PCBs in UHV
John Larkin
without serious outgassing?
And recommendations on materials/fabricators/whatever?
Thanks,
John
1PW
Hello John:
I'm not tuned in to the latest PCB materials these days. However, out
gassing of everything is part of the startup process. Put the
cleaned/washed board in and cook with externally applied artificial heat
for days if necessary. As your pumps achieve -9 to -10, you know you
got there.
HTH
Pete
--
1PW @?6A62?FEH9:DE=6o2@=]4@> [r4o7t]
Martin Brown
> Has anybody done PC boards to run in UHV (1e-9, maybe -10 torr)
> without serious outgassing?
Talk to one of the mass spectrometer makers to find out what is
available now. And how reliable it is. It will also have to survive
baking to whatever temperature is needed to enable a hard vacuum to be
achieved.
>
> And recommendations on materials/fabricators/whatever?
When I was in that game I think they used PEEK for the internal plastic
supports and copper pins. Not exactly mass production stuff. They put
the least electronics they could into exposed hard vacuum because of the
difficulties.
And not all PEEKs were created equal so they had to test every batch.
Regards,
Martin Brown
Jeroen Belleman
At those 'pressures', only a little outgassing can be a real
show stopper. If you can get away with putting the electronics
outside of the vacuum, that should be the way. Otherwise,
you might try ceramic substrates. Everything should be
thoroughly clean and dry. Outgassing of individual components,
or any crud stuck underneath is also likely to be an issue.
Regards,
Jeroen Belleman
bill....@ieee.org
Thick film hybrid construction on the standard alumina substrate?
If you can find anybody who still does this ...
--
Bill Sloman, Nijmegen
Rich Grise
I've seen them done on a ceramic substrate.
Have Fun!
Rich
Ecnerwal
It can also depend on how absurdly large/small your pumps are - a
massively overpumped system can tolerate all sorts of crap that an
underpumped system would never manage (10e-10 with a plexiglass window?
with a cryopump designed for a lower pressure and a larger connected
system, it can be done - with no baking!) - but I would 4th or 5th the
"minimize what's in there" advice. Any component with guts, or plastic
etc. that can offgas will offgas. Ceramic and metal packaging is the
order of the day, and a ceramic substrate is your best bet if you have
to put a board in there.
You might (depends on how this will be used, or what some idiot can do
wrong) need to take precautions against it being powered up as the
system is pumped down, as there's a delightful range well above where
you want to work that makes pretty plasma (I worked during college in a
plasma lab.) Could make any powered up electronics go a bit whacky, to
say the least - also IIRC tends to help lay down carbon tracks, if
there's any carbon to work with.
http://www.insulatorseal.com/searchs/doc/DielectricStrength.htm
Use feedthroughs and get out in the air as soon as possible.
--
Cats, coffee, chocolate...vices to live by
whit3rd
I've used PC board materials (fiberglass, high glass content) in high
vacuum
with no problems, BUT it was on the cold side of a cryostat.
Most components (the paint on resistors, the epoxy on ICs, the
vinyl sheath on electrolytic capacitors) aren't good in vacuum, and
aren't bakeable enough anyhow. If it's a simple circuit, you might be
able to weld one up, or if it's more complex, consider welding a box
for it that has glass/metal, or ceramic feedthroughs, so that only
some external wiring comes out to the vacuum.
For quick/dirty fabrication, a spark plug is a good ceramic
feedthrough,
and the base of a metal vacuum tube is an array of feedthroughs.
Phil Hobbs
Notoriously horrible. Use alumina.
Cheers
Phil Hobbs
John Larkin
Maybe in production; or even better, AlN, to keep the chips cool.
But we need to test a prototype, so some sort of polyimide or Rogers
laminate will have to do for now.
If I copper-pour most of the top and bottom, and gold plate, that
might cover a bunch of the surface, and help a bit.
John
Robert Baer
Yes, PEEK is god, but wouldn't glass be better?
Rene Tschaggelar
> Martin Brown wrote:
[snip]
>>> And recommendations on materials/fabricators/whatever?
>>
>>
>> When I was in that game I think they used PEEK for the internal
>> plastic supports and copper pins. Not exactly mass production stuff.
>> They put the least electronics they could into exposed hard vacuum
>> because of the difficulties.
