Frank-
I have some DuPont literature that says..."Nonwoven aramid reinforced
laminate is typically supplied at 50% resin content, by weight, to meet
the needs of low in-plane CTE applications (8-10 ppm/C). By varying
resin and copper content in final boards, CTE can be tailored to any
design point between (8-16 ppm/C)." DuPont calls the nonwoven aramid
reinforcement "Thermount", which is a DuPont registered trademark.
In looking for additional aramid info, I found that the terms Aramid,
Thermount, and Kevlar might be used interchangeably, and finding the
chemical origin of aramid wasn't an easy task. On this note, the
following references clarify the names and polymer system information:
1) "...aramid (aromatic polyamide polymer) fibers...have been developed
over the last 20 years"
2) "The aramid fiber is manufactured by E. I. DuPont de Nemours & Co.
under the trade name Kevlar. IPC-A-142 documents the specifications for
finished fabrics woven from aramid material."
Excerpt 1) is taken from pg.2.13, and 2) is taken from pg.2.14,
respectively, of "Electronic Materials & Processes Handbook", Eds.
Charles Harper and Ronald Sampson, 2nd Ed., McGraw-Hill, ISBN
0-07-054299-6, (1993).
Table 2.1, pg. 2.14 of the same text lists the CTE of Aramid fiber as
-5.0 ppm/deg C (along the fiber axis; radial CTE = +60 ppm/deg C).
Note that the axial CTE is a negative number!
-Michael Alderete
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You wrote...
------------------------------
Date: Thu, 23 Jul 1998 13:30:12 +0000
From: "Frank K. Frimpong" <[log in to unmask]>
Subject: CTE of PCB material.
Hi Techie persons,
I need some help on this.
1. Carbon fibre has a negative CTE. The result of combining it with a
high
positive CTE resin such as epoxy is a composite with a good dimensional
stability.
Can any one tell me if Aramid fibres also posess a negative CTE and
if
so what is it?
2. Various constraining layers can be introduced within PCB's in order
to
improve the thermomechanical properties. One such system is the
introduction of a copper-invar-copper layer. Can anyone point me towards
some published articles or manufacurers of this system or other similar
systems. I would also like to know at what stage of the manufacturing
process is the system introduced, and what effect does it have on the
cost,
performance and reliability of the assembly. Thank you.
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