Resources

Explore more information for high-performance conformal coating, potting and mission-critical PCB protection.

Choosing the Right Conformal Coating

Selecting the proper conformal coating is essential to ensuring long-term reliability of printed circuit boards (PCBs), especially in mission-critical environments. At SpecCoat, we guide customers through this decision by evaluating the environmental threats, mechanical demands, and electrical performance requirements of each application.

Key Factors to Consider

Coatings must match the operational environment and assembly characteristics. We analyze:

Environmental exposure: Moisture, chemicals, dust, and thermal cycling
Mechanical stress: Vibration, shock, flexing, or CTE mismatch
Thermal performance: Continuous and peak temperature tolerance
Electrical insulation: Dielectric strength and resistivity
Physical demands: Viscosity, adhesion, and coverage uniformity

Rigid coatings may cause stress on delicate leads or miniaturized components during temperature shifts. Flexible coatings are preferred in such scenarios to prevent cracking, delamination, or joint failure.

Coating Types and Properties

We work with all major coating chemistries and tailor solutions to meet your specific application demands:

Acrylic (AR)

Easy to apply and remove
Moderate moisture resistance
Best for general-purpose protection
Temp range: -59°C to 132°C
Dielectric strength: >1500 volts

Silicone (SR)

Excellent flexibility and thermal resistance
Withstands wide temperature variations
Higher film build without cracking
Temp range: -65°C to 200°C

Polyurethane (UR)

Tough, durable, and chemically resistant
Difficult to remove; best for long-term protection
Temp range: -59°C to 132°C

Epoxy (ER)

Strong barrier against moisture and solvents
Very rigid; used when rework is not required
Typically used in high-reliability industrial assemblies

Parylene (XY)

Ultra-thin and uniform, even on complex geometries
Chemically inert, biocompatible, and pinhole-free
Ideal for aerospace, medical, and high-reliability applications
Dielectric strength: 6800–7000 volts/mil
Elongation: Up to 200%
Temp range: Up to 290°C (Parylene C), 410°C (Parylene N)

Nano Coatings

Hydrophobic barrier against moisture and oils
Requires minimal masking
Maintains component appearance and functionality
Commonly applied at 400nm thickness

UV-Curable Coatings

For rapid production cycles, we offer UV light-curable coatings that cure instantly under ultraviolet or visible light. These coatings are solvent-free, VOC-free, and ideal for applications requiring fast turnaround and reduced handling risks. Most UV coatings use acrylated-urethane hybrids that cross-link instantly when exposed to UV, forming robust and reliable protection layers.

Expert Guidance for Mission-Critical Builds

With over two decades of experience and certifications including AS9100D, NADCAP, and ITAR, SpecCoat helps customers select the right coating for each application—from early prototyping to volume production. We support:

Harsh environments: space, aerospace, defense, industrial
Complex designs: fine-pitch leads, high-density assemblies
Audit-ready programs: full traceability and compliance assurance

We don’t just apply coatings—we engineer reliability into your electronics from the ground up.

Table 1: Electrical and Thermal Properties of Conformal Coatings
Properties	Acrylic	Urethane	Epoxy	Silicone	Parylene
Surface resistivity, ohm/cm (50% RH, 23°C)	-	2 × 10¹⁵	-	-	1×1013 - 4.7×1017
Volume resistivity, ohm/cm (50% RH, 23°C)	10¹⁵	1.1 × 10¹⁵	10¹² – 10¹²	2 – 10¹⁵	8.8x1016-1.4x1017
Dielectric constant, 60 cycles	3 – 4	5.4 – 7.6	3.5 – 5.0	2.7 – 3.1	2.65 - 3.15
Dielectric constant, 10³ cycles	2.5 – 3.5	5.5 – 7.6	3.5 – 4.5	-	2.65 - 3.1
Dielectric constant, 10⁶ cycles	2.2 – 3.2	4.2 – 5.1	3.3 – 4.0	2.6 – 2.7	2.65 - 2.95
Dissipation factor, 60 cycles	0.02 – 0.04	0.015 – 0.048	0.002 – 2.7	0.001 – 0.007	0.0002 -0.020
Dissipation factor, 10³ cycles	0.02 – 0.04	0.043 – 0.060	0.002 – 0.02	-	0.0002 -0.019
Dissipation factor, 10⁶ cycles	2.5 – 3.5	0.05 – 0.07	0.03 – 0.05	0.001 – 0.002	0.00066 -0.0136
Thermal conductivity (cal/sec·cm·°C)	3 – 6	1.7 – 7.4	4 – 5	3.5 – 7.5	0.0002008 - 0.00003006
Thermal expansion (×10⁻⁵/°C)	5 – 9	10 – 20	4.5 – 6.5	> 25	35-65
Resistance to heat (°F) continuous	250	250	250	400	176 -392
Effect of weak acids	None	Slight dissolve	None	Little to None	Little to None
Effect of weak alkalis	None	Slight dissolve	None	Little to None	Little to None
Effect of organic solvents	Attacked by ketones, aromatics, and chlorinated solvents	Resists most	Generally resistant	Attacked by some	Little to None

