Do you know of an appropriate EMI material for a rotary seal, where one
mside of the seal rotates against the seal? What is your experience with an
EMI seal interfacing with conductive
Iridited(Chromate conversion coating)on Aluminum?

-----Original Message-----
From: Misner, Bruce [mailto:[log in to unmask]]
Sent: Wednesday, July 26, 2000 9:35 AM
To: [log in to unmask]
Subject: Re: [TN] Plugging Vias With Conductive Epoxy


Hans,

All the experiments (extensive) and experiences (20 years of use with the
high purity types; I'm not associated with the epoxy manufacturers) I have
run with Silver filled epoxies has shown them to  work well in a compressed
state sandwiched between 2 surfaces with compatible finishes (typically
noble metals) in low current applications.

They will experience higher and somewhat varying resistance's when used to
bridge gaps and fill voids (read that as unreliable) like a PTH. I have
found these resistance's to typically be small (usually less than a few
ohms, often in the milliohm range) but can, of course, be detrimental to
some critical electrical performance.  I would also question the
compatibility with White Tin and would not be surprised if that interface
further contributes to varying (increasing) resistance over time and temp,
but you would need to perform that experiment for yourself. Use in a PTH for
continuity test purposes may be fine but could also mask a barrel plating
problem until the resistance goes up over time and temp.

Regards,
Bruce Misner

> ----------
> From:         Hans Rohr[SMTP:[log in to unmask]]
> Reply To:     TechNet E-Mail Forum.;Hans Rohr
> Sent:         Tuesday, July 25, 2000 9:10 PM
> To:   [log in to unmask]
> Subject:      [TN] Plugging Vias With Conductive Epoxy
>
> One of our customers wants us to plug vias (.016-.020") with a
> conductive epoxy material.  The board is finished with white tin so
> plugging with solder is out. The vias do not have to be completely
> filled but the plugs must be strong enough to withstand test probe
> pressure.  The epoxy filled vias will be used as test points.  We have
> used carbon and silver epoxy on conductive surfaces but never to plug
> holes.  Has anyone ever done this and can you suggest a conductive epoxy
> that can be screened on?
>
> Hans Rohr
>
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