Do you need mil spec qualification for your conformal coating?

1

The Mil Standard (MIL-I-46058C) is a US military conformal coating standard.

It has been inactive for new designs since November 1998.

However, the standard is still widely used for independent certification of conformal coatings.

This means that an independent test house will test the conformal coating. It is not self-certified.

All companies tested to the Mil standard are listed on a Qualified Product List (QPL).

Therefore, conformal coatings listed on the QPL will have been through rigorous 3rd party testing.

MIL-I-46058C is a guideline for quality. However, other standards like IPC-CC-830 may be equally relevant.


2

What is the role of a qualification or standard in conformal coating?

The role of a standard and qualifications is to give a guideline for users on the quality of a product.

For conformal coating standards and qualifications there are two areas that they cover.

These are:

  • Material manufacture
  • Production process

The conformal coating material manufacture standards are used for making the conformal coating.

They are only really relevant to suppliers so that they can measure their coating performance against a set of tests.

The conformal coating production standards are used for qualifying a process.

They are used in the production environment.


Need to find out more?

Click conformal coating standards 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 important facts about polyurethane (UR) conformal coatings

conformal coated PCBs Collage 640x480_NEXUS

  1. Polyurethane (UR) conformal coatings generally provide good humidity & moisture protection although not always as good as the acrylics. However, it normally is enough to protect the circuit board.
  2. Normally, urethanes are selected for their excellent chemical resistance. This is because the coatings cure rather than dry. That is they cross-link by one of many different methods including heat, UV, moisture and catalysed cure.
  3. Typically they have higher dielectric properties compared to the acrylic conformal coatings.
  4. Their chemical resistance, however, can be a limitation since rework and repair generally is more difficult than the acrylic coatings.
  5. UR coatings are normally available as either single or two-component formulations. Pot life is dependent on the cure mechanism but can be more limited than the acrylic coatings.

Need to find out more?

Click organic conformal coatings to find out about polyurethanes 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.

Why I have to clean my circuit board before conformal coating?

 

The cleaning of a printed circuit board (PCB) before conformal coating application is normally done for two key reasons:

These are:

  • Contamination removal
  • Process improvement

They have different effects on the lifetime of the circuit board but can be equally important.


Contamination removal

OLYMPUS DIGITAL CAMERA

The removal of contaminants from the surface of a printed circuit board before coating application could be important.

The contamination may be harmful and affect the long-term reliability of the circuit. Defects like corrosion can be devastating to a circuit performance in the field.

Also, applying the coating over the contamination will not necessarily improve the reliability.

Therefore, cleaning the PCB before coating could be advantageous.


Process improvement

OLYMPUS DIGITAL CAMERACleaning can aid the conformal coating application process.

It could avoid conformal coating defects like de-wetting and delamination. It can also help promote adhesion of the coating to the PCB.

The surface preparation can be extremely important, especially where some conformal coatings may have compatibility issues with the circuit board.

Therefore, cleaning a PCB before conformal coating may improve the coating quality and minimise defects.


What types of contamination may be present on a circuit board?

Cleaning is used to remove many different types of contaminants from the manufacturing and assembly processes.

They can affect the long-term reliability of the circuit after conformal coating.

The residues can come from many areas including:

  • Board laminate manufacture
  • Component manufacture
  • Soldering assembly processes (fluxes)
  • Glue and ruggedizing processes
  • Operator handling (finger prints, hair)
  • Machine contamination (oils and greases)
  • Environmental contamination (dust)

Removing the contamination may be a priority depending on their harmfulness.

How should I clean the printed circuit board?


Cleaning circuit boards before coating is a huge topic by itself.

Cleaning of a circuit before conformal coating at SCH 640_NexusSuccessful cleaning of circuits can be achieved by a variety of techniques.

These cleaning techniques include:

  • Aqueous
  • Semi-aqueous
  • Solvent & chemical
  • Plasma

The key to success in cleaning is similar to the success made with coating.

You need to match the cleaning process, materials and the circuit board together.

This will give the best results for application of the conformal coating.


How do I validate my cleaning process?

