Very simplistic answers to your questions:
1)  Invar is a primarily iron-nickel alloy.  CIC is invar with copper on both
sides.  CIC comes in a variety of thicknesses of both the copper layers
and the invar layer.

2)  It is used as a heatsink material, and useful for controlling the X-Y
movement of the PWB.  As you know, the CTE of copper alone is very
different from the epoxy-glass; the invar has a lower amount of
movement.  Other materials can be used for internal heatsinks, but they
often have much higher CTEs than invar (aluminum for example).

3)  There are many different processing methods required (at least from
a PWB fab viewpoint).  For example, it is difficult to drill through this very
hard material.  The sensitizing process is quite different than
conventional epoxy-glass, as any copper in a sulfuric acid solution will
deposit a copper smut on the exposed invar-you can imagine how this
affects the microetch step.  Ferric chloride microetches are frequently
required.

4)  It's expensive by itself, and the increase in processing
pain-in-the-hind end factors increase board cost by quite a bit.  There
are a few places that have a lot of experience in fabricating with the
stuff, but nobody I've ever seen builds a lot of it.  Can't remember where
people buy it from, tho.

FJ

>>> Robert Jordan <[log in to unmask]> 13:55    25 June 1998
>>>
Good Afternoon!
What is Copper Invar Copper?
Why is it used?
Are there any processing concerns differing from conventional copper?
How does it compare cost wise to conventional copper?

Thanks in advance,

Bob Jordan

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