JP2014090049A - Power module substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive power module substrate having both high thermal conductivity and high bending strength, and high in all mechanical reliability.SOLUTION: A power module substrate 10 comprises: a circuit copper plate 12 for mounting a semiconductor element 14 to form an electrical continuity circuit; and a heat dissipation copper plate 13 for dissipating heat generated from the semiconductor element 14, the circuit copper plates and the heat dissipation plate being joined on one main face and the other main face of a ceramic substrate 11, respectively. In the power module substrate, the ceramic substrate 11 contains alumina (AlO) as a main constituent, and zirconia (ZrO), and comprises joined bodies 20, 20a, 20b of two kinds of an alumina ceramic flat plate containing zirconia at a high rate and an alumina ceramic plate containing zirconia at a low rate, the alumina plates being obtained by adding a sintering assistant comprising at least one or more of yttria (YO), calcia (CaO), magnesia (MgO) and ceria (CeO) and having a different percentage content of zirconia each other.

Description

  In the present invention, a circuit copper plate is directly bonded to one main surface of both surfaces of a ceramic substrate, and a heat dissipation copper plate is directly bonded to the other main surface, and heat generated from a semiconductor element mounted on the circuit copper plate is dissipated through the ceramic substrate. The present invention relates to a power module substrate that radiates heat from a copper plate.

  Conventionally, a semiconductor element that generates high heat, such as a power transistor with higher power, higher speed, and higher integration, can be mounted, and heat generated from the semiconductor element can be quickly dissipated to maintain the reliability of the semiconductor element. Therefore, the power module substrate is used for consumer equipment and in-vehicle use such as automobiles and electric cars. For such a power module substrate, a large ceramic substrate that can be arranged in a matrix is usually used. To this ceramic substrate, a direct bonding method in which a copper plate that is approximately the same as or slightly smaller than the size of the ceramic substrate is directly heat-bonded using the melting point of copper, or heat bonding is performed using an active metal brazing. Joined by active metal brazing method. The ceramic substrate with a copper plate attached to almost the entire surface as in the case of a large ceramic substrate is formed by etching to form a pattern for mounting a semiconductor element on each main surface to form an electrically conductive state. The circuit copper plate and the heat radiating copper plate for transferring and radiating the heat generated from the semiconductor element are formed. In addition, a power module substrate assembly in which a plurality of power module substrates each having a pair of a circuit copper plate and a heat dissipation copper plate are arranged in a matrix on a large ceramic substrate is formed with a dividing groove for dividing into individual pieces. It is supposed to be.

  In the individual power module substrate, a semiconductor element is bonded with a bonding material onto a predetermined portion of the copper plate on the circuit copper plate side. Further, the power module substrate is configured such that the external connection terminals are bonded with a bonding material on a copper plate different from the copper plate with the semiconductor element bonded with the bonding material. Then, the power module substrate forms an electrical conduction circuit by connecting the semiconductor element and another portion of the copper plate with a bonding wire, and a high voltage and high current is supplied to the semiconductor element via the external connection terminal. To be able to flow. In addition, this power module substrate has a thermal conductivity in order to quickly dissipate heat from the semiconductor element generated by the flow of high voltage and high current from the circuit copper plate side using copper having good thermal conductivity. Heat is transferred to the heat radiating copper plate side using good copper, and is usually radiated from a heat sink plate joined to the heat radiating copper plate with a bonding material or the like.

In the power module substrate, ceramics such as aluminum nitride (AlN), alumina (Al ₂ O ₃ ), and zirconia-containing alumina containing alumina containing zirconia (ZrO ₂ ) are homogeneous. A fired substrate made of a material is used. In addition, a ceramic substrate used for these power module substrates is required to be a fired substrate that has low mechanical strength, particularly high bending strength, high thermal conductivity, and low cost.

  The ceramic substrate used for a conventional power module substrate is a composite ceramic substrate in which a silicon nitride layer and an aluminum nitride layer are combined and integrated, and is provided on the aluminum nitride layer surface on the aluminum nitride layer side of the composite ceramic substrate. There has been proposed one including a copper circuit board bonded by an direct bonding method through an oxide film (see, for example, Patent Document 1). According to this, the ceramic substrate can improve the mechanical reliability of itself, and can improve the bonding reliability when the copper plate is directly bonded.

