We have tried plugging vias by applying paste to them during stencil 
     printing.  The problem with this approach is that the hole does not 
     receive enough paste to completely fill.  The concave fillet formed 
     traps flux residue that is difficult to wash out.  Needless to say, 
     the flux residue is not condusive to incircuit test probing.
     
     Gary Camac  


______________________________ Reply Separator _________________________________
Subject: plugged vias
Author:  INTERNET:[log in to unmask] at CSERVE
Date:    6/17/97 1:04 PM


Sender: [log in to unmask]
Received: from simon.ipc.org (simon.ipc.org [209.42.29.3]) by 
arl-img-4.compuserv
     
e.com (8.6.10/5.950515)
	id NAA06663; Tue, 17 Jun 1997 13:01:28 -0400
Received: from ipc.org by simon.ipc.org via SMTP (940816.SGI.8.6.9/940406.SGI) 
	 id LAA00894; Tue, 17 Jun 1997 11:37:07 -0700
Resent-Date: Tue, 17 Jun 1997 11:37:07 -0700 
Received: by ipc.org (Smail3.1.28.1 #2)
	id m0wdiOO-000Bk0C; Mon, 16 Jun 97 15:28 CDT 
Resent-Sender: [log in to unmask] 
Old-Return-Path: <[log in to unmask]> 
Date: Mon, 16 Jun 1997 14:43:23 -0500 (CDT)
Message-Id: <[log in to unmask]> 
X-Sender: [log in to unmask]
X-Mailer: Windows Eudora Light Version 1.5.4 (16) 
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii" 
Subject: plugged vias
To: [log in to unmask]
From: David Arivett <[log in to unmask]> 
Resent-Message-ID: <"NBGZg.0.diP.-7Qfp"@ipc> 
Resent-From: [log in to unmask]
X-Mailing-List: <[log in to unmask]> archive/latest/13439 
X-Loop: [log in to unmask]
Precedence: list
Resent-Sender: [log in to unmask]
     
     
     
There have been several postings about plugged / tented vias over the last 
several days. It has been stated that you must tent vias to prevent 
contamination being trapped in the holes. It has then been pointed out that 
tents can crack and allow contaminants in the holes. Plugging with LPISM, 
plugging with epoxy mask, before hot air level, after hot air level have all 
been discussed with each being the way to do it or absolutely NOT the way to 
do it depending on the experience of the author. As a board manufacturer we 
have been involved in these discussions with customers for years (not to 
mention should it be plugged from the top-side or the bottom side, or both). 
Many of them feel passionatly about their position. We, of course, strive to 
give them what they want, resulting in our not being able to standardize on 
one process. 
  Since the desire for plugged vias is due to the need for vacuum at
in-circuit test, is there not a way to modify the test fixture so the vacuum 
isn't required? If that is not feasable, has anyone tried to leave the 
soldermask around the vias open, leaving solder on the hole walls after 
hot-air level. Then at the assembly level, have a small opening in the stencil 
corresponding to the vias. This would partially fill the via with solder paste 
and would plug after reflow. Has anyone attempted this? If it worked it would 
be able to be performed during an existing process step as opposed to the 
extra steps required to plug vias with soldermask.
     
David Arivett
Cuplex, Inc
     
*************************************************************************** 
* TechNet mail list is provided as a service by IPC using SmartList v3.05 * 
*************************************************************************** 
* To subscribe/unsubscribe send a message <to: [log in to unmask]>   * 
* with <subject: subscribe/unsubscribe> and no text in the body.          * 
*************************************************************************** 
* If you are having a problem with the IPC TechNet forum please contact   * 
* Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask]      * 
***************************************************************************
     

***************************************************************************
* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
***************************************************************************
* To subscribe/unsubscribe send a message <to: [log in to unmask]>   *
* with <subject: subscribe/unsubscribe> and no text in the body.          *
***************************************************************************
* If you are having a problem with the IPC TechNet forum please contact   *
* Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask]      *
***************************************************************************