You asked:

>Isn't it true that the 30u" requirement was in effect long before Bellcore
>was a
>gleam in Pa Bell's eye?

Yes, Bellcore came into being in 1984. Before that, there was Bell Labs,
and many other AT&T research facilities dating WAAAAY back. IMHO the AT&T
reliability arms were far advanced beyond almost any other commercial work
with the exception of IBM.

>This may be one of those situations where we do it 'because that's the way we
>have always done it'.

I don't think so, but I sympathize with questioning old doctrine. I can
tell you in the late 70's, 50 microinches Au over 100 microinches Ni was a
common callout for gold thickness on finger tabs. Gold is just generally
more forgiving in most regards.

>I don't think that soft gold is an option, but if hard gold could be plated at
>10u" or so, the benefit to the manufacturing operation is the savings in
>materials and labor for tape/untape, rework for bad tape, etc. and the
>bottleneck costs. It would seem that there would be higher equipment costs
>for a
>plating line, but automation would amortize the costs quickly.

Almost all volume PWB houses have fully automated gold tab lines to plate
Ni and Au. As far as the hardness goes, the co-plating of cobalt and nickel
are common to increase hardness and wear resistance. The subject of gold
quality is covered in MIL-G-45204, or in AT&T X-17199 (proprietary, but
well known).

>This assumes that the life of the surface finish is acceptable, of course.

A difficult thing to simply assume, unfortunately.

>I have heard that thinner gold is currently being used on some SIMMs and
>DIMMs.
>Does anyone have any feedback on this?

Depends strongly on the intended number of mating cycles, and the design of
the connector on the motherboard. Some SIMMS and DIMMS use tin or tin-lead;
even cheaper, if properly designed-in. You need 100g normal force, a larger
contact surface, and lubrication to prevent fretting corrosion. Look at:
http://www.amp.com/product/dd68_1.html
and pay close attention to what kind of mating connector you specify.

Jerry Cupples
Interphase Corporation
Dallas, TX
http://www.iphase.com