JP2003124584A - Ceramic circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ceramic circuit board in which the mechanical strength of the board is raised, the thermal characteristics are improved and the warping of the board can be suppressed. SOLUTION: The ceramic circuit board 1 comprises a metal circuit plate 3 connected to one main surface of a base 6 formed by interposing a Cu plate or a Cu alloy plate 4 between two silicon nitride plates 2 and connecting the plate between the plates 2, and a metal plate 5 connected to the other main surface. In this board 1, the Cu plate or the Cu alloy plate 4 has a thickness of 0.5 to 2.0 mm, and the ratio of the total sum of the thicknesses of the plate 3 and the Cu plate or the Cu alloy plate 4 and the plate 5 to the thickness of the entire board 1 is 50 to 90%. T2>=T1>=T3 is preferred, wherein T1 is the thickness of the plate 3, T2 is the thickness of the Cu plate or the Cu alloy plate, and T3 is the thickness of the plate 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic circuit board obtained by joining a metal circuit board to a ceramic board.

[0002]

2. Description of the Related Art In recent years, a ceramic circuit board in which a metal circuit board made of copper or the like is directly bonded onto a ceramic board via an active metal brazing material has been used as a circuit board such as a power module board or a switching module board. Has been.

Such a ceramic circuit board is specifically manufactured by the following method when a ceramic board made of an aluminum oxide sintered body is used.

First, a brazing paste is prepared by adding and mixing an organic solvent and a solvent to an active metal powder obtained by adding at least one of titanium, zirconium, and hafnium to a silver-copper alloy.

Next, a suitable organic binder, a plasticizer, a solvent and the like are added to and mixed with raw material powders of aluminum oxide, silicon oxide, magnesium oxide, calcium oxide and the like to form a sludge and this is well-known by the doctor blade method. After obtaining a plurality of ceramic green sheets by adopting tape molding technology such as or calender roll method, it is formed into a predetermined size,
Next, if necessary, the ceramic green sheets are stacked one on top of the other and fired at a temperature of about 1600 ° C. in a reducing atmosphere to sinter and integrate the ceramic green sheets to form a ceramic substrate made of an aluminum oxide sintered body. Form.

Next, a metal circuit board made of copper or the like is placed on the ceramic substrate with a brazing paste interposed therebetween.

Finally, the brazing material paste disposed between the ceramic substrate and the metal circuit board is heated to a temperature of about 900 ° C. in a non-oxidizing atmosphere to be melted, and the brazing material is used for the ceramic substrate. And a metal circuit board are joined together.

The ceramic circuit board manufactured as described above is an IGBT (Insulated Gate Bipolar Transistor).
And MOS-FET (Metal Oxide Semiconductor-Fiel
After connecting electronic components such as semiconductor devices such as d Effect Transistor) via an adhesive such as solder, they are joined to a heat dissipation member such as aluminum with solder to improve heat generation during operation of semiconductor devices. It becomes a semiconductor module that dissipates heat.

However, in such a semiconductor module, a ceramic circuit board (having a thermal expansion coefficient of about 3) is used.
~ 10ppm / ℃) and heat dissipation member (coefficient of thermal expansion is about 18-23p)
pm / ° C) and the coefficient of thermal expansion is very different,
In some cases, cracks may occur in the solder between the ceramic circuit board and the heat dissipation member, causing peeling and significantly degrading reliability. Therefore, a configuration is adopted in which the ceramic circuit board and the heat dissipation member are joined and mounted via a grease-like heat conductive composition instead of solder.

On the other hand, in the conventional ceramic circuit board for a power module as described above, generation of thermal stress due to the difference in thermal expansion between the ceramic circuit board and the heat radiation member is unavoidable, and repeated thermal history causes Since cracks easily occur in the ceramic substrate and solder, there is a problem in terms of long-term reliability. Further, there is a problem that a warp occurs when cooled after soldering due to a difference in coefficient of thermal expansion between the ceramic circuit board and the heat dissipation member. If this warp is large, the adhesion to the water cooler for cooling the heat dissipation member will be poor and the heat dissipation characteristics will be deteriorated. This warp increases as a large heat dissipation member is used. In order to make a power module, a heat sink is generally used as a heat radiating member, and the heat sink portion is screwed to a heat fin or a water cooler, so that a larger bending load is applied by repeated heating and cooling, There is a problem in that the ceramic substrate is cracked or cracked to lower reliability.

