How to clean “no clean” flux residues from printed circuit boards and do it right

Cleaning no clean flux residues remaining on a printed circuit board assembly (PCBA) is one of the most difficult cleaning processes.

By definition no clean flux residue are harder to clean than conventional rosin or modified resin based residues.  This is because the residue is not meant to be cleanable.

However, there are times when the residues do need to be cleaned.


So what do you do when you want to clean the no clean residues from the circuit?

Whether a flux residue can be cleaned effectively depends on the cleaning materials saponification factor and its compatibility with the no clean residues.

Saponification is the ability of the no clean residues to be softened to the point of being able to be dissolved by the alkali content (the saponifier) of the cleaning chemistry.

The higher the saponification factor of the cleaning fluid the easier it is to clean the residues. Also, if the saponifier is not compatible then it won’t work as well.

So the key here is to ensure that the saponifier is compatible and completely dissolves the residues.

What happens if the residues are only partially dissolved by the saponifier?

A no-clean residue that is only partly cleaned away could be far worse for a printed circuit board assembly than a no-clean residue left untouched from a corrosion point of view.

One of the reasons is because lead free flux activators are more active than those in earlier leaded flux formulations.

When un-cleaned the residues are locked up in the carrier resin matrix. They are stable (benign) at normal operational temperatures and therefore will not leach out dangerous residues and cause corrosion problems.

However, if the protective matrix around the residue is partially removed by an inadequate cleaning regime, then the activators could be exposed.

This may lead to a corrosion process starting on the circuit board and this process could be accelerated in the presence of heat, power on the boards in service or high relative humidity.

So how do you clean “no-clean” residues without problems?

It is important when considering cleaning “no-clean” residues on a circuit board that you check:

  • The ability of the residue to be cleaned is determined?
  • The cleaning chemistry is matched to the relative degree of difficulty and the available process.
  • The success of the whole process is validated by careful testing

Following these three guidelines can help you be successful. Not considering these three points could easily lead you to having real problems in the long term.

Need to find out more?

For further information on cleaning circuit boards for conformal coating then review our cleaning section or contact us directly.

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 thick should I apply my conformal coating?



The measurement of the conformal coating thickness on a printed circuit board (PCB) to ensure internal and international standards are met is now a standard process in production.

There are several methods for measurement of conformal coating thickness including dry and wet film processing. However, the most important factor is how thick should the coating be?

First, you can reference both internal and international standards like IPC A 610 for conformal coating application.  They can help a lot.

These standards will help guide you in the coating thickness required for a particular coating materials since the coating thickness suggested will be dependent on the resin of the conformal coating.

For example, an acrylic or polyurethane based conformal coating has a different coating thickness requirement to silicone-based materials.

Below are the suggested conformal coating thicknesses from the IPC A 610 standard:

  • Acrylic            30-130 μm
  • Urethane        30-130 μm
  • Epoxy             30-130 μm
  • Silicone          50-210 μm
  • Parylene        10-50 μm

Note, that this is the average thickness across the circuit board. It is almost impossible to achieve a homogeneous coating thickness with the liquid conformal coatings due to surface tension issues during drying.

Using this information you can now move forward and look at the application of the conformal coating.

Need to find out more?       

For further information on process control and conformal coating thickness then contact us directly.

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 key facts about plasma coating on printed circuit board assemblies

Plasmatreatment of circuits collage

  1. Plasma coating can be used for the application of a Nano-coating material onto a surface of a substrate like a printed circuit board assembly (PCBA).
  2. You can change the wetting energy of the PCBA surface to highly hydrophobic (water repellent) by applying a Nano-coating via the plasma.
  3. Plasma technology is based on a simple physical principle. Matter changes its state when energy is supplied to it. Solids become liquid. Liquids become gas. If additional energy is then fed into a gas by means of electrical discharge it eventually ionises and goes into the energy-rich plasma state.
  4. The Nano-coating material is injected into the plasma via a jet nozzle. The plasma excites the coating material and this increases the coating materials reactivity. The plasma coating is then applied to the surface.
  5. Due to the excited nature of the coating in the plasma, the material coverage is optimised and the bonding to the surface is improved.


Need to find out more?

For further information on Plasma coating of Nano-coatings then contact us directly.

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

Five key facts you should know about Atomic Layer Deposition (ALD)


  1. ALD belongs to the family of chemical vapor deposition methods (CVD). It was initially developed for manufacturing nano-laminate insulators and zinc sulfide phosphor films for thin film electroluminescent displays. The unique properties of the coatings, together with the high repeatability, were the main factors leading to successful industrial production.
  2. The ALD deposition technique is based upon the sequential use of a gas phase chemical process. Gases are used to grow the films onto the substrate within a vacuum chamber. Through the repeated exposure to alternating gases there is a buildup of a thin film through deposition.
  3. ALD has several advantages in its use. For example, the process is self-Limiting, the films are perfectly conformal, they are pinhole free and the process allows layers or laminates.
  4. Along with advantages are a few key considerations. They include the substrate has to be of a high purity, the price of the systems are not low, the process tends to be very slow and the masking process for ALD has to be perfect.
  5. The ultra-thin films can be grown onto virtually any substrate. They have been demonstrated on highly patterned wafers, polymer films, and fine powders of most compositions. ALD is used in many different areas including microelectronics, semiconductors, photovoltaics, biotechnology, biomedical, LEDs, optics and fuel cell system technologies.


