JP2001210455A - Ceramic heater and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent occurring of cracks on the surface of a ceramic heater on a way of raising the temperature and becomes impossible to use it, when the ceramic heater is intended to be raised to 1000 deg.C from room temperature in 5 seconds. SOLUTION: In the ceramic heater comprising a heating resister and a lead extraction part connected to the ceramic heater both of which is built in the ceramic body, the ceramic body surface side of the portion where the above- mentioned heating resister is built in, is worn in the covering layer which consists of other ceramics.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a soldering iron, a vaporizer heater for an oil fan heater, a hot water heater,
The present invention relates to a ceramic heater used for various types of heaters for general household use, such as heaters for automobile oxygen sensors, electronic heaters, and industrial equipment.

[0002]

2. Description of the Related Art Recently, products called digital home appliances, such as the Internet, mobile phones, and personal computer-integrated televisions,
It is expected to be a growth industry in the future. The production volume of personal computers has exploded as users shift from companies and corporations to individuals. Along with this, the demand for soldering irons used for connecting various circuits of such products is increasing. In terms of the market, a recent characteristic is that the market has shifted from Japan to Korea, Southeast Asia, and especially Taiwan. Under these circumstances, from the viewpoint of improving the production efficiency of personal computers, a soldering iron capable of rapidly increasing the temperature after soldering and capable of rapidly increasing the temperature has been required in the market.

Under these circumstances, a soldering iron with a sliding cover for preventing burns has been proposed in Japanese Patent Application Laid-Open No. Hei 7-314130, but no consideration has been given to the rising characteristics of ceramic heaters. . Also,
Japanese Patent Application Laid-Open No. 9-148053 proposes a small and high-performance soldering iron, and shows that the heating characteristics can be improved by connecting two layers of heating resistors in series and in parallel. However, it was not satisfactory with respect to the above-mentioned requirement for rapid temperature rise.

[0004] First, a conventional ceramic heater for a soldering iron will be described. As shown in FIG.
A conventional soldering iron 10 has a configuration in which a cylindrical ceramic heater 1 is inserted into a tip 11, and when the ceramic heater 1 is energized, the tip 11 is turned on.
Was heated to melt the solder. Further, in order to improve the heating efficiency, the tip 11 is formed so as to be in close contact with the ceramic heater 1.

In order to manufacture the cylindrical ceramic heater 1, as shown in FIG. 4, a ceramic core material 2 and a ceramic sheet 3 are prepared, and one surface of the ceramic sheet 3 is made of W, Mo, Re or the like. After forming the heating resistor 4 and the lead lead-out portion 5 by printing a paste of a high melting point metal, the ceramic sheet 3 is wound around the ceramic core material 2 so that the surface on which the heating resistor 4 and the lead lead-out portion 5 are formed is inside, The ceramic heater 1 was obtained by firing and integrating the whole.

FIG. 4A shows a pattern of the heating resistor 4 built in the ceramic heater 1 as shown in FIG.
The pattern width of the heating resistor 4 was uniform. On the ceramic sheet 3, the lead-out portion 5 is directly connected to the heating resistor 4, and a through hole 7 made of the same metal material as the heating resistor 4 is formed at the end of the lead-out portion 5. The electrode pad 8 on the back side and the lead extraction portion 5 were connected. The conductor paste was injected into the through holes 7 as needed.

[0007]

Heretofore, a soldering iron having a large heat capacity has been mainly used, and once heated, it has been used continuously for soldering. However, a disadvantage of the soldering iron having a large heat capacity is that it takes a considerable amount of time until the tip is heated when used. On the other hand, recently, a rising characteristic at the time of cold start has been required.

In order to improve the temperature rising characteristics of the soldering iron as described above, it is necessary to improve the temperature rising characteristics of the ceramic heater as its heat source. In order to cope with this, a ceramic heater of a type in which the temperature of the highest heat generating portion of the ceramic heater rises from room temperature to 700 ° C. in 3 seconds or less is required at present.

However, when trying to achieve such a rapid temperature rise, a crack is generated on the surface of the highest heat generating portion of the ceramic heater 1, and there is a problem that the heat generating resistor 4 is disconnected during use. This is the heating resistor 4
When heated rapidly, a part of it is rapidly heated and expands,
This is because the surface of the ceramic sheet 3 provided with the heating resistor 4 cannot be expanded because it is cooled by the tip 11, and a tensile stress is generated on the surface of the ceramic sheet 3.

[0010]

As a result of intensive studies on the above-mentioned problems, the present inventor has found that a ceramic heater in which a heating resistor and a lead lead portion connected to the heating resistor are built in a ceramic body, It has been found that the above problem can be solved by covering the surface of the ceramic body in a portion containing the heating resistor with a coating layer made of another ceramic.