Therefore, as shown in a cross-sectional view of an example of a conventional ceramic substrate in FIG. 4, a metal circuit plate 13 and a metal plate 15 are respectively joined to the ceramic substrate 12, and a ceramic circuit substrate 11 without a heat sink is used. Is used. Reference numeral 7 is a semiconductor element mounted on the metal circuit board 13. This ceramic circuit board 11 is directly attached to the water cooler,
Metal plate 15 through a heat transfer composition such as oil compound
Are joined. According to this, since the soldering step is omitted, there is no problem of cracks occurring in the solder, and the reliability is dramatically improved. Further, in the case of the ceramic circuit board 11 that does not use a heat sink, if the thickness of the metal circuit board 13 and the metal plate 15 is small, it occurs at the joint between the ceramic board 12 and the metal circuit board 13 and the metal plate 15. Since the thermal stress is small, the warp of the ceramic circuit board 11 is improved.

[0012]

However, in the conventional ceramic circuit board 11 which does not use a heat sink as shown in FIG. 4, the heat conduction efficiency to the water cooler is reduced because the heat diffusion effect by the heat sink is lost. However, there is a problem that the heat dissipation characteristic is deteriorated. As a result, if the temperature of the semiconductor element 7 exceeds the allowable temperature, the semiconductor element 7 may malfunction and the semiconductor element 7 itself may be destroyed. There was a problem.

On the other hand, it is conceivable to reduce the thickness of the ceramic substrate 12 having a low thermal conductivity and increase the thickness of the metal circuit board 13 or the metal plate 15 having a high thermal conductivity in order to improve the heat dissipation characteristics. However, if the ceramic substrate 12 is made thin, the mechanical strength is reduced, while if the thickness of the metal circuit board 13 or the metal plate 15 is made large, a large thermal stress is applied to the ceramic circuit board 11 to cause warping, and the ceramic board 12 There are problems that cracks are generated in the metal, that the dielectric strength is deteriorated due to the cracks, or that the metal plate 15 is peeled off.

The present invention has been completed in view of the above problems, and an object thereof is to increase the mechanical strength of a ceramic circuit board, improve the thermal characteristics, and suppress the warp of the board. To provide.

[0015]

In the ceramic circuit board of the present invention, a metal circuit board is provided on one main surface of a base formed by sandwiching a Cu plate or a Cu alloy plate between two silicon nitride plates, and the other. Is a ceramic circuit board formed by bonding a metal plate to the main surface of the Cu plate or the Cu alloy plate.
It is 0.2 mm or more and 2.0 mm or less, and the total ratio of the thickness of the metal circuit board and the Cu plate or the Cu alloy plate and the metal plate in the total thickness of the ceramic circuit board is
It is characterized by being 50 to 90%.

Further, in the ceramic circuit board of the present invention, in the above structure, the thickness of the metal circuit board is T1, and the thickness of the metal circuit board is C
When the thickness of the u plate or the Cu alloy plate is T2 and the thickness of the metal plate is T3, T2 ≧ T1 ≧ T3.

According to the ceramic circuit board of the present invention, it is assumed that the base body is bonded by sandwiching a Cu plate or a Cu alloy plate between silicon nitride plates made of a silicon nitride sintered body excellent in mechanical strength and fracture toughness. , Using this substrate, as a whole circuit board, metal circuit board / silicon nitride board / Cu board or Cu
Since it has a five-layer structure of an alloy plate / silicon nitride plate / metal plate, a Cu plate or C is used as an intermediate layer of the ceramic circuit board.
By providing the u-alloy plate, the rigidity of the base increases, so it is possible to reduce the average strain. Therefore, even if a thin silicon nitride plate is used for the base, a thick metal circuit board is joined to form a circuit. The substrate can be configured, and the mechanical strength can be increased without impairing the bonding reliability. Furthermore, when the thickness of the entire ceramic circuit board increases, the heat generated by electronic parts such as semiconductor elements is conducted while being diffused in the lateral direction, and the Cu plate or the Cu alloy plate between the silicon nitride plates is compared with the silicon nitride plate. Since it has high thermal conductivity, it can conduct heat while diffusing more effectively, so that the heat generated by electronic components such as semiconductor elements mounted on the metal circuit board can be effectively conducted from the metal circuit board to the metal plate. It is possible to dissipate.

