Many companies do what your design group dose and than indicates the
  design line width and spacing as "master pattern dimension."  They then
  give the minimum line width and spacing.  The PWB supplier can choose to
  use the designed lines or modify them for their process.
  To:       TechNet @ ipc.org at Internet@CCMAILEXCHANGE
  cc:        (bcc: Clark F Webster/CDev/Ceridian)
  From:     TechNet @ ipc.org at Internet@CCMAILEXCHANGE
  Date:     11/17/95 12:11:00 PM
  Subject:   Re: PWB artwork




 you are absolutely correct Mark. let your PCB suppliers adjust the gerber
 to meet your finished line specs. everyone has a little different etch
 factor.


______________________________ Reply Separator _________________________________
Subject: PWB artwork
Author:  [log in to unmask] at corp
Date:    11/16/95 4:36 PM


I have a question for the Printed circuit Manufacturers. First a little
history. The PWB design group in my company adjusts the artwork (track
width & Spacing) to conpensate for the loss of copper during the etching
process. I have a concern that the etching depends on each PWB
manufacturers process and that each manufacturer would like to make his (or
her) own adjustments to the artwork / gerber data to achieve the final
engineering requirements Which we also specify on the drawing (Example
shown below)

     Minimum conductor spacing:
     External layers to be .008 inch after plating and fusing or solder
     coating. Internal layers to be .008 after etching.

     Minimum conductor width:
     External layers to be .010 inch after plating and fusing or solder
     coating. internal layers to be .010 inch after etching.)

I feel that we are over controlling the PWB manufacturers. Is this true?
Please provide feedback. Thanh you in advance.


                            Mark Foster
                            Address: [log in to unmask]