Morgan Olsson <morgans.rt@TELIA.COM> wrote:
> This week I was selecting SMD caps for a design.
> I was looking at low temp coeff, and begun thinking...
>
> Suddenly i realized, in theory, temp coeff of a PCB mounted cap is probably
> not the same as for a cap freely suspended.
>
> Because, by temperature the cap expands mechanically, and also, the cirquit
> board expands.

I think you're confusing the temperature coefficient of the capacitance
value with the physical coefficient of thermal expansion. These are two
entirely separate things, although they may be related by some of the
underlying physics.

Thermal expansion of 2-pin SMD parts is generally a non-issue, except in
extreme environments. It is an issue, however, with larger ICs that have
fine-pitch pins on four sides -- with these they do go to some effort to
match the coefficients of thermal expansion, so as not to fatigue the
solder joints over time.

-- Dave Tweed

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