[SI-LIST] Re: current flow on a pwr plane
- From: "DAVID CUTHBERT" <telegrapher9@xxxxxxxxx>
- To: james.f.peterson@xxxxxxxxxxxxx
- Date: Sun, 13 Jan 2008 10:12:19 -0700
Jim,
perhaps this will help. The DC resistance per square for 1 oz copper is 500
u ohms. You can divide the connection between vias into small squares to get
an idea of the current flow and the resistance. My quick calculation says
the resistance between two vias spaced 1 inch, on 1 oz copper, is 2000 u
ohms. SPICE works well for this using a resistor matrix. How about a via? A
via plates to 1/2 oz, I believe. The DC resistance is 1000 u ohms per square
for 1/2 oz. For a 20 mil diameter via connecting to a layer 10 mils away it
is equivalent to 1/Pi of a square (10Pi mils wide by 10 mils long). The via
resistance is 300 u ohms.
When I worked at Micron someone got a patent for positioning three vias such
that they shared current equally.
Dave Cuthbert
Consultant
On Jan 10, 2008 12:04 PM, Peterson, James F (EHCOE) <
james.f.peterson@xxxxxxxxxxxxx> wrote:
> I've been looking at some simulators that predict DC current flow
> through a power plane...They can be used to evaluate the ability of a
> copper pour to support the DC current needs between a POL regulator and
> it's "consumer" (maybe the core voltage of a processor or ASIC). This is
> becoming important because of the "swiss cheese" effect under these
> components and the huge DC currents that they need.
> Anyway, on to my question : the results of these simulations often show
> current densities that are not intuitive to me. For example, 4 vias
> connecting 2 pwr planes together, they are somewhat close to each other
> (say, within an inch), yet the current densities through these 4 vias
> are very different.
>
> Is there a white paper or someone out there that can explain this
> behavior? I'm not looking for a complex equation, more like an
> explanation that makes it more intuitive.
>
> Thank,
> Jim Peterson
> Honeywell
>
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