[time-nuts] The ultraAtomic clock for home
csteinmetz at yandex.com
Fri Apr 7 22:10:34 EDT 2017
> Charles wrote:
>> [blob over wire bond construction]
>> is also extremely unreliable, particularly WRT environmental effects
>> such as temperature changes, humidity, and atmospheric pollutants.
>> In my view, it is unsuitable for use in anything but dirt cheap, purely
>> disposable devices like greeting-card audio players and disposable
> Interestingly enough it *is* used in space flight hardware. It is much
> less expensive, lighter weight and easier to inspect than thick film
> hybrids and similar schemes.
> I suspect that there is a wide variation in the material you blob on
> there and so forth.
No doubt. I suspect also that space flight hardware doesn't use blobs
on plain FR4. While one problem with the blob technique is the
permeability of the blob material, another is the permeability of the
substrate -- and FR4 is pretty bad in this regard.
It would not surprise me to find that space-qualified blob material is
very different from consumer-grade blob material, and is actually *more*
expensive than using consumer-grade packaged die would be (which would,
of course, defeat the purpose of using it for consumer circuits).
I suppose in the vacuum of space permeability to gasses and humidity may
be less of a problem than it is in Earth's atmosphere, so the blob may
need to be the primary means to prevent ingress of gasses and humidity
only from the time of construction until launch.
Makers of space flight hardware can also afford to spend more for
materials with similar coefficients of thermal expansion than makers of
consumer devices can.
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