Your Definitive Guide to the PTC Thermistor Manufacturing Process

Your Definitive Guide to the PTC Thermistor Manufacturing Process

Posted by Adelle Webber on

My husband “Sparky” asked me last night if I ever stopped to think about how many industries benefit from PTC heaters?  My answer; “not once, not ever”, but he continued anyway.

Windmills that provide clean energy for our home use them. 3D printing, an industry that's revolutionizing everything from engineering to healthcare, relies on them. Even outside electronic devices, such as ATMs, rely on PTC heaters to maintain an ideal working temperature. 

You're probably wondering how these heaters can operate without getting too hot and damaging electrical components, he says.  My answer again; not once, not ever” but he persists on telling me more. 

 A PTC thermistor is inside each heater that helps protect against overcurrent positions. These thermistors achieve this by increasing resistance as temperatures rise. The great physicist and master of electricity Michael Faraday discovered the first thermistor in 1833. 

Since these elements are essential to industrial heaters, let me tell you about the manufacturing process of PTC thermistors!

A Powdered Mix is the First Step to Creating a Thermistor

The first step involves creating a powder out of substances that lead to the desired electrical and thermal characteristics. 

Different companies use various materials. Some use titanium oxide, barium carbonate, and other materials, while others use manganese and copper. Experts precisely measure, weigh, proportion, and mix the materials with deionized water..

Once mixed, the materials go into a ball mill mixer to ensure and blend evenly. After the powder dries, spray granulation occurs, which improves the flow characteristics of the powder and increases the density, surface area, and particle size. This step is an essential one when it comes time for sintering.

Pressing And Sintering The Thermistor Ingredients

The powder from the previous step goes into a presser where it gets shaped. Thermistors come in several shapes due to their multiple uses. Pressing shapes them into a disk, chip, bead, or rod shape depending on the material monitored. 

The sintering process establishes the resistance value of the thermistor. Sintering uses high temperature along with a secondary force (in this case, pressure). During sintering, the control of temperature is an essential aspect of the process, along with the composition of the materials and size and distribution of the particles in the powder. 

There are two possible configurations from the sintered material. Most commonly, a disk form, but it can also get cut into smaller sizes for chip thermistors. 

Electrode Metalization Of the thermistor

During this stage in the creation of a PTC thermistor, the bottom ohmic electrode and surface electrode gets created. Silver printing, baking, and electrode saturation play a role in this step. For chip-type PTC thermistors, the saturation of current flowing through ceramic PTCs happens at shorter intervals than for disk-types. 

After this stage, it's important to check the ohm resistance and solderability of the thermistor. Once the thermistor passes these quality checks, it's time for more testing. 

One of the most important tests is the Hi-Pot test. This checks the dielectric strength of insulation in thermistors, transformers, and several other electrical parts. This test helps show the potential for deterioration of insulation, which is important when determining electrical safety. Since a large majority of faults in electrical devices and systems come from weak insulation, this is an essential part of any manufacturing process. 

Lead Wire Attachment Is Next

After each of these steps and tests, the lead wire gets attached. For chip style thermistors, there's no need for a lead wire, but the majority of thermistors require a wire. Attaching the wire requires either immersion or manual soldering. The parts then go through a cleaning process before final coating. 

During the coating process, thermistors receive a protective resin coating. The coating must go on even and not create any bubbles. This coating protects the thermistor from environmental dangers, such as dirt, grease, and condensation.  

After coating, any requested marks and coding go onto the finished product before a final round of testing. 

Final Testing Is Critical for PTC Thermistors

Much of the manufacturing process for a PTC thermistor involves testing. Given the importance of the part in industrial heating products, quality control is of vital importance during the manufacturing process. 

The thermistor receives a visual check to make sure there are no cracks or imperfections that could affect its performance. Any imperfection could lead to equipment failure and cause a malfunction in industrial heating products. There are also tests to make sure that the thermistor can perform under a range of temperatures. Resistance testing takes place to make sure that the thermistor increases resistance as temperatures rise. 

The lead wire undergoes tensile testing to make sure it's durable enough for the application it will perform. If the lead wire malfunctions, it will cause the failure of the entire part. 

A non-trip test shows the maximum continuous current that the thermistor can withstand without switching. These final tests also determine: 

  • Transition temperature - The temperature when the resistance starts to rises quickly
  • Minimum resistance - The lowest resistance measured on a switched thermistor
  • Dissipation constant - The relationship between the applied power and body temperature increase
  • Rated resistance - Normally at 25°C, but can vary depending on the thermistor
  • Maximum rated current - The maximum current that can flow through the thermistor 
  • Maximum rated voltage - The maximum voltage that can flow through the thermistor

These tests and others ensure the quality and help determine the practical use of the thermistor that goes into industrial heating products. 

Industrial Heating Solutions For Your Business 

No matter what type of industry you're in, we have custom solutions to meet your needs. Each industrial heater we sell has a top-notch PTC thermistor and other high-quality parts and are safe, reliable, and will provide you with the consistent results you need to keep your business operating. We have over 50 years of experience in providing world-class solutions for a variety of businesses. 

Do you need a custom solution to your industrial needs? DBK is one of the best PTC heating element component manufacturers in the world.  All of the thermistors are thoroughly tested for quality and packaged into off the shelf components to fit industrial and commercial requirements.  Need a custom solution.  DBK USA can help find the right solution for your application.

Contact us today to learn more about our industry-leading products. 

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