MIL-I-46058CMIL-I-46058C: Military Conformal Coating Specification Complete Guide

Conformal coating is one of those topics that doesn’t get the attention it deserves until something goes wrong. I’ve seen perfectly good military electronics fail in the field because someone chose the wrong coating type, applied it too thick, or didn’t cure it properly. MIL-I-46058C established the framework for protecting military electronics with conformal coatings, and even though the specification was technically canceled in 1998, its influence shapes how we protect PCBs today.

This guide covers everything engineers need to know about MIL-I-46058C—the coating types it defined, the requirements it established, why it still matters, and how it relates to modern specifications like IPC-CC-830.

What Is MIL-I-46058C?

MIL-I-46058C was the U.S. Department of Defense specification for insulating compound, electrical, conformal coatings used to protect printed circuit boards and electronic assemblies from moisture, fungus, corrosion, and environmental contamination. The specification defined five types of conformal coatings based on resin chemistry, along with testing requirements and performance criteria.

Although the Defense Logistics Agency (DLA) officially canceled MIL-I-46058C in 1998, replacing it with IPC-CC-830, the military specification remains widely referenced in the industry. Many manufacturers still qualify their coatings to MIL-I-46058C requirements, and countless active military programs continue to call out the specification in their documentation.

Why MIL-I-46058C Still Matters

The specification’s continued relevance stems from several factors:

Legacy programs: Military systems with 20-30 year lifecycles still reference MIL-I-46058C in their technical data packages.

Industry familiarity: Engineers and manufacturers understand the coating type designations (AR, ER, SR, UR, XY) that MIL-I-46058C established.

Proven requirements: The testing methodology and performance criteria defined in MIL-I-46058C remain technically sound.

Specification inertia: Changing qualified materials lists and approved processes requires significant effort, so many programs continue using MIL-I-46058C-qualified coatings.

MIL-I-46058C vs. IPC-CC-830

Aspect	MIL-I-46058C	IPC-CC-830
Status	Canceled (1998)	Active standard
Maintainer	DLA (formerly)	IPC
Coating types	AR, ER, SR, UR, XY	Same designations
Test methods	MIL-I-46058C specific	Updated, expanded
Qualification	QPL system	Manufacturer certification
Industry adoption	Legacy programs	New designs

IPC-CC-830 largely adopted the MIL-I-46058C framework while updating test methods and adding requirements for modern coating technologies. For new designs, IPC-CC-830 is the appropriate specification, but understanding MIL-I-46058C remains essential for anyone working with military electronics.

MIL-I-46058C Conformal Coating Types

The specification defined five coating types based on chemical composition. Each type has distinct properties that make it suitable for specific applications.

Type AR: Acrylic Resin Coatings

Acrylic coatings are among the most widely used conformal coatings due to their ease of application and reworkability.

Property	Type AR Specification
Base chemistry	Acrylic polymer
Cure mechanism	Solvent evaporation
Cure time	30-60 minutes at room temperature
Operating temperature	-65°C to +125°C
Moisture resistance	Good
Chemical resistance	Fair
Dielectric strength	Excellent
Reworkability	Excellent (solvent removable)

Advantages of Type AR coatings:

• Fast drying at room temperature
• Easy removal for rework using solvents
• Good humidity and fungus resistance
• Low cost
• Excellent dielectric properties
• Good optical clarity for inspection

Limitations of Type AR coatings:

• Limited chemical resistance
• Poor resistance to solvents and fuels
• Not suitable for immersion applications
• Limited abrasion resistance

Typical applications: General military electronics, ground support equipment, avionics where rework is anticipated, commercial aerospace.

Type ER: Epoxy Resin Coatings

Epoxy coatings provide superior chemical resistance and durability but sacrifice reworkability.

Property	Type ER Specification
Base chemistry	Epoxy resin
Cure mechanism	Chemical reaction (2-part or heat)
Cure time	1-4 hours at elevated temperature
Operating temperature	-65°C to +125°C
Moisture resistance	Excellent
Chemical resistance	Excellent
Dielectric strength	Excellent
Reworkability	Poor (burn-through or grinding)

Advantages of Type ER coatings:

• Excellent humidity and chemical resistance
• Superior hardness and abrasion resistance
• Good adhesion to most substrates
• Long pot life available
• Resistant to solvents and fuels

Limitations of Type ER coatings:

• Difficult or impossible to rework
• Longer cure times
• Potential for stress cracking
• Two-component mixing required (some formulations)
• Higher cost than acrylics

Typical applications: Harsh chemical environments, aerospace fuel system electronics, marine electronics, applications where rework is not anticipated.

