Matt,
2 of the secrets to bonding a liquid organic to a solid inorganic are
moisture and surface tension. If you can remove all the moisture from the glass
and then put down a bonding agent while the glass is still dry you have more
chance of success. For example if you wanted to put liquid photo resist on top
of glass a normal process is to vacuum vapor prime. The following happens,
inside the primer. First a series of vacuum/hot nitrogen interchanges to remove
Oxygen and moisture. Typically 3 purges to 10 Torr followed by hot Nitrogen.
At 10 torr water boils at 11 degrees C. then a vacuum to 1 Torr, water boils at
-20 degrees C. The glass is totally dehydrated then a primer HMDS is introduced
to the vacuum chamber to react with the glass. HMDS is looking for Hydrogen.
The only Hydrogen is part of Hydroxyl ions that are bonded firmly to the glass.
The HMDS react liberates NH3 leaving behind 2(Si(CH3)3) an inorganic/organic
molecule with the Si firmly bonded to the glass and the CH3 methyl, sticking up
in the air. This does 2 things, it makes the glass hydrophobic and presents a
Methyl for resist adhesion. Then by varying the time of HMDS you vary the
surface tension. Example 5 minutes of HMDS gives a water contact angle of 75
degrees which is a near perfect figure to match the liquid surface tension of
positive resist. The required surface tension figure will no doubt be different
for PDMS but we could find it quickly. If you have the luxury of a number of
test pieces, I could do a matrix of times of HMDS to see if this would give you
the best adhesion. Note of encouragement as soon as the HMDS treatment is done
we can ship it normal mail and leave it out for weeks with no change in the
surface and the adhesion properties. Bill Moffat
-----Original Message-----
From: matt cook [mailto:[email protected]]
Sent: Wednesday, January 29, 2003 9:11 AM
To: [email protected]
Subject: [mems-talk] Bonding PDMS to glass?
Hello-
I want to put liquid PDMS on glass and have the PDMS and glass be very
strongly bonded when I cure the PDMS, but so far I have no luck.
I read that for cured PDMS films, you can treat the surfaces of the PDMS and
the glass with oxygen plasma and then press together, any suggestions on
ways to treat glass so that liquid PDMS put on it will be bonded strongly
when cured?
Many Thanks!
-Matt Cook
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