  Further, the ceramic substrate used for the conventional power module substrate is provided with a sheet-type multilayer ceramic material and one surface side of the ceramic material, and at least connected to the ceramic material by direct bonding or active soldering. In the case of a metal ceramic substrate with one metal coating, the ceramic material includes at least one silicon nitride ceramic intermediate layer or base layer, and the surface side of the ceramic material with at least one metal coating is applied to the base layer. An oxide ceramic intermediate layer is proposed (for example, see Patent Document 2).

  However, although a ceramic substrate made of silicon nitride, aluminum nitride, or silicon nitride has extremely high thermal conductivity and high bending strength, these nitride compounds themselves are expensive and these nitride compounds are also expensive. Therefore, it is necessary to form an oxide film for directly bonding the copper plate to the substrate, which increases the cost of the power module substrate itself.

  In addition, ceramic substrates made of alumina have been widely used because they have a relatively high thermal conductivity of 27 to 30 W / mK and can improve heat dissipation. However, the power module substrate has a large difference in thermal expansion coefficient between the circuit copper plate and the heat dissipation copper plate as the heat generation temperature rises due to high power, high speed, high integration, etc. of the semiconductor element mounted on the power module substrate. It has become to. And since this ceramic substrate made of alumina has low bending strength, it is impossible to prevent the stress due to the difference in thermal expansion coefficient from concentrating on the ceramic substrate and generating cracks in the ceramic substrate.

  Therefore, a ceramic substrate made of zirconia-containing alumina in which zirconia is contained in alumina is often used for the power module substrate. The ceramic substrate made of zirconia-containing alumina with alumina containing zirconia has higher bending strength and higher toughness and higher mechanical reliability than a ceramic substrate made of alumina alone. The generation of cracks due to the difference in thermal expansion coefficient can be prevented. On the other hand, a ceramic substrate made of zirconia-containing alumina in which zirconia is contained in alumina has a thermal conductivity as low as 20 to 24 W / mK, which inhibits heat dissipation of the power module substrate. Therefore, in the case of a ceramic substrate made of zirconia-containing alumina with alumina containing zirconia, the thickness of the ceramic substrate is made thin by taking advantage of the high bending strength, and the low thermal conductivity is covered to provide heat radiation reliability. To ensure.

JP 9-172247 A Special table 2009-504547 gazette

However, the conventional power module substrate as described above has the following problems.
The power module substrate can cover the low thermal conductivity by reducing the thickness of the ceramic substrate itself as in the case where the ceramic substrate used for this is made of zirconia-containing alumina in which zirconia is contained in alumina. In this case, when the power module substrate is used under extremely severe environmental conditions such as in-vehicle use, it is difficult to ensure mechanical reliability other than thermal stress by reducing the thickness.
The present invention has been made in view of such circumstances, and has an object to provide a power module substrate that has high thermal conductivity and high bending strength, has high mechanical reliability, and is inexpensive. To do.

A power module substrate according to the present invention that meets the above-described object is generated from a circuit copper plate for forming an electrically conductive circuit by mounting a semiconductor element on one main surface of a ceramic substrate, and from the semiconductor element on the other main surface. In a power module substrate having a heat dissipation copper plate bonded to dissipate heat, the ceramic substrate contains alumina (Al ₂ O ₃ ) as a main component, zirconia (ZrO ₂ ), and yttria (Y ₂ O _3). ), Calcia (CaO), magnesia (MgO), ceria (CeO ₂ ), a zirconia high-content-containing alumina ceramic flat plate having different zirconia content ratios obtained by adding at least one sintering aid, and zirconia It consists of two types of joined bodies of low-rate containing alumina ceramic flat plates.

  In the power module substrate described above, the joined body has a difference between the zirconia weight ratio of the zirconia high-rate-containing alumina ceramic flat plate and the weight ratio of zirconia of the zirconia low-rate-containing alumina ceramic flat plate between 5% and 25%. Is good.

