[time-nuts] Helium and MEMS oscillators don;t mix well

[Mark Sims]

https://ifixit.org/blog/11986/iphones-are-allergic-to-helium/
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[Jeremy Elson]

I just came here to post that same link. Very interesting bit of hardware
detective work.

Post by Mark Sims
https://ifixit.org/blog/11986/iphones-are-allergic-to-helium/
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[Richard (Rick) Karlquist]

This reminds me of a Jack Kusters (of HP fame) anecdote.
He left HP for a while to work for Ephratom on Rb standards.
Some customer was raising hell about their Ephratom Rb
standards having lousy accuracy. Jack had them send
some of the "defective" units back to the factory, and
the units were indeed having accuracy problems at first,
but eventually returned to the good accuracy they had
when they left the factory. Jack decided that the
explanation must be helium. Jack tried to diplomatically
ask the customer if they used helium in their facility.
They said no and accused Jack of using helium as an
red herring to cover up their lousy product. Jack then
asked again that we wanted to make sure they don't use
helium in their plant. They again emphatically denied
any use of helium. At which point Jack pointed out
that in that case, it was clear than they had a radon
incursion in their facility. And he made them a deal:
if they would stop submitting warranty claims, he would
refrain from publicizing their radon situation. That
took care of the problem.

Rick

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[Poul-Henning Kamp]

--------

Post by Richard (Rick) Karlquist
This reminds me of a Jack Kusters (of HP fame) anecdote.
At which point Jack pointed out
that in that case, it was clear than they had a radon
incursion in their facility.

I have a hard time beliving radon was a relevant failure mechanism
for "telco-class" Rb units, things would literally glow in the dark
long before the Rb concentration became a problem.

It is true that Radon is a small atom, but it is 50% larger than
Helium and that is a big handical when diffusing.

More importantly, Radon decays in a matter of days, much faster
than it would "evaporate" out again, and it leaves a tell-tale
signature of lead atoms behind from the decay.

I find it far more likely that their problem were molecular hydrogen,
which is even smaller than Helium atoms, and present in copious
amounts near any rechargeable battery and a fair number of industrial
processes.
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[Richard (Rick) Karlquist]

Post by Poul-Henning Kamp
--------

Post by Richard (Rick) Karlquist
This reminds me of a Jack Kusters (of HP fame) anecdote.
At which point Jack pointed out
that in that case, it was clear than they had a radon
incursion in their facility.

I have a hard time beliving radon was a relevant failure mechanism
for "telco-class" Rb units, things would literally glow in the dark
long before the Rb concentration became a problem.
It is true that Radon is a small atom, but it is 50% larger than
Helium and that is a big handical when diffusing.
More importantly, Radon decays in a matter of days, much faster
than it would "evaporate" out again, and it leaves a tell-tale
signature of lead atoms behind from the decay.
I find it far more likely that their problem were molecular hydrogen,
which is even smaller than Helium atoms, and present in copious
amounts near any rechargeable battery and a fair number of industrial
processes.

According to Jack, radon emits alpha particles, AKA helium nuclei.
These capture stray electrons and become helium atoms. So the
presence of helium is a marker for radon. The fact that the half
life is a few days supports this hypothesis. At least that is what
Jack told me.

Rick

Rick

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Post by Richard (Rick) Karlquist
According to Jack, radon emits alpha particles, AKA helium nuclei.
These capture stray electrons and become helium atoms. So the
presence of helium is a marker for radon. The fact that the half
life is a few days supports this hypothesis. At least that is what
Jack told me.

Right, but you need a LOT of Radon before the Helium concentration
becomes a problem, and the alphas would literally make things
glow in the dark.
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[Bob kb8tq]

Hi

A lot of Radon and *really* poor ventilation….

There are a lot of ways for He to show up. In normal use, issue is hanging on to it.
It tends to run away from its source very quickly. Maintaining a measurable concentration
in something like a normal room …. not very easy at all.

