Re: [SI-LIST] : Modeling Package parasitics

Anders Ekholm (etxaek@al.etx.ericsson.se)
Tue, 17 Feb 1998 10:28:07 +0100 (MET)

Mark Nass wrote:
>
> Does anybody have an accurate way of modeling package parasitics,
> in particular in a QUAD simulation environment. I have been using
> a lumped inductance for a BGA & SQFP package but find this to be very
> inaccurate with fast edge rates and small voltage level swings. The ringing
> from the inductor causes the signal to cross switching thresholds in the
> simulation environment, but this ringing is not seen on the lab bench.
> My feeling is that a specified ZO, TPD & and Length should be used
> for the bonding wire, trace on the BGA package and the pin.
> Does anybody have any thoughts on what values I could use for
> the bonding wire?

Is the ringing seen at the recivers pad or at the package pin/ball ? Are
the simulation limited to the same bandwidth as the oscillscope, have you
added the probes effects in the simulation.

We use QUAD XTK.
We normally try to use the 2D field solver to model the package. We study
the leadframe of the package and describe it geometrically in a .xfx file
then we run the field solver and use the values we get in the .tlp file
to create a model.

Then you might add the bondwire and pin/ball parasitics.

We use topspec's to put the pin characteristics in the model.
How accurate the model is depends on how much work you like to spend on it
In one case I had a leadframe with approx. 17mm long traces and use about
10 crossections or configurations to describe it.
If you use topspec you can not get the crosstalk in package modelled, so
that would be sort of a timing model.

If you create and .isf file describing the package you could get the crosstalk
in the model.

Regards /Anders Ekholm