JP3115238B2 - Silicon nitride circuit board - 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 circuit board, and more particularly to a silicon nitride circuit board having improved reliability against the addition of a thermal cycle and improved heat dissipation and structural strength.

[0002]

2. Description of the Related Art In recent years, a ceramic circuit board in which a metal plate such as a copper plate is bonded on a ceramic substrate has been used as a substrate for mounting semiconductor components handling relatively high power such as a power transistor module and a switching power supply module. I have.

As a method of manufacturing a ceramic circuit board as described above, that is, a method of joining a ceramic substrate and a metal plate, an active metal such as Ti, Zr, Hf, or Nb is used for the purpose.
a method using an active metal brazing material in which 1% to 10% is added to a g-Cu brazing material or the like (active metal method),
A so-called direct bonding method (DBC method: direct bonding copper method) in which a ceramic substrate and a copper plate are directly bonded using tough pitch electrolytic copper containing 00 to 1000 ppm or copper whose surface is oxidized to a thickness of 1 to 10 μm.
Etc. are known.

For example, in the direct joining method, first, a copper circuit board having a thickness of 0.3 to 0.5 mm stamped into a predetermined shape is formed.
0.6 to 1.0 mm thick made of aluminum oxide (Al ₂ O ₃ ) sintered body or aluminum nitride (AlN) sintered body
Heated is disposed in contact with the ceramic substrate, the bonding interface to produce a eutectic liquid phase of Cu-Cu ₂ O, after wetting the surface of the ceramic substrate in the liquid phase by cooling and solidifying the liquid phase Then, the ceramic substrate and the copper circuit board are joined. A ceramic circuit board to which such a direct bonding method is applied has a strong bonding strength between the ceramic substrate and the copper circuit board, and can be miniaturized and mounted with a simple structure that does not require a metallization layer or a brazing material layer. And the manufacturing process can be shortened.

In a ceramic circuit board in which a metal plate is bonded to a ceramic substrate by the above-described direct bonding method or active metal method, the thickness of the metal plate is set to 0.3 to 0.5 mm so that a large current can flow. Due to the thickness, there was a problem that the reliability against the heat history was poor. That is, when a ceramic substrate and a metal plate having significantly different coefficients of thermal expansion are joined, a thermal stress due to the difference in thermal expansion is generated due to a cooling process after the joining or the addition of a cooling / heating cycle.
This stress exists as a compressive and tensile residual stress distribution on the ceramic substrate side near the joint, and the main residual stress mainly acts on the ceramic portion adjacent to the outer peripheral end of the metal plate. This residual stress causes cracks in the ceramic substrate or causes peeling of the metal plate. Further, even if cracks do not occur in the ceramic substrate, the ceramic substrate has an adverse effect of reducing its strength.

[0006] Of the above-mentioned residual stresses, those based on thermal stress generated in the cooling process after joining the metal plates can be reduced to some extent by adjusting the cooling rate or the like, but generate heat from the mounted components during actual use. Residual stress caused by the above cannot be reduced depending on external conditions, and is a serious problem. For this reason, the above-mentioned ceramic circuit board is usually the same as the front surface, that is, the mounting portion of the semiconductor component or 5 to 30 on the back surface of the ceramic substrate.
Although a thin metal plate is bonded to prevent the ceramic circuit board from warping, the problem of residual stress has not been fundamentally solved.

To cope with the above-mentioned problems due to thermal stress and residual stress, that is, measures against the decrease in bonding strength and the occurrence of cracks, for example, Japanese Patent Publication No. 5-25397 discloses
The outer peripheral edge of the copper plate as a metal plate has a thin shape (thin portion),
Specifically, it is described that the outer peripheral end has a stepped shape or a tapered shape. Also, Japanese Patent Application Laid-Open No. 3-145748
The publication describes that a groove is formed inside along the outer peripheral edge of a metal plate. Thus, the stress concentrated on the outer peripheral end of the metal plate is dispersed by the groove, thereby preventing a decrease in bonding strength and the occurrence of cracks.

[0008]

However, of the above-mentioned conventional methods for improving the reliability of the thermal history in the ceramic circuit board, the method described in Japanese Patent Publication No. 5-25397 discloses an outer peripheral end portion of a metal plate. Since the thin portion is formed by etching or the like at the same time as the formation of the circuit pattern, the manufacturing process becomes complicated, resulting in an increase in the number of manufacturing steps.

Japanese Patent Application Laid-Open No. 3-145748 also mainly describes that a groove is formed along the outer peripheral edge of a metal plate by an etching method. According to the etching method, a groove can be formed simultaneously with the formation of a circuit pattern. However, as described above, the etching method has a disadvantage that the steps are complicated and the number of manufacturing steps is increased. Further, it is also shown that the groove is formed by machining using a mold or the like.However, when the groove is formed over the entire inner periphery of the outer peripheral edge of the metal plate by this method of machining, the groove is formed by pressing or the like. When forming the metal sheet, plastic deformation occurs in the metal plate around the pressing portion, and accompanying this, deformation such as distortion occurs particularly in the central portion of the metal plate. The deformation of the metal plate causes poor bonding of the metal plate or a decrease in bonding strength.

[0010] From the above, by adding a cooling process or a cooling / heating cycle after joining the metal plates, thermal stress and residual stress generated in the metal plate are dispersed and relaxed, thereby effectively preventing cracks and strength reduction of the ceramic substrate. There is a strong demand for a technique capable of preventing deformation of a metal plate even by machining that can prevent the deformation and simplify the manufacturing process.

On the other hand, higher integration and higher output of the semiconductor element,
With an increase in size, there is an increasing technical demand for a circuit board structure capable of efficiently dissipating heat generated from an element to the outside and a high-strength circuit board structure capable of withstanding thermal stress. Therefore, an attempt was made to use a silicon nitride (Si ₃ N ₄ ) substrate having higher strength than a conventional alumina (Al ₂ O ₃ ) substrate as a ceramic substrate. However, Si ₃ N ₄
Substrates have excellent mechanical strength such as toughness, but their thermal conductivity is significantly lower than that of aluminum nitride substrates.Therefore, they are practically used as components of circuit boards for semiconductors that require heat dissipation. Not.

On the other hand, an aluminum nitride substrate has high thermal conductivity and low thermal expansion characteristics as compared with other ceramic substrates, but it does not provide satisfactory mechanical strength. The circuit board is easily damaged by the slight pressing force and impact force added in the process,
In some cases, the manufacturing yield of a semiconductor device is significantly reduced.

The present invention has been made in order to solve such problems, and has excellent heat dissipation and structural strength, and can reduce the thermal stress and residual stress generated in a metal plate even when a cooling / heating cycle is added. By dispersing, the stress concentration on the outer peripheral edge of the metal plate can be reduced, cracks and strength reduction of the ceramic substrate can be effectively prevented, and the metal plate is deformed even by machining which is advantageous in the manufacturing process It is an object of the present invention to provide a silicon nitride circuit board which can prevent the occurrence of the problem and is excellent in reliability and manufacturability.

[0014]

According to a first aspect of the present invention, there is provided a silicon nitride circuit board, comprising: a rare earth element in an amount of 1.0 to 17.5% by weight in terms of oxide; Li, Na, K, Fe, Ca, Mg, S as elements
r, Ba, Mn, B in total of 1.0% by weight or less, preferably 0.3% by weight or less (including 0% by weight as a detection limit) and a thermal conductivity of 60 w / mk or more. In a silicon nitride circuit board comprising a high thermal conductive silicon nitride substrate and a metal plate bonded to the high thermal conductive silicon nitride substrate, bonding of the metal plate to the high thermal conductive silicon nitride substrate A groove is formed on the inner side of the outer peripheral edge on the side opposite to the surface.

The content range of the rare earth element oxide, 1.0 to 17.5% by weight, is naturally understood as a mathematical expression, but the lower limit of the content is 1.0% by weight.
And an upper limit of 17.5% by weight.
Hereinafter, the same applies to other component ranges.

