From: Gary McInturff [mailto:[email protected]]
Sent: Wednesday, September 01, 2004 3:05 PM
To: EMC-PSTC (E-mail)
Subject: grounding and pressure contacts
Gentlemen,
I'm looking for some data on pressure versus resistance through
metal mating surfaces. Normally I avoid trying to make HF emc grounds
through a simple pressure fit, but I have an instance where this solves a
lot of problems inside a chassis. Basically, the part needing grounding
would be inserted into a large wide "ground finger" if you will. I have the
ability to control the pressure between the two parts with positive and
constant pressure, but I don't really have any logical way to describe the
amount of pressure per square inch to my mechanical guys - ft/lbs or
inch/lbs (or appropriate metric values). I made at least a quick search of
the finger stock folks but don't see any data - maybe I'm looking in the
wrong spot. I'm trying to insure that I can get a 1square inch area pressed
firmly against the second part and insure I get less than an ohm, hopefully
milliohms of resistance between the parts. _This is not a bonding issue for
current, but an emc ground over frequency.
Thanks
Gary
Gary:
As a quick rule, I assume about 1 pound per foot of average-size CuBe
fingerstock. Since the contact point on a row of fingerstock is only about
1/16 inch wide, this yields a contact pressure of about 16 psi. This will
yield milliohm performance, as long as the CuBe has the chance to
occasionally wipe the mating surface. So much of your bond quality is
dependent on disruption of surface oxides that the contact pressure is a
very secondary parameter.
Regards,
Ed
Ed Price
[email protected] WB6WSN
NARTE Certified EMC Engineer & Technician
Electromagnetic Compatibility Lab
Cubic Defense Applications
San Diego, CA USA
858-505-2780 (Voice)
858-505-1583 (Fax)
Military & Avionics EMC Is Our Specialty
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