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September 2006

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Subject:
From:
Dan Skweres <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Dan Skweres <[log in to unmask]>
Date:
Tue, 26 Sep 2006 12:16:19 -0500
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The undercutting of the mask is typically cosmetic in nature unless of course it violates IPC spacing etc. A problem that will eventually occur is the mask that is no longer bonded to the surface of the copper or base material (under cut) can and more than likely will  flake off at some time. If it happens after assembly and  solder doesn't adhere to the copper under the under cut mask there will be exposed copper. Another thing to question is are there mask dams between surface mount  pads you need? If the undercut is bad enough mask dams will come off base material leaving potential for solder shorting.  This is where consideration on your end needs to taken. We don't ship out peeling (undercut ) mask when it happens.
 
 
Dan Skweres
Engineering Manager
Bartlett Manufacturing
Phone:847-639-2102 Ext.#230
Fax:847-639-8838

>>> Kevin Glidden <[log in to unmask]> 09/26/06 11:26AM >>>
Question for the PCB fabricators...

One of our PCB suppliers is asking us to accept PCBs with a "minor" issue.
The problem is described as this: The panels were under-developed and some
residual solder mask was left over.  To eliminate this, the panels were put
through a second pass to ensure all residual solder mask was removed.  The
result is some overdevelopment of the solder mask.  Then, this apparently
resulted in an "undercut" along the demarcation lines.  They say during a
tape test, very small traces of mask from the undercuts comes off.  The mask
is still present between all features and is adhered to the PCB.   But, it
is over-developed and has undercuts.  They say that while it does not pass
the tape adhesion test, it is of no detriment to the PCB quality or
performance.

My question is if over-developed soldermask maintains the same properties as
normally developed soldermask?  When I asked about this, they said the
properties of the mask are determined by the initial (pre-developing) cure
and the final (post-developing cure), and the over-development does not
affect the properties.  True?

In case "it depends", these PCBs are used in avionics power supplies.

Thanks in advance!

Kevin

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