George, two documents that may be of use are IPC-2141 and IPC-D-317A.  I 
forget the titles, but they deal with high speed and controlled impedance 
issues.

I measure impedance using an HP 54120 time domain reflectometer set up.  
I recommend having a good coupon on the edge of the PCB panel, including 
a suitable connection to the 50-ohm cable from instrumentation.  The IPC 
documents will tell you how to make the coupon.

HP has several application notes that help in using the time domain 
reflectometer to measure impedance.  Alson Wong in Loveland, Colorado, 
knows a lot about these matters (he's at HP), and has helped me a lot.

Lou Hart 412-858-6117


.

On Sat, 31 Aug 1996, George Ioakimedes wrote:

> Hello:
> 
> I was hoping that someone could point me to a reference document that
> would explain controlled impedance practices and how the PCB houses
> implement this. I am looking for a good place to start to understand how
> to control the impedance of boards used for memory cards.
> 
> In my particular case, the application environment is 100MHz, and I am
> told by the designer that the PCB needs to be 72 ohm +/- 10%.
> 
> How do I work with the PCB facility to gaurantee that this is met and
> what are some good guidlines to measure the final product to see if it
> is meeting spec?
> 
> Anyone's help on these questions would be greatly appreciated since I
> have a meeting with the PCB vendor next week to discuss this topic.
> 
> Thanks in advance,
> 
> George Ioakimedes
> NEC Electronics, Inc.
> [log in to unmask]
> 
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