Bob,
What kind of pick and place machine are you using?
Bill
-----Original Message-----
From: bbarr [SMTP:[log in to unmask]]
Sent: Thursday, May 10, 2001 10:31 AM
To: [log in to unmask]
Subject: Re: [TN] Dumb question
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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