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?


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                           George Franck
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