JPH02155202A - Glass sealed type positive temperature coefficient thermistor - Google Patents

Abstract

PURPOSE:To stabilize an atmosphere in a glass tube, and to improve reliability for a prolonged term by holding a positive temperature coefficient thermistor by two parallel noble metallic wires or two slug leads covered with a noble metal installed into the hollow glass tube. CONSTITUTION:Strontium is added and solid-dissolved to barium titanate, the material of a composition system, in which yttrium oxide is added as an element changed into a semiconductor, is used, and a discoid sintered body is acquired through a ceramic manufacturing process. An Ni electrode is formed to the sintered body through a plating method, resistance values at 25 deg.C and 125 deg.C are measured as initial characteristics, the sintered body is cut in desired size, thus obtaining a positive temperature coefficient thermistor element 1. The thermistor element 1 is baked and fixed at the central section of two leads 2 previously fastened in parallel at a proper space by glass beads with silver paste, and a glass tube 3 is melted and sealed by the glass bead sections. The thermistor has the reliability of the change of a resistance value of a range of + or -10% after one thousand hr.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a glass-encapsulated positive temperature coefficient thermistor for use in environments where long-term reliability is required.

BACKGROUND OF THE INVENTION Conventionally, disk-shaped positive temperature coefficient thermistors have been used for temperature compensation, but these have not been satisfactory in terms of thermal shock resistance or long-term reliability. In response, studies have been conducted on the concept of hermetically shielding the thermistor element from the outside air, that is, glass-encapsulated positive temperature coefficient thermistors. However, a positive temperature coefficient thermistor is a semiconductor ceramic mainly made of barium titanate, and is extremely sensitive to heat or atmosphere, making it extremely difficult to encapsulate the thermistor element in glass.

As a result of various studies, the inventors of the present invention have found that glass encapsulation is possible by using a hollow type. However, even with this hollow type glass-enclosed thermistor, it was clear that the resistance value changed significantly before and after the glass-enclosure, depending on the temperature and atmosphere at the time of enclosing the glass, as well as the constituent members.

According to the problem to be solved by the invention, it is a problem to provide a glass-encapsulated positive temperature coefficient thermistor that suppresses the change in resistance value before and after glass encapsulation as described above and has excellent long-term reliability. That is, one object of the present invention is to solve this problem.

As a result of two various studies, it was discovered that the change in resistance before and after glass encapsulation depends not only on the temperature and atmosphere at the time of glass encapsulation, but also on the material of the components sealed within the glass tube, that is, the lead wire material. Specifically, it is necessary to select a material that does not cause oxidation reaction or oxygen adsorption within the limited space when the glass is sealed.

Means for Solving the Problems To achieve this object, the glass-encapsulated thermistor of the present invention consists of two parallel noble metal wires provided in a hollow glass tube or two slug lead wires coated with a precious metal. It has a structure in which a positive temperature coefficient thermistor element is sandwiched.

Function: With this configuration, it is possible to suppress a change in resistance value during glass encapsulation, stabilize the atmosphere inside the glass tube, and obtain a glass encapsulated positive temperature coefficient thermistor with excellent long-term reliability.

EXAMPLE 1 A glass-encapsulated positive temperature coefficient thermistor according to an example of the present invention will be described with reference to the drawings.

First, a positive temperature coefficient thermistor element is created. Now, a disk-shaped sintered body is obtained using a material with a composition in which strontium is added to barium titanate as a solid solution, and yttrium oxide is further added as a semiconductor element, using a normal ceramic manufacturing process. An N1 electrode is provided on this sintered body by a plating method. And, as initial characteristics, 25℃ and 125℃
After measuring the resistance value at , it is cut into desired dimensions to obtain a positive temperature coefficient thermistor element shown by 1 in FIGS. 1 to 3. This thermistor element 1 is fixed by baking with silver paste to the center of two lead wires 2 which have already been fixed in parallel with glass beads at an appropriate interval. This is further melted and sealed into the glass tube 3 using the glass beads. Here, considering the linear expansion coefficient of ceramic P and lead wire for glass,
Lead glass with a strain point of 400'C or less is used.

