Do you need UL qualification for your conformal coating?

June 1, 2017 Blog, conformal coating

UL are the Underwriters Laboratories and are a global safety certification body for consumer electronics.

They are a 3rd Party test service. There is no self-certification available.

A qualification to UL can be used as a sign of quality control and testing independently of the coatings protective ability.

When do you need UL?

Sometimes it may be required that the conformal coating needs UL approval to be applied to a circuit board. It will depend on the market the electronics goes into.

UL approved coatings can be used on electronics in many diverse sectors such as the domestic home, industrial controls, telecommunications and aerospace.

In fact, in nearly all areas conformal coatings tend to be used for protection.

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UL approved coatings can be requested in nearly all areas conformal coatings tend to be used for protection for electronics including domestic home, industrial controls, telecommunications and aerospace.

What standards are used from UL for conformal coatings?

For conformal coating, two parts of the UL standards are important.

These are:

UL 94: Standard for Safety of Flammability of Plastic Materials for Parts in Devices and Appliances testing.
UL 746E: Standard Polymeric Materials: Industrial Laminates, Filament Wound Tubing, Vulcanized Fiber and Materials Used in Printed-Wiring Boards

The two standards together control the quality of the conformal coating. They are discussed more in detail below.

UL 94

It is a plastic material flammability standard.

The standard classifies plastics according to how they burn in various orientations and thicknesses.

UL 94 measures conformal coating material’s tendency either to extinguish or to spread the flame once the test specimen has been ignited.

Classifications

For conformal coatings the test coupons are normally tested horizontally.

Tests are normally conducted on coupons of the minimum approved thickness with different types of laminate. The conformal coating thickness range also is normally specified.

The ratings are as follows:

V-2 burning stops within 30 seconds on a vertical specimen; drips of flaming particles are allowed.
V-1: burning stops within 30 seconds on a vertical specimen; drips of particles allowed as long as they are not inflamed.
V-0: burning stops within 10 seconds on a vertical specimen; drips of particles allowed as long as they are not inflamed.

Most conformal coatings aim to achieve V-0 status (top result).

UL 746E

UL 746E is the Standard Polymeric Materials: Industrial Laminates, Filament Wound Tubing, Vulcanized Fiber and Materials Used in Printed-Wiring Boards

UL 746E measures the ignition resistance of the conformal coating to electrical ignition sources.

The conformal coating material’s resistance to ignition and surface tracking characteristics is described in UL 746E.

Find out how we can help you with your conformal coating process now.

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How do I selective apply my conformal coating?

May 30, 2017 Blog, conformal coating

Selective conformal coating 640_SCH UK 2

Selective application of conformal coating is this case is applying the conformal coating without using masking to shield components from ingress.

Technically using masking tapes, latex and boots is a selective process. But, we want to look at coating application without masking.

This leaves a couple of different options.

The first is brushing. This is a simple selective process that can be highly effective.

Click Nexus conformal coating brushing technique to find out more.

The second, and the more obvious option, is selective robot.

This process uses a small spray valve (there are many conformal coating spray valve types) that is attached to a robot that follows a set pattern applying the conformal coating selectively to the circuit board.

Click Nexus selective conformal coating application to find out more.

Advantages and disadvantages of selective conformal coating robots

Selective spray robot applying conformal coating 640_SCHUK_1

The five advantages and disadvantages of selective application of conformal coating are:

Advantages

Masking can be eliminated or minimised
High speed coating process
High volume process
High quality finish when under control
Simple process to operate when set up

Disadvantages

High engineering skill required for set up and programming
High engineering skill required for troubleshooting and supervision
High capital cost initially
Process controls need to be enforced for good quality production
Environment can influence the process controls

Find out how we can help you with your conformal coating process now.

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How do conformal coating masking boots save money in your production process?

May 25, 2017 Blog, conformal coating

Three reasons conformal coating masking boots save you money

Here are three reasons that can save you up to 80% of your costs compared to masking tape:

Masking time is reduced. Masking boots can be 4-5 times quicker than masking tape.
De-masking time is reduced. Again it is much quicker to remove masking boots compared to masking tape.
Masking boots don’t leak. Masking tape has to be carefully applied. Any gaps will allow leaks. Boots don’t leak as easy so less repair.

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

Find out how we can help you with your conformal coating masking boots now.

Contact us to discuss your needs and let us explain how masking boots could work for you.

Or go directly to our website and see how you can get a quote on our conformal coating masking boots.

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Are there design rules for the conformal coating dip application?

