JP2975882B2 - Silicon nitride heatsink for pressure welding and pressure welding structural parts using it - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon nitride heat radiating plate for pressure welding and a pressure welding structural component using the same, and more particularly to a pressure welding device having high strength and heat dissipation and excellent dielectric breakdown resistance. The present invention relates to a silicon nitride radiator plate and a press-contact structure component using the same.

[0002]

2. Description of the Related Art A heat-dissipating plate for pressure welding, which is joined to a heat-generating component by pressure welding and dissipates heat from the heat-generating component to the outside of the system, is widely used in various electric equipment and electronic equipment. In addition, a pressure-contact structure component such as a thyristor is widely used as a semiconductor element having a current control function such as switching of a large current or converting an alternating current to a direct current.

FIG. 1 is a sectional view showing a structural example of a thyristor as a silicon controlled rectifier (SCR). The thyristor includes a silicon joint 3 interposed between a copper stud 1 serving as an anode and a cathode conductor 2, and a silicon joint 3
, A ceramic seal 5 and a case 6 for sealing the silicon bonded body 3 and blocking it from the outside air, and a pressure contact for dissipating heat generated inside through the copper stud 1 to the outside. A large current is controlled by switching between the positive and negative electrodes from an off (cut off) state to an on (starting) state by a gate current flowing through the gate conductor 4.

[0004] In recent years, the amount of heat generated from components tends to increase rapidly in response to higher integration and higher output of heat generating components.
There is a need for a heat sink having better heat dissipation. For example,
In order to cope with the increase in power demand, a thyristor having a larger capacity is demanded, and a heat radiating plate having more excellent heat radiation characteristics and insulation characteristics without inevitably causing dielectric breakdown due to heat generation is desired. .

Conventionally, alumina (Al ₂ O ₃ ) has been generally used as a material for forming the radiator plate 7 for such a thyristor. However, since the thermal conductivity is as small as about 20 W / m · K, It is difficult to form a radiator plate that has a low heat radiation property and is compatible with high output. Therefore, an aluminum nitride (AlN) sintered body having a thermal conductivity as large as about two to three times that of alumina and having better thermal conductivity is also being used as a constituent material of the heat sink.

On the other hand, a ceramic sintered body containing silicon nitride as a main component generally has excellent heat resistance even in a high temperature environment of 1000 ° C. or higher, and also has excellent thermal shock resistance. As a high-temperature structural material replacing the heat-resistant superalloy, application to various high-strength heat-resistant parts such as parts for gas turbines, parts for engines, and mechanical parts for steelmaking has been attempted.

Conventionally, as a composition of a silicon nitride ceramic sintered body, yttrium oxide (Y
It is known that an oxide of a rare earth element or an alkaline earth element such as ₂ O ₃ ), cerium oxide (CeO) and calcium oxide (CaO) is added as a sintering aid. Densification and strength are enhanced by improving sinterability.

[0008] A conventional silicon nitride sintered body is formed by adding the above-mentioned sintering aid to silicon nitride raw material powder and molding the obtained molded body at a temperature of about 1600 to 2000 ° C in a firing furnace. It is manufactured by a manufacturing method in which the sintered body obtained is calcined after sintering for an hour, and the obtained sintered body is ground and polished.

[0009]

However, although the silicon nitride sintered body manufactured by the above-mentioned conventional method has excellent mechanical strength such as toughness, it does not have the same thermal conductivity as other aluminum nitrides. AlN) sintered body, beryllium oxide (BeO) sintered body, silicon carbide (SiC) sintered body, etc., which are extremely low compared to sintered bodies, etc. However, there was a disadvantage that the range of application was narrow.

On the other hand, since the above-mentioned aluminum nitride sintered body has features of high thermal conductivity and low coefficient of thermal expansion as compared with other ceramic sintered bodies, high speed, high output, multi-function,
Although it is used as a circuit board component or a package material for mounting a semiconductor chip, which is increasing in size, a material which is sufficiently satisfactory in terms of mechanical strength has not been obtained.

Further, when a heat radiating plate mainly composed of the above-mentioned ceramic sintered body is joined to a heat-generating component by press contact or is fixed to a mounting boat by a screw or the like in an assembly process, the pressing force of the screw and the pressure contact are increased. There has been a problem that the heat sink is damaged by a slight deformation due to a force or an impact at the time of handling, and the production yield of the heat dissipation component is greatly reduced.

When a high voltage is applied as in a radiator used for a thyristor, a radiator having a certain thickness is required in order to secure a predetermined dielectric strength. There is also a problem that the heat resistance increases and the raw material cost of the heat sink increases.

SUMMARY OF THE INVENTION The present invention has been made to address the above-mentioned problems, and has a high-strength property, a high heat conductivity, a high heat-dissipation property and a greatly improved insulation breakdown property. An object of the present invention is to provide a press-contact structure component such as a thyristor using the same.

[0014]

In order to achieve the above object, the present inventor has set forth the types of conventionally used silicon nitride powder, the types and amounts of sintering aids and additives, and the sintering conditions. In addition, a silicon nitride sintered body having a high thermal conductivity (90 W / m · K or more) three times or more that of a conventional silicon nitride sintered body was developed. Furthermore, when this silicon nitride sintered body is used as a heat sink and a heat generating component such as a rectifier is integrally joined to the heat sink by pressure welding to produce a press-contact structure component such as a thyristor, mechanical strength and toughness are increased. It was confirmed by an experiment that a pressure-welded structure component such as a sice litter, which satisfies all values, dielectric strength characteristics, and heat dissipation properties, was obtained.

