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 ________________________ Reply Separator ___________________________ 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? Resent-Message-Id: <"Fp2ST2.0.j6G.Q0lIo"@ipc> Resent-From: [log in to unmask] X-Mailing-List: <[log in to unmask]> archive/latest/6510 X-Loop: [log in to unmask] Resent-Sender: [log in to unmask] 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 *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * ***************************************************************************