May 23, 2017 Blog, conformal coating

There are design guidelines that can be used to help make conformal coating of circuit boards using the dip process a lot easier.

Having these specific design rules for dipping conformal coating can help save a lot of time, money and trouble on the production line.

Here are a list of rules and guidelines that could be considered.

Design the board so the masking components are at one end of the circuit. This allows the board to be dipped to a depth before the connectors are coated.
Design to hold the board correctly. Make it easy to hold the circuit easily.
Design the fixture correctly to avoid coating contamination. Don’t let the fixture get coated.
Match the coating material to the dip process. Ensure compatibility.
Design the board to drain to a corner. It ensures less build up is found on the board.
Avoid using components that can hold conformal coating. When the board drains ensure the component can too.
Use the correct components. Use components that are easy to mask.

To find out more click dipping design rules for conformal coating.

Why use conformal coating design rules?

Circuit board design rules and guidelines, when using conformal coating, can save you money, time and problems.

Nexus, the independent conformal coating resource, have split the conformal coating into sections.

They include:

General design
Selective Robot
Dipping
Batch Spraying
Parylene

Each has overlapping rules and guidelines that also can be very specific to the application process.

Why it all can go wrong in the design stage for conformal coating

Most companies have successfully adopted Design for Manufacture (DFM) principles.

They have increased the level of communication between design teams and those required to manufacture the product, to eliminate or reduce the number and variety of production challenges.

However, this is not always the case.

Conformal coating is not simply a consumable material.

Unfortunately, for too many designers, conformal coating is simply a part number, to be applied to circuit boards.

For companies embracing lean philosophies and applying coatings, this failure to appreciate the subtleties of the application process can result in an un-coatable (at least as specified) assembly process.

The design rules for conformal coating are straightforward.

Follow them and you can save money and time in your application process.

However, if the rules are not followed, the resultant circuit board design can challenge even the most sophisticated conformal coating system and its operator to achieve the finish desired.

It is almost certain that the majority of these ‘nightmare’ scenarios could have been headed off during the design and or prototyping stages of development.

Find out how we can help you with your conformal coating application selection now.

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What application methods are available for applying conformal coating?

May 18, 2017 Blog, conformal coating

SCH UK_1 Conformal coatings can be applied to printed circuit boards (PCB) in the production process environment in many alternative ways.

Listed below are the common methods of applying the conformal coating materials.

Brushing
Aerosol spray
Batch spray
Selective spray
Dipping
Vapour deposition

It is possible to split the different application methods and their suitability in many different ways including:

Compatibility with the conformal coating material
Design of the circuit board
Suitability to low, medium and high volume
Manual versus automatic process
Type of method of application
Level of control required

Each of the various methods has different advantages and disadvantages and should be carefully considered.

This thought process relates to the Nexus holistic approach to conformal coating processing that states that you should consider the conformal coating material, the application process and the circuit board together and not as three separate entities.

Find out how we can help you with your conformal coating application selection now.

Contact us to discuss your needs and let us explain how our coating equipment could work for you.

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What is a hydrophobic acrylic conformal coating?

May 16, 2017 alternative, Blog, conformal coating

Nano-coating fluoropolymers Collage 640_SCH UK

There are several reasons for using a conformal coating or Parylene to protect a printed circuit board (PCB).

They include:

High insulation protection
High moisture and humidity protection
Chemical and temperature resistance
Ruggedisation
Improve dielectric properties
Barrier protection against particulates

However, one property that most liquid conformal coatings do not possess that is extremely useful to have is being water repellent or hydrophobic.

A coating that is hydrophobic repels water from the surface by changing the surface energy of the coating.

This makes it energetically unfavourable for the water to wet the surface. Hence, the water “balls up” and rolls off the surface.

This occurs in the fluorinated nano-coatings that are hydrophobic and is an extremely useful property when protecting a circuit board where water may be present.

However, typical conformal coatings are not hydrophobic.

Materials like acrylics and polyurethane coatings are excellent against moisture but not so good as water repellent materials. They do not have a low surface energy.

*Conformal coatings like acrylics and urethanes do not have water repellent properties (left). A hydrophobic conformal coating repels the water and does not allow it to wet the surface (right).*

A hydrophobic acrylic conformal coating – the best of both coatings

Now, there exists a hybrid acrylic coating that has both the properties of an acrylic conformal coating at the same thickness plus the benefits of a hydrophobic nano-coating.

These benefits include:

Hydrophobic (water repellent) surface
High Insulation protection
High moisture and humidity protection
Ruggedisation
Improved dielectric properties
Barrier protection against particulates

This new range of conformal coatings can now offer the best properties of both without any cost penalty.

