Jiang,

The glass transition temperature (Tg) of unexposed SU-8 is ~55C.  Your
bond is currently running at 75C.  The further you get away from the Tg,
the less viscous the material will become.  One thing to try would be to
reduce your bonding temperature to increase the viscosity of the SU-8.

For the second suggestion, it really becomes important as to how you are
applying your bonding force.  If you are using an actual dedicated
bonding system (such as an EVG520 or EVG501), the force is very
controllable, so you may want to experiment with different bonding
forces.  If you are pressing by hand, then try placing objects of known
weight and uniform weight distribution on top of the stack, and slowly
ramp the "weight" up.

Best Regards,
Chad Brubaker

 -----Original Message-----
From: Jiang Ziling
Subject:  Su-8 bonding clogging problem

  I tried to make channel by bonding two Glass wafers, one with a 50um
exposed Su-8 layer with channel on it, another with a 50um unexposed
Su-8 layer. According to some research, at 75 degree centigrade the
unexposed Su-8 can reform shape and bond with the exposed layer when
certain pressure is applied. But I tested and found that the 100um
wide channels on the exposed su-8 surface are always clogged by the
soft Su-8 flowing from the unexposed layer during pressing-bonding.
However, if I don't press, there will be no bonding. Does anyone have
experience in solving this clogging problem?