In general, when a ceramic substrate constituting a ceramic circuit board is formed into multiple layers, mechanical strength is improved and rigidity is increased. However, when the circuit board is joined to an external water cooler or the like by screwing or the like, the ceramic circuit is formed. Since the board is less likely to bend, it becomes difficult for the ceramic circuit board to come into close contact with the water cooler or the like, and the thermal resistance increases. However, according to the ceramic circuit board of the present invention, the metal circuit board is formed on one main surface of the base body and the metal plate is formed on the other main surface of the base body in which the Cu plate or the Cu alloy plate is sandwiched and joined between the two silicon nitride plates. Since the circuit board has a minimum required five-layer structure as a whole, the thickness of the ceramic circuit board increases too much even when a silicon nitride plate having a sufficient mechanical strength is used, and the circuit board does not easily bend. Since it does not occur, it becomes possible to secure the mechanical strength while allowing the circuit board a sufficient amount of deflection.

On the other hand, while allowing the ceramic circuit board to have sufficient bending, for example, the substrate is formed from three layers of silicon nitride plate / Cu plate or Cu alloy plate / silicon nitride plate to silicon nitride plate /
Cu plate or Cu alloy plate / silicon nitride plate / Cu plate or C
5 layers of u alloy plate / silicon nitride plate and 7 as a whole circuit board
When considering the use of multiple layers or more layers, a silicon nitride plate that has a low thermal conductivity compared to the metal part in order to avoid the increase in the overall thickness and rigidity of the circuit board. If the silicon nitride plate is thinned in order to reduce the ratio of the thickness of the silicon nitride plate, cracks easily occur in the silicon nitride plate due to the thermal stress generated at the time of bonding. On the contrary, if the metal part is thickened to improve the heat dissipation characteristics by using a silicon nitride plate with sufficient mechanical strength, the rigidity of the ceramic circuit board itself becomes unnecessarily strong and it is difficult to bend. Become. Further, if the number of joint interfaces between the stacked members increases due to the multilayer structure, the contact resistance may increase and the thermal characteristics may deteriorate. Therefore, the five-layer structure of the ceramic circuit board of the present invention provides good characteristics in terms of heat dissipation characteristics and the balance of bending and warpage of the ceramic circuit board.

Further, according to the ceramic circuit board of the present invention, the Cu plate or Cu alloy plate between the two silicon nitride plates is a Cu plate or Cu alloy plate having a high thermal conductivity of 0.2 mm or more and 2.0 mm or less. In addition, since the ratio of the metal circuit board, the Cu plate or the Cu alloy plate, and the metal plate in the ceramic circuit board is set to 50 to 90%, the heat easily spreads in these metal parts having high thermal conductivity. Further, the heat diffusion in the lateral direction can be effectively performed, and the thermal characteristics can be improved.

Furthermore, according to the ceramic circuit board of the present invention, when the thickness of the metal circuit board is T1, the thickness of the Cu plate or the Cu alloy plate is T2, and the thickness of the metal plate is T3, T2 is given.
By setting ≧ T1 ≧ T3, the influence on the warp of the board is small, and the Cu plate or the Cu arranged over the entire surface of the circuit board
Since the thickness T2 of the alloy plate is thickest and the thickness T1 of the metal circuit board having a small bonding area is thicker than the thickness T3 of the metal plate having a large bonding area, the rigidity of the circuit board as a whole is secured, and the silicon nitride plate and the Cu The thermal stress on the front and back of the circuit board due to the difference in thermal expansion coefficient between the metal plate and the base body made of a metal plate or a Cu alloy plate is well-balanced, and the warp of the ceramic circuit board is suppressed to an extremely small level. be able to. Further, by suppressing the warpage of the ceramic circuit board, the close contact with the water cooler is improved, the heat dissipation characteristics are improved, and further, the occurrence of cracks or breaks due to thermal / mechanical stress can be prevented. As a result, it is possible to prevent insulation failure due to cracks and improve the reliability of the ceramic circuit board.

As a result, according to the ceramic circuit board of the present invention, the heat dissipation characteristics are improved, and it is possible to prevent malfunction of electronic parts such as semiconductor elements mounted on the metal circuit board due to heat, and to improve reliability. It is possible to obtain a high semiconductor module.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a sectional view showing an example of an embodiment of a ceramic circuit board of the present invention. 1 is a ceramic circuit board, 2 is a silicon nitride plate, 3 is a metal circuit board, 4 is a Cu plate or Cu. Alloy plates 5 are metal plates. Further, 6 is a base body formed by sandwiching and bonding a Cu plate or a Cu alloy plate 4 between two silicon nitride plates 2, and 7 is a semiconductor element mounted on the metal circuit plate 3. In the ceramic circuit board 1 of the present invention, a Cu plate or a Cu alloy plate 4 (hereinafter, “Cu plate or Cu alloy plate” is referred to as “Cu plate or the like”) is sandwiched between two silicon nitride plates 2 and joined. A metal circuit board 3 is bonded to one main surface, here the upper surface, of the base body 6 formed as described above, and the metal plate 5 is bonded to the other main surface, here, the lower surface, which has a five-layer structure as a whole. .

