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  for Metal Finishing since 1989
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Cu-Ag grain boundary etch

I am looking for a grain boundary etch for several micron thick copper-silver layers, which are mounted in cross-section and polished to a 0.05 micron finish. I have tried many combinations of NH4OH/H2O2/H2O and have had very limited success. In all cases, the Cu seems to etch much more quickly than the Ag. Thanks in advance for any suggestions!

Heather Ludtke
- Santa Barbara, California
1999

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Different rates of etching will be a problem with chemical etching of these materials. One problem that can exacerbate this problem is if your polish is less than ideal. Your final polish may be leaving a thin layer of deformed metal on the surface of the copper and/or silver. You should be able to get good grain structure of the copper even if the silver does not etch. Some mix of the etchant that you are using should give good results for copper and silver. If you don't see the structure of the copper, you probably need to improve your polish. I prefer colloidal silica to alumina for final polishing of copper and silver, usually with a touch of ammonium hydroxide and hydrogen peroxide mixed in to get a little bit of chemical polishing reaction. Also remember that if this is a deposited layer structure that the grain structure will not be the same as you see for copper and silver wrought products in the microstructure handbooks. Good luck.

Larry Hanke
Minneapolis, Minnesota
1999