KR960016071B1 - Plate Ceramic Heating Element - Google Patents

Abstract

The ceramic heat building has a resistor of titanium nitride base comprising 1-30 wt.% a silicon nitride, 1-15 wt.% an erbium oxide(Er2O3) or ytterbium oxide(Yb2O3), 1-10 wt.% a silicon oxide(SiO2) and a residual titanium nitride, an insulating substrate of silicon nitride base comprising 1-18 wt.% a sintering aid agent, 1-20 wt.% a silicified molybdenum or tungsten carbide as a controlling agent of the thermo expansion coefficient, and a residual silicon nitride, and the thermo expansion coefficient being changed gradually from the surrounding of said resistor to the surface. Thereby, the plate-like ceramic heat building shows a high strength at high temperature and excellent thermo shock resistance.

Description

Plate Ceramic Heating Element

The accompanying drawings schematically illustrate a lamination process of a plurality of silicon nitride tapes and resistors in the plate ceramic heating element manufacturing process of the present invention.

The present invention relates to a plate-shaped ceramic heating element in which a titanium nitride resistor is embedded in a silicon nitride substrate, and in particular, the thermal expansion coefficient of the substrate is gradually changed from the periphery of the resistor toward the outer surface, thereby reducing the difference in the coefficient of thermal expansion between the resistor and the substrate. A plate ceramic heating element having high strength and excellent thermal shock resistance at high temperatures.

Generally, a plate ceramic heating element is provided in a state in which a metal resistor such as molybdenum (Mo) or tungsten (W) is embedded on an insulating aluminum oxide (Al ₂ O ₃ ) substrate, as disclosed in Japanese Patent Application Laid-Open No. 60-19632. The form in which the surface is covered with aluminum oxide has been mainly used.

This type of ceramic heating element has the advantages of excellent chemical resistance and abrasion resistance, while the sintered aluminum oxide that forms the substrate has a bending strength of about 300 kg / cm2 at a temperature of 800 ° C. and a thermal shock resistance (ΔT, breaking limit). The temperature difference) is about 200 ° C., and the sintered aluminum oxide substrate has a disadvantage of high temperature strength and thermal shock resistance, such as being broken when rapidly cooled to 0 ° C. at a temperature of 200 ° C.

Therefore, in recent years, a heating element using silicon nitride (Si ₃ N ₄ ), which has a higher temperature strength than the aluminum oxide and has excellent thermal shock resistance, has been developed.

That is, the sintered silicon nitride has a strength of about 5,500kg / cm2 at a temperature of 800 ℃ and a thermal shock resistance of about 600 ℃, which is superior to aluminum oxide, one of the known literature that uses silicon nitride as a substrate Japanese Patent Publication No. 55-126989 is mentioned.

In Japanese Patent Application Laid-Open No. 55-126989, sintered silicon nitride is used as an insulating substrate, and tungsten or molybdenum is used as a resistor.

However, such a heating element is such that tungsten or molybdenum metal constituting the resistor reacts with the silicon nitride substrate at a high temperature during the use of the heating element so that tungsten silicide (WSi ₂ ) or molybdenum silicide (MoSi ₂ ) is formed at the interface between the metal resistor and the silicon nitride substrate. As well as reactants such as these, the reactants such as tungsten oxide (WO ₃ ) or molybdenum oxide (MoC ₃ ) are formed by reacting with oxides added as sintering aids of silicon nitride to rapidly change the resistance of the heating element. have.

On the other hand, U.S. Patent No. 4,804,823 uses a titanium nitride (TiN) or tungsten carbide (WC) resistor on a silicon nitride or aluminum nitride (AlN) insulating substrate to solve the above disadvantages of the heating element made of a silicon nitride substrate.

