Electrical Feedthroughs

Multipin instrumentation feedthroughs contain more than one conductor path or pin and are also fitted with a fastening air-side connector. These feedthroughs are used for the transmission of signal voltages and currents. They are commonly referred to as instrumentation feedthroughs because of their use in instrumentation control applications such as electron microscopes, electron-beam evaporation, electron microscopy, surface science analysis and semiconductor process controls.

Type-D Subminiature offer complete air and vacuum multipin connectivity solutions. Nine, fifteen, twenty-five and fifty pin configurations are hermetically sealed using the latest in glass-ceramic bonding technology. Air-side interfaces are designed to mate with standard off-the-shelf serial cable connectors. Vacuum connectivity is made possible with ISI’s unique UHV compatible connectors and ribbon cable assemblies. These instrumentation feedthroughs provide the same conveniences of circular type multipin products, but offer higher pin density with smaller footprints.

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Coaxial feedthroughs are those products constructed with two concentric conductor paths. One outer metal tube or shield path, concentric with, and enclosing, a cylindrical center conductor path. The inner and outer paths are separated and insulated with a high purity alumina ceramic. Coaxial components are offered for industry standard BNC, MHV, SHV, Type N, SMA, SMB, Triaxial, Microdot, Between Series and SHV Bakeable connector interfaces. Coaxial style feedthroughs for most any application, from instrumentation signals to 20kV high voltage power are included.
In-vacuum coaxial cables are available in various styles and configurations. All are constructed with vacuum grade materials and components, including stainless steel braided shielding, high purity alumina ceramic or Kapton® insulation, beryllium copper contacts and aluminum or stainless steel terminations. These cable assemblies are suitable for high temperatures and rated for high and ultra-high vacuum service.

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Thermocouple feedthroughs are used in applications for in-vacuum temperature measurement. A thermocouple is a device that measures temperature as a function of the electromotive force induced when heat is applied to two dissimilar metal wires, which are joined at both ends. ISI thermocouple feedthroughs are not temperature sensing devices as such, but components used to conduct a thermocouple’s voltage (EMF) through the bulkhead of a chamber to external instrumentation. In other words, an air-to-vacuum environmental splice in a thermocouple’s conductor path. ISI offers base, refractory and noble metal compatible feedthroughs with various connector options including miniature, circular MS, push-on and screw-type connectors.

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Power feedthroughs are used to transmit either high voltage, high current or a combination of both. These can be used for a multitude of vacuum applications including vacuum furnaces, sample heating or biasing, in-vacuum coating applications such as electron-beam evaporation, resistive heating evaporation, and DC plasma sputtering. Proven and time tested designs are used to optimize the electrical performance of ISI power feedthroughs. Where space is not a limitation, ceramic surfaces are made as long as possible to maximize strike and creep distances. If space is limited, ceramics are convoluted in order to achieve increased surface distances with minimal impact on an insulator’s overall length. All air-side ceramic surfaces are glazed with a high temperature glass coating that reduces ceramic surface roughness and minimizes surface contamination. This glass coating enhances a ceramics’ electrical surface tracking characteristics. Some ISI power feedthroughs are fitted with tubular conductors that can be used to transmit both power and coolant simultaneously. These products are referred to as watercooled feedthroughs. Watercooled electrical components are typically used with grounded, closed-loop cooling systems and nonconductive coolants such as deionized water or ethylene glycol. If using plain tap water, the cooling system must be grounded and lines must employ nonconductive materials such as polypropylene tubing. Properly grounded water lines will provide a safe dissipation path for any power conducted by the water. Current or power ratings are usually not given for watercooled feedthroughs as the ratings are dependent on coolant flow rates and their heat dissipating capacity. Tap water temperatures can vary dramatically from one region to another, so too will its heat dissipating capacity. Users are advised to establish safe and practical coolant flow rates based on the power requirements for their specific application and coolant heat dissipation capacity. 

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PowerBoot™ are ISI high voltage silicone connectors. They can be used to carry high voltage, high current or a combination of both. PowerBoot™ Feedthroughs are designed for use with these connectors. ISI PowerBoot™ Feedthroughs are used in a multitude of applications including vacuum furnaces, sample heating, biasing and in-vacuum coating applications. The PowerBoot™ products are ideally suited for electrically challenging atmospheric environments. 

