JPH09157054A - Circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silicon nitride-based circuit board which is excellent in both of thermal conductivity and strength and is excellent in productivity without requiring a special sintering operation. SOLUTION: This circuit board is formed by disposing a metallic circuit board via a joint layer on a silicon nitride sintered compact. This silicon nitride sintered compact contains an Ma component and/or Ca component at <=7.0wt.% in total in terms of oxide. More particularly, the number of the grain boundaries observed at the polished surface of the silicon nitride sintered compact is <=10 pieces per 10μm length of the straight line drawn in an arbitrary direction on the polished surface. Further, the Al of the impurities included in the silicon nitride sintered compact is <=0.25wt.% in terms of metal and F is <=0.3wt.% in terms of metal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit board having a structure in which a silicon nitride sintered body and a metal circuit board are integrally bonded via a bonding layer, and particularly a semiconductor module requiring high reliability and heat dissipation. A circuit board suitable for use.

[0002]

2. Description of the Related Art Conventionally, alumina (Al2 O3), aluminum nitride (Al
N), beryllium oxide (BeO), and other ceramics sintered body substrates in which a copper (Cu) circuit board as a conductive layer is integrally joined to the surface of the ceramics sintered body substrate are widely used.

In these ceramics circuit boards, the circuit board is made of a metal such as copper having excellent thermal conductivity and electrical conductivity, so that the delay of the circuit operation is reduced and the life of the circuit wiring is improved. , Wettability to a bonding material such as solder is improved, and a semiconductor element (IC chip) or an electrode plate can be bonded to the surface of the ceramic sintered body with high bonding strength. As a result, heat dissipation from the semiconductor element is dissipated. And the operation reliability of the element can be kept good, and stress relaxation and warpage (thermal deformation) of the ceramic substrate can be achieved by bonding a metal plate such as copper to the back surface of the ceramic substrate.
It has the advantage that the preventive purpose can also be achieved.

However, among the above-mentioned ceramic circuit boards, the circuit board using an Al2 O3 board is
Since the thermal conductivity of l2 O3 is low, good heat dissipation cannot be obtained, and there has been a problem that it is not possible to sufficiently cope with heat dissipation measures associated with high-density integration and high output of semiconductor elements. Also, Be
Regarding the circuit board using the O substrate, BeO is the material having the highest heat conductivity and excellent heat dissipation property among the oxide-based ceramics, but due to its toxicity, there are many difficulties in manufacturing and handling.

A circuit board using an AlN substrate has a high thermal conductivity and a sufficient heat dissipation property, but since the AlN substrate itself has a low strength, cracks occur due to repeated thermal loads in actual use. However, there is a problem that the so-called heat resistance cycle is small, and as a result, the metal circuit board is peeled off from the AlN board due to repeated heat loads during use, the heat dissipation is sharply reduced, or cracks occur and the withstand voltage is increased. There is a problem that the operation reliability of the electronic device is deteriorated such as deterioration of characteristics. In addition, the circuit board using the AlN substrate requires A in order to secure its structural strength to some extent.
It is necessary to set the thickness of the 1N substrate to be large, which is an obstacle to high-density mounting, and the circuit board is difficult to bend due to the large thickness of the AlN substrate. In addition, there is a problem that the AlN substrate is easily cracked by the bending stress acting on the AlN substrate.

For the purpose of solving these problems, a ceramics copper circuit board using a high thermal conductivity silicon nitride sintered body has been proposed. That is, a predetermined amount of rare earth element oxide,
By using a sintering aid to which aluminum nitride and / or alumina is added, the grain boundary phase is changed by a special sintering condition that the cooling rate up to the temperature at which the liquid phase solidifies during sintering is gradually cooled at 100 ° C. or less per hour. By setting the area ratio of the crystal compound phase in the entire grain boundary phase to 20% or more, the thermal conductivity is 60 W / (m
-K) or more of the high thermal conductivity silicon nitride sintered body can be obtained (see Japanese Patent Laid-Open No. 6-135771).
Further, in Japanese Unexamined Patent Publication (Kokai) No. 6-216481, a ceramics copper circuit board in which the high thermal conductivity silicon nitride sintered body and a copper circuit board on which a circuit is formed in advance are integrally bonded using a bonding material containing an active metal. Discloses that it has excellent heat dissipation, heat cycle resistance and bonding strength, and is suitable as a component for a semiconductor power module.

[0007]

However, Japanese Patent Application Laid-Open No.
Since the silicon nitride sintered body disclosed in Japanese Patent No. 357771 requires a special operation called gradual cooling during its production,
It has the disadvantage of low productivity. Further, regarding circuit boards, further improvement in bonding strength and thermal cycle resistance is required, and high thermal shock resistance is required in order to withstand heat treatment such as soldering when manufacturing modules from circuit boards. Is desired. The present invention has been made in order to solve the above problems, and can be manufactured under normal sintering conditions and is excellent in productivity, and moreover, due to the presence of specific components in the silicon nitride sintered body, the bonding strength and the heat resistance cycle It is an object of the present invention to provide a circuit board suitable as a semiconductor module component that is excellent in heat resistance and thermal shock resistance.

