Design of Electrical Interconnect for SU-8 Microfluidic Systems

In this paper, metal press-together contacts for electric interconnection between free-standing polymer microfluidic substrates is presented. In previous work, we have demonstrated fabrication and mechanical assembly and fluidic pressurization of interlocking SU-8 chip-to-chip connections. The addition of electronic routing to the microfluidic polymer chips and electronic interconnect between chips via polymer dip packaging would facilitate microfluidic and microelectronic integration. Towards this goal, metal press-on contacts are presented whereby two polymer substrates containing metals lines can be contacted while maintaining electrical continuity. A 50 nm thick chromium layer and 100 nm thick gold are patterned on enclosed polymer microchannels via metal etching. The metal lines are aligned in parallel and along side the whole length of the microchannels on each fluidic chip. Individual metal lines were tested for electrical resistance and continuity. For the 9000 mum long, by 500 mum wide, and 0.1 mum thick gold lines, the resistance varied from 7.6 to 9.6 Omega, which is on the same order of magnitude as the theoretical resistance of 4.4 Omega. Preliminary results show that removal of the SU-8 platform from the substrate, thus creating free-standing SU-8 microchips with enclosed channels, causes the resistance to increase to 550 Omega due to stress through reduction of the surface area of the conduction path. When the released SU-8 platform is aligned with another platform with metal lines in pressed together contact, electrical continuity is maintained.