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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