Plasma enhanced bonding of polydimethylsiloxane with parylene and its optimization

Polydimethylsiloxane (PDMS) and parylene are among the most widely used polymers in biomedical and microfluidic applications due to their favorable properties. Due to differences in their chemical structure and fabrication methods, it is difficult to integrate them together on a single microfluidic device. In this paper, we have demonstrated a method to bond patterned PDMS with parylene without the use of high temperature or pressure in a two-step process. The steps include (1) the attachment of cured PDMS surface to parylene using microcontact printing to form a weak bond followed by (2) a plasma exposure of sealed assembly to SF6, N2 and O2 gases, which enhanced the quality of bond by approximately fourfold to 1.4 MPa. We systematically investigated the effect of gas flow rates, chamber pressure, plasma time and power using Taguchi's design of experiment method. Composition of the bond formed in this process was evaluated to understand the mechanism of bond formation. Microfluidic channels fabricated from a PDMS replica and a flat parylene-coated surface, bonded using this method, have been able to withstand burst pressures of up to 146 kPa compared to 35 kPa for PDMS prepolymer microcontact printed assembly.