Why are polyurethane conformal coatings used for protecting electronic circuit boards and in which sectors?

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The majority of conformal coatings used in the world to protect electronic circuit boards are made from organic based resins.

These organic conformal coatings can be further subdivided into resin types such as

  • Acrylic
  • Polyurethane
  • Epoxy
  • Acrylic urethane blends

Although the majority of conformal coatings being used in this group are acrylic materials there is a considerable amount of coatings made from polyurethane.

Solvent based acrylic conformal coatings have been historically the number one choice for moisture protection of printed circuit boards and they provide excellent humidity resistance.

They also dry quicker than nearly all the other conformal coating types, they are easy to use in production and are easily repaired.

However, acrylic conformal coatings have very little chemical resistance. So, they are poor at protecting circuit boards in harsh chemical environments.

This is where polyurethane conformal coatings are considered.


Using polyurethane conformal coatings to protect against chemical attack

OLYMPUS DIGITAL CAMERA

Polyurethane (UR) coatings also provide good humidity & moisture protection compared to acrylic materials.

But, what is key to their selection as a protective conformal coating is that they also offer excellent chemical resistance to the circuit board.

The reason for this is that UR coatings cure rather than dry. That is they cross-link once applied to the circuit board by one of the many methods including solvent evaporation (initial stages), heat, UV, moisture and catalysed cure.

This cross-linking of the polymer chain provides the chemical resistance for which the UR coatings are generally selected.

This makes them excellent conformal coatings where the chemical attack is a potential hazard for the electronic circuit boards. This includes sectors such as aerospace, military and industrial sectors plus other diverse areas such as medical and commercial electronics.


Need to find out more?

Find out more about using polyurethane conformal coatings to protect printed circuit boards in a chemical environment here 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.

The science behind Molecular vapour deposition (MVD) in protecting circuit boards

Nexus has been examining a new, novel technique that may be able to superior protection for electronic circuit boards compared to the standard coating methods like conformal coatings and Parylene but also actually be cost-effective.

This process is a hybrid ALD (Atomic Layer Deposition)/CVD (Chemical Vapor Deposition) technique called Molecular Vapor Deposition (MVD).

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


So, why is this new coating so good compared to Parylene and other conformal coatings?

The final MVD 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.

Key performance indicators like Water Vapor Transmission Rate (WVTR), optical clarity, temperature resistance and hydrophobicity have been found to be much better than the other coatings.

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

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.

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.


So what does the science of Molecular Vapor Deposition coating (MVD) look like?

The actual 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. The CVD film provides the barrier protection.

First, an ALD layer is applied to the substrate. Then a CVD layer is applied. Then a further ALD layer is applied and so on.

This continues until the correct number of layers is built that has the right protection.

Description of Hybrid ALD_CVD Technology

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


So, just how good is the hybrid coating as a protective material for electronic circuit boards?

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

So, Nexus compared Parylene with the MVD material.

Property Parylene MVD Coating
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 Nexus also identified for the material were some key properties.

  • The Water Vapor Transmission Rate (WVTR) is superior to Parylene so the coating is far more waterproof.
  • Coating adhesion is superior as it covalently bonds to the substrate. So, the lifetime of the material will be better on the circuit.
  • The temperature range of the material can be up to 350C without any degradation.
  • The hybrid coating is UV stable whereas Parylene in general is not. This is an important criteria for coatings exposed to UV light.
  • The coating stayed 100% transparent during testing (no loss of lux).
  • 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 industries like the automotive and LED sectors are looking for in protecting their circuits where cost and protection abilities are critical.


Need to find out more?

Contact us directly and we can help you with this new material.

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 important facts about acrylic conformal coatings

conformal coated PCBs Collage 640x480_Nexus

The  majority of conformal coatings used in the world are organic coatings.

The acrylic conformal coatings are part of that group.

Here are five reasons to use acrylic conformal coatings:

  1. Acrylic conformal coatings have excellent humidity resistance. This is the number one use for using an acrylic conformal coating.
  2. Solvent based acrylic conformal coatings are one of the easiest materials to apply to printed circuit boards. They are easily applied using every method including spraying, dipping and brushing.
  3. Acrylic solvent-based coatings dry quicker than nearly all other types of coatings. They dry within minutes. This is because the acrylic resin does not polymerise (does not cure) and actually just dries out as the solvent evaporates away. They are also very easy to dry artificially using heat and can reach optimum properties very quickly.
  4. Acrylic coatings are very easy to repair and rework since they have very little chemical resistance. They are easily chemically removed and stripping a complete board is relatively straightforward.
  5. Finally, acrylic coatings have excellent pot life compared to many other types.