Bob

Post by Poul-Henning Kamp
--------

Post by Richard (Rick) Karlquist
According to Jack, radon emits alpha particles, AKA helium nuclei.
These capture stray electrons and become helium atoms. So the
presence of helium is a marker for radon. The fact that the half
life is a few days supports this hypothesis. At least that is what
Jack told me.

Right, but you need a LOT of Radon before the Helium concentration
becomes a problem, and the alphas would literally make things
glow in the dark.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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--------

Post by Bob kb8tq
A lot of Radon and *really* poor ventilation….

Yup.

But a LOT of Radon is not without interesting "side-effects", such as
much easier ionization due to the alpha radiation.

To get to relevant He levels via the Radon route, we are talking
deep unventilated mineshaft kind of concentrations...

Hydrogen is a lot more plausible in my view.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
***@FreeBSD.ORG | TCP/IP since RFC 956
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and

[jimlux]

Post by Poul-Henning Kamp
--------

Post by Bob kb8tq
A lot of Radon and *really* poor ventilation….

Yup.
But a LOT of Radon is not without interesting "side-effects", such as
much easier ionization due to the alpha radiation.
To get to relevant He levels via the Radon route, we are talking
deep unventilated mineshaft kind of concentrations...
Hydrogen is a lot more plausible in my view.

Yeah, but in concentrations typical in the "room", I doubt you'd see the
effect. The experimenters put the phone in a bag full of helium and it
took hours. I would expect the same in hydrogen.

That's a lot different than a <1% concentration. I assure you, that if
there was a helium leak/vent/boil off that made the room concentration
1%, the room oxygen sensor would be alarming (having dropped to 20%) and
people would be running for the doors.

I'd be betting more on some RFI/EMI issue from the RF fields or the
magnetic fields, both of which are quite strong in an MRI facility.



However, in true time-nuts fashion, I'm going to rummage around for some
older SiTime oscillators on an eval board at work, and we can do a
*real* test.

I got some samples from them a few years ago, so all I have to do is
find that tiny plastic bag with the tiny 2x2mm parts in it.

Then I have to find some spare hydrogen and helium..

After all, we really need to evaluate it in an atmosphere of Argon and
CO2, (Mars gas) - I'll see if we've got some around - we were doing RF
breakdown tests in simulated Martian atmosphere <grin> (BTW, the
Martian atmosphere is unique in that it probably has the lowest "minimum
sparking voltage" in the universe)







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[Poul-Henning Kamp]

--------

Post by jimlux

Post by Poul-Henning Kamp
To get to relevant He levels via the Radon route, we are talking
deep unventilated mineshaft kind of concentrations...
Hydrogen is a lot more plausible in my view.

Yeah, but in concentrations typical in the "room", I doubt you'd see the
effect. The experimenters put the phone in a bag full of helium and it
took hours. I would expect the same in hydrogen.

We're talking across each other here, I was referring to the PRS
anecdote from Karl.

I'll absolutely belive that you can screw up certain kinds of MEMS
devices when you dump 90 kg of Helium into a building.

Post by jimlux
That's a lot different than a <1% concentration. I assure you, that if
there was a helium leak/vent/boil off that made the room concentration
1%, the room oxygen sensor would be alarming (having dropped to 20%) and
people would be running for the doors.

That's not my experience, most ${GAS}-level detectors are based on
some kind of chemical reactivty (or spectroscopy if they are _really_
expensive) and they tend to just ignore helium and other noble gasses.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
***@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

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[jimlux]

Post by Bob kb8tq
Hi
A lot of Radon and *really* poor ventilation….
There are a lot of ways for He to show up. In normal use, issue is hanging on to it.
It tends to run away from its source very quickly. Maintaining a measurable concentration
in something like a normal room …. not very easy at all.
Bob

a couple interesting things to think about (I personally think the
original story has some other confounding factor they forgot):

1) MEMS pressure sensors have been around for decades, and they're used
with helium all the time.
2) MEMS accelerometers (which have moving parts, vs the pressure sensor)
have also been around for a long time. I've not checked, but I'll bet
some are in hermetic packages which get He leak tested. If there was a
Helium problem, you'd have heard about it.
3) There *are* stories about trace contaminants affecting the
performance of MEMS RF switches, specifically water vapor - it affects
the stiction of the moving contacts.
4) What is the proposed mechanism for Helium affecting the oscillator?