A part of such a high thermal conductive silicon nitride sintered body having a thermal conductivity of 90 W / m · K or more has already been applied for a patent by the present inventors.
The application is published by Japanese Patent Publication No. 1359771 and Japanese Patent Application Laid-Open No. 7-48174. The silicon nitride sintered bodies described in these patent applications contain 2.0 to 7.5% by weight of a rare earth element in terms of oxide. However, as a result of further improvement research, the present inventor has found that when the content of the rare earth element exceeds 7.5% by weight in terms of oxide, the sintered body has higher thermal conductivity, and The inventors have found that they have good binding properties and completed the present invention. In particular, when the rare earth element is a lanthanoid element, the effect is remarkable. Incidentally, even when the ratio of the crystalline compound phase in the grain boundary phase to the entire grain boundary phase is 60 to 70%, the sintered body can achieve a high thermal conductivity of 110 to 120 W / m · K or more.

Specifically, a raw material mixture obtained by adding a predetermined amount of a rare earth element oxide or the like to fine and high-purity silicon nitride powder is molded and degreased, and the obtained molded body is heated at a predetermined temperature for a predetermined time. After carrying out the densification sintering while holding, a sintered body with high characteristics can be obtained by slow cooling at a predetermined cooling rate or less and manufacturing. When this thermal conductivity is 90 W / mK or more,
In addition, when a silicon nitride sintered body having high strength is applied to a heat sink, it is possible to realize a silicon nitride heat sink for pressure welding and a pressure welding structural component having excellent heat dissipation characteristics, durability and dielectric breakdown characteristics at the same time. found.

A glass phase (amorphous phase) in a grain boundary phase is obtained by sintering under the above conditions using a high-purity silicon nitride raw material powder having a reduced content of oxygen and impurity cation elements. Can be effectively suppressed. By setting the proportion of the crystalline compound phase in the grain boundary phase to 20% or more (based on the whole grain boundary phase), more preferably to 50% or more, 90 W can be obtained even when only the rare earth element oxide is added to the raw material powder. / M · K or more, more preferably 100
It has been found that a silicon nitride sintered body having a high thermal conductivity of W / m · K or more can be obtained.

Conventionally, when the sintered body is cooled by turning off the heating power supply of the firing furnace after the sintering operation is completed, the cooling rate was as fast as 400 to 800 ° C. per hour. According to the experiment of the inventor, in particular, the cooling rate was set to 10
By controlling the temperature slowly to 0 ° C. or less, the grain boundary phase of the silicon nitride sintered body structure changes from an amorphous state to a phase containing a crystalline phase, and high strength characteristics and high heat transfer characteristics are simultaneously achieved. Turned out to be.

As described above, a silicon nitride sintered body satisfying both high strength characteristics and high heat transfer characteristics is used as a heat sink material, and a heat-generating component such as a rectifying element is joined to the heat sink by pressure welding to form a press-contact structure component such as a thyristor. By forming a thyristor, it is possible to improve the toughness and thermal conductivity of a pressure-welded structural component such as a thyristor, and in particular, it is possible to effectively prevent the occurrence of cracks due to tightening cracks and the addition of a heat cycle in a heat sink assembly process. There was found.

The present invention has been completed based on the above findings. That is, the silicon nitride radiator for pressure welding according to the present invention converts the lanthanoid-based elements into oxides.
More than 5% by weight and not more than 17.5% by weight, comprising silicon nitride crystals and a grain boundary phase, wherein the ratio of the crystalline compound phase in the grain boundary phase to the whole grain boundary phase is 20% or more, and 90 W / m · A heat-dissipating silicon nitride heat-dissipating plate composed of a high-thermal-conductivity silicon nitride sintered body having a thermal conductivity of K or more, and the surface roughness of the press-contact surface of the high-thermal-conductivity silicon nitride sintered body pressed against a heat-generating component, etc. Is 1 based on the maximum height (R _max ).
It is not more than 0 μm.

The high thermal conductivity silicon nitride sintered body has a three-point bending strength of 650 MPa or more. Further, the surface roughness of the press contact surface of the high thermal conductive silicon nitride sintered body pressed against a heat-generating component or the like is preferably set to 10 μm or less based on the maximum height (R _max ). By setting the surface roughness of the press contact surface of the high thermal conductive silicon nitride sintered body to 10 μm or less on the basis of Rmax, heat from the heat generating component can be effectively dissipated.

Further, the high thermal conductive silicon nitride sintered body is composed of silicon nitride crystals and a grain boundary phase, and the ratio of the crystalline compound phase in the grain boundary phase to the entire grain boundary phase is 50.
% Is more preferable.

It is particularly preferable to use a lanthanoid element as the rare earth element in order to improve the thermal conductivity of the sintered body.

Further, the silicon nitride sintered body may be constituted so as to contain 1.0% by weight or less of aluminum nitride or alumina. Further, 1.0% by weight or less of alumina and 1.0% by weight or less of aluminum nitride may be used in combination.

