Pete,

It is true that with inner layer pads left in, that FR-4 boards
usually will be less prone to z-axis problems such as lifted
pads or even cracking copper in small holes.  However - poor
PWB processing and special assembly conditions contribute to
these "z-axis" problems as well.

For special motherboard/module characteristics (thickness) and/
or assembly conditions (more/higher thermal excursions) that
create more stringent z-axis expansion, the treatment of
leaving in the non-functional pads provides only marginal
additional protection compared with changing from 130-140 to
170 Tg laminate materials.

For boards whose thickness and/or processing create truely
higher z-axis expansion, the use of the higher 170 Tg laminate
materials has been the preferred solution for my company.  We
have no issues with the attached position held by many and
described very well by Greg Lucas of Zycon.


[log in to unmask]

Sun Microsystems, Inc.
Mountain View, CA

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From: [log in to unmask]
Date: Thu, 26 Sep 96 14:26:57 MST
To: [log in to unmask]
Subject: Re[2]: Inner layer PAD Suppression or NOT?
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     I completely agree.
     
     [log in to unmask]
     
     Continental Circuits Corp.


______________________________ Reply Separator _________________________________
Subject: Re: Inner layer PAD Suppression or NOT?
Author:  [log in to unmask] at INTERNET
Date:    09/26/96 1:02 


     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]
     
     

>Pete Waddell wrote:
>
>>
>> Subject: Inner layer PAD Suppression or NOT?
>>
>> 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.


>I have been told two advantages:
>  + increasing the life of drill bits,
>  + less chance of clearance problems (shorts).

>.....

>Anyway, just recently I have heard that plated holes are
>stronger with the extra pads.

>OK, what's the scoop, guys?
>Jack


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