Here's an article from 2006 discussing SiTime's stuff
https://www.rdmag.com/article/2006/04/new-paradigm-time-silicon-mems-resonators-vs-quartz-crystals

They discuss how hydrogen diffuses *out* of the area where the resonator is.

Now, it's possible that in the interests of saving fractions of a penny,
Apple is using resonators that aren't packaged as well as the SiTime
units (which are awfully cheap). (although the news stories say Apple is
using SiTime's parts)

"Apparently, SiTime also is aware of this problem and says its newer
devices are “impervious to all small-molecule gasses.” But they admit
older parts were not immune." I'd be interested in the context for that
quote.

off SiTime's FAQ page:
How effective is the hermetic seal of MEMS oscillators??
One of the key elements enabling extremely stable MEMS resonators is
SiTime’s EpiSeal™ process which hermetically seals the resonators during
wafer processing, eliminating any need for hermetically sealed ceramic
packaging. SiTime’s EpiSeal resonator is impervious to the highest
concentration elements in the atmosphere, nitrogen and oxygen, and
therefore acts as a perfect seal. Previous generations of EpiSeal
resonators may have been impacted by large concentrations of
small-molecule gas. Newer EpiSeal resonators are impervious to all
small-molecule gases. Please contact SiTime in case you are planning to
use a SiTime device in large concentrations of small-molecule gas, so
that we can recommend an appropriate, immune part.






http://memtronics.com/files/Zero%20Level%20Packaging%20for%20RF%20MEMS%20Switches%20v7.pdf



ANother paper on packaging

https://file.scirp.org/pdf/JST_2013122009560886.pdf


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[Bob kb8tq]

Hi

Helium leak testing is a *very* common thing in the oscillator industry. I’d bet it also is done in the
MEMS oscillator business as well. A normal oscillator can fail leak testing. I’ve never seen one that
stoped working as a result of the test.

Bob

Post by Bob kb8tq
Hi
A lot of Radon and *really* poor ventilation….
There are a lot of ways for He to show up. In normal use, issue is hanging on to it.
It tends to run away from its source very quickly. Maintaining a measurable concentration
in something like a normal room …. not very easy at all.
Bob

1) MEMS pressure sensors have been around for decades, and they're used with helium all the time.
2) MEMS accelerometers (which have moving parts, vs the pressure sensor) have also been around for a long time. I've not checked, but I'll bet some are in hermetic packages which get He leak tested. If there was a Helium problem, you'd have heard about it.
3) There *are* stories about trace contaminants affecting the performance of MEMS RF switches, specifically water vapor - it affects the stiction of the moving contacts.
4) What is the proposed mechanism for Helium affecting the oscillator?
Here's an article from 2006 discussing SiTime's stuff
https://www.rdmag.com/article/2006/04/new-paradigm-time-silicon-mems-resonators-vs-quartz-crystals
They discuss how hydrogen diffuses *out* of the area where the resonator is.
Now, it's possible that in the interests of saving fractions of a penny, Apple is using resonators that aren't packaged as well as the SiTime units (which are awfully cheap). (although the news stories say Apple is using SiTime's parts)
"Apparently, SiTime also is aware of this problem and says its newer devices are “impervious to all small-molecule gasses.” But they admit older parts were not immune." I'd be interested in the context for that quote.
How effective is the hermetic seal of MEMS oscillators??
One of the key elements enabling extremely stable MEMS resonators is SiTime’s EpiSeal™ process which hermetically seals the resonators during wafer processing, eliminating any need for hermetically sealed ceramic packaging. SiTime’s EpiSeal resonator is impervious to the highest concentration elements in the atmosphere, nitrogen and oxygen, and therefore acts as a perfect seal. Previous generations of EpiSeal resonators may have been impacted by large concentrations of small-molecule gas. Newer EpiSeal resonators are impervious to all small-molecule gases. Please contact SiTime in case you are planning to use a SiTime device in large concentrations of small-molecule gas, so that we can recommend an appropriate, immune part.
http://memtronics.com/files/Zero%20Level%20Packaging%20for%20RF%20MEMS%20Switches%20v7.pdf
ANother paper on packaging
https://file.scirp.org/pdf/JST_2013122009560886.pdf
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[Wayne Holder]