The high thermal conductive silicon nitride sintered body used in the present invention is Ti, Zr, Hf, V, Nb, Ta, C
It is preferable that at least one selected from the group consisting of r, Mo, and W is contained in an amount of 0.1 to 0.3% by weight in terms of oxide. These Ti, Zr, Hf, V, Nb, Ta,
At least one selected from the group consisting of Cr, Mo, W
The seed can be contained as an oxide, carbide, nitride, silicide, or boride by adding to the silicon nitride powder.

Further, the press-bonded structural component according to the present invention contains more than 7.5% by weight to 17.5% by weight or less of oxides of lanthanoid series elements, and is composed of silicon nitride crystals and a grain boundary phase. At the same time, the ratio of the crystalline compound phase in the grain boundary phase to the entire grain boundary phase is 20% or more;
/ N · K heat-dissipating plate composed of a high-thermal-conductivity silicon nitride sintered body having a thermal conductivity of not less than / m · K and having a surface roughness of 10 μm or less on the basis of a maximum height (R _max ). A heat-generating component is press-contacted with the first component.

The high thermal conductive silicon nitride sintered body used as a constituent material of the silicon nitride heat sink for pressure welding and the component of the pressure welding structure according to the present invention is produced, for example, by the following method.
That is, oxygen is 1.7% by weight or less, and Li, Na, K, Fe, Ca, Mg, Sr,
An oxide of a lanthanoid element is added to silicon nitride powder having a total of 0.3% by weight or less of Ba, Mn, and B and 90% by weight or more of α-phase silicon nitride and an average particle diameter of 1.0 μm or less. A raw material mixture is formed by adding more than 7.5% by weight and not more than 17.5% by weight and, if necessary, 1.0% by weight or less of at least one of alumina and aluminum nitride to prepare a formed body. Then, after degreasing the obtained molded body, it is subjected to atmospheric pressure sintering at a temperature of 1800 to 2100 ° C., and the sintering is performed from the sintering temperature to a temperature at which a liquid phase formed during sintering by the rare earth element solidifies. The cooling rate of the aggregate is 1 hour
Slowly cool to below 00 ° C.

In the above production method, it is preferable that at least one of alumina and aluminum nitride is further added to the silicon nitride powder in an amount of 1.0% by weight or less.

Further, Ti, Z are added to the silicon nitride powder.
oxides of r, Hf, V, Nb, Ta, Cr, Mo, W;
At least one selected from the group consisting of carbides, nitrides, silicides, and borides may be added in an amount of 0.1 to 3.0% by weight.

According to the above manufacturing method, a grain boundary phase containing a rare earth element or the like is formed in the silicon nitride crystal structure, the porosity is 2.5% or less, the thermal conductivity is 90 W / m · K or more, and A silicon nitride sintered body having a point bending strength of 650 MPa or more at room temperature and excellent in both mechanical properties and heat conduction properties is obtained.

By using a fine raw material powder having an average particle size of 1.0 μm or less, it is possible to form a dense sintered body having a porosity of 2.5% or less even with a small amount of a sintering aid. Is also possible, and the possibility that the sintering aid impairs the heat transfer properties is reduced.

Further, a high-density sintered body can be produced by using a silicon nitride raw material powder containing 90% by weight or more of α-phase type silicon nitride which is superior in sinterability as compared with β-type type. can do.

The rare earth elements to be added to the silicon nitride raw material powder as a sintering aid include Ho, Er, Yb, Y,
Oxides such as La, Sc, Pr, Ce, Nd, Dy, Sm, and Gd, or substances that become these oxides by sintering operation alone or in combination of two or more oxides are included. Good, but especially holmium oxide (Ho ₂ O
₃ ) Erbium oxide (Er ₂ O ₃ ) is preferred.

In particular, by using Ho, Er, and Yb, which are lanthanoid series elements, as a rare earth element, sinterability or high thermal conductivity is improved, and sufficiently dense sintering can be performed even in a low temperature range of about 1850 ° C. Solidification is obtained. Therefore, the effect of reducing the equipment cost and running cost of the firing apparatus can be obtained. These sintering aids are
It reacts with the silicon nitride raw material powder to form a liquid phase and functions as a sintering accelerator.

The amount of the sintering aid to be added is in the range of more than 7.5% by weight and 17.5% by weight or less based on the raw material powder in terms of oxide. When this addition amount is 7.5% by weight or less,
If the sintered body is insufficiently densified, especially when the rare earth element is an element having a large atomic weight such as a lanthanoid-based element, a sintered body with low strength and low thermal conductivity is formed. on the other hand,
If the added amount exceeds 17.5% by weight, an excessive amount of grain boundary phase is generated, and the thermal conductivity and strength start to decrease.

In addition, Ti, Zr, Hf, V, Nb, T
The oxides, carbides, nitrides, silicides, and borides of a, Cr, Mo, and W promote the function of the sintering accelerator of the rare earth element, and also have the function of strengthening the dispersion of Si _{3 in the} crystal structure. It is intended to improve the mechanical strength of the N ₄ sintered body, and particularly, compounds of Hf and Ti are preferable. When the added amount of these compounds is less than 0.1% by weight, the effect of the addition is insufficient, while when the added amount exceeds 3.0% by weight, the thermal conductivity and mechanical strength and electric breakdown are caused. Since the strength is reduced, the amount of addition is in the range of 0.1 to 3.0% by weight. In particular, it is desirable that the content be 0.2 to 2% by weight.

The above compounds such as Ti, Zr, and Hf also function as a light-shielding agent that imparts opacity by coloring the silicon nitride sintered body black.

