Phil Hinton asked about dewetting and pumice scrub. Several years ago we had
this problem. We had changed from bristle brush to pumice scrub prior to
soldermask. Suddenly everything we hot-air levelled had dewetting. We had
some luck increasing the weight loss prior to hal but had to etch too much
(about 100 microinches). We decided it had to be pumice imbedding in the
surface. Realizing that pumice is silica and rather than etch copper until
we undercut the pumice, we looked for ways to etch the pumice also. We were
using sodium bifluoride for glass etch on the desmear line so we mixed some
into our cleaner/microetch. (You do desperate things fighting a problem at
2:00 AM) Immediately the dewetting went away. We were able to etch about 25
microinches and got great results. Subsequently, we called our chemical
manufacturer (OS-Tech) and they began blending a cleaner/microetch with
sodium bifluoride blended in. OS-322 is the product. We continue to have
good luck using it but it etches any metal it comes in contact with so it
must be used in a spray unit with all plastic parts. Hope this helps.

David Arivett
Cuplex Inc.

***************************************************************************
* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
***************************************************************************
* To unsubscribe from this list at any time, send a message to:           *
* [log in to unmask] with <subject: unsubscribe> and no text.        *
***************************************************************************