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'[EE] SMT 4MHz crystals'
2011\01\12@182455 by peter green

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Sorry reposting with tag, I think EE is the best fit though PIC could also 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 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

2011\01\12@192539 by Vitaliy

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peter green wrote:
{Quote hidden}

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

Vitaliy

2011\01\13@073826 by Olin Lathrop

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peter green wrote:
> I'd like to know what others here do for crystals with SMT PICs

If space is important, start at 8MHz.

Other than some HC49 variants, every manufacturer has their own packages.
Abracon seems to be ahead when it comes to small packages.


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