Type SR: Silicone Resin Coatings

Silicone coatings excel in high-temperature applications and provide excellent flexibility.

Property	Type SR Specification
Base chemistry	Silicone polymer
Cure mechanism	Moisture cure or heat cure
Cure time	24-72 hours (moisture) or 30 min (heat)
Operating temperature	-65°C to +200°C
Moisture resistance	Excellent
Chemical resistance	Good
Dielectric strength	Very good
Reworkability	Moderate (specialized solvents)

Advantages of Type SR coatings:

• Widest operating temperature range
• Excellent flexibility and stress relief
• Vibration damping properties
• Good moisture resistance
• Corona resistant

Limitations of Type SR coatings:

• Lower abrasion resistance
• Higher cost
• Longer cure times (moisture cure)
• Potential adhesion issues without primer
• Not resistant to some solvents

Typical applications: High-temperature electronics, engine compartment systems, aerospace applications with thermal cycling, LED lighting, power electronics.

Type UR: Polyurethane Resin Coatings

Polyurethane coatings offer a balance of properties including good chemical resistance and reasonable reworkability.

Property	Type UR Specification
Base chemistry	Polyurethane resin
Cure mechanism	Moisture cure or 2-part reaction
Cure time	3-7 days (moisture) or 1-2 hours (2-part)
Operating temperature	-65°C to +125°C
Moisture resistance	Excellent
Chemical resistance	Very good
Dielectric strength	Excellent
Reworkability	Moderate (solvent softening)

Advantages of Type UR coatings:

• Excellent moisture and chemical resistance
• Good abrasion resistance
• Solvent resistant
• Good dielectric properties
• Reasonable reworkability with effort

Limitations of Type UR coatings:

• Extended cure times (moisture cure)
• Potential for bubbling if applied too thick
• May yellow with UV exposure
• Two-component mixing required (some formulations)

Typical applications: Marine electronics, outdoor equipment, chemical processing environments, industrial controls, automotive electronics.

Type XY: Paraxylylene (Parylene) Coatings

Parylene coatings are applied through a unique vapor deposition process, producing ultra-thin, pinhole-free films.

Property	Type XY Specification
Base chemistry	Poly-para-xylylene
Cure mechanism	Vacuum vapor deposition
Cure time	During deposition (no post-cure)
Operating temperature	-65°C to +125°C (N), +80°C (C)
Moisture resistance	Excellent
Chemical resistance	Excellent
Dielectric strength	Exceptional
Reworkability	Poor (abrasive removal only)

Advantages of Type XY coatings:

• Truly conformal—coats all surfaces uniformly
• Pinhole-free at thin film thickness
• Excellent barrier properties
• No liquid handling or mixing
• Consistent thickness control
• Penetrates tight spaces

Limitations of Type XY coatings:

• Expensive equipment required
• Batch process (not inline)
• Difficult to mask
• Cannot be reworked conventionally
• Higher per-unit cost
• Requires specialized application facility

Typical applications: Medical implants, aerospace sensors, high-reliability military electronics, MEMS devices, hybrid circuits.

MIL-I-46058C Coating Type Comparison

Property	AR (Acrylic)	ER (Epoxy)	SR (Silicone)	UR (Urethane)	XY (Parylene)
Moisture resistance	Good	Excellent	Excellent	Excellent	Excellent
Chemical resistance	Fair	Excellent	Good	Very good	Excellent
Abrasion resistance	Fair	Excellent	Fair	Good	Fair
Temperature range	-65/+125°C	-65/+125°C	-65/+200°C	-65/+125°C	-65/+125°C
Flexibility	Good	Poor	Excellent	Good	Good
Reworkability	Excellent	Poor	Moderate	Moderate	Poor
Cure time	Fast	Moderate	Slow-moderate	Slow	N/A
Relative cost	Low	Moderate	High	Moderate	Very high
Typical thickness	25-75 µm	25-125 µm	50-200 µm	25-75 µm	5-25 µm

MIL-I-46058C Testing Requirements

The specification established testing protocols to verify coating performance. These tests remain relevant for evaluating conformal coating quality.