The difference between the coefficient of thermal expansion of the coating layer and the coefficient of thermal expansion of the ceramic body is 3 × 10 ⁻⁶ deg ⁻¹ or less,
In addition, the thermal conductivity of the coating layer is preferably 4 to 42 W / m · K.

The covering layer is provided so as to cover an area larger than the heating resistor portion, and the thickness of the covering layer is preferably 10 to 500 μm.

The ceramic heater according to the present invention is a ceramic heater in which the heating resistor and a lead lead portion connected to the heating resistor are built in a ceramic body. It can be obtained by providing a coating layer on the surface by any of spraying, screen printing, CVD, PVD, dipping and firing.

[0014]

Embodiments of the present invention will be described below.

First, the structure of the soldering iron will be described with reference to FIG. A cylindrical ceramic heater 1 is inserted into the inside of the tip 11, and when the ceramic heater 1 is energized, the tip 11 is heated to melt the solder.

FIGS. 1 and 2 show an example of the ceramic heater of the present invention. Ceramic heater 1
The ceramic sheet 3 having the heating resistor 4 and the lead lead-out portion 5 formed on the surface thereof is arranged such that the heating resistor 4 and the lead lead-out portion 5 are sandwiched between the ceramic sheet 3 and the ceramic core material 2. The heat generating resistor 4 and the lead extraction portion 5 are built in the ceramic body by being closely adhered to the periphery of the material 2 and integrated by firing. The same material as the core material 2 is generally used for the ceramic sheet 3. The lead lead-out portion 5 is connected to the electrode pad 8 through the through-hole 7, and after Ni plating is applied to the surface thereof, the lead 9 is joined with a brazing material (not shown) to form a ceramic heater.

Further, the present invention is characterized in that, as shown in FIG. 1, the outer surface of the ceramic sheet 3 having the heating resistor 4 is further covered with a coating layer 6 made of another ceramic.

The main function of the coating layer 6 is heat insulation. By covering the outer peripheral portion of the ceramic heater 1 with the coating layer 6, a heat insulating effect due to the interface between the coating layer 6 and the ceramic sheet 3 is obtained. The thermal shock due to the cooling of the surface of the heater 1 can be reduced, and the occurrence of cracks can be reduced by holding the outer peripheral portion. in this way,
The present inventors have found that forming an interface between the coating layer 6 and the ceramic sheet 3 is very effective in reducing thermal shock resistance.

That is, the cause of the cracks when the ceramic heater 1 is rapidly heated is that the outer surface of the ceramic sheet 3 where the heating resistor 4 is provided when the heating resistor 4 rises rapidly. This is because the temperature cannot be increased because the ceramic sheet 3 is cooled by the tip 11, and a tensile stress is applied to the ceramic sheet 3. On the other hand, as in the present invention, by further covering the ceramic sheet 3 with the coating layer 6, the influence of the cooling by the tip 11 is reduced, and when the temperature of the heating resistor 4 rises rapidly, By making the ceramic sheet 3 easy to be heated, the ceramic sheet 3
Can reduce the thermal stress generated at the time, and can prevent the occurrence of cracks.

What is important here is that the coating layer 6 is formed on the surface of the ceramic sheet 3 to form an interface between them. For that purpose, the coating layer 6 is preferably made of a material different from the surface of the ceramic sheet 3.

When the heating resistor 4 is heated, heat is diffused from the heating resistor 4 to the surroundings.
Since an interface is formed between the coating layer 6 and
The heat conduction at this interface is slightly delayed. Due to this delay, the surface of the ceramic sheet 3 is effectively heated, so that the tensile stress on the ceramic sheet 3 due to the expansion of the heating resistor 4 can be reduced, and the occurrence of cracks in the ceramic sheet 3 can be prevented. It is estimated.

Here, the action of the coating layer 6 is assumed to be heat insulation, which means the action for a few seconds in the initial stage of rapidly increasing the temperature of the ceramic heater 1 and heating the soldering iron tip. It is not a level that affects the time of tens of seconds.
That is, the heat insulation of the ceramic heater 1 for several seconds can prevent cracks from being generated in the ceramic sheet 3 on the surface of the ceramic heater 1 and heat the soldering iron tip for several tens of seconds. It can be done quickly.

In the ceramic heater 1 of the present invention,
The ceramic core material 2 and the ceramic sheet 3 are generally made of the same material, and use ceramics such as alumina, silicon nitride, and mullite. As a material of the heating resistor 4, a high melting point metal such as tungsten, molybdenum, rhenium, platinum, rhodium or the like is used alone or in combination. The thickness of the heating resistor 4 is 5 to 50 μm.

