[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.



To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field

List FAQ wiki page is located at:

List technical documents are available at:

List archives are viewable at:     
or at our remote archives:
Old (prior to June 6, 2001) list archives are viewable at:

Other related posts: