The main characteristics of NTC thermistor are high temperature sensitivity, low thermal inertia, long service life, small size, simple structure, which can be made into a variety of shape structures. NTC thermistor is mainly used in a variety of temperature detection, temperature compensation, temperature control circuits, which play a central role in the conversion of temperature variables into the required electronic signal. With the continuous development of society, this kind of component has been widely used, such as liquid surface determination, air pressure determination, fire alarm, Meteorological sounding, switching circuit, overload protection, pulsation voltage suppression, time delay, stable amplitude, automatic gain adjustment, microwave and laser power measurement and so on. Due to its wide range of applications, NTC thermistors are also required to adapt to a wide range of environments and temperatures, especially environment of high humidity and high temperatures.
In existing technologies, common NTC thermistors are generally made using the following methods:
(1) choose NTC chip;
(2) Welding leads on NTC chips;
(3) The NTC chip is sealed using the coating slurry, thus making NTC thermistor;
(4) The resistor of NTC thermistor is tested.
Due to the existing NTC thermistor, generally using tin furnace of 265±5℃ to weld up NTC chip and lead. The melting point of the soldering tin is about 227℃, which belongs to low temperature tin. So, even if the insulating encapsulated layer can withstand the high temperature of 250℃, the melting point of the soldering tin at both ends of the NTC chip is far lower than 250℃, which leads to the NTC thermistor can't withstand the high temperature of 250℃. In addition, in the existing technology, the outer insulating encapsulated layer is generally covered with epoxy resin, due to the poor temperature and water resistance of epoxy resin, the maximum temperature resistance is 200℃, long-term use is generally not allowed to exceed 125℃.
In order to overcome the shortcomings of existing technology, EXSENSE Electronics introduces a high-temperature resistant moistureproof NTC thermistor, the resistance to high temperature and moisture resistance of the thermistor far exceeds that of most existing NTC thermistors. It can work for a long time at temperature up to 250℃, and in wet environments, which has a higher mechanical strength than the glass sealed NTC thermistor, with a long service life and a high usefulness. This high-temperature resistant moistureproof resistant NTC thermistor, is on both sides of the NTC chip, through high-temperature resistant soldering tin welding two leads. At the periphery of NTC chip and lead welding point, a high-temperature resistant silica gel layer is sealed from inside to outside, then a silicone resin layer, and finally a high-temperature resistant silica gel layer. Among them, the high-temperature resistance range of soldering tin is 350 to 400℃, the high-temperature resistance range of the first encapsulated layer is 260 to 320℃; The high-temperature resistance range of the second encapsulated layer is 280 to 300℃; The high-temperature resistance range of the third encapsulated layer is 260 to 320℃.
This high-temperature resistant moistureproof NTC thermistor, using high-temperature resistant silica gel layer to make the first and third encapsulation, high-temperature resistant silica gel not only has better high-temperature resistant performance, but also its moisture-proof moisture resistance is also very good, which can effectively prevent infiltration of water and water vapor, give better protection of thermistor and moistureproof performance is better.