The VT series NTC thermistors produced by EXSENSE Electronics Technology Co.,Ltd. are widely used in automobiles, motorcycles and ships as temperature monitoring and temperature control components because of their high accuracy, good heat cycle resistance and great stability. In recent years, with the rapid development of IT industry, automobile and home appliance products have put forward higher requirements on the consistency and reliability of NTC thermistors. In order to produce high-quality NTC thermistors, one of the keys is to realize the ultra-pure, ultra-fine and uniform powder raw materials.
Today, EXSENSE Electronics introduces a manufacturing method of thermistors. By comprehensively controlling the pH value, temperature, reactant concentration and adding an appropriate amount of surfactant in the co-precipitation reaction, uniform and dispersed nanometer powder is prepared, which greatly improves the repeatability, consistency and stability of thermistor materials. In the mass production of NTC thermistors, the rate of finished products, stability and reliability of thermistors can be greatly improved.
NTC thermistor for automobile are mainly composed of nitrate and sulfate of cobalt, manganese, nickel, iron, aluminum, and can be industrialized batch production of NTC thermistors by using improved liquid phase co-precipitation method. Co-precipitation reaction through strict control of pH value, concentration of reactants, reaction temperature, and matching join the size of molecular weight of non-ionic surfactant polyethylene glycol (PEG), improve the reunion phenomenon of sediment particles, sediment is dehydrated by absolute ethyl alcohol, control the temperature and time of decomposition and pre-sintering, dispersed uniformed nanometer powder was prepared. NTC thermistor ceramic material is prepared by preforming powder, isostatic pressing and sintering. The prepared thermistor material has the characteristics of good stability, good consistency and good repeatability. NTC thermistor can be made by sealing glass or epoxy resin. It is suitable for temperature measurement and temperature control of automobile, motorcycle, refrigerator, etc. The specific preparation method is as follows:
First, with nitrate and sulfate of cobalt, manganese, nickel, iron, aluminum as raw materials, prepared 1.0~1.5M ion mixed solution;
Second, Tthe precipitant solution of 1.5~2M is prepared with ammonium bicarbonate, the pH value of the solution is adjusted with ammonia water at 7.5~8.5. At the same time, add the polyethylene glycol with weight percentage of 1~ 5%, molecular weight of 400~1500 and surfactant with molecular weight of 1500~5000 are added to the precipitant;
Third, when the reaction temperature is 30~40℃, the ionic mixed liquor is uniformly added to the precipitant under intense agitation to make the co-precipitation reaction occur;
Fourth, after the complete co-precipitation reaction, the precipitate is washed with ionized water for 3~5 times, then dehydrated with anhydrous ethanol for extraction and suction filtration. After drying, the precursor powder is obtained;
Fifth, after grinding, the precursor powder is decomposed by heat at 400~500℃ for 2~5h, and pre-sintered at 650~750℃ for 2~5h;
Sixth, after the powder is pre-pressed into raw green, it is subjected to cold isostatic pressure, intensity of pressure is 2.0~4.0MPa/cm2, and then sintered at 1150~1200℃ for 2h, to get the NTC thermistor ceramic materials;
Seventh, NTC chip can be obtained by slicing ceramic material through conventional process and coating silver electrode on both sides;
Eighth, the NTC chip is sealed with epoxy resin, obtain NTC thermistor for automobile.