>From personal experience, removal of inner layer non functional pads has
resulted in pad lifting rejects as per MIL-P-55110. The same designs, with
non functional pads replaced, exhibited no pad lifting.

Just out of curiosity, can anyone out there explain why pad lifting is
rejectable? I understand that it's origin was based on solder iron touch up
of leaded components, IE boards that had excessive pad lifting resulted in
pad removal during post assembly rework. Is this still valid? Comments please...

D. Rooke


>Dave
>
>Re:  Effect of removing non-functional lands
>
>My recollection is that many years ago we did a set of careful TMA 
>measurements of expansion in the neighborhood of a plated hole with and 
>without lands.  The result was that lands reduce expansion.  As a matter of 
>fact,  I believe that the data fit a rule of mixtures model in which the 
>excess expansion associated with removing a land can be predicted by replacing
>1.4 mils of copper with 1.4 of resin. I believe the effect was most pronounced
>below Tg.  At higher temperature, the strength of the barrel resists the resin
>expansion and the effect is reduced.  Our conclusion was that this was a real 
>effect, but that it is small and has a minimal impact of PTH reliability.  As 
>a result we approved the removal of non-functional lands.
>
>Bob Holmes
>Lucent Technologies
>[log in to unmask]
>
------------- Begin Original Message -------------
>From: kcig1.att.att.com!ipc.ipc.org!TechNet-request
>Date: Thu Sep 5 10:08:56 -0500 1996
>Subject: FAB or DES: Z-Axis expansion
>To: [log in to unmask]
>Content-Type: Text     
>Content-Length: 957
>
>
>Has anyone got any information on z-axis expansion comparisons on boards
>with non-functional pads versus typical boards which do not have
>non-functional pads. We have a customer who is concerned about removing the
>pads from their design. Since the board is a high-layer count the pads are
>causing us much grief at drill by prematurely wearing the drill bits.
>Results of any tests that have been conducted (preferably with data) would
>be appreciated.
>
>David Arivett
>Cuplex Inc.
>
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