• October 04, 2023

Ceramic Seals vs. Glass Seals in Hermetic Connectors

Pin sealing options are just one of many considerations when designing or specifying hermetic connectors. And while it may seem trivial, material selection here can greatly impact other connector performance parameters.

Here are 5 reasons to consider polycrystalline ceramic over glass seals for hermetic DC connectors:

1. More Pin Material Options: The glass sealing process requires a highly heat-resistant pin material (typically Kovar) that can survive the melting temperature of glass intact. Ceramics seal at a lower temperature, accommodating the use of copper alloy pins (beryllium copper, chrome copper, etc.) as well as platinum, platinum clad or Inconel pins.
2. Higher Electrical Conductivity:  Beryllium copper (BeCu) is a common pin material in connectors that use ceramic-to-metal seals. In a Micro-D format (.018″ pin diameter), for example, a Kovar pin will carry  .45 amps while that same pin size in BeCu carries 2.58 amps.
3. Crack-Proof Seals:  If you’ve ever had a stone hit the top your car windshield, you know that it’s only a matter of time before that crack makes its way  across the glass. It’s the same with a glass-sealed connector pin – if a fissure starts at the top of a seal, it will likely follow a path to the bottom, resulting in a hermetic failure. Ceramics, such as Kryoflex, have a randomized crystalline structure that doesn’t allow a crack to propagate, thus eliminating hermetic failures related to cracked glass.
4. Weight Savings: Copper alloy pins can be integrated into aluminum connector bodies with a ceramic-to-metal seal. This material combination can deliver very light and highly conductive connectors that are very well suited for applications without rigorous thermal cycling requirements. With this material combination, hermetic performance degrades from 1×10-9 He @ 1 ATM to 1×10-5 after repeated thermal cycles. For many applications that don’t have a thermal cycle concern or require more of an environmental seal and where weight and electrical performance are priorities, direct seal aluminum connectors are a great option.
5. Robust insulator: Ceramic functions as an excellent electrical insulator at very high temperatures, unlike glass, which conducts more electricity at elevated temperatures. For example, Kryoflex has a resistivity of 1×1018 ohms/cm with easily maintained resistance values in the 50K megohm range – even in micro-miniature designs. Standoff voltage capability is such that breakdown will always occur in the air media surrounding the terminal, never through the dielectric.