======== Original Message ========
Sender: [log in to unmask]
Received: from simon.ipc.org (IPC.ORG [168.113.24.64]) by
dub-img-6.compuserve.com (8.6.10/5.950515)
	id XAA23595; Wed, 28 Feb 1996 23:59:03 -0500
Received: from ipc.org by simon.ipc.org via SMTP
(940816.SGI.8.6.9/940406.SGI)
	 id UAA24502; Wed, 28 Feb 1996 20:42:10 -0800
Resent-Date: Wed, 28 Feb 1996 20:42:10 -0800
Received: by ipc.org (Smail3.1.28.1 #2)
	id m0trzoe-0000DfC; Wed, 28 Feb 96 22:18 CST
Old-Return-Path: <[log in to unmask]>
From: [log in to unmask]
Date: Wed, 28 Feb 1996 22:26:55 -0500
Message-ID: <[log in to unmask]>
To: [log in to unmask]
Subject: Soldermask over vias
Resent-Message-ID: <"6yRUc2.0.Lt9.-ZIDn"@ipc>
Resent-From: [log in to unmask]
X-Mailing-List: <[log in to unmask]> archive/latest/2935
X-Loop: [log in to unmask]
Precedence: list
Resent-Sender: [log in to unmask]

We haave a captive double sided plated-thru-hole shop for in-house products.
 The finished raw boards before component insertion are Copper with Nickle
plating (not HALS) and selective solder mask.  For certain mechanical
considerations with the interface of the PWBs to other non-conductive parts
(plastic housings) of the finished products, we do not wish to have solder
bumps on the back of the finished board at via interfaces after wave
soldering that side (the actual electronics are on top).  Simple solder mask
seems to prevent these bumps from being formed.  Is there an IPC
recommenddaation about soldermasking over thru-hole vias?  The hole may or
may not be closed by the mask.
======== Fwd by: Tony King / N ========
As a board manufacturer, we are requested by an increasing number of
customers to plug via holes from one side of the panel to prevent solder
from getting under components and to improve vacuum draw at In Circuit Test.
The best way to do this is to use a secondary dot pattern to fill the vias
from one side of the panel. The dot pattern mask should be applied after the
hot air level process to insure adequate flux removal at HAL. A hole plugged
from one side is very difficult to clean otherwise, and contamination would
gradually leach out and cause solderability problems at assembly.  Any
standard UV or thermal cure mask can be used to plug the holes.

Another option could be the application of peelable mask prior to wave, and
then removal afterwards. There is a very good peelable mask on the market
manufactured by Peters which is easily and cleanly removed from boards and
holes after soldering operations.