Vapor honing or vapor blasting is used by several comapnies for cleaninf the
debris from small holes and not as a surface prep.  It works well for the
thicker panels (0.060 and thicker) as the thinner panel will grow due to the
peening of copper surface..  The thinner panels must be protected by a mask
that exposes only the holes and it tasks longer to apply the mask and it
takes longer to load them.  Typically the mask is made of epoxy glass
material that has the holes drilled 0.02 larger than the holes in the panel,
it is applied to both sides.  Many grits and materials including pumice may
be used but the best is a acidified aluminum oxide, 325 mesh available from
Norton.  It will clean and partially desmear down to 0.010 diameter holes,
maybe smaller, I have not tried it.  I heard that it worked for blind vias
down to 4x4, but you must also use a high pressure water-rinse spray to make
sure all of the grit is removed.  It also works with Teflon boards in place
of Tetra-etch to roughen the hole enough to cause electroless and some of the
DM products to stick.  If using  with Teflon you must use the mask.  It also
preps the surface very well, but is not used in the PCB industry primarily
for that purpose.  If you want some better information, suggest you call
Vapor Blast at 414-871-6500 which is Milwaukee WI, I think.  

Phil Hinton   

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