>>
>> And not all PEEKs were created equal so they had to test every batch.
>>
>> Regards,
>> Martin Brown
> Yes, PEEK is god, but wouldn't glass be better?
Glass is somewhat limited in how it can be machined ...
Rene
Martin Brown
> Yes, PEEK is god, but wouldn't glass be better?
Have you ever tried to drill a lot of holes in glass?
My recollections are that they did have trouble with batch to batch
variation that only really showed up when they tried to bake the machine
down to full hard vacuum working pressure. So you should be pretty
careful and do tests to avoid making boards that cannot be pumped down.
It may be better now, but I wouldn't hold your breath.
Regards,
Martin Brown
Glen Walpert
wrote:
But Macor glass-ceramic is easily machined and suitable for UHV
bake-out.
Ecnerwal
John Larkin <jjla...@highNOTlandTHIStechnologyPART.com> wrote:
> If I copper-pour most of the top and bottom, and gold plate, that
> might cover a bunch of the surface, and help a bit.
>
> John
It may actually do the opposite - whatever is in there to offgas _will_
offgas - if you make it harder for it to get out, it will offgas for a
longer period of time. You might do better to minimize surface coverage
and/or swiss-cheese the board with non-plated holes to allow trapped
material to get out and be pumped away.
If the system is overpumped, and the location of the board is nearer the
pump than the location that really needs to be UHV, "sealing" it might
be OK. If the board is closer to the location that really needs to be
UHV, making it as easy as possible to offgas will be better, as you'll
get the material that needs to leave out of the system faster.
At low pressures, you don't have "mass flow" and pumping as we are used
to thinking of pumping with normal fluids - it becomes a game of
individual molecules bouncing about - so even if you have a massive
pump, if your gassy board is near the area of interest, it will be
raising the local pressure as long as it's offgassing.
As a crappy and possibly useless analogy, consider a wet sponge in an
area you are trying to keep bone dry with a dehumidifier. If the sponge
is just exposed, it will dry out fairly fast. If you put plastic wrap
over the sponge, it will take much longer to dry out.
John Larkin
Yes, the diffusion situation gets complex if the board is partially
covered with copper. If I cover 95%, the crud rate drops by (almost?)
20:1 but long diffusion-type exponentials are introduced, some of
which may have decades-long tails if the escape distances are long.
Messy math.
Seems like it may be better to cover as much as I can; the fast stuff
will get out near the openings, and then maybe I can get my testing
done. I suppose I'll have to talk to a real UHV jock before I finalize
things.
John
Rich Grise
>
> Yes, the diffusion situation gets complex if the board is partially
> covered with copper. If I cover 95%, the crud rate drops by (almost?)
> 20:1 but long diffusion-type exponentials are introduced, some of
> which may have decades-long tails if the escape distances are long.
> Messy math.
>
> Seems like it may be better to cover as much as I can; the fast stuff
> will get out near the openings, and then maybe I can get my testing
> done. I suppose I'll have to talk to a real UHV jock before I finalize
> things.
>
I'd suspect that with any of today's boards, you'd never achieve UHV in
the first place.
Just bite the bullet and use ceramic.
Or, if you've got a UHV-capable bell jar, just have one of your techs do
the experiment.
I'd also suspect that after the test, the bell jar and pumps would have
to be thoroughly baked out.
You don't use oil diffusion pumps, do you?
Thanks,
Rich
Robert Baer
And wires can be integrated for power and signal connections as long
as one chooses metals and glasses that have rather similar expansion vs
temp coefficents.
whit3rd
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> On Wed, 29 Apr 2009 10:41:36 -0400, Ecnerwal
>
> covered with copper. If I cover 95%, the crud rate drops by (almost?)
> 20:1 but long diffusion-type exponentials are introduced,
> Seems like it may be better to cover as much as I can;
It sounds like you don't like the alumina substrate idea; there
are also (in mass production, I've seen 'em) steel circuit board
options. Porcelainized steel, with additive copper wiring, can
support
a lot of circuit complexity, and it's heatsink-friendly (which
could be important; vacuum DOES act as an insulator).
gghe...@gmail.com
I postdoced in a lab that did a lot of UHV. (I was/am far from an
expert and just did what they told me to do.) But they did not want
any lead or tin in the UHV system. You'd have to look up the vapor
pressure of these metals. But they can be a problem... especially
during the bakeout process.
