Re: gEDA-user: IPC standard SMT footprints (0603, 0402 vs. RESC0603N etc.)

[Gabriel Paubert <paubert@xxxxxxx>]

On Wed, May 25, 2011 at 02:40:58PM -0700, Colin D Bennett wrote:
> On Wed, 25 May 2011 23:03:06 +0200
> Gabriel Paubert <paubert@xxxxxxx> wrote:
> 
> > This said, most capacitors look to have a square profile, but
> > resonance frequencies observed on microstrip line change between
> > mounting the layers parallel or perpendicular to the ground plane.
> > The problem is that, for most capacitors, it is very hard to
> > determine the orientation of the layers.
> 
> That's interesting.  Are you saying that for high-frequency, critical
> signals, the orientation of the chip capacitor affects its performance
> in the circuit?  Is the SMD tape/reel packed in such a way that the
> capacitors are optimally oriented, ready for pick-and-place onto a
> PCB?

Yes, at least for some high frequency capacitors; look at the following, 
the last 2 graphs are really amazing:
 
http://dilabs.com/pdfs/Pg%2010-11%20MLC%20Application%20Notes.pdf

I have never seen such a large difference myself, but I have seen
a measureable difference in some cases. 

I don't know about capacitors from other manufacturers. 

When I use capacitors from Dielectric Labs, that's in small quantity,
so I get them in bulk in plastic bags and I have to orient them myself.

	Regards,
	Gabriel


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