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Breaks and envelopes are tube-like adapters with metal tube hardware bonded to the ends of a ceramic tube. The bonded metal tube ends provide a means of attaching the breaks and envelopes to vacuum tube lines using flange mounts or welding. The central ceramic portion of a break or envelope provides electrical insulation between the two conductive metal ends. In other words, the ceramic produces an electrical break in an otherwise continuous and conductive metal tube geometry. 

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Electrical Connectors are an essential accessory for the user of electrical feedthroughs as power must be transmitted between the application within the vacuum and the external or air-side instrumentation. ISI offers a wide variety of Electrical Connectors for service in air or vacuum environments. Most connectors featured in Section 9 are either included or used with the standard electrical feedthroughs in this catalog. Please refer to specification tables for general characteristics of each Connector and refer to the relevant page numbers where full descriptions, recommendations and wiring instructions may be found. 

In-vacuum coaxial cables are available in various styles and configurations. All are constructed with vacuum grade materials and components, including stainless steel braided shielding, high purity alumina ceramic or Kapton® insulation, beryllium copper contacts and aluminium or stainless steel terminations. These cable assemblies are suitable for high temperatures and rated for high and ultra-high vacuum service

A wise variety of bare wire, rod and tube materials, all of which are suitable for high and ultra high vacuum applications are also offered. Special purpose materials such as stainless steel braided shielding ang Gildtop® copper alloy wire, insulated with fish spine alumina ceramic beads are ideal for the fabrication of flexible, vacuum ready coaxial cables. also available are thermocouple wire and rod materials. Thermocouple wire types C, E, J, K, R, S, T and N are supplied as matched pairs. Type C, R and S are supplied in extension grades only.

Insulators and spacers are fabricated using high purity Alumina which is ideal for high and ultra-high vacuum service. Alumina is a multi-crystalline form of sapphire and its properties include high compressive and mechanical strength, high wear and heat resistance, good radiation resistance and high electrical resistivity. It also has zero porosity and is hence impervious to all gases. All of these properties make alumina an excellent engineering material suitable for some of the most extreme and demanding applications. Shielded ceramic standoffs are an ideal solution for the routing of high voltage power lines inside a vacuum system. Bare conductor power lines can be safely and conveniently fastened to a vacuum chamber walls. The shielded ceramic construction makes these standoffs ideally suited for use in vacuum coating environments where deposition onto ceramic surfaces is not desirable.

Fluid Feedthroughs

Water or Liquid Feedthroughs are used to transfer coolant to processing equipment inside a vacuum. For example, electron beam evaporation sources must be in a high vacuum environment and generating a densely focused electron beam to produce enough heat to evaporate Alumina ceramics; water cooling is therefore required to prevent damage to evaporation crucibles and electromagnetic coils used respectively to contain the molten alumina and focus the electron beam.

Liquid Nitrogen Feedthroughs are used for the same cooling purposes as Water Feedthroughs but offer lower temperature (-200°C) capabilities and therefore greater cooling rates. Liquid Nitrogen Feedthroughs are designed so as to minimize heat transfer between coolant lines and vacuum mounts. Ice build up can be detrimental to the sealing characteristics of a vacuum mount.

Thermal insulation in liquid nitrogen lines is achieved through double wall coaxial construction. A .25 inch cooling line is inserted and welded to one end of a 1/2 inch support tube. The opposite end of the 1/2 inch support tube is welded to the vacuum mount which, when evacuated, creates a coaxial vacuum cavity between the two tubes. This cavity is an excellent thermal barrier, which prevents ice build up on the vacuum mount flange. 

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Optical Components

Sapphire is a synthetic, hexagonal single crystal anisotropic material which displays substantially different physical, thermal, dielectric and optical characteristics when measured along different axes. ISI offers a wide selection of sapphire viewports suitable for high and ultrahigh vacuum applications. The use of high purity sapphire and low expansion nickel-iron alloys enables these viewports to be repeatedly baked to temperatures as high as 450°C. ISI sapphire viewports are offered in ultraviolet and regular grade substrate materials. 

