Hi Steve
One thing I have noticed is that if you do not have your voiding under
control you can create bridging. I have seen a voids large enough to
expanded the ball enough to invade in the space of the next ball, and if
that ball has a large void also a bridge can occur. If this is an known
issue then a new paste may be in order.
I see two issues with your profile that could possibly be causing a
problem, I don't think all the balls on the BGA are reflowing at the same
time. I think you can improve this by setting up your reflow closer to 183
before spike. There could also be a hot slump issue also at the beginning or
reflow, I would recommend you try this to get a more simultaneous reflow.
130 160 180 183 240
130 160 180 183 240
How you guys doing in Seattle after that shake up?
We felt it up here in Vancouver.
Bob Perkins
SMT Manufacturing Process /
Automation Technician
Aitmronics-Delta
-----Original Message-----
From: Stephen R. Gregory [mailto:[log in to unmask]]
Sent: Tuesday, February 27, 2001 1:34 PM
To: [log in to unmask]
Subject: [TN] Heat-sinked BGA Bridging...
Hi all!
This topic is a "moldy-oldie", but I've started to experience bridges again
with this TI DSP (TMS320C6201GJC200). I've been doing okay up unil recently.
We build these boards in work orders of around 25 pieces.
Our last run we had 7 boards bridged out of 25!! Sent the boards out to be
reworked. I asked that they be x-rayed before and after, and to my surprise
after looking at the x-ray images, they were all bridging in the same
general
area.
It's a 4-row periphery BGA, and the bridges are occuring on the inner two
rows, around the center of the part, at the same side of the part.
What's funny, is that the vendor we use to rework the boards for us is
having
difficulty as well. We've been asking him to remove, re-ball, and re-install
the part, they said they've been having about a 50% success rate doing
this...they've been getting the bridges too. They have a nice full-blown SRT
BGA rework station and do this for a living.
I print 6-mils of paste (square apertures for the BGA), have a Conceptronic
HVN-70 which I run:
150 160 170 180 240
150 160 170 180 240
25-in. per min
We never have had these problems before...it all started when TI put the
heatsink into the top of the part. I've looked at our paste print and it's
dead on, placement is dead on too, we verify that with a Ersascope.
My question is could there be something wrong with the part? Warping causes
bridges at the corners, right? Why would it bridge in the interior rows at
the same general area?
Thanks in advance!
-Steve Gregory-
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