The water wets the surface (left) on a normal acrylic conformal coating. A hydrophobic acrylic conformal coating, with a low surface energy, makes water de-wet from the surface (right) and still has all the benefits of the acrylic conformal coating.

Find out how we can help you with your acrylic hydrophobic coatings now.

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How do I spray coat my conformal coating?

May 11, 2017 Blog, conformal coating

SCH UK Image 3conformal coating batch spraying Collage 640x480

Batch spraying is one of the widest used techniques used in low and medium volume conformal coating processing.

Whether you are using a compressed air spray gun or an aerosol can, the conformal coating is sprayed across the whole of the circuit board.

It can produce a high quality coating finish that gives the best protection due to good edge coverage.

However, it is not a selective process. All parts are coated on the circuit board.

Therefore, masking may be required to protect components that must not be coated.

What equipment do you need for batch conformal coating spraying?

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If you are not using aerosols then for conformal coating spraying a typical set up is:

Spray gun
Air Compressor for the Air Supply
Spray booth

This is a low cost set up that can handle a fairly high volume of product.

However, the quality of the finish is dependent on the quality of the spray equipment itself and the operator.

How do you apply the conformal coating by spraying?

Although the process can be material specific there are a few general guidelines for applying conformal coating by spraying.

These include:

Only apply thin, consistent coats. It may be necessary to apply more than one coat.
Apply the coating in a narrow raster pattern across the circuit.
Rotate the board 90 degrees and repeat. Continue until the whole board is coated to avoid 3D effects.
Allow the coating to dry enough to avoid problems like bubbles before applying a second coat.

Following a few simple guidelines can save a lot of problems.

What variables control the quality of the conformal coating in batch spraying?

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Variables that influence the quality of the coating process in spraying are:

The operator skill
Quality of the spray equipment
Viscosity of the conformal coating
Blending the conformal coating to the right viscosity is critical.
The level of masking required

Find out how we can help you with your conformal coatings now.

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The ABCs of ultra-thin fluoropolymer coatings for electronic circuit boards

May 9, 2017 alternative, Blog, conformal coating, Fluoropolymer

Nano coatings are no mask conformal coatings with great water repellent properties

What is a fluoropolymer coating?

A fluoropolymer coating is typically comprised of fluorocarbons and characterised by carbon-fluorine bonds.

They have many interesting properties and especially for printed circuit boards.

However the three key properties for electronics are that the coatings are:

Hydrophobic
Chemically resistant
No masking required

These properties can be key to protecting the electronics and providing a highly cost effective production process.

Hydrophobic coating

Fluorocarbons are not susceptible to Van der Waals force.

This gives the coatings their signature characteristics. That is they are non-stick, hydrophobic and friction reducing.

Therefore, water does not like to wet the surface of the circuit board and this gives the circuit excellent protection.

Chemically Resistant

These fluorinated coatings are chemically inert.

Owing to the fluorine bonds, fluoropolymer coatings demonstrate a high level of durability as well as resistance to acids, bases and most solvents.

This gives the circuit board a high degree of protection from chemical attack.

No masking required

Finally, what is really interesting is that these properties are exhibited at ultra-thin film thicknesses.

Typically a dry film can be 1-2um or even less.

This means that masking generally is not required for circuit boards before application. Therefore, you can dip the whole product into the liquid and there is no issue with electrical contact.

This can lead to significant cost savings in production.

What other properties do the fluoropolymer coatings have that may be relevant in electronics?

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As already mentioned these hydrophobic coatings have very specialised properties.

They can include:

Being highly hydrophobic (water repellent)
Having a high moisture barrier
Requiring no masking before application
Being highly oleophobic (oil repellent)
Having a high chemical resistance
Having a high lubricity
Having high dielectric properties
Providing high corrosion resistance
Providing good abrasion / wear resistance

Note, not all fluoropolymer coatings have all of the above properties. But, some coatings can in fact have almost all of the properties.

The fluoropolymer coatings are extremely flexible coatings and becoming more prolifically used throughout engineering.

What sectors of industry are fluoropolymer coatings being used in protecting electronics?

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Fluorinated coatings are used to protect electronics in almost all industrial sectors.

They include:

Aviation
Aerospace
Defence
Automotive
Industrial
Oil & Gas
LEDs
Medical
Optics
Telecommunications
White goods / Commercial

This list is limited and there are a lot more areas that they are used.

What are the major differences between a fluoropolymer coating and a conformal coating for protecting an electronic printed circuit board or assembly?