Table 2: Application and Performance Comparison of Conformal Coatings

(‘A’ rating is optimal selection for each property)
Properties	Acrylic	Urethane	Epoxy	Silicone	Parylene
Ease of application	A	A/B	C	C	D
Ease of rework/removal (chemically)	A	B/C	-	C	D
Ease of rework/removal (burn through with soldering iron)	A	A/B	C	-	D
Abrasion resistance (rubbing)	C	B	A	C	B
Mechanical strength	C	B	A	B	A
Temperature resistance	A	B	D	A	B
Humidity resistance (moisture)	A	A	B	C/D	A
Humidity resistance (extended periods)	A	A	C	C/D	A
Pot life	A	B	D	D	A
Optimum cure	A	B	B	C	A
Room-temperature cure time	A	B	B	C	A
Elevated-temperature cure time	A	B	B	C	A
Cost	A	A/B	A	D	D

Table 3: Typical Thickness Ranges by Coating Type

Recommended conformal coating thickness per J-STD-001, IPC–CC-830, MIL-I-46058, NASA-STD-8739-1 and IPC-A-610 guidelines:
Type of Coating	Thickness in inches	Thickness in mm
Acrylic	0.00118 – 0.00512	0.03 – 0.13
Polyurethane or Urethane	0.00118 – 0.00512	0.03 – 0.13
Silicone	0.00197 – 0.00827	0.05 – 0.21
Epoxy	0.00118 – 0.00512	0.03 – 0.13
Parylene	0.0005 – 0.002	0.012- 0.0050

Properties	Acrylic	Urethane	Epoxy	Silicone	Parylene
Surface resistivity, ohm/cm (50% RH, 23°C)	-	2 × 10¹⁵	-	-	1×10¹³ - 4.7×10¹⁷
Volume resistivity, ohm/cm (50% RH, 23°C)	10¹⁵	1.1 × 10¹⁵	10¹² – 10¹²	2 – 10¹⁵	8.8×10¹⁶ - 1.4×10¹⁷
Dielectric constant, 60 cycles	3 – 4	5.4 – 7.6	3.5 – 5.0	2.7 – 3.1	2.65 - 3.15
Dielectric constant, 10³ cycles	2.5 – 3.5	5.5 – 7.6	3.5 – 4.5	-	2.65 - 3.1
Dielectric constant, 10⁶ cycles	2.2 – 3.2	4.2 – 5.1	3.3 – 4.0	2.6 – 2.7	2.65 - 2.95
Dissipation factor, 60 cycles	0.02 – 0.04	0.015 – 0.048	0.002 – 2.7	0.001 – 0.007	0.0002 - 0.020
Dissipation factor, 10³ cycles	0.02 – 0.04	0.043 – 0.060	0.002 – 0.02	-	0.0002 - 0.019
Dissipation factor, 10⁶ cycles	2.5 – 3.5	0.05 – 0.07	0.03 – 0.05	0.001 – 0.002	0.00066 - 0.0136
Thermal conductivity (cal/sec·cm·°C)	3 – 6	1.7 – 7.4	4 – 5	3.5 – 7.5	0.0002008 - 0.00003006
Thermal expansion (×10⁻⁵/°C)	5 – 9	10 – 20	4.5 – 6.5	> 25	35 - 65
Resistance to heat (°F) continuous	250	250	250	400	176 - 392
Effect of weak acids	None	Slight dissolve	None	Little to None	Little to None
Effect of weak alkalis	None	Slight dissolve	None	Little to None	Little to None
Effect of organic solvents	Attacked by ketones, aromatics, and chlorinated solvents	Resists most	Generally resistant	Attacked by some	Little to None

