Phil,
the one failure we have discover regarding the conductive adhesive to Sn/Pb
eutectic solder is that depletion of Sn at the interface.  The failure mode
is adhesive failure.  It is believed that poor joint strength is
predominantly attributed to the formation of a mechanically weaker lead rich
layer due to the depletion of the tin.  The published paper is:
"XPS Studies of the Interface Properties of Conductive Adhesive/Eutectc
Solder" by Y.C. Koo et.al. MRS Symp. Proc. Vol. 390 p.219 (1995)
If you don't required mechanical strength, it may not be an issue...(the
study is part of effort to use Ag filled conductive adhesive to replace
solder..The termination on the components is solder finishing.. not much
"adhesive potterable" termination components exist in early 90s).
good luck...
                                jk
At 09:14 AM 8/12/99 -0700, you wrote:
>Our design group just brought a new technology (to me at least) out
>yesterday and I find it hard to believe that this is proven technology in
>the industry.
>
>In order to transfer heat away from a part which generates quite a lot of
>heat (upwards of 4 watts?), they have placed a matrix of vias below it and
>then filled them all with silver filled epoxy, expecting us to then screen
>solderpaste on top of this in order to connect the supposedly solid barrel
>of the via with the belly of the component.  The assembly consists of
>essentially a CCA mounted inside of small chassis and the only cooling
>transfer is through the boards which sits on a boss in the chassis.
>
>Is there published reliability data on solder connections made by
>interfacing silver filled epoxy and eutectic solder?  If so, please direct
>me to it. We do have a very small percentage of silver in our alloy.
>
>The solderability of silver filled epoxy when exposed to solderpaste on top
>of a nickel gold substrate does not leave me with a warm and fuzzy feeling.
> I am confused how the intermettalics (I know, I know, which one?) are to
>be formed, or even if the silver filled epoxy wets with solderpaste under
>normal reflow temperatures.  If there are other concerns I need to focus on
>as well, I'm open to all suggestions.  Someone mentioned galvanic
>interactions......
>
>My hunch is that we will have large voids in the connections below the part
>and this will reduce the heat transfer ability of the assembly when
>compared with a solid solder filled via that wets all the way up to the
>belly of the component.
>
>But then again I could be wrong..........please enlighten me.
>Phil Bavaro
>
>##############################################################
>TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
>##############################################################
>To subscribe/unsubscribe, send a message to [log in to unmask] with following
text in
>the body:
>To subscribe:   SUBSCRIBE TECHNET <your full name>
>To unsubscribe:   SIGNOFF TECHNET
>##############################################################
>Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
>information.
>If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or
>847-509-9700 ext.5365
>##############################################################
>

##############################################################
TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
##############################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in
the body:
To subscribe:   SUBSCRIBE TECHNET <your full name>
To unsubscribe:   SIGNOFF TECHNET
##############################################################
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information.
If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or
847-509-9700 ext.5365
##############################################################