George Herold
John Larkin
wrote:
Once I test some circuits in a real instrument, a ceramic hybrid is
seriously possible; I have a friend who has a hybrid company in
Sunnyvale. Aluminum nitride would be great; it conducts heat almost as
well as aluminum, and way better than alumina. But a PCB is a better
way to do some prototypes. And I'll really need multilayer, which is
messy in ceramic.
This is a porcelainized steel resistor:
ftp://jjlarkin.lmi.net/Welwyn.JPG
John
Carl Ijames
system (Agilent puts circuit boards at the detector end of their little
quadrupole mass specs, the MSD series, but they only need 10-7 torr at best
and I don't recall any components, just traces for connections). I've read
that fiberglass boards can be a real problem in UHV - if there are voids in
the epoxy the trapped air can leak out along a glass fiber essentially
forever. You can bandaid that with a really big pump :-). Actually I think
that the board will be the easiest part - hardly any component you would
solder on the board, or the solder, will be UHV compatible. What
temperature range do you need the electronics to handle, and what pumping
speed and type of pump do you have?
-----
Regards,
Carl Ijames
"John Larkin" <jjla...@highNOTlandTHIStechnologyPART.com> wrote in message
news:jckfv452jbnnrlq26...@4ax.com...
John Larkin
wrote:
>On Wed, 29 Apr 2009 09:19:14 -0700, John Larkin wrote:
>>
>> Yes, the diffusion situation gets complex if the board is partially
>> covered with copper. If I cover 95%, the crud rate drops by (almost?)
>> 20:1 but long diffusion-type exponentials are introduced, some of
>> which may have decades-long tails if the escape distances are long.
>> Messy math.
>>
>> Seems like it may be better to cover as much as I can; the fast stuff
>> will get out near the openings, and then maybe I can get my testing
>> done. I suppose I'll have to talk to a real UHV jock before I finalize
>> things.
>>
>
>I'd suspect that with any of today's boards, you'd never achieve UHV in
>the first place.
>
>Just bite the bullet and use ceramic.
>
>Or, if you've got a UHV-capable bell jar, just have one of your techs do
>the experiment.
I don't have any UHV gear. Hey, I don;t have any techs, either!
>
>I'd also suspect that after the test, the bell jar and pumps would have
>to be thoroughly baked out.
No, really, there are some UHV-compatible PCB materials, polyimide and
teflon based. I think.
>
>You don't use oil diffusion pumps, do you?
Do they still make them? My customers use turbomolecular pumps,
basically fans. A few extreme cases use cryo and ion pumps, too.
John
John Larkin
>Done a fair amount of UHV work in the past but never put a pc board in a UHV
>system (Agilent puts circuit boards at the detector end of their little
>quadrupole mass specs, the MSD series, but they only need 10-7 torr at best
>and I don't recall any components, just traces for connections). I've read
>that fiberglass boards can be a real problem in UHV - if there are voids in
>the epoxy the trapped air can leak out along a glass fiber essentially
>forever. You can bandaid that with a really big pump :-). Actually I think
>that the board will be the easiest part - hardly any component you would
>solder on the board, or the solder, will be UHV compatible. What
>temperature range do you need the electronics to handle, and what pumping
>speed and type of pump do you have?
>
The system uses turbo pumps. It has existing ghastly electronics that
uses plastic DIP ic's and axial passives that are hand point-to-point
wired, with solder, on a drilled ceramic slab maybe 2" square. That
means they have essentially only radiation cooling, and I calculate
the critical (jfet!) opamps run at maybe 120C. If dips and solder
joints running at 120C don't outgass enough to trash the system, it
must be pretty hardy. Operating ambient is room temp. They obviously
don't bake it really hard.
It was designed by chemists. What can I say?
In addition to all the other problems, chip cooling is an issue when
there's no air! That's where an AlN substrate would eventually be
great. But a multilayer PCB would sure be easier.
John
James Arthur
> In addition to all the other problems, chip cooling is an issue when
> there's no air! That's where an AlN substrate would eventually be
> great. But a multilayer PCB would sure be easier.
