I agree with Fred J. upon that airbubbles as a cause for mousebites also is very rarely seen in our factory. 
When we see mousebites on outerlayers it is commonly due to overloading of the developer. The mousebites is then only appearing in the plated copper layer, not in the base-copper. The cause is residues of photoresist in areas, where the photoresist is thicker due to the surface-topography of the weave.

Mousebites on innerlayers in our factory was in a period mainly caused by the opposite phenomenon; when the photoresist not is laminated down in the "valleys" of the weave causing low adhesion with "under-etching" in etching line as a result.

With best regards

Jan Thuesen


-----Oprindelig meddelelse-----
Fra:    Fred Johnson [SMTP:[log in to unmask]]
Sendt:   23. november 1997 01.24
Til:    [log in to unmask]
Emne:   Re: [TN] Mouse Bites -Reply

I'd like to elaborate a little bit more about what you are describing here.
You are correct in that air bubble can get sucked into the pump inlet (the
air can also get sucked in to leaky fittings on the inlet side of the pump);
this creates a supersaturated condition where the air bubbles then come
out of solution on the surface of the parts being plated.  The analogy a
good friend of mine used is a bottle of soda or beer which contains liquid
bottled with compressed carbon dioxide.  When you open the bottle,
nothing really happens, but when you pour this liquid into a supposedly
clean glass there are sites on the glass where bubbles form (and form
and form and form....).  The same thing can happen in a copper plating
tank with the gas being air rather than CO2.  It is relatively simple to
check; just shut of the air sparger for 8 hours (minimum!) to allow the
solution to de-gas, and then plate and see if the plating is better.
However, this problem causes plating pits, which occur throughout the
copper surface, and not just on the circuit or land edges.  Real
mousebites, only on the edges, are usually the result of a problem with
exposing or developing the photoresist, or with the copper plating
preclean process.  However (again), bubbles can be the cause (it's just
not as common).

There has been a fair amount of recent interest in airless acid copper
plating in part because of plating pits.

Fred J.

>>> Al Hamilton <[log in to unmask]> 11/20/97 03:09pm >>>
Mousebites come from lots of places, one of the more common being from
micro
air bubbles. These are usually caused by the air sparger(s) being too
close
to the intake of the recirculation pump. The pump "micronizes" the bubbles
and they can then lodge on the circuitry, causing a nice round mouse bite.

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