Vishwa,

I think the power is too low to treat the surface. Increase the RF power to
70-80W. Try both piece at the same time. When the treatment is done and when
you unload the sample, do the bonding ASAP. If you can not do the bonding
fast enough, you can drip a little IPA on the treated surface to achieve a
longer time.

For the PDMS preparation, I would prefer pouring the composed sticky stuff
on the wafer first and then do the degas, followed by 30 minutes 60-90C
hotplate curing.

Good luck,

Hongjun Zeng, PhD
Microfabrication Application Laboratory(MAL)
University of Illinois at Chicago

-----Original Message-----
From: Vishwanath Somashekar
Subject: [mems-talk] PDMS to PDMS bonding

Hi,
I have been having problems with bonding PDMS to PDMS.

One of the layers have the microchannel (3 mm X 100 microns). I cast this on
a SI wafer on which contains the replica of the channel manufactured using
SU-8. I use 10:1 ratio of sylgard 184 from Dow Corning. I mix the two
solutions for about 3 mins and then degas for about 30 minutes till there
are no air bubbles present. When I pour them, the over all height of the
layer will be around 3 to 4 mm.( 20 ml + 2ml)

The other layer is just a covering layer to close the top of the channel. I
just cast in on a cleaned SI wafer. Again, I use the same
10:1 ratio of sylgard 184 here. The over all thickness here is about 2 mm.
(15ml + 1.5ml)

I then sonicate both of these layers in Ethanol for about 15 mins. I then
rinse them with ethanol and let them sit in a 60 degree oven till they are
dry.

I then plasma treat them. I use a plasma cleaner manufactured I think by
Yield Engineering Systems. I use O2 plasma at 1 to 1.2 torr, for 1min at
about 22 watts. As soon the plasma treatment is done, I then bond them only
to realize that the bonding is no good. I have been reading some discussions
on the forum about using different proportions for different layers. I would
appreciate if you could guys could suggest something to improve my dilemma.