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Date: | Wed, 28 Nov 2012 10:23:18 -0600 |
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Hi Joe - as Doug would say "it depends" as there are a number of inputs on
the collapse of a solderball under a BGA or CSP (i.e. reflow temperature,
pad size, solder paste deposit, component mass, etc.). However, as a first
order approximation, you can use a 2-3 mil decrease in solderball diameter
for tin/lead eutectic solder alloys (i.e. a 30 mil diameter will reduce to
a 27-28 mil diameter). We have observed the "2 mil" number over a large
number of DOEs and production investigations using metallographic
cross-sections to confirm the value. Its not a perfect value but gives you
a place to start.
Dave Hillman
Rockwell Collins
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From: Joe Macko <[log in to unmask]>
To: <[log in to unmask]>
Date: 11/28/2012 09:55 AM
Subject: [TN] estimating collapsed solder ball diameter change
Sent by: TechNet <[log in to unmask]>
Good morning.
I am trying to estimate the typical change in a solder ball's diameter
after reflow. IPC-7095B has great discussion about the typical change in
a ball's height after reflow but I did not see anything about
diametrical changes. Maybe there is another IPC document that addresses
this. Factors such as package weight, # of solder balls, ball alloy,
etc. influence collapse so I am sure there is no quick answer buy maybe
there is a rule of thumb to estimate the diametrical change.
Look forward to any advice. thx
Regards,
-Joe
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