There are many techniques that can be used to measure cleanliness. They include many IPC test methods.

The techniques available include:

  • Ionic Contamination Testing (ROSE)
  • Ion Chromatography (IC) or High Performance Ion Chromatography (HPLC)
  • Surface Insulation Resistance (SIR) testing

Further information can be found in the IPC HDBK 001 on different cleanliness assessment methods or talk to us.


Need to find out more?

Click conformal coating cleaning 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.

What are conformal coating masking boots?

Nexus Image 1Masking boots are formed shapes used to cover components before conformal coating.

They are made to replace tape and dots in the conformal coating masking process for both Parylene and liquid conformal coating processes.

Using masking boots in protecting printed circuit boards (PCBs) from conformal coating application errors can be a lower cost, more reliable solution to using tapes.

The use of masking tapes, dots and liquid latex can be an effective process in protecting components from ingress of conformal coating.

However, the masking can be labour intensive, difficult and time consuming.

Masking boots can offer a labour saving alternative in both the masking and de-masking stages of the coating process. This saves time and money.

Further if the boots are recyclable then the savings can be even higher.

Three reasons to use masking boots

  1. Masking time is normally reduced. Masking boots can be 4-5 times quicker than masking tape.
  2. De-masking time is reduced. Again it is normally much quicker to remove masking boots.
  3. Masking boots are much less likely to leak. So there is potentially less damage and rework of the circuit.

This means you could save a lot of money very quickly when switching to masking boots.

Nexus Image 2
Masking boots can offer a labour saving alternative in both the masking and de-masking stages of the coating process. This saves time and money.

 Need to find out more?

Click conformal coating masking 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.

Why use plasma cleaning for cleaning circuit boards?

NEXUS 1Normally, conformal coatings must exhibit good adhesion to the PCB in order to be effective in the long term in protecting the circuit.

Therefore, the surface properties of the circuit board can be critical to the success of the coating adhesion.

Cleaning of circuit boards before conformal coating has taken place for many years.

The reasons for doing this have always remained the same:

  • Improve the surface cleanliness of the circuit to protect against corrosion and the effects of contamination on the surface from the process.
  • Improve the surface energy of the surface to improve the adhesion of conformal coating.

Traditionally, cleaning and adhesion promotion has been achieved by either using a wet chemistry treatment like washing or applying extra undercoats (priming).

Now, there are new methods and techniques appearing on the market for improving cleaning, adhesion and actually coating circuit boards differently to the traditional methods.

One of these techniques is plasma treatment.


Why use Plasma to clean circuit boards?

Here are a few key reasons to use plasma cleaning and surface treatment of printed circuit boards:

  • Plasma cleaning can clean surfaces of a product 100% to improve adhesion and surface energy of the product.
  • Many wet chemistry cleaning processes can be eliminated. Methods using cleaning chemistries, water processing and drying energy are unnecessary.
  • Activate the surface of the circuit by changing the surface energy. This allows easier bonding and better adhesion to the surface. The significant improvement in adhesion enables the use of alternative coatings that may have difficulty adhering to surfaces without the treatment.
  • The plasma process is a simple, safe and environmentally friendly technology.
  • The plasma process has both batch (offline) and inline capability.

This means the plasma process can be highly effective on printed circuit boards.


Need to find out more?

Contact us directly and we can help you with your plasma treatment requirements.

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.

How do I brush coat my conformal coating?

The application of a conformal coating using a brush to “paint” on the material to the circuit board is a common practice all over the world.

Generally, it is done as a final touch up process after the main application method is used.

However, it can also be done in mainstream production.

Conformal coating brushing in an inspection booth_NEXUS1

Applying the conformal coating

The operator according to the requirements of the circuit board applies the conformal coating selectively with the brush.

Areas not be coated are avoided.

The key for success with brushing conformal coating is the technique of application.

The correct method is to flow the coating on. The coating should be loaded on to the brush and flowed onto the circuit.

The material should not be brushed on like paint.

Screenshot of Nexus brush coating
Watch a video on brushing conformal coating.

Need to find out more?

Click conformal coating brushing 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.