From experience, applying paste during reworks works well. Only that
sometime you may consider paste application on the BGA spheres, instead of
screening it on to the pads. Or use a paste dispenser system if you have one
handy.
I guess it depends on what kind of processes you or your customer prefer
most; specific application, board configuration, operator skills, rework
volumes, component type, etc.
Here is a link, just in case:
http://www.minimicrostencil.com/CPF_Process.html
Regards,
Liviu
-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: May 14, 2002 10:34 AM
To: [log in to unmask]
Subject: [TN] BGA replacement
The M.E.s at my company are struggling with replacing a defective plastic
BGA.
We have an Air Vac BGA machine. The lead M.E. feels that he needs a solder
pad
deposit in place before putting the replacement BGA on the board for reflow.
He
feels that he will compensate for irregular solder balls on the part and
also
possible surface differences on the existing pads which have been wicked
clean
of solder.
The problem is in putting down the paste. He is teaching a technician to use
a
small medium stiff plastic stencil. The paste is applied with a wide chisel
blade x-acto knife looking tool. They are getting uneven solder cakes and
icicles between the solder deposits.
I ask, is that the best way to put down paste? Is it necessary on a plastic
BGA
to put down a paste deposit? Will the stringers pull in when heated or will
they
results in shorts after reflow?
Any info appreciated.
Thanks,
Stu Korringa
Quality Engineer
Smiths Industries Electronic Systems
Grand Rapids, Mi.
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