  In the above power module substrate, the joined body is composed of three layers, and the central layer has a zirconia low-rate-containing alumina ceramic flat plate, and zirconia low-rate-containing alumina ceramic flat plates on both sides of the zirconia low-rate-containing alumina ceramic flat plate. Good.

  In the above power module substrate, the joined body is composed of three layers, and the central layer has a zirconia high-rate-containing alumina ceramic flat plate, and zirconia high-rate-containing alumina ceramic flat plates on both sides of the zirconia high-rate-containing alumina ceramic flat plate. Good.

  In the power module substrate described above, the joined body may be composed of two layers, one layer being a zirconia high-rate-containing alumina ceramic flat plate and the other layer being a zirconia low-rate-containing alumina ceramic flat plate.

In the power module substrate, the ceramic substrate contains alumina (Al ₂ O ₃ ) as a main component and contains zirconia (ZrO ₂ ), and yttria (Y ₂ O ₃ ), calcia (CaO), magnesia (MgO), and ceria. (CeO ₂ ) From two types of joined bodies of a zirconia high-rate-containing alumina ceramic flat plate and a zirconia low-rate-containing alumina ceramic flat plate each having a different zirconia content rate, to which one or more kinds of sintering aids are added. Therefore, it contains alumina as a main component, zirconia is contained at a relatively high rate in this, a zirconia high-rate-containing alumina ceramic flat plate to which a sintering aid is added, and alumina as a main component, and zirconia is contained at a relatively low rate. It is easily sintered with an inexpensive material with a low-zirconia ceramic plate containing zirconia and containing a sintering aid. This is a harsh environment that combines high bending strength with high zirconia-containing alumina ceramic plates and high thermal conductivity with low-zirconia-containing alumina ceramic plates. By using a ceramic substrate that can be used under conditions, it is possible to provide a power module substrate that is highly mechanically reliable and inexpensive.

  In particular, in the power module substrate described above, the joined body has a difference between the zirconia weight ratio of the zirconia high-rate-containing alumina ceramic flat plate and the zirconia weight ratio of the zirconia low-rate-containing alumina ceramic flat plate between 5% and 25%. Because it consists of a high zirconia high-rate-containing alumina ceramic plate side bending strength, a high zirconia low-rate-containing alumina ceramic flat plate side that has high bending strength and high thermal conductivity A ceramic substrate made of a joined body that can be used even under environmental conditions is used, and an inexpensive power module substrate with high mechanical reliability can be provided.

  In particular, in the power module substrate described above, the joined body is composed of three layers, the central layer is a zirconia low-rate-containing alumina ceramic flat plate, and zirconia low-rate-containing alumina ceramic flat plates on both sides of the zirconia low-rate-containing alumina ceramic flat plate. Therefore, by using the same zirconia high-rate-containing alumina ceramic flat plate on both sides of the central layer zirconia low-rate-containing alumina ceramic flat plate, the zirconia low-rate-containing alumina ceramic flat plate and the zirconia high-rate-containing alumina ceramic flat plate at the time of firing It is possible to provide a power module substrate including a joined body with less bending without being affected by a difference in thermal expansion coefficient.

  In particular, in the power module substrate described above, the joined body is composed of three layers, and the central layer is a zirconia high-rate-containing alumina ceramic flat plate, and both sides of the zirconia high-rate-containing alumina ceramic flat plate are zirconia low-rate-containing alumina ceramics. Since it has a flat plate, the same zirconia low-rate-containing alumina ceramic flat plate is used on both sides of the zirconia high-rate-containing alumina ceramic flat plate in the center layer, so that the zirconia high-rate-containing alumina ceramic flat plate and the zirconia low-rate-containing alumina ceramic flat plate It is possible to provide a power module substrate including a joined body with less bending without being affected by a difference in thermal expansion coefficient at the time.

  Further, in particular, in the above power module substrate, the joined body is composed of two layers, and one layer is composed of a zirconia high-rate-containing alumina ceramic flat plate, and the other layer is composed of a zirconia low-rate-containing alumina ceramic flat plate. By directly joining the circuit copper plates that are scattered in the shape, the ceramics at the joint can be easily destroyed, and the zirconia high-rate-containing alumina ceramic flat plate with relatively high bending strength can be obtained. It is possible to provide a power module substrate that can be a zirconia low-rate-containing alumina ceramic flat plate having a relatively high thermal conductivity on the side where heat transfer from the ceramic is easily promoted by direct bonding.

