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From: mmm@cup.portal.com (Mark Robert Thorson)
Newsgroups: sci.electronics
Subject: Re: Which is a better conductor: gold or silver?
Message-ID: <20483@cup.portal.com>
Date: 15 Jul 89 22:27:25 GMT
References: <14172@swan.ulowell.edu> <19729@louie.udel.EDU>
Organization: The Portal System (TM)
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As John Berryhill said, gold is used for corrosion resistance on contact
surfaces.  It's not a very good conductor, as metals go.  It's electrical
resistance is not important because it's a thin layer.

The other important feature of gold is its ductility.  Integrated circuits
in plastic packages use gold bond wires because the packages flex with
temperature.  This is one reason IC's in plastic packages are less reliable;
the gold bond wire interacts with the aluminum bonding pad on the chip.
Gold diffuses into the pad, and aluminum diffuses into the wire.  This can
create voids in the bond, and it creates a brittle gold-aluminum alloy.

Military chips, on the other hand, use ceramic packages.  These don't flex,
so aluminum bond wires can be used.