Hello Hakan:

We have found that the strength of bulk micromachined parts can be
significantly increased by a thermal oxidation. The thermal oxidation fills in
any microscopic cracks that develop during dicing and polishing. A good
reference on the increase of silicon strength due to thermal oxidation is:

"Micromechanical fracture strength of silicon"
Fredric Ericson and Jan-Ake Schweitz
J. Appl. Physics. Vol. 68 No. 11. DEc. 1990. pp5840-5844.

Stress concentration and the related fracture failure at the V-grooves can be
avoided by a plasma or isotropic etch of silicon to reduce the radius of
curvature. A good paper is in the Transducers 1991 proceedings written by Kurt
Peterson and others.

With these two techniques we have been able to achieve 5 MPa fracture stresses
in ultrasonically driven silicon structures.

Amit Lal.
Dept. Of. Electrical Engineeering.
Berkeley Sensor and Actuator Center.
University of California, Berkeley.

On Mon, 15 Apr 1996, HaKAN ELDERSTIG -1080 wrote:

> Silicon is a strong material they say....
>
> We have put our bulk micromachined silicon chips in a plastic
> package. Some of the chips breaks or we can  se fine cracks, usually
> close to the v-grooves. There is a bonded glass lid on top of the
> v-grooves that should strengthen the device. The chips also had been
> edge polished after dicing with 3 microns and 0.3 micron papers.  Do
> anyone know if the polishing itself can lower the mechanical strength
> of the chips? Or is the dicing bad enough?
>
> Hakan Elderstig
>