Flexible Thinking: Thermal Management—Electronic Technology’s Rodney Dangerfield

“I tell ya, I don’t get no respect,” was an opening line made famous by one of the funniest comedians of the last century, Rodney Dangerfield. And while decidedly not funny in the world of electronics, thermal engineering has, unfortunately, often been treated with less respect than it deserved. Dealing with the heat generated by electronics was often not given full consideration until after the design was completed and prototyped, and the problem manifests as a failure. 

It’s a simple fact that where there are electrons flowing (superconductors aside), there is heat. “How much heat?” is the salient question, as well as, “Will it be a problem?” The next question is how to deal with it. To the first point, heat in electronics is almost always a problem. The reason is that there is an inverse relationship between heat exposure and the reliability of electronic devices. Integrated circuit transistors are vulnerable to failure due to diffusion of metals through insulators causing shorts. In short form, the higher the heat, the lower the reliability. Thus, keeping devices cool is a vital objective. 

There is another reason to keep things cool, however, which is to mitigate the mechanical strain that is manifested when devices having vastly different coefficients of thermal expansion (CTE) are intimately joined, such as a BGA soldered to a PCB. It is a well-known fact that solder joint failure is a leading cause of assembly failure. 

There used to be a saying employed by thermal engineers that helped succinctly frame both the challenge and the solution. “It all goes back to air,” and that has remained true since it was first observed and uttered, perhaps as early as the first vacuum tube amplifier. The challenge that has remained ever since is how to get the heat generated by electronics “back to air.” 

There are multiple ways that heat can be managed. At the earliest steps, the choice of technology is important. To provide some perspective, the world’s first electronic computer, the ENIAC, had some 30 separate computing units plus a power supply. The system weighed some 60,000 pounds, was 100’ x 10’ x 3’, and contained roughly 19,000 vacuum tubes; 1,500 relays; hundreds of thousands of resistors, capacitors, and inductors; and required 500,000 hand-soldered interconnections. Its power consumption was about 200 kilowatts. The smartphones we carry in our pockets are several orders of magnitude both smaller and more powerful than the ENIAC, but use a fraction of the energy. Transistors are much more efficient; however, the energy density of the processor chip in watts per square millimeter is still arguably many times greater. It’s all a matter of perspective. 

Both computers require cooling to perform efficiently. The ENIAC employed a forced-air cooling system to deal with the massive amount of heat generated by the tubes. Those who remember cathode ray televisions will likely remember just how warm the area around the TV was. 

When it comes to managing heat, there are only three fundamental ways: conduction, convection, and radiation, as well as a number of ways to augment them. Of these, conduction is arguably the easiest, fastest, and most efficient, but conduction needs a thermal sink to further remove heat from the conduction source to keep it cool, and that is convection—the means by which the heat is transferred to air. Radiation is the least efficient (it’s also the way the Earth attempts to rid itself of excess heat at night as the Earth rotates and at least part of the reason global warming is a problem), but for electronics, all three methods can be and often are combined to keep things cool. 

To help deal with the heat, thermal engineers have developed many clever solutions over the years to protect electronics from overheating. This often happens in concert with system designers. One such solution is what has been called a “stepped phased system protection” protocol. The first level of thermal protection is passive thermal protection. These include heat sinks, heat spreaders, heat pipes, and the like to remove heat directly through conduction aided by convection from the device (normally a CPU). If things get too hot for the passive and semi-passive solutions, a fan is often engaged to assist heat removal at the first thermal threshold. Additional sophistication and the use of software is the next solution, where the CPU/system clock speed is reduced to reduce energy generation when a threshold is reached. This is followed by an overheat condition warning to the user. If that fails, to get a response, the system will automatically shut down. 

There have been many solutions to the thermal problem as watt densities increase. It is recommended that the designers familiarize themselves with both the solutions and to not ignore the importance of thermal interface materials (TIM), which are vital to assuring that the first thermal pathway is a good one. 