However, such a heating element has a thermal expansion coefficient of 5.8 × 10 ⁻⁶ / ° C. of titanium nitride used as a resistor, and a thermal expansion coefficient of silicon nitride, which is a substrate material, of 3.3 × 10, whereas the thermal expansion coefficient of tungsten carbide is 5.1 × 10 −6 / ° C. ^It is pointed out that the cracks in the substrate are caused by thermal fatigue when the heating element is used for a long time due to the difference in thermal expansion coefficient between the resistor and the insulating substrate because it is ^-6 / ° C.

Accordingly, in view of the problems and disadvantages of the conventional heating element, the present invention uses titanium nitride as a resistor and variously changes the coefficient of thermal expansion of the silicon nitride substrate so that the coefficient of thermal expansion between the substrate and the resistor around the resistor is close to each other. The thermal expansion coefficient of the substrate is gradually changed toward the outer surface of the substrate, thereby eliminating thermal fatigue caused by the difference of the thermal expansion coefficient between the resistor and the substrate and subsequent crack occurrence, thereby improving high temperature strength and thermal shock resistance. The purpose is to provide a plate-like ceramic heating element.

The present invention refers to molybdenum silicide or tungsten carbide (hereinafter, referred to as "coefficient of thermal expansion regulator") having a larger coefficient of thermal expansion than silicon nitride but a reaction with silicon nitride and a sintering aid in order to control the coefficient of thermal expansion of a silicon nitride substrate. ) Will be added.

In this case, as the sintering aid for silicon nitride, 1 to 15% by weight of yttrium oxide (Y ₂ O ₃ ) and 1 to 10% by weight of aluminum oxide (Al ₂ O ₃ ), or 1 to 15% by weight of silicon oxide and silicon oxide 1 ˜10% by weight, or 1-18% by weight of one group selected from 1-15% by weight of ether oxide and 1-10% by weight of silicon oxide is added.

In addition, the thermal expansion coefficient modifier is added to 20% by weight or less, after varying the content of the sintering aid and the coefficient of thermal expansion modifier within the range added by ball milling methyl alcohol (CH ₄ O) for 24 hours with a solvent dried to 100kg / a cm2 pressure uniaxially molded in the following 1300kg / cm2 by pressure hydrostatic pressure molding by a then charged into a graphite furnace, 1kg / cm ² in a nitrogen atmosphere from when the sinter for 3 hours at a temperature variously changed the thermal expansion of 1770 ℃ A silicon nitride sintered body having a coefficient is obtained.

Table 1 below shows the results of the physical properties of the silicon nitride sintered body obtained through the above process, the thermal expansion coefficient in Table 1 is the thermal expansion coefficient from room temperature to 800 ℃.

Table 1. Composition and Physical Properties of Silicon Nitride Sintered Body for Heating Element Substrate of the Present Invention

In Table 1, when the thermal expansion coefficient modifier, molybdenum silicide (MoSi ₂ ) or tungsten carbide (WC), is added at 20 wt% or less, the thermal expansion coefficient does not affect the sintered density, bending strength, and non-constant constant of silicon nitride. It can be seen that can effectively increase the.

In other words, the thermal expansion coefficient of the silicon nitride substrate can be controlled by adjusting the amount of molybdenum silicide or tungsten carbide added during the production of the silicon nitride substrate.

The more specific manufacturing process for each of the silicon nitride sintered specimens 1 to 9 shown in Table 1 is shown in the examples described later.

Next, the manufacturing process of the titanium nitride resistor used in the heating element of the present invention will be described.

Titanium nitride resistors are printed in the form of a paste on a thin plate of silicon nitride tape, which is mainly composed of TiN, in which small amounts of Si ₃ N ₄ , Y ₂ O ₃ and Al ₂ O ₃ are added as resistance regulators. It is obtained by addition-type ball milling of a solvent such as ethyl alcohol to the mixed powder.

The process of manufacturing a plate-shaped ceramic heating element using such a silicon nitride substrate and a titanium nitride resistor according to the present invention will be described in detail with reference to the accompanying examples and manufacturing process drawings.