The silicon nitride plate 2 is a plate-like body made of a silicon nitride sintered body. To obtain the silicon nitride plate 2, first, a silicon nitride powder is mixed with a sintering aid such as a rare earth oxide powder or an aluminum oxide powder to prepare a silicon nitride sintered material powder. Next, an organic binder and a dispersion medium are added to and mixed with the raw material powder of a silicon nitride sintered material to form a paste, and the paste is formed into a sheet by a forming method such as a doctor blade method to produce a silicon nitride green sheet. A required number of such silicon nitride green sheets are laminated, press-processed, etc. and pressure-bonded (pressure-bonded) to produce a silicon nitride-based molded body. After this, after degreasing the silicon nitride compact in air or in a non-oxidizing atmosphere such as a nitrogen atmosphere,
By firing in a non-oxidizing atmosphere such as a nitrogen atmosphere, the intended silicon nitride plate 2 can be obtained.

The silicon nitride plate 2 effectively conducts and dissipates the heat generated by the electronic components such as the semiconductor element 7 mounted on the metal circuit plate 3 from the metal circuit plate 3 to the metal plate 5 to dissipate the ceramic circuit. In order to improve the heat dissipation characteristics of the substrate 1, the thermal conductivity is preferably at least 60 W / mK or more, particularly 80 W / mK, and further preferably 100 W / mK.

The silicon nitride plate 2 preferably has a thickness of 0.2 to 1.0 mm in order to improve the mechanical strength of the ceramic circuit board 1 and not deteriorate the heat radiation characteristics. If the thickness is less than 0.2 mm, the silicon nitride plate 2 tends to be cracked due to the stress generated when the silicon nitride plate 2 and the metal circuit plate 3, the Cu plate 4 and the metal plate 5 are joined. is there. On the other hand, when the thickness exceeds 1.0 mm, it tends to be difficult to satisfactorily transfer the heat generated from the semiconductor element 7 to the external heat dissipation member via the metal plate 5.

In the ceramic circuit board 1 of the present invention, a Cu plate 4 or the like is sandwiched between the silicon nitride plates 2 manufactured as described above and bonded by a direct bonding method or an active metal method to form a substrate 6. Then, the metal circuit board 3 and the metal plate 5 made of a conductive metal material such as copper or aluminum are bonded to the upper surface and the lower surface of the base body 6 by a direct bonding method or an active metal method, respectively. It

For example, in the case of using the active metal method, silver brazing powder made of silver-copper alloy powder or aluminum brazing powder made of aluminum-silicon alloy powder is added to active metals such as titanium, zirconium, and hafnium. The active metal brazing material paste obtained by adding and mixing a suitable organic solvent / solvent to the active metal brazing material in which 2 to 5% by weight of the active metal powder comprising at least one kind of hydride is added to the silicon nitride plate 2 A predetermined pattern corresponding to the Cu plate 4 and the metal circuit board 3 and the metal plate 5 is printed on the upper and lower surfaces using a conventionally known screen printing technique.

Then, from below, the metal plate 5, the silicon nitride plate 2,
A Cu plate or the like 4, a silicon nitride plate 2, and a metal circuit plate 3 are placed in this order so that the printed active metal brazing material paste pattern is sandwiched between them, and this is placed in a vacuum / neutral atmosphere or reduction. In the atmosphere, at a specified temperature (about 900 for silver wax)
℃, 600 ℃ for aluminum brazing material) to heat the active metal brazing material to melt the silicon nitride plate 2 and Cu.
The plate 4 and the metal circuit plate 3 and the metal plate 5 are joined together.

Metal circuit board 3 made of copper or aluminum
The metal plate 5 and the Cu plate 4 have a thickness of 0.5 mm, for example, by subjecting an ingot (lump) of copper, aluminum or the like to a conventionally known metal processing method such as a rolling method or a punching method. It is manufactured in a predetermined pattern shape corresponding to the shape of the substrate 6 and the shape of the circuit wiring pattern. Here, the thickness of the metal circuit board 3 and the metal plate 5 suppresses heat generation of the metal circuit board 3 due to a large current,
In order to suppress cracks due to the heat load generated at the bonding interface during bonding between the silicon nitride plate 2 and the silicon nitride plate 2, 0.1 to 1.0 mm is preferable. If the thickness of the metal circuit board 3 is less than 0.1 mm,
Since the electric resistance increases, it tends to be difficult for a high current signal from the semiconductor element 7 to propagate. On the other hand, if it is larger than 1.0 mm, the silicon nitride plate 2, the metal circuit plate 3 and the metal plate 5
Due to the stress generated when joining and
Tends to be cracked. The metal circuit board 3 and the metal plate 5 are preferably made of the same material in order to reduce the warpage of the circuit board 1 as a whole by matching the thermal expansion coefficients of both main surfaces of the ceramic circuit board 1.

