Sensible Design: The Role of Resins and Conformal Coatings in Your Applications

phil_kinner-100x100.jpgThis month, I examine some of the key differences between conformal coatings, encapsulation resins, and potting compounds to help designers make more informed decisions, and ultimately help increase the performance, reliability and lifetime of your electronic circuitry. I also look at issues that some of you may have with mixing resin packs and air bubbles, what can go wrong and why.

No one wants a product recall, or worse still, a product failure. Therefore, protecting circuitry for its intended purpose and end-use environment is imperative to extend product lifetime and maintain your brand’s reputation.

Resins are an excellent way of protecting electronic circuitry, however, there are some excellent conformal coating alternatives on the market as well. For instance, we have created a two-part 2K coatings range, which provides more resin-like protection, with the application ease of a coating. This has been a great success with applications in aerospace and automotive, where protection in harsh environments is absolutely critical, whilst minimising the increase in product weight. I will be exploring coatings vs. resins in a little more detail, using my usual five-point Q&A format.

1. What are the main differences between resins and coatings?

The first difference between resins and coatings regards the various methods of application. For instance, there are aerosols, conformal coating spray equipment, manual spray guns, and brushing for coatings, compared to mixing and dispensing equipment, and resin packs for resins. Then there is the thickness of the application to consider:500 microns for resins, as well as approval ratings (coatings are generally approved to UL746, while for resins it is very much dependent upon the application).

Due to the coating thickness, coatings occupy less volume and give a much smaller increase in overall weight compared to resins. There are both coatings and resins based on epoxy, polyurethane, and silicone chemistries, but there are also acrylate, acrylic, and parylene coatings which do not have a direct resin equivalent. Most resins are 100% solids systems, so that few or zero VOCs are released during curing with minimal shrinkage, while many coatings are solvent-based, although there are two-component (2K), UV-curable acrylate systems, and solvent-less silicone coatings that are also 100% solid.

In particular, 2K coatings are designed to be applied more thickly, without cracking during thermal shock testing, and enable a greater degree of component lead coverage to be achieved, resulting in improved performance during thermal shock, powered salt-spray testing, MFG testing and condensation testing (traditionally gruelling test regimes, commonly used during automotive qualification campaigns). The 2K series is also VOC-free, solvent-free, and fast-curing, whether by thermal or the revolutionary UV/chemical dual-cure mechanism.

2. What are the main considerations for choosing a resin instead of a coating?

The main considerations for choosing between a resin and a conformal coating are normally down to the specifics of the application. If the housing is designed to be the primary protection against the environment, then a conformal coating is generally a more appropriate choice. However, if the housing is not the primary environmental protection or if the unit involved is to be subject to long-term immersion in various chemicals, then a resin is generally a preferred, more appropriate choice. Also, if there are many tall and heavy components on a PCB that is expected to encounter significant vibrational loads during use, then an encapsulation resin might be a more appropriate choice. Further consideration should also be given if the unit is to be used in a situation where it is not easily accessible or if a long continuous service life is required, in which case a resin might be recommended to provide the extra protection and durability needed.

3. What is the best way to mix a resin pack and what can go wrong?

Remove the resin pack from the outer packaging. In the case of polyurethane and silicone resins, don’t remove it from the foil pack until ready to use. Lay the pack out onto a flat surface and remove the centre clip. Use the clip to push the resin from one half of the pack to the other, then pick the pack up in both hands and mix in a circular motion for a couple of minutes. Place the pack back on the flat surface and use the clip to push the resin from the corners into the centre. Pick the pack up in both hands and continue mixing for a further minute. Repeat, pushing the resin from the corners into the centre of the pack, and then continue to mix for another minute to ensure that the material is fully mixed and is a uniform colour. Use the clip to push the mixed resin to the side of the pack with the angled seam. Roll the pack film up so that the pack fits into the hand. Cut the corner of the pack off and then tilt the pack to dispense the resin, applying slight pressure as required to maintain the flow.