Further, in the above-mentioned manufacturing method, alumina (Al ₂ O ₃ ) as another optional additive component plays a role of promoting the function of the rare earth element sintering accelerator, This has a remarkable effect when sintering. When the addition amount of Al ₂ O ₃ is less than 0.1% by weight, sintering at a higher temperature is required. On the other hand, when the addition amount exceeds 1.0% by weight, an excessive amount of grain boundaries is required. Since a phase is formed or a solid solution starts to be formed in silicon nitride to cause a decrease in heat conduction, the amount of addition is set to 1% by weight or less, preferably 0.1 to 0.75% by weight.
In particular, in order to ensure good performance in both strength and thermal conductivity, it is desirable that the amount of addition be in the range of 0.1 to 0.5% by weight.

When used in combination with AlN, which will be described later, the total addition amount is desirably 1.0% by weight or less.

Aluminum nitride (AlN) as another additional component serves to suppress the evaporation of silicon nitride during the sintering process and to further promote the function of the rare earth element as a sintering accelerator. It is.

When the addition amount of AlN is less than 0.1% by weight (less than 0.05% by weight when used in combination with alumina), sintering at a higher temperature is required, while
If the amount exceeds 0% by weight, an excessive amount of the grain boundary phase is generated, or the solid solution starts to be dissolved in silicon nitride to cause a decrease in thermal conductivity. % By weight. In particular, in order to ensure good performance in sinterability, strength, and thermal conductivity, it is desirable that the addition amount be in the range of 0.1 to 0.5% by weight. When used in combination with Al ₂ O ₃ , the addition amount of AlN is 0.05 to 0.5% by weight.
Is preferable.

Since the porosity of the sintered body greatly affects the thermal conductivity and strength, the sintered body is manufactured to be 2.5% or less. If the porosity exceeds 2.5%, it hinders heat conduction,
As the thermal conductivity of the sintered body decreases, the strength of the sintered body decreases.

Although the silicon nitride sintered body is systematically composed of silicon nitride crystals and a grain boundary phase, the proportion of the crystalline compound phase in the grain boundary phase greatly affects the thermal conductivity of the sintered body. However, in the high thermal conductivity silicon nitride sintered body used in the present invention, it is necessary that the content be 20% or more of the grain boundary phase,
More preferably, it is desirable that the crystal phase accounts for 50% or more. When the crystal phase is less than 20%, the thermal conductivity is 90 W / m.
This is because it is not possible to obtain a sintered body having excellent heat dissipation characteristics such as K or more and high temperature strength.

Further, as described above, the porosity of the silicon nitride sintered body is set to 2.5% or less, and the crystal phase accounts for 20% or more of the grain boundary phase formed in the silicon nitride crystal structure. The silicon nitride compact was heated to a temperature of 1800 to 210
It is important to perform pressure sintering at 0 ° C. for about 2 to 10 hours and gradually cool the sintered body immediately after completion of the sintering operation at a cooling rate of 100 ° C. or less per hour.

When the sintering temperature is lower than 1800 ° C., the densification of the sintered body is insufficient, the porosity becomes 2.5 vol% or more, and both the mechanical strength and the thermal conductivity decrease. On the other hand, when the sintering temperature exceeds 2100 ° C., the silicon nitride component itself tends to be vaporized and decomposed. Especially not pressure sintering,
When normal-pressure sintering is performed, decomposition and evaporation of silicon nitride starts at about 1800 ° C.

The cooling rate of the sintered body immediately after the completion of the sintering operation is an important control factor for crystallizing the grain boundary phase, and when a rapid cooling is performed such that the cooling rate exceeds 100 ° C./hour. In the method, the grain boundary phase of the structure of the sintered body becomes non-crystalline (glass phase), and the ratio of the liquid phase generated in the sintered body as a crystalline phase to the grain boundary phase is less than 20%, and the strength and thermal conductivity are reduced. Decrease together.

The temperature range in which the cooling rate should be strictly adjusted is a temperature range from a predetermined sintering temperature (1800 to 2100 ° C.) to a temperature at which a liquid phase produced by the reaction of the sintering aid solidifies. Is enough. Incidentally, the liquidus freezing point when using the sintering aid as described above is approximately 1600 to 15
It is about 00 ° C. The cooling rate of the sintered body at least from the sintering temperature to the above-mentioned liquid phase solidification temperature is set to 10
0 ° C. or lower, preferably 50 ° C. or lower, more preferably 2 ° C.
By controlling the temperature to 5 ° C. or less, 20% or more of the grain boundary phase can be obtained.
Particularly preferably, 50% or more becomes a crystalline phase, and a silicon nitride sintered body excellent in both thermal conductivity and mechanical strength can be obtained.

The silicon nitride sintered body used in the present invention is manufactured, for example, through the following process. That is, a predetermined amount of a sintering aid, a necessary additive such as an organic binder, and optionally Al ₂ O are added to the fine silicon nitride powder having the predetermined fine particle size and a small impurity content. _A raw material mixture is prepared by adding ₃ or an AlN or Ti compound, and then the obtained raw material mixture is molded to obtain a molded body having a predetermined shape. As a forming method of the raw material mixture, a general-purpose mold pressing method, a sheet forming method such as a doctor blade method, or the like can be applied.

