The main features of NTC thermistor are high sensitivity to temperature, small thermal inertia, long operating life, small size, simple structure, which can also be made into a variety of different shape structures. NTC thermistor researched and developed, produced by EXSENSE Electronic Technology Co., Ltd. is mainly used in temperature control, temperature detection, temperature compensation, temperature controlling circuit,etc., which plays a central role in converting variable of temperature into the required electronic signals in the circuit. With the continuous development of society, this type of component has been widely used, such as liquid-surface determination, air pressure measurement, fire alarm, meteorological sounding, switching circuit, over-load protection, pulsating voltage suppression, time delay, stable amplitude, automatic gain adjustment, microwave and laser power measurement, etc. It’s precisely because of the wide application, NTC thermistor are required to adapt a variety of environments, especially humid and high-temperature environments.
In the existing technology, the common NTC thermistor is generally made by this method:
(1) Select NTC thermistor chip;
(2) Solder leads on NTC thermistor chip;
(3) The NTC thermistor chip is encapsulated with an outer insulating layer to made into an NTC thermistor;
(4) Test the resistivity of the NTC thermistor.
Therefore, the NTC thermistor made by existing technology generally use 265±5℃ for soldering leads, solder melting point is about 227℃, which belongs to low-temperature tin, so even if the insulating layer is resistant to high temperature of 250 ℃, NTC thermistor is also unable to withstand high temperatures of 250 ℃ due to the temperature of solder melting point at both ends of the NTC thermal chip is well below 250 ℃. In addition, in the existing technology, the outer insulating layer is generally coated with epoxy resin, because the epoxy resin is poor in temperature-resistance ability and waterproof ability, temperature resistance is up to 200 ℃, long-term use generally doesn’t allow more than 125 ℃.
So the manufacture of high-temperature and moisture-proof NTC thermistor can improve the qualified rate of finished products effectively, save cost of production and prolong their operating life.