----- Original Message -----
From: Chris Wells
To: EMC-PSTC Discussion Group
Cc: [email protected]
Sent: Friday, May 31, 2002 8:07 AM
Subject: Bonding to conductive plastic - best method??
Recently we had a good string going on conductive platics.
I would appreciate some help coming up with the ideal electrical bond to this
type of plastic.
We use a 6% Stainless Steel Fiber mix in Poly carbonate and I was looking for
the best method to electrically bond to the plastic to drain off ESD or for
high frequency bonding with the metal portion of our product. This would
include Printed Circuit Board to plastic, Cable to plastic and metal housing to
plastic type connections.
For joining metal housing and PCB connections we have been using plastic
screws that mechanically are designed for plastic.
The threads are widely spaced, tall and thin - They cut into the plastic with
out breaking the mounting bosses (studs).
The engagement with the plastic (screw thread in plastic boss hole) is ~ 100%
leaving little or no air gap between the screw and the plastic.
First set of Question -
If using screws what would be the best type of screw to insure good contact
to the stainless steel fibers?
a.. High profile, thin thread, plastic screw like I described?
b.. Self tapping type screw?
What should the platting be?
a.. Clear Zinc
b.. Zinc Chromate?
c.. Nickle on brass?
d.. Stainless Steel?
Is there any sort of liquid/paste like adative that could be added to the
screw hole to enhance the electrical connection?
We have experimented with metal inserts (PEM nut brand for example).
What sort of bonding does one get when molded in? I suspect poor relative to
press in.
Can the inserts be plain brass or should they be plated like with nickle?
Depth of inserts - Longer inserts should be better but I am concerned about
cracking of the boss.
Screen matterial in the screw boss.
I have seen screen matterial embedded in conductive plastic.
Perhaps it could help screws bond to the plastic as well.
Any comments? Sounds messy.
Coatings on top of conductive plastic?
If a coating were placed on the inner surface of the conductive plastic it
might make a good hybrid sollution but costly.
Are there other considerations?
If you respond today try CC to
[email protected]
So I get it at work too (the ITE guys can't handle this subscription list at
work)
This group is the best resource I have for this sort of topic - thanks in
advance!!
Chris Wells
Senior Design Engineer
Cutler-Hammer
Pittsburgh, Pa. USA
[email protected]