According to another aspect of the present invention, there is provided a silicon nitride circuit board containing 1.0 to 17.5% by weight of a rare earth element in terms of oxide. A highly thermally conductive silicon nitride substrate comprising a crystal phase and a grain boundary phase, wherein the ratio of the crystalline compound phase to the entire grain boundary phase in the grain boundary phase is 20% or more, preferably 50% or more; A metal plate bonded to a conductive silicon nitride substrate, wherein a groove is formed on the inner side of the outer peripheral edge of the metal plate opposite to the bonding surface with the high thermal conductive silicon nitride substrate. Is formed.

Here, the inside of the outer peripheral edge portion of the metal plate is defined as FIG.
As shown in the figure, the width D of the metal plate 2 is defined as a portion that is within 1/3 of the width D of the metal plate 2 from the outer peripheral edge toward the center. That is, based on the width D of the metal plate 2, a portion within one-third of both sides from the outer peripheral edge not including the outer peripheral edge toward the center is defined as the inner peripheral edge, and the central metal plate 2
Is set as the center (in FIG. 6, the inside of the outer peripheral edge is indicated by oblique lines).

In the silicon nitride circuit board according to the present invention, as the grooves, discontinuous grooves may be formed at predetermined intervals in addition to the continuous grooves. . Further, a plurality of holes may be formed in place of the continuous groove or the discontinuous groove.

Further, in the silicon nitride circuit board of the present invention in which a groove is formed in a metal plate, the continuous groove or the discontinuous groove is formed in all the metal plates joined to the high thermal conductive silicon nitride substrate. It is preferable that the continuous groove or the discontinuous groove is formed in at least one metal plate bonded to the high thermal conductive silicon nitride substrate, but the present invention is included in the present invention. . Also, it is included even if it is not the entire circumference of the metal plate.

On the other hand, in the silicon nitride circuit board of the present invention in which a plurality of holes are formed in a metal plate, the plurality of holes are formed in all the metal plates joined on the high thermal conductive silicon nitride substrate. It is preferable that the plurality of holes are formed in at least one metal plate, which is included in the present invention.

According to a more preferred form of the silicon nitride circuit board of the present invention in which grooves are formed in the above-described metal plate, the continuous grooves or the discontinuous grooves are formed by press working. Wherein the continuous groove or the discontinuous groove is formed linearly along the outer peripheral edge of the metal plate, as described in claims 5 and 9. , The width of the continuous groove or the discontinuous groove is 0.2 to 0.2.
Assuming that the length of the discontinuous groove is L ₀ , and the shortest distance between the adjacent discontinuous grooves is L ₁ , as described in claim 12, wherein the length of the discontinuous groove is L ₁ , 10L ₀ ≦ L
An embodiment that satisfies ₁ ≦ 1 / 2L ₀ may be mentioned.

On the other hand, in a preferred embodiment of the silicon nitride circuit board of the present invention in which a plurality of holes are formed in a metal plate, the plurality of holes are formed on an outer peripheral edge of the metal plate. And the plurality of holes are non-through holes as described in claim 15. The plurality of holes are through holes as described in claim 16. Wherein the plurality of holes are holes formed by press molding, wherein the shortest distance between the adjacent holes is L ₃ , and the adjacent holes are L ₃ , as described in claim 18. Assuming that the distance between the centers of the holes to be formed is L ₄ , a form satisfying 1 / 5L ₄ ≦ L ₃ ≦ 1 / 2L ₄ may be mentioned.

The high thermal conductive silicon nitride substrate used in the present invention has a rare-earth element converted to an oxide of 1.0 to 1 in terms of oxide.
7.5% by weight, Li, N as impurity cation element
a, K, Fe, Ca, Mg, Sr, Ba, Mn, and B in a total content of 1.0% by weight or less, preferably 0.3% by weight or less (including 0% by weight as a detection limit). It is composed of

In another embodiment, the high thermal conductivity silicon nitride substrate is formed by converting a rare earth element into an oxide in an amount of 1.0 to 17.
5% by weight, comprising a silicon nitride crystal phase and a grain boundary phase, wherein the ratio of the crystalline compound phase in the grain boundary phase to the entire grain boundary phase is 20% or more, preferably 50% or more. May be formed.

Further, it is particularly preferable to use a lanthanoid element as the rare earth element in order to improve the thermal conductivity.

Further, the high thermal conductive silicon nitride substrate 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 substrate used in the present invention is made of Ti, Zr, Hf, V, Nb, Ta,
At least one selected from the group consisting of Cr, Mo, W
It is preferable to contain the seed in an amount of 0.1 to 3.0% by weight in terms of oxide. This Ti, Zr, Hf, V, Nb, T
At least one selected from the group consisting of a, Cr, Mo, and W can be contained as an oxide, carbide, nitride, silicide, or boride by being added to the silicon nitride powder.

Further, the method of manufacturing a silicon nitride substrate having high thermal conductivity used in the present invention is characterized in that oxygen is not more than 1.7% by weight, and Li, Na, K, Fe, Ca,
Mg, Sr, Ba, Mn, B in total of 1.0% by weight or less, preferably 0.3% by weight or less, containing 90% by weight or more of α-phase silicon nitride and having an average particle size of 1.0 μm or less. Rare earth elements are converted to oxides in silicon nitride powder,
A raw material mixture containing 17.5% by weight or less and, if necessary, at least one of alumina and aluminum nitride added at 1.0% by weight or less is molded to prepare a molded body. After the obtained molded body is degreased, Atmospheric pressure sintering at a temperature of 1800 to 2100 ° C, and a cooling rate of the sintered body from the sintering temperature to a temperature at which a liquid phase formed at the time of sintering by the rare earth element solidifies is set to 100 ° C or less per hour. And gradually cooled.

In the above method, at least one of alumina and aluminum nitride may be 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 60 W / m · K or more, A silicon nitride substrate 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.

The silicon nitride powder used as the main component of the sintered body used in the above-mentioned production method has an oxygen content of 1.7% by weight or less in consideration of sinterability, strength and thermal conductivity. Preferably 0.5-1.5% by weight, Li, Na,
Α-phase silicon nitride in which the total content of impurity cation elements such as K, Fe, Mg, Ca, Sr, Ba, Mn, and B is suppressed to 1.0% by weight or less, preferably 0.3% by weight or less. Containing 90% by weight or more, preferably 93% by weight or more, and having an average particle size of 1.0 μm or less, preferably 0.4 to
A fine silicon nitride powder of about 0.8 μm can be used.

By using a fine raw material powder having an average particle diameter of 1.0 μm or less, a dense high thermal conductive silicon nitride substrate having a porosity of 2.5% or less even with a small amount of a sintering aid. Can be formed, and the possibility that the sintering aid impairs the heat conduction characteristics is reduced.

Further, Li, Na, K, Fe, Ca, Mg,
Since the impurity cation elements of Sr, Ba, Mn, and B are substances that hinder thermal conductivity, the content of the impurity cation element must be as follows in order to secure a thermal conductivity of 60 W / m · K or more. It can be achieved by setting the total to 1.0% by weight or less. In particular, for the same reason, the content of the impurity cation element is preferably not more than 0.3% by weight in total.
More preferred. Here, the silicon nitride powder used for obtaining a normal silicon nitride sintered body includes, in particular, Fe, C
a, Mg are contained in a relatively large amount, so that Fe, C
The total amount of a and Mg is a measure of the total content of the impurity cation element.

In the high thermal conductive silicon nitride substrate used in the present invention, the content of the impurity cation element cannot be completely 0% by weight in a mathematical sense. Therefore, the content of the impurity cation element specified in the present invention substantially includes 0% by weight as a detection limit.

Further, 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-phase type, a high-density silicon nitride substrate can be formed. Can be manufactured.

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 the lanthanoid series elements Ho, Er, and Yb as rare earth elements, 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 1.0 to 17.5% by weight based on the raw material powder in terms of oxide.
When the addition amount is less than 1.0% by weight, the sintered body is insufficiently densified. In particular, when the rare earth element is an element having a large atomic weight such as a lanthanoid element, a relatively low strength is obtained. A sintered body having a relatively 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. It is particularly desirable to set the content to 4 to 15% by weight for the same reason.

