JPH1116664A - Ceramic heater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the reliability of tensile strength of a lead wire by fixing an end of a lead wire to an electrifying pad for electrifying a heating resistor of a ceramic heater at a central part except for the peripheral edge having a specified width with the gold-copper group brazing material, and plating the surface with nickel. SOLUTION: A heating resistor is embedded in a ceramic body having a desirable shape such as a plate-like or cylindrical shape, and an electrode pad 5 for electrifying the heating resistor is provided through a metallized material 4. In this ceramic heater H, an end of a lead wire 9 is fixed to the nickel-plated electrode pad 5 at a central part except for an area of the peripheral edge having a width W at 0.03 mm or more by the gold-copper group brazing material 6, and a coating layer 10 is formed on the surface of the electrode pad 5, which includes the gold-copper group brazing material surface, by nickel plating so as to form an electrifying terminal 2. With this structure, when the brazing material 6 is hardened, a contraction difference of the metallized material 4, the electrode pad 5 and the brazing material 6 is absorbed by the peripheral edge of the electrode pad 5 having the width W so as to prevent the generation of peeling inside the metallized material 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic heater in which a heating resistor is embedded in a ceramic body.
Particularly, the present invention relates to a ceramic heater having excellent durability in a high temperature range.

[0002]

2. Description of the Related Art Conventionally, flat, tubular or cylindrical ceramic heaters in which a heating resistor is embedded in a ceramic body have been widely used in various fields.
Ceramics having a heat-generating resistor and a temperature-sensitive resistor as described in, for example, Japanese Patent No. 71281 have been put to practical use.

FIG. 8 shows such a cylindrical ceramic heater H, in which a strip-shaped heating resistor 1 as a heater is embedded in a cylindrical body made of ceramic, and provided at both ends of the heating resistor 1. Although heat is generated when electricity is supplied from the terminals 2 and 2 ′, the heat-generating resistor 1 and the temperature-sensitive resistor 3 used as a temperature sensor are embedded in the structure.

FIG. 9 shows a cross section of the terminals 2, 2 '.
As shown in the figure, in the conventional ceramic heater H, the brazing material 6 flowed over the entire Ni-plated electrode pad 5 formed on the metallization 4 and completely covered the electrode pad 5. In the case of such terminals 2 and 2 ′, in the brazing material 6 containing two or more kinds of metals, stress is applied to the creviced (end) portion 7 of the expansion of the brazing material 6 due to shrinkage when the brazing material 6 is solidified. Easy to concentrate. And such a ceramic heater H
When the electrode pad 5 is used in a severe environment at a high temperature, there is a problem that the electrode pad 5 is easily peeled off from the metallized 4.

[0005]

SUMMARY OF THE INVENTION The present invention has been developed in view of the above circumstances, and has an electrode pad for supplying a current to a heating resistor embedded in a ceramic body having a desired shape such as a plate shape or a cylindrical shape. The ends of the leads are fixed with gold-copper-based brazing material to the central portion of the electrode pad excluding the area of 0.03 mm or more, and nickel plating is applied to the electrode pad including the gold-copper-based brazing material surface. It is another object of the present invention to provide a ceramic heater characterized in that the ceramic heater is applied.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a partially developed view showing a state before firing a cylindrical ceramic heater H, and FIG. FIG. 2 is a cutaway view of a main part of the ceramic heater before terminals are formed. A strip-shaped heating resistor 1 as a heater is buried in a cylindrical body made of ceramic, and electricity is supplied from terminals (described later) provided at both ends of the heating resistor 1. The heating resistor 1 generates heat when it is needed.
Resistance 3 for use as a temperature sensor in conjunction with
May be formed in a structure in which the heat generating resistors 1 are provided side by side over the entire heat generating region K in which the heat generating resistors 1 are densely embedded.

In the process of manufacturing such a cylindrical ceramic heater H, as shown in FIG. 3, a ceramic made of a powder of alumina, mullite or the like having excellent electrical insulation and heat conductivity even at a high temperature is used. In order to form the resistor pattern R1 as the heating resistor 1 on the raw sheet S1,
A comb-like shape that allows the resistance value to be set to the required heat value,
It is formed in a desired width, thickness, and length in an arbitrary shape such as a spiral shape using a paste of tungsten, molybdenum-manganese, or the like, by a thick film technique such as screen printing, and forming the heating resistor pattern R1. At the same time, the resistor patterns R1 and R2 for use as a temperature sensor are sandwiched and laminated on a cylindrical core material S2 formed of the same material as the ceramic raw sheet S1, and the obtained cylindrical green ceramic body is fired in a firing atmosphere. What is necessary is just to sinter and integrate inside.

