›Chambers & Weldments

Nor-Cal Europe products has earned a reputation as a world-class manufacturer of high and ultra-high vacuum chambers. The quality, appearance and performance of our chambers are unequaled. We supply single chambers designed from customer specifications for university or national laboratory research projects, as well as production quantity chambers that are built-to-print for equipment manufacturers. Thin-film deposition and compound semiconductor processing are common applications for our high-vacuum, O-ring sealed chambers that operate at pressures down to 1x10-9 mbar. Vacuum fired 316L stainless steel, electropolishing and metal seals are recommended for ultra-high vacuum surface science chambers that operate at pressures in the 1x10-11 mbar range. Nor-Cal can fabricate vacuum chambers up to approximately 5 x 5 x 5 feet (1.52 x 1.52 x 1.52 Meters) with doors, stands, water jackets and Mumetal shields. (Consult the factory for exact capabilities.) We offer a complete line of vacuum chamber accessories that include load locks, sample transfer and positioning devices, liquid and electrical feedthroughs, viewports and roughing components.

Manufacturing

Machining procedures are consistent with good UHV practices. Machine coolant is sulfur-free to reduce outgassing. All Nor-Cal components are designed to minimize entrapments that cause virtual leaks under vacuum. State-of-the-art CNC machining equipment is used to produce parts with consistently high quality.

GTAW fusion welding is used exclusively for a vacuum-tight metal bond. Purging with an inert gas reduces or eliminates oxygen entrainment and carbide precipitation that cause outgassing. Whenever possible welds are made on the inside, or are full penetration to eliminate entrapments and virtual leaks. External stitch welds are used in conjunction with internal vacuum welds for structural reinforcement, as necessary.

Materials

Nor-Cal Europe products uses 304 stainless steel tubing, spheres or roll-ups to fabricate vacuum vessels; however, 304L, 316, 316L or 316LN stainless steel can also be supplied. We have found that optimal vacuum performance can be obtained by using 2B rolled sheet with no secondary grinding for the body followed by electropolishing after ports are welded. Normally our standard material is dual certified 304/304L low carbon range stainless steel.

Flanges and baseplates are made from 304 stainless steel that has been specially treated to remove impurities inherent in 300 series steels. Special UHV-flanges 4 ½ inches (114.3mm) OD and smaller can be made from 304 electroslag remelt (ESR) bar stock. ESR is a refining process that produces stainless steel with higher purity, fewer inclusions and more uniform grain structure to eliminate microscopic leak paths.

Our standard flange material is certified to meet ASTM A-240 and has less than 0.01% sulfur to prevent sulfur stringers. Grain size is 3 to 6 per ASTM E-112. Maximum inclusion size is 2.5 per ASTM E-45. Roll-forged rings, Mumetal, aluminum and other materials can be supplied upon request.

Cleaning

A biodegradable detergent is used to remove machine lubricants before the parts are washed and rinsed with deionized water. Nor-Cal offers in-house bead blasting, chem cleaning and electropolishing of vacuum chambers. Glass shot cleans, hones, polishes and peens while removing scale. Some customers request bead blast on the exterior of the chamber with electropolish on the interior.

Electropolishing is considered the most desirable cleaning and surface conditioning process for stainless steel vacuum chambers. It is an electrochemical process that benefits the finished part in a number of ways simultaneously. Deburring, passivation and stress relieving are achieved while the machine-produced surface roughness is eroded. Electropolishing attacks the microscopic “peaks” of the surface more rapidly than the “valleys”; thereby maintaining critical dimensions while improving surface finishes. Normally .0003 to .0004 inches (.00762 to .01016mm) would be removed to lower the microfinish from 32 to 8 RMS. Electropolishing a 2B stainless steel rolled sheet achieves approximately a 90% reduction in surface area. This is most important for vacuum chambers because it produces faster pumpdown and a lower base pressure. In addition to the improved mechanical properties of the surface, iron is removed electrochemically. This leaves the surface rich in chromium and nickel, which have extremely low vapor pressures. The result is the lowest outgassing rates possible from stainless steel. Having an in-house facility allows Nor-Cal to do multi-step electropolish in order to reduce “shadowed” areas on chambers with difficult geometries. Our electropolish tanks can accommodate chambers up to 60 x 50 x 65 inches (1.52 x 1.27 x 1.65 Meters).

