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August 2005

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Subject:
From:
Hal Winslow <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Hal Winslow <[log in to unmask]>
Date:
Tue, 2 Aug 2005 15:06:54 -0400
Content-Type:
text/plain
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text/plain (94 lines)
Steve,
This might be a case where a note on the fab drawing stating "Soldermask
must be aligned to outer layer features +/-.002 inch" or something to
that effect would help you.  Course, you better check that the fab house
is comfortable signing up to that spec, or you better let them
micromodify the SMASK openings around any BGAs to give added clearance.

Not sure what to do about boards "as received" without any preexisting
notes on the drawing.

Hal

-----Original Message-----
From: Stephen Gregory [mailto:[log in to unmask]] 
Sent: Tuesday, August 02, 2005 1:33 PM
To: [log in to unmask]
Subject: [TN] Soldermask registration for NSMD BGA pads...

Afternoon All!

Just sitting down for lunch, and I have a question about Non Solder Mask
Defined (NSMD)
BGA pads. I have a picture at:
http://www.stevezeva.homestead.com/files/MaskMisregistration2.jpg

Now according to IPC-A-600G, that misregistration is not rejectable,
"because the solder resist does
not encroach on the land except at the conductor attachment"...that's a
quote right out of the - 600. I've
looked at it very closely, the mask is right up against edge of the pad.

Knowing what kind of solder joint you're trying to acheive with a NSMD
pad,
and having the mask up
against the edge of the pad, the solder is not going to wet and flow
down
around pad like you want, right?
Is that a problem? Will that introduce the possibilty for reliability
issues? Can one reject these boards?

I've heard the statement made that if indeed you want a clear area
around
the pad, a note needs to be
put on the fab drawing stating that. Because as it stands now according
to
the IPC-A-600G, it is not rejectable.

Any thoughts?

Kind regards,

-Steve Gregory-
Senior Process Engineer
LaBarge Incorporated
Tulsa, Oklahoma
(918) 459-2285
(918) 459-2350 FAX
__________________________________________________________________
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If you are not the intended recipient, you may not copy, use or deliver
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