I have to agree with thermount and CTE. It is difficult to realise a
functional design with a CTE less than about 11-12ppm using thermount
material. We've also had very bad experience with this material and humidity
testing which I won't go into here.

Ian Fox


-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: 11 March 2002 16:32
To: [log in to unmask]
Subject: Re: [TN] CIC... ONCE AGAIN


Hello...

Wait, wait and wait...  I am no advocate of CIC, but Thermount does have its
flaws.  The attractive low CTE in the nonwoven configuration takes on
similar
CTE properties as adjacent copper planes, negating much if not all its CTE
advantages.  Conservative design criteria must me employed due to the
.003-.007 Kevlar fibers and their resistance to drilling.  This resistance
has them pullout of drilled holes giving the PTH a much more "leaching"
appearance.  These copper fingers horizontally extending to opposite
polarity
planes is reason for concern.  Add to this the moisture absorption and there
is real "potential" trouble in HDI type packaging (pun intended).  The "BI"
(and even BF) material has a difficult and challenging time passing the
stringent moisture acceptance criteria of boards.  My advice I hand out for
Thermount Customers is watch out for PTH to plane clearances, don't go below
8 and 8, and don't place planes directly below SMT layers (i.e. layer two).
From a bare board fab perspective the layer stability is somewhat erratic
and
not stable registration as it was thought.

Every material and configuration is application specific.

Boston Brad
781 858 0783

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