T P Time Real Leak: - Rate of Rise ( P/ T) remains STEADY over time Pressure P T P T Time

28 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 Pump Speed at Operating Pressure Maintenance Simplicity Audible Noise 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.

29 Vacuum Education Programs For Information on Agilent s Vacuum Technology Products and Services, please vpl-customercare@agilent.com or call , 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 Robin Arons (robin.arons@agilent.com), or call Customer Care at (Option 3) for more details on these programs Confidentiality Label December 12,

30 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. To Register, Visit: