David Tandy: 
     
     Our position at Zycon is that non-functional pads should be 
     suppressed.
     
     Stack height at drilling is a function of the amount of copper within 
     the panel (among ather things). In order to maintain the quality of 
     the drilled hole, parts with non-functional pads present are drilled 
     at lower stack heights. Since most board shops are constrained at 
     drilling this results in a resistance to doing jobs with 
     non-functionals present, especially when business is strong.
     
     As far as reliability and quality are concerned we have done extensive 
     testing (through temp cycling) and find no evidence to support the 
     position that non-funtionals improve reliability. In fact we have come 
     to the same conclusion which Delco reached that on some more 
     conservative designs that the opposite is true. Most of our testing 
     however has been on 0.093" thick product drilled at 0.0135".
     
     [log in to unmask]


______________________________ Reply Separator _________________________________
Subject: Inner layer PAD Suppression or NOT?
Author:  [log in to unmask] at corp
Date:    9/26/96 12:27 AM


I am currently debating the pro's & con's of suppressing  non-functional 
inner layer pads and have found our PCB fabricators have differing views 
on which is best. Here are the 2 views.
     
1.  Suppressing inner layer pads will give a better drilled hole, and so
    will produce a more consistant & cleaner plated hole.
     
2.  NOT suppressing inner layer pads will produce a stronger & more 
    reliable PTH less prone to failiure.
     
We first changed to using inner layer pads after a new design, which 
required 2 reflow soldering processes & 1 wave solder process, failed
ICT afer assembly.  The cause was a process problem at our supplier which 
resulted in via's cracking in the barrel. Having this problem made us 
consider what we could do with the design to reduce the risk of similar 
problems happening again.
     
I would appreciate any views you may have on this topic.
     
     
  ________________________________________________________________________
 | [log in to unmask]         David Tandy. EDA Specialist.               | 
 | Tel: (+44) 161 486 1511     GenRad ADS, Monmouth House, Monmouth Road, | 
 | Fax: (+44) 161 486 1989     Cheadle Hulme, Cheshire, SK8 7AY, England. | 
 |________________________________________________________________________|
     
     
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