Thermal challenges are unlikely to go away so long as electronics persist. Photonics have been suggested as one prospective solution. There have also been suggestions that biologic computers using neural networks assembled by DNA are in the future by some futurists, but—come to think of it—isn’t that what humans are? 

Stay cool—and give all those thermal management engineers some well-deserved respect.

This column originally appeared in the September 2020 issue of Design007 Magazine in the FLEX007 section.

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2020

Flexible Thinking: Thermal Management—Electronic Technology’s Rodney Dangerfield

09-17-2020

Thermal engineering has, unfortunately, often been treated with less respect than it deserved. Dealing with the heat generated by electronics was often not given full consideration until after the design was completed and prototyped, and the problem manifests as a failure. Joe Fjelstad emphasizes why keeping devices cool is a vital objective.

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Flexible Thinking: Designers at the Edge

07-15-2020

Designers often play it safe in the center, but step out on the edge and you’ll likely see things much differently. Joe Fjelstad shares his thoughts.

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Flexible Thinking: Lead-Free Solder—Panacea or Pandemic?

06-26-2020

Solder has been used as the primary means of interconnecting electronic components for more than seven decades. For the benefit of all those who are new to the electronics interconnection industry, Joe Fjelstad shares how we got to this point.

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Flexible Thinking: When Expectations and Results Don’t Line Up

05-15-2020

Around 20 years ago, I had the good fortune of receiving a recommendation to read the book The Four Agreements by Don Miguel Ruiz and subsequently picking it up. It is a short and simple book that the author says is based on ancient Toltec wisdom.

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Flexible Thinking: DFM or Design With Manufacturing?

04-15-2020

The great Irish author, playwright, and humorist Oscar Wilde once defined a cynic as an individual who knows the price of everything and the value of almost nothing. Unfortunately, over the decades, that same analysis could often be applied to procurement agents in electronic product companies around the globe. The reward for a purchasing agent is too often derived not from getting the best solution for their company but the best price

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Flexible Thinking: Profitability—A Vital Design Requirement

03-27-2020

The decisions designers make will impact virtually every manufacturing step in the fabrication and assembly of electronics products. Joe Fjelstad explains how applying “design for” guidelines can help create products that can be made both reliably and profitably when applied.

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Flexible Thinking: Power and Thermal Management—Dealing With the Heat

02-15-2020

Without power, electronics are useless. With power, miracles happen. Managing that power is critical in both design and operation in terms of heat generation and energy conservation, especially for battery-powered devices. Moreover, often in electronic products, designers find themselves providing power to an electronic module or system at multiple different voltages and currents.

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Flexible Thinking: Looking Back and Looking Forward

01-27-2020

The month of January is upon us once again. The month is named after the Roman god Janus. According to Wikipedia, Janus is the god of beginnings, gates, transitions, time, duality, doorways, passages, and endings. He is usually depicted as having two faces: one on the front of his head, and one on the back since he looks to the past and future.

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2019

Flexible Thinking: The Value of Experience

12-15-2019

For many people, December is a month in which to reflect on the experiences and lessons encountered and learned over the past year. As the years pass, I am increasingly thankful for the many experiences that have brought me to this point. In sitting down to collect and share my thoughts, what first came to mind was a timeless story about the value of experience. It goes something like this.

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Flexible Thinking: Additive Manufacturing of PCBs

11-23-2019

We are seeing increasing interest in technologies that will allow one to make electronic substrates in near real-time using additive processing techniques and 3D printers. It is a true game-changer in product development. The surge in interest in additive manufacturing technologies shown in recent times—as indicated by the significant increase in published articles and press releases—suggests that the electronic interconnection manufacturing industry could be on the verge of a manufacturing renaissance.

