[Milsurplus] Crystal History Book and tips on etching
Bob kb8tq
kb8tq at n1k.org
Sun Jul 31 18:11:08 EDT 2022
Hi
The etching process does not so much remove cracks as it removes
debris that is sorta / kinda still attached to the crystal. Turns out that
this “stuff” damps the oscillation. Despite many decades of doing this
and doing that, it still pops up from time to time …..
Crystals are not that nutty to manufacture in large volume. You slice
up this and to that then something else. Out come a couple thousand
all on nearly the same frequency. If you only have an order for three,
you have a lot of excess to put on the shelf ….
Bob
> On Jul 31, 2022, at 1:31 PM, Brooke Clarke via Milsurplus <milsurplus at mailman.qth.net> wrote:
>
> Hi Dennis:
>
> My reading of patent 2479286 is that after grinding, quartz crystals have micro cracks that propagate with aging and temperature cycling. By using an HF etch the cracks are removed thus stabilizing the crystal for both aging and temperature (See Fig 6, 7 & 8 in patent). The patent also includes a slide rule design (Fig 10) which, for a given frequency change and cut, tells you the etch time.
> https://prc68.com/I/Xtal.shtml#Bliley
>
> PS I worked in microwave semiconductors and they used HF. Extremely dangerous stuff since it attacks humans in such a way that they are not aware of it.
> https://en.wikipedia.org/wiki/Hydrofluoric_acid#Health_and_safety
>
> --
> Have Fun,
>
> Brooke Clarke
> https://www.PRC68.com
> axioms:
> 1. The extent to which you can fix or improve something will be limited by how well you understand how it works.
> 2. Everybody, with no exceptions, holds false beliefs.
>
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