I believe this would fall under the category of standing waves, which are a=
ffected by all kinds of things, up to and including the way the operator ho=
lds its mouth during the "sound off".  A single well placed self-tapping sc=
rew is nearly as fast and allows later disassembly.  Unless of course you r=
eally need a hermetic seal for waterproofing, etc.  In that case, a weighte=
d object near the sensitive component(s) to dampen the vibrations may help.=
  As others have mentioned, post assembly testing would be key here.

Cheers,
Robert=20

Sent from my iPad

On Dec 18, 2014, at 5:31 AM, RussellMc <apptechnz@gmail.com> wrote:
>>>> ... MEMES devices are usually destroyed by ultrasonic cleaning
>=20
>>> Does the same apply to assemblies ultrasonically welded  into a box I
>>> wonder? If so, this post could have saved us a bit of future strife -
>=20
>> .... if open ultrasonic cleaning essentially always destroyed a given ME=
MS
>> device it would almost certainly be possible to produce a housing such
>> that, by design, ultrasonic sealing of the housing almost always destroy=
ed
>> the MEMs device. If you can do it by design then Murphy can too. Equally=
,
>> it would be possible to produce a housing by design where destruction
>> almost never occurred. Murphy will work on "optimising" almost-never.
>=20
>> On 18 December 2014 at 22:58, Richard Prosser <rhprosser@gmail.com> wrot=
e:
>>=20
>> Yes, I was thinking it is a consideration, and worth checking up on. I'm
>> not even 100% sure the product is going to have MEMs in it, but it's qui=
te
>> likely and I know ultrasonic welding is being considered. It might be as
>> simple as providing some damping to the pcb. We do carry out significant
>> vibration & drop testing, but this is a bit different.
>> Obv
>> io
>> usly, ultrasonic cleaning will apply vibration pretty well directly to
>> the components, but welding could excite resonances not otherwise expose=
d.
>=20
> Here is some confirmation that it MIGHT be an issue.
> This is from a technically very  experienced friend who I copied my prior
> comment to offlist.
>=20
> A crystal and a MEMS device are obviously different but also have some
> similarities.
>=20
> It sounds like doing some tests on a sample board with a suitable sensor
> during welding may be a very worthwhile thing to do.
>=20
> Ken said:
>=20
> One of our customers has been using ultrasonic welding for many years to
> seal a PCB assembly in a plastic housing.
>=20
> The PCB has among other things on it a 32.768kHz crystal.  Such crystals
> from many manufacturers do not like this treatment and many die during
> welding leaving some that are walking wounded.  Some products from some
> manufacturers seem to survive much better than others.
>=20
> Moving the crystal on the PCB suggests that the problem is worse in some
> positions compared with others  - though how you would determine a
> "good" position other than by trial and error I don't know.
>=20
>=20
>=20
> Life is so rich and full :-)
> Yet another can of (vibrating) worms.
>=20
>=20
>                 Russell
>=20
> --=20
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--=20
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