Gareth is correct. This will work fine (I've gotten it to work with up
to six layers) but don't mix solvents (I've tried; it's ugly). You
will never completely evaporate the solvents, and the interface
between the two solvent systems will cause very poor adhesion.

- Kevin

On Wed, Oct 27, 2010 at 5:18 AM, Gareth Jenkins  wrote:
> Microchem advise to thermally process each layer as an individual layer
> (i.e. do not extend bake times on subsequent layers). The exposure will need
> to extended for the 2nd mask.
>
> I.e.:
> Spin, softbake, expose, PEB as for a 30um layer
> Spin, softbake, (expose as for 45um) and PEB as for a 15um layer
> Develop 45um combined layer
>
> As always, some tweaking may be required for but generally this is how it
> should be done.
>
> As mentioned, I have only ever done multiple layers using the standard
> series which uses GBL as a solvent. I am really not sure what will happen
> with an SU-8 3000 layer on top of SU-8 2000. As far as I know they use
> different solvents which may cause problems during the baking steps but I
> really couldn't say for sure.
>
> Gareth