[SI-LIST] Re: ground planes at top / bottom layer
- From: Richard Jungert <r_jungert@xxxxxxxxxxx>
- To: <earlalbin@xxxxxxxxx>, si list freelist <si-list@xxxxxxxxxxxxx>
- Date: Fri, 2 Jan 2009 13:15:51 -0800
Earl
If one designs them right then you won't need a blanket to cover up the
mistakes. I have done over 180 of them and not once did we add extra copper on
the outer layers to control EMI. I still think that extra copper is something
to cover mistakes.
Richard Jungert
> Date: Fri, 2 Jan 2009 12:42:49 -0800
> From: earlalbin@xxxxxxxxx
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: ground planes at top / bottom layer
>
> Lee:
> The Sun rises in the East and sets in the West. "ground layers on the
> outside of PCBs to control EMI", East-West thing here.
>
> "Xbox didn't do it and it passes," ok, yes. Obviously their four layer board
> had enough margin. Likely as well they started with a six layer solution
> (safe), added up the cost (consumer vs profit) made appropriate changes and
> they pass with a four layer. Six layers in not the only tool in your tool
> box, many ways to skin the cat, etc...
>
> If you don't own an Xbox and you haven't torn it apart, why, if your goal is
> similar. I hope you have the time to gain a critical understanding of what
> Xbox did, mostly though why, they did what they did.
> ----------------------------------------------------------------------------------------------------------------------------------
> To all of those who recommend ground layers on the outside of PCBs to
> control EMI, take a look at a PC mother board or the motherboard in the
> Xbox. They are 4 layer PCBs that have signals on both outside layers and
> the products in which they are shipped pass EMI standards.
>
> Where did the notion that outer layers had to be ground in order to pass
> EMI come from? My guess is it is an RE.
>
> Lee Ritchey
> ----------------------------------------------------------------------------------------------------------------------------------
>
>
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