In the step of forming the resistor patterns R1 and R2, terminal portions U and R are connected to the ends of the resistor patterns R1 and R2.
U ', V, V' are formed in advance. These terminals U,
U ', V, and V' form through holes in the corresponding portions of the raw sheet S1 before printing the resistor patterns R1 and R2, and fill conductive materials such as tungsten and molybdenum-manganese in the through holes. After that, the resistor patterns R1, R
Print 2.

FIG. 4 shows a ceramic heater H having a terminal 2 formed after firing. The terminal 2 is connected to a Ni-plated electrode pad 5 formed on a metallization 4 as shown in an enlarged view of FIG. A gold-copper brazing material 6 is flowed and solidified in the central portion except for the peripheral portion 8 having a width w of 0.03 mm or more, and Ni
Are coated with a Ni coat layer 10.

There are three points for the peripheral portion 8 to remain on the entire circumference. First, the melting temperature of the brazing material 6 is controlled to be higher than the melting point of the brazing material 6 by 50 ° C. or more. Second, when the brazing material 6 is melted, a tunnel furnace is used. Then, the transfer speed of the product in which the lead is put in the carbon mold is increased after passing through the final circuit, and the cooling speed is increased. As a result, it has been found that in the case of the gold-copper brazing material 6, the brazing flow can be controlled well.

Third, the area of the Ni-plated electrode pad 5 is made large and the amount of the brazing material 6 is adjusted to be small. This allows fine adjustment of the brazing flow.

The ceramic heater H constructed as described above has a width w = w =
0.03 mm or more is left, so it is possible to absorb the difference in shrinkage of the metallization 4, the electrode pad 5, and the brazing material 6 when the brazing material 6 is hardened. Reliability is improved. Moreover, since the peripheral portion 8 is secured without using an etching technique,
When the surface of the ceramic surface in the vicinity of is observed with an SEM image photograph, it can be confirmed that the glass component is sufficiently present. Therefore, there is an advantage that the tensile strength of the current-carrying terminal 2 is large. On the other hand, when the flowing brazing material is selectively removed using an etching technique, the vicinity of the energizing terminal 2 is also affected by the etching solution, and as a result, the tensile strength of the energizing terminal 2 is reduced. . In this case, in the SEM image photograph, it can be confirmed that a large amount of glass is removed from the ceramic surface portion near the energizing terminal 2.

In the above-described embodiment, the ceramic raw sheet S1 on which the resistor patterns R1 and R2 are printed is rounded on the cylindrical core material S2 and overlapped. As shown in FIG. 6, a flat ceramic heater H can be obtained. In addition, it is possible to form a desired shape by processing before firing. Further, the ceramic heater is not limited to the above-described manufacturing method. For example, the ceramic heater is manufactured by printing a resistor pattern on a ceramic body previously fired in a flat plate or a columnar shape, applying an insulator thereon, and then firing. Alternatively, it can be manufactured by bonding a ceramic sheet which has been printed with a resistor pattern on a raw sheet, and then firing and integrating the ceramic body.

It is needless to say that the present invention is not limited to the above-described embodiment, but can be in any form without departing from the object of the invention.

[0015]

EXPERIMENTAL EXAMPLE 1 The following experiment was conducted to confirm the effects of the present invention.

The alumina ceramic heater H shown in FIGS. 1 to 5 is left at normal temperature and high temperature (400 ° C./500
After hr), as shown in FIG. 7, the lead 9 was pulled in the 90 ° direction, and the strength was measured. Each sample has a width w (refer to FIG. 5) of the peripheral portion 8 between the brazing material 6 and the electrode pad while adjusting a brazing temperature (a temperature higher than the melting point of the brazing material 6 by 50 ° C. or less) and a brazing amount. We prepared several different ones. The measurement of the peripheral portion 8 was performed at the time of preparing each sample.
At a stage before the coating layer 10 is coated on the brazing material 6, the baking is performed using a binocular x10 or x100.
That value was obtained for the narrowest width w. The brazing material 6 is made of gold-copper (gold / copper / nickel) and the metallization 4 is made of tungsten.
m, and the diameter of the nickel lead 9 was 0.4 mm.

The criterion for determining the experimental results is as follows: 5 Kg or more of the strength was passed on average on the strength at normal temperature. Fail was less than 5 kg, and 1 K on average on the strength when left at high temperature.
g or more was evaluated as acceptable, and less than 1 kg was evaluated as unacceptable.

Table 1 shows the minimum value of the width w of the peripheral portion 8 in each sample and the results.

[0019]

[Table 1]

As is apparent from Table 1, when the peripheral portion 8 is not present (w = 0), the terminal 2 is not exposed at room temperature or at a high temperature.
Had a width w of 0.03
When it was not less than mm, all passed.

