Hello,

  Several years ago we went through a pretty severe mousebite problem. We
tried most of the things that have been mentioned already. We examined and
optimized air agitation, pre-plate chemistry, developer rinse temperature,
and exposure levels. Many of the changes helped but did not eliminate the
problem. Finally, we looked at the developer spray nozzles. They were brass
nozzles and the inside had eroded over time until the opening was 50% larger
than it should have been. The breakpoint was good and SEMs showed good
sidewalls but I suppose the impingement was not sufficient to get a perfect
removal of unexposed resist residues. We changed the nozzles, implemented a
routine nozzle change out schedule (every 6 months), and have not had the
problem for many years.

David Arivett
Cuplex 



At 12:24 PM 7/1/97 -0500, you wrote:
>Tony,
>
>I agree that mousebites are caused by precipitation of air from a
>supersaturated bath, and that it is not a single aspect problem, both
>plating and dry film processes must be examined.  In addition to the
>items that others have contributed, there are three additional conditions
>that we have observed that may contribute to the problem:
>
>1.  Supersaturation of air in the plating solution can also come from
>temperature changes.  As the temperature goes up, the solubility of air
>in the bath goes down.  This is similar to the effect seen in a cold can
>of beer vs. a warm one, the CO2 is less soluble at the higher temperature
>resulting in higher pressure.
>
>The bath becomes saturated with air at the temperature at which it is
>running, no problem at this point.  If the bath temperature rises, the
>solubility of the air decreases resulting in supersaturation and, if the
>conditions are right, mousebites.
>
>Track your bath temperature through the day. If you have a variation of
>more than a couple of degrees, this may be a contributor.
>
>2.  A majority of the shops in which we have observed mousebites also
>have an "exaggerated resist foot" or residue problem out of dry film. 
>The foot is usually greater than 0.5 mil in length and has been observed
>to be up to 2 mils long.
>
>The foot can be observed by turning off the plating current completely
>for about 30 sec. every 8-10 min. during the plating cycle.  A properly
>prepared x-section across narrow traces will show grain boundaries at the
>current interruptions revealing that the plating does not start up
>against the resist side-wall.  In extreme cases, a normal x-section
>across narrow traces (with the resist still on the sample) will show that
>the plating never reaches the side-wall.  Most epoxy mounting compounds
>will allow mounting of the x-section sample with minimal effects on the
>dry film.
>
>This condition would indicate that an examination of the dry film process
>is appropriate.
>
>3.  Mousebites tend to show up mostly on one side of the panels.  We have
>found that panels that are not hanging vertically in the tank can
>exaggerated the problem.  Angled panels also contribute to poor
>distribution of the copper deposit.
>
>Good luck, and if you require further discussions you can e-mail me
>directly.
>
>Paul Galatis
>Electrochemicals
>
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