How do I selective apply my conformal coating without using masking?

Selective spraying of conformal coating using an automated robot system is one of the widest used application methods in high volume processing.

The principle is that the conformal coating is applied selectively by a small spray gun to the circuit board to the areas requiring coating only.

The selective process deliberately does not apply the conformal coating to areas that normally require masking such as connectors and other components.

This selective application of the conformal coating to the circuit board can avoid using a time consuming masking process and costs can normally be reduced.


What equipment do you need for selective spraying?

A specialist robotic system designed for application of conformal coatings is normally required for selective coating.

The robotic system will be fitted with various conformal coating spray valves that apply the different types of conformal coating material to the circuit board using different spray patterns.

The level of movement of the robot can vary with systems having three, four, five and even six axes of movement for the spray valves.

Want to find out more about application of conformal coatings to circuit boards by selective robots?

Click to find out more about questions such as:

  1. What equipment do you need for selective spraying?
  2. What specialist valves are required for applying different types of conformal coating?
  3. Which conformal coatings can be used in selective spraying?
  4. Is selective spraying of conformal coating a complex process?
  5. How cost effective is selective spraying of conformal coating as a process?
  6. What variables control the quality of the conformal coating finish in selective spraying?
  7. What are five advantages of the selective spray conformal coating process?
  8. What are five disadvantages of the selective spray conformal coating process?

Need to find out more?

Go directly to our conformal coating selective spray application section 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.

Images 1 and 2 courtesy of PVA (Precision Valve Automation).

How do I spray coat my printed circuit board with conformal coating?

Nexus 1Batch spraying of conformal coating on printed circuit board assemblies (PCBA) is one of the most widely used techniques in low and medium volume production processing.

Typically, using either a compressed air spray gun or an aerosol, the conformal coating is sprayed across the whole of the circuit board to provide the protection it requires.

The batch spray process can produce a high quality conformal coating finish that gives the best protection due to good tip edge coverage of components.

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

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


What is a typical spray process for application of the conformal coating to the circuit board?

Nexus 2

Batch spraying using an aerosol or hand spray gun is normally a simple process.

A typical method of application for spraying is as follows:

  1. Dilute the conformal coating with thinners according to the manufacturers recommended instructions (typically the viscosity is close to 24cps and almost like water).
  2. Mix the blend thoroughly but without creating bubbles (if bubbles occur wait for them to dissipate) and apply a test pattern to ensure the material from the spray gun is flowing properly.
  3. If “spider webs” occur (similar to candy floss in the air) then dilute further with more thinning solvents.
  4. Position the circuit board horizontally
in front of the spray gun operator.
  5. Hold the spray gun at a 45° angle and at the recommended distance (typically 20 to 25 cm from the circuit board).
  6. Spray a thin and uniform coat onto the circuit board with an even motion using “spray and release” strokes in a raster pattern. Do not over apply too much liquid.
  7. Turn the circuit board 90°and repeat until the board has completed one complete 360° rotation.
  8. If a second coat is required, wait 2-3 minutes (may be longer with certain solvent types so check manufacturers recommended instructions) and repeat steps 5-7.

Once complete follow the cure instructions for the coating on the circuit board.


Need to find out more?

Go directly to our conformal coating batch spraying section 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.

How do I dip coat my circuit board with conformal coating?

 

NEXUS1

Dip coating is a traditional conformal coating application method that has been used to conformal coat circuit boards for a very long time.

The printed circuit board (PCB) is dipped into a tank of conformal coating liquid. This can be complete submersion or partial dip.

The board can be dipped vertically, horizontally or at another angle. The board can be dipped manually or automatically.

The board is removed from the coating and the excess conformal coating drains away.

This leaves a conformal coated circuit board.


The key areas for dipping with conformal coating

Find out more by clicking these links:


Need to find out more?

Go directly to our conformal coating dip section 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.

Outsourcing your conformal coating project – The key points

So, you are considering outsourcing your conformal coating or Parylene process to a subcontract supplier.

What’s the next step?

Assuming you have decided this is the right choice then the next task is to choose the right service provider.

This can be as difficult as selecting the right PCB manufacturer or laminate provider. There are good contractors and there are others. There are small providers and there are large-scale turnkey solutions.

The obvious answer is “the right one for me” but how do you ensure that you make the right decision?

Here are a few of the questions you should ask before signing up to the wrong coating solution provider and stop you wishing you had kept the coating process in house.

NEXUS1
There are several questions you should ask before signing up to the wrong coating solution provider and stop you wishing you had kept the coating process in house!

The three key points to consider when choosing a subcontractor

When considering the supplier look at the three main areas.

The order you look at is up to you but ultimately you need to be happy in all three to keep sending the work out.

These three key areas are:

  1. Quality
  2. Turnaround time
  3. Price

If you get these three key areas correct then you have succeeded. Everyone will be happy and there are no more problems with conformal coating.

