Hi Steve - sorry about the confusion but until everyone in the electronics
industry starts manufacturing printed wiring assemblies only for one use
environment and one set of life conditions most issues will have less than
yes/no solutions (besides, if there was only one answer most of us would be
out of a job!).  The number of insertions/extractions an edge connector can
'survive' is dependent on the following variables:

- use environment
- connector finish (both underplating and final plating, eg. gold over
nickel)
- insertion/extraction force
- stress environment

The use environment variable deals with humidity (does the card get rained
on?), chemistry (is the use environment hostile, e.g. acid rain, sulfur
fumes), and configuration (is the circuit card enclosed or exposed?).  The
connector finish variable deals with the underplating system (was a nickel
plate used for a hard sliding surface?) and the final finish (was gold used
to prevent oxidation?). The insertion/extraction force variable deals with
amount of force/pressure that the mating connector segment exerts on the
edge connector surface (i.e. is the force intended to push thru an oxide or
is it just a sliding force?). Finally the stress environment is important
(does the circuit card under go constant vibration or are things under
minimal motion?). A pretty interactive set of variables. A good example is
the use of tin/lead as a connector final finish. Many design guidelines
restrict the use of tin/lead as a final finish for a connector but if you
have a benign use environment, a one time - large insertion force, have a
good underplate, and a benign stress environment then tin/lead would meet
your needs. However if you need to insert/extract a tin/lead connector
finish multiple times then you could have problems. The connector
manufacturers (e.g. AMP, Berg, Ney, many others) have a great deal of
design information that would be helpful. As Phil Hinton said there are
general rules of thumb that work a majority of the time but if you want to
get more specific you have to match your connector to your use environment.
Good Luck.

Dave Hillman
Rockwell Collins
[log in to unmask]





[log in to unmask] on 02/06/98 10:25:41 PM

Please respond to [log in to unmask]; Please respond to [log in to unmask]

To:   [log in to unmask]
cc:    (bcc: David D Hillman/CedarRapids/Collins/Rockwell)
Subject:  Re: [TN] Gold for edge-board connectors thickness




Phil,
     Your post brings up some interesting information. Does anyone recall
the
posts from a day ago regarding a gentleman that had asked if he was doing
any
harm by removing cards from equipment when doing his scheduled preventative
maintenance? He worked in a sawmill if I remember correctly.
     There was the reply from others that stated that he wasn't doing any
harm
at all because the gold could withstand thousands of insertions....quite a
difference between that number and the numbers that you refer to. I'm not
questioning you at all, I'm just confused as to what the correct answer
should
be.
                                                                     Anyone
care to comment?

-Ste
ve Gregory-
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