Hi

Ok, you could write a book or three on this. Let’s keep it simple.

(see below)

Typically the backfill is “optional” on a precision part. If it is present, it’s more like a “trace”
of gas than a full backfill.

The crystal blank is cleaned before any metal plating goes on.

The holder and cap are cleaned before anything happens with them.

All of this involve high temperatures and (likely) vacuum.

Yes, they all are cleaned and baked in the vacuum system. There is likely a bit of
processing before they go into the system.

There is a step before this where the blank is finish plated to put it on frequency.

The manipulation process is a “that depends” sort of thing. It could simply be “folks” using
their hands via big black “vacuum gloves”. It could be something more automated.

Yes, it has to be in the chamber.

No

The machine pushes on “rods" that run through structures that keep the vacuum “tight”.

You spend about $2M on each machine. The machine likely does hundreds per day.
If you need more, you buy another machine or three.

The unasked questions:

Does the baseplate happen in the same machine as the final plate? It may.

Does the epoxy process happen in this same machine? It may.

Are all parts cleaned the same way? Probably not. The cover may well get more aggressive
cleaning. (it’s just a piece of metal).

Is there “only one way” this is done? Nope, everybody has tweaks to how they do things.

How are things cleaned? That’s a whole book all by itself.

Fun

Bob

Bob kb8tq via time-nuts writes:

Somewhere, possibly BSTJ, I read about quartz for precision crystals
being 'stress-tested' and 'annealed' a process which involved forced
oscillation while gradually lowering temperature and voltage/(amplitude?)

Was that (only) a thing with natural quartz ?

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phk@FreeBSD.ORG        | TCP/IP since RFC 956
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Never attribute to malice what can adequately be explained by incompetence.

Hi

Well, never say never :) :) :).

It’s certainly not been part of any process I have been involved with. However it may well have
been done by others. I am not aware of it being done by anybody these days. Again that could
just be my not having talked to the right folks. It also may (as you suggest) be something done
“long long ago”.

One important note not mentioned earlier:

That assumes that “precision crystal” = stuff like OCXO crystals. Even that term may have
multiple meanings to various folks. A 3rd or 5th overtone crystal in the 4 to 12 MHz region in a
cold weld or glass package is what comes quickly to mind.

What is indeed done when processing these crystals:

The crystal growth process for synthetic quartz gets more involved when precision parts
are involved. You go from a fairly quick growing approach to one that takes much longer.
That does involve a range of steps past just the basic growth process.

Sealed crystals after fabrication are normally run through bake and thermo-cycle processes.
The objective is to reduce the “front end aging” (or whatever you want to call it). Having a
fabricated OCXO hit spec in 5 days vs 5 weeks saves money.

Occasionally processes do include running a crystal in a circuit prior to fabricating the
final oscillator. The most common example is with low volume OCXO’s that have a very high
BOM. Sorting crystals for aging makes sense if > 90% of the crystals will be tossed out. For
the vast majority of OCXO’s made, this is not needed / not useful.

Fun

Bob

 
The "make some blanks and run them in an oscillator for a while, before finalizing the assembly" is what APL does for Ultra Stable Oscillators for space flight.
I can't recall if they actually assemble the physics package (the part that goes in a dewar) and run them before choosing the ones to fully integrate. It would make sense, because one thing you want to deal with the the residual stresses of the crystal in the holder, etc.  And to identify those that were "on frequency and didn't drift too far" and "didn't have oddities in the aging process".  They might have put them in the dewar before the long duration burn in. I think there is some pretest too, I mean you have to make sure that you've ground/finished/plated them to hit the desired frequency. 

As I recall for one batch of USOs, there were several dozen fabricated and aged, of which 2 got finally used.  From roughly 1000 blanks. 

At $1M a copy, that fairly fits Bob's high BoM cost description.

On Mon, 9 Feb 2026 11:05:30 -0500, Bob kb8tq via time-nuts time-nuts@lists.febo.com wrote:

Hi

Well, never say never :) :) :).

It’s certainly not been part of any process I have been involved with. However it may well have
been done by others. I am not aware of it being done by anybody these days. Again that could
just be my not having talked to the right folks. It also may (as you suggest) be something done
“long long ago”.

One important note not mentioned earlier:

That assumes that “precision crystal” = stuff like OCXO crystals. Even that term may have
multiple meanings to various folks. A 3rd or 5th overtone crystal in the 4 to 12 MHz region in a
cold weld or glass package is what comes quickly to mind.

What is indeed done when processing these crystals:

The crystal growth process for synthetic quartz gets more involved when precision parts
are involved. You go from a fairly quick growing approach to one that takes much longer.
That does involve a range of steps past just the basic growth process.

Sealed crystals after fabrication are normally run through bake and thermo-cycle processes.
The objective is to reduce the “front end aging” (or whatever you want to call it). Having a
fabricated OCXO hit spec in 5 days vs 5 weeks saves money.