When the Cu plate 4, etc. and the metal circuit board 3 and the metal plate 5 are made of copper, if they are made of oxygen-free copper, the oxygen-free copper will have a copper surface when brazing. The wettability with the brazing material is improved without being oxidized by the oxygen existing in the copper, and the bonding via the brazing material can be strengthened. Therefore, the Cu plate 4 and the metal circuit plate 3 and the metal plate 5 are preferably made of oxygen-free copper.

If the metal circuit board 3 is made of nickel and has good conductivity, corrosion resistance, and wettability with the brazing material, the metal circuit board 3 is deposited by plating.
The electric connection between the metal circuit board 3 and the external electric circuit can be made good, and the electronic components such as the semiconductor element 7 can be firmly adhered to the metal circuit board 3 via the solder.
Therefore, it is preferable that the surface of the metal circuit board 3 is made of nickel, which has good conductivity, corrosion resistance, and wettability with the brazing material.

The thickness of the Cu plate 4 or the like is preferably 0.2 mm or more and 2.0 mm or less in order to sufficiently diffuse heat in the lateral direction and to give the ceramic circuit board 1 an appropriate flexibility. If the thickness is less than 0.2 mm, the effect of heat diffusion in the lateral direction becomes small and tends to be insufficient. On the other hand,
If the thickness is thicker than 2.0 mm, the mechanical strength is improved and the rigidity is increased, but when the base 6 is joined to an external water cooler or the like with screws or the like, the ceramic circuit board 1 does not easily bend, and the ceramic circuit board 1 is water cooled. It tends to be difficult to adhere to a vessel or the like and the thermal resistance tends to increase. Further, since a large thermal stress is generated at the bonding interface between the silicon nitride plate 2 and the Cu plate 4 or the like, the base 6 tends to be largely warped. Further, the base body 6 and thus the ceramic circuit board 1 become thick, and it tends to be difficult to reduce the size and height.

When the thickness of the metal circuit board 3 is T1, the thickness of the Cu board 4 is T2, and the thickness of the metal plate 5 is T3, the thicknesses of the Cu plate 4 and the metal circuit board 3 and the metal plate 5 are T
It is preferable that 2 ≧ T1 ≧ T3. The Cu plate 4 or the like has a wide area, that is, a so-called solid pattern shape, and since it is located at the center of the ceramic circuit board 1 in the thickness direction, the influence on the warp of the ceramic circuit board 1 is small, so the thickness T2 can be increased. When T2 is made thicker, the mechanical strength of the base 6 becomes stronger, and further, the heat diffusion in the lateral direction becomes better, and the heat dissipation characteristics are improved. Further, while the metal circuit board 3 joined to one main surface of the ceramic circuit board 1 has a circuit pattern shape, the metal plate 5 joined to the other main surface of the ceramic circuit board 1 has a large area. Since it is a so-called solid pattern shape, the thermal stress generated at the bonding interface between the silicon nitride plate 2 and the metal circuit plate 3 and the metal plate 5 is different, so that the ceramic circuit board 1 is warped. By setting T1 ≧ T3, it becomes possible to balance the thermal stresses on the upper and lower main surfaces of the base body 6, and it is possible to reduce the warpage of the ceramic circuit board 1. Therefore, by setting T2 ≧ T1 ≧ T3, it becomes possible to obtain the ceramic circuit board 1 having excellent heat dissipation and small warpage.

In the ceramic circuit board 1 of the present invention, the ratio of the total thickness of the metal circuit board 3, the Cu plate 4 and the metal plate 5 to the total thickness of the ceramic circuit board 1 is
It is important to be 50-90%. If the total ratio of the thicknesses is less than 50%, the ratio of the silicon nitride plate 2 having a lower thermal conductivity than that of the metal, which is a high thermal conductor, becomes larger than that of the metal, which is a high thermal conductor. This is because the effect of improving the thermal conductivity of the whole 1 becomes small and becomes insufficient. If the total thickness is more than 90%, the stress generated when the silicon nitride plate 2 and the metal circuit plate 3 / metal plate 5 are joined easily causes cracks or the like in the silicon nitride plate 2. Is.