Need to find out more?

Click for further information on organic and acrylic conformal coatings 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.

 

What is Parylene?

Parylene is the trade name for a variety of chemical vapor deposited poly (p-xylylene) polymers used as moisture and dielectric barriers.

Although Parylene is a conformal coating it is different compared to the standard “wet” liquid conformal coatings in that it is deposited as a gas in a vacuum chamber and it is a dry process.

nexusphoto1Although Parylene is a conformal coating it is different compared to the standard “wet” liquid conformal coatings in that it is deposited as a gas in a vacuum chamber and it is a dry process. Image courtesy of Plasma Rugged Solutions

This method of chemical vapour deposition (CVD) and the Parylene dimer material itself give Parylene unique properties compared to other traditional conformal coatings.

For Parylene there are five key areas that Nexus can help with.

These are:


Need to find out more?

For further information on Parylene then contact us directly or go to our Parylene section in Nexus. See how 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.

 

Coating LEDs with a hybrid ALD / CVD Process

Coating LEDs to protect them is big business. The volume of manufactured LEDs globally is growing at an exponential rate and there is no end in sight.

However, the challenges to protect them are not small especially in an outdoor environment.

The LED circuits are placed in exposed areas and subjected to the full force of the elements. Then they are expected to survive for long periods of time.

Further, the protection placed on the circuits must not affect the light output of the LED (the lux) or cause heating problems due to thermal demands.

Finally, due to the low cost of the LED products in the first place then the protective method of coating and application has also to be extremely low in price.

Coatings LEDs
Due to the low cost of the LED products in the first place then the protective method of coating and application has also to be extremely low in price.

This final point can be the most challenging. After all protecting the LEDs is relatively easy with certain coating materials. Coating the unit for the right price is the key challenge.

This price challenge is due in most cases to the insulative properties of the majority of coatings applied. Nearly all of the traditional coating methods require components like connectors not to be coated since they would ruin the electronic properties of that component.

This leads either to masking of components in process or selective processing that leads to increased costs in prodution.

To provide a high level of protection whilst being low cost is not a trivial task for a coating. Processes like Parylene, conformal coatings, encapsulates and potting compounds continuously find it difficult to meet all of these criteria and customers are continuously compromised.


So, is there an alternative protective coating for LEDs besides Parylene, conformal coatings and encapsulates?

Nexus has been examining a new, novel technique that may be able to meet all of the environmental demands for LEDs and actually be cost-effective.

This process is a Hybrid ALD (Atomic Layer Deposition)/CVD (Chemical Vapor Deposition) technique.

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.


Sounds 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 hybrid ALD / CVD 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
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 hybrid coating perform in protecting LEDs?

Nexus actually worked with live LED circuits from a customer.

The customer LED product was for outdoor application. For testing the customer used their own 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 effect the integrity of the connectors.


So what about the cost of process?

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

Further, the protective properties of the hybrid 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 hybrid 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 hybrid ALD / CVD material.

Property Parylene ALD/CVD Coating
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 hybrid ALD / CVD material could just be what the LED industry is looking for in protecting their circuits. Nexus will let you know how the material performs on other types of circuits shortly.


Need to find out more?

If further information on these topics and the key question you can go to our free eBook by clicking conformal coating design now.

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


Dr Lee Hitchens, Author of Nexus

Dr Lee Hitchens, Author of Nexus website and ebook
Dr Lee Hitchens, Author of Nexus

Dr Lee Hitchens is the author of the Nexus conformal coating website and eBook.

Send me an email at lhitchens@nexus3c.com and let me know what you think?

 

What are Atomic Layer Deposition Coatings?

test-tubes low resAtomic Layer Deposition (ALD) belongs to the family of chemical vapor deposition methods (CVD).

It is a deposition process of a coating at a nano-scale level within a vacuum chamber.

The deposition process forms ultra-thin films (atomic layers) of coating with extremely reliable film thickness control.

This provides for highly conformal and dense films at extremely thin layers (1-100nm).

ALD is used in many different areas including:

  • Micro-electronics
  • Semiconductors
  • Photovoltaics
  • Biotechnology
  • biomedical
  • LEDs
  • Optics
  • Fuel cell systems

Find out more here by clicking what is atomic layer deposition?

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