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.

NEW conformal coating Process Control section for eBook

 

Nexus are preparing a new section for its eBook on conformal coating Process Control.

We are aiming to publish this in September 2016.

The section will cover all aspects of the topic including all of the key process control variables that affect production including the equipment, materials and people involved.

viscometer image 500.jpeg
The Nexus eBook section on Process Control of conformal coatings will examine many of the areas that give you the key to the perfect production line.

Since Nexus is peer reviewed and we want the content to be relevant we are asking if anyone would like to add input into the section?

Help could be given in the form of guidance on topics and technical input and expertise on a particular area.

Let us know if this is of interest and get in touch with me directly by email lhitchens@nexus3c.com or mobile +44 7862 253321.

I can show you what we are planning and perhaps you can guide us in the final format.

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.

 

What are my options for conformal coating application methods?

This is a question I am asked time and again.

Of course most people know of the selective robot and how it applies conformal coating.

However, there are many different application methods available for both liquid conformal coatings and Parylene and listed below are the common techniques:

Click on each to examine individually for details or click conformal coating application techniques for an overview.

Note, each of the various methods has different strengths and weaknesses.

However, each of these application methods should be considered in relation to the holistic approach to conformal coating processing 

What is the holistic approach to conformal coating?

The holistic approach states that you should consider the conformal coating material, the application process and the circuit board together and not as three separate entities.

I consider this approach the most fundamental issue and crucial factor in all of conformal coating processing.

Ironically, it is ignored on a regular basis.

In fact, I find that the failure to apply the holistic approach at the beginning of the conformal coating selection process is normally the root cause of many conformal coating problems.

 

Click conformal coating application techniques to find out more.


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.

 

What type of problems can you have with conformal coating?

Normally, when I am working with customers I see two types of problems.

Those are problems relating to the conformal coating process and those relating to the actual product reliability.

They are two very different issues to deal with.

Conformal coating reliability problems

Ultimately, there are many factors that can affect the short, medium and long-term reliability of a circuit board.

It is not just the conformal coating that can influence this.

However, if the conformal coating material is not correctly specified at the reliability design stage then this could be the major issue and the reason for failure.

Once the product reliability requirements have been defined as part of the conformal coating design procedure then the resulting information needs to be combined with the data from the conformal coating holistic approach.

This will ensure that the risks of a failure due to the conformal coating are minimised.

if the conformal coating material is not correctly specified at the reliability design stage then this could be the major issue and the reason for failure.
If the conformal coating material is not correctly specified at the reliability design stage then this could be the major issue and the reason for failure.

Conformal coating process problems

Typical failure mechanisms in conformal coating processing normally come from the conformal coating masking process or the application process.

Conformal coating masking failures

Failures in the masking process are generally a known quantity and easy to understand.

Adopting best practice methods for conformal coating masking can help to minimise these problems.

Masking with tape and latex 1 600
Using best masking techniques can minimise some problems found in conformal coating processing

Conformal coating application failures

Failures in the conformal coating application process are very well understood.

Typical failure mechanisms include:

  • Bubbles
  • Blushing
  • Contamination
  • Capillary Flow
  • Orange Peel
  • Shadowing
  • Cracking
  • Delamination
  • De-wetting
  • Fish Eyes

Understanding and troubleshooting why these conformal coating failures occur can quickly lead to a solution to the failure in the conformal coating process.


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.

 

How do I select a conformal coating?

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

I am regularly asked how I would go about choosing a conformal coating?

I normally respond to the person involved by asking an awful lot of questions and they wonder what they got themselves in to!

Why do I have to ask a lot of questions?

The questions are there because choosing a conformal coating process is a complicated process usually balancing a lot of important trade-offs and compromises.

When I consider the question I actually see three major parts of the complete process.

These parts are:

  1. The conformal coating material
  2. The application method
  3. The circuit board design

When you consider these three points you have to balance them to create the best compromise process solution that suits your requirements.

This is what I call the Holistic Approach to conformal coating.

So, what should you do next?

It is tempting to consider one of these parts in isolation.

However, this could be a mistake.

After all, the wrong choice can be devastating to the conformal coating production process as a whole and even worse, the reliability of your product.

 

I feel that to identify the best conformal coating material and application process there are several key factors that you need to consider that, if you are lucky, will add up to at least one sensible process choice.

Factors to be considered include:

  • Temperature operating range
  • International, customer or National Standards
  • Environmental considerations of the circuit board
  • Requirement to rework the conformal coating
  • Conformal coating material type
  • Application process considerations
  • Curing the conformal coating
  • National, State, Regional Legislation and Insurance
  • Supplier performance and availability
  • Price

To find out more about these factors visit Nexus and see how we recommend you select a conformal coating through the holistic approach.

 

What are the critical points to correctly design your conformal coated circuit board to meet the highest standards?

When designing for reliability with conformal coating then there are several important areas to consider for the product:

  • Reliability Requirements
  • Life Cycle
  • Environment
  • Materials and Parts selection
  • Electrical Effects

The purpose of the conformal coating is to protect the printed circuit board. This is to increase the circuit and product reliability.

corroded circuit board
The purpose of the coating is to protect the circuit. Understanding the key points will ensure that the coating does its job

To ensure the right level of reliability is achieved with the conformal coating then a complete understanding of the design requirements for the circuit board is critical.

This should be the starting point for most engineers when considering designing for reliability.

Click designing for reliability with conformal coating to find out more.

 

Where are conformal coatings used?

Conformal coatings are being used as protection in ever increasing electronic applications across a wide range of market sectors.

Due to the fact conformal coatings provide several key benefits including moisture and insulation properties, chemical resistance and particulate protection, this means they are used anywhere there is a need for a higher reliability than that which is achieved without the coating.

However, it is possible to identify traditional and emerging sectors where conformal coatings are applied.

To find out more click Nexus: Where are conformal coatings used?

Useful Links

Ebook Overview

Why use a conformal coating to protect a circuit board?

What is a Conformal Coating?