It is explanatory drawing of the board | substrate for power modules which concerns on one embodiment of this invention. (A)-(C) are explanatory drawings of the ceramic substrate used for the board | substrate for power modules, respectively.

Next, embodiments of the present invention will be described with reference to the accompanying drawings to provide an understanding of the present invention.
As shown in FIG. 1, a power module substrate 10 according to an embodiment of the present invention includes a circuit copper plate 12 provided in an island shape on one main surface of a ceramic substrate 11, and the other main surface. A solid heat-dissipating copper plate 13 is joined. The circuit copper plate 12 and the heat radiating copper plate 13 are bonded directly to the ceramic substrate 11 or heated and bonded by active metal brazing material bonding. In this direct bonding method, the circuit copper plate 12 and the heat radiating copper plate 13 whose surfaces have been oxidized in advance are brought into contact with the surface of the ceramic substrate 11 and fired in a nitrogen atmosphere to be close to the melting point (1083 ° C.) of the copper oxide. In this method, the Cu—O eutectic liquid phase generated by the reaction between copper and a small amount of oxygen is directly bonded to the ceramic substrate 11 by using a binder. The active metal brazing material joining method uses an active metal brazing material in which a so-called active metal such as titanium, zirconium, beryllium or the like, which has a very high reactivity, is added to an Ag-Cu brazing filler metal. In this method, the ceramic substrate 11, the circuit copper plate 12, and the heat dissipation copper plate 13 are joined. In this method of joining, first, a paste made of an active metal brazing material is applied to each surface of the ceramic substrate 11, and a circuit copper plate 12 and a heat radiating copper plate 13 that have been previously oxidized on the surface are brought into contact with each other. In this method, heating is performed at about 750 to 850 [deg.] C., and the material is directly bonded to the ceramic substrate 11 using the strength of affinity with oxygen such as titanium.

  On the power module substrate 10, a semiconductor element 14 that generates high heat, such as a power transistor, is mounted on a predetermined island in the circuit copper plate 12, and the external connection terminal 15 is connected to another predetermined island in the circuit copper plate 12. Are to be joined. The power module substrate 10 is configured such that an electrical conduction circuit is formed by connecting the semiconductor element 14 and another predetermined island of the circuit copper plate 12 with bonding wires 16. Further, the power module substrate 10 quickly transfers heat from the semiconductor element 14 bonded to the upper surface of the circuit copper plate 12 to the heat radiating copper plate 13 via the ceramic substrate 11, and the heat radiating copper plate 13 is further transferred to the heat sink plate 17. It is possible to further promote heat dissipation.

  In some cases, one power module substrate 10 is produced on a fired ceramic substrate 11 having a predetermined size. Usually, a plurality of power modules are formed on a fired large ceramic substrate 11. The substrate 10 is manufactured as an assembly in which the substrates 10 are arranged. Then, the power module substrate 10 is divided by dividing grooves provided to individually separate the power module from the assembly, thereby forming one power module substrate 10 having a predetermined size.

The ceramic substrate 11 of the power module substrate 10 contains alumina (Al ₂ O ₃ ) as a main component and zirconia (ZrO ₂ ), and further contains yttria (Y ₂ O ₃ ), calcia (CaO), magnesia. A material to which one or more sintering aids of (MgO) and ceria (CeO ₂ ) are added is used. The ceramic substrate 11 includes a zirconia high-rate-containing alumina ceramic flat plate 18 (see FIGS. 2 (A) to (C)) and a zirconia low-rate-containing alumina ceramic flat plate 19 (FIG. 2 (A). ) To (C)) and the joined bodies 20, 20 a and 20 b (see FIGS. 2A to 2C) which are fired at about 1550 ° C. in the atmosphere.

