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 > On Nov 1, 2018, at 12:14 PM, jimlux <jim...@earthlink.net> wrote: > > On 11/1/18 8:47 AM, Bob kb8tq wrote: >> 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 > > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
