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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.

A challenge in selecting and applying lead‐free solders lies in separating the influences of materials' properties, fluxes and processes to obtain robust assembly conditions that are compatible with PCB finishes and all component terminations. This paper discusses simple steps towards establishing a lead‐free assembly process. With reference to results of solder paste spread and wetting tests and component solderability tests, some of the current limitations in applying standard test methods to lead‐free evaluations are highlighted.

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