Even in the process described above, the characteristics of the thermistor element 1 change depending on heat and atmosphere. That is, the resistance value changes before and after the thermistor element 1f'i is enclosed in glass. In particular, the rate of change varies greatly depending on the material of the lead wire 1, and the long-term reliability characteristics are also affected. Examples and comparative examples are shown in Table 1 below. Here, the lead wires whose surfaces were coated in Table 1 were obtained by fixing two slag leads with glass beads and then coating them with a noble metal.

(Left below) Table 1 shows the type of lead wire, the average rate of change in resistance value at 25°C of 10 thermistor elements before and after glass encapsulation, and the coefficient of variation of the rate of change in this case. There is. Furthermore, after leaving the glass-encapsulated positive temperature coefficient thermistor thus prepared at 126°C for 1000 hours,
The rate of change in resistance value at °C is shown on the right side. Here, the criterion for judgment is that the change in resistance value before and after glass encapsulation is ±25%, which can be sufficiently controlled during production, and that the variation is small.As for reliability, the change in resistance value after 1000 hours is was determined to be within ±10%. This 10% is a very strict value compared to the reliability standard (±30%) for conventional positive temperature coefficient thermistors. Then, in Table 1, sample Nn
1, 5, and 7 are outside the scope of the claims. Also, the fourth
FIG. 5 shows the resistance temperature curve and resistance value change rate of sample Nn6 of the above example, respectively.

The thermistor element used in the above example is a positive temperature coefficient thermistor for temperature compensation, and its Curie point is -20°C or lower, and its resistance temperature characteristic α is 3.6% between -16°C and +86°C. /°C, but a conventional positive temperature coefficient thermistor with a Curie point of around 120°C and α of 8 to 18%6 may be used.

It is not particularly limited. Although not shown in the examples, a clad wire whose surface is coated with a noble metal such as platinum cladding is also effective.

Effects of the Invention By adopting the configuration described above, it is possible to provide a glass-encapsulated positive temperature coefficient thermistor for temperature compensation that is stable in manufacturing and has excellent long-term reliability.

Now, it is considered that the change in the resistance value of the thermistor element before and after glass encapsulation largely depends on the oxygen defect concentration on the element surface. The material of the lead wire is considered to be one of the main factors influencing this, and in the present invention, by using an inert noble metal wire or a lead wire whose surface is treated with a noble metal, which has excellent heat resistance, the By encapsulating the thermistor element in a stable atmosphere in which changes in resistance can be suppressed, it is possible to provide a glass-encapsulated positive temperature coefficient thermistor with excellent long-term reliability. The glass-encapsulated positive temperature coefficient thermistor of the present invention is significantly different from conventional disk-shaped ones in terms of temperature accuracy and long-term reliability, and has great industrial significance. In particular, it has enabled practical use under harsh environments such as humidity, gas, and vacuum.
The industrial significance is extremely large.

[Brief explanation of the drawing]

FIGS. 1 and 2 are half-sectional views of the glass-encapsulated positive temperature coefficient thermistor in Example 3 of the present invention, viewed from two directions, the front and top surfaces, and FIG. A cross-sectional view, FIG. 4 is a diagram showing a resistance temperature curve of an example of a positive temperature coefficient thermistor according to the present invention, and FIG. 5 is a diagram showing a resistance value change rate in a high temperature storage test at 125°C. 1...Positive characteristic thermistor element, 2...
Lead wire (precious metal wire or slag lead wire coated with precious metal) %3...Glass tube. Name of agent: Patent attorney Shigetaka Awano and 1 other person 1st
Figure 2 Figure 3

Claims (1)

[Claims] A glass-encapsulated positive temperature coefficient thermistor characterized in that a positive coefficient thermistor element is sandwiched between two parallel noble metal wires or two slug lead wires coated with a noble metal provided in a hollow glass tube.