Have you considered the possibility of plating Ni/Au prior to your
functionalization? This will give you the advantage of a non oxidizing
contact top layer so that your aluminum will no longer change in its contact
resistance. This process can be done after your foundry and there is a clean
during process that removes the Al2O3 prior to electroless Ni/Au Drop me a
line if you would like more information.

Bob Henderson
Process Integration,LLC
Phone: 480-558-1156