[SI-LIST] Re: Article discussion on bad packages
- From: steve weir <weirsp@xxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Sat, 25 Dec 2004 17:29:51 -0800
Lee, there are two very important issues here with regard to bounce
conclusions alone:
1) Mr. Hecker described the bounce at the board:
"Mahi was designing what Hecker describes as a "cutting-edge application"
involving 3.125-GHz backplane links. The design called for FPGAs with
integrated serdes capability to be used as serial links. But test data
showed severe ground bounce and power bounce on the board, as well as
performance problems related to the operation of the serdes links in the
system environment."
I assume Mr. Goering took care to quote Mr. Hecker accurately. You
acknowledge your role in the piece. So are you now stating the quote is
wrong? If so, what the heck is going on here with these articles? If that
quote is wrong, what else is wrong in those pieces?
2) Even when the board appears quiet, it is easy to mistake excessive plane
spreading, and/or via attachment inductance for package inductance.
As I stated a complete impedance budget for those things that we can
control, which is all elements up to the package attachment is
imperative. And I fully stand by my statement that this is the system
engineer's responsibility alone.
The switching current that will stand on top of that impedance is something
that we can characterize. In an FPGA application we, not the IC
manufacturer have the final control on whether the combined switching
current and PDS impedance are compatible with device requirements. What a
suboptimal package does is limit the tolerable current. The system
engineer adopting the FPGA must marry the finite capabilities of the FPGA
to an appropriate environment and application. This problem is as old as
switching, even with relays.
I suggest that we maintain decorum here. If you have facts that render my
statements and/or conclusions incorrect, then please by all means share
them, and we will all be educated. I fully accept my own limitations, and
despite the care that I try to use when posting, the possibility always
exists at anytime that I have missed information, and/or concluded in
error. If shown to be in error, I will happily be corrected and apologize
for any errors. But be assured, I make all my posts in good faith. I ask
that you concentrate on advancing the conversation with verifiable facts on
this important subject, and leave unjustified attacks on my character at home.
Regards,
Steve.
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