atlasuhv

CASE STUDY: Atlas Aluminum Vacuum Chambers with Titanium/Aluminum Bimetal Flanges used in Lightweight UHV Suitcases

Fri, 20 Jun 2025 20:43:25 GMT

VolkVac Instruments teamed up with Atlas Technologies to develop lightweight UHV suitcases that are used to transport delicate samples long distances while under vacuum.

THE CHALLENGE:

Our customer, VolkVac Instruments, needed a UHV chamber small enough and light enough to easily carry by hand and that

could connect to another UHV chamber to allow transfer of samples under vacuum to a chamber in a new location. The sample handoff had to occur without opening the chambers or requiring bake-out. And the chamber had to be completely non-magnetic to allow transport of samples with delicate magnetic properties.

THE SOLUTION:

Atlas Technologies machined a vacuum chamber out of a single, solid block of aluminum for enhanced vacuum integrity. Then Atlas bimetal aluminum titanium flanges were welded to multiple ports of the chamber to allow connection to different vacuum systems. VolkVac fitted the chamber with passive and battery-powered vacuum pumps to maintain UHV pressure.

WHAT MAKES A UHV SUITCASE SO SPECIAL?

UHV suitcases solve a critical issue for researchers and others who need to move delicate samples from one ultra high vacuum (UHV) system to another without contamination or loss of vacuum pressure. Some UHV experiments are self-contained, but others require the cutting-edge analytical techniques available at large facilities such as synchrotrons, free-electron lasers and neutron sources.

Normally, fabricating a UHV sample in one place and studying it in another involves breaking the vacuum to remove and transport the sample. This creates two problems. First, exposing a sample to air may change or destroy its material properties. Second, the opened UHV chamber must be baked out before it can be used again — and a bakeout can take a few hours for an aluminum chamber, or several days for a stainless-steel chamber – significantly delaying critical projects.

These problems can be avoided by connecting a portable UHV system (called a UHV suitcase) to the main vacuum chamber and then transferring the sample into the UHV suitcase. The suitcase can then be used to move the sample down the hall, across campus, or around the world – where it can then be transferred to another UHV system.

PORTABLE UHV CHAMBERS FEATURE MULTIPLE PUMPS

VolkVac founder, PhD physicist Igor Pinchuk, explained further. “The idea of a UHV suitcase is not new. Researchers have been creating their own rough but workable solutions for decades”. The earliest iterations were simply standard vacuum chambers that were disconnected from one UHV system and then quickly wheeled to another — without being pumped.

This has changed in recent years with the arrival of new materials, vacuum pumps, pump controllers and batteries. It is now possible to create a lightweight, portable UHV chamber with a combination of passive and battery-powered pumps. Having an integrated pump is crucial because it is the only way to maintain a true UHV environment during transport.

Because pumps, controllers and batteries must be a part of each UHV suitcase, the material used to create the chamber of a UHV suitcase must be as light as possible to keep the overall weight to a minimum.

ALUMINUM UHV SUITCASES ARE ULTRALIGHT AND NON-MAGNETIC TOO

While commercial designs have improved significantly over the past two decades, many UHV suitcases are still heavy and

unwieldy. To address these shortcomings, VolkVac Instruments developed the ULSC ultralight aluminum suitcase, which weighs

less than 10 kg, and an even lighter version – the ULSC-R –which weighs in at less than 7 kg.

The use of a custom Atlas aluminum chamber with bimetal aluminum-titanium flanges is integral to the success of VolkVac’s

UHV suitcases. Aluminum was used instead of stainless steel, another common chamber material, as aluminum is lighter and

much easier to machine. The chambers for the UHV suitcases were efficiently machined from a single piece of aluminum for

increased integrity. The lightweight material is also non-magnetic. This allows the suitcases to be used to transport samples with

delicate magnetic properties.

BIMETAL ALUMINUM/TITANIUM FLANGES COMPLETE THE CHAMBER

Access to UHV chambers is provided by conflat (CF) flanges which have sharp edges that are driven into a copper-ring gasket to create an exceptionally airtight seal. While aluminum is the best material for making UHV suitcase chambers, it is too soft to provide durable long-lasting sharp knife edges on flanges. That’s why VolkVac came to Atlas Technologies — our expertise in dissimilar metal bonding and fabrication as well as aluminum chamber development. Atlas fabricated the aluminum flanges with titanium knife-edges. Using aluminum and titanium ensured that the suitcases would be non-magnetic as well as lightweight.

ATLAS AND VOLKVAC WORKED CLOSELY TO OPTIMIZE THE NEW SUITCASES

Jimmy Stewart, Technical Sales Manager at Atlas, coordinated the collaboration with VolkVac. Jimmy explained that VolkVac

continues to work very closely with Atlas’s lead machinist and lead engineer to develop the suitcase chambers. Several chambers

have now been manufactured, with more in the works. Stewart said “This close relationship is necessary because bimetal materials have special requirements when it comes to welding and stress relief. We often work like this with our customers across various industries to produce the specialized equipment they require.”

