Stu,

I have not found a need to add solder paste for BGA replacements of any size
and use flux only, typically No Clean. I do prefer to leave an extremely
small dome of solder on each pad as part of pad prep to ensure no exposed
intermetallic and enhance wetting.  We accomplish this under a microscope
and perform a 10X visual prior to placement of the new part with a Sniper
System (TM).  We have had excellent success with the exception of the Altera
part with the known warpage problem.

Regards,
Bruce Misner

> ----------
> From:         [log in to unmask][SMTP:[log in to unmask]]
> Reply To:     TechNet E-Mail Forum.;[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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