Causes of Bubbles and Voids

The method of applying the adhesive is the most frequent source of air entrapment.

High Dispensing Pressure or Speed: Too much pressure or too fast a dispensing rate can inject air directly into the adhesive or cause turbulence, trapping air within the fluid stream.
Improper Nozzle Design: If the dispensing tip is too narrow or the syringe/reservoir contains headspace, air can be incorporated during application.
“Tailing” or Lifting the Dispenser: Pulling the dispensing needle away from the adhesive too quickly can create a vacuum that pulls air into the material.

Air can be introduced from the components being bonded.

Porous or Rough Substrates: Materials like ceramics, composites, or lightly-abraded plastics may have microscopic pockets or surface roughness that trap air, which is then released into the adhesive when the substrates are mated.
Mating Technique (Air Vents): When two flat substrates are brought together, air can be trapped in the center.

In rare cases, the adhesive itself can generate gas.

UV Intensity Spike: If the UV light intensity is too high, the polymerization reaction becomes extremely rapid and exothermic (heat-generating). This rapid chemical change can cause volatile components or gasses to “outgas” within the adhesive, forming bubbles.

2. Solutions for Eliminating Voids

Degassing: Use a vacuum chamber to degas the adhesive in the syringe or reservoir before dispensing. This removes any air dissolved or trapped within the liquid adhesive, especially for large-volume applications.
Allow Equilibration: If the adhesive has been refrigerated, allow it to reach room temperature before use. Cold adhesive is thicker (higher viscosity) and holds air more easily.

Lower Dispense Rate and Pressure: Reduce the dispensing pressure and speed to ensure a smooth, laminar flow of adhesive without creating turbulence.
Dispense Pattern: Use a dispensing pattern that ensures the adhesive is applied to one substrate only (not both), allowing it to wet out properly when the parts are mated.
Controlled Mating (Air Vents): Bring the substrates together slowly, starting from one edge and applying a uniform closing pressure. This method, like closing a book, forces the air to escape out of the sides rather than trapping it in the center.
Increase Dwell Time: After dispensing and before curing, allow a short dwell time (a few seconds) for the adhesive to settle and for any small entrapped air bubbles to rise to the surface and burst.

Ramp Curing: Use a step-cure or ramped intensity curing profile. Start with a very low UV intensity and gradually increase it. This slower cure rate prevents the rapid heat spike and outgassing that causes bubbles.
Vacuum Curing: For high-reliability, void-free bonds in optics or medical devices, cure the adhesive while the assembly is temporarily held under a vacuum. This pulls any remaining dissolved or trapped air out of the liquid adhesive.