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Subject:
From:
Michael Fenner <[log in to unmask]>
Date:
12 Oct 95 18:06:34 EDT
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Reply:,
reconductive adhsives a solder substitutes

General comments
1) Don't forget that" conductive adhesives" is a slight misnomer, very
approximately silver filled adhesives are an order of magnitude less conductive
than solder which is an order below copper.
2) In terms of joint strength epoxies (the usual basis of a silver filled
adhesive) do not form as strong a joint  as solder - say about 50% less for sake
of a number. More importantly  epoxies  do not adhere well to tin or its alloys
so that  bond strength is lower still. 
3) In use there is an interaction between the silver and tin which gives very
high resistivity and a volume change.
4) Combine the volume change at the glue line with the low bond strength and the
best you can say is that you do not have a high reliability system.
So whereas conductive adhesives are in usein defined areas,  David Whalley 's
comments are quite apposite.
Presently I would only think of a conductive adhesive as a possible alternative
to solder conditional on  the assembly being designed for adhesive joining from
the start, (ie joint shape/ bonding surfaces/materials/conditions of use/current
carrying/temperature cycling etc) and probably only then after a breakthrough or
two has been made in conductive adhesive technology. 
I don't know of anyone  using conductive adhesive as a true solder substitute in
component attach for general PCB assembly and am watching this space with real
interest to see if anyone turns up...
Mike Fenner
BSP, UK
100760,[log in to unmask]



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