Mail*Link(r) SMTP               FWD>FAB or DES: Z-Axis expansion

David,

The z-axis expansion of a printed board interconnection substrate is very
close to being the same regardless whether the design has internal
non-functional lands or not.  The resulting Z-axis expansion is the summation
of all of the z-axix material expansion coeffients as a function of
temperature, this includes the total copper, the resin, the glass-fabric
reinforcement material, and any other material thickness located between the
reference points (surfaces, lands, etc).

In theory, for a "fixed" board thickness, non-functional lands will reduce the
z-axis expansion because the TCE (temperature coefficient of expansion) of
copper (~ 17 ppm/degreeC) is about 0.3 the expansion of epoxy below the Tg
(glass transition temperature);  this assumes the missing land thickness is
replaced with resin.

There are various arguements for design preferences, manufacturing advantages,
and reliability concerns in support and non-support of functional lands.  I
suspect all of these discussions are available in the IPC's technet archives
which can be accessed through their homepage, most probably with the subject
title "non-functional lands".

Ralph Hersey
[log in to unmask]

--------------------------------------
Date: 9/5/96 10:01 AM
From: David Arivett

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.

***************************************************************************
* 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.        *
***************************************************************************


------------------ RFC822 Header Follows ------------------
Received: by quickmail.llnl.gov with SMTP;5 Sep 1996 10:00:02 -0800
Received: from ipc.org by simon.ipc.org via SMTP (940816.SGI.8.6.9/940406.SGI)
	 id LAA11416; Thu, 5 Sep 1996 11:50:06 -0700
Resent-Date: Thu, 5 Sep 1996 11:50:06 -0700
Received: by ipc.org (Smail3.1.28.1 #2)
	id m0uyftQ-0000SUC; Thu, 5 Sep 96 09:58 CDT
Resent-Sender: [log in to unmask]
Old-Return-Path: <[log in to unmask]>
Date: Thu, 5 Sep 1996 10:08:56 -0500 (CDT)
Message-Id: <[log in to unmask]>
X-Sender: [log in to unmask]
X-Mailer: Windows Eudora Light Version 1.5.2
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
To: [log in to unmask]
From: David Arivett <[log in to unmask]>
Subject: FAB or DES: Z-Axis expansion
Resent-Message-ID: <"r0hjD2.0.-_A.egkBo"@ipc>
Resent-From: [log in to unmask]
X-Mailing-List: <[log in to unmask]> archive/latest/6080
X-Loop: [log in to unmask]
Precedence: list
Resent-Sender: [log in to unmask]



***************************************************************************
* 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.        *
***************************************************************************