Hi All

Here's the challenge of the century (and maybe beyond).  I know I'm almost
asking for the recipe to turn used solder into 24K gold, but here goes:

We design and build considerable numbers of circuit card assemblies for severe
environment service, both military and industrial.  In most cases, these are
conduction cooled.  We are currently using a one part, thixotropic epoxy which
has a gap fill capability up to about .050" under extreme conditions.  It also
has an appropriately low CTE and high Tg to minimize its expansion effects on
the soldered device.  The current material must be dipensed following paste
application, but cured after solder reflow.  (Its 120 to 150C cure isn't
healthy for the paste.)  The engineering properties of this current material
are outstanding, but it drives a number of producibility problems.

I am looking for alternates to this current material which have equal or
better properties:  Thermal conductivity 7 BTU in/ft2 hr. deg F; TCE of 32
PPM/deg C or lower; Tg 95C or higher and a lap shear value of 800 psi or
higher.  The material also needs to be process durable to the normal fluxes
(OA and RMA) and to various cleaning systems which include DI water, citric
acid and long chain alcohols.  And, not the least, obviously the stuff needs
to be reworkable, just for those times when things don't quite go right.

How 'bout it Tech Netters - ANY SUGGESTIONS (that are fit to print)?

Regards - Kelly

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