[0008]

In order to achieve the above object, the inventors of the present invention have investigated various sintering aids for producing a silicon nitride sintered body and have an activity on the silicon nitride sintered body. Various circuit boards are made by joining metal circuit boards such as copper using a brazing material containing a metal component, and their heat dissipation, bonding strength of the metal circuit board to the silicon nitride sintered body,
Thermal cycle resistance, thermal shock resistance, and flexure amount were compared and examined. As a result, a circuit board having a structure in which a silicon nitride sintered body containing 7% by weight or less of Mg component and / or Ca component and a metal circuit board are bonded via a bonding layer has a bonding strength, heat cycle resistance, The present invention has been completed by discovering that it has excellent thermal shock resistance and heat dissipation.

The present invention is a circuit board in which a metal circuit board is arranged on a silicon nitride sintered body with a bonding layer interposed therebetween, wherein the silicon nitride sintered body contains Mg component and / or Ca component. A circuit board characterized by containing a total amount of 7.0% by weight or less in terms of oxide, and in particular, the number of grain boundaries observed on the polished surface of the silicon nitride sintered body was drawn in an arbitrary direction. The number of straight lines is 10 or less per 10 μm, and further,
Regarding impurities contained in the silicon nitride sintered body, Al
Is 0.25 wt% or less in terms of metal, and Fe is 0.3 wt% or less in terms of metal.

Further, according to the present invention, the silicon nitride sintered body has a three-point bending strength of 600 MPa or more at room temperature and a thermal conductivity of 6 or more.
The circuit board is characterized in that it is 0 W / (m · K) or more.

Further, the present invention is the above-mentioned circuit board, wherein the metal circuit board is copper having an oxygen content of 50 ppm or less, wherein the active metal component and the silicon nitride sintered body are contained in the bonding layer. Including the reaction layer with, the thickness of the reaction layer is 2μ
It is a circuit board characterized by being m or less.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION First, a silicon nitride sintered body used for a circuit board according to the present invention will be described below. The silicon nitride sintered body used for the circuit board needs to have high thermal conductivity, high strength, and low porosity, but since silicon nitride has a high melting point and a high decomposition pressure, it is possible to sinter rare earth element oxides. Various measures have been taken, such as using it as an auxiliary agent and sintering it in a high-pressure nitrogen atmosphere. The inventors of the present invention have made it possible to use oxides of Mg and / or Ca components or their precursors as sintering aids, limit impurities more than ever, and control sintering conditions in detail. Based on the finding that a silicon nitride sintered body that is excellent in both thermal conductivity and strength and that is optimal for circuit boards can be easily obtained with high productivity,
This has led to the present invention.

In the present invention, the silicon nitride sintered body contains a Mg component and / or a Ca component. As a sintering aid for a silicon nitride sintered body, oxides of rare earth elements, alumina, and the like have been conventionally known, but according to the studies by the present inventors,
With the rare earth element oxides and alumina, the thermal conductivity of the silicon nitride sintered body obtained under normal sintering conditions is low and unsatisfactory, and when a silicon nitride sintered body having excellent thermal conductivity is obtained, it is sintered. It requires a high temperature and a long time, resulting in reduced productivity. On the other hand, when the Mg component and / or the Ca component of the present invention is used as a sintering aid, a silicon nitride sintered body having both excellent thermal conductivity and strength is relatively easily prepared at a relatively low temperature. It can be obtained with time sintering, and thus with high productivity. This effect can be obtained by using each of the Mg component or the Ca component alone, or can be similarly obtained by using both of them in combination.

The silicon nitride sintered body of the present invention contains the Mg component and / or the Ca component in a total amount of 7.0% by weight or less in terms of their oxides. The reason for this is that if it exceeds 7.0% by weight, the joining characteristics with the metal circuit board may not be sufficient when a circuit board is to be obtained. The lower limit value is not particularly limited, but if it is too small, the above effect as a sintering aid is insufficient, so about 0.5% by weight is preferable. In particular, when the total amount is 2.0% by weight or more and 5.0% by weight or less, the effect as a sintering aid is sufficiently exhibited, and the obtained silicon nitride sintered body is bonded to the metal circuit board. The characteristics are excellent and more preferable.

In the present invention, if the requirement that the Mg component and / or the Ca component is contained in an amount of 7% by weight or less in terms of their oxides is satisfied, it is used for usual sintering of silicon nitride except for the impurities described later. It can contain rare earth elements and other elements. For example, as rare earth elements, Y, L
a, Sc, Pr, Ce, Nd, Sm, Dy, Gd, etc., and other elements include, for example, Zr, T
i, Hf and the like.

