Hi Darrel
Definitely use a star washer or some washer type that will bite through the
oxidisation layer.  Another option, if you are doing SMT on the boards, is
to screen solder paste on the ground plane in a pattern that will contact
the bolt head.  Have seen this done on a board that needed a good ground
path, 150k produced with no ill effects.

regards,

Graham Collins
Process Engineer
Litton Systems Canada
(902) 873-2000 extension 215


> -----Original Message-----
> From: Darrel Therriault [SMTP:[log in to unmask]]
> Sent: Wednesday, May 13, 1998 7:22 PM
> To:   [log in to unmask]
> Subject:      [TN] OSP and EMI
>
> Technet,
>
> My Mechanical Engineers just brought something to my attention that I
> would
> like to get some opinions/advise/info from the TechNet expertise.
>
> We have recently switched from HASL to OSP (Entek 106 I believe) finish
> for
> our boards.  We run a ground plane around the perimeter of boards and
> backplanes to help with EMI shielding and grounding in general.
>
> Their concern is with the change to OSP finish, we are seeing bare copper
> now that is tarnishing/oxidizing and is this still an acceptable grounding
> contact where it bolts to the chassis or contacts a cardcage?
>
> Other Questions :
>
> 1.   When the board is processed (IR) does the OSP get removed or does it
> remain, and
>      is it conductive or an insulator?
>
> 2.   What are the options for having the ground perimeter copper finished
> so it won't
>      oxidize and will provide a conductive surface for acceptable
> ground/EMI contact?
>
> I would appreciate any comments/opinions/advise.
>
> Thanks..........DT
>
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