“Because of the historical use of stainless steel in UHV systems, some customers are unfamiliar with bimetal components. They may have heard about the benefits of bimetal,” says Stewart, “but they don’t have the expertise. And that’s why they come to us — for our 30 years of experience and in-depth knowledge of bimetal and aluminum vacuum.” Pinchuk agrees. “I know stainless steel UHV technology forwards and backwards, but now I’m benefitting from Atlas’s expertise in aluminum chambers and bimetal

technology for my latest products.”

Next Generation Vacuum Systems: Aluminum

Thu, 03 Oct 2024 21:19:16 GMT

Written by: Richard Bothell and Justin Bothell, Atlas Technologies; Glen Tisdale, Judith Offerle, UHV Aluminum Company

Achieving sub-micron feature sizes on a production basis requires an understanding of the complete processing environment including the vacuum reactor itself. Molecular level chemical contamination demands that all processes factor in the vacuum environment. The vacuum system base pressures are a critical parameter in determining the environmental contribution to wafer contamination. Actual processing levels may be decades above the base pressure, but the base pressure establishes the environmental noise of the system.

Ultra high vacuum (UHV) base pressures reduce the contamination contribution of the vacuum environment. For example, at high vacuum levels (~10 -9 Torr), mono-layer formation takes hours. In order to control molecular level contamination of sub-micron features, UHV base pressure environments must be considered.

One concern with producing UHV environments in aluminum vacuum systems is the cost of the massive pumping required to overcome o-ring seal leaks and vacuum surface outgassing. And to consider stainless steel UHV systems means that cycle times will be increased due to bake out and pump down times. Stainless is a notorious water sponge at these levels and iron and chromium contamination is an issue as well. In addition, stainless systems are heavy and require a large footprint of valuable clean room real estate.

Aluminum UHV Systems

Aluminum vacuum systems have been used in semiconductor production since the beginning. Its’ low cost of fabrication and overall cost of ownership are well understood. Aluminum has become the dominate vacuum system material for many low and high vacuum cluster tools and other processing reactors.

In many cases, the technology required to process aluminum into a UHV system has not been well understood. However, developments in physics laboratories worldwide made it possible. The methods, process, and components used to build large UHV systems for particle accelerators and synchrotrons are now easily adapted for semiconductor processing applications.

Three Technical Advances that Allow Ultra High Vacuum Performance with Aluminum Systems

There are three primary technical challenges that have been met in this endeavor. They are the development of aluminum surface treatment schemes and outgassing reduction, the development of ultrahigh-vacuum-capable aluminum welds, and finally the development of robust metal sealed aluminum flanges. To benefit from the many superior physical properties of aluminum for UHV systems, relatively minor changes in existing manufacturing processes and components are required. Current designs of aluminum process tools can be upgraded to improve vacuum performance. In particular this means improving the outgassing and permeation performance of these systems.

Aluminum Surface Treatment and Outgassing Reduction

Like untreated or machined stainless steel, the off-the-shelf mill grade surface of aluminum must be stripped and prepared for UHV application. Extruded and rolled plate stock cannot be used directly as it tends to be covered with a porous oxide that is relatively thick, typically 150 Å -200 Å. One of the primary reasons for this is that when aluminum is extruded, alloy impurities segregate to the surface where they combine to produce oxide impurities. Further, when aluminum is machined thick oxides can quickly form on the raw machined surface. These surfaces must be properly treated to obtain the thin dense uniform oxide needed to attain UHV. The left half of Figure 1 illustrates the morphology of a typical untreated aluminum surface.

Aluminum Surface Morphologies

For making aluminum UHV compatible, what is required is some means for ridding the surface of any contaminating constituents and then producing a surface oxide that is thin and non-porous.

Ishimaru, of KEK Japan, was the first to apply a concentrated effort toward solving these problems in his efforts to build aluminum vacuum systems for particle accelerators. He employed two primary processing techniques, one for extrusions and the other for machined components. For extruded surfaces Ishimaru would extrude aluminum into an argon-oxygen atmosphere. For machined components he used ethanol as a machining fluid. Both of these techniques enable the aluminum to form a thin native oxide which is dense and non-porous.

These techniques have since been refined to simplify their implementation. Through work at a number of particle accelerator facilities it has become apparent that surface cleaning with simple alkaline solutions is as effective as argon oxygen extrusion and ethanol machining. Alkaline solution cleaning will remove impurity oxides as well as the top layer of aluminum oxide. Any contaminants introduced from machining and that have been accumulated in the aluminum oxide layer will be removed when the aluminum oxide layer is removed. Additionally, when the top layer of the aluminum oxide is removed by these chemicals a thin, dense and non-porous native oxide will form on the newly exposed aluminum surface.

Aluminum Vacuum Flanging

Aluminum high vacuum systems have typically been sealed with elastomeric o-rings. Elastomers both outgas and are permeable to atmospheric gases. Permeation occurs because atmospheric gases are able to dissolve into the elastomer and then diffuse through the material where they are released into the vacuum chamber. Unlike outgassing, permeation cannot be eliminated by baking the system. Eliminating o-rings from the system can significantly reduce pumping requirements, and cost.

