Joe Lee wrote:-
>I am using microetch to treat surface prior to LPI and I would like to
>know what will be the reasonable etch depth. Some one suggest me to use
>pumice combine with microetch, Is that really necessary? By the way what
>is pumice exactly? ( some kind slice?) Could you apply it manually and
>how?

Pumice is a naturally occuring volcanic rock containing glass which has
abrasive qualities. When ground into powder and used in a cleaning
machine, the pumice is kept in suspension by continuous stirring while
being pumped into the cleaning chamber.

There are two basic systems:-
1 Jet pumice which blasts the slurry onto the pwb surface at high
pressure.
2 Brush pumice where the slurry is delivered at low pressure onto
brushes which rotate and scrub the panel surface.

The jet pumice machines tend to wear more quickly due to the
abrasiveness of the pumice. The cleaned surface is rinsed and dried and
is an ideal surface for LPI adhesion. Microetch is not necessary and
would be detrimental to the pumice surface.

There are proprietary pumice cleaners available with additives which can
be very effective for cleaning small quantities by hand. It is difficult
with a manual cleaning system to avoid copper oxidation because the
surface is very active, and so a subsequent treatment in an acidic anti-
tarnish solution may help.

Another problem with manual cleaning is the residual pumice in small
holes can block them. A pumice machine should have a high pressure rinse
section to ensure all pumice is cleaned from the surface and the holes.

Aluminium oxide is sometimes used as an alternative to pumice but I
don't know of any benefits.

Regards
Paul Gould
Teknacron Circuits Ltd
[log in to unmask]
Isle of Wight,UK

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