Abstract:
This paper presents a novel fabrication technique of a
photo-resist mask onto 3D curved wafer for micro-abrasive jet
machining (AJM) process. The photo-resist mask structure
selectively blocks the abrasive jet at the portion of the surface that is
not supposed to be machined. Previous studies on the photo-resist
mask fabrication process were mainly focused on planar wafers and
it was difficult to adapt the fabrication technology directly to
materials with 3D curved surfaces because besides UV power and
scanning speed, the solidifying action is strongly affected by the
beam size as well as hatching size. In this research work, a modeling
algorithm that uses images obtained from 3D CAD or no CAD mask
models of the wafer has been developed and validated through a
number of experiments. SU-8 a negative, epoxy-type, near-UV
photo-resist based on EPON SU-8 epoxy resin has been used for the
photo-resist mask fabrication. Even though, the SU-8 photo-resist is
highly sensitive epoxy resin to UV light, existing fabrication process
onto the wafer surface is still an ill-defined problem relying on
heuristic methods because of the lack of adequate knowledge on the
sensitivity variation. The UV laser limits the SU-8 photo-resist mask
to 300μm thickness where photo-resist is most sensitive; therefore a
spin coating technique is desired to allow the resist to acquire
uniform thickness. For 3D non-planar, the spinning technique is very
much demanding and sometimes unfeasible depending on the wafer
shape. In this study, the spinning issue has been consciously
analyzed and worked out through dilute, at defined ratio, of the
concentrated SU-8 epoxy resin with Cyclopentanone (C5H8O).
Through Taguchi method, the most effective controlling parameters
for fabrication of the mask with appropriate hardness and surface
quality as vital conditions for micro-AJM process have been ranked
and reported in this paper.
