1

What is a Conformal Coating?

printed circuit board PCB with corrosion without conformal coating

A conformal coating is a thin barrier film that is applied onto printed circuit board assemblies (PCBAs) for effective environmental protection against damage such as corrosion. Conformal coatings ‘conform’ to the shape of the board and underlying components, providing excellent coverage of delicate circuitries. Selecting the right conformal coating for your application can help eliminate warranty claims and improve or even extend functionality.

2

Why Do I Need a Conformal Coating?

Children playing in sea with camera that has waterproof parylene protection

Conformal coatings help manufacturers meet the demand for reliable, take-anywhere products that customers have come to depend on. Product designers use conformal coatings to impact customer satisfaction by producing dependable products that can be trusted to work in different types of environments.

Benefits of Conformal Coatings

  • Improve product reliability
  • Increase performance life
  • Extend use-environments
  • Minimize PCB spacing
  • Eliminate bulky enclosures
  • Reduce warranty claims

Reliability Case Study Comparison Automotive Receiver Board

Cost to apply conformal coating:

100mm x 150mm = 1.5cm3

Coating materials = $0.12

Labor to apply =$0.25

Approximate total: $0.37/board

Average direct cost of failure:

1 field failure = $270 to replace the receiver ($180 receiver board + $90 labor)

Summary: The cost to add a conformal coating for all parts is equivalent to having a field failure in 1 out of every 730 boards (0.1%).

Direct cost does not consider the impact of field failures on customer relationships & brand equity.

Common Application Challenges by Industry

IndustryChallenges to circuit board performance
AutomotiveGasoline, engine/brake fluids, temperature cycles
IndustrialWater, humidity, detergents, chemicals
MilitaryDust, abrasion, temperature, chemicals
AerospaceTemperature, pressurization/depressurization cycles; fluid/moisture resistance
MedicalFluid/moisture resistance; critical need for continuous performance
3

What are the Major Types of Conformal Coatings?

Conformal Coating Comparison Chart

The right conformal coating meets all the operational requirements for your application, reliably and consistently. There are several conformal coatings to choose from, each with distinct advantages for different applications. Below, we compare the various conformal coatings and their unique attributes.

Conformal Coating Comparison Chart parylene silicone epoxy urethane acrylic

Advantages & Disadvantages for Each Coating Type

Acrylic Conformal Coating

Acrylic conformal coatings are considered basic entry-level protection, due to their low cost and protection against a broad-level of contamination, but not best-in-class for any attribute. What generally distinguishes acrylic coatings from other conformal coatings is ease of removal. This makes rework and even field repair very practical and economical. On the other hand, this also means that acrylic coatings offer very weak solvent protection.

AdvantagesDisadvantages
  • Ease of application
  • Best for basic level protection
  • Ease of removal for field repair
  • Poor chemical resistance
  • High VOC potential
  • Difficult to maintain coating viscosity

Silicone Conformal Coating

Silicone conformal coatings offer excellent protection against temperature extremes and cycles. Silicone coatings are also often used in high humidity environments, like outdoor signage and offer good moisture, chemical and salt spray resistance. Though resilient against vibrational stresses, silicone coatings offer poor abrasion protection due to its rubbery, tacky nature.

AdvantagesDisadvantages
  • Excellent for extreme temps and cycling
  • Good humidity resistance
  • Flexible, resilient coating
  • Vibration dampening
  • Material tackiness create potential for contamination with other processes
  • Low abrasion resistance
  • Requires curing

Urethane Conformal Coating

Urethane conformal coatings are best suited for rugged and extreme chemical conditions. These coatings offer affordability due to low material costs and flexibility of application methods. However, very long cure times and/or additional equipment to improve cure times can quickly increase total coating costs.

AdvantagesDisadvantages
  • Very good dielectric properties
  • Excellent chemical resistance
  • Excellent abrasion resistance
  • Long cure times common (up to 30 days)
  • Expedited curing requires additional equipment
  • Typically thicker, less uniform coatings

Epoxy Conformal Coating

Epoxy Conformal Coatings are hard, rigid coatings known for their excellent resistance to mechanical wear. Available as two‐part mixtures, epoxy coatings also offer very good chemical and moisture protection from harsh environments. Epoxy coatings are not recommended where temperature extremes and/or excessive vibration is likely as failure can result via shrinking and cracking.

AdvantagesDisadvantages
  • Excellent abrasion resistance
  • Very good chemical resistance
  • Good moisture protection
  • Can crack or shrink, causing stress on components
  • Difficult to maintain viscosity, complex mix ratios
  • Requires curing

Parylene Conformal Coating

Parylene conformal coatings are ultra-thin, thermoplastic film coatings that provide best-in-class protection against solvents, extreme temperatures and moisture. Considered the gold standard for reliability among conformal coatings, it is often used in applications where failure, field repair or costly warranty claims are not a practical option.

AdvantagesDisadvantages
  • Excellent waterproof protection
  • Extreme chemical resistance
  • Outstanding dielectric properties
  • Uniform coverage with no pinholing
  • Vapor deposition only method for application
  • Requires specialized equipment
  • Batch processing
4

How are Conformal Coatings Applied?

