With a two-part epoxy, the mix ratio determines whether it cures. With a UV potting compound there is no mix ratio. The equivalent variable is UV dose, the combination of light intensity and exposure time, and controlling it is the difference between a fully protective encapsulant and a tacky, under-cured one.

This article explains what UV dose is, why an incorrect dose causes specific failures, and how to set and hold it in production.

What “dose” means for a UV potting compound

UV potting compounds are single-component systems. Their cure is driven by delivered energy, not a chemical blend. Two quantities define it:

• Irradiance (intensity): the optical power reaching the resin surface, in mW/cm2. Higher intensity cures faster.
• Exposure time: how long the resin sees the light, in seconds.

Their product is dose, expressed in mJ/cm2. A given compound needs a minimum dose at a suitable wavelength (commonly 365 or 405 nm) to reach full properties. The data sheet states that target.

What happens when the dose is wrong

Under-cure (dose too low). The compound stays soft, tacky, or poorly adhered. That degrades every function it was chosen for: lower chemical resistance, reduced mechanical and vibration protection, weaker dielectric strength, and slow property drift that turns into field failures and warranty claims. Under-cured resin can also outgas and corrode nearby metal.

Over-cure (excessive dose). Less common, but prolonged high-intensity exposure can embrittle some formulations and yellow optically clear grades. It also wastes lamp life and energy.

Inconsistent dose across a batch. Variation in lamp output, part position, or conveyor speed produces parts with different cure states and unpredictable service life, which is harder to catch than a uniform under-cure.

The variables that move dose in real production

Lamp aging. UV sources lose output over hundreds to thousands of hours. A recipe validated on a new lamp can drift below the minimum dose months later. This is the same degradation mechanism described in what causes UV light guide degradation over time.

Pot depth. Light attenuates as it passes through resin, especially filled or pigmented grades. A dose that cures a 2 mm section may not cure 6 mm. Thick sections need higher intensity, longer time, or a dual-cure grade.

Distance and geometry. Irradiance falls with distance from the source. Parts sitting lower in a fixture, or angled away from the lamp, receive less.

Shadowing. Any component that blocks the line of sight leaves resin beneath it under-cured regardless of the nominal dose.

Setting and holding the dose

Start from the compound data sheet for target dose and wavelength. Choose curing hardware that can deliver it consistently: a UV LED flood lamp for bench work, a conveyor system for volume with repeatable belt speed and lamp height.

Then instrument the process:

• Measure dose with a calibrated radiometer at the part surface, not the nominal lamp rating. Log it on a schedule and set a replacement or recalibration trigger when intensity drops below the minimum plus a margin.
• Validate cure-through at your real pot depth, not a thin test film. Section a potted sample and check hardness from top to bottom.
• Account for shadowing by specifying a dual-cure grade where components block light.
• Keep the resin and parts clean. Surface contamination scatters and absorbs UV, lowering effective dose.

Confirm the process with destructive checks on early parts, hardness, adhesion pull, solvent resistance, then thermal-cycle and humidity-age potted samples before ramping.

Incure supplies UV-curable and dual-cure potting compounds with defined cure schedules and supports manufacturers on dose setup and radiometer-based process control. Email Us with your compound, pot depth, and lamp type.

Oxygen inhibition at the surface

Free-radical UV chemistries, which cover most UV potting compounds, are inhibited by atmospheric oxygen at the exposed surface. Oxygen quenches the radicals faster than the light generates them in the top few microns, leaving a thin tacky skin even when the bulk is fully cured. This is normal and usually harmless under a lid or another layer, but where the surface stays exposed and needs to be tack-free, the options are: raise the intensity so cure outruns inhibition, flood the cure zone with nitrogen, apply a temporary oxygen barrier film during cure, or select a grade formulated with a surface-cure additive. Mistaking an oxygen-inhibited skin for a general under-cure leads to over-dosing the whole part, so confirm the bulk hardness before adjusting the recipe.

Wavelength and photoinitiator match

A compound’s photoinitiator package absorbs in a specific band. A 365 nm formulation cured under a 405 nm lamp may cure slowly or incompletely even at high measured irradiance, because the light is not where the initiator absorbs. Match the lamp’s peak output to the compound’s specified cure wavelength, and when changing lamp technology, for example from a mercury arc to an LED, re-validate the dose from scratch rather than assuming the mJ/cm2 number carries over.

Dose is the process, not a setting

A UV potting compound only performs at the dose it was formulated for. Reaching it once in a validation run is not enough; the intensity that delivers it drifts with lamp life, part position, and section thickness. A radiometer check and a cure-through validation turn a nominal recipe into a controlled process.

Contact Our Team to discuss cure-dose validation for your potting line.

Visit www.incurelab.com for more information.