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 compounds such as Ti, Zr, and Hf also function as a light-shielding agent that imparts opacity by coloring the silicon nitride sintered body to a black color. Therefore, in particular, when manufacturing a circuit board on which an integrated circuit or the like which easily malfunctions due to light is mounted, it is desirable to appropriately add the compound such as Ti and the like to obtain a silicon nitride substrate excellent in light shielding properties.

Further, in the above-mentioned production 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 additive 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 amount of AlN added 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.

Further, the porosity of the sintered body has a significant influence on the thermal conductivity and the strength, so that 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 ratio of the crystalline compound phase in the grain boundary phase greatly affects the thermal conductivity of the sintered body. However, in the high thermal conductive silicon nitride substrate used in the present invention,
It is necessary that the content be 20% or more of the grain boundary phase, and more preferably 50% or more is occupied by the crystal phase. If the crystal phase is less than 20%, it is not possible to obtain a silicon nitride substrate having high heat conductivity of 60 W / m · K or more and having excellent heat radiation characteristics and high temperature strength.

Further, as described above, the porosity of the high thermal conductivity silicon nitride substrate 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. To achieve this, the silicon nitride compact is heated to a temperature of 1800
Pressure sintering is performed at a temperature of ℃ 2100 ° C. for about 2 to 10 hours, and the cooling rate of the sintered body immediately after the completion of the sintering operation is 100
It is important that the temperature is lowered to below ℃.

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. Is that the grain boundary phase of the sintered body structure becomes non-crystalline (glass phase), 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. Both will fall.

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 sintered body excellent in both thermal conductivity and mechanical strength can be obtained.

The high thermal conductive silicon nitride substrate 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 molding method of the raw material mixture,
A general-purpose mold pressing method, a sheet forming method such as a doctor blade method, and the like can be applied. Subsequent to the above molding operation, the molded body is heated at a temperature of 600 to 800 in a non-oxidizing atmosphere.
C. or in air at a temperature of 400 to 500.degree. C. for 1 to 2 hours to sufficiently remove the organic binder component added in advance and degrease. Next, the degreased molded body is subjected to atmospheric pressure sintering at a temperature of 1800 to 2100 ° C. for a predetermined time in an inert gas atmosphere such as nitrogen gas, hydrogen gas or argon gas.

The silicon nitride substrate manufactured by the above method has a porosity of 2.5% or less and 60 W / m · K (25 ° C.).
It has the above thermal conductivity and a three-point bending strength of 65 at room temperature.
It has excellent mechanical properties of 0 MPa or more.

It should be noted that a silicon nitride substrate having a high thermal conductivity of 60 W / m · K or more by adding high thermal conductivity SiC or the like to low thermal conductivity silicon nitride is within the scope of the present invention. Is not included. However, the thermal conductivity is 60 W /
m.K or higher silicon nitride sintered body with high thermal conductivity Si
Needless to say, a silicon nitride-based substrate in which C is compounded is included in the scope of the present invention.

The silicon nitride circuit board according to the present invention is provided on the surface of the high thermal conductive silicon nitride substrate manufactured as described above.
It is manufactured by integrally joining metal plates having conductivity using the direct joining method or the active metal method.

In the silicon nitride circuit board of the present invention,
A continuous groove, a discontinuous groove, or a plurality of holes is formed inside the outer peripheral edge on the side opposite to the joining surface of the metal plate. Here, the thermal stress generated in the cooling process after the joining of the metal plate, the thermal stress due to the addition of a cooling / heating cycle, and the like, and the residual stress based on them are the above-mentioned continuous grooves provided inside the outer peripheral edge of the metal plate. Since the dispersion is performed by the discontinuous grooves or the plurality of holes, the stress concentration on the outer peripheral end of the metal plate is reduced. As a result, the stress value itself at the outer peripheral end of the metal plate can be reduced, so that it is possible to effectively prevent the occurrence of cracks and a decrease in strength of the ceramic substrate, which have conventionally been problems.

In particular, when the above-mentioned dispersion of stress is achieved by discontinuous grooves, even if the grooves are formed by machining, deformation of the metal plate due to pressing during machining is prevented by the grooves between the grooves. This can be alleviated by the non-formation region. Therefore,
It is possible to prevent deformation of the metal plate, especially the central portion of the metal plate during machining. However, a groove is preferably formed in the vicinity of the corner of the metal plate because thermal stress and residual stress are particularly concentrated.

On the other hand, when the above-mentioned dispersion of stress is achieved by a plurality of holes, the strength-reduced portions (thin portions) of the metal plate are reduced.
Makes it possible to effectively prevent the metal plate itself from being deformed or warped during machining. Therefore, it is possible to practically form a portion (hole) of the stress dispersion by machining such as press working, and to effectively prevent the metal plate itself from being deformed or warped by the press working or the like. It is possible to do.

[0059]

Next, an embodiment of the present invention will be described.
A specific description will be given with reference to the following embodiments and the accompanying drawings. First, a high thermal conductive silicon nitride substrate used in the present invention will be described, and thereafter, a silicon nitride circuit board using this high thermal conductive silicon nitride substrate as a ceramic substrate will be described.

First, various silicon nitride substrates having high thermal conductivity to be used as constituents of the silicon nitride circuit board of the present invention were manufactured by the following procedure.

Namely, a silicon nitride raw material containing 1.3% by weight of oxygen and 0.15% by weight of the impurity cation element in total and containing 97% of α-phase type silicon nitride and having an average particle size of 0.55 μm. As shown in Tables 1 to 3, as shown in Tables 1 to ₃ , rare earth oxides such as Y ₂ O ₃ and Ho ₂ O ₃ as sintering aids, and Ti, Hf compounds, and Al ₂ O ₃ powders as needed. ,
AlN powder was added, and the mixture was wet-mixed in ethyl alcohol using a silicon nitride ball for 72 hours, 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, followed by press molding at a molding pressure of 1000 kg / cm ² to produce a large number of molded bodies having various compositions. Next, after each obtained compact was degreased in an atmosphere gas at 700 ° C. for 2 hours, the degreased body was subjected to densification sintering under the sintering conditions shown in Tables 1 to 3, and then attached to a sintering furnace. The cooling rate of the sintered body until the temperature in the sintering furnace falls to 1500 ° C. is controlled by controlling the amount of electricity supplied to the heating device, and the sintering is performed by adjusting the cooling rate to the values shown in Tables 1 to 3, respectively. Cool the body,
Silicon nitride sintered bodies according to Samples 1 to 51 were prepared. Further, the obtained sintered body was processed and polished to obtain a high thermal conductive silicon nitride substrate having a predetermined shape.

The average values of the porosity, the thermal conductivity (25 ° C.), and the three-point bending strength at room temperature were measured for the silicon nitride substrates according to Samples 1 to 51 thus obtained. Furthermore, the ratio of the crystal phase to the grain boundary phase was measured by X-ray diffraction for each silicon nitride substrate, and the results shown in Tables 1 to 3 below were obtained.

[0063]

[Table 1]

[0064]

[Table 2]

[0065]

[Table 3]

As is clear from the results shown in Tables 1 to 3, in the silicon nitride sintered bodies according to Samples 1 to 51, the raw material composition and the amount of impurities were appropriately controlled, and the densified sintering was performed as compared with the conventional example. Since the cooling rate of the sintered compact immediately after completion 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. An elementary substrate was obtained.

On the other hand, 1.3 to 1.5% by weight of oxygen and 0.13 to 1.5%
A raw material powder having an average particle size of 0.60 μm containing 0% by weight and containing 93% of α-phase type silicon nitride was used, and Y ₂ O ₃ (yttrium oxide) powder was added to the silicon nitride powder in an amount of 3%. To 6% by weight and 1.3 to 1.6% by weight of alumina powder
The added raw material powder is molded, degreased, sintered at 1900 ° C. for 6 hours, and cooled in a furnace (cooling rate: 400 ° C./hour) to obtain a sintered body having a low thermal conductivity of 25 to 28 W / m · K. The value was close to the thermal conductivity of a silicon nitride sintered body manufactured by a conventional general manufacturing method.

Next, a metal plate is integrally bonded to both surfaces of each of the obtained high thermal conductive silicon nitride substrates according to Samples 1 to 51 by a direct bonding method or an active metal method, so that each of the silicon nitride substrates is obtained. A circuit board was manufactured.

