I have observed varying bonding strengths between PDMS (100um) and polyimide film (50um) at different mixing ratios. The plasma power is 10 W, the time is 40s, air is oxygen. When using a 1:10 ratio, the bonding is moderately strong, allowing the PDMS film to adhere to the polyimide film and resist some peel-off force. However, at a 1:3 ratio, the bonding strength significantly decreases. For assumption, while the peel-off force at a 1:10 ratio measures around 10 N, it drops to only 4 N at a 1:3 ratio. I understand that it is difficult to form a strong bond to the PDMS without adhesive, but "10 N" is enough for my application.

I am interested in understanding the underlying factors that contribute to this difference in bonding strength at different mixing ratios. Any insights, suggestions, or relevant literature on optimizing the bonding between PDMS and polyimide films at varying ratios would be greatly appreciated.