Burst Pressure and Bond Strength in Microfluidic Chips

What is burst pressure?

Burst pressure is the internal pressure at which a sealed chip first leaks or the bond between layers gives way. It is the practical ceiling on operating pressure: the chip should run comfortably below it, with margin to spare. To know how much margin you have, you first need an estimate of your working pressure — the pressure your fluidics actually generate in normal use.

Working pressure follows from flow rate and channel resistance: narrow, long channels at high flow rates build pressure quickly. You can estimate it from your geometry with our pressure drop calculator and the accompanying guide. Burst pressure should sit well above that figure, not just barely clear of it.

What sets burst pressure?

Several factors combine, and the weakest one usually decides the outcome.

• Bond method and quality — how the layers are joined matters more than almost anything else. Broadly, thermal-diffusion and fusion bonds, and well-controlled solvent bonds, tend to be strong and homogeneous because the join is continuous; plasma bonds (for example PDMS to glass) are typically moderate to strong; adhesive bonds vary widely and can become the weak point if the adhesive is uneven or incompatible. See our overview of bonding methods for how each works.
• Bond area around the channels — pressure acts on the projected area of a feature, so a wide channel or large chamber pushes harder on the lid than a narrow one at the same pressure. Wide unsupported features lower burst pressure; generous bonding land between channels raises it.
• Surface finish and flatness — the mating faces have to make intimate contact to bond. Rough, wavy or contaminated surfaces leave gaps and trapped particles that become leak paths. Our note on surface roughness covers why finish matters for sealing.
• Material and the world-to-chip connections — in practice the fittings, ports and tubing interfaces are often the real failure point rather than the bond itself. A perfectly bonded chip can still leak at a badly seated connector.

How burst pressure is tested

Testing is straightforward in principle: seal the chip, connect it, and pressurise. The medium is often liquid (safer, as a liquid stores little energy) or sometimes gas. You then either ramp the pressure steadily until the chip fails, recording the burst point, or hold at a fixed multiple of the intended operating pressure to confirm it survives. Because bonding and finish vary across a batch, it is important to test parts that are representative of real production, not a hand-finished one-off.

Design guidance

• Design in a safety margin — choose materials and a bond method that clear your estimated working pressure with room to spare, rather than aiming to just pass.
• Keep bonding area generous — leave plenty of bonding land between and around channels; crowded layouts with thin walls between features seal less reliably.
• Avoid very wide unsupported spans — break up large chambers or wide channels with support pillars so the lid is not free to bulge or peel.
• Validate on production-representative parts — confirm the bond on chips made by the same process you will scale to. See prototype to scale and injection moulding for how the process changes as volumes grow, then upload a design for manufacturing feedback.

An alternative: laser welding

Where a strong, localised seal is wanted without bonding the whole interface, laser welding can fuse the two parts along defined weld lines. It concentrates the join where it is needed and can leave the rest of the surface untouched, which is useful for some geometries and materials.

Frequently asked questions