Fused silica viewports are designed and rated for high and ultrahigh vacuum applications. They are constructed using vacuum grade materials including high purity silicon dioxide, 304 stainless steel metal components, and vacuum-tube grade braze alloys. They are available in base UV, Deep-UV and Excimer-UV grades. These are polycrystalline, isotropic materials with no crystal orientation. Their physical, thermal, dielectric and optical properties are uniform in all directions of measurement. The basic UV material is suitable for all but the most demanding optical applications. Fused silica viewports are preferred over glass viewports because of their transparency to ultraviolet radiation, higher abrasion resistance and a low coefficient of thermal expansion and their resistance to thermal shock. The only limitation with fused silica viewports is the braze alloy used in the bonding process. The lead-silver alloy used to seal and bond the window to a stainless steel sleeve melts at 305°C.

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Vacuum Hardware

Each Electrical Feedthrough offered in this catalog is supplied with a standard mount to install the feedthrough onto the vacuum chamber.
This section details a full range of accessories for use with the five standard vacuum mounts:Weldable, Conflat® compatable Del-Seal™ CF Flanges, ISO NW compatible Kwik-Flange™ , one-inch bolt Del-Base™ Baseplate Mounts, and National Pipe Tread (NPT) Mounts.

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Custom Engineering
At ISI we know that many of tomorrow’s standard components will evolve from the special fabrications produced today and to this end we listen all the more carefully to our customer’s individual requirements. The custom engineering of ceramic-to-metal seals is a central part of our manufacturing activity. Our Research and Development personnel are always available to discuss technical issues and we pride ourselves on the speed with which we can evaluate a particular application and propose the most cost-effective solution to the customer.

Methods of Sealing

Del-Seal™ (Conflat® compatible) metal seal flanges have become America’s industry standard and the world’s leading choice for ultra high vacuum flanges. They are listed with both the American standard size designations as well as the European DN CF standard. They are offered in 13 sizes from 1.33'' (DN16 CF) to 16.5'' (non-DN standard) diameters. Copper gaskets, Viton® elastomer gaskets and bolt kits are also detailed. 

ConTorr™ Gaskets are an ISI patented design offered in plain or gold-plated OFEcopper. What makes these gaskets unique from conventional copper gaskets is the revolutionary method by which they are installed, held in place and removed from metal seal flanges.

Kwik-Flange™ (ISO NW compatible) elastomer seal flanges were specifically designed for high vacuum system connections requiring quick and frequent assembly and disassembly. They have been modeled after the globally established ISO NW flange format. ISI offers the Kwik-Flange™ system, including mounting accessories, in tube sizes from .750'' (DN16 KF) to 2.00'' (DN50 KF).

Baseplate elastomer seal mounts are self-contained mounts, originally developed for the vacuum coating industry and designed for use with bell-jar systems or flat Baseplate vacuum chambers. These blank mounts fit through 1.00'' holes. As an added convenience, ISI blank Baseplate mounts are fitted with a female 3/8-16 thread to support custom vacuum structures.

National Pipe Thread (NPT) mounts are also offered as a line of standard blank mounts. These are made of 316 stainless steel material and used to blank-off unused NPT vacuum ports. These mounts are typically sealed using conventional plumber’s Teflon® tape and are suitable for rough vacuum  applications.

Ceramic-to-Metal ratings

Temperature Ratings...
The joining of ceramics to metals is a compromise between materials with dissimilar expansion coefficients. Low expansion metals combined with careful joint design bring expansion coefficients within an acceptable match and effectively minimize the stresses caused by differential expansion between the ceramic and metal components being bonded. Minute variations in expansion coefficients can be detrimental when ceramic to metal seals are subjected to severe thermal gradients. Please note that the maximum recommended thermal gradient for any ceramic-to-metal seal should not exceed 25°C per minute.

Electrical Ratings...
The electrical feedthroughs offered in this catalog are electrically rated for operation with one side in dry atmospheric conditions while the opposite end is in a stable vacuum environment with a maximum system pressure of 1x10^-4 Torr. We recommend that users make allowances for deviations from these stated operating parameters and take adequate safety precautions when working with high voltages or currents.

Dimensional Information...
Dimensions depicted herein are for reference only. Tolerances will vary by specific product line and will depend on various geometric parameters. Please consult with an ISI technical sales representative for applications requiring specific tolerances.