Hi! Cortland:
Thanks for your comments. In your experience, does the size/spacing of the
copper dots or islands matter as long as their dimension is much smaller than
the wavelength for the highest possible frequency on the card ? Any special
considerations other than that ?
Regards
Perry
Cortland Richmond wrote:
> Yes indeed. My preference is for thieving to be done with "dots" or
> "islands" small with respect to the shortest wavelength of concern. This is
> because thieving can be constructed so as to resonate and aggravate an EMI
> problem.
>
> Some years ago, at an employer far away (grin), we had obtained compliance
> on a computer using a plug-in processor board. On testing the first
> production items, we found they were some dB over -- at 350 Mhz! It took
> some time, but I found the PWB manufacturer had added a ring of thieving
> material around the board. This ring was resonating at 350 Mhz and
> significantly increasing the shielding required.
>
> Chopping it up into strips made the problem go away.
>
> (Many devices use so-called "ESD traces" to protect board-mounted devices
> from being affected by ESD during maintenance. Unless care is taken with
> these, they can act the same way as thieving copper above.)
>
> Cortland
>
> (cortland.richm...@usa.alcatel.com)
>
> The post above does not represent my employer's opinions or policies
>
> ====================== (some snipped) ====================
>
> Date: Tue, 16 Jan 2001 17:10:43 -0500
> From: "Perry Qu" <perry...@alcatel.com>
> Organization: Alcatel CID
> Subject: [Fwd: [SI-LIST] : Copper balance]
> Reply-To: "Perry Qu" <perry...@alcatel.com>
>
> Hi!
>
> We are looking for some advice on copper thieving on the PCB. The
> concern is the EMC impact of the floating copper. Anyone is willing to
> share his/her experience on the best configuration for high percentage
> of copper coverage and low EMI at the same time ? Refer to the post to
> SI list by my colleague Dorin on this issue.
>
> Any advice on this will be greatly appreciated.
>
> Regards
>
> Perry Qu
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