I have never had a problem not using local fiducials for 1.27mm and 1.0mm
pitch BGAs. I have not yet done .8mm pitch BGAs, but I think I would tend to
want to use locals for them. Of course, the usual caveat applies, you need
to know the capability of your placement machine. I have not even seen a
compelling need for locals with .5mm pitch leaded devices. I normally have
the machine find three panel fiducials and go with that.


Bob


Robert Barr
Manufacturing Engineering
Formation, Inc.
Voice: 856-234-5020 x3035
Fax: 856-234-6679
email: [log in to unmask]

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Jason Gregory
Sent: Thursday, May 10, 2001 9:00 AM
To: [log in to unmask]
Subject: [TN] Dumb question


OK, guys, here's one.
Why is it so important for local fiducials to be placed near diagonal
corners of BGA's. The keyword here is "SO". I've performed studies in the
past detailing the natural tendency of BGA's to self-align during reflow.
It's even lead to me to work on a patent concerning a BGA rework preform.
What I'm wondering is....ssop's, tssops, qfp's, etc. have greater impact on
placement quality when misplaced. And they do not self-align!!! I do,
however, understand that BGA's balls are not easily seen once placed (you
can only see the edges). But my point that I'm getting to is.....wouldn't
you want local fiducials more at the parts that will not "self-correct"
themselves during reflow than at the parts are more forgiving? Just
wondering.


Jason Gregory
Software Specialist - NPI Group
SCI Systems/Plant 2
13000 S. Memorial Pkwy.
Huntsville, AL. 35803
(256) 882-4107 x3728
[log in to unmask]

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