Five important facts about silicone conformal coatings

  1. Silicone (SR) conformal coatings are inorganic materials. They are polymers in which atoms of silicon and oxygen alternate in a chain. They differ to the organic polymers like the acrylics and urethanes.
  2. The silicone coatings normally have a very wide temperature range of operation compared to the other conformal coatings. Typical range can be -55°C to +200°C (-67°F to +392°F). Like the organic coatings (acrylics and urethanes) they have good moisture protection. They also have good chemical resistance to polar solvents.
  3. SR coatings are generally applied at 2-3 times the thickness dry film compared to organic coatings. This is reflected in the IPC standards on the recommended conformal coating thickness. This increase in material use can lead to increased costs but also better water repellency properties.
  4. Curing of silicones occurs through several different mechanisms, depending on the conformal coating, including RTV (Room Temperature Vulcanisation), Heat, UV, Moisture / Condensation and Catalysed Cure.
  5. In production they can be difficult materials to use due to the cure mechanism being difficult to control. Good housekeeping can minimise these effects. SR coatings can also require different coating equipment or options compared to the organic coatings. This should be considered as part of the holistic approach to conformal coating selection.

The different conformal coating material properties

Conformal coatings can be considered in many different ways.

This includes the different families of materials, their individual properties and the chemistries of these coatings.

The different ways we can examine conformal coatings include:

  • Classification
  • Physical Properties
  • Electrical Properties
  • Chemistry

There is a vast range of options and considerations available.

Click conformal coating material properties to gain a deeper knowledge of conformal coatings.


Need to find out more?

Click silicone conformal coatings for further information or contact us directly and we can help you.

If you are new to Nexus and our work on conformal coatings then a good place to go is our Start Here page or our free conformal coating eBook.

Five key facts about plasma cleaning for conformal coating processing

  1. Plasma cleaning can clean surfaces of the circuit board 100% to improve adhesion and surface energy of the product. Generally, conformal coatings must exhibit good adhesion in order to be effective.
  2. There is no single theory that describes the property of adhesion for coatings. There are several basic mechanisms for coatings that are known to define good adhesion. They are adsorption, chemical bonding, and mechanical interlocking:
  • Adsorption is where the molecules in the conformal coating wet or flow freely over the substrate and make intimate contact with the substrate. This forms interfacial (electrostatic) bonds with van-der-Waal forces.
  • Chemical bonds are formed at the interface between the conformal coating and the substrate.
  • The conformal coating film penetrates the roughness on the substrate surface. This results in mechanical interlocking once the coating dries.

All three of mechanisms do not have to occur to form good adhesion. Depending on the specific conformal coating system, substrate, and application method, different mechanisms could work. However, good wetting or adsorption is normally required.

  1. Many wet chemistry cleaning processes can be eliminated. Methods using cleaning chemistries, water processing and drying energy become unnecessary.
  2. The significant improvement in adhesion enables the use of alternative conformal coatings and other chemical vapour deposition coatings (CVD) that may have difficulty adhering to circuit boards without the treatment.
  3. The plasma cleaning process is a simple, safe and environmentally friendly technology.

Plasmatreatment of circuits collage

Plasma cleaning can clean surfaces of the circuit board 100% to improve adhesion and surface energy of the product. Generally, conformal coatings must exhibit good adhesion in order to be effective.

 


Need to find out more?

For further information on plasma cleaning for conformal coating processing then contact us directly.

If you are new to Nexus and our work on conformal coatings then a good place to go is our Start Here page or our free conformal coating ebook.

 

What is Molecular Vapour Deposition (MVD)?

Nexus has been examining a novel coating technique that may be able to meet all of the environmental demands for circuit board protection and actually be cost-effective.

This process is Molecular Vapour Deposition (MVD) and is brand new to the electronics coating market.

MVD is a hybrid coating technique using ALD (Atomic Layer Deposition) and CVD (Chemical Vapor Deposition) coating processes in combination.

