So far as I recall, bonding to pure aluminium with Ag epoxy results in
excellent adhesion, excellent thermal conductivity and excellent electrical
conductivity - which lasts a few hours. This was [originally] reported in
196? by Jack Brous of Ablestik. I think his paper was called something like
"Anomalous behaviour of aluminum with silver conductive epoxies".
Electrical conductivity can be restored by giving a big whack of volts, but
then declines again. Clearly a little aluminium oxide - aka alumina - is
being formed at the bondline. Conceivably this behaviour can be modified by
alloying additions to the aluminium and anyway may not be significant if you
are not looking for electrical continuity. Many people use silver
conductives for their thermal properties which are usually much better than
"thermal" conductive epoxies.

Mike Fenner
Indium Corporation of Europe
T: + 44 1908 580 400
F: + 44 1908 580 411
M: + 44 7810 526 317
W: www.indium.com


-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Creswick, Steven
Sent: Monday, August 13, 2001 9:21 PM
To: [log in to unmask]
Subject: [TN] Back-side Device Metallization


Technetters,

I ran into an interesting item the other day that I would appreciate a
sanity check on.  I realize that this is a rather oblique question for this
forum, but there are other (silent) hybrid types out there (I believe).



Most of the bare silicon die that I have used in the past have either been
grey-backed (bare silicon), gold-silicon (eutectic), or chrome-nickel-silver
(power mosfets).

I have recently encountered a supplier that uses aluminum (alloyed) for
back-side contact of generic, none speciallized, silicon devices.  Has
anyone else encountered this as well?  If so, have you observed any contact
resistance problems when used with normal silver-filled conductive
adhesives?

It makes sense that it would form an ohmic contact to the back-side of the
wafer - just never ran into an aluminum metallized back-side before....

.. Just wanted to know if my head has been .... in the sand.   (Will post on
ChipNet as well)

Thanks

Steve Creswick - Gentex

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