I fully agree with George with one additional good reason:
     In a previous life, the company I was with produced some boards that 
     used press-fit pins.  When we switched to a direct metallization 
     system ("What evil lurks in the hearts of men...), the plated through 
     holes decided they liked the pins more than the epoxy.  Adding back in 
     the non-functional pads that we had deleted from our customer's design 
     solved the problem.
     
     Regards
     Jamie Baumgart
     DSC Communication


______________________________ Reply Separator _________________________________
Subject: RE: Non-functional Pads
Author:  [log in to unmask] at SMTPLINK
Date:    2/6/96 11:26 AM


Here is my two bits in the Non-functional Pad discussion:
     
Non-functional Pads are bad because:
1) In the innerlayer print and etch process they greatly increase the 
chances of an innerlayer short.  Removing Non-functional Pads can increase 
your innerlayer yeilds, and also make them easier to inspect.  It doesn't 
make your process any better, it just makes the product easier to make.
2) Non-functional Pads increase the amount of copper drilled in the hole. 
Copper likes to be drilled a little slower than epoxy-glass.  So, they can 
slow down the drill process.
     
Non-functional Pads are good because:
1) They make it obvious when the designer has violated their/your design rules. 
2) During thermal cycling, they help redistribute the z-axis shear stresses 
between the epoxy and the copper within the hole.  Without the pads all the 
stresses are concentrated at the PTH knee.  With the pads, the stresses are 
shared by each pad/barrel innerconnect.  This is why Non-functional Pads
can reduce copper cracking.  They don't improve your plating, but they do 
reduce the stresses the plating must withstand.
3) For thin laminates, they make the innerlayer just a little stiffer. 
Fewer thin innerlayer end up wrapped around a roller, or in the stripper 
sump.
4) They leave more copper on the innerlayer, reducing innerlayer shrinkage, 
especially on thin laminates.
5) During the lamination process, the Non-functional padstacks create 
z-axis supports which help keep the layers flat.  If the pads are taken 
out, some designs can encourage a layer to "corrigate", like the center 
paper sheet in corrigated cardboard.  The corrigated layer shrinks, loosing 
all registration.  (If the truth be known, I think this effect is the main 
reason I could make good multilayers during my younger years, Multiline not 
withstanding.)
     
Five good reasons vs two bad ones tell me: "Non-functional Pads are your 
friends."
     
Even in the worse case, Non-functional Pads make you slow down and drill 
quality holes, and reduce your print and etch yields.  So what?  Quality 
holes are worth it, and if you have to take a yield hit anywhere in the 
process, Innerlayers is the right place to do it.  [You can even blame the 
etch or print operator for a while, I you have to.  ;-)  ]
     
     
Now, how do you get the customers to keep the Non-functional Pads in their 
designs in the first place?
     
     
  ====================================================================
                           George Franck
  PWB Product Assurance                     Phone (703) 560-5000 x2648 
  E-Systems M/S N408                              Fax   (703) 280-4613 
  7700 Arlington Blvd                  E-Mail: [log in to unmask] 
  Falls Church Va 22046                      E-Mail: [log in to unmask] 
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