Hi Stuart,
I regularly replace plastic bga.s on boards using gel flux only.
There was a debate on this forum some months ago regarding the solderability
of the cleaned board pads because there is the possibility that all the
solder will have been wicked off leaving tin copper intermetallic only.
Whatever, I have not seen a problem. I would advise your engineer to forget
the paste and use gel flux only. Watch that they don't put a thick layer of
the gel on the board or the bga may float off position. (Bitter experience!)
Regards
Eric Dawson
> -----Original Message-----
> From: [log in to unmask] [SMTP:[log in to unmask]]
> Sent: Tuesday, May 14, 2002 3:34 PM
> 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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