Re: sporadic non-oxiding of copper

We have seen this, and have done some significant research into the
phenomenon.  It is clearly not a cleaning problem, as the non-oxided areas
tend to be very regular in their pattern.  Also, we have cleaned and
microetched to the point that we removed more than 50% of the thickness of
the Copper, with no change in the oxide pattern.

It would appear to be some Copper chrystalization problem, with some areas of
the Copper becoming cathodic, or in other words reduction sites for the
Chlorite in the oxide solution.  This is the only explanation that we came up
with that made sense, as the problem areas would eventually oxide completely,
but would take about 50% longer to get full coverage as the rest of the
Copper.  We also noticed that the problem was definitely related to the
Copper source, and by changing source, the problem would go away completely.
  This lends credence to the idea that the problem is related to the
chrystallinity of the Copper.

In a related area, a paper was presented to the Electochemical Society last
spring that discussed differences in etching characteristics (speed, and etch
factor) due to differences in chrystal structure in the Copper substrate.  If
there is interest, e-mail me back, and I will provide details on who did the
paper, and what the title was.

Rudy Sedlak
RD Chemical Co.
fax 415-962-0370