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January 1998

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Tue, 20 Jan 1998 09:19:53 EST
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In a message dated 98-01-20 01:22:06 EST, you write:

>We are changing now our "  old thick black oxide "  ( 0.7 mg/sq cm )
>followed by DMAB reduction to thin oxide ( 0.35 mg /sq cm ) followed by DMAB
>reducer .

Our experience has been that thin oxide, for reasons that we cannot
understand, tends to not work as well with the DMAB reducer, and the failure
mode is perhaps the strangest we have seen, with some of the panels not being
reduced at all, while others are reduced perfectly.   Although, I guess by our
standards, 0.35 mg/sq cm is still pretty heavy.

Following my  previous question regarding  "conducting reduced
>black oxide" some additional points arosed :
>1 ) the thickness is being measured by stripping the oxide from dummy panel
>( both reduced and not-reduced ) . The differences between " reduced " and "
>not reduced " oxide are reasonable , but  we have different results with
>H2SO4 stripping and HCL stripping . Both stripping solution are fresh and
>the ammount of dissolved copper is even not visible . Which method is "
>common practice " and why the results are different .

Normally HCl is used, as H2SO4 is not real effective, even on unreduced oxide.
HCl works so much better because the Cl ion complexes with the Copper, (as in
the Cupric Chloride etcher) and dissolves the oxide much much faster..

>2 ) We are checking the quality of reducing process by 10% HCl for very long
>time . Just now we are not sure about proper definition of " 10 % HCl " : it
>is 10 % by volume of commercial HCl ( 35 % ) or 10 % by weight of pure HCl (
>1: 3 dilution of commercial HCl ) . What is the common practice and expected
>results ?

10% by volume of the commercial HCl is pretty common, and usually 1-2 minutes
tells the tale.  Try using unreduced oxide as a comparison standard.

Best,

Rudy Sedlak
RD Chemical Company

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