  The above-mentioned zirconia high-rate-containing alumina ceramic flat plate 18 can improve the bending strength by reducing the alumina content and increasing the zirconia content rate compared to the conventional ceramic substrate made of only one kind of zirconia-containing alumina. However, the thermal conductivity is decreasing. On the other hand, the low zirconia-containing alumina ceramic flat plate 19 has a lower zirconia content and a higher alumina content than the conventional ceramic substrate made of only one kind of zirconia-containing alumina. Although the bending strength can be improved, the bending strength is reduced. While the ceramic substrate 11 of the power module substrate 10 is made of the joined bodies 20, 20 a, and 20 b of the zirconia high-rate-containing alumina ceramic flat plate 18 and the zirconia low-rate-containing alumina ceramic flat plate 19, By taking advantage of each advantage, the bending strength and thermal conductivity can be maintained at a high level.

  The ceramic substrate 11 in the power module substrate 10 is not particularly limited in weight ratio of zirconia to be contained in each of the zirconia high-rate-containing alumina ceramic flat plate 18 and the zirconia low-rate-containing alumina ceramic flat plate 19. For example, the zirconia high-rate-containing alumina ceramic flat plate 18 has a weight ratio of alumina in the range of 70% to less than 95%, and a zirconia weight ratio in the range of 5% to less than 30%. Add a weight ratio of the total amount of one or more selected sintering aids of calcia, magnesia, ceria in the range of 0.1% or more and 2% or less, add a plasticizer, a binder, and a solvent, A sheet-like ceramic green sheet having a predetermined thickness can be used. Further, for example, the alumina ceramic flat plate 19 having a low zirconia content has a weight ratio of alumina in the range of 95% or more and less than 100%, and the weight ratio of zirconia is more than 0 and less than 5%. Add one or more of yttria, calcia, magnesia, and ceria selected sintering aid in a weight ratio of 0.1% to 2%, and add plasticizer, binder, and solvent. Thus, a sheet-like ceramic green sheet having a predetermined thickness can be used. Each of the ceramic green sheets is cut into an appropriate size, stacked one on top of the other with temperature and pressure, and fired at about 1550 ° C. in the atmosphere, so that the zirconia contents differ from each other. The ceramic substrate 11 includes two types of joined bodies 20, 20 a, and 20 b, which are a high-rate-containing alumina ceramic flat plate 18 and a zirconia low-rate-containing alumina ceramic flat plate 19.

  In the joined bodies 20, 20a, and 20b, the difference between the zirconia weight ratio of the zirconia high-rate-containing alumina ceramic flat plate 18 and the zirconia weight ratio of the zirconia low-rate-containing alumina ceramic flat plate 19 is 5% to 25%. It is good. The joined bodies 20, 20 a, and 20 b are bonded to each other with flat plates having different zirconia contents, and a gradient of the concentration of zirconia can be realized in the thickness direction. And this joined body 20, 20a, 20b makes bending strength in the zirconia high rate content alumina ceramic flat plate 18 side by making the difference of the weight ratio of the zirconia contained in each zirconia content alumina into 5% or more and 25% or less. Further, the bonded body 20 having high mechanical reliability that can be used even under severe environmental conditions having both high bending strength and high thermal conductivity capable of increasing the thermal conductivity on the low-zirconia-containing alumina ceramic flat plate 19 side. , 20a, 20b. The joined bodies 20, 20 a, and 20 b are used when the difference between the zirconia weight ratio of the zirconia high-rate-containing alumina ceramic flat plate 18 and the zirconia weight ratio of the zirconia low-rate-containing alumina ceramic flat plate 19 is less than 5%. This makes it impossible to provide a feature difference between the respective zirconia-containing aluminas. In addition, the bonded bodies 20, 20 a, and 20 b are formed when the difference between the zirconia weight ratio of the zirconia high-rate-containing alumina ceramic flat plate 18 and the zirconia weight ratio of the zirconia low-rate-containing alumina ceramic flat plate 19 exceeds 25%. The difference in thermal expansion coefficient between the respective zirconia-containing aluminas becomes too large, and the warpage of the joined bodies 20, 20a, 20b becomes too large.