This method uses multiple layers of ultra-thin coatings with differing properties to build a completely protective coating.

The final coating built up is much thinner than the other traditional coatings including Parylene. However, its protective performance has been found to be superior to them all in most categories of testing so far.

Further, the really exciting part about this technology is the cost of processing.

Since the coating is extremely thin then it has been found that no masking is required.

This is because when components like connectors are joined together then the ultrathin coating does not prevent electrical connection. Even better, the physical protection is not compromised.

This means that the cost of process is purely the cost of application of the material and nothing else.

Since the process is relatively low cost then this does offer a very interesting alternative to the traditional coating materials.

Does MVD sound complex?

Actually, although the technology and chemistry can be a little complex the process itself is fairly simple.

Once the process is set up in the machine the operator just loads, switches the machine on and unloads on completion.

This is a far cry from the sophisticated processes of robotic selective coating or the challenges of Parylene. Further, the process is actually very stable and in reality is tried and test in other industries.

So what does a MVD film look like?

The film is built up of alternating layers of ALD and CVD thin coating layers. The ALD is a ceramic-based material providing the insulating properties and the CVD film provides the barrier protection.

Once the required film thickness is achieved then a final hydrophobic layer is applied that combines with the ALD and CVD layers to provide a highly effective barrier.

Description of Hybrid ALD_CVD Technology

Label: The film is built up of alternating layers of ALD and CVD thin coating layers. The ALD is a ceramic-based material and the CVD film is an organic layer.

So how well did the MVD coating perform when protecting circuit boards?

Data was recently presented at Apex in Sand Diego looking at live LED circuits from a customer.

The customer LED product was for outdoor application. For testing, the customer used in-house test methods to prove the technology.

The LED circuit was exposed to customer tests for resistance against salt, moisture and temperature.

The test methods included:

  • Initial test submerged in DI water dip for 12 hours
  • Second test submerged in 25% concentration saltwater dip for 17 hours
  • Third test 2 x 6 hour cycles in water ramped from room temperature to 70°C

After each test the boards were tested for failure or problems.

The LED circuit passed on all tests. All results achieved were completed with no masking of components and zero light loss in LED opacity.

The electrical connections were found to be excellent and the coating did not affect the integrity of the connectors.

So what about the cost of process for MVD?

Since the process is masking and de-masking free then the cost per unit is incredibly low. The performance is also superior to nearly all the traditional methods of coating protection.

Further, the protective properties of the MVD coating in nearly all cases is superior to the conventional methods.

So, you get a lower cost coating with a higher technical performance.

So, just how good is the MVD coating as a protective material for electronics?

Generally, with protective coatings for electronics then Parylene is considered the gold standard in most cases.

So, we compared Parylene with the MVD coating material.

Property Parylene MVD
Hardness Soft Hard
Wear resistance/Handling Ease Poor Excellent
Water Vapor Transmission Rate Good Excellent
Temperature Resistance (extended time) 100°C 350°C
Color Gray/white Clear
Adhesion to various materials Poor Excellent
Scalable to large production Poor Excellent
Process Time 8 – 12 hrs 8 – 12 hrs
Hydrophobicity Good Good – Excellent
Cost High Low – Med

What we also identified for the material were some key properties for LEDs.

  • The Water Vapor Transmission Rate (WVTR) is superior to Parylene so the coating is far more waterproof for the LEDs
  • Coating adhesion is superior as it covalently bonds to the substrate. So, the lifetime of the material will be better on the circuit.
  • The hybrid coating is UV stable whereas Parylene in general is not. This is an important criteria for coatings exposed outside on LEDs
  • The coating stayed 100% transparent during testing (no loss of lux). That again is important for LEDs.
  • The coating thickness of the hybrid material is x10 LESS than the Parylene. This aids light transmission and electric connectivity

So, in reality the MVD material could just be what the high volume electronics industry is looking for in protecting their circuits.


Need to find out more?

