At 09:17 AM 11/30/2005, Peter Lee wrote:
>Hello Technet,
>
>Does anyone have experience with utilizing conductive via fill on PCB for
>heat dissipation?

Yes, lots of experience.
Key words: added expense, little if any benefit, additional leadtime and
risk of delam/assembly scrap

Risk:
Beware of overplated conductive fill in closely packed thermal via farms.
Materials like CB100 are just enough more expansive to do some serious
lifting/separation of surface copper.  Ormet's conductive material is an
entirely different wonderful thing -- it really works well but very few
fabs know how to work with it.


Limited Efficacy:
Most conductive via fills like CB100 don't help much at all w/ thermal
conductivity. Do a x-section for a view of the metal to metal contacts and
you'll see why.  The more granular fills (e.g. Taiyo, Methode might do a
little better).

Recommendation:
Pack your thermal vias as tight as your fabricator says is safe and
standback in amazement at how well copper conducts.

Next step up in complexity is to add another mil or so of annular copper to
your finished via.You'll get as much (or more) total conductivity than with
conductive fill w/out the expense, additional leadtime and risk of delam.

Just don't spec too addmuch copper or you'll dogbone the vias shut and risk
entrapped air lifting pads during reflow (been there, done that).

my $.02,
dw

>  How mature is the technology?

depends on the fabricator.

>Is there any shortcoming/impact on the overall design and manufacturing
>process?

Yes, see comments above.

>Comment is greatly appreciated.
>
>Rgds,
>Peter
>
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