[terryed]

What would react with copper but not aluminum?  Or, what reacts with copper much faster than it reacts with aluminum?  I need to etch some copper off of an aluminum substrate without damaging the aluminum.  Any ideas?

[Alberto_Kravina]

Or, what reacts with copper much faster than it reacts with aluminum?

Copper reacts vigorously with conc. nitric acid, Aluminium does not (or only a little) due to passivation.
Can I ask what area the etched surface should have?

[terryed]

You asked what area the etched surface should have.  Assuming you refer to the area in squares, it will have about 0.002 square inches. 

Where should I go for microliter quantities of nitric acid ?

[Alberto_Kravina]

You asked what area the etched surface should have.  Assuming you refer to the area in squares, it will have about 0.002 square inches. 

Argh - that's a very small area - that's pretty hard to achieve an accurate work with nitric acid - however - I think that the only solution would be to fill a capillary tube with an area of 0,002 square Inches with some nitric acid and then put it on the surface where you want to etch the copper off

Where should I go for microliter quantities of nitric acid

Do you mean where to buy it? mmm...hard to say, as I think that it is sold only in bigger quantities.
Watch out not to use dil. nitric acid, as in this case the Aluminium won't passivate.

[terryed]

   Alberto,  Thank you so very much.  Its great to have people helping you on a forum.

I'll make sure to try conc.   Terryed