Thank you everyone who told me what you know. My idea of non-round pads
was to
have a top-down X-ray view of the part show the ball's silhouette change
from a
circle to the shape of the pad, so I could know it had reflowed and
reattached
to the pad. My X-ray person said that tilting the chip & board at an
angle
doesn't work well because the other balls obstruct the view. We are on
.65 or .5
mm pitch, with .5 or .3 mm diameter balls, respectively. 

We work with small lots (prototype quantities) and can't afford the
parts or
boards to do destructive analysis, plus the chips are experimental grade
(pre-production), so we are trying to distinguish between silicon and
assembly
errors. Our assembler is new at BGA attachment, so were on the learning
curve
together. With these constraints, I wanted to figure an X-ray solution.
I've
seen advertisements for the Ersa scope, but it's depth is inadequate for
the
depth of rows involved.

For those of you who suggested another shape, like oval, etc., have you
ever
yourself seen how effective those shapes are for my goal? Sometimes
minor
changes are too small to give a definite conclusion. If you have a
successful
solution, with pictures, please show them to me
([log in to unmask]).

Peter Casparius
Analog Devices
Technician
ph. (781) 937-1464	

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