If the ceramic you are using is alumina, the black spots are likely to be
aluminium or some other form of aluminium oxide.  What assist gas are you
using?
If you are using a CO2 laser, you could try using Scotch tape (and yes, I am
referring to the brand.  I find their Magic Tape works the best) on the
surface.  Of course, you'll have to clean off the adhesive later but acetone
works nicely.

        -----Original Message-----
        From:   Adnan Merhaba [SMTP:[email protected]]
        Sent:   Tuesday, October 02, 2001 2:54 AM
        To:     [email protected]
        Subject:        [mems-talk] laser drilling

        Hello,

        I have a couple of questions with regard to laser drilling of
ceramics:

        - during laser drilling, we have observed black spots around the
drilled
        holes, I am curious to know where do they originate from (earlier it
was
        believed that the emulsitone that was applied onto the  ceramic
prior to
        drilling lead to carbon deposits, but I find it hard to believe that
carbon
        doesnt get oxidized at high temperatures in an oxygen environment).
        - secondly is there anyway to remove slags around the holes during
the
        drilling operation (say for e.g. by using coolants etc.), this is a
concern
        because when we remove the slag after the drilling operation by
scrubbing,
        we leave the substrate with plenty of scratches, so ideally I would
like to
        remove the slag as and when they are formed.

        Thank you for your patience.
        Regards,
        Adnan Merhaba
        Thin film process engineer
        American Technical Ceramics
        Jacksonville, Florida
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