Did you try APS100 from Transene.
also see
 "Etch rates for Micromachining processing Part II" K. Williams, J. MEMS Vol12,
No6, Dec 2003



>------------------------------
>
>Message: 4
>Date: Thu, 13 Apr 2006 17:27:47 -0700 (PDT)
>From: Srinivas Vanapalli 
>Subject: [mems-talk] Wet etching Copper selective to Nickel
>To: General MEMS discussion 
>Message-ID: <20060414002747.74231.qmail@web37309.mail.mud.yahoo.com>
>Content-Type: text/plain; charset=iso-8859-1
>
>Hello All,
>
>I have Nickel electroplated on Copper as a seed layer with photoresist as the
mask. I have to
>remove copper at those areas where photoresist was mask during electroplating.
I am looking for
>wet etching recipies selective to Nickel. If somebody has done this before pls
let me know. Thanks
>in advance.
>
>Srini.
>
>
>------------------------------

Kevin Denis
NASA Goddard Space Flight Center
Detector Systems Branch, Code 553
Bldg 11, Rm E020
Greenbelt, MD 20771

ph:  301-286-7935
fax: 301-286-1672
email: kdenis@pop500.gsfc.nasa.gov