If the material from the corners of the pack is not pushed into the centre of the pack then unmixed material can be dispensed. If the resin is not mixed long enough, then the resin might not cure, or have a patchy cure. In the case of filled resin systems, some sedimentation might have taken place over time, so it might take a little more mixing to ensure that the fillers are correctly distributed throughout the resin. With the optically clear resins, when first mixed, the resin may appear hazy. This is perfectly normal, and the haziness will disappear as the material cures.

4. What happens when air bubbles get trapped in encapsulation resins and how can this affect performance?

There are numerous effects that air bubbles can have on the performance of the cured resin. Depending upon the number and distribution of the bubbles, the actual thickness of the polymer layer applied will be decreased, hence the level of protection will also be reduced, particularly against chemical attack. If the air bubbles are next to components, wiring or tracks, and bridge conductors, then the insulation between those points is compromised and design rules around spacing and clearance may be broken. Ultimately, this can result in premature failures by creepage and clearance breakdowns. Voids also act as a weak point under thermal and physical shock, which can lead to the resin cracking in service.

5. What are the differences between encapsulation resins and potting compounds?

There is little difference in terms of the resins’s chemistry used, but there is a difference in how the resin is applied and the performance expected from it. An encapsulation resin will totally cover the PCB and the components and can act as the protective support structure, while a potting compound is used to fill a housing or enclosure containing the PCB and components.

So, an encapsulation resin will adhere to the PCB and the components, and its outer faces will act as the primary barrier to protect the unit. The encapsulation process may or may not be performed with the assistance of a mould. Without a mould, the flow characteristics of the material will be required to control the deposition of material, and a dam and fill process using two different resin chemistries may be used to ensure correct material deposition.

A potting compound must adhere not just to the PCB and components, but to all materials within the device, including the housing. In this case, the differences in CTE (coefficient of thermal expansion) between all the materials used are often a critical factor, as all the materials within the housing will be subjected to different rates of expansion and contraction due to the differences in the materials’ CTE values. This can put the resin, components, circuit board, and even the housing under extreme stress, and lead to failure over time.

If in doubt, it is always advisable to discuss with your suppliers which material is best suited to your application. The technical support teams of reputable suppliers have a wealth of experience to call upon and, should it become necessary, they have the expertise to modify chemical formulations to meet your application needs. I hope the points covered this month have been informative. Please do look out for my next column, where I’ll be covering more issues on getting the most out of conformal coatings.

This column originally appeared in the March 2021 issue of Design007 Magazine.

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2021

Sensible Design: The Role of Resins and Conformal Coatings in Your Applications

03-10-2021

This month, Phil Kinner examines some of the key differences between conformal coatings, encapsulation resins and potting compounds to help designers make more informed decisions, and ultimately help to increase the performance, reliability and lifetime of your electronic circuitry. He also looks at issues that some of you may have with mixing resin packs and air bubbles, what can go wrong and why.

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Sensible Design: How to Avoid Problematic ‘Blushing’ and ‘Bubbling’ in Conformal Coatings

02-15-2021

In this month’s column, Phil Kinner revisits a couple of general enquiries Electrolube has received about "bubbling' and also, the less common appearance of cloudy, white patches following the application of a conformal coating.

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2020

Sensible Design: To Coat or Encapsulate—Making An Informed Choice for Electronics Protection

12-28-2020

One of the most frequently asked questions we receive from customers is, “Which is better to protect my PCB: a coating or a resin?” In this month’s column, Phil Kinner demystifies why one may be more suitable for your application than the other and explores coatings and resins in more detail.

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Sensible Design: Top Tips for a Successful Thermal Management Process

11-10-2020

Jade Bridges concentrates on some of the complications you are likely to encounter when selecting and applying a thermal interface material and looks a little more closely at thermal resistance, viscosity, and vibration, as well as their effects on performance. Read on to learn how to fully optimize your thermal management process.

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Sensible Design: Pushing the Boundaries of Thermal Management

10-23-2020

Thermal management plays a central role in circuit and electronic assembly design, ensuring improved reliability and increased performance of devices. But what if you could push the boundaries even further and extend the long-term stability? To explore how this can be achieved, Jade Bridges touches on some of the latest advances in thermal management technology.

