Hello Mohsen,

I was also facing the same problem and I was planning to ask about
that issue to mems-talk.

I recently used Nickel Etchant (Type 1) from Transene Company. Content
of the etchant is FeCl3.6H2O, Hydrochloric acid, and water.
I had the same issue.

I contacted the company, and I explained the "huge" undercut issue.
They told me to agitate etchant container during the etching. They
also told me to dilute the etchant to reduce the etch rate of the
etchant.

I tried both, but the result is still not successful from my point of
view. I have ~10 micron diameter circle shaped etching patterns. When
I diluted the etchant, the circle diameter reduced to ~5 micron. But
this time the etch rate reduced significantly.

My final decision was to get rid of Nickel from my process.
If you have the option to use another material, I would say to try
other material options.

If you or somebody else give a solution to that problem, maybe I can
step back and use Ni in my process again.

Best regards,

Mehmet Yilmaz
Mechanical Engineer