Sensible Design: Pushing the Boundaries of Thermal Management

Jade Bridges_Electrolube_Oct2018.jpgThermal 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, I’m going to touch on some of the latest advances in thermal management technology.

Also, in keeping with our five-tip format, I will take a closer look at options for the automated application of thermal interface materials (TIMs) and discuss the feasibility of using a high thermal conductivity encapsulation resin instead of a TIM. There are a number of environmentally friendly thermal management materials available these days, so I will also examine ways to improve your green credentials, as well as demystify the importance of bulk thermal conductivity.

Without further ado, let’s get started with the new advances in thermal management.

1. What are the latest advances in thermal management technology, and how do these products differ from some of the more traditional pastes and greases?
Thermal pastes and greases have been leading the way in thermal management for many years and are expected to do so for many more years to come. Pastes are easy to apply and rework whilst providing a cost-effective alternative to thermally conductive encapsulants. However, make way for the new kids on the block: phase change materials (PCMs).

Once heated above their phase change temperature, PCMs become highly thixotropic liquids that perform as well as—and sometimes even better than—a traditional thermal grease. Moreover, their low phase change temperature ensures low thermal resistance over a wide temperature range and safeguards minimal bond line thickness with improved stability. With phase change technology, a key benefit is the greatly reduced effects of pump out, making PCMs an excellent choice for applications that undergo widely varying temperatures.

The application methods of PCMs for high volume production mean that most can be utilised in existing production processes with minimal—if any—changes, whilst also allowing for easy rework, offering many of the same benefits of traditional thermal pastes. PCMs offer greater long-term stability compared with thermal greases as they are better suited to thermally challenging applications where product life expectancy and reliability may be critical, such as automotive/aerospace electronics or remotely-located wind power inverters. Traditional thermal pastes/greases will continue to be a popular choice, although for some applications, especially those requiring greater long-term stability, a PCM is likely to win over the crowd.

2. What are the options for the automated application of thermal management products?
Automated applications involve the use of specialist equipment that typically consists of an applicator head where the material is fed to the applicator via dispensing equipment. Due to the high viscosities of the thermal management materials, the dispensing equipment is usually a follower-plate system that connects to the thermal paste container as supplied. In addition, automated stencil and screen applicators are widely used. For example, we work with a number of local and international equipment manufacturers.

3. When would I feasibly require an encapsulation resin with high thermal conductivity?
Electronic components and devices will produce varying levels of heat during their operation. Where significant amounts of heat are generated, intervention in the form of thermal management may be required to prolong working life and increase reliability. For certain types of applications, it may be beneficial to encapsulate the whole device in a heatsink enclosure using a thermally conductive encapsulation resin. This method offers both heat dissipation and protection from the surrounding environment, such as high humidity or corrosive conditions.

Once again, it is important to ensure that no air inclusions occur during the potting operation, as these will interfere with heat transfer to the metal case. Mineral fillers used in some resins systems have a higher thermal conductivity than the resin base, so filled resins are better than unfilled resins, as far as thermal control is concerned. The higher the filler level, the higher the thermal conductivity. However, higher filler levels will lead to higher viscosity and a greater possibility of air inclusions in the potting.

4. What options are available for more environmentally friendly thermal management products?
In recent years, we have seen demand increase for more environmentally friendly products across all our product groups. However, within the thermal management range, we have developed a high-performance thermal management paste that is entirely free from zinc oxide (ZnO). The non-silicone heat transfer compound is recommended for applications where the use of zinc oxide is restricted; for instance, in the marine industry, ZnO is a pollutant, and silicones are prohibited in places like offshore utilities. HTCX_ZF is a highly stable, non-curing paste that enables simple and efficient rework of components (if needed) and is recommended where efficient and reliable thermal coupling of electrical and electronic components is required, as well as between any surface where thermal conductivity and heat dissipation is important.

5. What is the importance of a bulk thermal conductivity value?
The initial selection of suitable TIMs for testing is often conducted based on high bulk thermal conductivity, indicating the efficiency of heat transfer through the TIM itself. However, bulk thermal conductivity alone could give a false impression of the expected performance. When tests are conducted under application conditions, low thermal resistance of the device indicates the true heat transfer efficiency of the TIM.

Conclusion
It can be a complex process deciding on the right choice of material and/or application technique regarding thermal management products. I strongly recommend getting expert advice before settling on any particular material or method. I hope this month’s column has shed some light on current thermal management issues.

Jade Bridges is global technical support manager at Electrolube. To read past columns from Electrolube, click here. Download your free copy of Electrolube's book, The Printed Circuit Assembler's Guide to… Conformal Coatings for Harsh Environments, and watch the micro webinar series “Coatings Uncoated!

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

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2020

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

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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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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: 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

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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

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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

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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

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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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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

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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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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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