>          Why do the major cell phone manufacturers use gold
>         as their preferred finish?


I'm not certain that I am speaking for ohter manufacturers, but here are
some of the reasons that my company uses gold finish for cellular products.

Often our circuit assemblies have elastomeric keypads added to them with a 
conductive carbon puck on the circuit side of the keypad. we have used 
carbon ink in the past for keypad contacts on the circuit. More and more of
our assemblies also have an LCD module mounted to the circuit, connected to
the ciruit by conductive elastomeric strip (we call them zebra strips) and 
becoming more common lately, heat seal bonding (anisotropic connection)

for coarse pitch features we have found carbon ink to be suitable, but with
LCD modules becoming more complex, the connection for the elastomeric strip
or for the heat seal connector are becoming finer pitch.

we have had difficulties in the past with carbon ink registration below a 
certain pitch, and had to look for an alternative.

Initially we looked at tin lead surface, but anisotropic heat seal 
connectors are not hermetic, and the tin-lead surface can oxidize over
a period of time, resulting in an ureliable connection. Gold plating addresses
this concern.

Also, as I am sure is the case for many other manufacturers, we prefer the
flat finish that the gold surface gives us for fine pitch devices,

hopefully this is some insight.

regards,

Vern Harrison