Unless that amount of soldermask shift is restricted by the fab notes or
a purchase agreement, the shift is acceptable according to "IPC 6012B
Qualification and Performance Specification for Rigid Printed Boards"
section 3.7.1 f.1), allowing 0.002" on the pad for 50mil pitch BGA and
0.001" on the pad for less than 50mil pitch.
I can't answer the question of how reliable the solderjoints might be,
but, if you want to reject them, you don't have any leverage from IPC
standards...
If its any consolation, I would accept them if they were my boards.
-Ryan
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stephen Gregory
Sent: Tuesday, August 02, 2005 11:33 AM
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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