All stainless steel parts are descaled and passivated in an acid solution to remove weld scale and other oxide layers. This process leaves the surface free from most contaminants that might impact the vacuum environment or promote intergranular corrosion. (Contact our factory for Ion Chromatography (I.C.) test data.) Chem cleaning can be used as a final cleaning step for chambers up to 35 x 53 x 33 inches (889 x 1346.2 x 838.2mm) to remove organic and metallic contaminants. The chamber is immersed in a series of controlled chemical baths and deionised water rinses and dried using filtered air. Chem cleaning results in the cleanest surface possible for ultra high vacuum components. (Contact our factory for I.C. test data.).

Inspection

Nor-Cal uses the most up-to-date equipment and procedures for the inspection of vacuum chambers. Every weld is leak checked with a helium mass spectrometer to insure leak rates of 1x10-9 mbar l/sec. or less. Mechanical inspection is accomplished with a coordinate measuring machine (CMM). We can provide our customers with CMM inspection reports of their chambers on request.

Our chamber qualification and test equipment is available to customers for an additional fee who request residual gas analysis (RGA) scans and leak checks of their chamber after vacuum baking. The test equipment includes vacuum pumps, gauges, RGA, quartz heaters, nitrogen back fill and a leak detector. Chamber bake out is achieved with high intensity infrared radiant lamps that are strategically placed throughout the chamber. Baking under vacuum removes high and low molecular weight volatile compounds. Non-water cooled UHV chambers are typically baked for at least 24 hours at 150˚C.(The maximum temperature of system components such as seals, chamber materials, valves, etc. may limit maximum baking temperatures.) Uniform bakeout temperature is achieved by wrapping the associated system components in high temperature fiberglass materials.

After cool down our RGA will provide partial pressure data, determining the level of residual volatile compounds. Typical scans produce atomic mass levels below 1x10-9 mbar for atomic masses greater than or equal to 44. Total system pressures are between 5x10-9 and 7x10-10 mbar. Chamber design, seals and pumps used, and the maximum bake temperature over time effect the residual gas composition and ultimate pressures reached. Following chamber scanning, chambers are leak tested using a NIST traceable helium mass spectrometer leak detector with a final allowable leak rate of 1x10-10 mbar l/sec. or less.

Frames

Frames are usually constructed from 1½ or 2 inch (38.1 or 28.8mm) mild steel box tubing, which is powder coated. However, aluminum or a variety of other materials are available. In addition to leveling pads and castor wheels, we can design and fabricate frames with precision rotational and linear bearings for moving components, such as chamber lids. Integrated hoist assemblies, pump mounting, cabinets and panel rack mounting are also available.

System Integration

Nor-Cal can assemble an entire system including chamber, frame, pumps, gauges, valves, manipulators and other components to customer specifications in our 1,100 square foot, class 1000, final assembly area. After completion our vacuum technicians can complete a thorough system qualification, including bake out, RGA scan and leak check using the procedures described above. Additionally, a functional test is performed on all system hardware.

Packaging

Vacuum chambers and other large components are packaged appropriately for truck, ship or airfreight to our customer’s location. Unless specified otherwise, flanges are covered with aluminum foil to prevent internal contamination and scratching of the flange faces. Protective plastic covers are placed over the foil for additional protection. The chamber is then wrapped in 4 mil plastic and placed in a wooden crate. Foam is injected into plastic “pillows” which expand to fill the voids in the crate, suspending the chamber inside. Depending on customer specifications for systems, after qualification the chambers can be disassembled or purged with nitrogen gas, clean room packaged and shipped. Alternatively, some chambers have been packaged and shipped under vacuum.