JPH07294568A - Evaluation method of positive-temperature-coefficient thermistor - Google Patents

Abstract

PURPOSE:To obtain an evaluation method in which a positive-temperature-coefficient thermistor whose reliability is defective can be sorted by measuring the impedance of the positivetemperature-coefficient thermistor is and a using resistance component value. CONSTITUTION:The positive-temperature-coefficient thermistor is a semiconductor ceramic which is composed mainly of barium titanate and whose resistance value has a positive temperature coefficient. Then, a displacement current by an applied electric field flows inside of a positive-temperature-coefficient-thermistor element across electrodes when an alternating electric field is applied. However, since the displacement current is the change amount in terms of time of an electric flux whose amount is equal to that of an electric charge (g) across the electrodes, it does not flow when a direct current is applied. Consequently, a minute ceramic defect, in the positive-temperature-coefficient-thermistor element, which does not offset a resistance value when the direct current is applied can be known by the resistance component (Re) of an impedance on the basis of a frequency characteristic in an abnormal part. By utilizing this, the defect can be estimated and evaluated by the value of the Re when the alternating electric field is applied, and the positive-temperature-coefficient thermistor whose reliability is defective can be sorted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating a positive temperature coefficient thermistor which cannot be evaluated by its initial characteristics.

[0002]

2. Description of the Related Art Positive temperature coefficient thermistors containing barium titanate as a main component are used in a wide range of applications such as warm air heaters and degaussing elements. A characteristic of the positive temperature coefficient thermistor is that it greatly depends on the manufacturing conditions. In the mass production process, the characteristics are deteriorated due to the mixing of impurities, and if the characteristics are greatly varied, the reliability of the product is deteriorated. In order to prevent this, the PTC thermistor was evaluated by initial characteristics such as resistance value and visual inspection.

In recent years, characteristic deterioration has become a serious problem particularly in a reducing atmosphere or when a reducing substance is attached, and when used in such a situation, the PTC thermistor may be burned out, which is dangerous. Met. Therefore, in order to manufacture a highly reliable positive temperature coefficient thermistor with less characteristic deterioration even when used in a reducing atmosphere, the reliability has been continuously improved by the material composition and manufacturing method. However, in the manufactured positive temperature coefficient thermistor, the large characteristic deterioration caused by use in a reducing atmosphere or the like could not be evaluated by the initial characteristics such as the resistance value. We conducted a sampling test from the manufactured PTC thermistor,
The reliability was evaluated and product production was controlled.

[0004]

In the above-mentioned conventional method, since the reliability of all the produced positive temperature coefficient thermistors cannot be evaluated without affecting the characteristic values, the positive temperature characteristics of the produced positive temperature coefficient thermistor cannot be evaluated. If there is a positive temperature coefficient thermistor with poor reliability in the thermistor, it is impossible to remove the defective product and it is possible to ship a defective reliability product that does not appear in initial characteristics such as resistance value or appearance. It had a certain problem.

The present invention solves the above-mentioned problems of the prior art, and non-destructively predicts and evaluates the reliability of the positive temperature coefficient thermistor without affecting the characteristics, and selects the positive temperature coefficient thermistor having poor reliability. It is an object of the present invention to provide a method for evaluating a positive temperature coefficient thermistor that can be used.

[0006]

To achieve the above object, the present invention measures the impedance (Z) of a positive temperature coefficient thermistor and uses the value of the resistance component (R _e ) (the real part of the complex impedance) to obtain the positive voltage characteristic. The thermistor is evaluated.

[0007]

[Function] The positive temperature coefficient thermistor is a semiconductor porcelain mainly composed of barium titanate and having a positive temperature coefficient of resistance, and its fine structure has crystal grains semiconductorized by valence control and grain boundaries which are insulators. And P
It is generally considered that the TC characteristic is generated by the grain boundary portion. Based on that fine structure,
Resistance component of impedance of positive temperature coefficient thermistor ( _Re )
It can be seen that is due to crystal grains and grain boundaries. Therefore, if the crystal grain size is small, the number of grain boundaries having high resistance in the thickness of the positive temperature coefficient thermistor element (between the electrodes) is large, so that the value of the resistance component (R _e ) is large, and if the crystal grain size is large, On the contrary, it decreases. The high resistance grain boundary portion is mainly in the low frequency region, and the low resistance crystal grain is mainly the reciprocal value of the electron mobility in an alternating electric field in the high frequency region, which means the impedance resistance component (R _e ). Therefore, in a normal PTC thermistor, both effects due to the state of the crystal grain and the grain boundary appear in the frequency range of several kHz to several tens of MHz.