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Sensible Design: Key Benefits of Resins and Differences From Coatings

09-17-2020

Alistair Little focuses on the benefits of using a thermally conductive encapsulation resin and compare the difference between using a resin and a conformal coating. He also looks more closely at the best way to mix a resin pack and what to be wary of if air bubbles get trapped in the cured resin.

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Sensible Design: How to Overcome Conformal Coating Challenges

08-19-2020

Phil Kinner takes a look at some issues you are sure to face, from areas of the coated board that simply refuse to cure fully to masking components to the orange peel effect and examining the difference between a critical and a non-critical area of a board.

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Sensible Design: Resins–Are They All About Chemistry?

06-15-2020

When it comes to resin selection and application, there are a plethora of factors to consider. Alistair Little looks at thermally conductive resins, flexible resins, elevated cure temperatures, resin types for different applications, and resin systems that enable wider operating temperatures.

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Sensible Design: Thermal Management—Keeping Cool Starts From Within

06-09-2020

Thermal management plays a significant role in protecting electronic circuitry. Jade Bridges takes a fresh look at popular subjects within the field of thermal management and explores what occurs when devices overheat, as well as the benefits of thermal gap fillers and how to best avoid pump-out.

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Sensible Design: Thermal Management—Five Tips for Application Success

05-25-2020

With so much to consider when choosing a thermal management material, it’s important to do your calculations, consider the equipment’s operational, and environmental conditions and experiments. Underestimating these could compromise the reliability of an electronic assembly and shorten its life expectancy. Jade Bridges shares five tips to improve your thermal management process.

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Sensible Design: Conformal Coating Enemies—Challenges Sabotaging Your Process

05-15-2020

Phil Kinner examines the arch enemies to conformal coatings.

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Sensible Designs: Resins—Five Tips for Potting and Performance

05-05-2020

Readers continue to ask, “Does thicker coverage achieve better performance? What is the best advice for manual potting? We chose an inappropriate resin, so how will this affect our application?” In this column, Alistair Little explores these and other issues based upon frequently asked questions from Electrolube’s customers.

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2019

Sensible Design: Top Tips for Conformal Coating Selection

12-31-2019

Over the past few months, I have covered the topic of conformal coatings in as much depth as possible. In this column, I’m going to explore some of the essential factors for designers in coating selection. As we have all experienced, sometimes, things are not always as simple or straightforward as we would like them to be, and in any engineering discipline, there is always the slightest chance that something might go wrong. Thankfully, the key to kicking that possibility is to be as fully prepared as possible. Thus, I’m going to concentrate on helping you avoid coating pitfalls in my five-point guide.

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Sensible Design: Design Challenges and the Impact on Coating Success

11-15-2019

Phil Kinner concentrates on essential factors regarding the challenges board designs can pose on designers to help you implement a more successful coating operation, as well as issues that may arise with coating coverage, cycle time, and coating flow.

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Sensible Design: Five Key Factors for Flexible Resins and Potting Sensitive Components

10-18-2019

In this month’s column, I am going to concentrate on protecting sensitive components and take a more in-depth look at flexible resins, their reworkability, and some of the common problematic consequences that you may encounter. Potting compounds play an important role in the electronics industry where they serve to protect sensitive components from chemicals, moisture, dust, and damage, but their selection can baffle many. Let’s explore some frequently asked questions in more detail.

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Conformal Coatings: How to Design Out Production Problems

08-29-2019

In my last few columns, I’ve covered quite a bit of ground regarding the important considerations for conformal coating selection and performance, and the suitability of conformal coatings for LEDs and protecting circuitry from the harshest environments. I hope these columns have provided plenty of food for thought as well as given you a basic understanding of coatings and their benefits and limitations. In this column, I’m going to look at the different angles that design engineers and purchasing professionals come from and explore how these can sometimes conflict when selecting conformal coatings.