Further, in the present invention, the number of grain boundaries observed on the polished surface of the silicon nitride sintered body has a structure of 10 or less per 10 μm of a straight line drawn in an arbitrary direction. To do. Since the silicon nitride sintered body having the above structure (microstructure) has excellent thermal conductivity, a circuit board excellent in heat dissipation can be easily obtained. Further, although the reason is unknown, the silicon nitride sintered body having the above-mentioned microstructure is preferable because it is excellent in bondability with a metal circuit board. Here, the polishing surface and the straight line drawn on the polishing surface may be selected in any manner.

Further, with respect to impurities contained in the silicon nitride sintered body, Al is 0.25% by weight or less in terms of metal and Fe is 0.3% by weight or less in terms of metal. Especially Al
Is preferably 0.15 wt% or less in terms of metal, and Fe is 0.2 wt% or less in terms of metal. The reason for this is not clear, but the present inventors have experimentally found a silicon nitride sintered body containing a Mg component and / or a Ca component. When the abundances of Al and Fe increase, silicon nitride firing is correspondingly performed. A silicon nitride sintered body having a high thermal conductivity is obtained when the thermal conductivity of the bonded body becomes small and Al is 0.25 wt% or less in terms of metal and Fe is 0.3 wt% or less in terms of metal. It is something that was discovered. The thermal conductivity of the silicon nitride sintered body is 40 W / (m · K) or more when Al is limited to 0.25 wt% or less in terms of metal and Fe is 0.3 wt% or less in terms of metal. It is possible to easily and stably obtain a silicon nitride sintered body having a thermal conductivity of, and further, Al is 0.15 wt% or less in terms of metal and Fe is 0.2 wt% or less in terms of metal. When limited to, a silicon nitride sintered body having a thermal conductivity of 50 W / (m · K) or more can be obtained. Further, in addition to limiting the above impurities, the silicon nitride sintered body having the above-mentioned microstructure has an excellent thermal conductivity of 60 W / (m · K) or more, and is therefore particularly preferable.

As the impurities that affect the thermal conductivity, the above-mentioned Al and Fe can be mentioned. In addition to the above, alkali metals such as Na and K are used when the obtained silicon nitride sintered body is used as a circuit board. Since it deteriorates the optical characteristics, Li, B
Since e, Mn, Ga, etc. also lower the thermal conductivity of the sintered body, they are not preferable. It is sufficient that the content of these impurity elements in the silicon nitride sintered body is suppressed to 0.3% by weight or less, preferably 0.2% by weight or less in total.

The silicon nitride sintered body of the present invention preferably has a three-point bending strength of 600 MPa or more at room temperature and a thermal conductivity of 60 W / (m · K) or more.
If the three-point bending strength at room temperature is 600 MPa or more, it can withstand the temperature changes and mechanical shocks that are repeatedly received in actual use, and has a thermal conductivity of 60 W / (mK).
If it is above, even if it mounts the semiconductor element which has comparatively large operating power, it has the advantage that it can be used reliably over a long period of time.

Next, a method for obtaining the above-mentioned silicon nitride sintered body will be described as an example. As the raw material silicon nitride powder,
Conventionally known silicon nitride powders for structural materials can be used, but in view of sinterability, strength and thermal conductivity of the obtained sintered body, Al and Fe, and further the aforementioned N
Alkali metals such as a and K and those containing a small amount of impurities such as Li, Be, Mn, and Ga are selected. That is, when it is made into a sintered body, it contains Al in an amount of 0.25% by weight or less, more preferably 0.15% by weight or less in terms of metal, and Fe is 0.3% by weight or less in terms of metal, more preferably 0%. .2
A silicon nitride powder having a purity of not more than wt% is selected. The total content of impurity elements such as Li, Be, Na, K, Mn, and Ga is 0.3% by weight or less,
It is desirable that the content be suppressed to 0.2% by weight or less.

Further, the oxygen content in the commercially available silicon nitride raw material powder for structural materials is generally 0.5 to 2.5% by weight.
In the present invention, a silicon nitride powder having the above oxygen content can be used without any problems, and the use of silicon nitride powder outside the above oxygen content range is restricted in the present invention. not.

Regarding the mineral phase of the raw material silicon nitride powder, it is generally preferable that the α phase ratio is high because it tends to be densified and a high-density sintered body is likely to be obtained, but the sintered body obtained in the present invention is preferable. The number of grain boundaries observed on the polished surface is not particularly limited as long as a structure is obtained in which the number of grain boundaries is 10 or less per 10 μm of a straight line drawn in an arbitrary direction.

The average particle size of the raw material silicon nitride powder is 3.0 μm or less, preferably 1.5 μm or less, and more preferably, because the sintered body has a high sinterability and a dense and high-strength sintered body is easily obtained. A fine one with a size of 0.8 μm or less is preferable. still,
The presence of coarse particles of 50 μm or more in the particle size distribution of the powder causes a decrease in strength, which is not preferable.
A particle size of less than is desirable.