In this way, a displacement current due to the applied electric field, that is, a conduction current generated by the movement of electrons flows inside the positive temperature coefficient thermistor element when an alternating electric field is applied in this way. Since the same amount of electric flux changes with time, it naturally does not flow when a direct current is applied. Therefore, a fine porcelain-like defect in the positive temperature coefficient thermistor element that does not affect the resistance value due to the direct current application is known from the value of the resistance component (R _e ) of the impedance due to the difference in the frequency characteristic of the abnormal portion. be able to.

Therefore, if impurities were mixed in the PTC thermistor during the manufacturing process, or if abnormal particles or fine cracks were present, these could not be identified by the resistance value when a DC voltage was applied. When a voltage is applied, the positive temperature coefficient thermistor with fine magnetic defects is significantly different from the normal frequency characteristic, and therefore the resistance component (R _e ) shows an abnormal value unlike the normal value. Becomes By using this, the initial characteristics of the resistance value or the like by the conventional DC applied to screen positive characteristic thermistor reliability failures becomes predictable evaluated by R _e values when an alternating electric field is applied for a reliability that could not be removed be able to.

[0010]

EXAMPLES An example of the present invention will be described below.

BaCO ₃ , PbO, Ca as starting materials
CO ₃ , TiO ₂ , Y ₂ O ₃ , SiO ₂ , Al ₂ O ₃ , MnO ₂
(Ba _0.702 Pb _0.198 Ca _0.100 ) TiO ₃ +
0.0022Y ₂ O ₃ + 0.027SiO ₂ +0.000
The composition was 3Al ₂ O ₃ + 0.0004MnO.

A sintered body was obtained, and Ni was formed on both upper and lower surfaces of this sintered body.
Plating, apply silver electrode on it, and bake it to a diameter of 1
A positive temperature coefficient thermistor having a thickness of 3 mm and a thickness of 2.5 mm was obtained.

Approximately 1 positive temperature coefficient thermistor thus obtained
The resistance value and resistance temperature characteristic (PTC characteristic) at room temperature (25 ° C.) of, 000,000 pieces were measured by the DC four-terminal method, and the resistance component of impedance (R _e ), capacitive reactance (X _c ), Q _{The c} value was measured with an impedance analyzer in the frequency range of 1 kHz to 20 MHz. After that, a reducing load test was conducted in which these positive temperature coefficient thermistors were energized with a voltage of 200 V (AC50 Hz) for 100 hours in a reducing atmosphere (in nitrogen gas). Then, the resistance temperature characteristic is measured again, and the difference (Δ) in the resistance value change width between the PTC characteristic of the positive temperature coefficient thermistor and that after the test is measured.
The deterioration of the positive temperature coefficient thermistor was judged by Ψ = initial Ψ−post test Ψ). Here, the resistance value variation width means a common logarithmic value of a value obtained by dividing the maximum resistance value in the PTC characteristic by the minimum resistance value.