>
> John
>
If you could add a heatpipe or, even better, a fluid-filled
cooling loop in the UHV, you could cool the amps and lower
noise a bunch.
Cheers,
James
Uwe Hercksen
John Larkin schrieb:
> The system uses turbo pumps. It has existing ghastly electronics that
> uses plastic DIP ic's and axial passives that are hand point-to-point
> wired, with solder, on a drilled ceramic slab maybe 2" square. That
> means they have essentially only radiation cooling, and I calculate
> the critical (jfet!) opamps run at maybe 120C. If dips and solder
> joints running at 120C don't outgass enough to trash the system, it
> must be pretty hardy. Operating ambient is room temp. They obviously
> don't bake it really hard.
Hello,
I suspect the plastic DIP ic's and axial passives will outgas too, not
only the PCBs.
Bye
Uwe Hercksen
Glen Walpert schrieb:
> But Macor glass-ceramic is easily machined and suitable for UHV
> bake-out.
Hello,
if the PCB material may be baked out, but the components mounted on the
PCB are not suitable for bake-out, it would not help much.
Bye
John Larkin
That would be the ultimate amp, something cooled a lot. Now I can add
a bunch of fun new problems to the mix, like thermal stresses and
semiconductor behavior and ceramic caps quitting.
Sounds difficult and expensive. I like that.
John
Robert Latest
> Seems like it may be better to cover as much as I can; the fast stuff
> will get out near the openings, and then maybe I can get my testing
> done. I suppose I'll have to talk to a real UHV jock before I finalize
> things.
Another issue is contamination of the UHV chamber. Some of the stuff
that outgasses during bake-out of the system or during operation will
recondense in cooler parts of the chamber (outbaking is never
homogenous, unless you have one of those cool "baking tents") and will
slowly keep evaporating from there. Whether or not this is a problem
depends on what your customer is doing in the vacuum system. Before
introducing long-chained organic material --and what's the
fire-retardant stuff they use nowadays? Some bromide compound?-- you
need to check back with them.
And I would second other suggestions made in this thread. I'd design the
board to be as out-gassable as possible and I'd bake it in a vacuum
system (doesn't need to be UHV) at a higher temp than the bakeout temp
of the destination system.
robert
Rich Grise
> On Apr 27, 11:19�pm, John Larkin
> <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
>> Has anybody done PC boards to run in UHV (1e-9, maybe -10 torr)
>> without serious outgassing?
>>
>> And recommendations on materials/fabricators/whatever?
>
> expert and just did what they told me to do.) But they did not want
> any lead or tin in the UHV system. You'd have to look up the vapor
> pressure of these metals. But they can be a problem... especially
> during the bakeout process.
I actually _worked_[1] at a place whose product was essentially based on
UHV. One day, one of the engineers came into the office bitching that
someone had specified a feedthrough or some part for inside the bell jar,
and he said, "It was _brass_ <spit>" with a demeanor of utter disgust.
Turns out zinc outgasses forever. And contaminates the whole system -
you need to take such dramatic heroic measures to get the zinc out
that it's cheaper to just toss the whole thing and start from scratch.
Cheers!
Rich
[1] a little dig on the academicians who have never done an honest day's
work in their life.
Rich Grise
>
> In addition to all the other problems, chip cooling is an issue when
> there's no air! That's where an AlN substrate would eventually be
> great. But a multilayer PCB would sure be easier.
Does AlN have better heat conductivity than BeO?
Or is it mainly that it's machinable without killing the machinist? ;-)
Thanks,
Rich
Rich Grise
> On Thu, 30 Apr 2009 06:41:32 GMT, James Arthur
>>
>>> In addition to all the other problems, chip cooling is an issue when
>>> there's no air! That's where an AlN substrate would eventually be
>>> great. But a multilayer PCB would sure be easier.
>>
>>cooling loop in the UHV, you could cool the amps and lower
>>noise a bunch.
>
> a bunch of fun new problems to the mix, like thermal stresses and
> semiconductor behavior and ceramic caps quitting.
>
> Sounds difficult and expensive. I like that.
At the UHV place I once worked (ca. 1976.77), one of their instruments was
an X-ray source. It had a copper anode with the -10 KV cathode off to the
side, and they were having trouble cooling the damn thing (it was
essentially 1/2" copper pipe with the tungsten welded to the end.). I
suggested a heat pipe and nobody had a clue what I was talking about.