First, as shown in the accompanying drawings, a silicon nitride insulating substrate is formed of a thin plate-like silicon nitride tape (1) (2) (3), and a plurality of sheets are formed on both sides of the heating circuit 4 formed by printing a silicon nitride paste. In this case, each silicon nitride tape has a different coefficient of thermal expansion.

On the other hand, the molding process of the silicon nitride tape is a silicon nitride powder by adding a sintering aid, a thermal expansion coefficient regulator and a dispersant together with a solvent and ball milling for about 8 hours to produce a primary slip, and further adding a binder and a plasticizer to the silicon nitride powder Secondary slips obtained by ball milling for about 24 hours are subjected to defoaming in a vacuum stirrer to maintain a viscosity suitable for the subsequent molding process, and then tape molded at a rate of 20 to 100 cm / min using a doctor blade device to obtain various compositions. You get a dry tape.

At this time, the dispersant is glyoxal (C ₂ H ₂ O ₂ ), 0.1 to 5% is preferably added, the solvent is methyl ethyl ketone (C ₄ H ₈ O), methyl butyl ketone (C ₆ H ₁₂ O) , Toluene (C ₇ H ₈ ), acetone (C ₃ H ₆ O), isopropyl alcohol (C ₃ H ₈ O) It is preferable to add 20 to 80% by weight relative to the dry solid weight as a mixture of one or two or more. .

In addition, the binder is polyvinylbutylal ((C ₈ H ₁₄ O ₂ ) n) and is preferably added in an amount of 1 to 20% by weight based on the dry solids, and as a plasticizer, polyethylene glycol (C ₂ H ₆ O ₂ ) n ), And it is preferable to add 1 to 15% by weight based on the dry solids weight.

In addition, the defoaming step is preferably performed in a vacuum of 0.01 to 20 torr using a stirrer of 100 to 2000 rpm.

Meanwhile, in addition to the silicon nitride tape molding process, a titanium nitride paste may be manufactured. The titanium nitride paste may be ethyl alcohol (C ₂ H ₆ O), propyl alcohol (C ₃ H ₈ O) or a mixture thereof in titanium nitride powder. It is obtained by adding a solvent consisting of a binder such as cellulose (C ₆ H ₁₀ O ₅ ) and milling for about 48 hours using a tungsten nitride ball mill and a ball.

At this time, the addition amount of the binder is 1 to 12% by weight is appropriate, 1 to 30% by weight of silicon nitride and sintered plasticizer may be added as a resistance regulator as necessary.

The titanium nitride paste obtained through such fixing has a screen mesh of 100 to 350, a thickness of 6 to 50 µm, and a heating circuit (4) on a tape (1) having a coefficient of thermal expansion in the range of 3.8 to 4.5 x 10 ^-6 / ° C. Print

The inner silicon nitride tape 1 in direct contact with the heat generating circuit 4 has a coefficient of thermal expansion of 3.8 to 4.5 × 10 ⁻⁶ / ° C., and the silicon nitride tape laminated to the outside thereof is 3.4 to 3.7 × 10 ⁶ / ° C., The outermost silicon nitride tape is preferably selected to exhibit a thermal expansion coefficient in the range of 3.0 to 3.3 × 10 ⁻⁶ / ° C.

On the other hand, the heat generating portion 4a of the heat generating circuit 4 printed on the silicon nitride tape 1 surface has a smaller cross-sectional area than the lead wire attaching portion 4b to minimize heat generation at the lead wire attaching portion 4b.

At this time, the length and the cross-sectional area of the heating circuit can be changed according to the desired resistance value, the heating element and the resistance is appropriate 10 ~ 500Ω and the electric capacity of the heating element is preferably 10 ~ 3000W.

After the printing of the heating circuit 4 and the sequential lamination of the silicon nitride tapes 1, 2, and 3 are completed, the laminate is thermally bonded using a press. The temperature is 30 to 90 ° C. and the pressure is 10. 350 kg / cm ² is preferred.

