Here at Epec, we provide various materials and key components used in our flexible heaters solutions. Our team carefully selects these materials to ensure optimal performance, flexibility, and durability in even the most demanding applications. From polyimide to silicone rubber, we offer a wide range of options to meet the specific needs of industries like aerospace, medical devices, and automotive.
In this blog post, we will discuss two important questions when picking out features on your heater, as well as some examples of how they can be used to aid etched foil and wire wound flexible heaters. We also will look at why it’s important for the heater to function properly as well as the most common materials, types, and examples.
Laminated Casing Material (Polyimide vs. Silicone)
Polyimide is a high-performance plastic encasing with high thermal stability and thermal conductivity, and it has excellent electrical insulation properties. This encasing is vital to the heater for its thermal conductivity as the thermal conductivity factor is vital to the performance of the heater, ensuring proper heater dispersion. The heat stability factor also plays a key role, as this allows them to be able to reach high temperatures and maintain high strength and flexibility for prolonged periods.
Example of a polyimide flexible heater and silicone rubber heater.
A great example of a polyimide heater is Kapton®, known for its exceptional heat resistance and flexibility. This encasing is commonly used in aerospace applications due to its key functions. Its thermal stability factor allows for it to be used as a barrier for areas that need resoldering. Its insulation factor allows it to be used as a protective layer on electrostatic-sensitive and fragile components commonly used in space applications.
Silicone is a rubber-like material well known for its flexibility and electrical insulation. It can be used with wire wound and etched foil elements (which we will get to later in this blog post). Furthering its capabilities, this material is known for its texture and water resistance. Protecting the heater from scuffs and scraping. The water resistance allows for this material to operate in wet outdoor environments and adds resistance to most chemicals.
Silicone rubber heaters are commonly used in medical fields due to it being hypoallergenic. It can be used in many applications due to its flexibility, such as pipes, automotive equipment, the food and beverage industry, and laboratory and analytical instruments to name a few.
Heater Element (Etched Foil vs. Wire Wound)
Etched Foil
Etched foil heaters use chemically etched circuits that are laminated between polyimide or silicone sheets. Their main features include wide traces and the ability to be printed. The wide traces help extend the coverage area in a uniform and efficient way due to the ability to space the traces as close as 0.004”. These features help our engineers route the traces to fit and be molded to several applications where regular non-flexible heaters cannot. A flexible heater can be used to wrap around and be molded into corners, pipes, and tight-fitting spaces.
Most etched foil heaters are nested in aerospace systems where precision temperature control and even heat distribution are crucial. These heaters can be as thin as 0.005”, making them a perfect candidate for military instruments as well as delicate medical devices.
Wire Wound
Only compatible with silicone rubber material, these heaters are used to ensure uniform heating with excellent physical strength.
The big advantages of using wire wound heaters include physical durability, larger application size applications, and the ability to provide more heat to specific sections of a heater as necessary. The ability to use either nickel, copper-nickel, or iron chrome aluminum further assists its potential.
Due to the overall strength and flexibility of these types of heaters, one can easily adjust them as needed, making it more than qualified to assist in the curing of GRP pipes commonly used in sewage and potable water lines. To areas such as drum heating and snow melting. These types of heaters are meant to exceed the limitations of etched foil heaters in most industries.
Both types of heaters are energy efficient due to their even heat distribution, precise temperature control, and low voltage operation, making them ideal for any project you can think of.
Thermistors
A thermal resistor works by acting as a resistor with temperature. The resistor will increase or decrease its resistance value. In simple terms, it is used as a sensor on a heater, the monitor you choose to read the value, determines whether to increase or decrease the overall temperature.
This integration of thermistors in all types of heaters has helped aid the ability to properly regulate temperatures. There are two types of these thermistors, positive temperature coefficient (PTC thermistors) and negative temperature coefficient (NTC thermistors). An NTC-type thermistor’s electrical resistance will decrease as the temperature rises. This is opposed to PTC thermistors, where resistance rises as the temperature increases.
Apart from its main appearance in automotive components to measure temperatures in oil and coolant levels, thermistors can also be found in ovens and refrigerators. With the use of flexible heaters, the medical, food, and laboratory applications benefit from them as well.
Thermostats
Thermostats, on the other hand, are regulating devices or tools that are used to regulate temperatures in heating and cooling systems. The main function of thermostats is to turn “ON” and “OFF” the heater. The way it works is using a bi-metal strip, which will allow electricity to flow in its normal state. When this strip reaches a high enough temperature, the strip will bend or curve, disrupting the flow of electricity and turning it “off”. When the heater cools down, this strip will return to its natural state and will let electricity flow, allowing the heater to increase temperature, it senses temperature either via a wired connection. Its simplicity allows for thermistors to be low-cost, allowing for easy and affordable replacement.
