HumiSeal® UV40-250 is a single component, high solids, UV curable, acrylated polyurethane conformal coating that possesses excellent chemical resistance, surface hardness, flexibility and moisture resistance.  The material is tack-free after exposure to UV light. A secondary moisture cure mechanism will cure unexposed areas of the coating within 2-3 days at ambient conditions.  The coating fluoresces under UV light to allow for coating inspection and can be applied by all selective coating equipment. HumiSeal® UV40-250 is recognized under UL File Number E105698 and is IPC-CC-830 and RoHS Directive 2011/65/EC compliant.

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Conformal coatings can be successfully applied to substrates that have been cleaned prior to coating and also to substrates assembled with low residue, “no clean” assembly materials. Users should perform adequate testing to confirm compatibility between the conformal coating and their particular assembly materials, process conditions and cleanliness level. Please contact HumiSeal® for additional information.

HumiSeal® UV40-250 can be applied via standard selective coating. The source air used for spraying must be dry (a dry inert gas is highly recommended) to prevent premature curing by the secondary cure mechanism.  The spraying should be done with adequate ventilation so that the vapour and mist are carried away from the operator.

HumiSeal® UV40-250 is a highly cross linked coating. In order to achieve maximum cross linking density, the product must be exposed to the correct spectral output. Humiseal® has modelled the performance of UV40-250 using Arc and Microwave based UV curing equipment. The table below outlines the required dosage and irradiance values necessary to render HumiSeal® UV40-250 tack free post UV exposure with both equipment types. Minimum figures should provide a tack free surface. The maximum recommendation represents highest tested values by Humiseal. The cure recommendations may change as curing technology develops.


Dose J/cm2*

Irradiance W/cm2*






Arc System 1.5 1.5 0.40 0.50 0.50



Microwave System 2.0 2.0 0.40 0.70 0.70



Arc System 2.8 2.7 0.80   0.90 0.80



Microwave System 3.0 3.0 0.60 1.15 1.15


Values measured with a Powerpuck II UV radiometer

Heat is also an important component with UV cure, and different systems produce different heat outputs. Higher heat levels allow UV cure at lower dose/irradiance levels. Consequently, Humiseal recommend that curing is discussed with HumiSeal® Technical staff to ensure the exact customer process being used will meet the coating cure requirements. After UV exposure and return to room temperature the coating should be tack free.

HumiSeal® UV40-250 contains a reliable secondary moisture cure mechanism which will cure any shadow areas on the assembly within 7 days at ambient moisture.

HumiSeal® UV40-250 was designed to be cured using a microwave UV oven equipped with an “H” style bulb. Arc systems can cure HumiSeal® UV40-250 however care must be taken during the equipment selection process to ensure minimum dosage and irradiance values obtained will properly cure the coating. Because of the variations possible in curing equipment type and configuration, it is strongly recommended that you contact HumiSeal Technical Support to discuss your equipment and process in detail.

Clean Up
To flush equipment and clean uncured HumiSeal® UV40-250, non-alcohol based solvents should be used. HumiSeal® Thinner 521 or Thinner 521EU is recommended.

HumiSeal® UV40-250 is a highly cross linked UV cured coating.  The cured film has a high degree of environmental and chemical resistance and will be more difficult to remove than traditional conformal coatings. Thermal displacement, mechanical abrasion and, where available, HumiSeal® Stripper 1100 are suitable options for rework of HumiSeal® UV40-250.

Product Specification

Product Specification
Density 1.06 g/cm3
Minimum Solids Content 95 %
Viscosity, per Fed-Std-141, Meth. 4287 300 ± 50 centipoise
Recommended Coating Thickness 25 – 125 microns
Recommended UV Dose* see curing section above
Shelf Life at Room Temperature, DOM 6 months
Recommended Stripper** HumiSeal® Stripper 1100
Thermal Shock, 50 cycles per MIL-I-46058C -65°C to 125°C
Glass Transition Temperature – DSC 26°C
Coefficient of Thermal Expansion 112 ppm/°C Below Tg
283 ppm/°C Above Tg
Modulus – DMA 1060 MPa -60°C
Flammability, per UL-94 V-0
Dielectric Withstand Voltage, per MIL-I-46058C >1500 volts
Dielectric Constant, at 1MHz and 25°C per ASTM D150-98 2.41
Dissipation Factor, at 1MHz and 25°C per ASTM D150-98 0.01
Insulation Resistance, per MIL-I-46058C 8.0 x 1014 ohms (800TΩ)
Moisture Insulation Resistance, per MIL-I-46058C 4.7 x 1010 ohms (47GΩ)
Fungus Resistance, per ASTM G21 Pass
Resistance to Chemicals Excellent

*Microwave UV cure ovens equipped with “H” style bulbs recommended
**Stripper 1100 is not available in the EU