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Sensible Design: Resins Fit for a Purpose—Failure Mitigation and Environmental Concerns

07-18-2019

So far, in my columns on resin chemistries and encapsulation/potting techniques, I have tended to concentrate on the properties of these materials. My insights have included how they are best applied in the factory, and the steps that must be taken to get the best performance from them once they are in the field to protect an electronic assembly or lighting fixture against the elements. In this column, I am going to address the question of resin failures—in particular, how to avoid them—and to get a better idea of where and how appropriately selected and applied modern resins are making a big difference in the world of extreme electronics installation and implementation.

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Thermal Management: Why It Should Be High on Your Circuit Protection Agenda

06-06-2019

In my previous column, Jade Bridges highlighted a few cautionary notes on the pain points associated with thermal management products, particularly the choices that you will be confronted with, such as which material or product type (i.e., pad or paste) is best suited to your application. In this column, she will underline the importance of getting it right, and touch on the consequences if you don’t.

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Sensible Design: Five Tips to Further Improve Resin Encapsulant Performance

05-16-2019

There are a number of different factors that influence the protection afforded by potting compounds. The act of encapsulating a component or PCB means that it is surrounded by a layer of resin, which completely seals a component or an entire PCB from the environment in which it operates. When mixed, a two-part resin starts a chemical reaction, which results in the resin becoming fully polymerised to provide a homogenous layer.

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Sensible Design: Important Considerations for Conformal Coating Selection and Performance

04-25-2019

Having covered the subject of conformal coatings in depth over the past few months, now is an appropriate time to review some of the key pointers I have tried to share in my various columns. I present some of my thoughts on the essentials in this five-point guide.

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Sensible Design: Thermal Management Materials—Golden Rules for Product Selection

03-28-2019

Selecting the right type of thermal management method that will suit a particular electronic assembly and its predicted operating conditions is far from easy. There are a number of stages in the selection process that you should consider taking before you decide upon a particular material or material format, whether paste or pad. In this column on achieving effective thermal management of electronic assemblies, I will revisit our trusted question-and-answer format to bring you some essential pointers, beginning with a few cautionary notes on pain points—the occasional pangs of agony you will have to face during the decision-making process.

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Sensible Design: Getting the Best Performance from Encapsulation Resins

03-07-2019

When I last broached the subject of potting and encapsulation resins, I went into some depth on the subject, explaining their chemistries and physical properties, how they behave when being mixed, applied and cured. For this column, I’m going to return to our tried-and-trusted Q&A format to offer four commonly asked questions about resins and their application, together with my responses, which I hope will help you achieve the best outcomes for all your potting and encapsulation jobs. So, setting material choice aside for the moment, let’s start with a key aspect of potting: getting the resin in place.

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2018

Sensible Design: Top Tips for Successful Potting

12-19-2018

For effective potting, ideally, the layout of the circuit components should be such that the material can flow smoothly around them without too much turbulence. When possible, it is always good practice to space components in a regular pattern. Irregular spacing—particularly bunching of components in discrete areas of the PCB—causes the formation of eddies in the resin as it is poured, which can lead to voids and air entrapment, which compromise the thermal performance of the resin.

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Do's and Don'ts of Thermal Management Materials

10-18-2018

Selecting a thermal management material that is broadly applicable to a particular electronic assembly and its predicted operating conditions is a good starting point; however, as with many of these things, the devil is very much in the details! Find out the key considerations in choosing your materials.

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Conformal Coatings: An Evolving Science

09-26-2018

One of the trends impacting the electronics assembly industry is the continuing miniaturization of electronics products. This article sheds more light on coating problems posed by this trend, as well as provide key considerations when it comes to coating properties, selections, and applications. Read on to find answers to five of the best coating-related questions that frequently arise during preliminary consultations.

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Thermal Management Materials: Easing the Decision-Making Process

08-02-2018

There are many different types of thermally conductive materials, and choosing between them will be dictated by production requirements and application design, as well as critical performance factors that must be achieved.