FIG. 1 is a diagram showing the structure of a silicon nitride circuit board according to one embodiment of the present invention. In FIG. 1, a copper plate 2 as a metal plate is bonded to a surface 1a of a silicon nitride substrate 1 having high thermal conductivity. Also, a copper plate 3 is similarly bonded to the back surface 1b of the high thermal conductive silicon nitride substrate 1,
These constitute a silicon nitride circuit board 4A.

The silicon nitride circuit board 4A shown in FIG.
Are bonded to the high thermal conductive silicon nitride substrate 1 by a direct bonding method, a so-called DBC method. Copper plates 2 and 3 when using such DBC method
As oxygen, such as tough pitch copper 100 to 300
It is preferable to use copper containing 0 ppm,
Oxygen-free copper may be used depending on the conditions at the time of joining. Instead of a single plate of copper or a copper alloy, a clad plate or the like with another metal member having at least a joining surface with the high thermal conductive silicon nitride substrate 1 made of copper can be used.

The copper plate 2 bonded to the surface 1a of the high thermal conductive silicon nitride substrate 1 is to be a mounting portion for semiconductor components and the like, and is patterned into a desired circuit shape.
The copper plate 3 bonded to the back surface 1b side of the high thermal conductive silicon nitride substrate 1 prevents warpage of the high thermal conductive silicon nitride substrate 1 at the time of bonding.
In a divided state, it is bonded and formed on almost the entire back surface 1b of the silicon nitride substrate 1 having high thermal conductivity. As the copper plate 3 on the back surface 1b side, a copper plate having the same thickness as the copper plate 2 serving as a mounting portion for semiconductor components or the like may be used.
% Of the copper plate is preferably used.

Here, the silicon nitride circuit board 4A shown in FIG.
Although bonded by the BC method, for example, as shown in FIG. 2, a silicon nitride circuit board 5A in which copper plates 2 and 3 are bonded to a high thermal conductive silicon nitride substrate 1 by an active metal method may be used. The active metal method includes, for example, Ti, Zr, Hf, N
b) a brazing material containing at least one active metal selected from the group consisting of
This is a method of joining the high thermal conductive silicon nitride substrate 1 and the copper plates 2 and 3. As the composition of the active metal-containing brazing material to be used, for example, a eutectic composition of Ag-Cu (72 wt% Ag-28
wt% Cu) or an Ag-Cu-based brazing filler metal or a Cu-based brazing filler metal having a composition in the vicinity thereof, and 1-10% by weight of T
Examples of the composition include at least one active metal selected from i, Zr, Hf, Nb, and the like. In addition, a low melting point metal such as In may be added to the active metal-containing brazing material.

As in the case of the silicon nitride circuit board 4A shown in FIG.
The one joined by the C method has advantages such that a high joining strength can be obtained with a simple structure and the manufacturing process can be simplified. In addition, as in the silicon nitride circuit board 5A shown in FIG. 2, the copper plates 2 and 3 joined to the high thermal conductive silicon nitride substrate 1 by the active metal method can obtain a high bonding strength, Since the brazing filler metal layer 6 also functions as a stress relaxation layer,
Reliability can be further improved. For this reason, it is preferable to select a joining method according to required characteristics, applications, and the like.

When a metal plate is bonded to the high thermal conductive silicon nitride substrate 1 by the active metal method, not only a copper plate but also various metal plates such as a nickel plate, a tungsten plate, a molybdenum plate depending on the application. It is also possible to use these alloy plates, clad plates (including clad plates with copper plates), and the like.

Then, the above-described silicon nitride circuit board 4
In FIGS. 1A and 1A, as shown in FIG. 1, a continuous groove 7 is formed inside the outer peripheral edge of the copper plate 2 serving as a mounting portion for a semiconductor component or the like, that is, each circuit pattern portion of the copper plate 2. Are formed along the outer periphery.

In place of the continuous groove 7, a discontinuous groove may be formed. FIG. 3 shows a silicon nitride circuit board 4B in which the copper plate 2 having the discontinuous grooves 8 formed thereon is integrally joined to the surface 1a of the high thermal conductive silicon nitride board 1 by a direct joining method. This silicon nitride circuit board 4B has the same configuration as the silicon nitride circuit board 4A shown in FIG. 1 except that a discontinuous groove 8 is formed.

On the other hand, FIG. 4 shows a silicon nitride obtained by integrally joining a copper plate 2 having discontinuous grooves 8 to a surface 1 a of a high thermal conductive silicon nitride substrate 1 via an active metal-containing brazing material layer 6. It is sectional drawing which shows the circuit board 5B. This silicon nitride circuit board 5B has the same configuration as that of the silicon nitride circuit board 5A shown in FIG. 2 except that a discontinuous groove 8 is formed.

Then, the above-described silicon nitride circuit board 4
In FIGS. 5B and 5B, as shown in FIG. 5, a discontinuous groove 8 is formed inside the outer peripheral portion of the copper plate 2 to be a mounting portion for a semiconductor component or the like.
Are formed along the outer peripheral edge, that is, along the outer peripheral edge of each circuit pattern of the copper plate 2.

The continuous groove 7 and the discontinuous groove 8 are
In order to avoid complication of the manufacturing process and to reduce the number of manufacturing steps, it is desirable to form the film by mechanical processing such as pressing using a die. However, application of another formation method is not necessarily excluded.

Here, the inside of the outer peripheral edge of the above-described copper plate 2 (metal plate) refers to the width of the copper plate 2 from the outer peripheral edge toward the center with respect to the width D of the copper plate 2 as shown in FIG. 1 of D
/ 3 or less. That is, based on the width D of the copper plate 2, a portion within 1 / 3D on both sides in the center direction from the outer peripheral edge not including the outer peripheral edge is defined as the inner periphery of the outer periphery (indicated by oblique lines in FIG. 6). The center 1/3 of the width D is defined as the center. If the region where the grooves 7 and 8 are formed reaches the center portion beyond the inside of the outer peripheral edge portion, stress concentration at the outer peripheral end portion of the copper plate 2 cannot be sufficiently reduced, and the mounting area is reduced.

The above-mentioned continuous groove 7 and discontinuous groove 8
Is preferably formed in a straight line at predetermined intervals along the outer peripheral edge of each circuit pattern portion of the copper plate 2. As described above, by forming the grooves 7 and 8 in a straight line, the copper plate 2 is formed.
The stress concentration on the outer peripheral end of the substrate can be efficiently reduced, in other words, the stress can be efficiently dispersed.

[0082] The shape of each single groove 8a constituting the discontinuous groove 8 shown in FIG. 5, i.e. the width W and the length L ₀ of the single groove 8a, the size of the formation interval and copper 2 unitary groove 8a to be described later depending etc., range of 0.2~1.0mm width W, it is preferable that the length range L ₀ following 20 mm. If the width W of the single groove 8a is less than 0.2 mm, the stress may not be sufficiently dispersed, and if it exceeds 1.0 mm, the strength of the copper plate 2 tends to decrease and the mounting area decreases. Will be invited.

A more preferable range of the width W is 0.4 to 0.8 mm for the same reason. Further, the length L ₀ of each single groove 8a exceeds 20 mm, it may not be possible to sufficiently suppress the deformation of the copper plate 2 with decreasing the groove-free region. The minimum length of each single groove 8a is not particularly limited, but is preferably 2 mm or more from the viewpoint that stress concentration on the outer peripheral end of the copper plate 2 is efficiently reduced.

In FIG. 5, the discontinuous grooves 8 linearly arranged are such that the shortest distance L ₁ between the adjacent single grooves 8a is 1/1 / the length L ₀ of each single groove 8a. 10L
It is preferable to form so as to satisfy ₀ ≦ L ₁ ≦ １ ／ L ₀ . Interval of formation of discontinuous groove 8 (closer single groove 8
When the shortest distance L ₁₎ is too large between a, and in particular with the L _{1> 1} / 2L _0, there may not be sufficiently obtained the effect of dispersing the stress due to the grooves formed, whereas discontinuous grooves If the formation interval of _No. 8 is too small, specifically, L ₁ <
If it is 1 / 10L ₀ , there is a possibility that the effect of suppressing deformation of the copper plate 2 due to the non-groove formed region may not be sufficiently obtained.