To the ceramic circuit board 1 of the present invention as described above, an electronic component such as the semiconductor element 7 is bonded to a predetermined position of the metal circuit board 3 on the ceramic circuit board 1 through solder or the like, and aluminum or the like is used. The semiconductor module is completed by electrically connecting the metal plate 5 to the heat radiating member via a grease-like heat conductive composition and the like by electrically connecting the metal plate 5 with the bonding wire.

[0038]

EXAMPLES The ceramic circuit boards of the present invention will be described in detail below with reference to the test results of Examples and Comparative Examples, but the present invention is not limited to the following Examples.

In the ceramic circuit board 1 of the present invention shown in FIG. 1, the average strain and the thermal resistance θj-w of the circuit boards in which the respective thickness configurations are changed as in Examples 1 to 4 shown in Table 1 were calculated. On the other hand, as Comparative Example 1, also in the conventional ceramic circuit board 11 shown in FIG. 4, the thickness of the ceramic board 12 (silicon nitride plate) is 0.32 mm, and the metal circuit board 13 (Cu) and the metal plate 15 (Cu) are The thickness was the same, and the average strain and the thermal resistance θj-w of the circuit board when the thickness was changed to 0.2, 0.5, 1.0, and 1.5 mm were calculated.

Further, in the ceramic circuit board 1 of the present invention shown in FIG. 1, a circuit board in which the Cu plate 4 has a thickness of 0.1 mm is a comparative example 2, and a circuit board in which the Cu plate 4 has a thickness of 2.5 mm. Was used as Comparative Example 3 and the same calculation was performed.

[0041]

[Table 1]

The thermal resistance θj-w is the circuit board size of 30 m.
m □, the chip size of the semiconductor element mounted on this is 10
mm □, the steady-state heat conduction analysis was performed for the chip temperature Tj and the cooling water temperature Tw when this ceramic circuit board was bonded to a water cooler using an oil compound, and the temperature difference was calculated by dividing the temperature difference by the applied power. It can be judged that the smaller the thermal resistance θj-w is, the higher the heat radiation capacity is.

On the other hand, the average strain (Δε _a ) is the thickness of each layer (h _i ), coefficient of thermal expansion (α _i ), Young's modulus (E _i ), Poisson's ratio (ν _i ), and temperature change after bonding (ΔT). _i ) using the equation Δε _a = Σ (h _i · E _i / (1-ν _i ) · α _i · ΔT _i ) /
A simple calculation can be performed with Σ (E _i / (1-ν _i ) · h _i ). It can be determined that the smaller the average strain, the smaller the thermal stress applied to the circuit board and the smaller the warp amount of the circuit board.

FIG. 2 is a diagram showing the results relating to changes in the thermal resistance θj-w. In FIG. 2, the horizontal axis represents the ratio of the total thickness of the metal circuit plate, the Cu plate, etc., and the metal plate to the total thickness of the ceramic circuit board (hereinafter referred to as the metal ratio. Unit:
%), And the vertical axis represents the thermal resistance θj-w (unit:%). In the conventional ceramic circuit board 11 shown in FIG. 4, the thickness of the ceramic substrate (silicon nitride plate) 12 is 0.32 mm, When the thickness of the metal circuit board 13 (Cu) and the metal plate 15 (Cu) is 0.5 mm, the thermal resistance θj-w is taken as 100%, and is shown as a ratio when compared with the thermal resistance θj-w. The reason for showing such a ratio is that the thickness configuration of the conventional ceramic circuit board 11 is judged in consideration of thermal and mechanical characteristics, and the thickness of the ceramic substrate 12 (silicon nitride plate) is set to 0.32.
mm, metal circuit board 13 (Cu) and metal plate 15 (Cu)
A thickness of 0.5 mm is a commonly used thickness configuration, so this is set to 100% of the standard. Each point in the figure shows the result of each of the examples and comparative examples shown in the figure.

From the results shown in FIG. 2, the thermal resistance θj-w decreases as the proportion of metal increases. Further, it can be seen that the ceramic circuit board 1 of the present invention is smaller than the comparative example 1 of the conventional ceramic circuit board 11. In particular, when the proportion of metal is large, and further, in the case of a five-layer structure and the overall thickness of the circuit board is large, thermal diffusion in the lateral direction is effective and thermal characteristics are improved. However, the proportion of metal when the thermal resistance becomes smaller than the standard thermal resistance is 50 to 90%. On the other hand, when the proportion of the metal is less than 50% as in Comparative Example 2, the proportion of the silicon nitride plate 2 having a lower thermal conductivity than that of the metal is large, so that the thermal conductivity of the entire circuit board is improved. The effect is small and the thermal resistance is large.

