In the 80?s, I was heavily involved with CIC (started out being called
copper clad Inver or CCI) using it both in constraining and tailoring core
applications to more closely match LCCC device TCE/CTE. Ceramic has a TCE of
between 5-7 PPM. With either core constructions it was possible to get to
around 9 PPM. TI did/does make the material using similar brazing processes
as required for Alloy 42 (CMC).

Tailoring core boards, as sample of which I will post with Steve Z if he is
still so kind, used a 10 mil CIC slab as near to the surface as possible in
the MLB structure. It became the material and core construction of choice
out of its ability to match requirements, lower costs, and relative ease of
processing.

Constraining core started out finding use in high layer count
military/flight hardware boards. Typically, it was sandwiched between, say,
two 10 layer boards and was about 60 mils thick. The MLB structure was
imposing as were its processing requirements. The two, usually identical
boards sandwiching the CIC were drilled, with whatever vias were required as
interfacial, to that point, and/or interstitial as required - before final
relamination. To get the things to work oversize holes first were drilled in
the core and the holes were resin filled. The lamination was effected.
Interfacial vias were drilled and those holes were plated through while not
making contact with the core unless thermal requirements were planned.

Processing tailoring core board types has its interesting points. I
developed some of the early processes at a shop with which I was closely
involved (partner). Just as with Kevlar, ?normal? drill bits and processing
had to be modified considerably. No more carbide or diamond tipped bits.
Good old tool steel types worked best but still wore out quickly (300 ? 500
hits max).

Plating processing provided another interesting challenge. We had to go from
drilling to resin smear removal using plasma to ensure very controlled
positive etch back (boards all polyimide), then into glass fiber removal
using standard ammonium bi-fluoride. The trick was, as Inver (composed of
iron and nickel mostly) oxidizes quickly and heavily (yellow frothy stuff)
preventing electroless and electroplating deposition. We found that
immersion in a 20% HCL solution for a specified time (don?t readily recall
but you get the picture), then directly into solution did the job well. The
picture on Steve?s site attests to the plated hole quality as, to me, it is
nearly a perfect plated through hole.

The other processing issue at the time was getting the thinnest dielectric
thickness possible at the board?s surface. Constraining core didn?t matter
but didn?t work well either. As, in those days, I never could get foil
lamination to work with polyimide, I had to used a special thin core at the
surface with .5 oz copper and one 106 ply of preg under that and directly
over the CIC. Of course strictly controlled cleaning and oxiding processes
were required as well.

With all this, besides using Kevlar and Carbon fiber materials as was also
popular to some degree at the time, the boards worked well and did their
jobs. Tailoring core MLB?s still are in wide military/aerospace use though
costly for consideration in more ?advanced? commercial applications. I get a
few calls from time to time concerning the mil stuff but, more often, I get
calls about the very question you posed for commercial applications
requiring TCE matching characteristics.

Oh yes, cost is out the window on this stuff.

MoonMan

---------------------------------------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
---------------------------------------------------------------------------------