The position of the non-groove region is not particularly limited as long as the discontinuous groove 8 satisfies the above-mentioned formation interval. However, as shown in FIG. It is desirable to arrange each single groove 8a so that a groove is formed in the vicinity. This is because thermal stress and residual stress are particularly concentrated near the corners of the copper plate 2. In addition, discontinuous grooves 8
The length L ₀ of each of the single grooves 8a that constitute the above-mentioned structure need not be all the same, and can be appropriately changed within a range satisfying the above-described conditions.

The continuous groove 7 and the discontinuous groove 8 may have a longitudinal cross-sectional shape that is substantially uniform in the depth direction as shown in FIG. 7 or an inverted triangular shape as shown in FIG. There may be. However, the depth d is 1 / th of the thickness t of the copper plate 2.
It is preferable to set the range of 3 to 2/3. If the depth of the grooves 7 and 8 is less than 1/3 of the thickness t of the copper plate 2, the effect of dispersing stress may be insufficient, and 2/3 of the thickness t.
When it exceeds, the strength of the copper plate 2 is likely to be reduced. The formation positions of the grooves 7 and 8, i.e. the shortest distance L ₂ from the outer peripheral edge portion of the copper plate 2 to the grooves 7 and 8, varies depending on the thickness and size of the copper plate 2, 0.3 to 1.0 mm It is preferable that Distance L ₂ is 0 which indicates the formation position of the grooves 7 and 8.
If it is less than 3 mm, the ability to maintain the shape of the copper plate 2 will decrease, and if the distance L ₂ exceeds 1.0 mm, stress concentration at the outer peripheral end of the copper plate 2 may not be sufficiently reduced.

The copper plate 2 bonded to the front surface 1a of the high thermal conductive silicon nitride substrate 1 serving as a mounting portion for semiconductor components and the like has been described in detail, but the back surface 1b of the high thermal conductive silicon nitride substrate 1 has been described.
It is preferable that grooves 7 and 8 are formed inside the outer peripheral edge of the copper plate 3 to be bonded to the inner surface, similarly to the copper plate 2 on the front surface 1a side. In particular, when a relatively thick copper plate (metal plate) is used in terms of heat dissipation and the like, the copper plate 3 on the back surface 1b side also has grooves 7,
8 is desirably formed. The shapes and the intervals of the grooves 7, 8 formed in the copper plate 3 on the back surface 1b are based on the grooves 7, 8 formed in the copper plate 2 on the front surface 1a.

The above-described silicon nitride circuit board 4 is manufactured, for example, as follows. That is, for example, an oxygen-containing copper plate such as tough pitch copper is processed into a predetermined shape (a circuit pattern shape for the copper plate 2), and a groove 7 or a discontinuous groove 8 that is linearly continuous, for example, is formed inside the outer peripheral edge thereof. It is formed by mechanical processing such as pressing. The copper plates 2 and 3 having such grooves 7 and 8 are arranged in contact with each other on a silicon nitride substrate having high thermal conductivity, and the melting point of copper (1356) is obtained.
K) By heating at a temperature equal to or lower than the eutectic temperature of copper and copper oxide (1338 K) or higher, the copper plates 2 and 3 are joined to produce the silicon nitride circuit board 4. When an oxygen-containing copper plate is used as the copper plate, the atmosphere for this heating is preferably an inert gas atmosphere.

The silicon nitride circuit board 5 in which metal plates are joined by the active metal method is manufactured, for example, as follows. First, copper plates 2 and 3 having continuous grooves 7 or discontinuous grooves 8 are prepared in the same manner as the silicon nitride circuit board 4 described above. On the other hand, a paste of the active metal-containing brazing material as described above is applied to, for example, the high thermal conductive silicon nitride substrate 1 side. The coating thickness of the brazing material layer is preferably such that the thickness of the brazing material layer 6 after the heat bonding is not too large in order to improve the thermal cycle characteristics. next,
High thermal conductive silicon nitride substrate 1 coated with brazing material paste
The copper plates 2 and 3 are laminated and disposed on the upper surface, and heat-treated at a temperature according to the brazing material used, thereby producing the silicon nitride circuit board 5.

In the silicon nitride circuit boards 4 and 5 having the above-described structure, the thermal stress generated during the cooling process after the joining of the copper plates 2 and 3 and the thermal stress due to the addition of a cooling / heating cycle and the residual stress based on the thermal stress. The stress is dispersed by the grooves 7, 8 provided inside the outer peripheral edges of the copper plates 2, 3, so that the copper plates 2, 3
, Stress concentration on each outer peripheral end is reduced. This allows
Since the stress value itself at the outer peripheral end of the copper plates 2 and 3 is reduced,
It is possible to effectively prevent the occurrence of cracks and a decrease in the strength of the ceramic substrate portion, which have conventionally been problems. Since the above-described dispersion of the stress is achieved by the grooves 7 and 8, even if machining such as press working is applied to the formation of the grooves 7 and 8, the deformation of the copper plates 2 and 3, particularly the central portion thereof, is performed. Can be prevented. Therefore, the manufacturing process can be simplified and the number of manufacturing steps can be reduced without lowering the bonding strength due to deformation of the copper plates 2 and 3.

Next, a specific example of the embodiment in which the above-described groove is formed and its evaluation result will be described.

Example 1 First, the above sample 1 was used as a high thermal conductive silicon nitride substrate 1.
The silicon nitride substrate according to any one of (1) to (51) is oxidized in air to form a 4 μm thick oxide layer (SiO
A high thermal conductive silicon nitride substrate having a thickness of 0.7 mm having _two layers) is prepared, and a linear continuous groove 7 or a discontinuous groove 8 is pressed inside the outer peripheral edge along the outer peripheral edge. Tough pitch copper (oxygen content: 300pp)
m), copper plates 2 and 3 having a predetermined shape and a thickness of 0.3 mm were prepared.

The shape of the continuous groove 7 is shown in FIG.
Approximately 0.5mm width W with a uniform shape, a depth d of 0.15 mm, also forming position distance L ₂ is 0.5mm from the outer peripheral edge portion of the copper plate 2 in the depth direction shown in It was made to become.

On the other hand, the shape of the discontinuous groove 8 is such that the longitudinal cross-sectional shape is substantially uniform in the depth direction shown in FIG. 7 and the width W of each single groove 8a shown in FIG. , Length L ₀
Is set to 10 mm, the depth d is set to 0.15 mm, the shortest distance L ₁ between the adjacent single grooves 8 a is set to 2 mm (= 0.2 L ₀ ), and the formation position is the distance from the outer peripheral edge of the copper plates 2 and 3. L ₂ was set to be 0.5mm.

Then, as shown in FIGS. 1 and 3,
Two copper plates 2, 3 on both sides of high thermal conductive silicon nitride substrate 1.
Are placed in direct contact with each other and
Heating and joining were performed under the conditions of 48K, thereby obtaining target silicon nitride circuit boards 4A and 4B.

The silicon nitride circuit board 4 thus obtained
A, 4B heat cycle test (TCT: 233K ×
30 minutes + RT × 10 minutes + 398 K × 30 minutes as one cycle), and the stress distribution at the time of applying the heat cycle was measured. FIG. 9 shows the result. In the comparative example (shown by a dashed line) in FIG. 9, a heat cycle was performed under the same conditions with respect to a silicon nitride circuit board manufactured under the same conditions as in Example 1 except that a copper plate 2 ′ having no groove was used. 7 shows the measurement results of the stress distribution when “” is added.

As is clear from FIG. 9, by forming the continuous groove 7 or the discontinuous groove 8 along the outer peripheral edge of the copper plates 2 and 3, the stress at the time of applying the thermal cycle is reduced.
It can be seen that the stress at the outer peripheral end is clearly reduced as compared with the comparative example having no groove. This makes it possible to prevent cracks and a decrease in strength of the silicon nitride substrate. Incidentally, the silicon nitride circuit board of Example 1 did not crack even after 100 cycles of TCT, whereas the silicon nitride circuit board of the comparative example had 25 times the silicon nitride circuit board in 100 cycles. % Cracked.

