[time-nuts] Opening an Isotemp OCXO
kb8tq at n1k.org
Fri Oct 28 17:09:51 EDT 2016
Well, the first issue would be the one that started this thread…. what’s the supply and pinout.
Yes, you can tear a couple open and work that out. Next step would be to verify that the other
couple hundred in the batch all are the same pinout and supply.
Assuming that you have all the same parts, next up would be making the test fixtures for the
units. It does not need to be super complex, but you need a way to solidly connect to the part.
If the leads have been cut off, this is a bit more complex than if you have full length leads.
Most processes age the units first. That would involve putting all hundred pieces on power and
looking at each of them with a counter every couple of minutes for a month or two. Based on that
data you could get a pretty good idea of what the aging will run. You also will weed out some
percentage of the units that didn’t survive whatever process got them to you.
After stabilization, They would go into temperature test. Likely something like a dozen or two
per run. Since you don’t know the top end, I’d do a search for that first. I’d then do a search for
the low end. Based on data from a few runs (several dozen parts) you should have some idea
of the upper and lower temp limits.
A formal temp run over that range would be next. I’d probably do 5 degree steps. That way if
you are off on the endpoint guess you might be able to see the correct end points. You would
test the whole batch of units and then look at the data. My guess is that you would re-guess the
end points and re-test the batch at that point.
Assuming you know the correct load and EFC from the original tear down, they would move on
to some sort of bench check. If not, you would need to work that out.
On the bench check, I’d run each one over the (assumed) EFC range at something like 0.1V steps.
Here if your range is off, the data probably is still ok. That should give you a proper EFC setting
for each one. Since they have been aged and TC’d at this point, the EFC center point should
be pretty good.
After that, things like phase noise and ADEV would be on the list. Same thing, run them all
and see what they do. Make some decisions and toss out the outliers.
So, yes it can be done. Because of the tear down process early on and the data redundancy
needed, you have to get a pretty good sized group of units. The risk is that you get a group
of parts with a common (to that batch) defect. They *were* headed to the garbage dump and
went to eBay instead ….
Lots of Fun
> On Oct 28, 2016, at 4:09 PM, Bob Stewart <bob at evoria.net> wrote:
> Hi Bob,
> Can't the OCXOs be characterized pretty closely by someone with the right tools and staff? I don't have a big sample to speak from, but the Trimbles I use only have a couple of ceramic coated pieces, and those can be exposed down to the die by hand and then characterized, can't they? Granted, that's beyond my capabilities, but given the right tools and employees...
> From: Bob Camp <kb8tq at n1k.org>
> To: peter at reilley.com; Discussion of precise time and frequency measurement <time-nuts at febo.com>
> Sent: Friday, October 28, 2016 2:46 PM
> Subject: Re: [time-nuts] Opening an Isotemp OCXO
> Roughly 99.9% of all OCXO’s made go to large OEM customers. The percentage may
> actually be a bit higher than that. There are relatively few markets that “catalog” OCXO’s
> sell into.
> Inevitably the first thing that an OEM wants is some form of customization. A specific
> supply voltage, a certain output format, a wider (or narrower) EFC range … there
> are lots of possibilities. For every OCXO that goes into production for these guys,
> five or ten other designs are done (all equally custom) that never see the light of day
> past the samples.
> The spec’s that these parts are built to are negotiated between the supplier and the OEM.
> In some cases they are the property of the OEM and the spec is their control drawing on
> the part. In other cases the drawing is done by the supplier for that OEM and is property
> of the supplier.
> The OEM often has competitors. They would *love* to get access to the OEM’s control
> drawings to see how the systems are designed. The supplier has competitors. They
> would love to get access to the suppliers drawings so they can make cheap knock off
> parts to those drawings. In both cases, the drawings (in general) have very real value.
> The net result of this is that both suppliers and OEM’s put fairly fancy rules in place about
> passing out drawings. More or less anything up to and including being boiled in oil is
> (if legal in the jurisdiction) fair recourse under most of these rules. Needless to say
> people learn pretty quick that you get fired for this sort of thing.
> The net result is that the drawings for most OCXO’s simply do not exist in the public
> domain. They do (or did) exist in some form somewhere. Getting at public copies of
> them is highly unlikely. Going by “similar looking” drawings is not a real good idea ….
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