Stu,

We have 5 Air-Vac systems and do our share of BGA rework. Although we use
the flux only method, we apply solder paste more often. We've found fewer
problems when we apply solder paste. Seems to provide a little extra solder
volume ensuring a more consistent joint.

When we do apply solder paste, we use a new type of adhesive backed BGA
solder paste stencil. These stencils is made from a flexible material, and
the adhesive backing seals around each BGA pad preventing the solder paste
from bleeding under the stencil due to the squeegee action. You get a
consistent deposit with these stencils, and you can simply throw it away
after it's used.

Jeff Ferry
CEO
Circuit Technology Center, Inc.
http://www.circuittechctr.com
[log in to unmask]
978-374-5000

Chairman
IPC Repairability Committee

Sign up for our Free E-mail Newsletter at:
http://www.circuittechctr.com/general/free_email.htm




-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Tuesday, 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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