When the discontinuous groove 8 was formed by press working, no deformation or the like occurred in the copper plates 2 and 3, but similarly, the entire periphery was formed along the outer peripheral edge of the copper plate by press working. When the continuous groove 7 was formed, there was a case where deformation occurred at the center of the copper plate. In addition, even when the copper plate is small in deformation at the time of press working, deformation occurs during heating bonding with the high thermal conductive silicon nitride substrate or cooling down.

Example 2 A high thermal conductive silicon nitride substrate having a thickness of 0.6 mm according to samples 1 to 51 was prepared as the high thermal conductive silicon nitride substrate 1, and a linear discontinuity was formed inside the outer peripheral portion. The copper plates 2 and 3 having a thickness of 0.3 mm and having a predetermined shape were formed by pressing a simple groove 8 along the outer peripheral edge. The shape of the discontinuous grooves 8, the longitudinal sectional shape with a substantially uniform shape in the depth direction shown in FIG. 7, 0.5 mm width W of each single groove 8a, the length L ₀ 10 mm, depth d is set to 0.15 mm, the shortest distance L ₁ between the adjacent single grooves 8 a is set to 2 mm (= 0.2 L ₀ ), and the formation position is set to the distance L from the outer peripheral edge of the copper plates 2 and 3.
₂ was set to 0.5 mm.

Then, as shown in FIG. 4, In: Ag: Cu: Ti = 1 on both surfaces of the high thermal conductive silicon nitride substrate.
An active metal-containing brazing material having a composition of 4.0: 59.0: 23.0: 4.0 is applied as a paste, and the copper plates 2 and 3 are stacked and arranged via this coating layer. The inside was heated and joined to obtain a target silicon nitride circuit board 5B.

The silicon nitride circuit board 5 thus obtained
When a heat cycle test was performed on B under the same conditions as in Example 1, the same good results as in Example 1 were obtained.
It has been confirmed that it has excellent reliability for cooling and heating cycles.
The deformation after forming the discontinuous grooves 8 in the copper plates 2 and 3 by press working was the same as in Example 1.

Next, an embodiment of the present invention in which a plurality of holes are formed in a metal plate (copper plate) will be described.

FIG. 10 shows a copper plate 2 having a plurality of holes 9 formed therein.
The silicon nitride circuit board 4C integrally joined to the surface 1a of the high thermal conductive silicon nitride substrate 1 by a direct joining method is shown. The silicon nitride circuit board 4C has a plurality of holes 9 instead of the grooves 7.
The silicon nitride circuit board 4A shown in FIG.
This is the same configuration as.

On the other hand, FIG. 11 shows a silicon nitride circuit in which a copper plate 2 in which a plurality of holes 9 are formed is integrally joined to a surface 1 a of a high thermal conductive silicon nitride substrate 1 via an active metal-containing brazing material layer 6. It is sectional drawing which shows board | substrate 5C. This silicon nitride circuit board 5C has the same configuration as the silicon nitride circuit board 5A shown in FIG. 2 except that a plurality of holes 9 are formed instead of the grooves 7.

The silicon nitride circuit board 4 described above
In C and 5C, as shown in FIGS. 12 and 13, along the outer peripheral edge of the copper plate 2 serving as a mounting portion for a semiconductor component or the like,
That is, a plurality of holes 9 are formed inside the copper plate 2 along the outer peripheral edge of each circuit pattern portion. The cross-sectional shape of the plurality of holes 9 may be a circular shape as shown in FIG. 12 or a rectangular shape as shown in FIG. In addition, the plurality of holes 9 avoid complication of the manufacturing process,
In order to reduce the number of manufacturing steps, it is desirable to form by pressing using a mold. However, application of another formation method is not necessarily excluded.

The plurality of holes 9 are preferably formed linearly at predetermined intervals along the outer peripheral edge of each circuit pattern portion of the copper plate 2. As described above, by forming the plurality of holes 9 in a straight line, the concentration of stress on the outer peripheral end of the copper plate 2 can be efficiently reduced, in other words, the stress can be efficiently dispersed.

The size of the hole 9 depends on its cross-sectional shape and the copper plate 2.
For example, in the case of a circular shape as shown in FIG. 12, the diameter is preferably 0.1 to 1.0 mm, although it depends on the size of the hole 9 and the formation interval of the holes 9 described later. If the size of the hole 9 is less than 0.1 mm, the stress may not be sufficiently dispersed, and if it exceeds 1.0 mm, the strength of the copper plate 2 tends to decrease and the mounting area decreases. A more preferable range is 0.3 to 0.7 mm for the same reason. On the other hand, when a rectangular hole 9 as shown in FIG. 13 is used, the length of the long side is preferably set to the above-described size.

Further, a plurality of holes 9 arranged in a straight line form
When the shortest distance between the adjacent holes 9 is L ₃ and the center distance between the adjacent holes 9 is L ₄ , 1/5 L ₄ ≦ L ₃ ≦ 1 /
It is preferable to form so as to satisfy 2L ₄ . Hole 9
If the formation interval (the shortest distance L ₃ between the adjacent holes 9) is too large, specifically, if L ₃ >＞ L ₄ ,
There is a possibility that the effect of alleviating the stress may not be sufficiently obtained. On the other hand, if the interval between the holes 9 is too small, specifically, L ₃
If <1 / 5L ₄ , for example, as described above, when forming the plurality of holes 9 by press working or the like, the copper plate (metal plate) 2
There is a possibility that the decrease in strength inside the outer peripheral edge portion (hole forming portion) cannot be sufficiently suppressed. Thereby, the copper plate 2 may be deformed, and the bonding strength of the copper plate 2 may be reduced.

The plurality of holes 9 described above may be non-through holes 9A and 9B as shown in FIGS. 14 and 15, or may be through holes 9C as shown in FIG. For example, the non-through holes 9A and 9B can be easily formed by press working or the like, which is effective in reducing the number of man-hours, and the through holes 9C do not contribute to the joining when the DBC method is applied. It also functions as a discharge hole for gasified oxygen and the like, and is effective in further improving the uniformity of the joined state by preventing swelling and the like. Thus, the non-through holes 9A, 9B
And the through-hole 9C, apart from the effect of dispersing and relaxing stress,
Since they have different efficiencies, it is preferable to appropriately select them according to the joining method, application, and the like.

Here, the plurality of holes 9 are formed in the non-through holes 9A and 9B.
In this case, the shape in the depth direction may be a substantially uniform shape as shown in FIG. 14 or an inverted conical shape (or inverted pyramid shape) as shown in FIG. However,
The depth d is preferably 1/3 to 2/3 of the thickness t of the copper plate 2. If the depth of the non-through hole 9 is less than 1/3 of the thickness t of the copper plate 2, the effect of dispersing stress may be insufficient.

Further, as shown in FIG. 14, the formation position of the plurality of holes 9, that is, the shortest distance L ₅ from the outer peripheral edge of the copper plate 2 to the hole 9 varies depending on the thickness and size of the copper plate 2. It is preferably 0.3 to 1.0 mm.

In the above, the copper plate 2 bonded to the front surface 1a of the high thermal conductive silicon nitride substrate 1 serving as a mounting portion for semiconductor components and the like has been described in detail. As with the copper plate 2 on the front side, it is preferable to form a plurality of holes 9 inside the outer peripheral edge of the copper plate 3 as well. In particular, when a relatively thick copper plate (metal plate) is used from the viewpoint of heat dissipation and the like, it is preferable to form a plurality of holes 9 in the copper plate 3 on the back side. The shape, the formation interval, and the like of the plurality of holes 9 formed in the copper plate 3 on the back side conform to the plurality of holes 9 formed in the copper plate 2 on the front side.

