Mail*Link(r) SMTP               FWD>FAB:  PCB thickness

Per the IPC's-T-50, Terms and Definitions-

Board Thickness -- "The overall thickness of the base material and all
conductive materials deposited thereon."

As one of the members of the T-50 committee, and based on memory; the
definition for the term "board thickness" was written the way it is so as to
have the board thickness dimension (and it's tolerance), as specified on the
master drawing, to control the thickness of the printed board for printed
edge-board connector requirements.

Board thickness did not include polymeric coatings of any purpose/type because
of the wide range of polymeric coating thicknesses.

IMO, it would not be in our best technical interests to modify the term to
include polymeric coatings.

The problem I see in the current definition is that it includes "all
conductive materials deposited thereon" and with tin/lead fused coatings this
would (could) include the meniscus.

At the time the definition was being discussed, I seem to recollect that we
felt "board manufacturers know where the board thickness is most critical" and
should be applied; and we don't need to extend the definition to delineate the
various areas of the printed board.  So yes, there's problems with the current
definition for critical thickness requirements if the definition is
"literally/liberally applied" by the printed board manufacturer'.

Ralph Hersey
e-mail:  [log in to unmask] 

--------------------------------------
Date: 6/4/96 10:31 AM
From: [log in to unmask]
Let me contribute my observations on thickness.

The quality manual here says (written by me) that boards will be built to 
class A tolerances in the latest revision of IPC-D-300, unless otherwise 
specified by the customer.

That said, I have questioned IPC about the meaning of "thickness".  David 
Bergman and Lisa Williams did some investigating and thinking and advised 
me that thickness was to be measured over plated copper, but before 
solder resist application.  They also told me that the committee 
responsible for D-300 planned on expanding upon the present statement on 
baords thickness in the standard, to direct the user to specify board 
thickness in any areas of importance.

Lou Hart


------------------ RFC822 Header Follows ------------------
Received: by quickmail.llnl.gov with SMTP;4 Jun 1996 10:30:15 -0700
Received: from ipc.org by simon.ipc.org via SMTP (940816.SGI.8.6.9/940406.SGI)
	 id MAA15166; Tue, 4 Jun 1996 12:25:31 -0700
Resent-Date: Tue, 4 Jun 1996 12:25:31 -0700
Received: by ipc.org (Smail3.1.28.1 #2)
	id m0uQyZv-0000FGC; Tue, 4 Jun 96 11:03 CDT
Resent-Sender: [log in to unmask]
Old-Return-Path: <[log in to unmask]>
Date: Tue, 4 Jun 1996 12:09:18 +0400 (EDT)
From: <[log in to unmask]>
Subject: FAB:  PCB thickness
To: [log in to unmask]
Message-ID: <[log in to unmask]>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
Resent-Message-ID: <"3Orbm3.0.3cJ.7v5jn"@ipc>
Resent-From: [log in to unmask]
X-Mailing-List: <[log in to unmask]> archive/latest/4519
X-Loop: [log in to unmask]
Precedence: list
Resent-Sender: [log in to unmask]