Electrical feedthrough for high-vacuum chamber - Page 1
Forum section: electronics / general

author: felisnigripes
author_rank: Newbie
timestamp: July 11, 2022, 11:10:47 am
content: Hello dear forum,Perhaps a little off-topic, but I was unable to find another forum online to ask this question. Please do inform me where else I could post this.For my university studies I require a high-vacuum chamber which can fit under a conventional microscope. We have the necessary pumps for this, my task is is to design a simple, small chamber which can be manufactured by our workshop.What the chamber requires are electrical feedthroughs with which I can connect electrical equipment from outside with inside. So far I have found some options in the form of a weldable sub-D adapter (https://www.vacuum-shop.com/shop/en_US/category/2073643/d-sub-feedthroughs-weld-adapter-male.html) , but it is very expensive.I know that some hermetically sealed adapters exists in various connector types, which would be much cheaper, but I have trouble finding the correct ones (none that I find say that they are specified for use in vacuum).Does anyone know how to find them or any cheaper alternatives?

author: RoGeorge
author_rank: Super Contributor
timestamp: July 11, 2022, 11:23:38 am
content: I've read automotive spark-plugs can work well. There might be many other ways, search for DIY feedthrough.https://gigabecquerel.wordpress.com/2019/06/02/quick-n-dirty-vacuum-feedthrough/

author: popeye2755
author_rank: Newbie
timestamp: July 11, 2022, 11:24:34 am
content: We used to use Fischer connectors for vacuum products:https://fischerconnectors.com/en/solutions/connectors/core-series/

author: jpanhalt
author_rank: Super Contributor
timestamp: July 11, 2022, 12:11:09 pm
content: Glass-metal seals have been used for many decades, e.g., vacuum TV and radio tubes, light bulbs, mass spectrometers, early cyclotrons, a long list. In my experience, appropriate metal is relatively cheap. They are easily made even by an amateur glassblower.Since it is for microscopy, I assume it will be largely glass. If it is metal with a glass window, then there are other solutions.Even rubber (low gassing) O-rings can be used.More information about the application would help. If it is an inverted microscope, that may help solve any space problem.

author: tooki
author_rank: Super Contributor
timestamp: July 11, 2022, 03:30:16 pm
content: I had to do a few wire harnesses for high vacuum earlier this year, and yep, it’s all insanely expensive because they have to be made from special plastics that don’t outgas at all. The fact that the plastic is much more expensive than ordinary plastics isn’t even the big issue, so much as the tiny numbers these things are made in. It doesn’t help that many of those begin with designs for high-end mil-spec connectors.I’m honestly not sure if lower cost options exist — and if the Chinese made them, would you trust them?Have you taken a look at Accu-Glass Products? That’s what the team I helped out was using, and not everything is quite that expensive.

author: langwadt
author_rank: Super Contributor
timestamp: July 11, 2022, 04:17:16 pm
content: how much of a vacuum? a piece of PCB with a connector, pins soldered on both sides?

author: Kleinstein
author_rank: Super Contributor
timestamp: July 11, 2022, 05:00:16 pm
content: Vaccum feed-throught tend to be expensive, though there may be somewhat cheaper versions with a more standard flange. I remeber a sub-D type as a relatively cheap one, but this is some 20 years ago and the prices do vary quite a bit between sources.It depends on the vaccum range: with not too high demands (e.g. mPa range) there is the option to use some feed through capacitors or even bare wire and epoxy.

author: Gyro
author_rank: Super Contributor
timestamp: July 11, 2022, 07:46:46 pm
content: How many wires do you need to pass into the chamber and is its wall solderable?A single row of hermetic glass feedthoughs soldered into holes in the side of the chamber would yield a low overall height (you presumably have more latitude on width). You certainly can't argue about the price...https://www.ebay.co.uk/itm/261672048845

author: TimFox
author_rank: Super Contributor
timestamp: July 11, 2022, 08:13:58 pm
content: In graduate school, we used many vacuum fittings from Ceramaseal.https://www.ceramtec.com/ceramaseal/feedthroughs/They make a wide range of product: weld/braze to vessel, Conflat flanges, multi-pin, tube-base multi-pin, etc.

author: felisnigripes
author_rank: Newbie
timestamp: July 12, 2022, 07:17:09 am
content: Thank you all for your suggestions.To answer the questions that some of you asked:It is standard upright microscope (sample is viewed from above). The chamber should in total not be larger than 45 mm. The design will not leave for a lot of space inside the chamber (~30 mm, depending on the wall thickness). The material will be stainless steel, due to weldability.We need at least 10^(-5) mbar inside the chamber. At least 16 contacts are needed, so the Sub-D weld connector seems like the best option at the moment..Edit:Fischer Connectors seem like a very good choice, by pin number and size, but I do not have information on the price. I am contacting the company.

author: Kleinstein
author_rank: Super Contributor
timestamp: July 12, 2022, 08:07:58 am
content: For 16 contacts the Sub D connector really looks like the best bet - possibly find a somewhat cheaper source. The price is still not that bad for scientific instrumentation and the custom made chamber would be expensive anyway.With the small size one could have a limited pumping power available (just limited by tube diameter) and thus not much tolerance for leaks and outgasing.It also depends on the pump - chances are a microscope would need a low vibration environment - so ideally something like a Ti based pump and aiming for 10^(-6) mbar.

author: Gribo
author_rank: Frequent Contributor
timestamp: July 12, 2022, 02:08:44 pm
content: Circular connectors might be easier to seal, the problem is, getting one with 16 positions.There are also Micro-D sealed connectors and cable assemblies, but those are very expensive.

author: felisnigripes
author_rank: Newbie
timestamp: July 13, 2022, 02:33:20 am
content: Quote from: popeye2755 on July 11, 2022, 11:24:34 amDo you remember how much they cost?

author: David Hess
author_rank: Super Contributor
timestamp: July 13, 2022, 04:46:56 am
content: A long time ago we used a glass/metal feedthrough but it was the construction which caught my eye. It was a penny sized disk of green glass, with 4 hooked feedthrough pins, and a metalized edge. So the feedthrough "penny" was literally soldered into a hole in the metal side of the steel chamber with a big soldering iron to make a hermetic seal. The secret words are apparently kovar and fusite k-glass.If you want to hack it, then the base of a TO-3 transistor is constructed this way and can be cut up to make a double vacuum feedthrough. Some older TO-3 style parts have 4 or even 8 leads.

author: jonpaul
author_rank: Super Contributor
timestamp: July 13, 2022, 05:01:25 am
content: Bonjour the standard for glass to metal seals is Kovar.https://en.m.wikipedia.org/wiki/Kovarold lamp or tubes have multi conducteur Kovar seals.The Kovar seals are available from vacuum equipment vendors.Bon chanceJon

author: felisnigripes
author_rank: Newbie
timestamp: July 20, 2022, 03:50:07 am
content: Thanks everyone for your suggestions.I decided to go with a sub-D weldable adapter from CeramTech which was locally available for a lower price.