Hi Ning, That hadn't occurred to me; thanks for the insight. If this was the driving mechanism, wouldn't I expect higher reflectance from the gold areas than from the areas where the alumina surface was bare (alumina is dull white whereas the gold is shiny)? The resist seems to be preferentially exposed where it is adjacent to the bare alumina; the other areas (adjacent to gold) develop out normally, indicating relatively less exposure. Regards, Rob -----Original Message----- From: mems-talk-bounces+rob.james=crc.ca@memsnet.org [mailto:mems-talk-bounces+rob.james=crc.ca@memsnet.org] On Behalf Of ning xue Sent: Wednesday, February 02, 2011 5:06 PM To: General MEMS discussion Subject: Re: [mems-talk] patterning SU8 on alumina Hi Rob That is because the rough surface of Au and Al, so there is UV reflection to the via hole. Then the via hole is exposed. Thanks Ning