Good day Connie,

Where mechanical brushing is used as the cleaning method prior
to coating printed circuits with soldermask, it is possible to
produce fine hair-like slivers of copper which can (but should not)
remain on the board surface. These are due to variables such as
circuit design and orientation, conductor profile, etch undercut,
grade of brush etc.

Copper slivers which remain on the circuit encapsulated in the
soldermask are a definite hazzard, their favourite hiding place is
between closely spaced conductors, and short circuits DO happen.

The circuit frabricator should ensure that his process is under
control. This includes especially the correct functioning of the high
pressure rinse stage that follows the mechanical brushes. As well,
it is handy to include a 'Teknek' type tacky roller at the end of the
process to remove any remaining solid contaminants.

My Revision E of IPC-A-600 doesn't mention inclusions in
soldermask. Maybe somewhere else?

Regards,

Mike.

Mike Holst.
TraX Interconnect (Pty) Ltd
Tel:(++27 21)712 5011
Fax:(++27 21)712 5798
Cape Town
South Africa

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