Spinning over uncured SU8 will not result in twice the thickness because the
solvent of the top layer will mix with the bottom layers. If you spin over
cured SU8 (after exposure) that should result in twice the thickness. You
could also try and bake a small quantity of SU8 in a bottle to reduce the
solvent content to make it more viscous. I am not sure how that would affect
its photosensitivity. Best option is to buy a different batch of SU8
formulated for your desired thickness range (such as SU8-2005).


On Tue, Apr 22, 2008 at 6:50 PM, vaibhav mathur 
wrote:

> hi all,
>
> I use microchem SU-8 2. At 2000 rpm I achieve 2micron thickness. Now I
> want
>  to increase the height to 5-6 microns. how do i do this??
>
> 1) when I spin coat at 1000 rpm I get about 5 microns, the height is
> inconsistent though, and i get very bad edge bead. can someone suggest
> how to do this properly
>
> 2) also, if I do double spin coating, I should get 4 microns, right? but I
> get only about 2.4 microns, an increase of just 20 percent, I dont
> understand.
> Does someone have a recipe for double spin coating of SU-8?
>