sou zou wrote:
>Hi folks !
>
>I am looking for some advices to get a very uniform surface of nickel
electroplated layers (especially on silicon). Through my bibliography
research, it seems that the trick is mainly to get an uniform current
density across the coated surface (parallel current lines). The problem is
the resist pattern wich does'nt allow to obtain that kind of strictly
vertical current lines. Does anyone has an ingenious idea or a good web
address to help me overcoming such a problem, please ?
>
>Thank you in advance,
>
>sz
>
_________
Dear sz:
I am affraid the answer to your question is not that simple. You may find
some of the information related to this matter on our website
www.fibrotools.com.

Briefly (if possible), the current lines direction and density depend on
electric field and the electrolyte composition.  Electric field again
depends on a number of factors including the resist pattern. Resist pattern
may affect the field distribution by many ways including the sidewalls
quality (vertical, slanted, rough, clean, contaminated etc.) and by the
actual pattern design (sharp points, edges etc.).

With vertical current lines you may still have the problem of current
density distribution since the pattern design may generate the "edge effect"
thus causing excess current density in some sites of your pattern.  This may
be overcome with corrections in design and/or also by introducing the so
called "dummy sites" (pattern sections that are not functional).

You may still have the problem of uneven nickel electroplate. Under same
electric field the current density also depends on electrolyte composition
especially additives. If your specific pattern combined with equipment
utilized in electroplating do not result in providing a uniform distribution
of electrolyte and byproducts to and from the electroplated sites, the
current density may be affected. This effect will be stronger as the
features in your pattern become finer.

Finally, assuming you met the requirements for a uniform current
distribution the nickel finish may still be "rough" (depending what you
consider smooth). This will be determined by the selection of electroplating
solution (type of additives), electroplating parameters (temp., current
density, pH etc.) and the electroplating equipment.

Sincerely,
IK
www.fibrotools.com