How thick is the gold seed layer, it should be a least 200nm thick for good
current spreading. How long is the O2 plasma clean, you may want to extend it to
ensure that there is no scum on the gold surface you are trying to plate.
What kind of gold bath do you have sulfite or cyanide based?
How many electrical contacts are you using? Do you have a low resitance contact?
What current density are you using?
Rick
-----Original Message-----
From: Sunshine Littlecreek [mailto:[email protected]]
Sent: Thursday, June 22, 2017 7:32 AM
To: [email protected]
Subject: [mems-talk] Problem with SU-8 Thick film
Hello,
I’m working with SU-8 2025 and 2075, 100 um - 500 um thick on top of gold. My
features are 20 um - 300 um wide. When I try to electroplate the features, some
of them don’t plate. Here’s my process: Clean substrates (acetone, IPA, diH20 10
minutes each), dehydrate for 30 min. Spin Omnicoat at 3000 rpm, bake for 1 min
at 200 C. Spin SU-8 at 1000 rpm, soft bake for 7 min at 65 C, ramp to 95 C, bake
for 20 min (thinner films)-45 min (thickest films). Expose with UV 3 cycles of
270 mJ/cm^2 and post exposure bake : 5 min at 65 C, 15 min at 95 C up to 25 min
for thickest films. Development is done using MicroChem SU8 Developer on a
shaker plate (usually about an hour). When I rinse with IPA and diH20, no white
haze forms, so it should be fully developed. Omnicoat gets developed in an O2
plasma chamber at 100 W.
I’ve looked around the web, and tried some of the suggestions like using a
sonicator (developed features quickly, but resulted in sheets of SU8 coming off
taking features with it), rinsing more frequently, and eliminating the PEB (SU8
dissolved in developer), but I haven’t had better outcomes.
I do a visual inspection using a stereoscope to check if the bottom looks clean,
which it usually does. However, when I electroplate, not all of the features
plate or plate evenly. I’ve gone from having no plating at all (resulted in
higher exposure and longer development times being used) to partial plating. I
need to get all my features to consistently plate across all features. Any ideas
or suggestions would be greatly appreciated.
Thank you,
Sunshine Littlecreek
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