[SI-LIST] Re: Power intergrity simulations using FEMM?
- From: "Istvan Nagy" <buenos@xxxxxxxxxxx>
- To: <kelvin.harding@xxxxxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Thu, 3 Jul 2014 18:58:54 -0700
Hi
Ome more thing:
Here is the step by step setup for the FEMM DC voltage drop simulation:
(It is like a software manual, the article will not be this detailed for the
exact menus, it will be more introduction type with colorful images )
Step by step setup for the FEMM DC simulation:
1. Create a project: File > New > Current Flow Problem. Then set up with
„Problem” on the menu bar. Here we set the plane copper thickness (depth),
length unit (mm), frequency (1Hz), minimum mesh angle (5deg) and other
parameters.
2. File > Import DXF. Select DXF file and wait. Before DXF import we should
simplify the geometry in a DXF editor like the freeware A9CAD. Even then the
import process might take minutes or an hour.
3. Simplify the geometry by deleting unnecessary points and lines. Reduce
arcs to polygon lines, by selecting all of them, then press space, then set
the „Max Segment” filed to 45 degrees. Make sure that all poly-lines and
plane edges are closed and lines and arcs separate the different areas.
4. Set up materials, copper and air using the Properties > Materials > Add.
Sigma is 59600000 for copper, and 0 for the air, assuming the units were
millimeters.
5. Set up the boundary conditions, source and load at Properties >
Conductors. For the source (DC/DC converter) we create one conductor with
fixed voltage option and VCC voltage value. For the load (BGA chip) we use
the „Total Current” option with the load current with negative sign.
6. Assign the materials by „Assign block Labels” button. Place one in the
copper area, and one outside of the power plane shape („Air”. Also select
„Default” option to cover all the plane voids with default Air material).
Right click select, then space-key to select one of the pre-defined
materials.
7. Assign the conductors. Select multiple edges (in line or arc mode) using
right click, then press space for the properties dialog. Select multiple via
(all power pin vias) edges under the BGA chip for the load conductor, and
multiple vias at the DC/DC converter for the source conductor. Which via is
a power via – we have to check them one by one in the PCB layout viewer.
8. Mesh > Create Mesh. If it fails, then back to geometry simplification.
The mesh should not be larger that 100k nodes. We can also try to reduce the
min angle.
9. Analysis > Analyze. If this is not complete in an hour, then again back
to geometry simplification. If successful then we can open the result widow
with Analysis > View Results.
10. Measure voltage drop: In line edit mode click on one point of the DC/DC
converter, and then one one point of the BGA power vias. Then from the menu
click: Integrate > Voltage Drop. This gives a complex number, but normally
with a 99.99% real part, so we can go with the real part only, close enough.
To get the DCR, we can calculate: DCR = V_Source / I_Load. If we use
multiple layers to deliver the power, then we can simulate on all layers
separately, calculate DCR separately, then calculate the effective total DCR
as parallel circuit effective resistance 1/Re = 1/R1 + 1/R2 +... Then the
total voltage drop in the system will be V_drop = Re * I_Load.
11. It is useful to see which parts of the plane carry more current than
others, so we can optimize the plane shape to reduce DCR by eliminating
hot-spots. For this select View > Density Plot > „|J|” in the menu. If the
colors are not telling the story very well, then we can change the red and
blue thresholds by experimenting with the numbers in the View > Density Plot
> „Upper Bound”, or „Lower Bound” fields.
Regards,
Istvan Nagy
-----Original Message-----
From: Istvan Nagy
Sent: Thursday, July 03, 2014 6:53 PM
To: kelvin.harding@xxxxxxxxxxxxxxx ; si-list@xxxxxxxxxxxxx
Subject: Re: [SI-LIST] Power intergrity simulations using FEMM?
Hi,
I do that often. I think my results are sensible.
Actually my new article on the very same topic will come out in PCD&F
magazine in August.
Regards,
Istvan Nagy
Fortinet
-----Original Message-----
From: kelvin.harding@xxxxxxxxxxxxxxx
Sent: Thursday, July 03, 2014 1:45 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Power intergrity simulations using FEMM?
Hi, Has anyone done IR drop analysis of power planes with FEMM? I can
make pretty pictures of planes but haven't got any sensible results yet.
How can I enter parameters to simulate current flow between two or more
points and plot the resultant voltages. I think someone posted that them
had done this (and possibly AC PI analysis) with FEMM. Can you share an
example project? Thanks in anticipation, Kelvin
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