Bubbles in UV-cured encapsulants are a defect with structural, optical, and electrical consequences. In structural encapsulation, bubbles create stress concentration points and reduce the mechanical strength of the encapsulated assembly. In optical applications, bubbles scatter and refract light, degrading optical performance. In electrical insulation, bubbles are void sites where partial discharge can initiate dielectric breakdown. Eliminating bubbles requires identifying where they originate — and that depends on when in the process they appear.

Bubbles Introduced During Mixing or Dispensing

For two-component UV encapsulants (mixed immediately before application), air entrained during mixing is the most common bubble source. Manual mixing — stirring with a paddle — inevitably folds air into the mixture. Even mechanical mixing can introduce air if the mixer speed is too high or the mixing geometry creates vortex that pulls air into the material.

Fixes for mixing-introduced bubbles:
– Use vacuum degassing after mixing: place the mixed encapsulant in a vacuum chamber at 1–10 mbar for 1–5 minutes to extract entrained air. Bubbles rise and burst at the surface during vacuum dwell.
– Use a dual-component cartridge dispensing system with static mixing elements rather than manual mixing — static mixers minimize air entrainment compared to manual mixing while providing consistent mix ratio.
– Centrifuge mixing (planetary centrifugal mixing) mixes and degasses simultaneously, producing bubble-free mixtures for high-quality encapsulation.

For single-component UV encapsulants dispensed from bulk containers, air introduced by dispensing — particularly from positive displacement dispensers that introduce air pockets at stroke end — can also create bubbles.

Bubbles from Entrapped Air During Application

When the encapsulant is dispensed into a cavity or onto a substrate, air can be trapped beneath the flowing adhesive as it fills the encapsulation space. If the encapsulant fills a cavity from the top, air is trapped below the descending liquid. If it fills around components, air pockets can form in component shadow areas, corners, and under component overhangs.

Fixes for application-entrapped air:
– Fill from the bottom of a cavity upward, displacing air upward as the encapsulant rises — use a needle tip that deposits material at the bottom of the cavity
– Tilt the assembly during filling to allow air to escape from one side while encapsulant enters from the other
– Reduce dispensing rate — slower, more controlled filling allows air to escape before the encapsulant seals the cavity
– Pre-wet contact surfaces with a thin encapsulant coat before full potting to improve wetting at corners and under component bodies

Outgassing from Substrates or Components

Some substrates and components release dissolved gases when wetted by the encapsulant or when exposed to UV during cure. Plastic component housings can contain dissolved gas from the molding process; ceramic substrates can outgas from surface contaminants or adsorbed moisture. When the encapsulant contacts the substrate, outgassing produces bubbles at the adhesive-substrate interface before cure.

This is most common when substrates are at elevated temperature (outgassing is temperature-dependent), or when the substrate is porous or has surface microvoids that trap gas.

Fixes for outgassing-related bubbles:
– Bake substrates before encapsulation to drive off adsorbed moisture and dissolved gases (typically 60–100°C for 30–60 minutes)
– Vacuum impregnation: apply encapsulant under vacuum so that dissolved gases in the substrate cannot form bubbles when the adhesive contacts the substrate — atmospheric pressure applied after encapsulant is in place drives the adhesive into microvoids rather than allowing gas to escape
– Confirm substrate cleanliness and moisture content with representative samples before production commitment

If you need help diagnosing the source of bubbles in your UV encapsulant process, Email Us and an Incure applications engineer will review the dispensing process and material conditions.

Bubbles Formed During UV Cure

The UV cure process itself can generate bubbles through:

Rapid gas release from the adhesive during fast polymerization. At very high irradiance, rapid exothermic polymerization can locally heat the encapsulant significantly, reducing gas solubility and causing dissolved gas to come out of solution as bubbles. This is most likely at irradiance levels substantially above the minimum required and with encapsulants that have high exotherm.

Photoinitiator decomposition byproducts. Some photoinitiator systems release gaseous byproducts during UV cleavage. If the encapsulant is thick and the gas cannot escape the viscous adhesive matrix before cure completes, it is trapped as bubbles. This is an inherent characteristic of some photoinitiator chemistries and should be disclosed by the adhesive supplier for their formulations.

Fix: Reduce irradiance and extend exposure time to achieve the same dose with less thermal shock. For photoinitiator byproduct problems, evaluate alternative photoinitiator systems with the adhesive supplier.

Bubbles from Adhesive Too Viscous for Deaeration

High-viscosity encapsulants trap air during mixing and dispensing more effectively than low-viscosity materials, and the air bubbles are more difficult to remove because they rise very slowly through the viscous matrix. Standard vacuum degassing may not be sufficient for very high viscosity materials.

Fix: Vacuum degas at elevated temperature (warm the encapsulant to reduce viscosity before vacuum degassing) to increase deaeration efficiency. Use centrifugal mixing which is more effective for high-viscosity materials than vacuum alone.

Confirming Bubble Origin

Determine when bubbles appear:
– Bubbles visible in the uncured material before UV exposure → mixing or dispensing origin
– Bubbles visible after dispensing but before UV exposure → outgassing or application origin
– Bubbles visible only after UV cure → cure-generated (gas release or thermal)

This diagnostic helps narrow the fix to the right process step. Curing a thin film of the adhesive in an open dish (no substrate contact) and comparing to material cured in the encapsulation geometry isolates substrate outgassing from adhesive-inherent bubble formation.

Contact Our Team to discuss UV encapsulant bubble elimination and process design for your encapsulation application.

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