Furthermore, research has been conducted to understand the influence of common vacuum impurities on aluminum sputtered films. One study observed the impact of nitrogen contamination generating from atmospheric permeation through O-ring seals. The upshot of this particular study is that nitrogen will readily incorporate itself into an aluminum film while the film is being grown and this nitrogen impurity will noticeably impact the electromigration resistance.

There are two methods for eliminating o-ring gas permeation, both of which support aluminum ultrahigh vacuum systems. The first is an old solution and involves using differentially pumped seals.

Differentially Pumped Sealing Geometry

In a differentially pumped sealing geometry, the main vacuum chamber is isolated from the atmosphere by a secondary evacuated channel which is separately pumped. Since permeation is proportional to the pressure differential, even a rough vacuum in the pump channel can reduce the permeation by several orders of magnitude. The drawback to this sort of scheme is that it requires an auxiliary channel for each vacuum flange and a pump to evacuate these channels. However, for ports that require quick access such as sputter target ports differential pump schemes do provide a solution that can provide the required vacuum performance.

The other solution is to replace the elastomeric seals with metal sealed flanges. The early metal sealed flanges were composed entirely of aluminum and had a ConFlat style knife edge which could seal an aluminum gasket. Typically, the knife edges of these flanges are coated with titanium nitride to strengthen the knife edge. These flanges were subject to three important limitations. First the knife edge, since it is composed of aluminum, is readily damaged because of the softness of the underlying aluminum. Second, overheating the flanges during weld up or while heat cycling, anneals the aluminum, making the knife edge more subject to failure. The third issue is more subtle. Because most vacuum components are stainless steel a typical aluminum flange will serve as a mount for a stainless component. These types of joints do not tolerate temperature cycling well because the differential thermal expansion between the aluminum and stainless steel will loosen the knife edge seal to the gasket and cause the seal to leak. The standard solution for this type of problem has been to provide a temperature differential during system bakeout between the two materials so that the thermal expansions are matched.

A creative solution to this problem was developed by Atlas Technologies and involves the construction of a bi-metal flange. This flange consists of a stainless-steel surface which contains a ConFlat knife edge bonded to an aluminum nipple used for weld up.

Bimetal Flange Detail

The bimetal flange provides a robust sealing surface which is composed of stainless steel, yet it may be readily welded to an aluminum vacuum system. Because the stainless and aluminum surfaces meet at the bond rather than at the gasket, the sealing surfaces are not subjected to differential thermal expansion and consequent leaking. These bimetal flanges serve as ready replacements for elastomeric seals in flanges that do not need to be routinely opened.

Aluminum Welding

The aluminum surface of a vacuum system can be treated so that the outgassing is minimized and the system sealed with flanges to minimize permeation. However, the flanges must still be joined to the system in a fashion that allows for the system to achieve superior vacuum performance. In the case of aluminum vacuum hardware this implies that the flanges must be welded to the remainder of the system with welds that are non-porous so as not to create virtual leaks, and mechanically strong to maintain the structural integrity of the system.

Producing non-porous welds in aluminum is difficult for a number of reasons. First, at high temperatures, hydrogen becomes highly soluble into molten aluminum. When the aluminum subsequently cools, the hydrogen bubbles through the melt and forms pores in the material. Second, aluminum oxide has a high melting temperature which implies that any aluminum oxide that is present at the weld surface will collect within the weld and form a defect layer. Third, because aluminum has a high thermal conductivity, the heat of the weld will tend to be dissipated within the material bulk. And finally, because aluminum shrinks when it solidifies, aluminum welds will be more subject to cracking than their counterparts in steel.

Presence of the effects above does not imply that aluminum welds cannot be produced, it does however mean that producing them will require adequate material preparation and tight control over the processing parameters to insure repeatability. To meet the challenges of welding aluminum, the vacuum community has developed automated TIG welding processes, which when coupled with careful material preparation, yield reliable ultrahigh vacuum welds.

Aluminum as a Vacuum Chamber Construction Material

When learning how to use aluminum for UHV, a vacuum system engineer experienced in stainless steel UHV system designs will be first skeptical, then interested, and then excited by the powerful capabilities that the properties of aluminum offer. Here we shall discuss those properties of aluminum that are of interest to vacuum designers, in our description of these properties we use stainless steel as a convenient benchmark.

Alloys

Aluminum comes in a wide range of alloys which vary as to characteristics. Wrought aluminum alloys are suitable for vacuum chamber fabrication and are designated by a four-digit number which is followed by a temper specification. The first digit specifies the primary alloy composite as indicated in Table 1.

Table 1: Aluminum Alloy Designations

All of the wrought alloys have been used for vacuum chamber fabrication except for the 7000 series which has zinc which has a high vapor pressure at low temperature. The 2000 series alloys are highly weldable. The 6000 series alloys, particularly 6061, and 6063, are commonly and successfully used for ultrahigh vacuum systems.