Resistance change width Ψ = log_Ten(Maximum resistance value R
_max/ Minimum resistance value R_min) Degree of deterioration before and after the reducing load test
Resistance component of impedance of positive temperature coefficient thermistor before test
(R _e), Capacitive reactance (X_c), Q_cRelationship with value
The results of the investigation are shown in FIGS. 1, 2 and 3. (This
R in these figures_e, X_c, Q_cThe value is at a frequency of 10 MHz
It is the measured value. ) As a result, the resistance component is
(R_e) Is the capacitance of the positive temperature coefficient thermistor
The crystal grain surface was used as an electrode, and the grain boundary thickness was used as the distance between electrodes.
Since it can be defined as the capacitance of the grain boundary,
If the size of the crystal particles in the mister is small,
It means an increase in surface area or electrode area, and an increase in capacitance.
However, when the grain boundary thickness increases, it decreases on the contrary. this
Therefore, the capacitive reactance (X_c) Key
The grain size, grain boundary thickness and their
You can get all the information. In addition, the resistance component (R_e)
Similarly, do not affect the resistance value due to DC application.
The fine porcelain defects in the thermistor
Capacitive reactance (X_c)The value of the
Can be found by In addition, the resistance component (R_e) And Yong
Quantitative reactance (X_c) Can be considered as a series connection
Frequency ω in the equivalent circuit of a positive temperature coefficient thermistor
(= 2πf) and resistance component R_eAnd capacitive reactance X_cof
Product (ωX_cR_e) Is relatively larger than 1, this product
Q of this circuit system_c(Quality factor)
Can be approximated by
You can get information. This Q_cWhen using the value method,
The initial resistance value and static
Accurate and reliable even if there is an extremely large difference in capacitance
You can evaluate the sex. If abnormally large, also capacitive rec
Closet (X_cIf the value of) is abnormally small,_cThe value of
When the load is abnormally small, the deterioration tendency after the reducing load test is large.
Is recognized. Therefore, the positive characteristic thermistor in the initial state
T's R_e, X_c, Q_cDepending on the value of
It can be seen that it is possible to predict what shows normal deterioration.
In particular, a positive PTC thermistor that causes abnormal deterioration and a positive
The boundary with the ordinary is clear. Correcting these poor reliability
Analyzing the characteristic thermistor, R in Fig. 1_evalue
Is a positive thermistor that shows abnormalities,
And impurities are mixed in, X in Fig. 2_cValue is abnormal
Positive temperature coefficient thermistors have uneven particle shape and uneven grain boundary thickness.
One of them, Q in Figure 3_cValues are shown in Fig. 1 and Fig. 2.
For each of the factors
It turned out that he had a porcelain defect such as Ri. this
Such fine porcelain defects are caused by initial characteristics such as resistance and
With the conventional selection method
Could not be removed, but there is a big shadow on reliability.
It was known to give a sound. Such conventional selection is not possible
With fine porcelain defects that were thought to be
When a frequency is applied to the characteristic thermistor, the resistance in the alternating electric field is reduced.
Anti ingredient (R_e), Capacitive reactance (X_c), And Q_c
The value is greatly affected by the fine porcelain defects.
To sort defective products that were previously impossible to sort
Is possible. Manufactured by this evaluation and selection method
Of the positive temperature coefficient thermistors
-The mister can be removed. And of course the element
Similar results have been obtained with other shapes and composition systems.
Can be applied to the reliability evaluation of all PTC thermistors.
is there.

[0015]

As described above in detail, according to the present invention, the reliability of the positive temperature coefficient thermistor is determined by the resistance component (R _e ) of the impedance of the positive temperature coefficient thermistor element, the capacitive reactance (X _c ), and the value of Q _c. Since the predictive evaluation can be performed, a highly reliable positive temperature coefficient thermistor can be provided easily and inexpensively, and its industrial utility value is great.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the value of the resistance component (R _e ) of the impedance of a positive temperature coefficient thermistor measured at a frequency of 10 MHz and the difference between the resistance value change widths at the initial stage and after the reduction load test in one example of the present invention.

FIG. 2 is a difference (ΔΨ) between a value of a capacitive reactance (X _c ) of impedance of a positive temperature coefficient thermistor measured at a frequency of 10 MHz and a resistance value change width between an initial stage and a reducing load test in one example of the present invention. Graph showing the relationship between the values of

FIG. 3 shows a frequency of 10 MHz in one embodiment of the present invention.
Q of the measured positive temperature coefficient thermistor _cValue and initial reduction load
Graph showing the relationship of the difference (ΔΨ) in resistance value change width after the test

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takuko Hata 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] 1. The impedance (Z) of a positive temperature coefficient thermistor is measured, and the resistance component (R) of the impedance (Z) is measured.
_A method for evaluating a positive temperature coefficient thermistor in which a positive temperature coefficient thermistor is evaluated based on the value of _e ) (real part of complex impedance). 2. An evaluation of a PTC thermistor in which the impedance (Z) of the PTC thermistor is measured, and the PTC thermistor is evaluated by the value of the capacitive reactance (X _c ) of the impedance (Z) (imaginary part of complex impedance). Method. 3. When the resistance component (R _e ) of the positive temperature coefficient thermistor and the capacitive reactance (X _c ) are considered to be connected in series, Q _c (Qual in the equivalent circuit system of the positive temperature coefficient thermistor).
The method for evaluating a positive temperature coefficient thermistor in which a positive temperature coefficient thermistor is measured and the positive temperature coefficient thermistor is evaluated based on the value of Q _c .