Printed circuit board PCB with circuitry diagram for parylene conformal coating

Even the best conformal coating, if it is applied incorrectly will provide inadequate levels of protection. Therefore, ensuring the right coating method is used is critical to the level of protection that you can expect from your conformal coating.

How a Conformal Coating is Applied Depends Mainly On:

Production throughput requirements: The prep work needed, the speed of the coating process, and how quickly the boards can be handled after the coating process.

Board design requirements: Connector laden designs, solvent sensitive components, and other issues impact your decision.

Equipment requirements: If a coating is only sporadically required, tying up capital and floor space with additional equipment may not make sense.

Pre-coating processing: Some processes require masking or taping before coating.

Quality requirements: Critical electronics that require a high degree of repeatability and reliability will generally move you to more automated application methods.

Conformal Coating Application Methods

AcrylicUrethaneEpoxySiliconeParylene
Application MethodBrush, Dispense, SprayBrush, Dispense, SprayBrush, Dispense, SprayBrush, Dispense, Spray, DipcoatVapor Deposition
Curing RequiredYesYesYesYesNo

Advantages & Disadvantages for Each Coating Method

Brush onDip CoatSprayingDispensingVapor Deposition
CoveragePoor/InconsistentFairPoor/InconsistentVery GoodExcellent
VolumeLowModerateLowHighModerate
SpeedSlowModerateSlowFastModerate
LaborIntensiveIntensiveIntensiveLightModerate
CostLow to ModerateLowLowModerate to HighLow to High

Brushing

Brushing is the simplest method of applying conformal coatings. Brushing is utilized mainly in repair and rework situations, where specific coating areas can be spot treated. It is a low cost but slow, labor intensive and highly variable process best suited for small production runs.

AdvantagesDisadvantages
  • Low capital investment/ unit cost
  • No masking required
  • Good for rework or touch ups
  • Low throughput
  • Least uniform coating and coverage
  • Difficult to control voids and bubbles
  • Quality is operator dependent

Spraying

Manual spraying is applied via an aerosol can or handheld spray gun. It is generally used for low volume production when capital equipment is not available. This method can be time-consuming because areas not requiring coating need to be masked. It is also operator dependent, so variations are common from board to board.

AdvantagesDisadvantages
  • Low capital investment/ unit cost
  • Simple process
  • Can coat complicated board design
  • Low throughput
  • Less uniform coating and coverage
  • Hard to contain overspray, more waste/emissions
  • May require multiple coat/cure cycles to reach desired coating
  • Masking required

Dispensing

Automated dispensing is an aerosol process that uses programmable robotic spray nozzles to apply the conformal coating to very specific areas on the circuit board. This method reduces the need for masking and produces more consistent coating at higher production volumes.

AdvantagesDisadvantages
  • High Throughput
  • Better, uniform coating and coverage
  • Minimal masking required
  • Capital investment required or increased unit cost
  • Programming and process maintenance required

Dip Coating

In dip coating, the entire circuit board is dipped into a vat of coating material, withdrawn and then allowed to dry. It is the fastest application method for high volume processing but can only be done with coatings of a lower viscosity, such as acrylic. Masking is required.

AdvantagesDisadvantages
  • High Throughput
  • Better, uniform coating and coverage
  • Manual or automated process
  • Application limited to low viscosity coatings.
  • Ambient conditions impact coating quality (temperature, humidity)
  • Boards with specific coating area requirements not applicable
  • Masking required

Vapor Deposition

Vapor deposition vaporizes the conformal coating into a mist which then deposits on the circuit board as a thin, ultra-protective film. As a batch production method, vapor deposition produces outstandingly consistent coating at moderate to high volume production runs. Masking is generally required.

AdvantagesDisadvantages
  • Moderate to high throughput
  • Best, uniform coating and coverage
  • Protection achieved with ultra thin coating thickness
  • Applied at room temp (no thermal stress)
  • Does not require curing
  • Requires specialized equipment
  • Batch production
  • Masking required
5

Selecting the Right Conformal Coating

Simplified Selection Criteria for Conformal Coatings

conformal coating selection chart parylene acrylic silicone urethane epoxy

Tying it All Together

Clearly, there are many factors to consider when deciding on the right conformal coating for your application. Each conformal coating material – acrylic, urethane, epoxy, silicone and parylene – provides a unique mix of overall benefits. Some coatings provide excellent moisture protection while others perform well in high heat or fluctuating temperature situations. Further yet, some coatings are better suited for on-the-spot field repair while others eliminate the need for field repair in the first place. In the end, the right coating is simply the one that works without failure.

The right coating answers yes to the following three questions:

  1. Is the coating effective at reliably protecting my PCB?
  2. Does the coating method fit into my production process?
  3. Is the process consistent, repeatable and scalable?

Getting Started

Looking for specific help on your current application? The single best way to ensure you make the proper decision is to schedule a complimentary consultation with a VSi Parylene expert. An experienced parylene coating specialist will meet with you and examine your production goals and supply chain activity to choose the best option for your application.

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