In the present invention, the silicon nitride sintered body obtained by sintering the silicon nitride powder contains 7% by weight or less of Mg component and / or Ca component in terms of oxides thereof. Mg and / or Ca in the silicon nitride powder
These oxides or the precursors to be these oxides can be added alone or in combination of two or more by the sintering operation. When only the oxides of Mg and Ca are blended in the silicon nitride powder, they react with silica (SiO2) contained in the silicon nitride powder to form an auxiliary phase. Therefore, as another compounding form, forsterite (Mg2Si
O4) or steatite (MgSiO3) can also be selected. The blending amount of these is set so that the components of Mg and Ca in the obtained silicon nitride sintered body fall within the above range in terms of oxide. When the oxides of Mg and / or Ca or the precursors to form these oxides are mixed in a powder form, a powder having a small particle size and easily dispersed when mixed with a silicon nitride powder is preferable.

Further, Y, La, Sc, Pr, Ce, N
An oxide of a rare earth element such as d, Sm, Dy, Ho, Gd or a substance that becomes an oxide of these by a sintering operation may be contained alone or in combination of two or more. In particular yttrium oxide (Y2 O3) and cerium oxide (CeO2)
Is preferable because it reacts with the silicon nitride raw material powder in the sintering operation to generate a liquid phase and functions as a sintering accelerator. However, the content of the oxide of the rare earth element in the silicon nitride sintered body is preferably 15% by weight or less in terms of oxide. This is because if the amount exceeds 15% by weight, an excessive amount of grain boundary phase is generated, and the thermal conductivity and strength are rather reduced.

Mg and / or Ca is added to the silicon nitride powder.
Oxide, or a predetermined amount of the precursor that becomes the above oxide, and if necessary, the oxide of the rare earth element is added, and if necessary, an organic binder or the like is added and mixed to form a raw material mixture. After obtained, the raw material mixture is molded to obtain a compact having a predetermined shape and further sintered, whereby the silicon nitride sintered body can be obtained.

As a molding method of the raw material mixture, a general molding method such as a die pressing method, a sheet molding method such as a doctor blade method or an extrusion molding method may be used. Also,
Regarding the sintering operation, first, the molded body is heated to a temperature of 300 to 800.
The organic binder component added in advance is sufficiently removed and degreased by heating at ℃, but the atmosphere at this time varies depending on the type of binder, etc., and it is an oxidizing atmosphere such as air or nitrogen, argon, hydrogen, carbon dioxide gas. , Non-oxidizing atmospheres such as hydrocarbons and vacuum are applied. Next, the degreased compact is generally subjected to atmospheric pressure sintering at a temperature of 1600 to 2000 ° C. for a predetermined time in an atmosphere of an inert gas such as nitrogen gas or argon gas. The sintering temperature varies depending on the characteristics of the silicon nitride raw material powder used, the type and blending amount of the auxiliaries, and the desired structure of the silicon nitride sintered body. When binding, a sintering temperature of about 1600 to 1800 ° C. is preferable.

The silicon nitride sintered body obtained by the above operation can be subjected to mechanical processing and surface polishing, if necessary, and can be provided for a circuit board. Regarding the circuit board application, the thickness of the sintered body is practically 0.1 to 1.0 mm, but it can be used even if it is out of this range.

As the material of the metal circuit board used in the present invention, it is common to use copper such as oxygen-free copper, tough pitch copper and copper phosphate, but other metals such as tungsten, molybdenum, iron and nickel. Any of high melting point metals such as cobalt and cobalt, and alloys thereof can be used.
The metal circuit board may be one in which a circuit is formed in advance, or may be a simple flat plate on which a circuit is formed by post-treatment, and the material of the metal circuit boards on both sides of the silicon nitride sintered body is the same. It need not be limited to. Among the copper, oxygen-free copper having an oxygen content of 50 ppm or less has a high electric conductivity in the portion where the circuit is formed in the metal circuit board,
Moreover, the bonding strength with the silicon nitride sintered body is high, which is preferable.

The thickness of the metal circuit board is appropriately selected according to the required function. For example, when the purpose is to form a circuit, the current flowing through the circuit and the metal circuit board are mounted. 0.2 to 0.5 mm or more is selected according to the amount of heat generated by the semiconductor component, and the warpage caused by the difference in thermal expansion between the metal circuit board and the silicon nitride sintered body is eliminated. 0.1 to 1.0 mm for prevention purposes
It is common for the degree to be selected. However, it is not limited to these. A circuit board has a structure in which a metal circuit board on which a circuit is formed is arranged only on one surface of a silicon nitride sintered body, and the other surface is covered with a flat metal circuit board (heat dissipation metal plate). In general, it is also possible to adopt a structure in which a circuit-formed metal circuit board is arranged only on one surface of the silicon nitride sintered body and no metal circuit board is arranged on the other surface.

