What are the key questions to ask when cleaning for conformal coating?

Of all the questions I am asked related to cleaning the most frequent is

“Do I need to clean my circuit board before conformal coating?”.

If only it was simple to answer!

Generally, cleaning of a circuit board before conformal coating application is desirable. For Parylene this requirement may be even more important due to the bonding issues of the material.

However, it may not be essential.

Ultimately, the cleanliness of the circuit can be crucial for both the short-term production process and the long-term reliability of the circuit.

But, its difficult to know for sure if you need to clean until you complete some trials.

For the process it is difficult to know until you attempt to apply the conformal coating in production.

Then you will know immediately if you need cleaning since if you have problems you will see conformal coating defects like de-wetting, de-lamination and poor adhesion.

For the long-term reliability unless you want to wait until your product fails then some sort of reliability testing should be tried.

After all the purpose of the application of the conformal coating is to improve reliability.

It has less value unless the board is clean enough in the first place.

Other key questions in cleaning

There are many questions relating to conformal coating and cleanliness that are regularly asked.

These include:

  • What is being cleaned when circuit boards are washed?
  • How should I clean my electronic circuit board?
  • How do I validate my cleaning process?

If further information on these topics and the key question you can go to our free eBook by clicking Nexus conformal coating and cleaning.

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 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 lhitchens@nexus3c.com and let me know what you think?


What is layering in conformal coating and is it a problem for the protection of the circuit board?

Layering is where multiple coats of material are applied to a circuit board and they do not adhere to each other or cause incorrect curing of the individual layers.

This can lead to a weakened performance in the conformal coating, which in turn can lead to the failure of the circuit board.

There are several causes of layering in conformal coating. These include incorrect adhesion, curing and keying of the coatings.

Click conformal coating layering to find out more and how to prevent this problem.

Need help with your process?

Contact us at Nexus and we can help solve your issues.

Subscribe to the Nexus Newsletter now.

My conformal coating has changed colour over time. Is this a problem?

Discolouration of a conformal coating can be a natural phenomenon due to the nature of the resin used. For example, a polyurethane conformal coating will naturally darken and go brown with time due to its inherent properties.

However, a change in the colour or loss of transparency of the conformal coating that adversely affects the performance or the identification of the components below the coating can be classed as a defect.

Causes of discolouration in conformal coating include UV light exposure and prolonged exposure to contaminants. But, this problem can be prevented with the right measures.

Click to find out more about discolouration of a conformal coating as a defect and how to prevent it.


Need help with your process?

Contact us at Nexus and we can help solve your issues.

Subscribe to the Nexus Newsletter now.

How to stop fisheyes creating a fail in your conformal coating process

fisheye defects found on a conformal coated circuit board
Fish eyes formed due to contamination on the circuit

In coating, a fish eye is a localised de-wetting defect.

It looks like a fish eye crater on the surface of the conformal coating.

Causes of fish eye defects in conformal coating

Fish eyes are normally caused by a contaminant on the surface prior to application of the conformal coating.

This contaminant is a substance like a silicon residue.

When coating is applied on top of the contaminant, the conformal coating is unable to adhere to the oily surface and a “fish eye” is caused.

Click to find out how to stop fish eye defects in conformal coating.


Troubleshooting your Conformal Coating Issues on the Production Line: Capillary Flow

Capillary 4 200x150When a problem occurs on the coating line and a circuit board is defective there is generally a good reason for the occurence. This week Nexus takes a look at Capillary Flow.

Capillary flow (or scavenging) in conformal coating processing is where the coating pulls or runs away from certain areas of a PCB to more favourable areas.

This is due to a combination of effects which leave a patchy finish on the surface of the board around the defective area.

There are several options to resolve this issue and prevent this occurring in production.

Find out more

China Nexus Workshop Topic: Troubleshooting your conformal coating process

Nexus are to hold a FREE conformal coating workshop in the Diamond SCH coating facility in Shenzhen China on the 17th October 2012.

Topics include Troubleshooting your conformal coating process. This presentation will look at all the failure mechanisms and defects that can occur when coating a printed circuit board and the practical aspects of improving the application process to minimise or eliminate the problems.

This One-day workshop will be held at the Diamond SCH Conformal Coating Facility. The address is 3rd Floor, A5 Building, Tianrui Industrial Park, Fuyuan Road1, FuYong Town, Baoan District, Shenzhen, China.

Click  Shenzhen China Conformal Coating Workshop October 2012 for further information or book your place.

Nexus Newsletter Feature: Conformal coating Defects – Why Do They Occur?


In conformal coating there are many common failure mechanisms in conformal coating including capillary flow (scavenging), delamination (loss of adhesion), cracking, de-wetting, orange peel, pin holes, bubbles and foam. This article briefly looks at reasons each of the defects occur in processing with potential solutions to avoid them in the future.

Click FEATURE “Conformal coating Defects – Why Do They Occur?” to read the article.

Nexus Newsletter looks at Conformal Coating Subcontract Services and houses

In this issue Nexus reviews subcontract conformal coating services provided by coating houses and the problems faced today. If you want to subcontract out then read this article. Nexus is also looking closer at conformal coating defects related to the IPC Standards and why they occur? The technical article Who Do Defects Occur? gives some insight into how to solve most of the main issues that can stop the line and cause a lot of heartache.

Also, we are introducing a new section at Nexus this month called Conformal Coating101. This section answers all the questions about why we use coating, what it does etc and answers many of the questions we are regularly asked.

Finally, Nexus starts its Conformal Coating Workshop Program off in October and November in China and India, respectively and we confirm further dates for North America and Europe in the New Year.

Click Nexus Conformal Coating Newsletter to access the full details.

Ask The Expert: Dr Lee Hitchens, Nexus on Key Conformal Coating Material Challenges

“Out of all the Key Material Challenges I see on a regular basis, one of the most prolific is difficulties in adhesion to solder resist or to no clean residues and contaminants.“
 “It can be as basic as the coating just will not stick to the PCB or it runs away from areas on the PCB. At other times, it’s interpreting just how well the coating is stuck and determining if it’s good enough for the customer? Normally, this cannot be answered instantly and leads to some serious thinking!”

Visit the Nexus Associate Experts Section and read what other experts have to say about conformal coating material challenges.

Nexus Series of Webinars: Conformal Coating Inspection and Quality of Coated Board Assemblies

Nexus are to hold a series of webinars on conformal coating topics in the Autumn of 2012.The series of four online conformal coating webinars will cover the following topics and each last 90 min. The third of the online training webinars will be:
Inspection & Quality of Coated Board Assemblies
Monday 7th January

Conformal Coating Inspection standards exist from a variety of sources and are based mostly on practical experience. There are many cosmetic defects that are reworked in industry which are unlikely to actually impact on product quality. The majority of coated products are inspected manually but with the growing use of coating application in high volume, automatic optical inspection is gaining in popularity.

Topics will include:

Inspection standards and what is important
Understanding some of the coating terminology
Manual & automated inspection
Common process defects & why they occur
Recording & charting defects in a process
Cosmetic process indicators

Please click online conformal coating webinars for further information.