Subsequent to the above molding operation, the molded body is heated in a non-oxidizing atmosphere at a temperature of 600 to 800 ° C. or in air at a temperature of 400 to 500 ° C. for 1 to 2 hours to prepare an organic binder previously added. The components are sufficiently removed and degreased.
Next, the degreased compact is placed in an inert gas atmosphere such as nitrogen gas, hydrogen gas or argon gas in an atmosphere of 1800 to 210 g.
Atmospheric pressure sintering is performed at a temperature of 0 ° C. for a predetermined time.

The silicon nitride sintered body manufactured by the above method has a porosity of 2.5% or less and 90 W / m · K (25
° C) or more, and 100 W / m · K or more, and has excellent three-point bending strength at room temperature of 650 MPa or more, further 800 MPa or more.

The silicon nitride sintered body of which the thermal conductivity as a whole is 90 W / m · K or more by adding high thermal conductivity SiC or the like to low thermal conductivity silicon nitride is the present invention. Not included in range. However, the thermal conductivity is 90W
/ M · K or higher silicon nitride sintered body with high thermal conductivity S
Needless to say, in the case of a silicon nitride-based sintered body in which iC or the like is compounded, as long as the thermal conductivity of the silicon nitride sintered body itself is 90 W / m · K or more, it is included in the scope of the present invention. .

Since the surface roughness of the press contact surface of the high thermal conductive silicon nitride sintered body pressed against a heat-generating component or the like has a great effect on heat dissipation, the maximum height (Rmax) is used in the present invention.
It is set to 10 μm or less on a standard basis. The surface roughness is 10
If it exceeds μm, the heat transfer resistance at the press-contact surface rises sharply, and the heat radiation characteristic of the heat sink decreases. Therefore, the surface roughness is set to 10 μm or less, but more preferably 5 μm or less.

A thyristor as a press-contact structure component according to the present invention is manufactured by press-contacting a rectifying element as a heat-generating component to the high thermal conductive silicon nitride sintered body manufactured as described above.

According to the silicon nitride heat radiating plate for pressure welding according to the present invention, in addition to the high strength and high toughness characteristics inherently possessed by the silicon nitride sintered body, the high thermal conductivity silicon nitride sintered body having significantly improved thermal conductivity is provided. Since it is formed by a united body, no tightening crack of the heat radiating plate occurs in the assembly process, and it becomes possible to mass-produce a pressure contact structure component such as a thyristor using the heat radiating plate at a high production yield.

Further, since the silicon nitride sintered body has a high toughness value, the heat radiating plate is less likely to be cracked by a heat cycle from a heat-generating component, the heat-resistant cycle characteristics are remarkably improved, and the durability and reliability are excellent. It is possible to provide a pressure contact structure component such as a thyristor.

Further, since a silicon nitride sintered body having a high thermal conductivity, which has not been achieved conventionally, is used as a heat radiating plate, even when a heat-generating component for high output and high integration is pressed, it can be used. Demonstrates excellent heat dissipation characteristics with little deterioration of thermal resistance characteristics.

Particularly, since the mechanical strength of the silicon nitride sintered body itself is excellent, when the required mechanical strength characteristics are fixed, the heat radiating plate is compared with the heat radiating plate made of other ceramic sintered bodies. Can be further reduced.
Since the thickness of the heat radiating plate can be reduced, the thermal resistance value can be further reduced, and the heat radiation characteristics can be further improved.
Further, the required mechanical characteristics can be sufficiently coped with even a thinner heat radiating plate than before, so that high-density mounting of heat-generating components is also possible, and it is possible to further reduce the size of the press-contact structure components.

[0058]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be specifically described with reference to the following examples.

First, a silicon nitride sintered body constituting each heat sink will be described, and then a thyristor using the silicon nitride sintered body will be described.

Examples 1-2 : 1.3% by weight of oxygen, L as impurity cation element
i, Na, K, Fe, Ca, Mg, Sr, Ba, Mn,
B containing 0.15% by weight in total, and α-phase silicon nitride 9
With respect to the average particle size silicon nitride material powder of 0.55μm containing 7%, an average particle size of 0.7μm as a sintering aid Y ₂ O
₃ (yttrium oxide) powder 5% by weight, average particle size 0.5
1.5 wt% of Al ₂ O ₃ (alumina) powder of μm was added, wet-mixed in ethyl alcohol for 24 hours, and dried to prepare a raw material powder mixture. Next, a predetermined amount of an organic binder is added to the obtained raw material powder mixture, and the mixture is uniformly mixed, and then press-molded at a molding pressure of 1000 kg / cm ² ,
A number of disk-shaped compacts were manufactured. Next, after degreasing the obtained molded body in an atmosphere gas at 700 ° C. for 2 hours,
This degreased body was placed in a nitrogen gas atmosphere at 7.5 atm for 1900 hours.
C. for 6 hours, and after performing the densification sintering, control the amount of electricity to the heating device attached to the sintering furnace to control the sintered body until the temperature in the sintering furnace drops to 1500 ° C. Cooling rates of 50 ° C./hr (Example 1) and 25 ° C./hr, respectively
The sintered body was cooled so as to be (Example 2), and each of the obtained sintered bodies was polished so that the surface roughness was set to 5 μm- _Rmax and the thickness was further reduced to 0 μm. .3mm ×
By processing to a diameter of 70 mm, the silicon nitride radiator plates for pressure welding of Examples 1 and 2 were prepared.

