Epoxy-based Feedthroughs Provide Design Flexibility, Rapid Prototyping and Cost Savings

Multi-conductor, flanged feedthrough.

The point of view that epoxy-based feedthroughs are inferior to glass-to-metal feedthroughs in terms of sealing and outgassing may have once been true, but modern manufacturing techniques and new epoxy compounds have all but eliminated those concerns. Modern epoxy formulations are more capable of enduring greater mechanical stresses, operating under wider temperature ranges, and sustaining exposure to harsher chemicals than ever before. Today's epoxy-based feedthroughs are excellent choices for even the most challenging feedthrough applications.

Take BCE's proprietary epoxy compound for instance. It seals to 1 X 10E-9 cc/sec of Helium under high vacuum and high pressure. Concerns of outgassing have been erased with the formulation meeting NASA’s ASTM E-595 low-outgassing specification, the industry standard test for measuring outgassing in adhesives and other materials. Developed to screen for low outgassing materials for use in deep space, the test determines the volatile content of material samples placed in a heated vacuum chamber under tightly controlled humidity, temperature, and vacuum conditions.

PCB feedthrough with clear epoxy feedthrough.

Epoxy feedthroughs allow designers and engineers to procure a feedthrough built for the specific task, rather than to accommodate off-the-shelf connectors that are rarely ideal for the specific requirement. Off-the-shelf connectors and feedthroughs impose restrictions on the number and gauge of conductors, as well as the geometry of the device. The use of epoxy-based feedthroughs opens the door for virtually any combination of conductors, tubes, fiber optic cables, sizes and geometries.

It’s important to use the right feedthrough for a given application. Epoxy feedthroughs are not always the right choice, and consultation with an applications expert is always recommended.  But from the viewpoint of engineers and designers, epoxy-based feedthroughs usher in design freedom, prototyping, and cost advantages that once didn't exist. 

What is a Vacuum Feedthrough?

Electrical Vacuum Feedthrough
(Epoxy)

A vacuum feedthrough is designed to pass matter or energy, without leakage, from the outside of a vacuum chamber to the inside. The term vacuum feedthrough is often used interchangeably with electrical feedthrough, glass feedthrough, ceramic feedthrough, epoxy feedthrough and hermetic feedthrough. There are of course differences, but they all provide the same function - provide a leak-tight seal between the inside and outside of a vacuum chamber.

Epoxy, glass or ceramic feedthroughs refer to the materials used to seal the conductor, tube, or fiber optic cable from the vacuum/process connection. Hermetic feedthrough refers to the device's nature of being airtight or vacuum tight, such as "hermetically sealed".

Fiber Optic Vacuum Feedthrough

Vacuum feedthroughs are used for 2 primary functions: delivering energy (usually in the form of electricity or light pulse); and for delivering matter in the form of liquids and gases.

Electrical feedthroughs use electrical conductors such as wires to deliver electricity inside the vacuum chamber.

Liquid and gas feedthroughs use metal tubes or fiber optic cables to introduce fluids or light beams.

Liquid & Gas Vacuum Feedthrough

There is debate over what sealing material provides the best over-all performance-to-cost benefit.  Glass to metal seals and ceramic seals are ubiquitous and provide very good sealing properties, but they are expensive and difficult to customize, making prototyping and small production runs challenging. Early epoxy seals were limited in temperature range and were known to outgas, but new, modern epoxy compounds have been developed to perform as well as glass to metal and ceramic.

Modern epoxy feedthroughs can now achieve vacuum up to 10^-8 Torr, temperatures up to 200°C continuous (300°C intermittent), and meet NASA's outgassing requirement of <1.0% Total Mass Loss (TML).

For more information, contact BCE by visiting http://bcemfg.com or call (510) 274-1990.