FreeLists / si-list / [SI-LIST] Re: AW: Vias on decoupling pads

[Paul Levin <levinpa@xxxxxxxxxxxxx>]

Dear Sol,

I would definitely like to hear more about plugging.
I bet others would too, so please post any further
thoughts and/or information on the entire reflector.
Thanks.

Regards,

Paul
_______________________

Sol Tatlow wrote:

> Hi Chris,
> 
> 
>>Is it ok to put vias actually on the pads of
>>a ceramic decoupling cap in terms of manufacture?
>>Do other people do this?
> 
> 
> yes, you CAN do this, BUT it can require technologies
> (micro-via or via-plugging techniques) that are
> otherwise not needed - this can make the PCB more
> expensive, as well as extending delivery times, plus
> can limit your choice of PCB manufacturers: it is NOT
> simply a case of placing normal vias in pads at the
> layout stage and end of story (solder paste disappears
> into the holes=3Dbad/no joints, solder paste application
> difficulties on other side, etc.).
> 
> Obviously, via-in-pad CAN give you the best technical
> result/performance with very small decoupling caps,
> where there is no space to put the vias for the
> individual pads BETWEEN the pads (0603 and smaller),
> and in the case of micro-vias allows the placement
> of caps directly under full matrix BGAs where it might
> otherwise not be possible (good against 'bounce'),
> but needs to be weighed against cost requirements.
> 
> On a more detailed level, before you use something like
> micro-vias, you perhaps also need to do analysis
> (comparison) of the impedances of the various
> possibilities of connecting the pads to the planes,
> since micro-vias are (obviously!) small. Plus, micro-
> vias (normally) only connect between neighbouring
> layers - stacking is possible, but EXPENSIVE! - which
> means they are perhaps ok for GND (L1-L2) but not
> for PWR (L1-Lx).
> 
> Plugging is yet another different story, with different
> methods and (plugging) materials.
> 
> If you want more info, let me know, and I can give
> you more info on manfg. techniques that will help
> you evaluate the pros and cons.
> 
> Hope this helps!
> ____________________________________
> Sol Tatlow, M.Eng. (Oxon)
> ProDesign Electronic & CAD Layout GmbH
> Product Developer
> Albert-Mayer-Str. 16
> D-83052 Bruckmuehl
> Phone: +49 (0) 8062-808-302
> Fax:   +49 (0) 8062-808-333
> Mailto:sol.tatlow@xxxxxxxxxxxxxxxxxxxx
> www.prodesign-europe.com
> ____________________________________=20
> 
> -----Urspr=FCngliche Nachricht-----
> Von: Chris Chalmers [mailto:cchalmers@xxxxxxxxxxx]=20
> Gesendet: Dienstag, 6. April 2004 12:48
> An: si-list@xxxxxxxxxxxxx
> Betreff: [SI-LIST] Vias on decoupling pads
> 
> 
> 
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> 

-- 
Paul Levin
Senior Principal Engineer
Xyratex Storage Systems

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