Michael,

In the good old days. Jees, I'm getting tired of saying this. Anyway, in the
military/aerospace industry, during warring times, we "heatsank" in so many ways.

First came heavy copper, or was it aluminum, followed by CIC core material. Considering heavy
copper or aluminum, we were able to either buy heavy weight clad material or attach etched
(chem milled) heat sinks to outer layers (over .060" we machined mechanically). As copper is
a pretty good heat conductor, often this was used. The weights were in the range of 8-11
ounces. Sometimes, we even attempted to use only one sided multilayer metal planes - very
exciting.

Copper Invar Copper (CIC) was developed and used primarily as a core material (.060" thick in
the MLB center with clearance holes, epoxy fill, re-drill, plate, etc. - first) to achieve
TCE matching characteristics close to ceramic in the leadless ceramic chip carrier days
(LCCC's).

Then came CIC not as a constraining/heat sink core (.060" thick), but as a tailoring core
(electrically and thermally) that was .010" thick placed very cose to the MLB's surface
providing all the thermal and TCE matching attributes as CIC core without the headaches
associated with multiple processing requirements.

Many others have used heavy copper cores (up to 10 oz.) as heat sinks placed in the MLB
center. I've done all this and it's all exciting - especially the part when you laminate and
expect to achieve heavy plane resin fill, high dimensional stability, and required laminate
integrity.

Which works best? So many have tried and so many have failed or succeeded. We succeeded most
with matched weight heat sinks bonded to MLB outers while remembering these were the through
hole only days - mostly.

I have done internal copper heat sink cores for SMT as early as 1982. To effect efficient
heat transfer, "heat pipes" or relatively large through holes plated to the "sinks" were used
as it was often difficult to drill and plate small diameter holes in the same way.

I could go on, but I'm getting tired of trying to remember all I forgot. If you would like to
discuss this more off line, contact me. Of course you could hire me as a consultant, but I'm
not very good though very cheap. Oh yes, I have some pretty/ugly pictures as cross sections
you may wish to see - no charge but have plenty of time and disk space.

Earl Moon

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