>We currently have a PCB that will be put in an extrusion with front and
>back panels that will be screwed on.  Would anyone have any information
>on grounding criteria or techniques for attaching all three parts of the
>case to earth ground on the PCB?  I have looked at UL508, but it seems a
>little too wide open.  Any help would be appreciated!!
>
>Thanks,
>
>Joe Reichert
>Lake Shore Cryotronics, Inc.
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> You can put a 5-10mil clearance (each side) around the non-plated thru mtg
hole and run the copper plane up to that point on external layers. This
earth gnd plane can run under the extrusion and must be free of soldermask.
If this is a multi-layer bd that needs internal earth ground you can put 2
to 3 small plated thru holes (.050 mil pad)  out side the screw mounting
clearances (each mtg location) and thermal spoke to earth gnd on every
layer. To have a non-plated thru mtg hole is better than a plated thru mtg
hole because of the possiblity of barrel cracking under stress and loss of
conductivity.
                                doug brusig
                                primex tech.
                                redmond,wa.

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