Alex,
        Unlike a QFP or CCGA, a BGA with eutectic balls floats on top of the
solder.  This mean there is no such thing as a maximum weight for self
centering.  There is however, a maximum weight before you squash the balls
into each other, causing shorting.  (I don't know what it is, but Daan
might.)
        For bottom side reflow, I have heard John Thorup and Phil Zarrow
claim that the grams per square inch of pad mating area should be less than
30.

Hope this helps

Ryan Grant
Advanced Technology Engineer
MCMS
(208) 898-1145
[log in to unmask]


> -----Original Message-----
> From: Alex L Chan [SMTP:[log in to unmask]]
> Sent: Thursday, October 12, 2000 2:22 PM
> To:   [log in to unmask]
> Subject:      [TN] Question about max. g/ball for BGA self center
>
> Hi Technetters,
>
> Do anyone have a quick answer about what is the maximum weight in term
> of g/ball for BGA self center?  Which means that if the component is
> over this limit it will not self center.  Also for double sized reflow,
> what is the maximum g/ball that the BGA component will fall off?
> Assuming 1.27 mm pitch and using 0.75 mm eutectic balls.
>
> Thanks,
> Alex
>
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