Dear Adnan:
      The problem you met is mostly  the plating underneath the resist  at
the bottom of  the opening. So after you strip resist you will see
unexpected deposit. This is caused by poor adhesion of resist and metal(seed
layer). So plating solution goes into the interface of resist and metal. One
or more of the followings is possible root cause:
 1. pH of cyanide solution. High pH solution will attack the resist., reduce
the adhesion. So use the gold solution with pH of ~6.
2. Photo process, The steps which effect adhesion,such as, dehydration etc,
3. seed layer contamination.
       I did above analysis basing on your limited information and my
experience. If you have more detailed information, such as thickness &
location of unexpected deposit, the issue can more easily be addressed.

Eddy

 Message: 1
 To: mems-talk@memsnet.org
From: "Adnan Merhaba" 
Date: Wed, 26 Sep 2001 13:33:40 -0400
Subject: [mems-talk] gold electroplating

Hello,

My name is Adnan Merhaba and I am a process engineer with the American
technical ceramics. I have a question regarding pattern plating of gold, we
are currently using a cyanide bath and use 1818 photoresist to mask the
areas not to be plated, however during the plating process, we often find
that the resist shrinks, and hence plating occurs in region where it is not
supposed to. Does anyone know the root cause of this and what are the
possible solutions to avoid it?
Thank you
Regards,
Adnan