For further information on Molecular Vapour Deposition (MVD) then contact us directly.

If you are new to Nexus and our work on conformal coatings then a good place to go is our Start Here page or our free conformal coating ebook.

 

What are the important physical properties of a conformal coating material?

When thinking about a conformal coating’s physical properties then I always consider that there are three states.

They are the properties during the:

  • Liquid Stage (When the conformal coating is a liquid ready for production).
  • Process Stage (During the conformal coating process).
  • Dry Stage (When the conformal coating has dried and or cured).

The key properties will vary depending on which state you are looking for.

For example, for the liquid state the critical properties for the conformal coating  include:

  • Flash point
  • Storage lifetime
  • Appearance and colour
  • Density
  • Solids content
  • Viscosity

These properties are important for the conformal coating process and completely influence the outcome of the production line.

However, for the process state the critical properties the conformal coating exhibits include:

  • Wetting
  • Capillary
  • Viscosity
  • Wet Film Thickness
  • Surface Tension
  • Pot life
  • Drying and curing

These properties of the conformal coating material will again influence the final outcome.

Finally, for the dry state the critical properties of the conformal coating include:

  • Abrasion Resistance
  • Chemical Compatibility and Resistance
  • Coefficient of Thermal Expansion
  • Corrosion Resistance
  • Edge Loss
  • Flammability
  • Flexibility
  • Fungus Resistance
  • Glass Transition Temperature
  • Hydrolysis Stability
  • Outgassing
  • Permeability
  • Refractive Index
  • Temperature Gradient
  • Thermal Shock
  • Thermal Stability
  • UV Stability

Note, there are a lot of physical properties but many not be important to you.

Also, most of these physical properties may be defined by the manufacturer and contained on a data sheet.

However, many other properties may be required and you may need to test.

To find out more click key physical states for conformal coating.

Or Contact Nexus now and let us show you how we can help you.


Dr Lee Hitchens, Author of Nexus website and ebook

Dr Lee Hitchens is the Author of the Nexus eBook and a main contributor to Nexus.

How are conformal coating materials classified?

I am asked quite often about conformal coating classification. The reality is conformal coatings can be classified in many ways.

However, the IPC do a great job of splitting out the various subdivisions.

They include:

  • Liquid or vapour deposition materials
  • Organic or inorganic coatings
  • The resin types (AR, UR, SR, XY, FC)
  • Drying and curing mechanisms
  • One or two part materials
  • Solvent or non-solvent based

A typical family tree for conformal coatings is shown below:

Conformal coatings can be categorised by many different factors including inorganic
Conformal coatings can be categorised by many different factors

To find out more click conformal coating materials classification.


Need help with your conformal coating process?

Contact Nexus now and let us show you how we can help you.


Dr Lee Hitchens, Author of Nexus website and ebook

Dr Lee Hitchens is the Author of the Nexus eBook and a main contributor to Nexus.

 

 

Our five most popular areas in the Nexus conformal coating eBook

People come to the Nexus eBook for several reasons.

Looking at our visitor statistics most people go to the following five sections:

  1. Designing for conformal coating
  2. Troubleshooting your conformal coating process
  3. The basics of conformal coating
  4. Conformal coating removal
  5. How to select a conformal coating material

Click on each to find out more about the five most popular conformal coating areas.

How to avoid de-wetting of conformal coating

De-wetting is the where the conformal coating material refuses to wet the surface of the circuit board that it has been applied to in an even way. The coating ends up being patchy.

The de-wetting effect tends to act locally due to local contamination.But, it can be a global affect right across the board.

 

OLYMPUS DIGITAL CAMERA
De-wetting of the conformal coating can be localised or all over the circuit board.

There are many causes of De-wetting in Conformal Coating.

These include contaminants such as residues and oils, and processes such as soldering and cleaning.

To find out more click conformal coating de-wetting.

Need help with your process?

Contact us at Nexus and we can help solve your issues.

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