The circuit board of the present invention can be obtained by using the above-mentioned silicon nitride sintered body and the above-mentioned metal circuit board, and further joining them using a brazing material containing an active metal component. Here, the brazing filler metal containing the active metal component is melted in the joining operation, and a part thereof reacts with the surface of the silicon nitride sintered body and the surface of the metal circuit board to form a joining layer. However, in detail, this bonding layer is formed on the surface of the silicon nitride sintered body where the reaction layer of the silicon nitride sintered body and the active metal component in the brazing material containing the active metal component contacts the brazing material. Has been formed. For example, when a copper circuit board and a silicon nitride sintered body are joined using a brazing material containing copper and silver having Ti as an active metal component, the joining layer has a copper layer on the side of the joining layer in contact with the copper circuit board. An alloy layer containing silver as a main component and a reaction layer containing titanium nitride as a main component are formed on the side of the bonding layer that contacts the silicon nitride sintered body. The reaction layer can be easily identified because the emissivity of the secondary electrons is different from that of other portions in the observation with the scanning secondary electron microscope.

The circuit board of the present invention is characterized in that the above-mentioned reaction layer has a thickness of 2 μm or less. We have:
When the thickness of the reaction layer exceeds 2 μm, the bonding strength between the silicon nitride sintered body and the metal circuit board and the circuit board characteristics,
In particular, the thermal cycle resistance and the thermal shock resistance may decrease, and it is experimentally found that it is preferable that the thickness of the reaction layer is 2 μm or less, because the characteristics are not deteriorated. In particular, when the thickness of the reaction layer is 1 μm or less, the above effect is remarkable, which is preferable. On the other hand, when the thickness of the reaction layer is further reduced, the reaction layer cannot evenly exist on the surface of the silicon nitride sintered body, and the above effect cannot be obtained. According to the study by the present inventors, the lower limit is 0.
It is about 05 μm.

A method of obtaining the circuit board of the present invention will be described below with reference to an example. That is, an acrylic resin binder, terpineol and oleic acid are added to a powder or a powder mixture having a composition corresponding to a brazing material containing an active metal component to prepare a bonding material paste, and the bonding material paste is subjected to a screen printing method or the like. The surface of the silicon nitride sintered body is printed with a predetermined pattern. Next, a metal circuit board is arranged along the print pattern, and a weight is placed on the metal circuit board to press-bond the metal circuit board. The metal circuit boards are stacked and housed in a heating furnace, and heated in a vacuum at a temperature of 700 to 950 ° C. for 5 to 30 minutes to perform a bonding process. A circuit board having a reaction layer having a desired thickness can be obtained by adjusting the content of the active metal component in the brazing material containing the active metal component, the heating temperature, and the heating time.

When the circuit of the metal circuit board is formed after the bonding, the bonding material paste is applied to the entire surface of both surfaces of the silicon nitride sintered body, and then the metal circuit of a size that covers the entire surface where the circuit is not formed. Plates are placed on both sides of the silicon nitride sintered body and bonded under the above conditions. An etching resist is printed on the bonded metal circuit board in a desired circuit pattern, and then the metal circuit board is etched and removed to form a circuit.

The active metal component in the brazing filler metal containing the active metal component of the present invention refers to a metal component such as Ti, Zr, Hf, Nb, Ta having a high reactivity with the silicon nitride sintered body, and particularly, Ti is excellent in the bonding strength between the silicon nitride sintered body and the metal plate. These active metal components are generally added as powder in the bonding material paste in the form of metals and their compounds or alloys. It can also be used by being arranged between silicon sintered bodies, and examples of the compound or alloy containing the active metal component include titanium hydride, Ti-Ag alloy, Ti-.
Cu alloy, Ti-Al alloy, etc. are mentioned.

As the metal component other than the active metal component contained in the active metal component-containing brazing material, the silver component is effective when the metal circuit plate is copper, although it depends on the material of the metal circuit plate to be joined. Is. The silver component is an important component because it mainly reacts with the copper component to form a low melting point compound, promotes melting of the active metal bonding material, and plays a role of wetting the bonding surface. When the metal circuit board is copper or a copper alloy, the copper component is supplied from the metal plate into the active metal bonding material, and the same effect as when the copper is contained in the active metal bonding material paste in advance is obtained. can get.

The present invention will be described in more detail with reference to examples.

[0038]

【Example】

(Silicon Nitride Sintered Body of Example 1) Oxygen Content 1.5% by Weight
90% by weight of silicon nitride powder having an average particle size of 0.8 μm, 3% by weight of MgO powder having an average particle size of 1.0 μm, and an average particle size of 0.8
7% by weight of Y2O3 powder of μm was added, and the above powder 1 was added.
9 parts by weight of polyvinyl butyral, 4 parts by weight of butyl furarate, 1 part by weight of glycerin trioleate, 45 parts by weight of toluene, and 1 part by weight of isopropyl alcohol with respect to 00 parts by weight.
5 parts by weight were added and mixed using a ball mill. next,
The slurry obtained by the above operation is subjected to defoaming treatment to reduce the viscosity to 20.
After adjusting to 000 cps, it was formed into a sheet by the doctor blade method. Furthermore, 30m from the obtained sheet
A m × 80 mm plate was punched out, degreased in air at 500 ° C., and then sintered at 1800 ° C. for 6 hours under a nitrogen gas pressure of 0.9 MPa. The sintered body obtained by this operation had a thickness of 0.6 mm.