Comparative Example The brazing temperature was set to a temperature higher than the melting point of the brazing material 6 by 50 ° C. or more, and then a part of the brazing material 6 was sodium cyanide so that the width w of the peripheral portion 8 was 0.1 mm. Is selectively etched at high speed by chemical etching.
A tensile strength test was performed according to Example 1.

As a result, the tensile strength at room temperature was as low as 2.5 kgf, and at a high temperature, peeling was observed, and the result was unacceptable.

EXPERIMENTAL EXAMPLE 2 In the same manner as in Experimental Example 1, a plurality of samples having different widths w were prepared for the ceramic heater H made of alumina shown in FIGS. These samples were used for the brazing material 6 of the terminal 2.
Was not covered with the coating layer 10. In this state, using a binocular x10 or x100, the value of the narrowest portion of the width w of the peripheral portion 8 was obtained, and it was confirmed whether peeling had occurred in the metallization 4.
Table 2 summarizes the results.

[0024]

[Table 2]

As is clear from Table 2, when the peripheral portion 8 was not present (w = 0), peeling was observed. On the other hand, when the width w was 0.03 mm or more, peeling occurred. Did not.

EXPERIMENTAL EXAMPLE 3 In the experimental example 2, 30 ceramic heaters (products of the present invention) having a peripheral portion 8 having a width w of 0.3 mm were prepared, and the voltage applied to each of the 10 ceramic heaters was 1, 2, and 3 V, respectively. It took one minute to measure the presence or absence of the current leak, and the insulation state was confirmed. There was no leakage current in the case of the applied voltage of 1 and 2 V, but there was leakage current in three cases of the applied voltage of 3 V.

On the other hand, the insulation state of the ceramic heater of the comparative example, in which the width w of the peripheral portion 8 was set to 0.3 mm (by chemical etching), was confirmed in the same manner. Nine,
There were 10 at 2 and 3 V, respectively.

Experimental Example 4 Nine of the products of the present invention of Experimental Example 3 were prepared, and a voltage was applied.
A cycle life experiment was repeated in which the temperature was repeated between 00 ± 2 ° C. and room temperature (23 ° C.). 10,000 cycles, 20,000 cycles, and 30,000 cycles were added to each of the three tubes, but no disconnection occurred in any of them.

On the other hand, a similar experiment was performed using the comparative example product in Experimental Example 3, and as a result, one disconnection was detected in 20,000 cycles.
Two disconnections were confirmed in 10,000 cycles.

[0030]

As described above, according to the present invention, in the current-carrying terminals of the ceramic heater, the peripheral portion of the brazing material with respect to the electrode pad is left with a width w of 0.03 mm or more over the entire circumference. Absorbs the difference in shrinkage of the metallization, electrode pad, and brazing material when the material hardens, and prevents peeling in the metallization. Moreover, by controlling the flow of the brazing material by adjusting the melting temperature and the like of the brazing material without using an etching method or the like and securing the peripheral portion, there is sufficient vitreous material on the ceramic surface near the current-carrying terminal. Not only that, the reliability of the lead tensile strength after leaving at high temperature is improved, and a ceramic heater with high durability can be obtained even in a severe use environment, and the practical effect is extremely large.

[Brief description of the drawings]

FIG. 1 is a partial development view showing a state before firing of a ceramic heater according to an embodiment of the present invention.

FIG. 2 is a fragmentary cutaway view of the ceramic heater before firing in FIG. 1;

FIG. 3 is a development view of a raw sheet constituting the ceramic heater before firing in FIG. 1;

FIG. 4 is a perspective view of a ceramic heater in which a current-carrying terminal is formed after firing.

FIG. 5 is an enlarged sectional view of an energizing terminal of the ceramic heater of FIG.

FIG. 6 shows another embodiment of the present invention and is a partially broken perspective view of a flat ceramic heater.

FIG. 7 is a schematic diagram illustrating a method of Experimental Example 1 of the present invention.

FIG. 8 is a perspective view of a conventional ceramic heater.

FIG. 9 is an enlarged cross-sectional view showing an energizing terminal of the heater of FIG.

[Explanation of symbols]

 H Ceramic heater 1 Heating resistor 2 Current terminal 3 Temperature sensitive resistor 4 Metallization 5 Electrode pad 6 Brazing material 8 Peripheral edge 9 Lead 10 Coat layer w Width S1, S1 'Raw sheet R1, R2 Resistor pattern U, U', V, V 'terminal section S2 core material, base K heat generation area L temperature sensitive area

Claims (1)

[Claims] An electrode pad for supplying a current to a heating resistor embedded in a ceramic body having a desired shape such as a plate or a cylinder is provided with a lead at a central portion excluding a region of 0.03 mm or more in a peripheral portion of the electrode pad. A ceramic heater wherein an end portion is fixed with a gold-copper brazing material and nickel plating is applied to an electrode pad including a surface of the gold-copper brazing material.