Table 2: Application and Performance Comparison of Conformal Coatings

(‘A’ rating is optimal selection for each property)

Property	Acrylic	Urethane	Epoxy	Silicone	Parylene
Ease of application	A	A / B	C	C	D
Ease of rework/removal (chemically)	A	B / C	-	C	D
Ease of rework/removal (burn through with soldering iron)	A	A / B	C	-	D
Abrasion resistance (rubbing)	C	B	A	C	B
Mechanical strength	C	B	A	B	A
Temperature resistance	A	B	D	A	B
Humidity resistance (moisture)	A	A	B	C / D	A
Humidity resistance (extended periods)	A	A	C	C / D	A
Pot life	A	B	D	D	A
Optimum cure	A	B	B	C	A
Room-temperature cure time	A	B	B	C	A
Elevated-temperature cure time	A	B	B	C	A
Cost	A	A / B	A	D	D

Table 3: Typical Thickness Ranges by Coating Type

Recommended conformal coating thickness per J-STD-001, IPC–CC-830, MIL-I-46058, NASA-STD-8739-1 and IPC-A-610 guidelines:

Type of Coating	Thickness in inches	Thickness in mm
Acrylic	0.00118 – 0.00512	0.03 – 0.13
Polyurethane or Urethane	0.00118 – 0.00512	0.03 – 0.13
Silicone	0.00197 – 0.00827	0.05 – 0.21
Epoxy	0.00118 – 0.00512	0.03 – 0.13
Parylene	0.0005 – 0.002	0.012 - 0.0050

Frequently Asked Questions

Explore answers to common questions about SpecCoat's advanced coating solutions and how we can meet your specific project requirements.

What are the primary functions of conformal coating?

The primary function of conformal coating is to prevent the electronic circuit boards from long-term corrosion due to moisture condensation. Other desirable features include a better prevention of electrical shorts in high humidity days.

If I have protected my electronics in a sealed plastic or metal box but the electronics are used outdoors, do I still need to conformal coat my circuit boards inside the sealed box?

Having a sealed electrical box is good for rain. Moisture can still pass through the plastic boxes and rubber gasket.

Sealed boxes do not “breathe” and thus trap moisture that cannot escape and will condense to become sitting water inside the box at night or in colder weather. Condensed with potentially contaminating ionics from the air is one of the most potent corrosive ingredients.

How thick should the conformal coatings be for optimum protection?

Per IPC-A-610 Traditional conformal coatings such as polyurethane, acrylic, and silicone should be:

Type AR	Acrylic	25.4 – 127.0um (0.001– 0.005 in)
Type ER	Epoxy	25.4 – 127.0um (0.001-0.005 in)
Type UR	Urethane	25.4 – 127.0um (0.001-0.005 in)
Type SR	Silicone	50.8 – 203.2um (0.002 – 0.008in)
Type XY	Para-xylylene	10.2 – 50.8um (0.0004 – 0.002in)

Are there advantages offered by conformal coating that are physically stronger and harder?

Conformal coating is not designed as physical protection media.

General mechanical strength is not required. As long as the conformal coating remains intact at low and high temperatures, low and high humidity, and resists water and common chemicals and solvents, they will be effective conformal coating.

What are dielectric strength and its relevance in conformal coating?

Dielectric strength is a measurement of the insulation strength of the coating. Generally higher the better.

However, the circuit boards are supposedly designed to have adequate protection against normal operation. As long as the conformal coating does not negatively affect the dielectric strength in air, they generally will be adequate.

What are the different methods of applying conformal coatings and their relative advantages and disadvantages?

Brush coating is used for smaller-volume production. It has the advantage of applying conformal coating only on those needed areas. Labor with such a method is higher.

Spray coating is used for larger volume production and is generally faster. However, areas that must not be coated must be properly masked before coating.

Dip coating is used for those requirements that need complete coverage. Extensive masking is required because the boards will be fully submerged. This method is costly.

How do I mask the areas of circuit boards that cannot be coated over with conformal coating?

The typical masking method is taping with dots, high temperature tapes, boots and various peelable masks. The reason I put this in is because liquid latex masks are only one of many peelable mask that we use.