All About Flex: Considering a Flexible Heater?

Custom flexible heaters are available in an infinite variety of sizes, shapes and materials. The most common flexible materials are polyimide and silicone rubber. While silicone rubber has traditionally been thought of as the higher temperature flexible heater option, recent advances in polyimide-based materials have allowed high performance heater constructions to operate successfully at temperatures that exceed 250°C. But few customers are really interested in the temperature of the heater. They are using a heater to elevate the temperature of a “heat sink” (i.e., the device the heater is attached to). So, a discussion of engineering considerations for use of a flexible heater is often useful. 

The wattage of a heater is the overall watts the heater generates based upon the input voltage and resistance of the heater (assuming sufficient amperage at that stated voltage is available from the power supply). You could have a 100-watt heater that is a 4” X 4”, or another heater delivering 100 watts but is two square feet in size. The heat (thermal output) generated by the 100 watts in the 4” X 4” example pushes heat out through 16 square inches of area. The second example spreads that same wattage over 288 square inches. So, what we really look at is watt density, or watts per area. In these two examples, each are 100-watt heaters, but the first has a watt density of 100/16 or 6.25 watts per square inch. The second example is 288/100 or 2.88 watts per square inch. 

In a pure state, the first heater example will get much hotter compared to the second example, however, everything depends upon how the individual heater is used in its application. If each heater was suspended in still open air, the first will get much hotter than the second. But in an application, the first heater might realistically be mounted onto a thick aluminum plate which serves as the door of a freezer. The aluminum plate is normally cold to the touch and will “absorb” heat quickly. We could take the first ‘hotter’ heater and stick it onto the aluminum plate and the heat will be quickly extracted from the heater and into the cold plate using thermal conduction. No matter how long the heater is stuck there, the high mass door rises in temperature modestly, perhaps an increase of 10 degrees as it transitions from a cold to semi-cold state. In addition, the heater itself, even though it may get hot if it was hung in the air, no longer gets hot. It is still generating 100 watts but the heat is rapidly transferred from the heating element into the aluminum. 

Another example is in an application where the starting temperature is very cold, like -50°C, and the application needs to heat it to +150°C. This would require a high watt density heater to provide that type of thermal rise. Similarly, an application may have a requirement to heat quickly then shut off. In these situations, the heater is likely to require a high wattage/thermal output. But the heater itself never gets above 150°C. In this example a heater could work well provided the heat from within the heater can be transferred before the heater itself gets too hot to maintain structural integrity. 

Customers generally need three key pieces of information for each individual application: 1) how hot they want their “product,” (i.e., the eventual stabilization temperature); 2) how fast they want that heating to occur; and 3) at what temperature the device will be when it begins heating. These multi-dimensional factors can drive the heater design and material construction. Finite Element Analysis (FEA) software can be used to model an accurate estimate of thermal performance in complex scenarios. Other times, sample heaters are used with a variable power source to define watt density required through empirical testing. This information can then be used to define a custom part. 

In a nutshell, specific applications drive whether an individual heater can survive or not. A very high watt density heater might be sandwiched between two cooling plates and the heater will survive just fine at a high watt density. But the same heater, if wrapped around a glass tube, might burn up because the heater is unable to handle the heat generated since the glass effectively insulates and slows thermal transfer. When considering ultra-hot heating applications (250°C+), the application may require the heater to achieve 300°C and not degrade. New materials are allowing successful designs at this elevated temperature. 

Dave Becker is vice president of sales and marketing at All Flex Flexible Circuits LLC.

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2017

All About Flex: Considering a Flexible Heater?

03-02-2017

Custom flexible heaters are available in an infinite variety of sizes, shapes and materials. The most common flexible materials are polyimide and silicone rubber. While silicone rubber has traditionally been thought of as the higher temperature flexible heater option, recent advances in polyimide-based materials have allowed high performance heater constructions to operate successfully at temperatures that exceed 250°C.

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All About Flex: Volume Considerations

02-16-2017

With any new electronic interconnection project, one immediate question the supplier will inquire about is program volume expectations. Customers often ask “What is your capacity?” with low-, medium- and high-volume having different meanings to different people.

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All About Flex: Creating a Flexible Circuit Cutline

02-02-2017

The perimeter dimensions of a flexible circuit are often referred to as the cutline. While rigid printed circuits are often rectangular and generally a less complex outline, the requirement for a flexible circuit to be an integrated part of the product packaging often involves unusual sizes, shapes and features in the circuit perimeter.

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All About Flex: Are Manufacturing Companies Susceptible to Ransomware?

01-12-2017

Every business (and every individual) needs to pay attention to cyber security. There are many sophisticated hackers throughout the world looking for ways to access or corrupt systems. While manufacturing companies have not been a common target, there are certainly risks that need to be considered.

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2016

All About Flex: Customer Acquisition

12-22-2016

The “Customer Acquisition” process can be thought of as consisting of three major segments: collection, selection and execution. While these sub-divisions should be considered as intimately interrelated, examining them as separate disciplines can be enlightening.

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All About Flex: Disruption in the Supply Chain

12-08-2016

Manufacturers need a highly dependable supply chain to successfully support their products. This is especially true of custom designed and built components, as many times, only one supplier is available for a component since tooling and development costs discourage dual sourcing.

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All About Flex: Packaging Flexible Circuits and Assemblies

12-01-2016

Many facets are involved in delivering a flexible circuit. During the quote and design phase, requirements are reviewed. So assuming the relevant product documentation was gathered, the salesperson turned around the quote, and the customer placed an order and parts were built, it’s all over, right? Not quite. One critical aspect that does not get much discussion is packaging and shipping.