The coating layer 6 is coated on the outer surface of the ceramic sheet 3 so as to cover the portion provided with the heating resistor 4.
The material of the coating layer 6 differs depending on the material of the ceramic body composed of the core material 2 and the ceramic sheet 3, and it is preferable that the difference in the coefficient of thermal expansion from the ceramic body be 3 × 10 ⁻⁶ deg ⁻¹ or less.

For example, when the ceramic sheet 3 is made of alumina (Al ₂ O ₃ ), MgAl ₂ O ₄ ,
Al ₂ O ₃ , 3Al ₂ O ₃ .2SiO ₂ or the like is used. When the ceramic sheet 3 is made of Si ₃ N ₄ , Si is used as the coating layer 6.
C and Si ₃ N ₄ are preferably used. When the ceramic sheet 3 is 3Al ₂ O ₃ .2SiO ₂ , it is preferable to use Al ₂ O ₃ or MgAl ₂ O ₄ as the coating layer 6. This is because the difference in the coefficient of thermal expansion between the ceramic sheet and the coating layer 6 is 3 × 10
^{If the} difference is more than ^-6 deg ^-1, the stress generated between the ceramic body and the ceramic body increases, which may cause cracks.

The thermal conductivity of the coating layer 6 is 4 to 42 W
/ M · K. This is because if the thermal conductivity is too small, it will be difficult to heat the object to be heated such as a soldering iron,
This is because the heating rate of the object to be heated becomes slow. Also, if the thermal conductivity of the coating layer 6 is too large, it may cause cracks in the ceramic sheet 3.

Further, the coating layer 6 includes at least the heating resistor 4.
It is preferable to cover the outer surface of the portion of the ceramic heater 1 provided with the above, and to set the thickness of the coating layer 6 in the range of 10 to 500 μm.

This is because the absence of the coating layer 6 on a part of the heating resistor 4 causes cracks in the ceramic sheet 3 in that part. If the thickness of the coating layer 6 is smaller than 10 μm, the effect of preventing cracks in the ceramic sheet 3 will be lost, and if the thickness of the coating layer 6 is larger than 500 μm, heat transfer will be poor, and heating of the object to be heated by the soldering iron will be poor. As a result, a desired heating rate cannot be obtained. In addition,
The thickness of the coating layer 6 is more preferably 10 to 30.
0 μm is good.

The ceramic heater 1 according to the present invention is supplied with electric power by the leads 9 joined to the electrode pads 8. Generally, the material of the lead 9 is Ni wire, Fe
-Ni-Co alloy wire or the like is used, and tungsten is used as a metal material of the electrode pad 8;
It is joined to the electrode pad 8 by brazing.

FIG. 3 is a sectional view showing a state where the ceramic heater 1 of the present invention is mounted on the soldering iron 10. When the ceramic heater 1 inserted so as to be in close contact with the tip 11 is energized, the tip 11 is heated, so that the solder can be melted by touching the solder. The size of the soldering tip 11 is selected according to the heat capacity of the soldering work, and the calorific value of the ceramic heater 1 is also selected according to the heat capacity of the soldering tip 11. .

Next, a method of manufacturing the ceramic heater 1 according to the present invention will be described.
Will be described as an example.

First, a core material 2 made of alumina is prepared. A raw material for alumina is prepared, and a raw material for molding is prepared by mixing a sintering aid such as CaO, MgO, SiO ₂ , a binder for molding, and the like. Using this raw material, an alumina core material 2 having a desired shape is molded by a molding method such as extrusion molding or press molding.

Next, using the same raw materials as above, a sheet-like ceramic sheet 3 made of alumina is prepared by a molding method such as a knife blade. Then, the heating resistor 4 and the lead lead-out portion 5 are printed by means such as screen printing. The ceramic sheet 3 is wound around the alumina core material 2 prepared previously and degreased integrally, and then fired under predetermined conditions to obtain the ceramic heater 1.

The outer surface of the ceramic heater 1 is made of, for example, MgAl ₂ O ₄ , Al by using any method such as thermal spraying, PVD, CVD, screen printing, and dipping.
_A coating layer 6 made of ₂ O ₃ is formed in a desired shape.

As an example of the formation of the coating layer 6 by the PVD method, an electron beam is irradiated on an alumina target, and the scattered alumina is fixed on the surface of the ceramic heater 1 to form the coating layer 6. .

