I can also see from the micrograph that the plating surface to hole
ratio is skewed - the PTH appears to have adequate copper ~ .0012" while
the surface plating appears to be 2-3X the PTH.  This would indicate an
issue in plating distribution and current density.  I also see that the
process was possible a panel plate followed by a pattern plate, further
contributing to the overhang.



Jeffrey Bush
Director, Quality Assurance and Technical Support

                          76 Technology Drive - POB 1890
                             Brattleboro, Vermont 05302-1890
                                Tel. 802.257.4571.21 Fax. 802.257.0011
                                    [log in to unmask]
                              http://www.vtcircuits.com	



-----Original Message-----
From: Susan Mansilla [mailto:[log in to unmask]] 
Sent: Sunday, September 12, 2004 6:26 PM
To: [log in to unmask]
Subject: Re: [TN] PWB Conductive Contamination Under Solder Mask; What
Can ...


I received the photo - I realize Technet did not.  The one surface land
does show over hang, but the one on the bottom from another coupon shows
NO overhang.

The one with overhang also shows severe UNDERCUT of the solder mask next
to the land.

I am puzzled by the "scotch brite" comment as I can think of no reason
for using this in a SMOBC product.  Any and all tinlead plating should
have been stripped off prior to cleaning and solder mask application,
The overhang of copper that was present on the top coupon would not have
been removed by an abrasion process.

The real proof would be seeing what the sample looked like in the "as
plated" tin/lead condition and finding out why an abrasion process was
used.  The few times I have used an abrasion process only caused the
overhang to become splinters that then came loose later on and caused
problems.

The undercut of the solder mask is also a potential threat for trapping
contamination later on during HASL or assembly processing.

Susan Mansilla
Technical Director
Robisan Laboratory, Inc.
6502 E 21st Street
Indianapolis, IN  461219
www.robisan.com
317-353-6249


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