I do a lot of PDMS bonding and I've found it to be a very subtle, finicky art.
For example I'll expose PDMS and glass to plasma and then bond them by hand. As
I align stuff, my (unsteady) hand sometimes taps a tiny bit of PDMS against the
glass. Then when I place the whole thing down, and let it bond, I'll find that
the spot I tapped didn't bond. So it seems to be a one shot deal when it comes
to making contact. I'm not sure how accurate that is, but it's been my
observation.

With that in mind, my guess is that as the methanol evaporates, it does so
unevenly and points make contact then lose contact then make contact and so on.
The few times I tried using methanol to do alignment I found that it would
evaporate out of one area first and that spot would bond well, but then the rest
of the PDMS would not bond well.

So things to try would be:
Put some kind of weight on the film after alignment to make sure there is even
contact.
Try less plasma time (I found shorter times work better)
Try roughing up the surface of your glass with a quick HF dip.

good luck,
Joe Grogan

Quoting "[email protected]" :

> Dear All,
>       I posted this msg last week. I think I need to describe my
> problems with more details.
> I have had this methanol surfactant or lubricant problem for a while,
> and couldn't figure out why. I hope you can give me some hints.
>       I am trying to align and attach a thin-layer of PDMS (100 um thick)
> onto a glass slide. Because PDMS will permenantly bond to glass, it
> will be extremely difficult to align patterns without lubricant.
> Lubricant provides PDMS some short-time freedom of motion.
>       As suggested by many others, I applied 99.9% methanol
> onto the surface of PDMS film after oxygen plasma treatment (60sec @ 30W),
> then bring the PDMS film with glass slide together. Immediately after
> alignment (less than 1 min), I place them in an oven or on hotplate
> (85C) for 15-20 min, in
> order to evaporate methanol.
>       But after that, I only found that PDMS doesn't stick to glass slide at
> all. I mean, not just certain areas don't stick, it is the entire piece of
> PDMS doesn't stay on the glass slide.
>       In contrast, if I don't apply methanol in between, PDMS would have a
> pretty good adhesion on glass slides.
>       Has anyone had such problem before? What would you think the problem
> is? Should I clean my glass slides further? Should I try purer methanol?