Re: [SI-LIST] : Modeling Package parasitics

Gregory P. Fitzgerald (gpf@cadence.com)
Mon, 16 Feb 1998 18:42:15 -0500

There are several tools on the market that will allow you to model package
parasitics. Assuming you don't have access to Pacific Numerics (offers
tools specifically designed for modeling packages) or Ansoft 2D/3D, or any
of a host of other parameter extraction tools (some are even available on
the web
from MIT I'm told), calculation is the next best thing.

When I worked at DEC doing medium-high end packaging we had good correlation
when we modeled the wirebonds as lumped R-L's, the traces as impedances (or
distributed lumped elements, ie. pi or T sections cascaded together), and the
via/ball as a lumped R-L. We also were big fans of coupled models since
neighbors often cannot be ignored at higher edge rates, and correlation was
almost always better.

Depending on the size and stack up of your BGA package, here are some typical
values:

Wirebond ~Tens of milliohms, 1-3 nH's depending on length, ~.060"-.180"
Trace section ~Tens of milliohms, 75-90 ohms for uStrip - enhanced BGA
40-60 ohms for stripline in Custom BGA's
trace lengths from .2"-.8" in length
Via/Ball a few tenths of a nH, depending on bottom (dispersion) trace

If you can enter these lumped values into your QUAD tool you're half way
there.
If you can specify slightly more complicated coupled or lossy models with QUAD
you'll be that much better off (ie. closer with correlation) at higher edge
rates.

/Greg Fitzgerald

At 02:43 PM 2/16/98 -0800, 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?
>
>Thanks,
>Mark Nass
>
>