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Protecting PCBs from Harsh, Challenging Environments

07-03-2018

Think very carefully about the sort of environment your PCB is likely to encounter. It is easy to over-engineer a product so that it will survive the very worst of conditions, but worst conditions may only be fleeting or transient. Therefore, a resin solution with a lower temperature performance specification will often cope. Take temperature extremes, for example. Your application may experience occasional temperature spikes of up to 180°C, which you might feel deserves treatment with a special resin.

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My Top Coating Queries

04-04-2018

This is my first of many columns for 2018, and I have decided to share some top trending queries that concern many different applications and areas. LEDs are always a hot topic, as are volatile organic compounds (VOCs) and harsh environment concerns.

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2017

Heat Transfer and Thermal Conductivity: The Facts

12-26-2017

In my first two columns, I presented a broad introduction to the subject of thermal management of electronic circuits. This month I’m taking a closer look at thermal interface materials—how they can be applied to achieve efficient heat transfer, and the significance of bulk thermal conductivity in relation to heat transfer and thermal resistance.

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Thermal Management—The Heat is On

09-25-2017

Thermal management materials are designed to prolong equipment life and reduce incidences of failure. They also maintain equipment performance parameters and reduce energy consumption by reducing operating temperatures, and minimising the risk of damage to surrounding components. Indirectly, they maintain brand reputation, as the reliability of the equipment will be very dependent upon the effectiveness of the thermal management technique used.

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Resins: Cutting Through the Technical Jargon

08-21-2017

This month, I’m going to cut through some of the more heavy-going tech-speak, taking a few of my customers’ more frequently asked questions about resins to try to help you refine your selection process. There’s a lot of ground to cover, but for the purposes of this column, let’s concentrate on the PCB’s operating environment, caring for the components that are to be encapsulated, and the special needs of applications like LED lighting and RF systems.

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Casting a Spotlight on Resin Applications

05-03-2017

Over the last few columns, I’ve given readers pointers on virtually every aspect of potting and encapsulation resins, ranging from their formulations and special properties to their applications, benefits and limitations. It’s probably high time, therefore, to take a step back from the do's and don’ts and focus instead on how these resins are bringing very real benefits to practical electronic and electrical engineering applications. A good starting point is to look at the special requirements of an industry that is enjoying explosive growth: LED lighting.

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2016

Resins: Five Essentials to Achieve the Right Cure

12-19-2016

In my previous column, I looked at some of the critical things you need to consider before selecting your resin. Of course, when it comes to the choice and application of resins, there’s a lot of information to take in, and over the following months I hope to distill this and provide some useful tips and design advice that will help you in your quest for reliable circuit protection.

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Why are Resin Properties So Important?

11-21-2016

I started this series of columns on resins by going back to basics, questioning the core rationale for potting and encapsulation with resins, their fundamental chemistries and how each resin type differs one from the other—indeed, how their individual properties can be exploited to maximise performance under a wide range of environmental conditions. I hope readers found this useful. Of course, when it comes to the choice and applications of resins, there’s a great deal more to discuss.

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The Little Guide to Resins

10-17-2016

I would like to start this series of columns by going back to basics, questioning the core rationale for potting and encapsulation with resins, their fundamental chemistries and how each resin type differs one from the other—indeed, how their individual properties can be exploited to maximise performance under a wide range of environmental conditions.

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Conformal Coatings - Beware the Boards that ‘Bare’ All!

09-21-2016

This month, Phil Kinner departs from his usual format of providing five essential facts about conformal coatings. Instead, he provides an account of a customer’s problem—no company names mentioned, of course—that brought into question the adhesion performance of a coating that they had been using successfully for some time.

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When Coatings Go Wrong

08-23-2016

This month, I consider some of the more common, and often very frustrating, problems that may be encountered when coating electronic circuit boards and components. I also discuss some practical solutions. As we all know, nothing in life is straightforward.

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Coatings—Five Essentials for Designers

06-28-2016

In an ideal world, PCB designs would not have an inherent weak point for corrosion; unfortunately, in the real world, they do. When a weak point is revealed, you are better equipped to deal with it. Often the spacing of components, board finish and distance to ground planes can be optimised for corrosion resistance.

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