Qualification Testing

Test	Method	Purpose
Insulation resistance	MIL-I-46058C para 4.6.3	Verify dielectric properties
Dielectric withstanding voltage	MIL-I-46058C para 4.6.4	Breakdown voltage verification
Moisture resistance	MIL-STD-202 Method 106	Humidity exposure performance
Thermal shock	MIL-STD-202 Method 107	Temperature cycling survival
Flexibility	MIL-I-46058C para 4.6.7	Coating integrity under stress
Fungus resistance	MIL-STD-810 Method 508	Biological resistance
Flammability	UL 94 or equivalent	Fire safety compliance
Salt spray	MIL-STD-202 Method 101	Corrosion protection

Insulation Resistance Requirements

Condition	Minimum Requirement
Initial (as received)	1.0 × 10¹⁴ ohms
After humidity exposure	1.0 × 10¹⁰ ohms
After thermal shock	1.0 × 10¹¹ ohms

Moisture Resistance Test Conditions

Parameter	Specification
Temperature	65°C ± 2°C
Relative humidity	90-95%
Duration	10 cycles (24 hours each)
Voltage applied	50V DC (optional)

Thermal Shock Requirements

Parameter	Specification
Cold temperature	-65°C ± 3°C
Hot temperature	+125°C ± 3°C
Dwell time	30 minutes minimum
Transfer time	≤5 minutes
Number of cycles	5 minimum

MIL-I-46058C Application Methods

Proper application is critical to achieving the protection conformal coatings are designed to provide.

Application Techniques

Method	Advantages	Limitations	Best For
Spray	Fast, good coverage	Overspray waste, masking required	High volume production
Brush	Low equipment cost, selective	Inconsistent thickness, slow	Touch-up, small lots
Dip	Uniform coverage, efficient	Complete immersion required	High volume, simple boards
Selective	Precise application	Equipment cost	Complex assemblies
Vapor deposition	Pinhole-free, conformal	High cost, batch process	Parylene only

Thickness Requirements per MIL-I-46058C

Coating Type	Minimum Thickness	Maximum Thickness
AR (Acrylic)	0.03 mm (1.2 mil)	0.13 mm (5 mil)
ER (Epoxy)	0.03 mm (1.2 mil)	0.13 mm (5 mil)
SR (Silicone)	0.05 mm (2 mil)	0.21 mm (8 mil)
UR (Urethane)	0.03 mm (1.2 mil)	0.13 mm (5 mil)
XY (Parylene)	0.01 mm (0.4 mil)	0.05 mm (2 mil)

Surface Preparation Requirements

Proper surface preparation is essential for coating adhesion:

Step	Purpose	Method
Cleaning	Remove contaminants	Solvent wash, aqueous cleaning
Drying	Remove moisture	Baking at 65-125°C
Flux removal	Eliminate ionic contamination	Per IPC-A-610 requirements
Inspection	Verify cleanliness	Visual, ionic testing
Masking	Protect no-coat areas	Tape, liquid maskant, boots

Areas Typically Masked (No-Coat)

Component/Area	Reason
Connectors	Prevent mating issues
Test points	Allow electrical access
Switches/potentiometers	Maintain adjustability
Heat sinks	Prevent thermal insulation
RF shields	Maintain ground contact
LED lenses	Maintain optical clarity
Batteries	Prevent damage/swelling
Socketed components	Allow replacement

MIL-I-46058C Inspection Requirements

Visual inspection is the primary method for verifying conformal coating quality.

Acceptance Criteria

Condition	Acceptable	Rejectable
Coverage	Complete over specified areas	Bare spots, holidays
Thickness	Within specification range	Too thin or too thick
Adhesion	No delamination or lifting	Peeling, flaking
Bubbles	≤3 per cm², ≤0.75mm diameter	Large or excessive bubbles
Foreign material	None visible	Embedded particles
Orange peel	Minor acceptable	Severe texture variation
Dewetting	Minor acceptable	Significant pullback
Cracks	None	Any visible cracking

Inspection Methods

Method	What It Detects
Visual (white light)	General defects, coverage
UV/fluorescent	Coating presence, thin areas
Cross-section	Thickness, adhesion, structure
Ionic contamination	Under-coating cleanliness
Adhesion test	Bond strength
Thickness measurement	Coating depth

Selecting the Right MIL-I-46058C Coating Type

Coating selection depends on application requirements, environmental conditions, and manufacturing constraints.

