Humans make errors. It doesn't matter what kind of an inspection 
     process you have, eventually something will be missed.
        
        The absolute best thing a designer can do when he outputs his design for
     a fabricator is to output a good CAD netlist. This does several things:

        1.      It allows for the board shop to do a "Net compare" against the 
"extracted" net list. If the net list and the design do not match, it would be 
possible to detect the problem before the job is even tooled. There have been 
many times when customers have supplied us with gerber data that did not match 
the "intent" of the design. 

        2.      It can speed the tooling process up significantly. First, you do
not need to wait until all of your check plots (1 up gerbers) are plotted and 
inspected before starting the tooling process. Second, many customers require 
that they approve check plots before the fabricator starts building the boards. 
This may require sending a Fed-X package across the country and take several 
days.

        There are many things that can go wrong with a customer's data before it
becomes a circuit board. If any of these things go wrong, it doesn't matter 
whose fault it is, the boards are late to the customer, assembly lines may go 
down, time to market may be increased. All of this because a simple insurance 
policy of a "good" CAD net list was not deemed necessary.


        3.      Net list testing is generally based on a netlist which has been 
extracted from the gerber. If the gerber has not been verified correct against a
good CAD netlist, then all boards may be 100% netlist tested good, yet they are 
still bad.

        BOTTOM LINE:

        HARDWARE MALFUNCTIONS, SOFTWARE EXHIBITS BUGS, HUMANS MAKE ERRORS. 
WHENEVER POSSIBLE, YOU NEED TO HEDGE YOUR BETS AGAINST THESE SITUATIONS. 
THE EASIEST THING TO DO IS TO SUPPLY A GOOD CAD NETLIST.


______________________________ Reply Separator _________________________________
Subject: Re: FABRICATION: E-Test
Author:  [log in to unmask] at corp
Date:    02/21/96 08:11 PM


Thats why they have D Code lists to check against and thats why you
do Gerber Ins so that you check your artwork so that there are no
errors before you have film developed and go to board...food for
thought...

Henry R. Linneweh
CAD PCB Design Specialist.....


On Wed, 21 Feb 1996, Tom Kavendek wrote:

> You should be delivering a CAD generated netlist which identifies
> every pad on the board (top and bottom) and it's associated net name,
> and xy location. In this way, if the gerber post processing does
> something strange, it would be caught. You have to remember that gerber
> artwork generation is a post process that is normally robust, but may
> introduce errors. 
> If a gerber extraction is done by the bareboard mfr., number 1 - it is
> more expensive and 2) it will include these possible gerber errors.
> 
> Most bareboard mfrs can send you the format that this netlist file
> should be in.
> 
> Tom Kavendek
> Lucent Technologies
> Murray Hill, N.J.
>