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Subject:
From:
David Christopher Whalley <[log in to unmask]>
Date:
Wed, 11 Oct 95 16:36:52 bst
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>conductive adhesives as solder replacements for new
>designs or as retrofits to old designs.
>- Has anybody out there tried this?
They are widely used for hybrid assembly, i.e. die attach and SMT

>- What problems have been encountered?
printing and placement accuracy have to be high since the surface tension
is low compared with solder
bonding to tin or tin/lead is generally unreliable although some manufacturers
claim to have solved this problem (not seen any in``thorough or independant
validation of this)
humidity is their achilles heel (not a problem with hermetic hybrids)
they don't creep/stress relax like solders so fatigue is less of a problem
but stress related component failures more likely (I have just today seen
some alumina glued to aluminium samples which had curled up so much you
could practicaly use them as a wok!)

>- Please recommend material suppliers.
No. I don't want to offend anyone. Don't believe everything you read
in data sheets. Adhesives tend to be much more application specific
than solder. High Tg materials tend to be strong, but can't accomodate
expansion mismatch, low Tg materials the opposite. Silane additives
(adhesion promoters) seem to help humidity performance.

>- Is there a published workmanship criteria?
Not seen one

>- Are there standard test methods?
MIL883 contains some guidance


Hope this is useful,

David Whalley



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