On 2/18/21 4:38 PM, Bob kb8tq wrote:
Hi
Ok
On Feb 18, 2021, at 6:40 PM, Magnus Danielson <mag...@rubidium.se> wrote:
Hi,
A lot of fascinating steps. It would be real fun if one would do a
coarse in which one would actually build a handful of crystals oneself,
to learn the basics, and measure them up. It would be a fun
summer-coarse to do.
A crystal plant isn’t going to let you in to do this. The risk of breaking gear
/
stopping production isn’t going to work for them.
So what do you need to come up with for the group?:
You need some quartz bars. Forget about trying to grow them yourself unless
you have the ability to deal with battleship guns ….
Next you will need an x-ray setup for the angles you wish to deal with. For AT
cuts that may not be to bad. For SC’s … good luck at < $500K.
For a summer camp sort of setup, go with a diamond saw, dice up the blank
slowly,
but with cheap gear.
Now you need lapping equipment. Normally this is a device made from
cast iron and with “couple of meters in each direction” sort of dimensions.
Not much of an alternative out there so a fairly unique thing to find.
Rounding the blanks can be done a couple of ways, a fairly normal lathe
might be adapted to do this.
For the contour process, I’d just go with drum processing. I’ll take you a
couple of months, but there isn’t a lot of fancy gear involved.
Chemical etch is easy, but you need to do it.
(note that “polish” got left out …. )
Now you need to put the base plate on the blank after cleaning it. It’s
a thin film deposition process. If you are set up to make semiconductor
wafers, you likely have the gear to do it. Same sort of deal, masks,
mounting fixtures, thickness monitoring, gold evaporation at very
high vacuum.
Next up drop it in a solder seal base and solder it into an enclosure.
(note that finish plate got left out).
You now have a working device.
Bob
If you want RF resonators to build in a "simple lab", it's probably
easier to do SAW devices on a blank you buy. Then it's a single layer of
aluminum that you photo etch. Not hugely different than PC boards or a
thick film hybrid.
Getting small feature sizes might be a challenge - when we did it where
i used to work, they did photo reduction onto a photoresist covered
substrate. I wonder if someone has a laser rig that could programmed to
"draw" the pattern on the resist at the right scale. As I recall, 50
MHz has a wavelength of about 60 microns, and your transducer fingers
are half wavelength apart. You're probably not going to scribe those
with an X-acto knife by hand. But it's not particularly exotic.
We bought the substrates already plated, but that is something you can
conceivably do in a small lab - vacuum system and evaporation rig.
Then you have to bond wires onto the aluminum. But that's a "available
from surplus" thing - and if you are equipped for doing hybrids you're
all set.
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