Plus, they had sort of a "what does a lowly tech know about anything?"
attitude - the company was run by a PHD. I was tempted to make a heat
pipe at home and bring it in to demo it, but this was pre-internet, so
I wasn't exactly sure how to build one to demo.
If you built a heat pipe, say, 10" long, with copper tubing, copper wool
(or asbestos substitute), and water vapor, would you be able to hold it
in the middle, torch it at the end, and burn the hand of someone at the
other enc? IOW, would the middle get as hot as the condenser end?
Thanks,
Rich
James Arthur
> On Apr 27, 8:19 pm, John Larkin
> <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
>> Has anybody done PC boards to run in UHV (1e-9, maybe -10 torr)
>> without serious outgassing?
>>
If it's a simple circuit, you might be
> able to weld one up, or if it's more complex, consider welding a box
> for it that has glass/metal, or ceramic feedthroughs, so that only
> some external wiring comes out to the vacuum.
Whacky idea: seal the proto in a glass envelope, a "circuit in
a bottle"?
That wouldn't be terribly hard to do.
James Arthur
Rich Grise
> On Wed, 29 Apr 2009 19:46:36 GMT, Rich Grise <rich...@example.net>
You might also want to look at sorption pumps for roughing. Where I
worked (the place is now owned by Perkin-Elmer), they only used the
cryopump for the Molecular Beam Epitaxy rig. But, if your ion pumps
and getter pumps do their job, you can get a mind-bogglingly clean
vacuum.
My association with MBE was working on the control sequencer, which
the geriatric PhD in the lab had designed using relay logic. =:-O
Have Fun!
Rich
(BTW, before you offer me a job, I should tell you it'd cost a couple
thou to relocate me, and I only know enough about UHV to be dangerous. ;-) )
Rich Grise
Speaking of PhDs, the company parties sounded like a Phi Beta Kappa
convention. ;-D
Cheers!
Rich
Rich Grise
> Rene Tschaggelar wrote:
>> Robert Baer wrote:
>>> Martin Brown wrote:
>>
>>>>> And recommendations on materials/fabricators/whatever?
>>>>
>>>> When I was in that game I think they used PEEK for the internal
>>>> plastic supports and copper pins. Not exactly mass production stuff.
>>>> They put the least electronics they could into exposed hard vacuum
>>>> because of the difficulties.
>>>>
>>>> And not all PEEKs were created equal so they had to test every batch.
>>
>>
>> Glass is somewhat limited in how it can be machined ...
> And wires can be integrated for power and signal connections as long
> as one chooses metals and glasses that have rather similar expansion vs
> temp coefficents.
If you find a decent glass blower, some of their results can be
indistinguishable from magic. ;-)
Cheers!
Rich
Spehro Pefhany
wrote:
>On Wed, 29 Apr 2009 07:08:29 -0700, ggherold wrote:
BTW, John:-
A helpful fellow (happens to be a scientist who founded a major Mass
Spectrometer mfg. company) told me the standard reference is (I think)
O'Hanlon. I should see him again next week if you have any specific
questions.
John Larkin
wrote:
>On Wed, 29 Apr 2009 21:02:28 -0700, John Larkin wrote:
>>
>> In addition to all the other problems, chip cooling is an issue when
>> there's no air! That's where an AlN substrate would eventually be
>> great. But a multilayer PCB would sure be easier.
>
>Does AlN have better heat conductivity than BeO?
It's not as good but close, just about equal at some temperatures.
>
>Or is it mainly that it's machinable without killing the machinist? ;-)
Yup.
BeO still has the best ratio of thermal conductivity to dielectric
constant, except for diamond.
John
Jim Thompson
Not so wacky! If you have a university nearby with a vacuum and glass
shop. Maybe Kovar pins into a glass envelope?
Brings back memories. Haven't done any glass blowing/vacuum systems
since around 1960.
...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 http://www.analog-innovations.com | 1962 |
I love to cook with wine Sometimes I even put it in the food
John Larkin
Mass spec company? Which one?
O'Hanlon is on order. Thanks.
I guess the question is just, what's the best way to package a modest
(say, 20 parts or so) electronic circuit for UHV.
