How to Make a Microfluidics chip

How to Customize a Microfluidic Chip

1. Annual volume determines the process route (most critical)

Annual volume Process Unit cost order of magnitude

< 100 pcs PDMS soft lithography (SU-8 master, cast) Hundreds per unit, but high labor content

100–1000 pcs Hot embossing / CNC-machined thermoplastics Tens per unit

> 1000 pcs Injection molding (COC/COP) + steel tool Single-digit per unit, tooling capex in the low-to-mid hundreds of thousands

The break-even point for amortizing tooling generally falls between a few hundred and 1,000 pieces. Cut a steel tool below that and you are subsidizing samples with tooling money.

2. The application locks the material

Cell culture / organoids needing gas exchange → PDMS is irreplaceable (permeability is its core value, but the price is absorption of small-molecule drugs)

Organic solvents or high-temperature sterilization → glass / quartz

Integrated electrodes or sensors → silicon, or glass + ITO (electrodes must be defined before bonding; they cannot be modified afterwards)

Disposable diagnostic cartridges → COC/COP, injection molded, UV transparent

Mass-spectrometry coupling → avoid PDMS; oligomer leaching contaminates the signal

3. The detection method constrains structure, not the other way round

Optical imaging requires a transparent substrate with consistent thickness. PDMS transmits light but its thickness uniformity is poor, so quantitative imaging drifts; for demanding work go straight to glass.

Timeline and risk expectations (empirical)

Design + simulation: 2–4 weeks

Photomask + master mold: 1–2 weeks (mask ~RMB 10k–20k per layer)

First PDMS prototype: within 1 week

Bonding process development + yield stabilization: 4–8 weeks — the step most likely to overrun

Injection mold + mold-flow analysis + trial shots: 8–14 weeks

From zero to production-ready: 3–6 months

The four most common pitfalls

Designing only the channels and not the world-to-chip interface. Everything ends up stuck on leakage and bubbles, and interface design effort is routinely underestimated by half.

Losing control of aspect ratio. PDMS channels above ~5:1 aspect ratio tend to roof-collapse; injection-molded features above ~10:1 do not fill completely. Feature width and depth must always be calculated together.

Holding thermal bonding right at the material's Tg. Channels deform on the spot. The process window normally needs to sit 20–30 °C below Tg.

Doing surface treatment once and then scaling up. Hydrophilicity decays over time, batch-to-batch results diverge, and the problem only surfaces at the customer.

Material selection reference

Material Minimum feature Volume cost Bonding Positioning

PDMS 20 µm High, hard to automate Plasma, easy Go-to for prototypes

COC / COP 20 µm Low, single-digit per unit Thermal / UV, medium Workhorse for volume cartridges

PMMA 50 µm Low Solvent-assisted, medium General-purpose lab parts

PC 100 µm Lowest Difficult Low-cost disposables

Glass / quartz 5 µm High Thermal / anodic, difficult High precision, chemical resistance

Silicon < 1 µm Very high Anodic / eutectic, difficult Electrode and sensor integration

Notes from the comparison cards:

PDMS — cast from a lithography master, sample in a week. Gas-permeable, which favors cell culture, but it absorbs small-molecule drugs.

COC / COP — injection molded, UV transparent, extremely low water uptake; the industry-standard material for diagnostic cartridges.

PMMA — works with both CNC and hot embossing, cheap to prototype; solvent and temperature resistance are only average.

PC — lowest unit cost, suited to coarse-channel consumables; poor solvent resistance and a very narrow bonding window.

Glass / quartz — resists aggressive solvents and high temperatures, best optical performance, good for imaging and MS coupling, but high unit price.

Silicon — sub-micron precision, direct electrode and sensor integration, but requires a MEMS line and is not transparent.

Bonding route by material

Material system Bonding method Process window Trade-off

PDMS Plasma activation bonding Room temperature, 30–60 s Moderate strength; must be mated immediately

Thermoplastics (COC / PC) Thermal bonding or UV adhesive 80–140 °C, 0.2–1 MPa High strength; channels prone to deformation

Glass / silicon Anodic bonding 400 °C + 400–1000 V Very high strength; requires a conductive layer

Customization requirement checklist

Fill this in before drawing the first design revision. Nine out of ten customization projects that fail do not fail because the process was infeasible — they fail because the requirements were never stated clearly. The "annual volume" line in particular determines whether you go PDMS or cut a steel tool.

Application and metrics

Application: culture / droplets / detection / synthesis

Sample type and volume per run

Flow rate range and maximum pressure

Detection modality: optical / electrical / mass spectrometry

Number of parallel channels and throughput requirement

Structure and material

Minimum feature size and aspect ratio

Substrate: PDMS / COC / PMMA / glass / silicon

Number of layers and bonding method

Interface: punched holes / Luer / sealed cartridge

Surface treatment and coating requirements

Delivery and compliance

Demand: prototype quantity / annual volume

Sterilization method and single-use vs. reusable

Biocompatibility level, ISO 10993

Quality system, e.g. ISO 13485

Delivery documentation: drawings / COA / yield report

Eight-stage workflow

Stage Focus Key output

1. Requirements definition Application, metrics, compliance Requirement spec / PRD

2. Design and simulation Channel network, CFD, Re / shear / residence time Verified layout, process window

3. Material selection Material dictates process Substrate and process route

4. Mold and master fabrication Photolithography, injection tooling SU-8 master or steel tool

5. Bonding and packaging The yield watershed Leak-tight, high-yield device

6. Surface engineering Hydrophilicity / hydrophobicity, antifouling, ECM coating Stable surface, batch-consistent

7. Verification and QC Leakage, metrology, biocompatibility Test data, COA, yield report

8. Scale-up Hardened tooling, yield ramp Production-ready supply