As described above, the silicon nitride circuit board 4C,
5C, a metal plate such as a copper plate 2 or 3 having a plurality of holes 9 formed integrally with the high thermal conductive silicon nitride substrate 1 by using a direct bonding method or an active metal method in the same manner as in Examples 1 and 2. It is manufactured by bonding to

In the silicon nitride circuit boards 4C and 5C having the above-described configuration, the thermal stress generated in the cooling process after the joining of the copper plates 2 and 3 and the thermal stress due to the addition of a cooling and heating cycle and the residual stress based on the thermal stress. The stress is dispersed by the plurality of holes 9 provided inside the outer peripheral ends of the copper plates 2 and 3, and the stress concentration on the outer peripheral ends of the copper plates 2 and 3 is reduced. As a result, the stress value itself at the outer peripheral edges of the copper plates 2 and 3 is reduced, so that it is possible to effectively prevent the occurrence of cracks and a decrease in strength of the ceramic substrate portion, which have conventionally been problems.

Then, the dispersion of the stress described above is reduced to a plurality of holes 9.
Thus, the strength-reduced portions of the copper plates 2 and 3 are discontinuous along the outer peripheral edge. Therefore, even if machining such as press working is applied to the formation of the plurality of holes 9,
Since the copper plates 2 and 3 are not deformed or warped, the manufacturing process can be simplified and the number of manufacturing steps can be reduced without lowering the bonding strength of the copper plates 2 and 3.

Next, a specific example of an embodiment in which a plurality of holes are formed and evaluation results thereof will be described.

Example 3 First, the silicon nitride substrate used in Example 1 was employed as the silicon nitride substrate 1 having high thermal conductivity. That is, a high thermal conductive silicon nitride substrate having a thickness of 0.7 mm having an oxide layer having a thickness of 4 μm on the surface, and a plurality of holes 9 formed by pressing along the outer peripheral edge, tough pitch copper (containing oxygen) Quantity: 3
Copper plates 2 and 3 having a predetermined shape were prepared. The shape of the hole 9 was a circular shape (diameter = 0.6 mm, depth = 0.2 mm) shown in FIGS. The interval between the plurality of holes 9 is determined by the shortest distance L ₃ between the adjacent holes 9.
Was set to 0.25 mm (= １ ／ L ₄ ), and the forming position was such that the distance L ₅ from the copper plates 2 and 3 was 0.5 mm.

Then, as shown in FIG. 10, two copper plates 2 and 3 are placed in direct contact with each other on both surfaces of the silicon nitride substrate 1 having a high thermal conductivity, and heated at 1348 K in a nitrogen gas atmosphere. To obtain the desired silicon nitride circuit board 4C.

The silicon nitride circuit board 4 thus obtained
When a thermal cycle test was performed on C under the same conditions as in Example 1, almost the same good results as in Example 1 were obtained, and a stress distribution as shown in FIG. 9 was obtained. Note that FIG.
In the comparative example (indicated by the alternate long and short dash line), a heat cycle was performed under the same conditions on a silicon nitride circuit board prepared under the same conditions as in Example 3 except that a copper plate 2 ′ having no plurality of holes 9 was used. It is a measurement result of the stress distribution at the time of adding.

As is clear from FIG. 9, by forming a plurality of holes 9 along the outer peripheral edge of the copper plates 2 and 3, the stress at the time of applying the cooling / heating cycle is dispersed by the holes 9, and the stress at the outer peripheral edge is reduced. It can be seen that is clearly reduced as compared with the comparative example having no holes 9. This makes it possible to prevent cracks and a decrease in strength of the high thermal conductive silicon nitride substrate 1. Incidentally, the silicon nitride circuit board of Example 3 hardly cracked even after 200 cycles of TCT (cracks occurred at 1%), whereas the silicon nitride circuit board of Comparative Example had 200 cracks. Cracks occurred in 35% of the high thermal conductive silicon nitride substrate 1 during the cycle.

The copper plates 2 and 3 in which the plurality of holes 9 were formed by pressing did not warp or deform during the pressing, but similarly along the outer peripheral edge of the copper plate by pressing. In a copper plate having a groove formed on the entire circumference, there is a case where the outer peripheral edge of the copper plate is warped or deformed during press working. In addition, even in the case of a copper plate having a small deformation at the time of press working, a deformation has occurred during the heat bonding to the high thermal conductive silicon nitride substrate and the cooling.

Example 4 The silicon nitride substrate used in Example 2 was employed as the silicon nitride substrate 1 having high thermal conductivity. That is, a highly thermally conductive silicon nitride substrate having a thickness of 0.6 mm and a plurality of holes 9 along the outer peripheral edge.
Is a predetermined shape formed by pressing 0.3mm thick
Copper plates 2 and 3 were prepared. The shape of the plurality of holes 9 is shown in FIG.
2 and the through hole (0.5 mm in diameter) shown in FIG. Further, formation interval of the plurality of holes 9, the shortest distance L ₃ between the adjacent holes 9 and _{0.25mm (= 1 / 2L 4)} , also forming position, the distance from the copper plate 2 and 3 shown in FIG. 14 L ₅ was set to be 0.5mm.

As shown in FIG. 11, the weight ratio of In: Ag: C is set on both surfaces of the silicon nitride substrate 1 having high thermal conductivity.
An active metal-containing brazing material having a composition of u: Ti = 14.0: 59.0: 23.0: 4.0 was applied as a paste, and the copper plates 2 and 3 were laminated via this applied layer. rear,
Heating and bonding were performed in a nitrogen gas atmosphere to obtain a target silicon nitride circuit board 5C.

The silicon nitride circuit board 5 thus obtained
When a heat cycle test was performed on C under the same conditions as in Example 3, the same good results as in Example 3 were obtained.
It has been confirmed that it has excellent reliability for cooling and heating cycles.
The same applies to the strength after forming the plurality of holes 9 in the copper plates 2 and 3 by press working.

Further, according to the silicon nitride circuit boards 4 and 5 according to the above embodiments, in addition to the high strength and toughness characteristics inherently possessed by the silicon nitride sintered body, the high heat A conductive silicon nitride substrate 1 is used. Therefore, heat generated from a heat-generating component such as a semiconductor element mounted on the substrate is quickly transmitted to the outside of the system through the silicon nitride substrate 1 having high thermal conductivity, so that heat dissipation is extremely good.

Further, since the high thermal conductivity silicon nitride substrate 1 having high strength and high toughness is used, a large amount of maximum deflection of the circuit board can be ensured. For this reason, the circuit board does not suffer from tightening cracks in the assembly process, and it is possible to mass-produce semiconductor devices using the circuit board at a high production yield and at low cost.

Further, since the high thermal conductivity silicon nitride substrate 1 has a high toughness value, cracks are less likely to occur at the junction between the substrate 1 and the metal circuit board or the metal plates 2 and 3 due to thermal cycling. Is significantly improved, and a semiconductor device excellent in durability and reliability can be provided.

Since the silicon nitride substrate 1 having a higher thermal conductivity is used, even when a semiconductor element for higher output and higher integration is mounted, the deterioration of the thermal resistance characteristics is small, and excellent. Demonstrate heat dissipation.

In particular, since the mechanical strength of the silicon nitride substrate itself is excellent, when the required mechanical strength characteristics are fixed, the thickness of the substrate is larger than that when other ceramic substrates are used. It becomes possible to reduce. Since the substrate thickness can be reduced, the thermal resistance value can be further reduced,
The heat radiation characteristics can be further improved. In addition, since the required mechanical characteristics can be sufficiently coped with even a thinner substrate than before, the substrate manufacturing cost can be further reduced.

[0130]

As described above, according to the silicon nitride circuit board of the present invention, even when a thermal cycle is applied, the thermal stress and the residual stress generated in the metal plate can be reduced by the continuous groove and the non-continuous groove. By dispersing through continuous grooves or multiple holes, stress concentration on the outer peripheral edge of the metal plate can be reduced, and deformation of the metal plate can be prevented by machining that is advantageous in the manufacturing process. Can be. Therefore,
After simplifying the manufacturing process and reducing the number of manufacturing steps,
It is possible to effectively prevent the occurrence of cracks and a decrease in the strength of the ceramic substrate portion due to the addition of a cooling / heating cycle, and to provide a silicon nitride circuit board excellent in reliability and manufacturability.

