Chip crack can be caused by the size of media it is exposed to.
Consideration must be taken when the artifact is the chip versa a BGA
solder bump/ PTH / IMC / IP Sep.   Unintentional artifacts can be
created by media grinding/polishing.

The media size id the answer.

Victor,

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge
Sent: Wednesday, November 25, 2009 10:03 AM
To: [log in to unmask]
Subject: [TN] Preparing for microvia examination

Schrekxscht!
That was the way the aliens from planet Mars saluted us in the funny
film
that ended in their heads exploding when a guy played Elvis Presley on
his
car radio. What does that have to do with microvias?  Anyone with
experience
from cutting a board into small pieces and mold them in epoxy for cross
section analysis? I use a thin blade, high rpm diamond blade for
cutting.
The board was equipped with SuperBGAs down to smallest QFNs. We
suspected
via problems and looked for such after polishing. In fact we found
extremly
good barrels and no sign of via issues. Instead we saw that some
cross-sectioned semi chips had fine microcracks. In some cases, the
microcrack ran all the way across the chip, i.e. the whole active area
was
more or less separated from the rest of the chip.My q is this:  has
anyone
of you got microcracks in the semi chips caused during the cutting
operation? I,ve cross sectioned hundreds of boards during my time here,
but
never seen cracks like these be caused by the diamond cutting. Can there
be
a Schrekxscht when you use the diamond saw?
/Inge

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