Machinability

One of the overriding impetuses for fabricating vacuum systems from aluminum is that it is inherently more machinable than materials, such as stainless steel, which have been traditionally used for vacuum component fabrication. The machining cost for 300 series stainless steel is up to 5.5 times that of aluminum.

As indicated previously this ease of machinability is the reason that aluminum has become the material of choice for fabricating semiconductor equipment. Cluster tool components are machined from a single plate of aluminum. These tools are exceptionally rigid, and have a minimal vacuum surface area and occupy a minimal floor space considering their throughput.

Thermal Conductivity

Aluminum has a thermal conductivity that ranges between 170 watt / m K and 230 watt / m K depending on the alloy. Stainless steels by contrast have thermal conductivity’s that are between 14 watt / m K and 16 watt / m K.

High thermal conductivity is an advantage when designing systems that require temperature cycling. This is the case for systems that must be baked to achieve ultrahigh vacuum. An aluminum chamber may be baked and then cooled much more rapidly in development of ultrahigh vacuum than a stainless chamber. And its’ conductivity allows for a complete bake out without the problems of re-condensation of gasses on cool spots common in stainless systems.

Weight

Aluminum is 1/3 the weight of stainless steel. The cost burden associated with weight starts with raw materials handling and progresses through out the manufacturing process including shipping, installation and even architectural engineering and construction.

Magnetic Properties

Aluminum is not magnetic whereas stainless steel, being essentially an alloy of iron exhibits residual magnetism. For applications that involve charged particle beams, the absence of magnetic properties in aluminum is of advantage because it implies that the vacuum system will not modify the fields from the beam control magnets.

Radioactivity

Aluminum in comparison to stainless steel has a much more rapid decay of induced radioactivity. Generally, if both types of materials are bombarded with the same flux of charged particles, the residual radioactivity will be between one and two orders of magnitude less for an aluminum sample than for an identical sample of stainless steel. The nuclear half-life of elements that make up stainless suggests that a particle contamination is always present in stainless steel and a possible source of circuit damage.

Corrosion Properties

The corrosion of both aluminum and stainless steel alloys in reactive gases is a complicated process. However much experimental work has been performed on various alloys in different reactive gaseous environments. The general thrust of these results is that both aluminum and stainless steel are subject to attack by reactive gases, that halogen containing species are typically the most damaging, and that the corrosion activity of any given compound is usually no worse than that of its halogen component alone.

Importantly aluminum is not a worse corroder but simply one with different reaction dynamics.

Outgassing Properties

Vacuum surface gassing is a primary source of process contamination. Water vapor is the most significant contaminate, placing heavy demands vacuum pumping. Metal contamination is a major yield-limiting factor for silicon IC production and iron is one of the most significant contaminates.

The required level of outgassing has not always been achievable with aluminum. Only recently have techniques been developed allow these levels of performance to be achieved repeatably. This improvement in outgassing performance has been one of the principal breakthroughs that has allowed aluminum to become a competent material for the construction of ultrahigh vacuum systems.

Conclusions

Through years of research and improvement, aluminum vacuum systems have become the ideal choice for UHV wafer processing and for base pressure system conditioning. Aluminum ultrahigh vacuum systems are integrated into many leading-edge semiconductor processing systems.

Acknowledgments

We would like to pay our respects to Dr. Hajime Ishimaru deceased. Dr. Ishimaru pioneered the use of aluminum for UHV. We are all forever in his debt The authors would also like to acknowledge James Garner of SMC Corporation for many helpful discussions. Additionally, we would like to thank the vacuum group of the Advanced Photon Source at Argonne National Laboratory for their work in this area.

Richard Bothell
Richard Bothell is former President of Atlas Technologies.

Jed Bothell
Jed Bothell is owner and President of Atlas Technologies and co-inventor of the Atlas Flange. Atlas Technologies supplies aluminum/stainless and copper/stainless bonded flanges.

Customer Highlight: Dynavac

Fri, 23 Aug 2024 15:37:03 GMT

Our customers at Dynavac were crucial participants in a compelling project for NASA’s Magnetospheric Multiscale Mission at the Goddard Space Center.

The Solar Terrestrial Probes mission were scheduled to fly four identically instrumented satellites to investigate how the sun and Earth’s magnetic fields transfer energy from one to the other. This transfer, called Magnetic Reconnection, affects space weather and by studying it, scientists at NASA gained the ability to observe how this process affects systems like communications networks, GPS navigation, and power grids back on Earth.

Dynavac, an industry leader in the design and manufacture of thermal vacuum systems, supplied the project with aluminum cryopanel assemblies that allowed for thermal isolation of the satellites while they went through space simulation exercises in the lab prior to their journey in space. Each assembly was comprised of multiple panels joined together to form a thermally controlled and uniform test area. Aluminum extrusion was welded to each of the panels in a serpentine pattern which ultimately connected to stainless steel lines that delivered the liquids and gases to the assembly.

Dynavac uses Atlas ATCR fittings to provide a compatible, demountable transition from the aluminum lines to their stainless-steel counterparts. Atlas has supplied Dynavac with thousands of ATCR fittings for the manufacture of their equipment.