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Flexible Thinking: Standards—An Industrial-strength Glue

10-21-2019

Standards are frequently viewed as cumbersome nuisances and impediments to progress by those pressing for rapid change. The process of writing, getting approval, and promulgating standards can be arduous and frustrating. It has a lot of similarities to the creation and passage of laws in various government bodies in that there are many opinions and interested parties who engage in the process to make sure that it results in a product that does not damage or favor one solution or party over another.

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Flexible Thinking: Making Flexible Circuits Stretchable

09-05-2019

It is my opinion that the initial driving impetus for the development of stretchable circuits was a bit different than normal, meaning that military and aerospace have traditionally driven the development of arcane electronic interconnection technologies as they did with the development of both flexible and rigid-flex circuits. In contrast, it was a consumer-driven market that appears to have been the gate opener in the form of wearable electronics.

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Flexible Thinking: How to Get From Here to There

04-26-2019

To begin any process, you must first know where you are going. This is true for any project or life pursuit, I believe, and I often try to bring it to mind as I start any new project. With respect to developing products that might benefit from flexible circuit technology, this is no less true. Find out why.

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Flexible Thinking: Ways to Conserve Flex Circuit Material in the Design Process

02-25-2019

In summary, the decisions made by the flex circuit designer when laying out a flex circuit will have an impact that lasts the entire process. By considering how the circuit might fit onto a panel before submitting the design to a manufacturer, it may be possible to save a considerable amount of material and money.

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Flexible Thinking: A Few Simple Lessons in Designing Reliable 3D Flex

02-11-2019

There is an old and familiar adage that goes something like this: “If the only tool in your tool chest is a hammer, you tend to see every problem as a nail.” We all have a tendency to stick close to the familiar and use the tools we know to create solutions to problems confronting us; we’re only human.

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Flexible Thinking: A Few Simple Lessons in Designing Reliable 3D Flex

01-15-2019

We all have a tendency to stick close to the familiar and use the tools we know to create solutions to problems confronting us; we're only human. Unfortunately, using only familiar tools limits our ability to come up with optimal or even superior solutions. This article will help you avoid some of the traps conventional wisdom doesn't always give guidance on.

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2018

Flexible Thinking: Achieving Continuous Flexible Circuit Innovation

12-07-2018

Since their introduction, flexible circuits have continued a steady climb from relative obscurity to center stage in the world of electronic interconnections. Today, they are among the most popular choice for solving challenging electronic interconnection problems. Those who use this technology on a regular basis are familiar with the many reasons for the popularity of flex.

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Flexible Thinking Redux

07-02-2018

Flexible circuits are known by a few different names depending on one’s global location and language: flexible printed circuits, FPCs, flex circuits, flexi circuits, flexibles, bendables and a few others that are application-specific such as flexible heater circuits and controlled impedance cable constructions. While flex circuits are an original and foundational interconnection technology for electrical and electronic products (one of the first patents for electrical interconnections, issued at the turn of the last century, was arguably a flexible circuit), over the years there have been several forays into technological extensions of the basic idea.

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2017

Flexible Thinking: The Benefits of Employing a Standard Grid Pitch in Design

03-31-2017

The industry at large needed to jump on the learning curve and overcome its fear of the unknown. One of the most vexing concerns at the time (an arguably still today) is that terminations beneath the area array package were unseeable. Given the fact that then, as today, solder joints were a major cause of failure, there was much consternation over the quality of the joints.

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2016

Flexible Thinking: Process Engineering—PCB Manufacturing’s ‘Delta Force’

05-11-2016

Process engineers serve a vital function on the front line of printed circuit manufacturing. They are often, if you will, the “Delta Force” that subdues and controls that which is one of the mortal enemies of manufacturing…process variation.

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2015

3D Printing in Electronics - A Perspective

01-14-2015

Knowing the value of a product or technology is key to making the right decision. Appreciating the value of an element of business is evermore important as the rate of change surrounding an industry accelerates. This brings us to one of the current buzz subjects in our industry: 3D printing. Understanding what it is and what its value is to a company and that company's ability to improve its place in the industry is vital.