Next, FIG. 3 is a diagram showing the results regarding the change in the average distortion. In FIG. 3, the horizontal axis represents the metal circuit board 13 (C
u) and the thickness (unit: mm) of the metal plate 15 (Cu), and the vertical axis represents the average strain (unit:%). In the conventional ceramic circuit board 11, the ceramic substrate (silicon nitride plate) 12 Has a thickness of 0.32 mm, and the metal circuit board 13 (C
u) has a thickness of 0.5 mm, and the metal plate 15 (Cu) has a thickness of 0.5
The average strain when mm is set to 100%, and the ratio is shown when compared with the average strain. 100% average distortion
The thickness of the circuit board is shown in Fig. 2 as the thermal resistance θj-w.
Is the same as 100%. The points and characteristic curves in the figure show the results of the examples and comparative examples shown in the figure, respectively.

From the results shown in FIG. 3, in the conventional ceramic circuit board 11, when the thickness of the metal circuit board 13 (Cu) and the metal plate 15 (Cu) is increased, the average strain is increased. In the ceramic circuit board 1, Cu
It can be seen that the increase rate of the average strain is smaller than that of the ceramic circuit board 11 even if the thickness of the plate 4 or the like is increased. Comparative Example 1
, The metal circuit board 13 (Cu) and the metal plate 15 (C
When the thickness of u) is 1.5 mm, the average strain increases by more than 20% from the standard 100%, and the influence of the warp of the circuit board becomes a problematic area for the thermal characteristics. Therefore, metal circuit board
It can be seen that the thickness of 13 (Cu) and the metal plate 15 (Cu) is preferably 1.0 mm or less. In Example 5 in which the thickness of the Cu plate 4 is 2 mm, the average strain is larger than that in Comparative Example 1, but
The average strain is 20% or less compared to 100% of the standard. This result is at a level that does not pose a problem when comprehensively considered in consideration of thermal characteristics.

Therefore, from the results shown in FIGS. 2 and 3, in the ceramic circuit board 1 of the present invention, the thermal characteristics can be improved without significantly impairing the reliability and the warpage amount of the board. I was able to confirm that.

It should be noted that the present invention is not limited to the examples of the above-described embodiments, and various modifications can be made without departing from the gist of the present invention. For example, in the example of the above-described embodiment, the ceramic circuit board 1 is manufactured by brazing the metal circuit board 3, the Cu plate 4 and the metal plate 5 to the silicon nitride plate 2 through the active metal brazing material. Silicon nitride plate 2
A metallized metal layer of tungsten, molybdenum, or the like is previously deposited on the surface of the metal circuit board, and the metal circuit plate 3, the Cu plate 4 or the metal plate 5 is attached to the metallized metal layer via a brazing material to form a ceramic circuit board 1. May be formed.

In the example of the above-described embodiment, the metal circuit board 3 formed in advance in the circuit wiring pattern shape is brazed to the silicon nitride plate 2 through the active metal brazing material.
The metal circuit plate 3 may be formed by brazing a metal plate having substantially the same shape as the silicon nitride plate 2 and then removing unnecessary metal portions by etching to form a circuit wiring pattern.

[0051]

According to the ceramic circuit board of the present invention,
A circuit board comprising a metal circuit board bonded to one main surface of a base body formed by sandwiching a Cu plate or a Cu alloy plate between two silicon nitride plates, and a metal plate bonded to the other main surface thereof. Cu
The plate or the Cu alloy plate has a thickness of 0.5 mm or more and 2.0 mm or less, and the total ratio of the thickness of the metal circuit plate and the Cu plate or the Cu alloy plate and the metal plate to the total thickness of the ceramic circuit board is 50. Since it is up to 90%, it is assumed that the base is formed by sandwiching a Cu plate or a Cu alloy plate between silicon nitride plates made of a silicon nitride sintered body having excellent mechanical strength and fracture toughness and using this base. Since the circuit board as a whole has a five-layer structure of metal circuit plate / silicon nitride plate / Cu plate or Cu alloy plate / silicon nitride plate / metal plate, the Cu plate or Cu alloy plate is used as the intermediate layer of the ceramic circuit board. Since the rigidity of the base is increased by providing it, it is possible to reduce the average strain. Therefore, even when a thin silicon nitride plate is used for the base, a thick metal circuit board is bonded to form a circuit board. thing And the mechanical strength can be increased without impairing the joint reliability. Furthermore, when the thickness of the entire ceramic circuit board increases, the heat generated by electronic components such as semiconductor elements is conducted while spreading laterally,
Since the Cu plate or the Cu alloy plate between the silicon nitride plates has higher thermal conductivity than the silicon nitride plate, it conducts while diffusing more effectively, and therefore electronic components such as semiconductor elements mounted on the metal circuit board. It is possible to effectively conduct and dissipate the heat generated by the metal circuit plate to the metal plate. Further, according to the ceramic circuit board of the present invention, the metal circuit board is provided on one main surface of the base body in which the Cu plate or the Cu alloy plate is sandwiched between the two silicon nitride plates, and the metal plate is provided on the other main surface. By combining them, considering the balance between the improvement of heat dissipation characteristics and the suppression of warpage of the board, the circuit board as a whole has a minimum required five-layer structure, so that the mechanical strength is sufficient. Even if a silicon nitride plate is used, the thickness of the ceramic circuit board does not increase excessively and it is difficult for the ceramic circuit board to flex. Therefore, it is possible to secure mechanical strength while allowing a sufficient flexure amount in the circuit board.

