Hi,
I casted PDMS (10:1 base to curing agent) on a patterned SU-8 master mold at 80 C for 3 h on a hotplate. When I removed the PDMS, the underlying pattern of the SU-8 master mold was damaged. Previously I used a similar SU-8 master mold (but from a different batch) which was good for up-to 5 times to fabricate microfluidic device using same conditions. But this time,it can no longer be used again.
Any precaution/ special treatment while fabricating master mold or removing PDMS which I need to take?
Thank you for your time.
There are some anti-stiction materials that can be deposited on top of the Su8 before the PDMS coating, such as FOTS.
Thank you for helpful answer. I will consider using FOTS or FDTS on my master mold before casting.
Hello Shoaib,
After the development step, I always hard bake my wafers with. It seems that it makes the SU-8 layer more durable. In addition, you can coat the wafer with Sigmacote. This coating will minimize the adhesion of PDMS to the wafer!
My own experience is that this is quite common. I made wafers with smallest feature size approx 30 um. Larger features, typically over 100 um, nearly always had good adhesion and could be used many times, while the small feature sizes required very careful removal of the PDMS and then sometimes still a problem. My only advice is to follow the manufacturing process very closely, and as previously suggested, extra baking may help. One other point: if your SU-8 is quite thick (say more than 30 um), then it may also be that the walls have a negative slope - in this case PDMS is actually under the SU-8 and removal pulls on the SU-8 structures with more force - this is usually also a process issue.
Thank you Dr. Kevin for valuable advice. My SU-8 is nearly 58-60 um thick. Reasons you mentioned above are more likely to be involved in my case. I am going to consider these points while manufacturing processes.
You can silanized your SU-8 master mold, before using first time.
Thank you everyone for suggestions. I coated the SU-8 with FDTS and find it suitable for repeated use.
Hi Shoaib,
Are you using the weight or volume ratio for the PDMS to curing agent?
Thanks.
@Niazul
I used mass ratio of 10:1 (PDMS to curing agent) and degassed before pouring over the mold.
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