All,
Beware plugging vias that have solder inside them.  No matter how good the 
plugging and overlying soldermask job, during reflow the underlying solder 
will expand as it heats.  When the solder hits liquidous, the pressurized 
fluid can force a jet of molten solder through any point of  thin coverage 
due to misregistration or pinholes, leaving either solder balls or solder 
strings .  I have seen microscopic "wires" of solder that have been extruded 
through pinholes as the pressure of the molten solder forces it out.  These 
strings can be longer than 0.100" and are virtually invisible to the naked 
eye.  If you must plug vias, do it in direct contact with the base metal.
 ----------
From: [log in to unmask]
To: [log in to unmask]
Subject: via plugging
Date: Wednesday, June 11, 1997 7:46AM

I'd recommend you fill them with solder if you can.  Coating can be used, 
but
its best if you do this AFTER a protective coating is applied to the board
like
Hot Air Solder Level (hasl) or on a patern plated board (SnPb plated) from
which you DO NOT strip the Sn Pb .

See my other append about solutions getting trapped in the vias.


If at all Possible DO NOT Plug/Tent/Fill vias with anything other than a
solder
like material that fills them 100% of their depth.

hope that helps

Jim Herard
IBM Microelectronics
Quality Engineering
[log in to unmask]
 ---------------------- Forwarded by Jim Herard/Endicott/IBM on 06-11-97 
08:39
AM
 ---------------------------

        suixin @ elis.rug.ac.be
        06-10-97 03:59 PM
Please respond to [log in to unmask] @ internet


To: TechNet @ ipc.org @ internet
cc:
Subject: via plugging

Hello, everybody
I want to get some information on via plugging technology. In my
work, the plated through vias are 1.6mm deep and 300 micron in
diameter. I have to plug them before further processing. Any input
will be greatly appreciated.
Thanks in advance.
suixin zhang
ELIS-TFCG/IMEC, University of Ghent
Sint-Pietersnieuwstraat 41, B-9000 Ghent, Belgium
tel: 0032-9-2643371
fax: 0032-9-2643594
Email: [log in to unmask]

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