[SI-LIST] Re: bypass-caps: trade-off between capacitance and inductance

Sarah

If the power is for core, I suggested that as many capacitor as possible is 
placed on the board. If the power is for IO, I suggusted that as many vias as 
possible is placed on the board. Moreover, as Istvan proposed, the impedance 
should be simulated to invest if there is resonance or not.

Best Regards

Zhangkun
2005.4.24

----- Original Message -----
From: Sarah Bates <sarah@xxxxxxxxxx>
Date: Saturday, April 23, 2005 9:54 am
Subject: [SI-LIST] bypass-caps:  trade-off between capacitance and inductance

> Si-folk,
> I am pinning-out a chip that will be used on a board that
> does not use via-in-pad technology.  In order to place
> bypass caps in the 1mm ball field, I'll need to place 2 power
> balls in a row and two ground balls adjacent to the power balls,
> and drop an 0402 cap in between them.  In order to maximize the number
> of caps, I could then keep adding a pair of power and gnd balls,
> and a cap.  However, this will place all powers in one row and
> all grounds in aonther row and so the mutual inductance of the
> caps/vias in the power-delivery path will be increased.  If I
> try to alternate power and ground, I will not be able to place
> as many caps, so how do I go about quantifying the trade-off between
> the two scenarios.  (Scenario 1 is having more caps, but a topology
> in-which the mutual-inductance works against me.  Scenario 2 is
> having fewer caps, but alternating occasionally so that the mutual-
> inductance works for me.)
> For this analysis, I'm estimating a 10 layer board and via inductance
> on the order of 0.9nH.  I think this is reasonable.  I would use 0.1uF
> 0402 caps.
> 
> Here are pictures to clarify the question:
> P represents a power ball
> G represents a ground ball
> || represents an 0402 capacitor
> 
> Scenario 1:
> P  P  P  P  P  P  P  P  P  P  P  P
> || || || || || || || || || || ||
> G  G  G  G  G  G  G  G  G  G  G  G
> 
> 
> Scenario 2:
> P  P  P  G  G  G  P  P  P  G  G  G
> || ||    || ||    || ||    || ||
> G  G  G  P  P  P  G  G  G  P  P  P
> 
> Please point me to any relevant books/papers if you know of any.
> 
> Thanks,
> Sarah
> 
> 
> ------------------------------------------------------------------
> To unsubscribe from si-list:
> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
> 
> or to administer your membership from a web page, go to:
> http://www.freelists.org/webpage/si-list
> 
> For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
> 
> List FAQ wiki page is located at:
>                http://si-list.org/wiki/wiki.pl?Si-List_FAQ
> 
> List technical documents are available at:
>                http://www.si-list.org
> 
> List archives are viewable at:     
>               http://www.freelists.org/archives/si-list
> or at our remote archives:
>               http://groups.yahoo.com/group/si-list/messages
> Old (prior to June 6, 2001) list archives are viewable at:
>               http://www.qsl.net/wb6tpu
>  
> 
> 

------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field

List FAQ wiki page is located at:
                http://si-list.org/wiki/wiki.pl?Si-List_FAQ

List technical documents are available at:
                http://www.si-list.org

List archives are viewable at:     
                http://www.freelists.org/archives/si-list
or at our remote archives:
                http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
                http://www.qsl.net/wb6tpu

Other related posts: