Re: [SI-LIST] : Ground gap problem

Jon Keeble (j.keeble@fairlightesp.com.au)
Thu, 25 Mar 1999 02:42:34 +1000

>At 02:09 PM 3/23/99 -0800, you wrote:
>>>>>
>> Hi all,
>> I am trying to find the effects of the gaps on the ground plane for
>> the high-speed circuits.
>> Even though I have a couple of references about the via, which has the
>> ground gap problem, I need more specific data about the ground gap
>> problem regarding the gap size, gap location.....
>> Either measured data or simulated data will be fine ( papaers or
>> refernce book...)
>> Looking forward to your answers.
>>
>> Thanks
>> Sangil Lee

The high frequency component of return current in a plane is concentrated
under the track.

I recall a number of 90% within 1.5 times the track-plane distance.

So intuitively one might expect less effect if the track is close to the
plane.

Say the vias are 50 drilled 16 with 10 clearance. This makes a bridge of
copper between voids of

50 - (16 + 2x10) = 14.

Best result would be obtained if the track follows the centre line of the
bridge (good argument for gridded routing).

If the above is correct, then the above geometry would support a track to
plane distance of upto 10.

Jon Keeble

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