Jack,

  It sounds to me like the area that you need to concentrate on is cleaning.
The PDMS should bond well directly to very clean Si or glass.  Particulates will
cause voids in your bond.  Another thing to look into is plasma oxidation just
prior to attempting the wafer bond, in order to get a better oxide layer for the
bond.

Regards,

Brian Douglas
Suss Microtec Inc.
Applications Engineer - Bonders
Phone: (802) 244 - 5181 x202
Fax:  (802) 560 - 0001