Selection Matrix by Environment

Environment	Recommended Types	Avoid
High humidity	UR, XY	—
Chemical exposure	ER, UR, XY	AR
High temperature (>125°C)	SR	AR, ER, UR
Thermal cycling	SR, AR	ER
Outdoor/UV exposure	SR, ER	AR (some), UR
Immersion	ER, XY	AR
Salt spray/marine	ER, UR, XY	AR
Vibration	SR, AR	ER
Medical implant	XY	AR, ER

Selection Matrix by Manufacturing Needs

Requirement	Recommended Types	Avoid
Fast production	AR	SR, UR (moisture cure)
Frequent rework	AR	ER, XY
Low cost	AR	XY
Room temperature cure	AR	ER (some)
Thick coating needed	SR	XY
Ultra-thin coating	XY	SR
In-house application	AR, ER, UR	XY

Decision Flowchart Considerations

When selecting a coating type, consider these questions in order:

1. Temperature range: Does the application exceed +125°C? → Consider SR
2. Chemical exposure: Will the assembly contact solvents or fuels? → Consider ER, UR
3. Rework expected: Will components need replacement? → Consider AR
4. Coverage criticality: Are pinholes absolutely unacceptable? → Consider XY
5. Budget constraints: Is cost a primary driver? → Consider AR
6. Production volume: High volume with fast turnaround? → Consider AR

MIL-I-46058C and Modern Standards

Understanding how MIL-I-46058C relates to current specifications helps navigate requirements.

Standards Relationship

Standard	Relationship to MIL-I-46058C
IPC-CC-830	Direct replacement/successor
IPC-A-610	Workmanship acceptance criteria
IPC J-STD-001	Soldering and coating requirements
IPC-HDBK-830	Application guidelines
MIL-STD-202	Test methods reference
NASA-STD-8739.1	NASA workmanship standard

Transitioning from MIL-I-46058C to IPC-CC-830

Aspect	MIL-I-46058C	IPC-CC-830
Coating designations	Same (AR, ER, SR, UR, XY)	Same designations
Qualification	QPL required	Manufacturer certification
Test methods	MIL-I-46058C specific	IPC/ASTM/ISO referenced
Thickness specs	Identical ranges	Identical ranges
Updates	Frozen (canceled)	Periodically revised

For new designs, specify IPC-CC-830 rather than the canceled MIL-I-46058C. However, recognize that many coating products are qualified to both standards.

Practical Coating Application Tips

From experience applying and inspecting conformal coatings on military assemblies, here are lessons learned:

Common Application Problems

Problem	Cause	Solution
Pinholes	Contamination, air entrapment	Better cleaning, degas coating
Bubbles	Too thick, solvent entrapment	Multiple thin coats, slower cure
Orange peel	Wrong viscosity, distance	Adjust spray parameters
Dewetting	Surface contamination	Improve cleaning, use primer
Cracking	Too thick, thermal stress	Reduce thickness, flex coating
Poor adhesion	Contamination, incompatibility	Clean surface, verify compatibility
Incomplete coverage	Shadowing, access issues	Multiple angles, selective touch-up

Best Practices

Before coating:

• Verify cleanliness with ionic contamination testing
• Ensure all flux residues are removed
• Pre-bake assemblies to remove moisture
• Apply masking carefully with no gaps
• Verify coating is within pot life

During coating:

• Apply multiple thin coats rather than one thick coat
• Allow flash-off time between coats
• Maintain consistent spray distance and overlap
• Inspect under UV light after each coat (if fluorescent coating)
• Document batch, date, and application parameters

After coating:

• Follow cure schedule exactly
• Don’t handle until fully cured
• Inspect under both white light and UV
• Measure thickness on coupons or non-critical areas
• Document inspection results

Useful MIL-I-46058C Resources

Government and Industry Resources

Resource	URL	Description
IPC	https://www.ipc.org/	IPC-CC-830 and related standards
DLA ASSIST	https://quicksearch.dla.mil/	Military specifications database
GIDEP	https://www.gidep.org/	Problem alerts
NASA Technical Standards	https://standards.nasa.gov/	NASA workmanship requirements

Related Specifications

Document	Description
MIL-I-46058C	Original military conformal coating spec (canceled)
IPC-CC-830	Current conformal coating qualification standard
IPC-A-610	Acceptability of electronic assemblies
IPC J-STD-001	Requirements for soldered electrical assemblies
IPC-HDBK-830	Conformal coating handbook
MIL-STD-202	Test methods for electronic components

Coating Manufacturer Resources

Manufacturer	Product Lines
Dow (formerly Dow Corning)	Silicone coatings
Henkel (Loctite)	Multiple coating types
HumiSeal (Chase Corp)	Full range of coatings
MG Chemicals	Acrylic, urethane, silicone
Specialty Coating Systems	Parylene
Electrolube	Full range of coatings
Peters	European coating supplier

MIL-I-46058C FAQs

Is MIL-I-46058C still valid for military contracts?

