I've recently started to work on a PDMS microfluidic device for cell culture using su-8 to create master molds and I was wondering how do other researchers fabricate devices with different channel heights. Do you need to simply make two masks and firstly expose the thinner channels and then spincoat another layer on top of it and expose the higher channels? Or is there a simpler way of achieveing this goal?
If you are molding on different substrates, basically the thickness of the master mold will depend on two parameters: the first is the family of the SU-8 photoresist you are using (3025, 3050 etc) and the second parameter will be the speed in rpm, if you are using spin coating process. Please refer to the table in figure 1 and the attached SU-8 file to observe the thickness range recommended by the manufacturer for an equivalent rotation in rpm. In addition, if your height precision is an very important requirement for your process, you can use profilometer for double check your channel height. In this case you will just need one mask, for achieving different heights. If you have any additional question, do not hesitate to ask it. Thanks. Enjoy the process!
I may have not expressed myself clearly enough or you misunderstood my question. I know that the thickness is defined by the viscosity of the resist and the spin speed but I'd like to fabricate a single chip with channel height of 60 microns that has a structured area in the center with a height of 25 microns. So single chip but with two channel heights. According to the literature it is a common procedure but the experimental sections in articles are usually very brief and not stating detailed information.
Now your project requirement is more clear for me, different heights in the same substrate, in that case, I would use the multi layer SU-08 technique. I recommend these interesting articles, one article describes up to 6 layers.
Best regards,
Salomão Moraes
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