A flexible heater with a thermostat can be used in applications for lower costs, being that the thermostat automatically shuts off at the ideal temperature compared to a thermistor, which needs to be monitored. A good non-flexible heater example of a thermostat’s application is in heater fans, which can sense ambient temperature to determine when to shut off.
Thermal Fuses
These fuses are a type of safety device where the circuit opens when it senses a higher-than-normal temperature. The fuses play a vital role in safety by opening their circuit, also known as thermal cutoffs, prohibiting current from flowing when they exceed set temperatures, much like a thermostat would. These fuses sacrifice themselves to decrease the risk of a fire.
Materials for these fuses are meant to break in case of higher temperatures, much of which include lead wires, sealant epoxy, flux resin, tin, bismuth, and antimony to name a few.
PSA Rear Adhesive
Pressure sensitive adhesive (PSA) is a double-sided adhesive where one side sticks to your heater of choice, and the other side to what you want to heat or regulate temperature on. This adhesive is one of the most ideal ways to get your flexible heater to stick onto the surface of your choice. With the added benefit of being thermally conductive. Allowing for heat to efficiently travel from the heater onto objects and heatsinks.
Brands like 3M and TESA for these adhesives include many types of PSAs, including previously mentioned thermally conductive PSA, and electrically conductive PSAs. These electrically conductive PSAs help ground and attach both electrically and mechanically to a metal enclosure, this being possible by leaving exposed traces on the flexible heater.
Polyimide flexible heater with pressure sensitive adhesive.
Wires
A wire is a simple connection, providing transport for electricity. A flexible heater could not possibly function without electricity, and the best way to transport electricity to a heater is by using wires. Not just any wire can allow heaters to function, heaters need a steady supply of power to operate, and if the AWG rating does not suffice, a fire can break out.
In 1856, J.R. Brown and Sharpe created the American Wire Gauge Standard (AWG). Using this standard, we can calculate the proper wire gauge to ensure that the correct amperage can travel through.
Below is a simple list of common AWG wire sizes and their current carrying capabilities.
- 14 AWG – 15 AMPS
- 12 AWG – 20 AMPS
- 10 AWG – 30 AMPS
- 8 AWG – 50 AMPS
- 6 AWG – 65 AMPS
- 3 AWG – 100 AMPS
- 1/0 AEG – 150 AMPS
The larger the diameter of a wire, the lower its resistance will be, this is because the charge carriers (electrons) have more of a path on which to travel. The longer the length of a wire, the greater the resistance will be. This is because the electrons have more ions to collide with.
Strain Relief
Strain relief is an epoxy placed on the connection of a flexible heater and the wires that reduces tension where applied. A flexible heater cannot have a high life expectancy without the use of strain-relief epoxy. The main purpose of it is to reduce the risk of disconnection from a heater and the wires. Without one, an accidental tug on the connecting wires could sever the power connection or worse, rip the etched foil/ wire apart causing irreparable damage to the heater.
There are many kinds of applications where we use reliefs, every single flexible heater leaves our factory with a different kind of relief. In addition to heaters many flexible PCBs and rigid PCBs use a type of relief for their connections as an added safety, this helps to limit the number of damaged components and unnecessary repairs.
Backer Plate/Heatsinks – Aluminum
A heat sink’s main purpose is to dissipate heat away from the source, it can also be used to acclimate a surface or object so that it is not in direct contact with heat. In addition to heat dissipation, heat sinks, such as those made from aluminum, can also serve as protective barriers. By acclimating the surface or object, they prevent direct exposure to intense heat, reducing the risk of damage or degradation. This dual functionality makes aluminum-backed heat sinks especially valuable in applications where heat-sensitive components need both thermal regulation and physical protection.
Aluminum
If the intended purpose is dissipation, then aluminum takes the cake. This material has a high heat capacity, meaning that it takes less heat energy to raise the temperature of aluminum.
Silicone rubber heater with aluminum backer plate.
A good example of an application of aluminum is a water heater, while the heater does not have to be in direct contact with water, aluminum can, and since this is true, some factories have decided to use aluminum rods to heat water. Also, due to its low heat retention, it can cool down faster than most materials.
Summary
Selecting the right features for your flexible heater project involves considering various materials, heating elements, and components to ensure optimal performance for specific applications. Additionally, selecting between etched foil or wire wound heaters can affect durability, heat distribution, and application flexibility. Ultimately, the right combination of materials and features ensures that the heater meets the unique demands of industries like aerospace, medical, automotive, and more.
