Lab-on-a-Chip Microfluidics & Capillary Electrophoresis Phototool Guide

Comprehensive technical guide to phototool mask scaling, isotropic etch choke factors, electrokinetic injection geometry, and cleanroom vector standards.

1. Microfluidic Channel Prepress & Lithography Physics

Lab-on-a-Chip (LOC) and micro-total analysis systems (µTAS) rely on microchannels ranging from 10 to 500 µm in width. When transferring CAD vector artwork onto photomasks (chrome-on-quartz or emulsion phototools), engineers must compensate for material-specific etching kinetics and optical exposure diffractions.

In isotropic glass etching (e.g., HF/NH₄F buffered oxide etch on fused silica), the etchant attacks laterally beneath the photoresist at the same rate it etches downwards ($U_{ ext{factor}} = 1.0$). If a 60 µm wide by 20 µm deep channel is required, the phototool aperture must be exactly 20 µm wide. Failing to choke the vector line will yield a 100 µm over-etched trench.

2. Capillary Electrophoresis (CE) Column Design

Microchip capillary electrophoresis separates biomolecules (DNA, proteins, pharmaceutical metabolites) using high electric fields (200–1000 V/cm). Achieving high resolution depends on minimizing sample dispersion:

• Racetrack Turn Compensation: Molecules traveling along the inner radius of a curved turn travel a shorter distance than outer molecules, causing band broadening. Designing synchronized turn geometry with narrowed inner widths restores planar wavefronts.
• Double-T vs. Cross-T Injectors: Offset double-T injectors allow precise volumetric sampling ($V_{ ext{plug}} = w \cdot d \cdot L_{ ext{offset}}$), essential for quantitative analytical chemistry.
• Joule Heating Limits: Excessive electric field strength generates thermal parabolic flow profiles. Maintain $E \le \sqrt{8 k \Delta T / (\sigma d^2)}$ to ensure laminar plug flow.

3. Fabrication Methods Comparison

4. Vector & DXF Mask Export Standards

Microfluidic CAD systems (AutoCAD, L-Edit, KLayout) require closed polygon boundaries with zero self-intersections and zero duplicate vertices. SpotItLive converts bitmap schematics, microscope micrographs, and sketches into sub-micron accurate DXF and SVG phototool files.