Hi Victor,

We use a colloidal silica solution (0.05 micron) for our final polish. We
polish for about one and a half minutes, with the final half minute running
water on the cloth (Buehler's micro-cloth) and cross-section. This cleans
the cloth and the cross-section mount of the colloidal solution. We then
rinse just the cross-section mount again with water and then quickly rinse
with alcohol (IPA) and blow dry with nitrogen and wipe lightly with a cotton
ball.  This usually gives us a clean, stain free surface. However, if you
have pull-away (separation) of your mounting epoxy to the sample surface, it
can be very difficult to get all the water and polishing solution out of the
separation area.

Hope this helps.
Wade McFaddin
Nextek Inc.

-----Original Message-----
From: Victor G. Hernandez [mailto:[log in to unmask]]
Sent: Monday, April 25, 2005 1:48 PM
To: [log in to unmask]
Subject: [TN] Lead Free, Ball Grid Array, solder bump cross section

Fellow TechNetters:

   I have conducted many of LF solder bump cross section and final
polish is conducted with a Buehler Masterprep

Polishing Suspension Alumina 0.05 microns.   Micro craves, epoxy
shrinkage/voids, on the sample surface retain

the polishing compound which contaminate the surface appearance.   This
step can cause staining and/or water

marks on the bulb solder prior to mid range magnification examination
with inverted stage microscope.

   Can some one recommend a LF chemical etchant that I can replace the
alumina step in my process?

Victor,




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