Its probably related to nonuniform temperature distribution or too much
convection that is cooling the top surface of the SU8. Much of these can be
corrected by slowing down the ramp rate. I typically ramp to 100C over
about 2hrs and ramp down over several hours or overnight. Even with 300um
thick SU8 I don't see the problems you are seeing.
On Oct 23, 2014 5:41 PM, "KarthiKeyan K"  wrote:

> Dear sir,
>
> Thanks for your mail and information.
>
> Actually the SU8 photo resist is spined by spin coater at 2500rpm during
> this process I got uniform coating and then I goes to soft backing for 65c,
> when I put it on the hotplate or hot air oven (with in 2-3 min) the coated
> su 8 layer will be shrinkaged and or some times non uniform surface layer
> on su8 layer during soft backing process.
>
> Which one is prefereable for soft/hard backing whether hot plate or air
> oven???
>
> Looking forward to your suggestion.
>
> Thanking you,
>
> Best regards,
> Karthi
>
> On Oct 24, 2014 12:55 AM, "Andrew Sarangan"  wrote:
> >
> > Can you elaborate how you are determining this shrinkage? During softbake
> > there will be loss of solvents and a change in thickness, but it should
> not
> > cause any stresses because the uncured SU8 should reflow above 65C.
> Perhaps
> > your ramp rate is too fast causing part of the SU8 to flow while other
> > parts are still solid?
> >
> > On Wed, Oct 22, 2014 at 10:49 PM, KarthiKeyan K 
> > wrote:
> >
> > > Dear All,
> > >
> > > I am facing shrinkage problem on SU8 2075 photoresist layer on Silicon
> > > Substrate. Actually this problem accruing on soft backing process at
> 65C on
> > > hotplate & hot air oven also.
> > >
> > > Kindly suggest to over come this problem.
> > >
> > > Thanking you,
> > >
> > > Best Regards,
> > > Karthi
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