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Production of High-accuracy NTC Thermistor Chip-2
2018/11/19 08:11:42

Production of High-accuracy NTC Thermistor Chip-2


        With the <Production of High-accuracy NTC Thermistor Chip-1>, we knew the shortcomings of the existing manufacturing technology of NTC thermistor chip. Now, let’s introduce a manufacturing method of high-accuracy NTC thermistor chip, which can realize the adjust resistance value in high accuracy well and 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%. The detailed steps are as follows:

 

(1)  NTC thermosensitive semiconductor ceramic powder preparation

(2) Strip molding/sintering

(3) Glass sealing

(4) Resistance test

(5) Size cutting

(6) Coating terminal electrode

 

As steps (1) above, the preparation methods of NTC thermosensitive semiconductor ceramic powder can be physical method or chemical method:

 

A. Physical method (Ball Milling): ingredients (according to a specific formulation)-ball milling-discharging-drying-sieving-presintering-grinding-drying-sieving-powder spare. 

 

B. Chemical method (Sol-gel Method): the preparation of sol-gel-gelation-gel drying-calcination-powder spare. 

 

As steps (2) above, strip molding/sintering is done using isostatic pressure molding method or extrusion molding method, then sinter at high temperature into NTC thermosensitive semiconductor ceramic strip:

 

A. Isostatic pressure molding method: 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;

 

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 thermosensitive ceramic substrate with thickness of 200-2000 μm as required. Then doing high temperature sintering to make NTC thermosensitive semiconductor ceramic spindle.

 

B. Extrusion molding method: the prepared NTC thermosensitive ceramic powder is based on the weight ratio of porcelain powder: PVA Binder =100:40, place in the mixing tank and mix evenly; After the smelting mud, stale, use the extruding machine to extrude the strip (rod)-shaped ceramics as required size.

 

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 ℃. 

 

As steps (3) above, the surface glass protective cover coating include:

 

A. Configuration of glass slurry: the composition of glass slurry according to the weight ratio is: glass powder 30~60%,  PVB resin 10~30%, Plasticizer 0.5~5%, Dispersant 0.1~3%, Solvent 30~50%. The PVB resin is B-76PVB resin; the plasticizer is Dioctyl Phthalate; The dispersant is AK- 3501 dispersant; The solvent is N-propyl Acetate.

B. Arrange the NTC thermosensitive semiconductor ceramic strips on the bracket;

C. The glass slurry is sprayed on the top and bottom of the bracket by the upper and lower two spray guns to spray the ceramic strips, and the bracket can be continuously forward or rotated to complete the glass slurry coating of the batch product;

D. The NTC thermosensitive semiconductor ceramic strips/rods coated with glass slurry are placed in the oven with a bracket at 80~150℃ drying for 1-3 hours.

E. Remove the ceramic strips and place it on the Furnace plate sintering (800~900) ℃/0.5 hours, after cooling,  a tire uniform and dense glass protective cover is formed on the surface of the ceramic strip, adjusting the thickness of the spraying layer, to control the thickness of the sintered glass sealing coating at 20~30 μm.

 

As steps (6) above, coating terminal electrode is 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.

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