According to the <Production of High-accuracy NTC Thermistor Chip-2>, the method of making 0603~10kωb (25/50) =3435k SMD Type NTC thermistor is used as an example to illustrate.:
First, the NTC thermistor semiconductor ceramic powder preparation method is made by Sol-gel chemical method. The detailed steps are: the preparation of sol-gel-gelation-gel drying-calcination-powder spare.
Second, Strip molding/sintering: NTC thermosensitive Ceramic strips (rods) Isostatic Pressure Molding Method:
Molding: put the prepared NTC thermosensitive ceramic powder into the rubber mold, loose, vibration; place in the isostatic press, pressure 30 minutes with intensity of pressure at 300~400mpa, release pressure, get the ceramic spindle from the mold;
High temperature sintering: The pressurized raw embryo ceramic spindle is warmed slowly (1℃/min) to 1200±50℃ in a high temperature sintering furnace, and keep heat preservation 5~10hours, then cools slowly (1℃/min) to 100 ℃, get the ceramic spindle;
Third, chip cutting
According to the needs of NTC thermistor design, the pressure sensitive resistance ceramic spindle after sintering are cut by inner circle cutting machine to the NTC thermistor ceramic substrate with thickness of 200-2000 μm as required, then the NTC thermosensitive ceramic substrate cut into strips, that can be made of square type NTC thermosensitive ceramic strips.
Forth, resistance test
Coating the terminal electrode at both ends of the sintered NTC thermistor chip, test and calculate its resistance.
Fifth, size cutting
Calculate the cutting size of the chips by the resistance value, the NTC thermosensitive ceramic strip (the NTC thermistor strip) with a surface glass protective tier, are cut into NTC thermistor chip according to the corresponding size. At the moment, the resistance value of NTC thermistor chip can adjust the length according to the resistivity, through accurate calculation and precision cutting can make the R25 values control in the design value of ±0.3%, therefore, it can achieve a better high-accuracy resistance.
Sixth, coating terminal electrode
Using the printing method, evenly coated the terminal electrode slurry at both ends of the NTC thermistor chip, the silver electrode and NTC thermosensitive porcelain body medium are closely firing and permeating by the resistance furnace, the surface of the NTC thermistor chip is glass sealing tier (equivalent to the glass protective tier on the NTC thermosensitive ceramic strip)
This production method of high-accuracy NTC thermistor chip, which can realize the adjust resistance value in high accuracy well, has high reliability. In high-accuracy temperature measurement applications, the accuracy of R resistance value and B value is controlled in 0.3%, that is, the temperature accuracy can be controlled in 0.1℃, and the annual drift rate of electrical performance (R resistance value and B value) after use in the application circuit is less than 0.1%.so the NTC thermistor chip produced by this method, the hit rate of high-accuracy product (±0.3%) will be greatly improved, the steady state-damp heat property, change rate of high temperature loading and thermosensitive shock of the product are small.