There are several key differences between a conformal coating and a fluoropolymer coating.

They include:

Hydrophobic Properties – A fluoropolymer coating is generally hydrophobic in nature. It repels water when the water is on the surface of the coating.
Extremely thin coating – The fluoropolymer coating is normally applied a lot thinner than a typical liquid conformal coating. This is due to its superior performance when repels liquids
No masking – Due to the extremely thin fluoropolymer coating applied (<1-2um), the components that normally require protecting (connectors, switches etc) from the insulating liquid conformal coating may not need to be masked for the fluoropolymer. The circuit board can be completely submerged in the liquid with no masking applied without fear of damaging the connections.
Simple process – No masking means an extremely fast application process
Fast drying – due to the thin nature of the fluoropolymer coating and the solvents normally used the coating dries extremely quickly.

Find out how we can help you with your ultra-thin hydrophobic coatings now.

Contact us to discuss your needs and let us explain how hydrophobic coatings could work for you.

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Improve your conformal coating masking process reliability with custom boots

May 2, 2017 masking boots

One of the most underestimated reasons for using conformal coating masking boots is that they improve the reliability of the process.

This is because they don’t leak as easily as conformal coating masking tape can!

Diamond MT saved more than 60% of their current masking costs by switching to the SCH range of conformal coating masking boots. The reality is that a well-designed boot will not allow conformal coating to penetrate into a component if it’s placed correctly; and the fact is that this is a very easy thing to do.

An operator using masking tape has to continuously show care and attention when applying the tape to the components. The level of skill required is high.

The level of skill required to apply a masking boot is much lower.

So, fewer errors are made and there are less costly repairs due to leaks.

Therefore, not only do you save up to 60% of your conformal coating masking costs due to reduced process times with boots but you can also improve the reliability of the masking process.

Need to know more about conformal coating masking boots in your application process?

Contact us now and we can discuss how we can help you.

Call us on +44 (0) 1226 249019, email your requirements on sales@schservices.com, contact our distributors direct or complete the details in the contact form.

How thick should I apply my conformal coating?

April 27, 2017 Blog, conformal coating

So, here is a question I am regularly asked. How thick should the conformal coating be on the circuit board?

Well, the simple answer is thick enough so the conformal coating works and protects the circuit board.

But not too thick as this can cause problems for the circuit board in the long term.

After all, the performance of the conformal coating is dependent on the thickness applied.

But, it is possible to quantify this a little more.

Help for determining the right conformal coating thickness

First off it’s probably best to use guidelines from International Standards like IPC A 610.

These standards specify the conformal coating thickness based upon the generic material types like acrylics, polyurethanes, and silicones.

Further, you can also reference this data against the material manufacturers technical recommendations.

Combining these two pieces of information should give you a target range for the conformal coating thickness.

However, ultimately, the coating thickness is down to the user.

How you decide if the conformal coating thickness is good enough is up to you. Too thin and you will not protect the circuit as effectively as you may need. Too thick and you could have reliability issues in the future. So, monitor your conformal coating thickness with care.

So what do the IPC Standards recommend when considering conformal coating thickness?

The IPC A 610 standard defines ideal liquid conformal coating thickness values as:

Acrylic: 30-130μm
Polyurethane: 30-130μm
Silicone: 50-210μm

However, this is not the end of the story.

Using the target coating thicknesses as an absolute value can be problematic.

The reality is that the conformal coating thickness will vary massively across the circuit board due to many factors including the surface tension of the liquid, the surface energy of the board surface, the design of the board, the material properties and the application method used.

So, there may be areas on the board that could fall outside of the range where the coating thickness will be less or more than the ideal values.

Therefore, it is highly recommended that the range should be considered as an average value across the board for the conformal coating thickness.

In fact, the IPC go further and suggest using flat test coupons coated in the same way as the process you use for the circuit boards. Then, these test coupons are measured against the standards.

In the end how you decide if the coating thickness is good enough is up to you.

Too thin and you will not protect the circuit as effectively as you may need. Too thick and you could have reliability issues in the future.

So, monitor your conformal coating thickness with care.

Using the target coating thicknesses as an absolute value across the circuit board can be problematic. The reality is that the thickness will vary across the circuit board due to many factors including the surface tension of the liquid, the surface energy of the board surface, the design of the board, the material properties and the application method used.

Need to know more about measuring conformal coating thickness in your application process?

Contact us now and we can discuss how we can help you.

Give us a call at (+44) 1226 249019 or email your inquiries at sales@schservices.com