Fine line screen printed electrodes for polymer microfluidics

Plastics or polymer sheets are promising materials for microfluidic applications due to lower material cost and easy technologies for structuring. Screen printing of conductors on plastics with line widths above 150 µm are well established with minimal ink spreading. Fine lines with line resolution below 100 µm have high aspect ratios. The ink spreading increases as line widths gets smaller. Ink spread factor of 50∼100% was observed on plastic sheets such as polycarbonate (PC) and acrylics (PMMA). Majority of polymer thick film pastes are developed for dry function but microfluidic applications require wet fluids such as electrolytes in direct contact with printed electrodes. Several commercially available inks were screened for particle size, cure temperatures and viscosity and other factors. The inks were tested for chemical resistant and surface adhesion. The selected inks were used for fine line screen printing. Screen openings of less than 50 µm were considered to compensate for high ink spreading. Small volume productions were simulated with data such as screen life, ink viscosity change, ink consumption and printing yield captured. Line width resolution below 75µm was demonstrated.