  As shown in FIG. 2A, the joined body 20 is a ceramic substrate 11 composed of three layers, the center layer is a zirconia low-rate-containing alumina ceramic flat plate 19, and the zirconia high-rate-containing alumina ceramic is formed on both side layers. It is preferable to have a flat plate 18. Further, as shown in FIG. 2B, the joined body 20a is a ceramic substrate 11 composed of three layers, the central layer is a zirconia high-rate-containing alumina ceramic flat plate 18, and the zirconia low-rate content is contained in both side layers. It is preferable to have an alumina ceramic flat plate 19. Further, as shown in FIG. 2 (C), the joined body 20b is a ceramic substrate 11 composed of two layers, and one layer is an alumina ceramic flat plate 18 containing a high ratio of zirconia, and the other is in contact with the other. The layer is preferably a zirconia low content alumina ceramic flat plate 19.

  The joined bodies 20 and 20a have the same type of flat plate arranged on both side layers, thereby canceling the difference in thermal expansion coefficient between the zirconia high-rate-containing alumina ceramic flat plate 18 and the zirconia low-rate-containing alumina ceramic flat plate 19 and the ceramic substrate 11. The occurrence of warping can be prevented. Further, the joined body 20b is provided with the circuit copper plate 12 scattered in an island shape on the side of the alumina ceramic flat plate 18 having a high zirconia content and excellent in bending strength, and the ceramic substrate 11 is cracked by being scattered in the island shape. It is possible to prevent it from being easily caused. At the same time, the joined body 20b is provided with a solid heat-dissipating copper plate 13 on the side of the alumina ceramic flat plate 19 containing low zirconia having excellent thermal conductivity, and heat generated from the semiconductor element 14 is quickly transferred through the ceramic substrate 11, Heat dissipation from the heat dissipation copper plate 13 and the heat sink plate 17 can be promoted.

  The power module substrate of the present invention is mounted with a semiconductor element that generates a large amount of heat through a high voltage, and can be used as a power module substrate for use in, for example, an inverter or an automobile part. .

  10: Power module substrate, 11: Ceramic substrate, 12: Circuit copper plate, 13: Heat dissipation copper plate, 14: Semiconductor element, 15: External connection terminal, 16: Bonding wire, 17: Heat sink plate, 18: Zirconia high content alumina Ceramic flat plate, 19: Alumina ceramic flat plate with a low zirconia content, 20, 20a, 20b: joined body

Claims (5)

A circuit copper plate for mounting a semiconductor element on one main surface of the ceramic substrate to form an electrically conductive circuit, and a heat dissipation copper plate for dissipating heat generated from the semiconductor element are bonded to the other main surface. In the power module substrate,
The ceramic substrate contains alumina (Al ₂ O ₃ ) as a main component and zirconia (ZrO ₂ ), and any of yttria (Y ₂ O ₃ ), calcia (CaO), magnesia (MgO), and ceria (CeO ₂ ). Or a zirconia high-rate-containing alumina ceramic flat plate having different zirconia content rates, and one or more kinds of sintering aids added thereto, and a low-zirconia low-rate-containing alumina ceramic flat plate. Power module substrate.   2. The power module substrate according to claim 1, wherein the joined body has a difference between a weight ratio of the zirconia of the zirconia high-rate-containing alumina ceramic flat plate and a weight ratio of the zirconia of the low-zirconia-containing alumina ceramic flat plate of 5. % Or more and 25% or less, A power module substrate.   3. The power module substrate according to claim 1, wherein the joined body includes three layers, and a central layer is the zirconia low-rate-containing alumina ceramic flat plate, and the zirconia is formed on both sides of the zirconia low-rate-containing alumina ceramic flat plate. A power module substrate comprising a high-rate-containing alumina ceramic flat plate.   3. The power module substrate according to claim 1, wherein the joined body includes three layers, and a central layer is the zirconia high-rate-containing alumina ceramic flat plate, and the zirconia is formed on both sides of the zirconia high-rate-containing alumina ceramic flat plate. A power module substrate comprising a low-rate-containing alumina ceramic flat plate.   3. The power module substrate according to claim 1, wherein the joined body includes two layers, one layer from the zirconia high-rate-containing alumina ceramic flat plate, and the other layer from the zirconia low-rate-containing alumina ceramic flat plate. A substrate for a power module.

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