The oscillator mentioned in the article is a SiT1532 made by SiTime
<http://SiT1532>. It's sold in a chip scale package that's only 1.5mm x
.9mm, which means it'a no much more than a chip of silicon with some solder
balls attached. The data sheet indicates there is a "polymer" coating on
the back side of the chip, but the working surface would be in the bottom
where the solder balls are. There is a rectangular protrusion shown on the
"Dimensions and Patterns" section (page 12) that's right over where the
MEMS mechanism would sit that might be some type of seal, but there is no
descriptive text.

The curious thing to me is that some iPhones are said not to recover from
exposure to helium but, as an essentially mechanical device, I can think of
no reason that the SiT1532 would not recover from exposure to helium after
the gas had migrated out. I wonder off the iPhone could be damaged by an
oscillator failure, o one that's running off frequency? The devices sell
for about $1.25 at Mouser and I have a tank of helium in the garage, so I'm
thinking about doing an experiment. The only problems is finding a way to
solder wires to such a small part? Might have to make a PCB, instead.

Wayne

Post by Mark Sims
https://ifixit.org/blog/11986/iphones-are-allergic-to-helium/
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[Bob kb8tq]

Hi

If you take an IC package up to fairly high pressure for a few hours (and it’s
defective) you can pretty well fill it with helium and have it well above 1 ATM internal
pressure. It will then leak out (maybe over a few years) until it gets back down to one
atmosphere internally.

In some really rare conditions, you can pressurize it to high enough PSI to inflate the
package when the pressure goes back to 1ATM. Even then the oscillators generally still work ok.
This is inflation not really a function of helium. It’s just a function of what a lot of PSI does to
a sealed package. You could inflate it with air and see the same thing.

Getting helium in a properly sealed package *without* a lot of pressure *and* very
high concentrations (like 100%) …. very difficult.

Bob

Post by Wayne Holder
The oscillator mentioned in the article is a SiT1532 made by SiTime
<http://SiT1532>. It's sold in a chip scale package that's only 1.5mm x
.9mm, which means it'a no much more than a chip of silicon with some solder
balls attached. The data sheet indicates there is a "polymer" coating on
the back side of the chip, but the working surface would be in the bottom
where the solder balls are. There is a rectangular protrusion shown on the
"Dimensions and Patterns" section (page 12) that's right over where the
MEMS mechanism would sit that might be some type of seal, but there is no
descriptive text.
The curious thing to me is that some iPhones are said not to recover from
exposure to helium but, as an essentially mechanical device, I can think of
no reason that the SiT1532 would not recover from exposure to helium after
the gas had migrated out. I wonder off the iPhone could be damaged by an
oscillator failure, o one that's running off frequency? The devices sell
for about $1.25 at Mouser and I have a tank of helium in the garage, so I'm
thinking about doing an experiment. The only problems is finding a way to
solder wires to such a small part? Might have to make a PCB, instead.
Wayne

Post by Mark Sims
https://ifixit.org/blog/11986/iphones-are-allergic-to-helium/
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[Poul-Henning Kamp]

--------

Post by Wayne Holder
The curious thing to me is that some iPhones are said not to recover from
exposure to helium but, as an essentially mechanical device, I can think of
no reason that the SiT1532 would not recover from exposure to helium after
the gas had migrated out.

Most likely: Because some piece of MEMS machinery broke of ?
--
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***@FreeBSD.ORG | TCP/IP since RFC 956
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