There is definitely reflow of the un-exposed SU-8 during the bond - SU-8 has a
Tg of 55ºC. Depending on the design of your patterns, the bond pressure and
reflow may cause the unexposed SU-8 to completely fill the patterned areas.

I would take a two step approach.  First, use a slightly thicker layer for the
patterned material (maybe as high as 15 µm). Then try to spin an even thinner
layer onto the second substrate (if you can manage).

A second alternative may be to attempt bonding using only the patterned SU8
layer - see the following reference:

C. Brubaker, T. Matthias, M. Wimplinger, G. Mittendorfer, "SU-8 Bonding for
Optoelectronics Packaging," Proc. Of IMAPS Device Packaging 2007, Scottsdale, AZ
March 19-22, 2007

Best Regards,
Chad Brubaker

EV Group       invent * innovate * implement
Senior Process Engineer - Technology - Tel:  480.727.9635, Fax:  480.727.9700
e-mail: c.brubaker@EVGroup.com, www.EVGroup.com

-----Original Message-----
From: Hyun Chul Jung
Sent: Monday, May 14, 2007 8:53 AM
To: mems-talk@memsnet.org
Subject: [mems-talk] Su-8 to Su-8 bonding

I am trying to make SU-8 to SU-8 bonding.
This is my procedures.
1.Spin coat of SU-10 on pyrex glass around 10um.
2.prebake 2min for 65 and 5min for 95 on hotplate.
3.exposure 15 sec with 365nm line and postbake 1min for 65 and 2min for
95
4.develope
5.Spin coat of SU-5 on another pyrex glass around 3um.
6.bake 1min for 65 and 3min for 95 on hotplate.
7.place them together using wafer bonder at 95 with 500N force for 10
min.

The bonding look strong but I do not see any patterns. I guess there is
some resist reflow duing bonding process.
Could you guys please take a look my procedures?