In particular, according to the silicon nitride circuit board of the present invention, in addition to the high strength and toughness characteristics inherently possessed by the silicon nitride sintered body, in particular, the high thermal conductive silicon nitride having significantly improved thermal conductivity. Since the elementary substrate is used, heat generated from a heat-generating component such as a semiconductor element mounted on the substrate is quickly transmitted to the outside of the system via the high thermal conductivity silicon nitride substrate, so that heat dissipation is extremely good. In addition, since a silicon nitride substrate having high strength and toughness is used, a large amount of maximum deflection of the circuit board can be secured. For this reason, the circuit board does not suffer from tightening cracks in the assembly process, and it is possible to mass-produce semiconductor devices using the circuit board at a high production yield and at low cost.

[Brief description of the drawings]

FIG. 1 is a view showing a structure of a silicon nitride circuit board according to one embodiment of the present invention, wherein (a) is a plan view and (b) is a sectional view thereof.

FIG. 2 is a sectional view showing a structure of a silicon nitride circuit board according to another embodiment of the present invention.

3A and 3B are diagrams showing a structure of a silicon nitride circuit board according to another embodiment of the present invention, wherein FIG. 3A is a plan view and FIG. 3B is a cross-sectional view thereof.

FIG. 4 is a sectional view showing a structure of a silicon nitride circuit board according to another embodiment of the present invention.

FIG. 5 is a plan view showing one example of a shape of a discontinuous groove in the present invention.

FIG. 6 is a plan view showing positions where grooves or holes are formed in the present invention.

FIG. 7 is a view showing an example of a longitudinal sectional shape of a groove in the present invention.

FIG. 8 is a view showing another example of the longitudinal sectional shape of the groove in the present invention.

FIG. 9 is a diagram showing a measurement result of a stress distribution near an end of a copper plate when a thermal cycle is applied to a silicon nitride circuit board according to an embodiment of the present invention, in comparison with a conventional example.

10A and 10B are diagrams showing a structure of a silicon nitride circuit board according to one embodiment in which a plurality of holes are formed, wherein FIG.
(B) is a sectional view thereof.

FIG. 11 is a sectional view showing a structure of a silicon nitride circuit board according to another embodiment in which a plurality of holes are formed.

FIG. 12 is a plan view showing an example of a shape of a plurality of holes and a preferable forming interval in the present invention.

FIG. 13 is a plan view showing another example of the shape of a plurality of holes in the present invention.

FIG. 14 is a sectional view showing an example of a longitudinal sectional shape of a plurality of holes in the present invention.

FIG. 15 is a cross-sectional view showing another example of a vertical cross-sectional shape of a plurality of holes according to the present invention.

FIG. 16 is a sectional view showing still another example of the longitudinal sectional shape of a plurality of holes according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 High thermal conductive silicon nitride substrate 1a Surface of high thermal conductive silicon nitride substrate 1b Back surface of high thermal conductive silicon nitride substrate 2,2 ', 3 Copper plate (metal plate) 4,5,4A, 5A, 4B, 5B , 4C, 5C Silicon nitride circuit board 6 Active metal-containing brazing material layer 7 Continuous groove 8 Discontinuous groove 8a Single groove 9 Multiple holes 9A, 9B Non-through hole 9C Through hole

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takayuki Nami 2-4, Suehirocho, Tsurumi-ku, Yokohama-shi, Kanagawa Prefecture Inside Keihin Plant, Toshiba Corporation (72) Inventor, Toshun Sato 8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Toshiba Corporation Yokohama Office (56) References JP-A-4-343287 (JP, A) JP-A-3-145748 (JP, A) JP-A-6-152078 (JP, A) JP-A-6-135771 (JP, A) JP-A-7-48174 (JP, A) JP-A-7-187793 (JP, A) JP-A-5-41566 (JP, A) JP-A 8-250823 (JP, A) Kaihei 5-167205 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 23/12 C04B 35/584 H01L 23/373

Claims (18)

(57) [Claims] 1. The method according to claim 1, wherein the conversion of the rare earth element to oxide is 1.0 to 1.0.
17.5% by weight, Li, N as impurity cation element
Contains a, K, Fe, Ca, Mg, Sr, Ba, Mn, and B in total of 1.0% by weight or less (including 0% by weight as a detection limit), and has a thermal conductivity of 60 w / mk or more. A high thermal conductive silicon nitride substrate, and a metal plate bonded to the high thermal conductive silicon nitride substrate, wherein the high thermal conductive silicon nitride substrate of the metal plate A groove is formed on the inside of the outer peripheral edge on the side opposite to the bonding surface, and it is necessary to ensure that no cracks occur in the silicon nitride substrate when a thermal cycle test is performed on the silicon nitride circuit board for 100 cycles. Characteristic silicon nitride circuit board. 2. The high thermal conductive silicon nitride substrate is composed of Li, Na, K, Fe, Ca, M as impurity cation elements.
2. The silicon nitride circuit board according to claim 1, wherein g, Sr, Ba, Mn, and B are contained in a total of 0.3% by weight or less (including 0% as a detection limit). 3. The method according to claim 1, wherein the conversion of the rare earth element to oxide is 1.0 to 1.0.
17.5% by weight, composed of a silicon nitride crystal phase and a grain boundary phase, wherein the ratio of the crystalline compound phase in the grain boundary phase to the entire grain boundary phase is 20% or more, and the thermal conductivity is 60 W / m · k or more, and a silicon nitride circuit board comprising a metal plate bonded to the high thermal conductivity silicon nitride substrate, wherein the high thermal conductivity silicon nitride A groove is formed inside the outer peripheral edge on the side opposite to the bonding surface with the silicon substrate, and cracks are formed in the silicon nitride substrate when 100 cycles of the thermal cycle test are performed on the silicon nitride circuit board. A silicon nitride circuit board characterized by not generating. 4. The high thermal conductive silicon nitride substrate is composed of a silicon nitride crystal phase 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.
5% or more. 5. The silicon nitride circuit board according to claim 1, wherein said groove is formed linearly along an outer peripheral edge of said metal plate. 6. The silicon nitride circuit board according to claim 1, wherein said groove is a groove formed by press working. 7. The silicon nitride circuit board according to claim 1, wherein the width of the groove is in the range of 0.2 to 1.0 mm. 8. The silicon nitride circuit board according to claim 3, wherein said grooves are formed discontinuously. 9. The silicon nitride circuit board according to claim 8, wherein said discontinuous groove is formed linearly along an outer peripheral edge of said metal plate. 10. The silicon nitride circuit board according to claim 8, wherein said discontinuous groove is a groove formed by press working. 11. The discontinuous groove has a width of 0.1 to 1.0 mm.
9. The silicon nitride circuit board according to claim 8, wherein: 12. When the length of the discontinuous groove is L ₀ , and the shortest distance between adjacent discontinuous grooves is L ₁ ,
9. The silicon nitride circuit board according to claim 8, wherein 10L ₀ ≤L ₁ ≤1 / 2L ₀ is satisfied. 13. Conversion of rare earth elements to oxides is 1.0
-17.5% by weight, comprising a silicon nitride crystal phase and a grain boundary phase, wherein the ratio of the crystalline compound phase to the entire grain boundary phase in the grain boundary phase is 20% or more, and the thermal conductivity is 60 W / M · k or more, a silicon nitride circuit board comprising: a high thermal conductive silicon nitride substrate; and a metal plate bonded to the high thermal conductive silicon nitride substrate. A plurality of holes are formed inside the outer peripheral edge on the side opposite to the bonding surface with the silicon substrate, and a thermal cycle test is performed on this silicon nitride circuit board.
A silicon nitride circuit board, wherein cracks do not occur in the silicon nitride board when the cycle is performed. 14. The silicon nitride circuit board according to claim 13, wherein the plurality of holes are formed linearly at predetermined intervals along an outer peripheral edge of the metal plate. 15. The silicon nitride circuit board according to claim 13, wherein the plurality of holes are non-through holes. 16. The silicon nitride circuit board according to claim 13, wherein said plurality of holes are through holes. 17. The silicon nitride circuit board according to claim 13, wherein said plurality of holes are holes formed by press working. 18. The shortest distance between adjacent holes is L ₃ ,
When the distance between the centers of adjacent holes was _{L 4,} 1 / 5L ₄
≦ L ₃ ≦ 1 / 2L ₄ silicon nitride circuit board according to claim 13, characterized by satisfying the.