May 16, 2017
World's largest portfolio of NTC thermistors
Sensors for temperature measurement can be found in every field of electronics applications. Apart from simple measurement in thermometers, they are used for open- and closed-loop process control as well as for the protection of valuable systems where critical temperatures have to be detected, for example, in the drives of electric vehicles.
The negative temperature coefficient (NTC) of special ceramics is used to measure temperatures. The electrical resistance of these ceramics diminishes as the temperature rises.
With these NTC thermistors, TDK is a global market leader and offers not only a uniquely broad product range, but also the competence to customize the characteristic curves and the resistance values of NTC thermistors for a wide range of applications.
The ceramic mixtures and the material combinations of leads and coatings are a decisive factor with regard to durability and particularly to long-term stability. Only if the combinations are optimally matched, can the constant parameters be realized, thereby ensuring low tolerances over a long period. EPCOS temperature sensors therefore have special epoxy coatings or are encapsulated in glass. In tests compliant with IEC 60068-2-67 (1000 h, 85 °C and 85 percent relative humidity) these variants feature a resistance change of less than two percent compared to the resistance value at 25 °C.
The right NTC thermistor for every application
NTC thermistors are available in a very wide range of designs – often also in customer-specific versions – in order to meet the needs of the many different devices, equipment and systems they are used in. This mainly concerns the housing as well as the terminal configuration.
Reliable measurement of temperatures up to 650 °C
The measurement of high temperatures was previously the preserve of platinum elements. These, however, are expensive and, in comparison with NTC thermistors, they exhibit a relatively flat characteristic curve. As an alternative, TDK offers an innovative EPCOS NTC sensor element designed for measuring temperatures up to 650 °C.
The 650-degree high-temperature sensor is based on a glass-encapsulated high-temperature ceramic with connection pads on a ceramic carrier. The new NTC sensor element offers high-precision measurement with a temperature tolerance of just ±1 K at 200 °C. The high-temperature sensor is qualified to AEC-Q200 and specified for use in automotive electronics, for example in exhaust gas recirculation systems. In electrical drives the sensors are able to monitor the temperature of fuel cells. But applications can also be found in household electronics, for example in ovens with catalytic cleaning.
Embedding temperature protection with chip-NTC thermistors
IGBT modules in inverters must deliver maximum possible efficiency. For this reason, they are operated at their upper temperature limit. Precise monitoring of the operating temperature is necessary in order to prevent damage to the semiconductors.
For this purpose, TDK has developed a special wafer-based EPCOS chip NTC thermistor, which can be embedded directly into the IGBT modules. Furthermore, these components save space because no special pads are necessary for soldering them to the semiconductor substrate. For wafer-based NTC thermistors, the configuration of the electrical terminals is crucial, because – unlike conventional SMD components - they are not located on the sides of the component, but on the upper and lower surfaces. In this way, they enable the lower terminal to have a direct and very even contact with the semiconductor substrate when using conventional semiconductor processes. The upper terminal is contacted by means of conventional bonding.
Due to the tight thermistor tolerance of just ±1.5 K at 100 °C, IGBT modules can be operated at temperatures very close to the performance limits without premature derating and can thus be used more efficiently. This NTC thermistor solution is also suitable for new generations of semiconductors, such as those based on SiC.
Multilayer NTC and PTC thermistors complete the range
In addition to monolithic types, TDK also offers EPCOS multi-layer NTC thermistors in SMD design for temperature sensing, as well as PTC (positive temperature coefficient) thermistors which are named after their extremely steep characteristic curve.
Whereas the multilayer NTC thermistors are intended for mounting on printed circuit boards and are used mainly for monitoring heat-sensitive semiconductors, PTC thermistors are used primarily for sensing temperature limits – integrated, for example, into the windings of motors in order to detect overheating.