Carlos R. Robert said:
>Although IPC-6012 specifies a minimum thickness of 0.8 micrometers (30
>micro inches) of gold for Class 1 and 2 edge-board connectors, it seems
>that more and more suppliers are suggesting thinner and thinner gold
>plating as a low cost alternative.
Yes, you often see a premium increase or a "cost reduction" for eliminating
or reducing the gold thickness requirement on a connector.
>Looking back into this forum's archives, I found the 1995 tread 'Where
>did 30m" for gold Tab plating come from?' with very good information
>but no definite answer. One poster performed an experiment about
>thickness and connection cycles (see attached message fragment), and
>found out that a 20m" finger gave up at about 10 cycles. If these
>results are still valid (I don't see why not), how come PCB vendors are
>even suggesting flash gold (2 to 7 micro inches) as an acceptable
>option?
The general reason is probably that they wish to increase the speed of the
plating line. Most such connectors and PWB edge contacts are plated in a
moving line in which the conveyor rate controls the time in the plating
solution, and less gold thickness = faster production rate. It is my belief
metal price is not the major cost driver.
>I also posed this question (via E-mail) to two connector manufacturers,
>AMP and Burndy. AMP answered immediately but did not provide a definite
>thickness (I got their connector's specs and insertion rates thought).
>I have not received a reply from Burndy yet.
There are too many variables to permit any definitive statements about how
much gold is required. But if I get any vote, it will be for 30 microinches
minimum. IMO, the porosity of gold plating is a major problem, and even
apart from the environmental exposure and the mating cycles, etc. I've seen
too many gold finger tabs turn a shade of red like a cheap blonde hair dye
job. Witness the common field "fix" of reseating circuit boards in a
backplane. If those connectors had "good" gold, it would not be necessary.
>Do anyone has more information or pointers about this issue?
There are a great many articles in the technical journals. I believe that
the literature AMP provides is the most informative and accurate from any
connector supplier. Norm Einarson is a very solid source, too - as you
quoted.
>Has
>technology advanced so much that thin flash gold is acceptable for
>edge-board connectors in a Class 1 product?
I doubt it. If you buy an Interphase board (and HP does, thankfully), it
will have 30 microinches minimum gold over 100 microinches nickel. It costs
a little more, yes. But given the fact that five volt logic is going to
three, and that the gold finger tabs are smaller with each generation of
computer board (PCI compared to EISA, etc), it would seem that the need for
reliable low-Ohm contacts is greater than ever. It is without a doubt a
reliablility issue to use inferior plating on separable connectors.
regards,
Jerry Cupples
Interphase Corporation
Dallas, TX USA
http://www.iphase.com
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