FreeLists / si-list / [SI-LIST] Re: distributed packaging model

["Ozgur Misman" <omism@xxxxxxxxx>]

Hi Perry,



1. divide lumped RLC into sections of Pi/T circuit and interconnect them
together.


Package interconnect is typically electrically small, unless the package
size is large and the risetimes are very fast ( 100 psec or so.) the lumped
approach works fine. Especially with chip scale or near chip scale packages
gaining dominance it is true that a lumped model should suffice for most
applications. So as you see as risetimes get faster packages shrink as
well.:)
However there are instances where a lumped model is not sufficient such
gigabit transceivers where the data transfer rates are quite high (OC-48,
OC 768 applications). I can tell you that extracting the lumped parameters
and then just segmenting it into 4-5 ( as determined by the bandwith
requirement ) is a shortcut and works very well for uniform transmission
lines only!. However, package interconnect structures are very complex with
wirebond, trace, via, solderball making the  signal transmission path.
Typically, a good lumped model should extract the wirebond and the rest of
the net seperately. So modeling the wirebonds as lumped and the rest of the
net  (trace via and solderball ) lumped should be good enough ( at leat you
are capturing the most obvious impedance discontinuity). Then if we need
segmentation you can do it on the  trace portion. My experience is that
this works quite well. I agree that you are not capturing the impedance
discontinuity  at the via, and solderball, however that is fine most of the
time.
We are constantly keeping an eye on commercial simulators  and actually in
the process of buying one to provide distributed models.
Even the commercial simulators however do not capture each impedance
discontinuity. They simply compare the risetime (and therefore the bandwith
required) and compare that to the physical length and decide how many
segments is required from the model. then analyze each segment seperately,
in each segment there maybe more than one discontinuity so you may not be
able to capture it.

Do you relly need that level of detail is another question, though!

2. instead of RLC, use a transmission line with impedance of Z
=sqrt(L/C) and delay calcuated from length of packaging trace and L/C.

Well this is the actually same as your question number one. Unless that Z
reflects all the discontinuities ( multiple Z segments) this is comparable
to the lumped model. so the same arguments apply.

I think if you would like a very detailed job, you should ask a model for
each  discontinuity,
a lumped model for the wire, a transmission line (Z,Td) or a distributed
R,L,C (enough segments) model for the trace , a lumped model for the via
and another lumped model for the solderball and then built  eqivalent
circuit manually if you have time for it:)


Regards,
Ozgur Misman
Amkor Technology





"Perry Qu" <perry.qu@xxxxxxxxxxx>@freelists.org on 11/08/2001 09:03:11 AM

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Subject:  [SI-LIST] distributed packaging model



Hi!

I'm aware that distributed packaging model should be used for rise time
signal simulation. However, most of the packaging model we got from
vendors are in terms of lumped RLC value, e..g, those listed in IBIS
model. When I asked for distributed model, I got two suggestions from
vendors as an easy go-around:

1. divide lumped RLC into sections of Pi/T circuit and interconnect them
together.

2. instead of RLC, use a transmission line with impedance of Z
=sqrt(L/C) and delay calcuated from length of packaging trace and L/C.

I have doubt about both approaches. Did any one tried and verified them
?

Thanks in advance

Thanks in advance

Perry

--
Perry Qu

Product Integrity         |      600 March Road
Alcatel Canada            |      Ottawa, ON K2K 2E6, Canada

DID: (613) 7846720        |      FAX: (613) 5993642


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