Aluminum Optics Chambers with Breadboard for Max Born

Fri, 23 Aug 2024 15:31:01 GMT

Several Atlas aluminum vacuum chambers with breadboards installed at Max Born in Berlin are used for the generation and application of ultra short x-ray pulses via a frequency conversion process called high order harmonic generation. The purpose is to record films of atoms and molecules on their natural time scales from the femtosecond (10^-15 seconds) to the attosecond (10^-18 seconds) range to capture atomic and molecular reactions.

Reliable vacuum is essential to the process because the pulses absorb air. The rectangular shape and accompanying breadboard allows the team to strategically and simultaneously position several optical elements for ease of filtering and focusing on the x-ray pulses. This permits additional laser pulses, from the near-infrared to the ultraviolet regime, to overlap with the x-ray pulses in order to make the atomic and molecular recordings.

Aluminum, says Dr. Bernd Schϋtte of Max Born, is the material of choice for the chambers because “it is cost effective and its low weight eases the handling of the chambers.”

The ATCR Fitting – a superior gas delivery system

Fri, 23 Aug 2024 14:54:20 GMT

The Atlas ATCR™ Fitting – the aluminum tube fitting with a stainless steel face-seal offers a superior gas delivery system to cryogenic and semiconductor industries

Industry leaders are taking advantage of the extensive benefits of aluminum in UHV to improve the performance of their most challenging applications in the fields of cryogenics, aerospace, physics, and semiconductors. For processes that require high thermal conductivity, light-weight materials, or chemical resistance aluminum delivers advanced functionality, and at a fraction of the cost.

When comparing aluminum to stainless steel, aluminum is ten times more conductive, one-third the weight , and stands up to a variety of chemicals that trigger destructive corrosion on stainless steel surfaces. Other documented advantages of aluminum over stainless steel include low levels of outgassing, contamination, nuclear activation, and magnetic permeability, along with high vibration dampening.

Additionally, aluminum provides superb machinabilty, space and weight reduction on site, and is lower in cost in terms of machining, shipping, and overall cost of ownership.

Atlas ATCR™ fittings produce a robust, demountable use of aluminum tubing for some of the most demanding applications worldwide. These fittings are fully compatible with Swagelok VCR® and Parker-Hannifin VacuSeal® fittings which makes incorporating Atlas ATCR™ fittings into existing stainless infrastructure uncomplicated.

Standard socket, butt, male and chamber mount weld fitting geometries are available in 1/4, 3/8, 1/2, 3/4 and 1 inch tube diameters. Chamber mount fittings are available in four length configurations suitable for 1/2, 3/4, 1 and 1-1/4 inch chamber wall thicknesses.

Atlas Socket, Butt and Male weld ATCR™ face-seal fittings are fitted with a durable stainless steel sealing face bonded to to an aluminum body. The bond produced is extremely rugged. All face-seal fittings are helium leak tested for service in UHV environments in excess of 1×10-9 Torr lt/sec He.

Welding Aluminum to Vacuum Standards Is an Atlas Technologies Specialty

Fri, 23 Aug 2024 14:51:16 GMT

Aluminum Welding REFERENCE

For Designers and Welders of Aluminum Ultra High Vacuum (UHV) Chambers

Aluminum UHV Weld Design

Most facilities familiar with Ultra High Vacuum (UHV) have experience welding stainless steel to UHV standards, however many have not had occasion to weld aluminum to UHV standards. We offer this brief guide for designing and welding aluminum chambers and Atlas Technologies’ aluminum/stainless bimetallic flanges and transitions to UHV standards.

Similar Masses:

We try to design weld geometries that have similar masses whenever possible. If there is a large difference between the mass of the chamber and the mass of a flange for example, this can cause frustration because the more massive chamber will tend to be cooler than the less massive flange and the flange will preferentially melt. If similar masses are not a possibility, oftentimes thermal chokes can be machined into the massive part, which constrain the heat loss. Also burying the less massive chamber in the massive flange will tend to spread the heat about in a more uniform manner.

It is convenient to have V-grooves machined into aluminum weld joints. This permits liberal use of filler rod which reduces cracking. If joining tubes, the V grooves should be on the inside of the tube and penetrate ~2/3 the thickness of the wall.

Cleanliness:

Cleanliness is very important when welding aluminum. Make sure that the weld surfaces including the filler rods are freshly cleaned and fully dried. Even though aluminum forms an oxide instantaneously in air, a freshly cleaned surface with scotch bite can reduce the thickness and contamination present in that oxide. This is important because aluminum melts between 580-650 C, but its oxide melts at ~1760+C and is heavier than the aluminum alloy. Because of this, the oxide crust can sink into the molten weld and be a source of porosity.

Preheating the aluminum:

Because aluminum is such an excellent thermal conductor, vast amounts of heat are required when beginning a weld. As this heat spreads ahead of the weld bead, it accumulates in the part. This tends to reduce the amount of required heat during a weld. Rather than stopping and starting which are often areas for leaks, we recommend using a foot pedal current controller.