As an example of the formation of the coating layer 6 by the CVD method, an AlCl ₃ gas using N ₂ as a carrier gas is caused to flow on the surface of the ceramic heater 1, and at the same time, a gas containing O ₂ is caused to flow from the other side and heated. On the surface of the ceramic heater 1, AlCl ₃ and O ₂ are chemically reacted to form Al.
_The coating layer 6 is formed by generating ₂ O ₃ .

In the method using screen printing,
There is a method in which a material that sinters at a temperature lower than the firing temperature of alumina is printed on the surface of the ceramic heater 1 by a curved surface printing method to form the coating layer 6 and then sintered and fixed at a predetermined temperature.

Further, when the dipping method is used,
After the ceramic heater 1 is inserted into a dispersion solution of a material that sinters at a temperature lower than the firing temperature of alumina, the coating layer 6 is formed on the surface of the ceramic heater 1 by removing the ceramic heater 1 from the dispersion solution. There is a method of fixing by sintering.

[0039]

Next, examples of the present invention will be described.

Example 1 A ceramic heater 1 according to the present invention, in which the outer surface of a ceramic body of a heating resistor 4 as shown in FIG.
And a conventional ceramic heater (shown as no coating material) 1 shown in FIG. Alumina was used as the material of the ceramic heater 1. The temperature was increased by applying electric power under the condition that the maximum temperature of the ceramic heater 1 was raised to 700 ° C. in 3 seconds in the sample without coating. Each sample was evaluated for 5 cycles for 5 cycles, and the presence or absence of cracks was confirmed by binocular inspection.

In the embodiment of the present invention, the coating layer 6
A coating layer 6 of spinel (MgO.SiO ₂ ) and mullite (2Al ₂ O ₃ .2SiO ₂ ) was formed on each sample by thermal spraying. As for the cracks of the sample on which the coating layer 6 was formed, both the coating layer 6 and the surface of the ceramic heater 1 from which the coating layer 6 was removed were observed. The results are shown in Table 1.

[0042]

[Table 1]

As can be seen from Table 1, no. In No. 1, cracks were observed on the surfaces of all the samples. On the other hand, No. 1 in which the coating layer 6 of spinel and mullite was formed. In Nos. 2 and 3, cracks did not occur in all samples.

Example 2 A sample for evaluation was prepared in the same manner as in Example 1.
In the examples of the present invention, six types of glass, mullite, spinel, alumina, porous MgO, and MgO were prepared as the material (coating material) of the coating layer 6 and formed by thermal spraying.
The porous MgO was made porous by changing the thermal spraying conditions. The thickness of the coating layer 6 was 200 μm, and the coating layer 6 was provided so as to cover an area larger than the heating resistor 4.
As an evaluation method, a temperature rise test and a durability test were performed.

The temperature rise test was performed under the same conditions as in Example 1, and the presence or absence of cracks after the test was examined to determine the superiority. In the durability test, the electric power at which the surface temperature of the uncoated ceramic heater 1 was maintained at 1100 ° C. was 2 hours.
After applying 5000 minutes of a cycle of forced air cooling, the coating layer 6 was washed, after the coating layer 6 was removed by a technique such as polishing, and then immersed in a liquid containing a red dye. A binocular inspection was performed by a red check to observe a liquid that oozes out on the surface when dried, and the presence or absence of cracks was examined.

When each of the ceramic heaters 1 is inserted into the iron tip 11, the temperature of the
The time until heating was performed by applying the same voltage. For comparison, a sample without coating 6 was also evaluated. In addition, the coefficient of thermal expansion of each coating layer 6 was evaluated by using one from room temperature to 400 ° C. The results are shown in Table 2.

[0047]

[Table 2]

As shown in Table 2, the ceramic heater 1
And the coating layer 6 having a thermal expansion difference of 4.5 × 10 ⁻⁶ deg ⁻¹ . Nos. 8 and 9 and Nos. In No. 10, cracks occurred in the coating layer 6 after the durability test. In addition, the thermal conductivity was as small as 3 W / m · K. 4 had cracks. On the other hand, no. No cracks occurred in 5 to 7 even after the durability test. That is, the coating layer 6
The difference between the coefficient of thermal expansion of the ceramic body and that of the ceramic body is 3 × 10 ^-6
deg ^-1 or less, and the thermal conductivity of the coating layer 6 is 4
It can be seen that a ceramic heater 1 with excellent heat resistance can be obtained by setting it to be ~ 42 W / mK.

Regarding the heating time of the tip 11,
In the example of the present invention in which the coating layer 6 was formed and the comparative example (No. 10) without the coating layer 6, the time was almost the same, and no significant difference was found.