The laminated molded product obtained through such a process is cut into a shape with a cutter and nitrided by the above-described process at the site where the lead wire is to be attached to connect the lead wire attachment portion 4b exposed to the outside of the laminate to the outside. The titanium paste is applied and then dried at 100 ° C. for 2 hours.

When drying is completed, a degreasing process for removing organic matters in the laminated compact is performed. This is accomplished by charging the laminated compact into a tubular furnace and maintaining the process for 2 hours at 350 ° C. in an oxygen atmosphere.

Sintering is followed by sintering, which is accomplished by maintaining the laminated body in a graphite furnace at a temperature of 1700 to 1900 ° C. for 1 to 5 hours using a nitrogen atmosphere of 1 to 100 kg / cm ² .

Finally, Ni-lead is bonded using Ti--Cu--Ag alloy paste to the lead wire attachment part of the sintered heating element, and then, at a temperature of 500 to 900 ° C. under a vacuum of 10 ⁻⁵ millitorr or less. By holding for 100 minutes, the plate ceramic heating element of this invention is obtained.

The plate ceramic heating element of the present invention obtained through the manufacturing process as described above gradually reduces the thermal expansion coefficient difference between the titanium nitride resistor and the silicon nitride insulating substrate, and the thermal fatigue phenomenon caused by the difference in thermal expansion coefficient of the two materials. As a result, the occurrence of cracks is suppressed, thereby providing an excellent thermal shock resistance.

Features and specific manufacturing process of the plate-shaped ceramic heating element of the present invention will be more clearly understood through the following examples.

Example 1

60 g of yttrium oxide, 20 g of aluminum oxide as a sintering aid, 200 g of molybdenum silicide as a thermal expansion coefficient modifier, 10 g of glyoxal as a dispersant was added to 720 g of silicon nitride powder, 110 g of methyl ethyl ketone, 30 g of propyl alcohol, and A primary slip was prepared by ball milling for 8 hours using an aluminum oxide ball mill and silicon nitride balls using 100 g of cyclohexanone as a solvent. 100 g of polyvinyl butyl al as a binder and 60 g of polyethylene glycol as a plasticizer were put into the slip, milled using the ball mill and the ball for 24 hours, and degassed at a speed of 200 rpm and a vacuum of 1 tor using a vacuum degassing machine for 1 hour. Then, the silicon nitride tape 1 was manufactured by drying through a tape molding process at a speed of 30 cm / min to obtain the specimen 9 of Table 1 having a thermal expansion coefficient of 3.90 × 10 ⁻⁶ / ° C.

To 820 g of silicon nitride powder, 60 g of yttrium oxide, 20 g of aluminum oxide as a sintering aid, and 100 g of molybdenum silicide as a thermal expansion coefficient regulator, 10 g of glyoxal as a dispersant, 110 g of methyl ethyl ketone, 30 g of propyl alcohol and 100 g of Using cyclohexanone as a solvent, silicon nitride (2) was produced in the same manner as in the above procedure to obtain Specimen 7 shown in Table 1 above.

60g yttrium oxide, 20g aluminum oxide, and 10g glyoxal as dispersant are added to 920g of silicon nitride powder and 110g methyl ethyl ketone, 30g propyl alcohol and 100g cyclohexanone are used in the same process. The silicon nitride tape 3 was produced, and the specimen 1 of the said Table 1 which has a coefficient of thermal expansion of 3.30x10 <^-6> / degreeC was obtained.

On the other hand, tungsten carbide balls were added to the titanium nitride powder by adding a resistance regulator in the amount shown in Table 2 below, 5% by weight of cellulose as the binder, and 25% by weight of ethyl alcohol as the solvent as the binder. A paste suitable for printing a heating circuit was prepared by milling for 48 hours using a ball mill. Print a heating circuit on the silicon nitride tape (1) using resistor paste specimens # 1 to # 7, and then use a silicon nitride tape (1), (2), or (3) as shown in the accompanying drawings for a temperature of 50 ° C. After laminating at a pressure of 80 kg / cm ² , the paste was applied to the lead wire attachment portion 4b, and then degreased for 2 hours at a temperature of 350 ° C. using an oxygen atmosphere. After sintering at 1770 ° C for 3 hours using a nitrogen atmosphere at 1kg / cm ² , 46mm × through a lead wire attachment process at a temperature of 830 ° C and a vacuum of 10 ^-5 millitorr A flat ceramic heating element having a size of 3.5 mm × 1.0 mm was manufactured.

