Nan,

Actually, what you are seeing could very well be a sign of insufficient
cross-link in the film.  When fully cross-linked, SU-8 is pretty much
immune to solvent chemistries.

This may indicate either insufficient exposure, insufficient PEB, or
both.

Best Regards,
Chad Brubaker

 -----Original Message-----
From:   Nan Xie
Subject: [mems-talk] SU-8 Developing Issue, advice required

I am developing SU-8 2050 after spun around 50um.
My procedures for soft baking, exposure, and PEB are correct.
I am having trouble getting clean develops after about 6min and 2-3s
acetone spray.
What I am getting are some milky residue around my features. I
understand I need to develop it more when this occurs, but this milky
residue still remains or the SU-8 would come off.

Anyone have any suggestions? Maybe I need to expose more?