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All About Flex: Non-Copper Flexible Circuit Applications

11-22-2016

While pure copper is the most common choice for flexible circuit fabrication, there are times a different metal is more suitable for an application. Copper is well known for its excellent electrical and thermal conductivity, but there are applications where the best thermal or electrical conductivity can be a disadvantage.

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All About Flex: Flex Circuit Specifications for Commercial and Military Applications

10-27-2016

Applications across the various markets for printed circuit boards can have significantly different specifications and performance requirements. Circuits for toys and games logically have lower performance requirements than those used in medical devices. IPC-6013 is an industry-driven specification that defines the performance requirements and acceptance features for flexible printed circuit boards.

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All About Flex: Five Characteristics of a Reliable Flexible Circuit Supplier

10-27-2016

Due diligence when selecting a source for a custom electronic product can be a critical sourcing procedure. Chains are only as good as the weakest link, and the electronic components assembled to create a marketable product need to combine into a robust solution.

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All About Flex: Flexible Circuit Prototypes

10-13-2016

Most electronic projects begin with at least one build of prototype parts before moving into volume manufacturing. But the definition of a flex circuit prototype can vary considerably from one project to another. In many cases, a prototype build is only a few parts used to verify form, fit and function, with engineering trying to determine if something actually works.

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Flex Circuit Specifications for Commercial and Military Applications

09-30-2016

Applications across the various markets for printed circuit boards can have significantly different specifications and performance requirements. Circuits for toys and games logically have lower performance requirements than those used in medical devices. IPC 6013 is an industry-driven specification that defines the performance requirements and acceptance features for flexible printed circuit boards.

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All About Flex: Lead-Free Soldering Flexible Circuits

09-23-2016

Ever since the European community adopted the RoHS directive in 2006, the U.S. electronics industry has been steadily increasing its use of lead-free solder. Medical was the first U.S. industry to go totally lead-free. Today, a significant percentage of electronics soldering is done with lead-free solder.

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All About Flex: FAQs on RoHS for Flex Circuits

09-02-2016

In 2003, the European Union (EU) adopted a standard called the Restriction of Hazardous Substances (RoHS), which restricts the use of certain materials in electronic products and electronic equipment. The intent is to reduce the environmental impact of known hazardous materials and has driven changes in manufacturing processes and materials used to manufacture a wide array of electronic products.

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2015

All About Flex: Embracing the Mess

12-03-2015

Marketing in the world of printed circuits is an important discipline, but I have learned it is better to be prepared with a nimble reaction than to expect the marketing department to consistently be successful in predicting the future. The path to the goal is often achieved much more quickly by making an early decision followed by a course correction rather than waiting for all the information.

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All About Flex: Flexible PCB: What’s in a Name?

11-12-2015

Flexible PCB is a common term that is synonymous with flexible circuits. While the term “PCB” is generally used to describe rigid printed circuitry, “flexible PCB” is a little contradictory because “boards” aren’t really flexible. Some companies, like All Flex, design and manufactures flexible PCBs, but not rigid PCBs. There are many similarities between the two, but also significant differences.

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Plated Through-holes in Flexible Circuits

10-29-2015

There is probably no more important feature than the plated through-hole (also called via or via hole) with regard to the reliability and integrity of a flexible circuit. The through-hole provides electrical connection between insulated layers and enables electrical functionality on double-sided and multilayer flexible circuits.

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Testing Flexible Circuits, Part 3: The Completed Flex Circuit

10-15-2015

Most flex houses perform a variety of tests on completed flexible circuits. The type, frequency, and complexity of these tests vary with customer and application. Test requirements are generally defined by the customer, but input is often solicited from the supplier during the quote process.

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Testing Flexible Circuits, Part I: Requirements and Procedures

09-17-2015

In this first of a three part series regarding tests for flexible circuits, I will examine overall requirements and procedures; the second installment will focus on raw materials, and the third and final part will focus on testing for bare flexible circuit and circuit assemblies.

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Catching Up to Yesterday

09-02-2015

Recently, KPMG, an international consultancy that operates as a network of member firms offering audit, tax and advisory services, came out with their 6th annual survey of manufacturing executives focusing on global manufacturing trends.

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The Butterfly Effect

08-20-2015

If a random initial disturbance from the wings of a butterfly can have a dramatic effect, just think what can be accomplished with intentional acts aimed at making sure our customers are receiving proactive attention.

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Is Wearable Technology Just a Fad?

08-13-2015

Wearable technology is in its infancy. The industry needs to mature and go back to basic marketing—finding a need and filling it. Flexible circuits have been around since the mid-1960s and have been successfully filling needs. Flexible circuits are ideal for wearable technology because they are thin and lightweight. As the marketing matures, the applications will come and flexible circuits will be there to fill the technical needs.

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Unique Single-Sided Flexible Circuits

08-06-2015

The number of iterations, sequences and combinations possible when manufacturing a flexible circuit can create unique product features to reduce hand assembly of wires, create switch contacts, or eliminate connectors. With minor alterations in basic processing steps, a flex circuit applications engineer can often imagine and configure a dramatically different flexible circuit.

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Agricultural Drones and Flexible Circuits

07-28-2015

According to MIT Technology Review, one of theTop 10 breakthrough technologies last year was the agricultural drone. I focused on drones in one of my recent columns, Flexible Circuits and UAV Applications, which briefly mentioned agriculture as one of the uses for drones.

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