Regarding the sintered body, a part of the chemical composition was confirmed by ICP analysis, and a part of the sintered body was subjected to alkali etching after polishing the surface to observe a microstructure. Bending strength and thermal conductivity were measured.
The results are shown in Table 1. The results of Al and Fe as impurities are shown, but other than these, Li, Be, Na, K, M
Impurities such as n and Ga were all below the detection limit. Further, the number of grain boundaries of the silicon nitride sintered body is measured by alkali-etching an arbitrary polished surface of the silicon nitride sintered body so that the grain boundaries can be identified, and then a scanning electron microscope (SEM) is used.
The number of grain boundaries on an arbitrary straight line having a total length of 500 μm was measured by and calculated as the number of grain boundaries per straight line length of 10 μm. The thermal conductivity of the sample cut into a shape of 25 mm × 25 mm was measured by the laser flash method at room temperature. The three-point bending strength was measured with a span of 30 mm for a silicon nitride sintered body having a width of 25 mm, and other conditions were in accordance with JIS-R1601.

(Silicon Nitride Sintered Products of Examples 2 to 18 and Comparative Example 1) In the method of Example 1, silicon nitride powder was used with an oxygen content of 0.8 to 2.1% by weight and an average particle size of 0.6. ~ 2.6
Various silicon nitride powders with a particle size of 0.8
~ 2.0μm various sintering aid powder, organic binder (polyvinyl butyral, etc.), organic plasticizer and additives (butyl phthalate, glycerin trioleate, etc.) and organic solvent (toluene, isopropyl alcohol, etc.) After obtaining various slurries by adjusting appropriately, each was subjected to defoaming treatment to adjust the viscosity and formed into a sheet by the doctor blade method. After degreasing the various sheets obtained at 400-600 ° C,
1750 to 1900 at nitrogen gas pressure of 0.1 to 0.9 MPa
It was made into Examples 2-15 and Comparative Examples 1-5 by sintering at 6 degreeC. The obtained silicon nitride sintered body has a thickness of 0.3.
.About.0.6 mm, and their characteristics are shown in Table 1.

(Circuit boards of Examples 1 to 18 and Comparative Example 1) Silver (Ag) powder, titanium hydride (TiH2) powder,
A predetermined amount of an acrylic resin-based binder and oleic acid were added, and terepineol was added to the mixture, which was then mixed with a liquor machine and kneaded with a three-roll mill to prepare a bonding material paste. Copper circuit boards were bonded to the silicon nitride sintered bodies of Examples 1 to 15 and Comparative Examples 1 to 5 by using the above bonding material paste by the following operation. First, the bonding material paste is screen-printed on the surface of each silicon nitride sintered body, and a circuit having a thickness of 0.3 is formed in advance in the same shape as the printed pattern.
A mm copper circuit board was placed. Further, the bonding material paste is screen-printed on almost the entire back surface to a thickness of 0.25 m.
The copper circuit board on which the circuit of m is not formed is arranged, and the whole is housed in the heating furnace with the weight placed with the copper circuit board having the thickness of 0.3 mm facing upward. Then, a circuit board was manufactured by heating and bonding at a temperature of 820 ° C. for 30 minutes in a vacuum better than 10 −4 Torr. The weight ratio of TiH2 to Ag in the bonding material paste used is as shown in Table 1.

In addition, heat treatment such as soldering is required in the process of assembling the circuit board into a module, and an impact resistance test of the circuit board was conducted for the purpose of investigating the durability at that time. As a shock resistance test, the circuit board should be
After holding for 0 minutes, a method of rapidly cooling to room temperature was applied, and the rate of occurrence of cracks was shown after three times of this thermal shock cycle. After the thermal shock cycle was completed, the cracks were evaluated by checking whether the copper circuit board was separated from the silicon nitride sintered body due to cracking of the bonding layer, and etching was performed to remove the copper circuit board and the bonding material layer to form a silicon nitride sintered body. It was performed by observing the generated microcracks by a fluorescent flaw detection test. In the heat cycle test, a heating / cooling operation of cooling at −40 ° C. for 30 minutes, holding at room temperature for 10 minutes, heating at + 125 ° C. for 30 minutes, and holding at room temperature for 10 minutes was performed as one cycle. 100
The presence or absence of a decrease in peel strength and three-point bending strength after 0 heat cycles was evaluated. The number of heat cycles was shown when the deterioration of the properties was observed on the way.

[0043]

[Table 1]

As is clear from the examples and comparative examples in Table 1, the circuit board of the present invention contains the Mg component and / or the Ca component in the silicon nitride sintered body in an amount of 7% by weight or less in terms of their oxides. It can be seen that the sintered body characteristics and the circuit board characteristics are all excellent, and particularly in the thermal shock test, there is no problem in the module manufacturing process, and in the heat cycle test, it is extremely excellent in practical use. Further, when the number of grain boundaries of the silicon nitride sintered body and the amounts of impurities of Al and Fe are within the range of the present invention, it is clear that the characteristics of the sintered body are excellent and the characteristics of the circuit board using the same are also excellent. is there.

