The photos do not provide sufficient detail to determine if weave is
exposed.  It is very difficult to discern weave exposure when the line of
sight is perpendicular to the plane of the board.  I would suggest both
evaluating and taking photos on an oblique angle so that one can see if the
fibers are exposed, cut or disturbed.  I normally work with the board in the
range of 30 to 45 degrees from horizontal (assuming both the observer and
microscope optics are vertical!).  "Cut and disturbed" are two conditions
that clearly indicate that the weave is exposed.  Discerning between weave
texture and weave exposure is a little more difficult...  The typical
"buttercoat" thickness (free resin covering the glass reinforcement) is in
the range of 50 to 100 microinches, but sometimes less.  As long as the
glass is covered, it is not weave exposure.  A good halogen light source and
the oblique angle viewing can help to discern the difference, as the glass
will usually appear bright white if it is exposed.  From there, one can
determine the percent exposed of the distance between the conductors.  I
hope that this helps.

> Richard Grannells
> Hamilton Sundstrand
> Mfg. Technical Specialist
> * Tel: (860) 654-9489
> * Fax: (860) 654-9475
> *[log in to unmask]
>
>


-----Original Message-----
From: John Perry [mailto:[log in to unmask]]
Sent: Tuesday, October 31, 2000 1:58 PM
To: [log in to unmask]
Subject: [IPC-600-6012] Potential Non-conforming Condition for
Exposed/Disrupted Fibers


Colleagues,

A member approached us for our interpretation of possible noncomformance due
to exposed/disrupted fibers per section 2.2.3 of IPC-A-600F.

The damaged areas were caused in removing solder shorts in the top layer of
the PWB's.  The first two photos, labeled MVC-0061 and MVC-013S, detail one
cut with a yellow arrow, while the second two images, labeled MVC-007S and
MVC-014S, depict a second cut area denoted by a red arrow.

The receiver feels that these indicate non-conformance per IPC-A-600F,
section 2.2.3.  I'd like for this group's review of that position.  The
criteria established in IPC-A-600F applies to bridging of conductors.  These
are pads, but does that apply as well?  Secondly, the ultimate decision, so
far as I can tell, goes to section 2.10.1.2 in IPC-A-600F wherein the
allowable percentage of conductor spacing reduction determines the
acceptance/non-acceptance based on the criteria, for the applicable class.

Your thoughts?  The images with the yellow arrow are quite discernable - the
ones with the red arrow, well, I can't really see any problem.  If the group
feels any of these pictures are worthy of usage in the next rev, let me
know.  Thanks!


Best Regards,






John Perry
Technical Project Manager
IPC
2215 Sanders Road
Northbrook, Il 60062
1-847-790-5318 (P)
1-847-509-9798 (F)
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