During welding, stainless steel will glow red at its welding temperature; aluminum however will not. Aluminum will melt before it will glow. The welder must observe the melted weld puddle rather than the glow.

Aluminum TIG Welding for UHV and Aluminum Atlas Flanges, Bimetallic Transitions Coupling and Fittings

Welding Thick Aluminum for Vacuum

Greater than 6mm + Thick (¼”):

Max Bond Temp:

Temperature at the bond should not exceed 300C. Keep a damp rag on the joint to prevent over heating during welding

Appearance of Weld:

The weld area will form a black soot cover with a bright metallic center. This can be cleaned off with scotch bright or a stainless steel wire brush after the welding. If a yellow discoloration forms on the weld, it is a result of oxygen contamination in the helium.

Welding Thin Aluminum for Vacuum

Less than 6mm + Thick (¼”):

Max Bond Temp: Temperature at the bond should not exceed 300 C. Keep a damp rag on the joint to prevent over heating during welding.

Appearance of Weld:

The weld will be bright metallic with no soot. If a yellow discoloration forms on the weld, it is a result of oxygen contamination of the helium.

Reduce Carbon Deposition: Synchrotron and Semiconductor Lithography Optics

Fri, 12 Jul 2024 10:00:07 GMT

Out gassed carbon from stainless steel can be a serious source of contamination and can damage synchrotron optics as well as deep Ultra Violet (DUV) and Extreme Ultra Violet (EUV) optics for semiconductor lithography. We are finding that many of these high profile labs are eliminating any potential carbon from stainless by using aluminum vacuum systems. Aluminum systems have essentially no carbon.

The carbon from stainless also reacts with the elemental hydrogen and departs the surface in a variety of hydrocarbons. Additionally, CO and CO² are produced by the abundance of carbon from the stainless steel when reacting with oxygen.

For some optical applications the vacuum level is less critical than the purity of the environment. This is typical in the semiconductor lithography market. Companies in this market are pulling UHV then backfilling with a pure gas and operating at relatively low vacuum but incredibly high purity levels: Ultra High Purity (UHP).

Also in the semiconductor lithography market some manufactures are looking for the inside of their ultra high purity system to be anodized. The dark anodized skin reduces the reflectance off the chamber wall and provides for a more controlled optical environment.

Atlas builds aluminum UHV and UHP chambers for synchrotron and semiconductor facilities seeking to eliminate these problems. Aluminum chambers can be sealed with rugged reliable Atlas flange joints which are aluminum flanges with a stainless knife-edge. These flanges permit aluminum vacuum chambers to offer superior UHV & UHP performance over stainless steel.

Low Permeability Solutions for Particle Physics, Cryogenics, and Thin Film Semiconductor Applications

Fri, 12 Jul 2024 09:40:06 GMT

Atlas Technologies builds a non magnetic model of its Atlas FlangeTM, the aluminum flange with a stainless steel knife-edge and face using 316LN stainless. This alloy ensures a minimal magnetic permeability from the stainless steel while providing an aluminum base for weld-up to an aluminum chamber that is not magnetized during welding. The magnetic permeability of aluminum, near unity, and its excellent vacuum properties such as extremely high thermal conductivity, low H2 and no C content, light weight and low Z make aluminum a superior vacuum material for many UHV applications. See our section on aluminum vacuum properties for more information.

Atlas also manufactures Atlas Flanges with hardened knife edges and faces using materials other than stainless. For example Atlas uses titanium instead of stainless as a knife edge material. This reduces the magnetic permeability even more than using 316LN and is ideal for extremely magnetically sensitive applications.

Some non magnetic applications are better served with copper Ultra High Vacuum UHV chambers and flanges. Atlas manufactures custom copper chambers with hardened flanges surfaces to meet your specifications.

Low permeability Atlas CF Flanges and chambers are in use at prominent national lab and accelerator facilities world wide. We would be delighted to talk with you about your application and assist you in the engineering and manufacture of flanges or chambers.

Atlas Technologies offers low magnetic permeability stainless steel Ultra High Vacuum Atlas Flanges. These flanges enable you to apply the excellent extremely low permeability of aluminum through-out your vacuum system and still enjoy rugged stainless knifes with magnetic permeabilities far below conventional stainless steel.

The low mu Atlas Flanges are carefully manufactured with atlas’ proprietary technologies yielding a very low permeability in the stainless around ~1.017 µ.

Because aluminum has a lower mu than the low mu stainless and is less expensive, Atlas’ low mu flanges are the clear choice for low permeability vacuum applications.

