I am not 100% sure I understand what you're trying to achieve but generally
you should spin & expose each layer and then develop in one go at the end.

On Sat, Mar 6, 2010 at 21:46, Jean Lo  wrote:

> Hi,
>
> I am trying to fabricate a device with 2 layer of SU8.
> The first layer is just a simple straight microfluidic channel which is
> around 200 um wide.
>
> I am planning on fabricate a second layer of SU8 on the top of the
> microchannel with a series of blocks along the length of the microchannel.
> The second lyaer of SU8 needs to be really thick since the PDMS thickness
> is
> going to be in between the first layer and the second layer,
> so that I will have holes within the microchannel.
>
> My question is that what might be the better process to process the second
> layer of SU8?
>
> Should I spin-coated and expose the first layer following a second layer
> spin-coated and exposure and develop the whole wafer all at once,
> or should I spin-coated, expose and develop the first layer and process the
> second layer afterwards?
>
> Any suggestion and opinions would be greatly appreciated.
>
> Thanks a lot!
>
> Jean