Comparative Example 1 On the other hand, immediately after the completion of the densification sintering, the power of the heating device was turned off and the sintered body was cooled at the conventional cooling rate by furnace cooling (about 500 ° C./hr). The sintering treatment was performed under the same conditions as in Example 1 to prepare a silicon nitride heat sink for pressure welding of Comparative Example 1.

Comparative Example 2 Silicon nitride containing 1.5% by weight of oxygen and a total of 0.6% by weight of the impurity cation element and containing 93% of α-phase type silicon nitride and having an average particle diameter of 0.60 μm Except that the raw material powder was used and the cooling rate was set to 100 ° C./hr, the treatment was performed under the same conditions as in Example 1 to prepare a silicon nitride heat sink for pressure welding of Comparative Example 2.

Comparative Example 3 Silicon nitride containing 1.7% by weight of oxygen and 0.7% by weight of the impurity cation element in total and containing 91% of α-phase type silicon nitride and having an average particle diameter of 1.1 μm Except that the raw material powder was used and the cooling rate was set to 100 ° C./hr, the treatment was performed under the same conditions as in Example 1 to prepare a silicon nitride radiator for pressure welding of Comparative Example 3.

Examples 1 and 2 and Comparative Example 1 thus obtained
Porosity and 2 for silicon nitride heat sinks for pressure welding
The thermal conductivity at 5 ° C. was measured. Furthermore, each Si ₃ N
₍₄ ) The ratio (volume ratio) of the crystal phase to the grain boundary phase was measured by X-ray diffraction for the heat sink, and the results shown in Table 1 below were obtained.

[0065]

[Table 1]

As is clear from the results shown in Table 1, the silicon nitride heat radiating plates for pressure welding of Examples 1 and 2 were compared with Comparative Example 1
Since the cooling rate of the sintered body immediately after the completion of densification sintering is set lower than before, the crystal phase is included in the grain boundary phase, and the higher the proportion of the crystal phase, the higher the thermal conductivity A high heat dissipation Si ₃ N ₄ heat sink for pressure welding was obtained.

On the other hand, when the cooling rate of the sintered body was set to a high value as in Comparative Example 1, and the material was rapidly cooled, all the grain boundary phases were formed in an amorphous state, and the thermal conductivity was lowered. Comparative Example 2
When silicon nitride powder containing as much as 0.6% by weight of impurity cation element is used, the whole grain boundary phase is amorphous even if the cooling rate of the sintered body is relatively low. And the thermal conductivity decreased.

Further, as in Comparative Example 3, the average particle size was 1.1.
When silicon nitride powder as coarse as μm was used, densification was insufficient in sintering, and both strength and thermal conductivity were reduced.

Comparative Example 4 On the other hand, instead of the Si ₃ N ₄ sintered body in the example, an aluminum nitride (AlN) sintered body having a thickness of 0.3 mm and a thermal conductivity of 170 W / m · K Was used to manufacture an AlN heat sink according to Comparative Example 4 having the same dimensions as the example.

Comparative Example 5 In place of the Si ₃ N ₄ sintered body in the example, an aluminum nitride (AlN) sintered body having a thickness of 0.8 mm and a thermal conductivity of 70 W / m · K was used. Was used to produce an AlN heat sink according to Comparative Example 5 having the same dimensions as the example.

Comparative Example 6 In place of the Si ₃ N ₄ sintered body in the example, aluminum oxide (Al ₂ O ₃ ) having a thickness of 0.3 mm and a thermal conductivity of 20 W / m · K was used. An Al ₂ O ₃ radiator plate according to Comparative Example 6 having the same dimensions as the example was manufactured using the sintered body.

In order to evaluate the strength characteristics and dielectric breakdown characteristics of each radiator plate according to the examples and comparative examples prepared as described above, the three-point bending strength of each radiator plate was measured.
A dielectric breakdown test was performed to measure the dielectric strength of the heat sink.

In the dielectric breakdown test, a voltage of 50 Hz was applied to the electrodes installed on both sides of each heat sink immersed in insulating oil, and the minimum voltage when the heat sink caused dielectric breakdown was measured. did. The dielectric strength is represented by a value obtained by dividing the measured minimum breakdown voltage by the thickness of the heat sink.

Further, a number of thyristors to be mounted on a vehicle as shown in FIG. 2 were prepared by using the heat radiating plates according to the above Examples and Comparative Examples. This thyristor is provided on a side surface of the cooling fin 8 with a heat radiating plate 7a for pressure contact, a terminal 9a, a rectifying element 10,
The terminal 9b, the insulating spacer 11, and the press contact plate 12 are laminated, the press plate 14 is attached to the bolt 13 raised from the cooling fin 8, the press contact screw 16 is further attached via the disc spring 15, and the press contact screw 16 is tightened. Rectifying element 1 by wearing
0 is pressed against the heat radiating plate 7a.

When a large number of thyristors are manufactured using various radiating plates as described above, cracks are generated by the pressing force of the pressing screws 16 at the time of assembling, and the ratio of the damaged radiating plates is measured to determine the thyristor manufacturing yield. Was calculated.

The results of each measurement are shown in Table 2 below.

[0077]

[Table 2]

As is clear from the results shown in Table 2 above,
According to the pressure-contact type Si ₃ N ₄ heat sink according to each of the examples, the three-point bending strength tends to be larger than that of the comparative example.
Therefore, it has been proved that tightening cracks are less likely to occur in the thyristor assembly process, and the production yield of the press-contact structure component using the press-contact heat sink can be significantly improved.