Atlas stocks low mu Atlas flanges:

Relative Permeability (µr) refers to the ratio of magnetic flux in any element of a medium to the flux that would exist if that element were replaced with air, magnetic-o-motive force (mmf) acting on the element remain unchanged (µ r = µ/µ 0)*

Permeability (µ) is the ratio unit magnetic flux density to unit magnetic field intensity in air (B/H) the Permeability of air is 1.257 x 10 ⁶ henry per metere*

*Marks standard handbook for mechanical engineers, 9th edition (ISBN 0-07-004127-X)

** A Physicist’s Desk Reference Second Ed. (ISBN0-88318-610 (pbk))

*** Electronic Properties of Materials (ISBN 0-412-49590-2)

Three Reasons to Incorporate Bimetal Components in Rocket Engines

mel@atlasuhv.com (Mel Janecka ) — Sat, 25 May 2024 01:21:23 GMT

Rocket engines reach such high temperatures that they melt most metals, yet some metals are too expensive to use exclusively. Bimetal components offer an effective solution.

Whether designed for low earth orbit, geostationary orbit, or open space, spacecraft must maneuver flawlessly and operate repeatedly in one of the harshest environments. Therefore, each component must interact with precision, provide leak-free operation, and support system longevity.

As our aerospace customers continually innovate and launch ever more sophisticated space craft, bimetal plays a critical role in their upgraded designs. Here are three reasons it makes sense.

HIGH-TEMPERATURE OPERATION

Satellites and spacecraft use a variety of chemical propulsion systems to provide maneuverability. Engine designs must incorporate materials that can withstand the heat generated by the thrusters without failing. For example, the use of niobium alloy as part of the thruster’s nozzle, where temperatures can reach 2000℉, must connect with the stainless-steel components used in the fabrication of other rocket engine parts.

Niobium can be expensive—more expensive than sterling silver—and offers a number of benefits to users, including oxidation and corrosion resistant properties, and a melting temperature of 4,491 ℉ for use in high pressure and high temperature applications. Using bimetal components combines the advantages of both metals—the heat and chemical resistance of niobium for example, and the lighter weight and/or lower cost

of stainless steel or aluminum—resulting in a more resilient, less costly, and longer-lived system.

Although bimetallic components can be joined using one of two primary operations (explosion bonding or diffusion bonding), most

aerospace components are explosion bonded at this time.

PRECISION FABRICATION

Stainless steel cannot be welded directly to niobium. The use of a conventional weld would result in a fragile, glass-like interconnection joint that would easily shatter under a high vibration and shock operation. Atlas Technologies has helped rocket engine designers develop new solutions through specially bonded metals and precision machining techniques to provide a bimetallic transition for such critical joints.

Our fully weldable dissimilar metal transitions allow us to help customers with specific requirements including light weight, ability to handle high temperatures, chemical resistance, and more.

EXTENDED LIFE CYCLES

Bimetallic joints are solid-state joints with long-term reliability that require no servicing, unlike joints utilizing adhesives, bolts, and elastomeric seals. This is especially beneficial in space where it is challenging to replace a component. These hermetic bimetallic joints enable engineers to reliably transition from one metal to another with metallurgically bonded joints.

For OEMs and end users, these robust dissimilar metal joints can be produced with a wide variety of metal combinations such as aluminum/titanium, stainless/titanium, copper/titanium, copper/aluminum, niobium/stainless, and many more.

Bimetallic Bonding for Ultra-High Vacuum

Fri, 24 May 2024 21:32:22 GMT

A bit about how bimetallic bonding works

Now in our third decade, Atlas Technologies continues to develop methods and processes to effectively bond dissimilar metals for use in Ultrahigh Vacuum (UHV) as well as other demanding applications. While the details are proprietary, you can get a working understanding of the process below.

Metallurgical Bonds

Atlas bimetallic flanges and fittings are constructed of metallurgically bonded plates created through our proprietary bonding process. To form the bonded metals, a flyer plate sits atop a base plate separated by a small gap. An explosive material, such as ammonium nitrate, is placed on top of the flyer plate and detonated from a point at one edge of the plate. The explosion is a controlled progressive ignition starting from one point on the surface of the flyer plate and progressing across it, like the ripples on a pond created from the drop of a rock.

The energy from the explosion accelerates the flyer plate against the base plate at impact velocities of 1800-2200 m/sec. A high energy surface plasma is formed between the plates, which moves ahead of the collision point stripping electrons from the two bonding surfaces. The electron hungry metals are then thrust against each other at extreme pressures forming an electron sharing bond.

Bonding Parameters
Atlas bonds several different metals but concentrates primarily on metals needed for UHV applications. The formation of multi-laminates by explosive bonding involves deep knowledge of the process variables and the ability to control them. The critical bonding parameters include explosive detonation velocity, explosive load, and interface spacing. The metallurgy of the dissimilar metals at the bond interface is an additional consideration. Imagine the constituent metals acting as a viscous fluid in the reaction zone (bond-line interface).

The key bonding parameters along with careful preparation of metals to be bonded results in a successful bonding event. Through the precise control of bonding parameters, interface turbulence is also controlled. An ultrahigh vacuum interface requires that a smooth flowing wave pattern be developed. Excessive turbulence may result in leak paths and possibilities.

