PCBs in UHV

Just take an old noval, (nine pin), glass tube, cut the glass envelope, remove the tube elements, and you've got a nice nine wire header, The envelope is lead glass, easy to attach to any similar enclosure.

The "pins" are Kovar, and other metal leads would need to be spot welded to them. The final electronic envelope would not need to be evacuated, but could be filled with dry nitrogen, and then sealed off.

--
Virg Wall, PE

That's what I was thinking: crack the bottom off a dead tube, just for a quickie.

Possible tutorial: some months ago someone here posted a beautiful video of a French guy who was making tubes from scratch.

--James

O'Hanlon has nice plots of elemental vapor pressures vs. temperature, to let you know what to avoid. At room temp even lead and zinc are actually ok,

10-18 and 10-12 torr, respectively. However, at 200C the vapor pressures rises to 10-12 and 7x10-6 torr. That means that anything that gets warm to the touch better not have any zinc or you will coat the entire chamber with it, so no brass plating on terminals or eyelets. If your base pressure goal is really 10-10 torr then lead should be ok since your plastic ic's will outgas lots of water and organics at their max temp of maybe 140-150C and the lead will still be negligible. All the usual structural metals (iron, aluminum, nickel, copper, even tin) are fine. You will have to limit your bakeout to what the electronics can take, and keep them powered down while baking, so 10-10 torr may not come that easy. It all depends on the surface area of your outgassing components, which is why those chemists (hey, I resemble that remark :-)) get away with the IC's but I don't think you could get away with many square inches of circuit board, especially a multilayer one that can trap gas in the layers. Let us know how it goes; this is interesting stuff.

----- Regards, Carl Ijames

Maybe a half-vacuum, which would split the max stress in half, both for UHV and atmospheric conditions?

There's something "steam punk" about sealing semiconductors in glass and bringing the leads out to a 9-pin base!

Here's the French guy's video:

Cheers, James Arthur

[snip] [snip]

I think it'll work nicely. I'll patent it ;-)

...Jim Thompson

-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at

| 1962 | I love to cook with wine Sometimes I even put it in the food

Ah. A toob.

OK if there's a way to get the heat out.

A production version might be a fairly cruddy board inside an aluminum clamshell sort of package, with hermetic feedthrus and connectors. O-rings apparently work at UHV. As do some epoxies.

John

OK. The circuit design is challenging enough, without all the other gotchas.

John

I was building brand new relay logic systems in labs in 1980's, and I wasn't geriatric. Seems they held up to actual use in pulsed power labs a lot better than the newfangled things that took offense to a few kiloamps here, a couple hundred KV there. Sure it was old tech, but it was old tech that worked in the environment. I can recall the general amazement of the lab when we got in some fiber optic links - you could run 9600 baud duplex right through the lab and not pick up any noise - those were the days.

(My only Phd is from the school of hard knocks.)

--
Cats, coffee, chocolate...vices to live by

yes. heat pipes work by evaporating the coolant at one place end and condensing it elsewhere, it will condense beneath your hand.

you could wrap the middle with a thermal insulator (eg several layers of paper) and not be burnt. when holding it by the insulator.

ss

The time for this kind of work has passed; the usual tube bases one finds nowadays are OLD, and glass which has aged is a glassblower's nightmare. I've heard from researchers who DO make their own vacuum tubes, that commercial glass/metal seals dipped badly in quality some decades ago, for best performance nowadays only the ceramic feedthroughs are recommended. Those, have metal surrounds and respond best to welding.

The other problem with glass is low thermal conductivity; you have to dump heat SOMEHOW, and it won't be by air circulation. Bolt a metal box to a hard point, or a heat pipe, and the problem goes away.

Tapping Macor without chipping it is a recreational impossibility.

Cheers

Phil Hobbs

Oil diffusion pumps are fine for small evaporators and such if you're religious about never, ever opening the high vac valve without LN2 in the cold trap. Oil buildup isn't so horrible because you have to clean evaporators fairly regularly anyway.

They're no good for UHV because of residual backstreaming.

Cheers

Phil Hobbs

That isn't what a surface scientist means by UHV. You'd never get into the 10**-10 torr range with that.

Cheers

Phil Hobbs

It helps to use an oversize pilot drill and only leave 40 to 50% thread vice the usual 60 to 75% in metals, also pre-bevel the hole entrance (and exit if through hole) to at least the thread major diameter. If you need the strength of a full thread in Macor you have made a design error :-). Probably easier with a tap for cast iron (every other tooth removed) if you can find one.

But returning to topic, Macor is easily had in 1/16" sheet which is almost as easily drilled as FR4, such that leaded components are easily mounted and wired with the usual perf-board prototyping hand wiring techniques, leaving only the outgassing of the components to worry about. Tapping not required. Use lead-free solder of course :-).

(random distributor - no personal experience)

Just hammer a Pem into it.

John