what is the cause for brown pad after the final passivation etch of ntiride film?

Answer 1

Color doesn't matter. It's usually just an optical response to a pattern on the metal.

Colors on the metal are usually apparrent under low magnification. But if you look at it under a high power microscope, then it looks like metal.

But, if a chemical analysis of the surface of the metal shows contamination, then you need to figure out how to clean it off.