Just run it like normal, provided you have your BGA reflow process in good
control.

You can expect to see the effect of gravity on the resultant solder
connections, anotherwards, the ones which were turned upside down and
remelted will elongate to some extent whereas the ones on the second reflow
operation will collapse the normal amount.
Our testing did not indicate that the elongation was detrimental, but I
would recommend that you perform your own testing to make sure it is ok on
your board.

The real issue is whether or not you are going to running the BGAs directly
on top of one another, because then inspection and trace routing gets trickier.

My mirror image experience has been with 560 1.27 mm pitch devices which
sounds close to the package you have.  Rework is a little bit harder on
this type of assembly, but still possible.

Phil


At 04:13 PM 4/11/00 -0600, Jorge A Rodriguez wrote
>Technetters,
>
>     We are trying to use BGA on both sides of a PWB. The BGA is a 50 mil
>pitch 27 mm x27 mm or 35 mm X 35 mm.
>We have some experience with BGA , but we have never used it with double
>reflow. Is there anyone that has this experience?. The only concern is the
>conditions of the BGA from first pass when doing the second reflow. Any
>ideas?,  has anyone deal with this issue?
>
>
>     Any comments, suggestions will be appreciated
>
>
>
>Jorge A Rodriguez
>Conexant Systems Inc
>
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