Thanks to all of you. I see now. One may get mechanical shock ways like
when doing ultrasonic wire bonding with too much energy, the result being
chipouts. I'll neglect the microcracks and look for other things that can be
the trouble.Typically, there are intermittent failures of some kind. Barrel
issues seem less likely as the via barrels are the best I can imagine. Maybe
eyelid problems. It's enough with a very light touch with the RF probe on
certain positions of the board, and you get an interrupt, or the opposite.
When the automatic tester has located the most probable line, we have
pressed a fine wire into some of the vias, and the electrical problem seems
to be removed, but I said to the Q-man, you can't ship those boards as
being MIL qualified products. How do you know that you have a stable
contact? There may be a Schrekxscht after one week, or one year. I have to
find out what's going on in the boards or the IC packages.
Will try my little low rpm superthin diamond blade machine then.
Thanks again
Inge
----- Original Message -----
From: "Bev Christian" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, November 25, 2009 5:53 PM
Subject: Re: [TN] Preparing for microvia examination
Ing,
We only use a slow speed saw.
Bev
RIM
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge
Sent: Wednesday, November 25, 2009 11:03 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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