In addition, the resistor paste specimens 3 and 5 of Table 2 were used to print in the drawing using silicon nitride tape 3 instead of silicon nitride tape 1 and the above described using silicon nitride tape 3 instead of silicon nitride tape 2. A comparative specimen was prepared by the method. The specimen thus prepared was a heating element having a large difference in coefficient of thermal expansion between the titanium nitride resistor and the silicon nitride substrate.

The initial resistance of the plate-shaped ceramic heating element manufactured according to the above method was measured, and the resistance change of the heating element was measured by removing electricity and cooling after continuously turning on for 3000 hours by applying an AC voltage of 110V, and visually observing whether the surface was cracked. The results are shown in Table 2. From the results shown in Table 2, it can be seen that the sample added with 5 to 30% by weight of silicon nitride, yttrium oxide, and aluminum oxide to the titanium nitride resistor had a lower resistance change and an excellent heating element than the sample without addition. In addition, cracks occurred on the surface of the heating part after 3000 hours for comparison specimens, and the change of resistance was very large as an average of 21.3%, whereas the samples produced by the present invention did not have such cracks and the average resistance of the samples 3 to 52 times. It can be seen that the change is very small as 3.5%. From this it can be seen that the plate-shaped ceramic heating element produced by the present invention is superior to the conventional heating element. In addition, it can be seen that it is preferable to add 10-30% by weight of the resistance regulator to the titanium nitride paste.

`` Table 2. Resistor composition and characteristics of ceramic heating element. ''

○: no cracking, x: cracking

Example 2

To 720 g of silicon nitride powder, 60 g of yttrium oxide, 20 g of aluminum oxide as a sintering agent, 200 g of tungsten carbide as a thermal expansion coefficient regulator, 10 g of glyoxal as a dispersant, 110 g of methyl ethyl ketone, 30 g of propyl alcohol and 100 g of cyclo A primary slip was prepared by ball milling for 8 hours using an aluminum oxide ball mill and silicon nitride balls using hexanone as a solvent. 100 g of polyvinyl butyl al as a binder and 60 g of polyethylene glycol as a plasticizer were put into the slip, milled using the ball mill and the ball for 24 hours, and degassed at a speed of 200 rpm and a vacuum of 1 tor using a vacuum degassing machine for 1 hour. Then, the silicon nitride tape 1 was manufactured by drying through a tape molding process at a speed of 20 cm / min to obtain the specimen 5 of Table 1 having a thermal expansion coefficient of 3.81 × 10 ⁻⁶ / ° C.

To 820 g of silicon nitride powder, 60 g of yttrium oxide and 20 g of aluminum oxide as a sintering aid and 100 g of tungsten carbide as a coefficient of thermal expansion and 10 g of glyoxal as a dispersant were added, 110 g of methyl ethyl ketone, 30 g of propyl alcohol and 100 g of cyclohexa Using the paddy as a solvent, a silicon nitride tape 2 was prepared in the same manner as in the above step to obtain the specimen 3 of Table 1 having a thermal expansion coefficient of 3.58 × 10 ⁻⁶ / ° C.

The silicon nitride tape 3 was prepared in the same manner as the tape prepared in Example 1 to obtain Specimen 5 of Table 1 having a coefficient of thermal expansion of 3.30 × 10 ⁻⁶ / ° C.