(Examples 19 to 36) Using the silicon nitride sintered bodies of Examples 1 to 18 and the bonding material paste, circuit boards were produced by the method described below. The bonding material paste is applied to the entire front and back surfaces of the silicon nitride sintered body, a copper circuit board having a thickness of 0.3 mm is provided on the surface side on which the circuit is formed, and a copper circuit board having a thickness of 0.25 mm is provided on the surface opposite to the surface. The whole substrate is placed in a heating furnace with the surface on which the circuit is formed facing upward and the weight placed on it, and in a crimped state, at a temperature of 800 to 860 ° C. in a vacuum better than 10 −4 Torr. Heat treatment was performed for 30 minutes to produce a joined body. Next, a circuit pattern is applied by screen printing on the upper copper circuit board surface of the bonded body, and an etching resist is applied to the entire back surface by an etching resist, and then an etching treatment is performed using a cupric chloride solution. Only formed the circuit. Furthermore, the bonding layer remaining between the circuits after the etching process is replaced with ammonium hydrogen fluoride (NH
The bonding layer was removed by immersing in an aqueous solution containing 4 F · HF) and hydrogen peroxide (H 2 O 2), and a circuit board was manufactured. The circuit boards manufactured by this method showed the same characteristics as those of Examples 1 to 18, respectively. Examples 19 to 3
The method of manufacturing the circuit board of No. 6 has an advantage that productivity is improved as compared with the methods of manufacturing shown in Examples 1 to 18.

(Examples 37 to 54) Examples 1 to 1 except that a molded body was manufactured by an extrusion method instead of the doctor blade method applied when manufacturing the sintered bodies of Examples 1 to 18.
A circuit board was manufactured in the same manner as in No. 8. In the extrusion method, the oxygen content is 0.8 to 2.1% by weight and the average particle size is 0.6 to 2.6.
Various silicon nitride powders of μm and average particle diameter 0.8 to 2.0 μ
A predetermined amount of water and a sintering aid powder of m, an organic binder (such as methyl cellulose), an organic plasticizer and an additive (such as glycerin) were mixed using a Henschel mixer. The obtained mixture was extruded into a sheet by a vacuum kneader. The characteristics of the circuit board using the silicon nitride sintered body obtained by this manufacturing method are the same as those of Examples 1 to 18,
All were good. The extrusion method has an advantage over the doctor blade method in improving the productivity of the silicon nitride sintered body.

(Examples 55 to 57) A circuit board was produced in the same manner as in Example 1 except that the silicon nitride sintered body of Example 1 was used and copper plates having various oxygen contents were used. Table 2 shows the oxygen content in copper of the obtained circuit board and the crack generation rate after 5 thermal shock cycles. From Table 2, it can be seen that the oxygen content is preferably about 80 ppm or less, and particularly when the oxygen content is 50 ppm or less, thermal shock cracking does not occur and is optimal.

[0048]

[Table 2]

(Examples 58 to 66) Using the silicon nitride sintered body of Example 5, the weight ratio of TiH 2 / Ag in the bonding material paste was 3/100 to 10/100, and the coating amount of the bonding material paste was 7. ~ 15g / cm2, bonding temperature 800 ~ 90
By bonding under various conditions of 0 ° C., circuit boards having different thicknesses of the reaction layer (TiN is the main phase) of the silicon nitride sintered body and the active metal component were produced. The conditions other than the above were the same as in Example 5. Table 3 shows the relationship between the thickness of the reaction layer and the incidence of cracking after 5 thermal shock cycles in these circuit boards. The thickness of the reaction layer is the area of the reaction layer in contact with a predetermined length along the interface between the reaction layer and the silicon nitride sintered body, which is obtained by analyzing the vertical cross section of the bonding layer with EPMA and SEM. The average thickness of the reaction layer was calculated from the predetermined length, and this was used as the thickness of the reaction layer. It is clear from Table 3 that the thickness of the reaction layer is preferably 2 μm or less, and particularly when it is 1.2 μm or less, thermal shock cracking does not occur and is optimal.