MIL-I-46058C was officially canceled by the DLA in 1998 and replaced by IPC-CC-830. However, many active military programs still reference MIL-I-46058C in their technical data packages because changing qualified materials requires significant effort. If your contract calls out MIL-I-46058C, you should use coatings qualified to that specification—many manufacturers maintain MIL-I-46058C qualification alongside IPC-CC-830. For new program development, specify IPC-CC-830 to use current standards. If you’re working on a legacy program, check whether a specification update has been issued; some programs have transitioned to IPC-CC-830 through engineering change proposals.

What is the difference between MIL-I-46058C Types AR, ER, SR, UR, and XY?

These designations indicate the coating’s base chemistry: AR is acrylic resin (easy to rework, fast cure, but limited chemical resistance), ER is epoxy resin (excellent chemical resistance but nearly impossible to rework), SR is silicone resin (widest temperature range, excellent flexibility, but higher cost), UR is polyurethane resin (good balance of properties with moderate reworkability), and XY is parylene (vapor deposited, pinhole-free, but requires specialized equipment). Selection depends on your operating environment, rework requirements, and manufacturing constraints. Most general military applications use Type AR for its ease of application and rework capability, while harsh environments requiring chemical resistance typically call for Type ER or UR.

How thick should conformal coating be applied per MIL-I-46058C?

MIL-I-46058C specifies thickness ranges by coating type: Type AR, ER, and UR require 0.03-0.13mm (1.2-5 mils); Type SR requires 0.05-0.21mm (2-8 mils); and Type XY requires 0.01-0.05mm (0.4-2 mils). Too thin provides inadequate protection, while too thick causes cracking, traps solvents, and extends cure time. For most applications, target the middle of the specification range. Apply multiple thin coats rather than one thick coat to avoid bubbles and ensure proper cure. Measure thickness using calibrated gauges on test coupons processed with production boards, or use non-contact measurement methods on actual assemblies.

Can conformal coatings be removed for rework?

Removal capability varies dramatically by coating type. Type AR (acrylic) is the easiest to remove—solvents like isopropyl alcohol or commercial acrylic strippers dissolve the coating quickly. Type UR (urethane) can be softened with specialized solvents but requires more effort. Type SR (silicone) requires specific silicone solvents and mechanical action. Type ER (epoxy) and Type XY (parylene) are essentially non-removable by chemical means—rework requires burning through the coating with a soldering iron or abrasive removal. When selecting coating type for assemblies that may require component replacement, Type AR’s reworkability is a significant advantage despite its lower chemical resistance. Always plan your rework strategy before selecting coating type.

How do I verify conformal coating coverage and quality?

Inspection typically combines visual examination under white light and UV light (for fluorescent coatings). White light inspection identifies obvious defects like bubbles, cracks, and foreign material. UV inspection reveals thin spots, holidays, and coverage boundaries that might be invisible under white light—most MIL-I-46058C-qualified coatings contain UV-fluorescent additives for this purpose. Thickness can be measured destructively by cross-sectioning test coupons, or non-destructively using calibrated coating thickness gauges. For critical applications, perform adhesion testing per tape pull methods and verify insulation resistance meets specification requirements. Document all inspection results and retain samples for reference.

Final Thoughts on MIL-I-46058C Conformal Coatings

Conformal coating seems straightforward until you encounter a field failure caused by inadequate protection or an improper coating selection. MIL-I-46058C established a framework for protecting military electronics that remains technically sound decades after the specification’s cancellation.

Key takeaways for working with conformal coatings:

Match coating to environment. Don’t default to Type AR just because it’s easy. If your application involves chemical exposure or extreme temperatures, invest in the right coating type.

Surface preparation matters. The best coating can’t protect a contaminated surface. Clean thoroughly and verify cleanliness before coating.

Follow thickness specifications. More isn’t better. Excessive thickness causes problems that thin coating won’t.

Plan for rework. If components will need replacement, factor reworkability into your coating selection.

Document everything. Record coating type, batch number, application date, cure schedule, and inspection results. You’ll need this data when questions arise.

Whether you’re working with the original MIL-I-46058C specification on a legacy program or transitioning to IPC-CC-830 for new designs, understanding conformal coating fundamentals ensures your electronics survive the environments they’ll face in service.