I agree if this was the actual EUT under test, but if it is a
peripheral that gets used lots, or if its a PC chassis for example I would
clean the surfaces at any point I got nervous about the performance.
One of the reasons that it is difficult to find a PC that meets the
emissions limits is that after shipping or opening and closing the fool things
a number of times the mating surfaces get crunged up (technically speaking) and
build up a certain amount of resistance. I can't afford new peripherals every
try so I just get these surfaces back to "as built" condition.
If you have to do this on the EUT it should only be done if you find it
a problem because it caused a failure. Then as suggested many times prior you
have to go back to the design guys and tell them they have to fix it before you
can certify it.
I haven't had had any problems with erasers and good electrical
cleaners like you can find in the lab. I would stay well short of sandpaper or
anything abrasive because it can go through whatever plating is being used for
corrosion protection. The problem only gets worse after that. So will many
cleanings with the eraser.
Gary
-----Original Message-----
From: John Juhasz [mailto:jjuh...@fiberoptions.com]
Sent: Thursday, February 28, 2002 1:08 PM
To: 'David Heald'; emc-p...@majordomo.ieee.org
Subject: RE: Pencil erasers for pre-EMI cleaning?
I'm sure there are products on the market
just for this purpose.
But I would be concerned about my design if pass/fail
depended upon how clean the mating surfaces are.
A component substitution or some other ECO to the
product down the line could put the product over
the limit. Refer to the thread on test margins.
John Juhasz
Fiber Options
Bohemia, NY
-----Original Message-----
From: David Heald [mailto:davehe...@mediaone.net]
Sent: Thursday, February 28, 2002 2:44 PM
To: emc-p...@majordomo.ieee.org
Subject: Pencil erasers for pre-EMI cleaning?
All,
I'm preparing for an emissions test and I had started cleaning some of
my chassis mating surfaces with a pen/pencil eraser then alcohol to
ensure the surface to surface contact was good. A friend then told me
that using an eraser would also remove the anti-corrosive coating that
was on the metal (Thanks Paul!). So I would end up with a very short
term benefit, then rust. What I am trying to determine is if maybe
light rubbing with a pencil eraser might only remove surface
contaminants and leave the metal and coatings intact. (the pencil eraser
is much less abrasive than the pen side)
So the real question is... Does anyone have direct good or bad
experience with the aftereffects of using a pencil eraser to clean
mating edges (card faceplates in a telco box for example)? I have both
steel and aluminum surfaces to worry about so info for either type is
welcome. (and don't worry the different metal types are not adjacent).
Any feedback would be greatly appreciated as the system is really dirty
right now.
Thanks and Best Regards,
Dave Heald
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