Occasionally processes do include running a crystal in a circuit prior to fabricating the
final oscillator. The most common example is with low volume OCXO’s that have a very high
BOM. Sorting crystals for aging makes sense if > 90% of the crystals will be tossed out. For
the vast majority of OCXO’s made, this is not needed / not useful.

Fun

Bob

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I have never heard of using "Glue" (whatever that it).
Rather they do brazing using a mixture of 2 metal powders that are
heated until they flow together into an alloy. The selection of the
metal is such that the melting point of the alloy is less than both of
the constituents.  So the "puddle" "instantly hardens, like 63/37
eutectic solder.

Rick N6RK

On 2/8/2026 8:33 AM, Attila Kinali via time-nuts wrote:

Hi

The problem is that you can’t measure the frequency of a bare blank very well. You need those plated
electrodes and the ultra clean package to get the “other stuff” out of the measurement.

In order to see what’s going on, you need to turn it into a finished crystal. This is what’s done on things like
the USO’s. They build lots of finished crystals and sort them out. Each one goes into a “dummy”
OCXO and is tested for various parameters. The ones that meet all the requirements move on into
the finished product.

Bob

Hi all,
I remember visiting a crystal manufacturing shop in the town where I grew up as a teenager in the 1970's. The guy would make the crystals to frequency or ever so slightly high. The ones that were slightly high he would draw a tiny line of lead pencil to "pull" the frequency low.

Thank you

Nic McLean
President & Squad Captain
VRA Rescue NSW - WICEN
6 Judy Jakins Drive, Dubbo, NSW 2830
1300 872 777 or 0417 822 728
wicen.president@vrarescue.org

-----Original Message-----
From: Bob kb8tq via time-nuts time-nuts@lists.febo.com
Sent: Tuesday, 10 February 2026 9:53 AM
To: Discussion of precise time and frequency measurement time-nuts@lists.febo.com
Cc: Bob kb8tq kb8tq@n1k.org
Subject: [time-nuts] Re: Question on quartz crystal manufacturing

Hi

The problem is that you can’t measure the frequency of a bare blank very well. You need those plated electrodes and the ultra clean package to get the “other stuff” out of the measurement.

In order to see what’s going on, you need to turn it into a finished crystal. This is what’s done on things like the USO’s. They build lots of finished crystals and sort them out. Each one goes into a “dummy”
OCXO and is tested for various parameters. The ones that meet all the requirements move on into the finished product.

Bob

time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-leave@lists.febo.com

Should anyone want any, I think I still have a whole bunch of quartz
slabs from a military crystal/SAW mfr that I'm willing to share. No
plating, some may be optical beam splitters, but most are quartz blanks
of a large variety of sizes. I might have tossed them in the most recent
Great Purge, but if anyone is interested, lmk, and I'll check next time
I'm in the garage.

Bob

On 2/9/26 10:21 PM, mcleannb--- via time-nuts wrote:

Hello Bob,

It’s difficult to find detailed documentation on the manufacturing process because each manufacturer keeps its methods proprietary, and the techniques have evolved significantly over the years.

For high-end crystal oscillators, there are multiple steps—from blank cutting, adjustment, cleaning, to encapsulation—to ensure optimal performance.

During lapping, the parts are not only measured but also optically inspected to verify whether they are perfectly planar or have the required convex profile.

After the electrodes are added, there are two main approaches for frequency adjustment:

• Depositing material to fine-tune the frequency
• Plasma removal to trim the frequency

Both techniques have their advantages and disadvantages.

As you mentioned, the base, crystal, and cap are cleaned using specialized detergents and handled in a cleanroom environment. Several high-temperature cycles are then applied to stabilize atomic migration in the plating material, which improves long-term aging performance.

The base and cap are handled with dedicated tools, and cold welding is carried out by applying high pressure under vacuum in a controlled low-temperature environment.

Another important consideration is avoiding any outgassing materials, including the adhesive used to mount the crystal on the base.

There is actually a lot to say about the process and the many steps involved in building a high-quality crystal. On our side alone, we have more than 20 process steps, which gives you an idea of why the crystal ends up being one of the main cost drivers in an OCXO design.

Best regards,

Jean-Charles

Best regards,
-----Message d'origine-----
De : Bob Bownes via time-nuts time-nuts@lists.febo.com
Envoyé : mardi 10 février 2026 16:48
À : mcleannb--- via time-nuts time-nuts@lists.febo.com
Cc : Bob Bownes bownes@gmail.com
Objet : [time-nuts] Re: Question on quartz crystal manufacturing

Should anyone want any, I think I still have a whole bunch of quartz slabs from a military crystal/SAW mfr that I'm willing to share. No plating, some may be optical beam splitters, but most are quartz blanks of a large variety of sizes. I might have tossed them in the most recent Great Purge, but if anyone is interested, lmk, and I'll check next time I'm in the garage.

Bob

On 2/9/26 10:21 PM, mcleannb--- via time-nuts wrote:

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