Multi-layer Composites
Metals such as copper and stainless are readily bondable. However other metals such as aluminum and stainless are incompatible if bonded directly to each other. Many materials are not directly bondable without the formation of brittle intermetallic compounds. Atlas has developed patented multilayer composite technologies to facilitate metallurgical compatibility between aluminum, stainless and other metals. Multi-layer composites also provide diffusion barriers to eliminate formation of the brittle intermetallic compounds during weld up or through repeated heat cycles such as bakeout and high heat processes. Titanium and copper are the typical materials used to achieve diffusion protection for aluminum/stainless flanges.

The time duration of the explosion welding event is small and the heated reaction zone between the metals microscopic. The remaining thickness of the metal remains near ambient temperature and acts as a heat sink to the reaction zone. Therefore, the bond-line is an abrupt transition between the metals with little, if any, degradation of the metals. This process allows Atlas to produce stainless/aluminum and stainless/copper flanges while retaining a T-6 temper in the aluminum and, in the case of copper, maintaining a half hard RF78 condition. Other processes would anneal these materials leaving them too soft for many UHV applications.

On close examination you will notice a wave pattern at the bond line. The pattern is more noticeable depending upon whether you are observing a crossing section or parallel section. The pattern develops in the bonding process as the flyer plate is accelerated against the base plate. The wave pattern increases the mechanical strength of the bond - in shear by offering mechanical interference and in tension by offering more bonded surface area. All materials used are UHV compatible and are metallurgically bonded using this solid state process. No adhesives are used.

Bond-Line Wander
The explosion bonding process is extreme, leaving the bonded plate with obvious extrusions, deformations and warpages. Atlas takes great care to flatten the plate after bonding. And as each flange is produced, careful attention is given to positioning the bond line – typically to ±0.04” variance and as small as ±0.012”. However, when carefully comparing one flange to another, you will observe that even though the flanges are dimensionally alike, no two flanges exhibit the same bond line location. Bond line wander does not affect the mechanical integrity or the function of the flange for UHV application.

UHV Metal Bonding Capability
The explosive bonding process has been used as an industrial process for over 40 years. However, the industrial applications for large heat exchanges and for ship building are not suited for UHV where bonds must operate at leak rates less than 1×10-9 to 1×10-12 Torr. Atlas Technologies has developed UHV bonding processes for a group of metals commonly used in UHV applications. Although our CF flanges and ATCR fittings are most commonly used, we have also developed successful bonding architectures and metal combinations suitable for use in semiconductor, particle physics, cryogenic, aerospace and other demanding applications.

Customer Solution: Foil Window Flange

Fri, 24 May 2024 20:57:37 GMT

Replaceable, low cost, extremely thin titanium UHV windows

Our customers at a large midwestern research university needed a very thin titanium window for an electron optics application. The idea they brought us included a permanently brazed approach that was thick and expensive to replace if the window failed. The customer wanted it thinner but found the risk of the part failing due to the force that brazing would exert upon it, less than ideal.

The solution, developed by Atlas, was a low cost, replaceable and extremely thin (.002”) titanium UHV window trapped between a standard knife edge flange. That product later became a standard solution - the Atlas Foil Window Flange. In addition to being thin and strong, the flanges contain zero beryllium and are Low Z.

Loadlock Chamber for Efficiency Upgrade

Mon, 18 Jun 2018 09:59:28 GMT

Denton Vacuum, a leading supplier of production scale thin film technology systems, uses an Atlas manufactured loadlock chamber in the Explorer Deposition System at its Customer Application Center (CADC). The loadlock chamber enables the loading and unloading of wafers in a highly efficient manner as the semi-automatic feeding allows the main processing chamber to remain at high vacuum while material is loaded and unloaded from the subsystem.

While the main process chamber remains at vacuum, the finished wafer is extracted from the chamber, a loadlock valve is closed and the chamber is returned to normal pressure. The wafer can then be replaced, the chamber pumped down and the wafer moved to the process chamber.

Savings as high as 90 minutes per cycle may be realized with the additional capability.
Dr. Craig Outten and his team are working on several groundbreaking processes at the CADC which include coatings for medical devices including Titanium Nitride fractal coatings, advanced sputtering of metals and dielectrics, optical coatings, atomic layer deposition, and coating macromolecules for TEM.
For projects like these, Atlas aluminum chambers advance the vacuum process with very low hydrogen, speedy pump down, lightweight and maneuverable equipment, and even bake out.

Titanium: a Superior Material for XHV

Thu, 14 Jun 2018 09:09:32 GMT

Atlas titanium chambers offer extreme vacuum performance with very low hydrogen permeation rates and secondary gasses. Due to the gettering properties of this metal, titanium vacuum chambers are, in many ways, the ultimate vacuum material.
For extreme high vacuum, titanium will often be the best choice. But, due to cost of the material and the slow machining capabilities, it is typically used only when extreme high vacuum is required.

Applications that may require XHV:

X-ray Lithography
Particle Physics
Accelerators
Cryogenics
None Magnetic Environments

At Atlas, we have been able to attain, XHV levels of 1×10 ^-12 Torr.

Customers using our titanium products to the same level of success include governments labs, universities, research lab, and semiconductor manufacturers.