Further, according to the ceramic circuit board of the present invention, the Cu plate or Cu alloy plate between the two silicon nitride plates is a Cu plate or Cu alloy plate having a high thermal conductivity of 0.2 mm or more and 2.0 mm or less. Furthermore, since the ratio of the metal circuit board, the Cu plate or the Cu alloy plate, and the metal plate in the ceramic circuit board is set to 50 to 90%, the heat easily spreads in these high heat conductive metal parts,
The heat can be effectively diffused in the lateral direction, and the thermal characteristics can be improved.

Further, according to the ceramic circuit board of the present invention, when the thickness of the metal circuit board is T1, the thickness of the Cu plate or the Cu alloy plate is T2, and the thickness of the metal plate is T3, T2 is given.
By setting ≧ T1 ≧ T3, the influence on the warp of the board is small, and the Cu plate or the Cu arranged over the entire surface of the circuit board
Since the thickness T2 of the alloy plate is thickest and the thickness T1 of the metal circuit board having a small bonding area is thicker than the thickness T3 of the metal plate having a large bonding area, the rigidity of the circuit board as a whole is secured, and the silicon nitride plate and the Cu The thermal stress on the front and back of the circuit board due to the difference in thermal expansion coefficient between the metal plate and the base body made of a metal plate or a Cu alloy plate is well-balanced, and the warp of the ceramic circuit board is suppressed to an extremely small level. be able to. Further, by suppressing the warp of the circuit board, the close contact with an external water cooler or the like is improved, the heat dissipation characteristics are improved, and further, the occurrence of cracks or cracks due to thermal / mechanical stress is prevented. It is possible,
As a result, it becomes possible to prevent insulation failure due to cracks and improve the reliability of the circuit board.

As a result, according to the circuit board of the present invention, the heat dissipation characteristics are improved, and it is possible to prevent malfunction of electronic components such as semiconductor elements mounted on the metal circuit board due to heat, and it is highly reliable. It is possible to obtain a semiconductor module.

As described above, according to the present invention, it is possible to provide a ceramic circuit board capable of increasing the mechanical strength of the ceramic circuit board, improving the thermal characteristics, and suppressing the warp of the board.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of an embodiment of a ceramic circuit board of the present invention.

FIG. 2 is a diagram showing an example of a change in thermal resistance θj-w with respect to a metal ratio in the present invention and the conventional ceramic circuit board.

FIG. 3 is a diagram showing an example of changes in average strain with respect to copper plate thickness in the present invention and conventional ceramic circuit boards.

FIG. 4 is a cross-sectional view showing an example of a conventional ceramic circuit board.

[Explanation of symbols]

1: Ceramic circuit board 2: Silicon nitride plate 3: Metal circuit board 4: Cu plate or Cu alloy plate (Cu plate, etc.) 5: Metal plate 6: Base

Claims (2)

[Claims] 1. A Cu plate or a C plate between two silicon nitride plates.
A ceramic circuit board in which a metal circuit board is bonded to one main surface of a base body formed by sandwiching and sandwiching a u alloy plate and a metal plate is bonded to the other main surface, wherein the Cu plate or the Cu alloy plate comprises:
The thickness is 0.2 mm or more and 2.0 mm or less, and the ratio of the total thickness of the metal circuit plate and the Cu plate or the Cu alloy plate and the metal plate in the total thickness of the ceramic circuit board is 50 to 90%. A ceramic circuit board characterized by: 2. The thickness of the metal circuit board is T1, the Cu
The ceramic circuit board according to claim 1, wherein T2 ≧ T1 ≧ T3, where T2 is the thickness of the plate or Cu alloy plate and T3 is the thickness of the metal plate.