Sensible Design: Resins–Are They All About Chemistry?

Alistair Little mug.JPGIn my previous columns, I have looked at many different aspects of resin systems by going right back to basics, questioning the key reasons for potting and encapsulation, examining how different resins systems vary from one another, and exploring how their individual properties can be exploited to maximise performance under a wide range of environmental conditions. I hope this has proven useful.  

When it comes to resin selection and application, there are a plethora of factors to consider. Resins come in many forms and have lists of properties that would challenge even a graduate chemist. For this month’s column, I’m going to take a closer look at thermally conductive resins, flexible resins, elevated cure temperatures, resin types for different applications, and resin systems that enable wider operating temperatures. Without further ado, let’s look at these topics in our signature five-point format. 

1. What are the benefits of a thermally conductive encapsulation resin? 

As electronics have become smaller and more powerful over the years, the amount of heat generated per unit area on a PCB has increased as well; however, it is well known that electronics will perform much better at low temperatures. Thermally conductive resins are designed to allow heat to be dissipated away from sensitive components. The typical thermal conductivity of an unfilled resin is 0.20-0.35 W/m.K. For a resin to be classified as being thermally conductive, it must have a thermal conductivity of >0.8 W/m.K. This is usually accomplished by using selected ceramic fillers, which offer a combination of thermal conductivity and chemical stability. 

2. Which resin chemistry types typically allow the widest operating temperature ranges, and why? 

Providing exceptional performance at high temperatures, silicone resins have the broadest temperature range (-50 to +250°C), but these are generally soft resins and are not as chemically resistant as some of the other resins. Some polyurethanes can go down to temperatures lower than silicones (-60°C) but have a maximum operating temperature of +150°C, while epoxies are designed more for higher temperature applications (-40 to +200°C) but have excellent adhesion to a wide range of substrates and excellent chemical resistance. 

3. Why are some resins suited to different applications?  

It’s all in the chemical bonds! Epoxies are tough yet can be brittle due to the high crosslink density that is possible. But this high crosslink density also means that the resins are very resistant to chemicals and have excellent adhesion to a wide range of substrates. Polyurethanes are generally made up of long flexible polyols linked together by reactive isocyanates, giving rise to the classic hard and soft segment polymer, which means the resins are normally tough yet flexible. The reactivity of the isocyanates also means the resins have good adhesion. Silicones are soft yet very flexible resins due to the presence of silicon in their chemical structure. This makes them very temperature stable and capable of withstanding a wide temperature range, particularly high temperatures. 

4. Is it a good idea to use elevated temperatures to accelerate the curing process? 

Elevated cure temperatures are used to speed up the production process and reduce the cycle time. However, there are a few points that need to be considered. It is best to wait until the material has reached its gel time before subjecting the resin to a high temperature; if this is not possible or desirable, then the use of a temperature ramp is advised.  

In the case of epoxy resins, care must be taken due to the exothermic nature of the epoxy curing reaction, particularly with fast-curing unfilled resin systems. Also, the amount of resin being cast at one time in a unit is critical. A large amount of resin has the potential to generate a lot of heat, which speeds up the curing reaction.  

For silicones, care must be taken when curing as the catalysts used are very susceptible to being poisoned. It is recommended that silicone resins be cured in a separate oven from other resin types. If they are to be cured in the same oven as other resins, then the oven should be well ventilated before putting the silicone resin inside—no other resin types should be present. 

5. Why would I potentially require a flexible encapsulation resin for my application, and what types of applications would typically suit this type of encapsulation resin? 

Flexible resins find a wide range of applications as they can accept and absorb physical and thermal stresses well. If a unit will be subjected to thermal cycling, either continuously or infrequently, then a flexible resin is designed to withstand the stresses induced under such conditions. Similarly, in the case of physical shock, where the electronics need to be protected against vibrations, then a flexible resin will absorb the stresses far more effectively than, perhaps, a more rigid resin. 

Conclusion 

Every customer and customer project is different; while we can advise a customer as to which products are best suited to their needs based on our years of experience, it all boils down to the unit, dispensing method/equipment to be used, curing times, and temperature limitations that may be imposed during the production process. The more information that the customer can provide regarding the resin’s ultimate operating conditions—temperature range, likely chemical exposures, and so on—the better.  

Certainly, technical datasheets can be a great help when you embark on a new production schedule with new components and resins, but if you foresee any problems with matching resin types to your production procedures that are not easily resolved by studying the literature, be sure to contact your supplier’s technical support team for further advice.  

Next time, I will take an in-depth look at some of the most frequently asked questions we get as resin experts and explore various options in response to these enquiries 

This column originally appeared in the July 2020 issue of Design007 Magazine.

 

 

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2020

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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Sensible Design: Encapsulation Resins—What Could Go Wrong?

02-15-2020

Alistair Little addresses some of the pain points with mixing resin packs and air bubbles, including what can go wrong and why. He also examines some of the key differences between conformal coatings, encapsulation resins, and potting compounds to help designers make decisions that are more informed, ultimately increasing the reliability and lifetime of your electronic circuitry.

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Sensible Design: Five Top Resin Tips

01-15-2020

Alistair Little provides some useful advice on encapsulation resins to help designers achieve even higher levels of reliability when it comes to protecting circuitry. He highlights five critical factors affecting encapsulation resins, including potential contaminants, no-clean/cleaning processes, adhesion, and best mixing practice.

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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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