[SI-LIST] Re: Inductance of PWR&GND plane and other signal line

Hello, Plus Lee,

Inductance depends on the geometry.  In particular, wires with larger
perimeters (such as planes) tend to have smaller inductance.  Wires with
small cross-section area and perimeter, such as solder balls, will have
larger inductance.

As Steve noted, if the return path has a large cross-section area, then the
inductance increases.  Since your ground and power planes are right next to
each other, this would decrease the inductance between them.  Since S2 is
further from the planes than S1, S2 would have a larger inductance.

Best regards,
Lynne


-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of plus lee
Sent: Thursday, December 23, 2004 12:47 AM
To: steve weir; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Inductance of PWR&GND plane and other signal line

 Hi, all experts,
 Sorry my poor English.
 The below inductance data was 4 metal layers BGA 
 simulated by Paksi-E package software.
             m1       m2        m3        m4         wire       ball
 GND   0.093   0.0043  0.0005   0.0031    0.084    0.235
 PWR  0.094   0.0001  0.0017   0.0036    0.114    0.268
 S1      1.42     0.0038  0.0077   0.3563    1.919    4.056
 S2      1.67     0.0024  0.0062   0.0782    2.176    4.271
 
 Why m1, wire, & ball inductance of S1,S2(signal line)
 is larger than GND&PWR plane?
 
 Is this the series circuit or other reason?
 
 I could understand m2 and m3 is minor because of large plane, but how
 about m1 and m4?
 
 
> On Wed, 22 Dec 2004 08:38:11 -0000, Chris Chalmers
> <cchalmers@xxxxxxxxxxx> wrote:
> > PlusLee,
> >
> > A plane is normally physically wider than
> > a signal trace.  Since a plane is wider then the
> > current distribution spreads out more across it.
> > Thus the number of field lines around it decreases
> > and thus the self inductance decreases.
> >
> > The combination of a power and ground plane next to
> > each other in a stackup will reduce the total inductance
> > of each because of the increased mutual inductance.
> >
> > inductance of power plane ->
> >
> > Ltotal for power plane  = self Lpowerplane - Lmutual   (where mutual is
between pwr and gnd)
> >
> > for more information I strongly recommend you get a book
> > like Eric Bogatins "signal integrity simplified" or
> > Dr Johnson's bible.
> >
> > Thanks
> >
> > Chris
> >
> >
> > -----Original Message-----
> > From: si-list-bounce@xxxxxxxxxxxxx
> > [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of plus lee
> > Sent: 22 December 2004 02:25
> > To: si-list@xxxxxxxxxxxxx
> > Subject: [SI-LIST] Inductance of PWR&GND plane and other signal line
> >
> > Hi, all experts,
> > I am a newcomer to learning SI & PI,and have some questions about
inductance
> > of power, ground, and signal line.
> > Why the inductance of PWR&GND plane is less than signal line?
> > Is the series of many nets or the plane wider than signal?
> > thanks for your help
> >
> > Best regard
> >
> > PlusLee
> > ------------------------------------------------------------------
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