[PCB_FORUM] Re: First Article Inspection

Hi Tom, Austin
 
It's of limited use to have the vendor put their own coupon on the fabrication 
panel or on a break-off.  Sure, it will be constructed to some IPC spec 
somewhere, but it will not match the "real life" of the signals you need proper 
control over.
 
As for a TDR, I guess we're lucky to have the equipment.  However, of the site 
visits I've seen recently, there's no reason to not trust the vendor's TDR 
impedance measurement.  Some of the software they use can vary, but at the end 
of the day, the measurements are normally fairly good.
 
What I'd suggest:  
 
1 - create your own test coupon, similar to the actual traces on your board, 
and send it with the design
2 - ask for a copy of the test results.
3 - get a copy of exactly what materials they used to achieve it
 
Cheers,
Richard

>>> austin@xxxxxxxxxxxx 26/01/2006 3:43 p.m. >>>

Hi Richard,

Agreed, and you also typically check impedance between signals and the
reference plane layer, not between plane layers.  Not something most
incoming inspection people know how to do, much less have the equipment to
do.  That is why I asked Tom if he would elaborate.

Regards,

Austin

Original Message:
-----------------
From: richard moffat richard.moffat@xxxxxxxxxxxxxxxxxxx
Date: Thu, 26 Jan 2006 15:26:09 +1300
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: First Article Inspection


You need a $30k TDR for impedance measurement, not a $30 multimeter!

>>> austin@xxxxxxxxxxxx 26/01/2006 2:54 p.m. >>>

Hi Tom,

> c.  get a Multimeter and check impedance between the various plane layers.

How do you do that with a miltimeter, and what does that tell you?

Regards,

Austin


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