However, within each of these areas, lie a lot of questions to be asked and if one of them isn’t working properly then who knows what the consequences are around the corner.

So, let’s consider each of these areas in turn in the order they are listed.


Quality

Everyone wants good quality. But what does that mean?

Whose quality are we judging against and how do we reach agreement?

One of the most important factors in subcontract conformal coating services is to agree what the PCB coating finish should look like.

Sound simple?

It can be if you define exactly what you want as a customer. The problem comes when you don’t know!

The reality is most customers have a preconceived idea of what a conformal coated printed circuit board should look like and the key for the customer is to communicate this to the provider.

Let me give you an example.

Consider a simple connector on a circuit board like the one below.

NEXUS2

Then decide on what statement you agree with below:

  1. Only the pins must not have coating on but the rest of the connector body does not matter.
  2. The whole of the connector must have no coating on it all but there can be a gap of 1-2mm around it free of coating.
  3. The whole of the connector must have no coating on it all and there can be no area around the connector free of coating.

All three options provide a connector free of coating.  All three options work. All three options could be considered fine by various different customers.

However, the order they are stated is also lowest difficulty (aka cost) to highest difficulty to actually complete the work in a coating production line.

So, defining how you want to coat the board intimately impacts on the price of the project.


A key issue highlighted

Unfortunately, this highlights a key problem in conformal coating processing.

There are no standards that state what is the best solution and only guidelines. Ultimately, it comes down to a decision made by the customer as to how the PCB should be coated.

This means it is a crucial factor for both the customer and the supplier to define the level of quality. Get this right and most of your problems are sorted.

If the coating house is good they will help you define this from the beginning. They will not assume any level of quality but ask you what you need.

If they don’t help you then hope that they can guess what they need to provide you with.

NEXUS3
A key problem in conformal coating processing is that there are no standards that state what is the best conformal coating finish and only guidelines. Ultimately, it comes down to a decision made by the customer as to how the PCB should be coated.

So what’s the next stage in quality?

So, you have agreed what quality of finish you want. Assuming that you know which conformal coating material you want then the rest should be easy.

Well, that statement is right as long as:

  • The supplier knows how to use your coating material correctly
  • Has the right equipment to apply the conformal coating
  • Has selected the right process for your PCB
  • Knows what to do when things go wrong

So, what you really need to do is find a subcontract conformal coating supplier that knows a lot about conformal coatings or Parylene.


Turnaround Time

So, you are considering outsourcing the coating work to an outside contractor but want the PCB coated when you need it.

Unfortunately, conformal coating is normally one of the last processes in a long line of operations so any delays in the manufacture of the PCB is normally being compounded by sending it out to a coating house.

Therefore, you need a fast turnaround option and your coating service should be flexible on this, allowing you choices on getting the PCBs coated.

However, you may want to consider the speed you require the PCB to be coated since it can lead to:

  • Extra costs
  • Potential problems with the process
  • Mistakes due to staff and machine availability
  • Availability of material
  • Local or global supply
  • Low cost offshore facilities
  • Capacity

These factors can influence the price significantly.

So, we have examined quality and turnaround time. The critical factor that ties these two areas together is price. Let’s take a look at this area.


Price

“I want this PCB coated for 45 cents”, says the customer.

“Okay can we see the board”, says the coating service provider.

The customer produces a 12”x6” PCB with 25 surface mount connectors with via’s everywhere and asks for coating both sides and wants all of the connectors not to be coated.

Okay, we have a mismatch in perception and this sounds ridiculous. But, it happens more regularly than it should.

Some customers have no idea of what it costs to coat a PCB. After all it’s just coating.

However, it’s up to the coating house to educate them so that they can get what they need and reach the happy point of all three areas satisfied.

So, what price should it be?

Well factors to be considered by the subcontractor are:

  • Material specified by the customer
  • Process to be used on the PCB
  • Volume of PCBs to be supplied
  • Amount of masking / keep out areas on the PCB
  • Amount of coating to be used per PCB
  • Is there cleaning involved before coating?
  • Yes cleaning is required, extra cost added in
  • No cleaning is not required, may be extra cost for finishing process if a lot of contamination
  • Speed of turnaround required (impact on resources, drying, curing)
  • Quality required (how much time finishing, inspecting, how close to look?)

So, the last two factors, turnaround and quality, tie directly back to the price and in reality have a huge impact.

Therefore, we find unsurprisingly all free factors should be considered as a whole and not separately.

NEXUS4
Some customers have no idea of what it costs to conformal coat a circuit board. After all it’s just coating….

Summary

Subcontracting out your conformal coating process isn’t difficult if you look carefully at the three areas of quality, turnaround time and price.

If you can achieve all three with your subcontract coating house then you will be happy.

If you ignore one of the factors then it may be a less pleasant position.


Need to find out more?

Contact us directly and we can help you. Or go to our supplier pages and look up coating services globally.

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 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.

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.

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.