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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