[0050]

[Table 3]

(Examples 67 to 77) In Example 1, the gap between the doctor blades was adjusted and the molded sheets having various thicknesses were used to obtain silicon nitride sintered bodies having various thicknesses. Using these silicon nitride sintered bodies, various circuit boards having different thicknesses of the front surface copper circuit board and the back surface copper circuit board (heat dissipation copper plate) shown in Table 4 were produced. In addition, in part, a circuit board having a structure in which a copper circuit board on one side was not joined was manufactured. At this time, the conditions other than the above were the same as in Example 1. The peel strength, the three-point bending strength, and the heat cycle test characteristics of all the circuit boards were good as in Example 1. Further, the thermal resistance of these circuit boards was measured, and the results shown in Table 4 were obtained. The thickness of the copper circuit board was 0.25 to 1.00 mm and the thickness of the silicon nitride sintered body was 0.25 to 0. It is clear that it can be produced without any problem with a size of 0.6 mm, and it is clear that a circuit board having a structure in which a copper circuit board is bonded to only one surface can be produced without any problem. Furthermore, it is clear that the thermal resistance of these circuit boards is less than 1 ° C./W and that they have excellent heat dissipation. The value of this thermal resistance of 1 ° C./W is as follows:
m, the thickness of the front surface copper circuit board is 0.3 mm, and the thickness of the rear surface copper circuit board (heat dissipation copper plate) is 0.2 mm. Also, the thermal resistance is measured by mounting a transistor having a bottom area of 16 × 20 mm as a heat source on the circuit board on the front surface of the circuit board, and soldering a copper plate with a thickness of 3 mm on the back surface of the circuit board as a heat sink to approximate the module. The condition was evaluated.

[0052]

[Table 4]

(Examples 78 and 79) A metal circuit made of Fe material in which a 0.6 mm-thick silicon nitride sintered body obtained by the same operation as in Example 1 was plated with Ni or the surface was plated with Ni to a thickness of 5 μm A circuit board was manufactured under the same conditions as in Example 1 except that a board was used and a bonding material paste containing a brazing material of Ag / Cu / Ti = 72/28/8 weight ratio was used. At this time, the thickness of the metal circuit board on the front surface is 0.25 mm and the thickness of the metal circuit board on the back surface is 0.23 mm, both of which are made of the same material. Table 5 shows the measurement results of the thermal resistance of the obtained circuit board. It is apparent that the circuit board of the present invention can be applied to metal circuit boards of various materials other than the copper plate.

[0054]

[Table 5]

(Examples 80 to 83) Circuit boards were manufactured under the same conditions as in Example 1 except that the composition of the brazing material in the bonding material paste and the bonding temperature were as shown in Table 6. The obtained circuit board was subjected to peel strength, three-point bending strength and heat cycle test. The results are shown in Table 6, and it is clear that good results can be obtained by using the brazing filler metal containing various active metal components.

[0056]

[Table 6]

[0057]

The circuit board of the present invention has a structure in which a metal circuit board is laminated and integrated through a bonding layer on a silicon nitride sintered body containing a specific component and having high thermal conductivity and excellent mechanical properties. The bonding strength between the metal circuit board and the silicon nitride sintered body is high,
The circuit board has high bending strength, less deterioration of the bonding strength and bending strength over time, excellent heat cycle resistance and thermal shock resistance, and high heat dissipation, high reliability and durability.

Since the circuit board of the present invention uses a silicon nitride sintered body having a high thermal conductivity, it can withstand thermal stress, and by increasing the thickness of the metal circuit board, it can be used in high load applications such as large current applications. Applicable to Furthermore, because of its excellent mechanical properties, even if a large external force is applied to the mounting board when it is screwed onto it, the circuit board is less likely to crack. Can be made with.

Since the circuit board of the present invention uses a silicon nitride sintered body having an extremely large mechanical strength as compared with the conventional AlN substrate and Al2 O3 substrate, the strength of the entire circuit board is the same as the conventional one. When the strength is set to, the thickness of the substrate can be reduced to about 1/2, so that higher density mounting is possible.

Since the circuit board of the present invention can be applied to metal circuit boards made of various materials in addition to the copper plate, it is possible to manufacture a special circuit board having a magnetic circuit or other functionalities. However, it is also possible to apply a copper alloy or the like to which an alloy component is added.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H01L 23/14 C

Claims (6)

[Claims] 1. A circuit board in which a metal circuit board is disposed on a silicon nitride sintered body via a bonding layer, wherein the silicon nitride sintered body contains Mg component and / or Ca component as oxides thereof. A circuit board comprising a total amount of 7.0% by weight or less in terms of conversion. 2. The number of grain boundaries observed on the polished surface of the silicon nitride sintered body is 10 μm in length of a straight line drawn in an arbitrary direction.
The circuit board according to claim 1, wherein the number is 10 or less per unit. 3. Regarding impurities contained in the silicon nitride sintered body, Al is 0.25 wt% or less in terms of metal, and Fe
3. The circuit board according to claim 2, wherein the metal content is 0.3% by weight or less in terms of metal. 4. The three-point bending strength of the silicon nitride sintered body at room temperature is 600 MPa or more, and the thermal conductivity is 60 W / (m.multidot.m).
K) or more, The circuit board of Claim 2 characterized by the above-mentioned. 5. The metal circuit board has an oxygen content of 50 pp.
The circuit board according to claim 1, claim 2, claim 3, or claim 4, wherein the circuit board is copper having a thickness of m or less. 6. The bonding layer includes a reaction layer of an active metal component and a silicon nitride sintered body, and the thickness of the reaction layer is 2 μm or less (not including 0). The described circuit board.