Furthermore, the Si ₃ N ₄ heatsink according to each of the examples has a heat conductivity about 2 to 5 times larger than the heatsinks of Comparative Examples 1 to ₃ made of the conventional Si ₃ N ₄ sintered body. Because of this, it has excellent heat radiation properties and is extremely effective as a heat radiating plate for high output and high heat generation.

The dielectric strength of the radiator plate according to each embodiment is as follows.
Large as 2 times the dielectric strength of the conventional AlN sintered body, Al ₂ O _3, or the sintered body shown in Comparative Examples 5-6 exhibit excellent dielectric breakdown characteristic.

As described above, compared with the conventional heat sink, 3
When the heat sink of this embodiment having a point bending strength and a dielectric strength that is twice or more is used, when the required mechanical strength and the dielectric strength are set to be the same as those of the conventional heat sink, the thickness of the heat sink is reduced to the conventional one.
/ 2 or less. In this case, since the thickness of the heat radiating plate can be reduced, the thermal resistance value of the heat radiating plate can be further reduced, and the heat radiating characteristics can be further synergistically improved. Further, by reducing the thickness of the heat sink, high-density mounting of heat-generating components becomes possible, which is also effective for miniaturization of press-contact structural components such as thyristors.

On the other hand, the pressure-contact type Si ₃ N according to Comparative Examples 1 to _{3
(4) The} heat sink has a good three-point bending strength, but its thermal conductivity is relatively low at 40 W / m · K or less.
It has been found that it is not suitable for a press-fitted structural component which is also aimed at increasing the output.

In the AlN radiator plate according to Comparative Example 4, since an AlN sintered body having high thermal conductivity was used,
Although the heat radiation characteristics were excellent, it was confirmed that the strength and the amount of deflection were small, and it was difficult to withstand the tightening cracks in the assembly process and the impact during handling. It was also found that the withstand voltage characteristics were low.

Further, the AlN circuit board according to Comparative Example 5 has a higher heat conductivity than the conventional Si ₃ N ₄ substrate, so that the heat dissipation is good, but the strength is insufficient. In addition, it was found that the withstand voltage characteristics were reduced.

On the other hand, in the conventional Al ₂ O ₃ heat radiating plate according to Comparative Example 6, since the heat conductivity, the three-point bending strength and the dielectric strength are all small, the heat radiating property and the durability are low, and the heat radiating at the time of assembling is low. Many cracks and damage of the board occur,
Thyristor manufacturing yields have dropped significantly.

Next, an embodiment of a radiator and a thyristor as a press-contact structure component using other silicon nitride sintered bodies having various compositions and characteristic values will be specifically described with reference to Example 3 shown below. I do.

Example 3 First, various silicon nitride sintered bodies to be used as components of the heat sink were manufactured by the following procedure.

That is, silicon nitride having an average particle diameter of 0.55 μm containing 1.3% by weight of oxygen and a total of 0.15% by weight of the above-mentioned impurity cation element and containing 97% of α-phase type silicon nitride. As shown in Tables 3 to 5, a rare earth oxide such as Y ₂ O ₃ or Ho ₂ O ₃ as a sintering aid and, if necessary, Ti and Hf compounds were added to the raw material powder, The mixture was wet-mixed for 72 hours using silicon nitride balls in ethyl alcohol, and then dried to prepare raw material powder mixtures. Next, a predetermined amount of an organic binder was added to each of the obtained raw material powder mixtures and uniformly mixed, and then 1000 kg / cm ²
Press molding was performed under the above molding pressure to produce a large number of molded articles having various compositions.

Next, each of the obtained compacts was degreased in an atmosphere gas at 700 ° C. for 2 hours.
After performing the densification sintering under the sintering conditions shown in to ５, sintering is performed until the temperature in the sintering furnace falls to 1500 ° C. by controlling the amount of electricity to the heating device attached to the sintering furnace. The sintered bodies were cooled by adjusting the cooling rates of the bodies so as to have the values shown in Tables 3 to 5, respectively, to prepare silicon nitride sintered bodies according to Samples 1 to 56, respectively.

The average values of the porosity, the thermal conductivity (25 ° C.), and the three-point bending strength at room temperature of the silicon nitride sintered bodies according to Samples 1 to 56 thus obtained were measured. Further, the ratio (area ratio) of the crystal phase to the grain boundary phase was measured by X-ray diffraction for each sintered body, and the results shown in Tables 3 to 5 below were obtained.

[0091]

[Table 3]

[0092]

[Table 4]

[0093]

[Table 5]

As is clear from the results shown in Tables 3 to 5, in the silicon nitride sintered bodies according to Samples 1 to 56, the raw material composition was appropriately controlled, and the silicon nitride sintered body immediately after the completion of the densification sintering was compared with the conventional example. Since the cooling rate of the sintered body is set lower than before, the crystal phase is included in the grain boundary phase, and the higher the proportion of the crystal phase, the higher the heat conductivity and the higher the strength of the silicon nitride sintered body. was gotten.

