Agree, filled thermal vias can cause trouble. If you have very tough
heat transportation requirements, you may copper plug the vias. But this
is only applicable if you plan for large scale production. I know the
guy who invented a method, can send his adress if you are interested.
Sounds simple as method, but ain't.
Ingemar Hernefjord
Ericsson Microwave Systems



-----Ursprungligt meddelande-----
Från: TechNet [mailto:[log in to unmask]] För Dwight Mattix
Skickat: den 19 oktober 2005 16:53
Till: [log in to unmask]
Ämne: Re: [TN] Delamination at Thermal Via area?

We have a lot of experience w/ this type failure.  I'm working on the
assumption that there's a thermal via farm in that center gnd slug area.
A couple recommendations ff the cuff...
    * Stay away from conductive via fill material whenever possible when
vias are tightly packed in "thermal via farms."   Conductive fill is
almost
never needed -- adds very little actual thermal/conductive benefit.
We've
modeled it and test it.  For my money, conductive fill is almost always
a
waste of time and a real pain in the patootie from reliability
standpoint.
The biggest benefit is that it's easier to plate over and get good
copper
adhesion and that usually only matters on probe sites. Esp
evil/unpredictable in this application is CB100 (I've had lots of
dialogue
w/ Dupont over the years on this type failure).
    * Use a non-conductive fill that's more closely matched in CTE
(e.g.San
eh) and don't overplate the fill.
    * Arguably the most significant factor:  don't plate over the
thermal
vias.  All overplating does is give the fill something to push against
and
force the whole plated area up during thermal excursions. It's like
screwing a cylinder head on tightly and then pushing all the pistons up
against it (expanding fill at temp).  Pop goes the weasel!  Overplating
doesn't add any grounding or thermal benefit. The solder joint in the
gnd
slug will still be fine w/ the dot pattern that emerges.
    * As a work around/mod: We've eliminated a couple of these problems
on
finished product by just etching or laser ablating a dot of copper off
over
the fill.

there's my $.02.  Free and worth every penny.  ;^)

cheers,
dw

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