I have found several factors affect bonding of PDMS

1)Chamber cleanliness.  If your chamber is not extremely clean (and I don't
mean cleaned with an oxygen plasma) there may be some contamination from
your chamber walls.  Put your PDMS and substrate in a Pyrex petri dish with
an appropriate cover (like VWR pyrex petri dishes).  I know it is not
sealed or airtight, but it's night and day when I use one.  Also, if your
plasma asher has not been under vacuum, run it  for a few minutes to get
out any water or other contaminants.

2)Water.  When I clean my substrate with acetone, alcohol, DI... I can't
bond afterwards unless I dry the substrate on a 200C hot plate.  I don't
have any data for cleaned PDMS.

3)Age.  As mentioned in several papers by Whitesides, or Beebe, if the PDMS
is exposed to air for too long it will not bond.  However, I have not had
any problems leaving the PDMS on its mold for a while until I was ready to
put it into the plasma.

4)Contact.  Sometimes it takes a few minutes for irreversible bonding to
occur.  If I try to reposition my PDMS during this time by lifting it up
and then putting it back down, the bonding is ruined.

Hope this helps

Glen

 > Message: 9
 > From: "Bo He" 
 > To: [email protected]
 > Date: Tue, 09 Apr 2002 23:37:29 -0500
 > Subject: [mems-talk] Bonding problem!
 > Reply-To: [email protected]
 >
 > Hi,everyone:
 >
 > I am trying to bond PDMS with silicon. I followed the recipe in some
 > references: cleaning both surfaces with aceton, alcolhol and N2 dry then
 > using oxygen plasma to treat both surfaces for 1 min. But results are
 > bad, they cannot be bonded together. Any other recipes I can follow or
 > some important steps missed in my operation? Please give me some
 > suggestions.


*********************************************
Glen A. Landry, Ph.D.
Naval Research Laboratory
Code 6340
4555 Overlook Ave. SW
Washington, DC 20375
USA
Tel.: 202-767-4474 Fax: 202-767-1697
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