On the other hand, oxygen is 1.3 to 1.5% by weight and the above-mentioned impurity cation element is 0.13 to 0.1% in total.
A silicon nitride raw material powder containing 16% by weight and containing 93% of α-phase type silicon nitride and having an average particle diameter of 0.60 μm was used, and Y ₂ O ₃ (yttrium oxide) powder was added to the silicon nitride powder by 3%. A raw material powder containing 1.3 to 1.6% by weight and 1.3 to 1.6% by weight of alumina powder was molded, degreased, sintered at 1900 ° C for 6 hours, and cooled in a furnace (cooling rate: 400 ° C / hour). The thermal conductivity of the sintered body was as low as 25 to 28 W / m · K, which was close to the thermal conductivity of a silicon nitride sintered body manufactured by a conventional general manufacturing method.

Next, the surface of each of the obtained silicon nitride sintered bodies according to Samples 1 to 56 was polished to adjust the surface roughness to 5 μm-Rmax, and further to a thickness of 0.3 mm × a diameter of 70 mm. Each was processed into a silicon nitride radiator plate for each thyristor. Further, a large number of thyristors according to Example 3 for mounting on a vehicle as shown in FIG. 2 were prepared using the respective silicon nitride radiating plates. In the same manner as in Examples 1 and 2, when the thyristor was assembled, cracks were generated due to the pressing force of the pressing screws 16 and the ratio of the damaged radiator plate was measured. It has been found that the production yield of the manufactured products can be greatly improved.

Further, the Si ₃ N ₄ radiating plate according to the _third embodiment has a thermal conductivity that is about 2 to 5 times larger than that of the conventional radiating plate made of a Si ₃ N ₄ sintered body. It is excellent in heat dissipation, and is extremely effective as a heat sink corresponding to high output and high heat generation.

[0098]

As described above, according to the silicon nitride heat sink for pressure welding according to the present invention, the thermal conductivity is greatly improved in addition to the inherent high strength and toughness characteristics of the silicon nitride sintered body. Since the heat-dissipating plate is formed of the high-thermal-conductivity silicon nitride sintered body, no tightening crack of the heat-dissipating plate occurs in the assembling process, and it becomes possible to mass-produce the press-contact structure component using the heat-dissipating plate at a high production yield.

Further, since the toughness of the silicon nitride sintered body is high, the heat radiating plate is less likely to be cracked by heat cycling from the heat-generating component, the heat cycle characteristics are remarkably improved, and the durability and reliability are excellent. It is possible to provide a pressure contact structure component such as a thyristor.

Further, since a silicon nitride sintered body having a high thermal conductivity, which has not been achieved conventionally, is used as a heat radiating plate, even when a heating element for high output and high integration is pressed, Demonstrates excellent heat dissipation characteristics with little deterioration of thermal resistance characteristics.

In particular, since the mechanical strength of the silicon nitride sintered body itself is excellent, when the required mechanical strength characteristics are fixed, the heat radiating plate is compared with the heat radiating plate made of other ceramic sintered bodies. Can be further reduced.
Since the thickness of the heat radiating plate can be reduced, the thermal resistance value can be further reduced, and the heat radiation characteristics can be further improved.
Further, the required mechanical characteristics can be sufficiently coped with even a thinner heat radiating plate than before, so that high-density mounting of heat-generating components is also possible, and it is possible to further reduce the size of the press-contact structure components.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a structural example of a thyristor as a silicon controlled rectifier.

FIG. 2 is a side view showing another example of the structure of the vehicle-mounted thyristor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Copper stud (anode) 2 Cathode lead 3 Silicon junction 4 Gate lead 5 Ceramic seal 6 Case 7, 7a Heat sink 8 Cooling fin 9a, 9b Terminal 10 Rectifying element 11 Insulating spacer 12 Pressure contact plate 13 Bolt 14 Holding plate 15 Disc spring 16 Pressure screw

Claims (4)

(57) [Claims] 1. A crystalline compound containing a lanthanoid series element in an amount of more than 7.5% by weight to 17.5% by weight or less as oxide, comprising silicon nitride crystals and a grain boundary phase and in the grain boundary phase. The ratio of the phase to the whole grain boundary phase is 20%
This is a silicon nitride heat radiating plate for pressure welding comprising a high thermal conductivity silicon nitride sintered body having a thermal conductivity of 90 W / m · K or more, and a high thermal conductive silicon nitride sintered body pressed against a heat-generating component or the like. The surface roughness of the crimping surface of the consolidated body is the maximum height (R
_(max ) a silicon nitride heat radiating plate for pressure welding, characterized in that it is not more than 10 μm on a standard basis. 2. The silicon nitride heat radiating plate for pressure welding according to claim 1, wherein the three-point bending strength of the high thermal conductive silicon nitride sintered body is 650 MPa or more. 3. The high thermal conductive silicon nitride sintered body is composed of silicon nitride crystals and a grain boundary phase, and the ratio of the crystalline compound phase in the grain boundary phase to the entire grain boundary phase is 50% or more. 2. The heat-dissipating silicon nitride radiator plate according to claim 1, wherein: 4. A crystalline compound comprising silicon nitride crystals and a grain boundary phase and containing a lanthanoid series element in an amount of more than 7.5% by weight and not more than 17.5% by weight as oxides. The ratio of the phase to the whole grain boundary phase is 20%
It has a thermal conductivity of 90 W / m · K or more, and has a surface roughness of 10 μm on the basis of the maximum height (R _max ) on the press contact surface.
A press-bonded structural part characterized in that a heat-generating component is pressed against a press-bonded silicon nitride heatsink made of the following high thermal conductive silicon nitride sintered body.