[SI-LIST] 回复:RE: the effect of box on EMI
- From: zhangkun 29902 <zhang_kun@xxxxxxxxxx>
- To: "Grasso, Charles" <Charles.Grasso@xxxxxxxxxxxx>
- Date: Thu, 31 Jul 2008 07:12:54 +0800
Hi Chas
The board which I have analyzed has the following stackup:
signal ---top
ground ---art02
ground ---art03
signal ---bottom
The power delivery is applied by means of trace in art03. You provide the
following advice:
1.Having a ground plane is number one
2.maintaining the integrity of the ground
3.defining the current return paths
4.having sufficient ground planes
5.no slots in the ground
6.build a Faraday cage into the PCB
I have check the board, all the six advices have been applied in the board.
However, the outer metal plane has obvious effect. Therefore I think the above
advices is not enough. Is there any other advice?
Best Regards
Zhangkun
2008.7.31
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----- 原邮件 -----
发件人: "Grasso, Charles" <Charles.Grasso@xxxxxxxxxxxx>
日期: 星期四, 七月 31日, 2008 上午0:47
主题: RE: [SI-LIST] the effect of box on EMI
> Hi Zhangkun,
>
> IMO (although there are several sources that can cause EMI) the
> primary effect that the plate is helping with is the partial
> inductance of the ground. So, in PCB design, the following should be
> effective: Having a ground plane is number one!. (Two layer
> designs are much harder!) Then other considerations are:
> maintaining the integrity of the ground, defining the current
> return paths, having sufficient ground planes, no slots in the
> ground etc.. and so on.
>
> Another possibility is to build a Faraday cage into the PCB. This
> can be
> achieved by either flooding the outer planes with ground pour or
> addingtwo distinct planes dedicated as ground only.
>
> Chas
>
>
>
>
> -----Original Message-----
> From: Zhangkun [mailto:zhang_kun@xxxxxxxxxx]
> Sent: Wednesday, July 30, 2008 4:58 AM
> To: Grasso, Charles; si-list@xxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
> Subject: 答复: [SI-LIST] the effect of box on EMI
>
> Hi Chas
>
> OK. The first question has been answered.
>
> How about the second question? "how to apply the effct of the
> metal plane
> by means of modification of the PCB, while without additional cost."
>
> As we know, the simple plate under the board could cancel the
> common-mode
> currents. What is the source of the common mode current and how to
> cancel it
> by means of PCB design. For example, adding decoupling caps?
>
> Best Regards
>
> Zhangkun
> 2008.7.30
>
>
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> is intended only for the person or entity whose address is listed
> above. Any
> use of the
> information contained herein in any way (including, but not
> limited to,
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> -----邮件原件-----
> 发件人: Grasso, Charles [mailto:Charles.Grasso@xxxxxxxxxxxx]
> 发送时间: 2008年7月30日 2:45
> 收件人: zhangkun 29902; si-list@xxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
> 主题: RE: [SI-LIST] the effect of box on EMI
>
> Hello Zhangkun,
>
> Assuming that you are using a simple plate under the board and not
> a box (as
> mentioned in your subject line), then the effect you are noticing is
> cancellation of common-mode currents in the plate. The plate in
> this case
> acts as an image plane. The bigger the plate the more effect it has.
>
> Chas
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-
> bounce@xxxxxxxxxxxxx]On Behalf Of zhangkun 29902
> Sent: Tuesday, July 29, 2008 8:41 AM
> To: si-list@xxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] the effect of box on EMI
>
> Dear all
>
> In the recent test, I found out that the effect of metal plane on
> EMI is
> obviously.
>
> Details:
> There is a product with only one PCB of 4 layer. The EMI of the
> PCB is
> measured at first. Then the PCB is put on a metal plane. The EMI
> is lessen
> very much(>6db).
>
> What is the theory of this case? The second and more important
> question is
> how to apply the effct of the metal plane by means of modification
> of the
> PCB, while without additional cost.
>
> Best Regards
>
> Zhangkun
> 2008.7.29
>
> ************************************************************************
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> This email and its attachments contain confidential information from
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