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2013

The E.I. Files: The Electronics Industry's Black Swans

07-31-2013

First proposed in 2007, there is a potential electronics industry "black swan" technology quietly being developed and refined. It is one that could greatly and positively impact, at once, the cost, reliability, and environmental friendliness of electronic manufacturing by simply eliminating the soldering process.

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Flex Circuits and Photonics: A Pairing for the Future, and the Here and Now

04-17-2013

Photons are making continuous headway into the world of electronics. One thing that the basic data carriers (electrons, microwaves and photons) have in common is that flexible circuits are being increasingly looked to for help in managing their data transmission function.

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2012

Stretching the Limits of Flex

11-29-2012

Those steeped in flexible circuit design and manufacture for any length of time fully appreciate the long list of benefits that only flexible circuits can offer. Some of the most fundamental benefits of flex circuit technology have been exploited since the earliest days of the technology. Joe Fjelstad explains.

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Flexible Thinking: Circuit Flexibility (and How to Achieve it)

10-04-2012

The most common interpretation of the word flexible, as applied to the flex circuits that the industry currently makes, is something capable of being bent repeatedly without breaking. Joe Fjelstad discusses a few other definitions of flexible that are worthy of consideration when using the term, for their ability to unlock new thinking patterns relative to what is flexible.

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Technology Roadmaps: Thoughts and Observations

09-26-2012

If one is without a sense of the direction their technology is headed, odds are that they will sooner find themselves on the road to ruin than the road to success. A technology roadmap is a critical tool in helping a company make informed decisions. By Joe Fjelstad.

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2011

Something Old, Something New: Stretchable Circuits and Elastronics

10-13-2011

The stretching of circuits to alternately increase and decrease the length of a circuit has proven useful for electronic products and assemblies for years. Stretchable circuit technology and elastronics are poised to take on challenges that cannot be easily met by flexible circuit technology alone. Keep them in mind next time you find yourself in need of a little more "spring" in your design. By Joe Fjelstad.

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Stretchable Circuits: The Emergence of "Elastronics"

07-14-2011

The stretchable circuit is an interesting and promising new branch on the flexible circuit tree. The stretching of circuits to alternately increase and decrease the length of a circuit has proven useful for many years. The European Union has funded research in this area through such initiatives as the STELLA project.

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2010

Flexible Thinking: An Alternative Approach to Rigid-Flex Assembly

11-18-2010

The fundamental approach to manufacturing rigid-flex has remained constant for the 40-plus years of rigid-flex history. But is there a better way? What if one could produce a circuit that was rigid throughout the manufacturing process and only become flexible in the final step? In other words, what if one could make a rigid circuit assembly, flex?

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Reasons Why The Flex Market Continues to Shine

10-07-2010

According to IPC market statistics, flexible circuits continue to be the brightest sector of the overall printed circuit market. The reasons for this are many but, at the end of the day, it generally boils down to the fact that flexible circuits are an excellent way to solve interconnection challenges in a cost-effective way.

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Flexible Thinking: Flexible Structures for Data Transmission

08-12-2010

Flexible circuit cables offer some significant advantages for facilitating the movement of data between elements of a system that must also be moved or flexed. However, there is a balancing act involved and there is more than one master to be served to create a system that is robust, reliable and easily manufacturable.

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Flexible Thinking: Supporting Components on Flex Circuit Assemblies

07-21-2010

With proper planning, stiffeners can be designed to aid assembly through the designed manufacture of a flex circuit that can be handled as if it were a rigid circuit board. Such constructions can be accomplished by using any one of several methods.

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A Simple Approach to Flex Manufacture, Assembly

04-29-2010

Flexibility, the single attribute that makes flex so attractive, also makes flex circuits more difficult to build. What if we could produce a circuit that was rigid throughout the entire manufacturing process and only become flexible in the final step?

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