COMPARISON OF HERMETICALLY SEALED CONNECTOR TECHNOLOGIES
Three primary methods exist to create a hermetically sealed electrical connector: Glass to Metal, Molded Epoxy, and Molded PEEK. Each method has distinct advantages and disadvantages.
Glass-to-Metal (GTM)
There are two GTM methods with one superior at extreme temperatures and the other superior for higher pressures. Both seals are short, and the glass is brittle, so the seal is prone to failure from minor impacts on the end of the conductors such as during maintenance.
A matched thermal expansion method requires the housing, glass seal and conductor to have near equal coefficients of thermal expansion (CTE). A matched thermal expansion GTM is superior sealing at temperatures exceeding 400 °F but is limited to low conductivity materials for conductors.
The compression seal method requires the housing to have a higher CTE thus compressing the glass onto the conductor after firing. The compression seal GTM is superior for sealing at pressures to 35,000 psi but is still limited to low conductivity materials for the conductors.
Epoxy
Epoxy seals are made in open cavity molds (aka potting) or in closed molds with injection molding. For low pressure applications epoxy with low amounts of filler and open molds are used. For high pressure applications epoxies filled with short glass fibers and closed molds are used. Both methods provide for a long seal and the epoxy is at least 2X more ductile than glass, so they are less prone to impact failures.
The open mold method allows for sealing odd shapes, requires low investment in manufacturing tooling but is costly due to the high amount of labor and slow cure time of the material. However, the main concern is the seal is very unreliable due to the absence of cavity pressure during molding.
The closed mold method is always combined with glass reinforced epoxy (GRE) and requires more manufacturing tooling investment but a lower labor level and faster cure time. The seal is quite reliable, but the insulating body is still brittle and subject to damage during maintenance.
PEEK
PEEK is the new kid on the block, first used for a hermetic connector in the 1990’s. Always made in expensive molds with high pressure injection so they are not low cost. PEEK, and PEK, a higher temperature variant, are 20-40X more impact resistant than epoxies and glasses. This impact resistance, and a long seal length provides the absolute most reliable and durable seal.
PEEK connectors are not limited to low conductivity conductors. A final trait of PEEK connectors, due to the material strength being near 300 series stainless steel or 6061-T6 aluminum, is mounting features can often be integrated into the insulator body thus providing a featherweight but super rugged electrical interconnect.