Need to find out more?

For further information on ALD and its performance then contact us directly or check out our section on Atomic Layer Deposition (ALD).

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


The ABCs of plasma cleaning and activation of printed circuit boards for conformal coating processing

Author: Dr Lee Hitchens

Plasma cleaning and surface activation of circuit boards is a process that is gaining more popularity in thin film applications like conformal coating due its highly effective performance on cleaning and modifying surfaces.

The reason for the increase in popularity is for two main reasons.

First, a clean circuit board surface improves the performance of the coating by ensuring no residues are present to harm the circuit in the long term.

Second, the activation of the surface can enhance the adhesion of the conformal coating.

So, lets look at how the process works. First what is plasma?


What is Plasma?

Plasma generation is based on a simple physical principle.

Matter changes its state when energy is supplied to it.

Apply enough energy and solids become liquids and liquids become gases.

If additional energy is then fed into a gas by means of electrical discharge it eventually ionises the gas.

The gas goes into an energy-rich plasma state that is known as the fourth state of matter. Plasma is created.

How can Plasma be used for cleaning printed circuit boards?


Plasma treatment can clean, activate or coat nearly all surfaces. These surfaces include plastics, metals, (e.g., aluminum), glass, recycled materials and composite materials.

This means the plasma process can be highly effective on many different products.

For electronic circuit surfaces, plasma treatment can be used in two highly effective ways.

That is it can:

  1. Clean the surface of the circuit board to be 100% contamination free. The surface will be free of residues and contamination.
  2. Activate the surface of the circuit board assembly to allow easier bonding and better adhesion of conformal coatings. It can change the surface energy of the surface to ensure complete adhesion is possible and in some cases it can make materials bond where it was previously impossible.

These properties make it a highly practical method for improving the surface performance of an electronic circuit board.

What are the typical plasma processes available for surface treatment?

There are traditionally three types of plasma treatment:

  1. Low-pressure plasma
  2. Corona treatment
  3. Atmospheric pressure plasma

Low-pressure plasma

These plasmas are generated in closed chambers in a vacuum (10-3 to 10-9 bar).

They can be used in conjunction with Chemical Vapor Deposition (CVD) coatings like Parylene before application.

Corona treatment

Corona treatment (corona process) is a physical process involving high voltage and is mainly used for treatment of films.

This is normally not suitable for electronic circuit boards.

Atmospheric pressure plasma

Atmospheric plasma is generated under normal pressure. This means that low-pressure chambers are not required.

The plasma is created with clean/dry compressed air (plant air) and does not require forming gases. It is possible to integrate plasma directly into manufacturing processes under normal pressure conditions.

This is an excellent process for improving adhesion and surface energy performance of circuit boards for conformal coatings. 

How is the plasma applied to a circuit board to clean it?

Typical plasma components used for cleaning surfaces on circuits are:

  • Plasma jets (nozzles) to apply the plasma to the surface of the circuit board. They could be controlled by a robotic system.
  • The plasma generators that create the plasma to clean or supply the coatings as required. They provide output power and, in conjunction with complete pretreatment stations, assume various control functions.
  • The process monitoring that controls the nozzles, the movement of the system and the quality of the output.

These three parts form the plasma cleaning process.

What sectors in the electronics industry is plasma treatment used in conjunction with conformal coatings?


There are many sectors that plasma cleaning is used for improving conformal coating performance.

They include:

  • Automotive
  • Telecommunications
  • Mobile phone and Tablets
  • Aerospace
  • Military
  • Transport
  • Consumer goods
  • Life sciences
  • LED Coating

Need to find out more?

For further information on plasma cleaning and conformal coating performance then contact us directly.

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

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 and let me know what you think?


Five key facts about ultra-thin, nano- coatings used in electronics protection

  1. Water repelling (hydrophobic) Properties – An ultra-thin coating is normally hydrophobic. This is because it is normally a fluoropolymer technology. The coating does not allow the water to wet on the on the surface of the coating. It modifies the surface and changes its dyne energy. A typical conformal coating like an acrylic or polyurethane is not water repellent and water wets the surface. nano coating
  2. Ultra-thin –Typical coating thickness is 1-2um for a coating (depending on application) compared to the acrylic, urethane and silicone conformal coatings that are applied at >25um.
  3. No masking of connectors required – The circuit board can be completely submerged in the coating liquid with no masking applied. Due to the extremely thin coating applied (<1-2um), the components can be connected together and the electrical connection is easily made. This would not be possible for a standard conformal coating. So, costs of processing are extremely low.
  4. Simple application process – The ultra-thin coating can be applied by dip, brush or spray.  But, the simplest method is dipping. Since there is no masking then the dip process is simple and is an extremely cost effective application method.
  5. Fast drying – Since the coating is ultra-thin and the solvents normally used are fast drying then the fluoropolymer coating dries extremely quickly. The coating can be dry in seconds and ready for use in a few minutes.

Need to find out more?

For further information on the ultra-thin, nano- coatings then contact us directly.

Or, you can go to our free eBook by clicking fluoropolymer coating materials now.

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