NTC thermistor chip researched, developed and produced by EXSENSE Electronic, with characteristics of high accuracy (accuracy can up to ±0.5%, ±1%, ±2%, ±3%), fast response speed, small size (minimum size can be 0.3*0.3mm) and so on, which is widely used in a variety of temperature detection, temperature control, temperature compensation circuit. It plays a central role in the circuit to convert temperature variables into the required electronic signal.
The silver electrode NTC thermistor chip prepared by the existing process has the following problems:
First, silver slurry in the screen printing and drying process is vulnerable to be contaminated, and the resulting silver electrode thermistor chip is also easy to oxidize, yellow, black, resulting in poor stability and reliability of the product;
Second, the pre-preparation of silver slurry, late silver slurry drying and silver electrode sintering process is more cumbersome;
Third, the thickness of printed silver electrode layer is thick and and covers unevenly on the surface of the thermosensitive ceramic substrate, which is easy to peel and produce burrs in the cutting process, resulting in more loss of silver slurry material;
Fourth, when the silver electrode layer is sintered at high temperature, the crystal from will recrystallize, thus the properties will change, resulting in the deterioration of the electrical properties of the product;
Fifth, the gases emitted in the process of burning silver at high temperature will pollute the environment.
Therefore, EXSENSE Electronics introduces a high-precision Cr-Ni-Au composite electrode NTC thermistor chip, which has good stability, great reliability, heat and cold impact and other advantages. This thermistor chip consists of a thermosensitive ceramic substrate and two composite electrodes located on two surfaces of the thermosensitive ceramic substrate, which are stacked from the inside out by the chromium layer, nickel layer and gold layer on the surface of the thermosensitive ceramic substrate. Among them, the thickness of the chromium layer is 0.01 to 1μm, as the transition layer, which mainly plays a transitional role, it can combine well with the thermosensitive ceramic substrate and play a certain blocking effect; The thickness of the nickel layer is 0.01 to 2μm, as the blocking layer, which is used to block the external damage to the transition layer, and has a welding effect; The thickness of the nickel layer is 0.01 to 2μm, which is not only the welding layer, but also the protective layer, its stability is high, can prevent oxidation, corrosion resistance, anti-destruction, high temperature resistance.
The preparation method of the high-precision Cr-Ni-Au composite electrode NTC thermistor chip is as follows:
1. The preparation of thermosensitive ceramic substrate
The thermosensitive ceramic powder is prepared according to the conventional formula, and then the thermosensitive ceramic powder is ball-milling, isostatic press molding, sintering and slicing to obtain the flake-shaped thermosensitive ceramic substrate.
2. The first cleaning
The thermosensitive ceramic substrate obtained in the first step is treated with cleaning fluid, then using an ultrasonic machine to clean, cleaning time is 5±1 minutes, then drying, drying temperature is 100±5℃, drying time is 30±5 minutes.
3. The second cleaning
The cleaned thermosensitive ceramic substrate obtained in the second step is placed in the plasma cleaner for second cleaning, the cleaning time is 5±1 minute, the drying temperature is 100±5℃, the drying time is 30±5 minutes, activating surface at the same time.
4. Sputtering chromium layer
First, the vacuum sputter coating machine vacuumized to the process range, then filled with argon as working gas, with chromium as target material, under the effect of electric field, Ar bombarded the target material, the target atom sputtering target material to the thermosensitive ceramic substrate obtained in the third step, respectively on two surface sputtering layer of chromium layer, sputtering thickness is 0.01 to 2μm.
5. Sputtering nickel layer
First, the vacuum sputter coating machine vacuumized to the process range, then filled with argon as working gas, with nickel as target material, under the effect of electric field, Ar bombarded the target material, the target atom sputtering target material to the thermosensitive ceramic substrate obtained in the fourth step, respectively on two surface sputtering layer of nickel layer, sputtering thickness is 0.01 to 2μm.
6. Sputtering gold layer
First, the vacuum sputter coating machine vacuumized to the process range, then filled with argon as working gas, with gold as target material, under the effect of electric field, Ar bombarded the target material, the target atom sputtering target material to the thermosensitive ceramic substrate obtained in the fifth step, respectively on two surface sputtering layer of gold layer, sputtering thickness is 0.01 to 1μm.
7. Testing, cutting
Test the resistivity of the thermosensitive ceramic substrate obtained in the sixth step, the size of a single thermosensitive chip is calculated according to the test results and the desired resistance value of the NTC thermistor chip, then the thermosensitive ceramic substrate is cut to obtain the single thermistor chip.
8. Testing, sorting
Use the thermistor tester to test the resistance value of the NTC thermistor chip produced in batch in the second step one by one, and sort out the products that do not meet the requirements.
The chromium layer, nickel layer and gold laye are stacked from the inside out into composite electrodes on the surface of the thermosensitive ceramic substrate, which can effectively improve the stability, temperature resistance, corrosion resistance, anti-destructive of the thermistor chip, and also control the electrode material cost of thermistor chip. High-precision Cr-Ni-Au composite electrode NTC thermistor chip has the advantages of good stability, great reliability, cold and heat impact resistance.
