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.

Thanks
Vishwa