Example 3 Next, using the same sample as in Example 1, the ratio of the area of the portion where the coating layer 6 was generated to the area of the portion where the heating resistor 4 of the ceramic heater 1 was installed was changed. The presence or absence of cracks in the heater 1 and the coating layer 6 was examined. Thermal expansion difference 3 × 10 ^-6 and the ceramic heater 1 as a covering layer 6 deg ^{- 1} a and the thermal conductivity of 17W /
The thickness of the coating layer 6 is set to 200 using a spinel of m · K.
The test was performed by changing the coating area (coating area) of the coating layer 6 as shown in Table 3.

In the test, the heating time until the surface temperature of the ceramic heater without the coating layer 6 reaches 900 ° C. is 3 hours.
After repeating a cycle of applying a voltage of 10 seconds, raising the temperature to 1000 ° C., and then cooling to room temperature, the occurrence of cracks was examined. The results are shown in Table 3.

[0052]

[Table 3]

As shown in Table 3, the installation area of the coating layer 6 was 2/3 or less of the installation area of the heating resistor 4. 11
Although cracks occurred in Nos. To 13, the coating area of the coating material 6 was equal to or larger than the area of the heating resistor 4. No cracks occurred in 14-19.

Example 4 Next, using the same sample as in Example 1, the influence of the thickness of the coating layer 6 was investigated. The influence of the thickness of the coating layer 6 was investigated by using the same spinel as the coating layer 6 and changing the thickness from 0 to 700 μm so as to cover an area larger than the heating resistor 4. For evaluation, each ceramic heater 1 was inserted and brought into close contact with the tip 11,
The same energy as when the surface temperature of the ceramic heater 1 without the coating layer 6 reaches 900 ° C. until the surface temperature reaches 900 ° C. is given, and the temperature rise time of the tip 11 is measured. After repeating 500 cycles, the ceramic heater 1 was examined for the occurrence of cracks. The results are shown in Table 4.

[0055]

[Table 4]

As shown in Table 4, the thickness of the coating layer 6 was 5 μm.
m. 21 was cracked. Further, in the case of No. 3 in which the thickness of the coating layer 6 was 700 μm. No. 27 was found to be outside the scope of the present invention because the temperature rise was slow and large. On the other hand, the thickness of the coating layer 6 is set to 10 to 500 μm.
m. 21 to 26 have no cracks,
The temperature rise time of the tip also showed a good value.

[0057]

As described above, the ceramic heater according to the present embodiment has a stable temperature because the outer surface of the ceramic body having the heating resistor is covered with the coating layer, so that the temperature can be prevented from rising more rapidly than before. It has excellent durability to maintain heating characteristics, and can be suitably applied as a heater for heating that requires a rapid temperature rise, and is extremely useful. Particularly, it is most suitable as a ceramic heater used for a soldering iron.

[Brief description of the drawings]

FIG. 1 is a view showing a ceramic heater of the present invention;
(A) is a perspective view, (b) is a partially cutaway view.

FIG. 2 is a structural development view showing a ceramic heater of the present invention.

FIG. 3 is a sectional view of a tip of a soldering iron incorporating a ceramic heater of the present invention.

FIG. 4 is a view showing a conventional ceramic heater;
(A) is a structural development view, (b) is a perspective view.

[Explanation of symbols]

 1: Ceramic heater 2: Core material 3: Ceramic sheet 4: Heating resistor 5: Lead extraction part 6: Coating layer 7: Through hole 8: Electrode pad 9: Lead 10: Soldering iron 11: Iron tip

Claims (5)

[Claims] 1. A ceramic heater in which a heating resistor and a lead lead portion connected to the heating resistor are built in a ceramic body, wherein the surface of the ceramic body in which the heating resistor is built is made of another ceramic. A ceramic heater covered with a coating layer. 2. The difference between the coefficient of thermal expansion of the coating layer and the coefficient of thermal expansion of the ceramic body is 3 × 10 ⁻⁶ deg ⁻¹ or less, and the thermal conductivity of the coating layer is 4 to 42 W / m · K. The ceramic heater according to claim 1, wherein 3. The apparatus according to claim 1, wherein said coating layer is provided so as to cover an area larger than a heating resistor portion.
The ceramic heater as described. 4. The ceramic heater according to claim 1, wherein said coating layer has a thickness of 10 to 500 μm. 5. A ceramic heater in which a heating resistor and a lead-out portion connected to the heating resistor are built in a ceramic body, wherein a portion of the ceramic body in which the heating resistor is built is made of another ceramic. A method for producing a ceramic heater, wherein the coating layer is provided by any one of thermal spraying, screen printing, CVD, PVD, and dipping.