Tungsten carbide balls and ball mills were added to titanium nitride powder by adding a resistance regulator, a binder of 5% by weight based on the amount of cellulose as a solid, and 25% by weight of ethyl alcohol as a solvent as a binder. A paste suitable for printing the heating circuit was prepared by milling for 48 hours. Print a heating circuit on the silicon nitride substrate (1) using resistor paste specimens 1 to 5, and then use a silicon nitride tape (1), (2), or (3) to obtain a temperature of 60 ° C. After loading at 80 kg / cm ² , it was degassed at 350 ° C. for 2 hours using an oxygen atmosphere. After sintering at 1770 ℃ for 3 hours using nitrogen atmosphere at 1kg / cm2, 46mm × 3.5mm × 1.0 after lead wire attachment at 830 ℃ and 10 ^-5 millitorr vacuum A mm size flat ceramic heating element was manufactured.

The initial resistance of the plate-shaped ceramic heating element manufactured according to the above method was measured, and the resistance change of the heating element was measured by removing electricity and cooling after continuously turning on for 3000 hours by applying an AC voltage of 110V. The results are shown in Table 3. From the results shown in Table 3, it can be seen that the specimens added with 5 to 20% by weight of silicon nitride, yttrium oxide, and aluminum oxide to the titanium nitride resistor had less resistance change and were excellent heating elements. In addition, the specimen prepared by the present invention did not cause cracking, and in the case of specimens 3 to 5, the average resistance change was 4.1%, which is very small. From this it can be seen that the plate-shaped ceramic heating element produced by the present invention is superior to the conventional heating element.

<Table 3. Resistor Composition and Characteristics of Ceramic Heating Element >>

○: no cracking

Example 3

A plate ceramic heating element was manufactured in the same manner as in Example 1, except that the composition of the sintering aid and the resistor paste of the silicon nitride substrate was changed as shown in Table 4 below. The heating element was subjected to the same method as in Example 1, and the results are shown in Table 4. From this, the specimen with the addition of arsenic oxide (Er ₂ O ₃ ) and silicon oxide (SiO ₂ ) as the sintering aid had the smallest change in resistance after 1.1 hours of use as 1.1, and in the production of the heating element of the present invention, sintering of silicon nitride As a preparation, it can be seen that aluminium oxide and silicon oxide are optimal.

Table 4. Composition and Characteristics of Ceramic Heating Elements.

Example 4

A plate ceramic heating element was manufactured in the same manner as in Example 1 using the paste specimen 5 of Example 3, except that the sintering aid of the silicon nitride substrate was 6% by weight of aluminum oxide and 2% by weight of silicon oxide, and the size of the heating element was 100 mm ×. The plate-like heating element was manufactured by setting it as 75 mm x 1.2 mm. The initial resistance of this heating element was 256 kW, the resistance after 3000 hours was 260 kW, the resistance change rate was 1.6%, and no crack was found in appearance. From this, it can be seen that the present invention can produce an excellent heating element having excellent thermal shock resistance regardless of the size of the heating element and removing thermal fatigue phenomenon and crack generation according to the thermal expansion coefficient difference between the resistor and the insulating substrate.

Claims (2)

1 to 30% by weight of silicon nitride, 1 to 15% by weight of aluminum oxide (Er ₂ O ₃ ) or ytterbium oxide (Yb ₂ O ₃ ), 1 to 10% by weight of silicon oxide (SiO ₂ ), and the balance of titanium nitride The coefficient of thermal expansion gradually changes from the periphery of the resistor to the surface of the titanium nitride-based resistor, 1 to 18% by weight of the sintering aid, 1 to 20% by weight of molybdenum silicide or tungsten carbide as the thermal expansion coefficient regulator, and the balance of silicon nitride. A plate ceramic heating element, characterized in that made of a silicon nitride insulating substrate. According to claim 1, wherein the sintering aid is 1 to 15% by weight of yttrium oxide (Y ₂ O ₃ ), 1 to 10% by weight of aluminum oxide (Al ₂ O ₃ ), 1 to 15% by weight of oxidized oxide and silicon oxide 1 A plate ceramic heating element, characterized in that one soldier selected from -10% by weight, or 1-15% by weight of ether oxide and 1-10% by weight of silicon oxide.