Hi,

We are making very thick SU-8-25 samples using a metal mold (several mm
thick).  The softbake goes fine, but when the sample is exposed to UV a thin
film layer forms on top of the evaporated sample.  Tests have confirmed that
this layer is crosslinked, but no heat has been applied.  It is believed the
UV lamp does not provide enough heat to start the crosslinlinking process.
The remaining SU-8 under the film does not crosslink when exposed to heat,
indicating that it is not receiving any UV radiation.  What is the maximum
depth that UV radiation can penetrate SU8-25?  Various literature sources
say layers of SU-8 ranging from 200 - 700 microns are possible using a
conventional spin coater, but are these figures due to limitations in the
spin coating process or in the UV absorption of the SU-8?

I would appreciate any thoughts/comments.

Thank you

Jason McCallum
email:  [email protected]