To all of you, who gave ideas how to solve the problem with poor wire
bonding on electroplated gold, I say thank you for your attention. In
a extremly short time I got some insight in what it's all about: how
grains are built up during the plating process. Begins with a few
nanometers thick  crystal pattern adopted to the structure of the
target, and when growing thicker will become more and more dependent
on the bath constitution.  Learned also that most plating processes
are designed to give a hard and bright and appetizing surface,
therefore the chemists put foreign atoms in between the gold atoms,
which changes the growth orientation from columnar to some other
structure.  

These atoms (alloying elements) in the Gold Bath seem most oftenly to
be Cobalt and Nickel. Concentrations from 0.5 to 3 at%.  Pure Gold has
hardness 80-100 Vickers, while electrolytic Gold over electrolytic
Nickel gives 200-500 Vickers.  

I also learned that a typical alloyed gold has, not only Gold and
Nickel or Cobalt, but also various quantities of Carbon, Nitrogene,
Hydrogene, Potassium, Oxygene and other elements or compounds. Many of
these nanometer big inclusions play a rôle for the microhardness. In
order to get as pure as possible a gold surface, you change the
current premises, one way of which is pulsed current instead of DC.
So, running a controlled process window with pulse plating can
decrease the microhardness considerably.

The specialists say there are three cathegories of explanations for
gold hardening in a wet process:  a) solid solution hardening due to
Cobalt (or Nickel or some other choice) atoms which are dissolved
substitionally in the Gold lattice  b)grain size  hardening  and  
c) dispersion hardening due to inclusions dispersed in the Gold
matrix. When you DC-plate it's difficult to control these three
parameters separately, but if you use pulse plating you can separate
these hardening mechanisms and control them better.

Our supplier is a neighbour of Lea-Ronal, so they will ask them
already today about a five 9'ns % Gold bath. It feels good to have an
idea what language to speak when you talk with the specialist, not
only : I cannot bond, what can you do? By means of SEM/EDAX,
Microhardness Tester and Auger etc. we have a good chance to eliminate
our wire bonding problem.

                            Thanks again

                               /Ingemar