John
Jim Thompson
<To-Email-Use-Th...@My-Web-Site.com> wrote:
>On Thu, 30 Apr 2009 21:10:18 GMT, James Arthur
><bogus...@verizon.net> wrote:
>
>>whit3rd wrote:
>>> On Apr 27, 8:19 pm, John Larkin
>>> <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
>>>> Has anybody done PC boards to run in UHV (1e-9, maybe -10 torr)
>>>> without serious outgassing?
>>>>
>>[...]
>>
>> If it's a simple circuit, you might be
>>> able to weld one up, or if it's more complex, consider welding a box
>>> for it that has glass/metal, or ceramic feedthroughs, so that only
>>> some external wiring comes out to the vacuum.
>>
>>Whacky idea: seal the proto in a glass envelope, a "circuit in
>>a bottle"?
>>
>>That wouldn't be terribly hard to do.
>>
>>
>>James Arthur
>
>Not so wacky! If you have a university nearby with a vacuum and glass
>shop. Maybe Kovar pins into a glass envelope?
>
>Brings back memories. Haven't done any glass blowing/vacuum systems
>since around 1960.
>
> ...Jim Thompson
Actually, you can probably buy the header as a unit (like a 7-pin-mini
tube), build your electronics onto the header, vacuum and seal.
VWWall
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
James Arthur
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
Carl Ijames
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
"John Larkin" <jjla...@highNOTlandTHIStechnologyPART.com> wrote in message
news:qj7iv4lq20ole18en...@4ax.com...
James Arthur
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:
http://blog.makezine.com/archive/2008/01/make_your_own_vaccum_tube.html
Cheers,
James Arthur
Jim Thompson
<bogus...@verizon.net> wrote:
[snip]
>
>There's something "steam punk" about sealing semiconductors in
>glass and bringing the leads out to a 9-pin base!
>
[snip]
>Cheers,
>James Arthur
I think it'll work nicely. I'll patent it ;-)
John Larkin
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
John Larkin
>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.
OK. The circuit design is challenging enough, without all the other
gotchas.
John
Ecnerwal
Rich Grise <rich...@example.net> wrote:
> My association with MBE was working on the control sequencer, which
> the geriatric PhD in the lab had designed using relay logic. =:-O
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
Jasen Betts
>
> If you built a heat pipe, say, 10" long, with copper tubing, copper wool
> (or asbestos substitute), and water vapor, would you be able to hold it
> in the middle, torch it at the end, and burn the hand of someone at the
> other enc? IOW, would the middle get as hot as the condenser end?
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.
whit3rd
> Jim Thompson wrote:
> >> Not so wacky! If you have a university nearby with a vacuum and glass
> >> shop. Maybe Kovar pins into a glass envelope?
>
> 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.
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.
Phil Hobbs
> Robert Baer wrote:
>> Martin Brown wrote:
>>
>>>
>>>> Has anybody done PC boards to run in UHV (1e-9, maybe -10 torr)
>>>> without serious outgassing?
>>>
>>> available now. And how reliable it is. It will also have to survive
>>> baking to whatever temperature is needed to enable a hard vacuum to
>>> be achieved.
>>>>
>>>> And recommendations on materials/fabricators/whatever?
>>>
>>> When I was in that game I think they used PEEK for the internal
>>> plastic supports and copper pins. Not exactly mass production stuff.
>>> They put the least electronics they could into exposed hard vacuum
>>> because of the difficulties.
>>>
>>> And not all PEEKs were created equal so they had to test every batch.
>
>> Yes, PEEK is god, but wouldn't glass be better?
>
>
> My recollections are that they did have trouble with batch to batch
> variation that only really showed up when they tried to bake the machine
> down to full hard vacuum working pressure. So you should be pretty
> careful and do tests to avoid making boards that cannot be pumped down.
> It may be better now, but I wouldn't hold your breath.
>
> Regards,
> Martin Brown
Tapping Macor without chipping it is a recreational impossibility.
Cheers
Phil Hobbs
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
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
Glen Walpert
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
:-).
http://www.morgantechnicalceramics.com/acatalog/
(random distributor - no personal experience)
John Larkin
<pcdhSpamM...@electrooptical.net> wrote:
Just hammer a Pem into it.
John