peter green wrote:
> Sorry reposting with tag, I think EE is the best fit though PIC could als=
o=20
> cover it.
>
> Most of my previous PIC designs were through hole and I just put the
> crystal on the top and the tracks on the bottom meaning no possibility
> of a short even if the board is not soldermasked or the soldermask gets
> damaged (I don't like to rely on soldermask).
>
> I have a design with a 4MHz crystal (I could change to a 16MHz crystal
> and disable the PLL but i'd rather not) and a 44 pin TQFP pic.  Currently=
=20
> I am
> using a through hole HC49/S crystal mounted on the bottom. This works
> fine and uses a crystal style that is readilly availiable but having
> just one component on the bottom seems plain weird and I could imagine
> it confusing those who will be doing the assembly. I dont want to put it
> on top because of the aforementioned risk of shorts if there is any
> issue with the soldermask.
>
> So I went looking for SMT 4MHz crystals on farnell and was surprised at
> how poor the range was. There were a number of what appear to be HC49/S
> crystals on SMT mounting plates but they take up a lot of board area
> (they would take up more top side area than the current soloution of a
> TH crystal on the bottom). There are also a few other packages but they
> don't appear to be much smaller and they all appear to be manufacturer
> specific. Checking RS and mouser gave much the same.
>
> I'd like to know what others here do for crystals with SMT PICs

We changed to a 16MHz crystal (from an 8Mhz) precisely for this reason: you=
=20
get more choices, and can generally find an inexpensive option.

Vitaliy=20

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