HI,

The bead edge diffuses into the inner area due to the gravity if it is a higher
thickness even the softbake temperature is lower than the Tg. The reflow can not
work at different circle height. In my opinion, the edge diffuse behaviour can
not be avoided if your thickness more than 30 um. so we just make the center
area to expose.

Regards



At 2011-06-15 22:20:13，"Shane GUO"  wrote:

>Hi Gareth,
>
>It could be. I cleaned my silicon wafer using acetone, IPA and DI water. Then
it is blown dry by N2 and baked for a while.
>
>Thanks