Patent Description:
As a power-module substrate with heat-sink, as described in <CIT> or <CIT> for example, known is a structure in which a circuit layer made of copper or the like is formed on one surface of a ceramic board that would be an insulating layer; a metal layer made of copper or the like is formed on the other surface of the ceramic board; and a heat sink (a heat radiation board) made of aluminum, copper, or the like is bonded on an opposite surface of the ceramic board to the metal layer. By soldering (mounting) electronic parts such as a semiconductor element and the like on a surface (an upper surface) of the circuit layer of the power-module substrate with heat-sink structured as above, a power module is manufactured.

The heat sink made from aluminum or copper has a large difference in coefficients of linear expansion from that of the power-module substrate. Accordingly, the power-module substrate with heat-sink is warped by being heated in a mounting process of the electronic parts or exposed in temperature change in environment of using a power module. For instance, if the power-module substrate with heat-sink is warped in the mounting process of the electronic parts, a position of the electronic part may be dislocated or a bonding reliability may be deteriorated by warps or cracks in a solder-bonded part.

Moreover, if the power-module substrate with heat-sink is warped in the environment of using the power module, thermal-electric conductive grease between the heat sink and a cooler flows out by a pump-out phenomenon, so that adhesiveness may be deteriorated between the heat sink and the cooler and thermal resistance may be increased. Furthermore, if the power-module substrate with heat-sink is warped repeatedly as above, so that the cracks may arise in the ceramic board.

Accordingly, in such a power-module substrate with heat-sink, by forming the heat sink from an aluminum-impregnated silicon carbide porous body with low thermal expansion and high thermal conductivity instead of aluminum or copper, it is attempted to reduce the warp owing to the difference of linear expansion between the power-module substrate and the heat sink.

The aluminum-impregnated silicon carbide porous body is, as described in <CIT> or <CIT>, a composite body of aluminum and silicon carbide in which aluminum (Al) or an aluminum alloy is impregnated in a porous body formed from mainly silicon carbide (SiC) and a coating layer of aluminum or the aluminum alloy is formed on a surface of the porous body.

Another example of the prior art can be seen in document <CIT> which described a power-module substrate with heat-sink in line with the preamble of claim <NUM>.

As described in <CIT> or <CIT>, it was conventionally attempted to reduce the warps of the power-module substrate with heat-sink by forming the heat sink from the aluminum-impregnated silicon carbide porous body with low thermal expansion and high thermal conductivity and reducing the difference of linear expansion between the power-module substrate and the heat sink. However, it is not enough to reduce the warp amount in the power-module substrate with heat-sink, and further improvement is required.

The present invention is achieved in consideration of the above circumstances, and has an object to provide a power-module substrate with heat-sink having high reliability against power cycles and hot-cold cycles.

A power-module substrate with heat-sink of the present invention includes: a power-module substrate in which a circuit layer made of copper or a copper alloy is disposed on one surface of a ceramic board and a metal layer made of copper or a copper alloy is disposed on the other surface of the ceramic board; and a heat sink which is bonded on the metal layer of the power-module substrate and formed from an aluminum-impregnated silicon carbide porous body in which aluminum or an aluminum alloy is impregnated in a porous body made of silicon carbide: in the power-module substrate with heat-sink, where yield stress of the circuit layer is σ1 (MPa), a thickness of the circuit layer is t1 (mm), and a bonding area between the circuit layer and the ceramic board is A1 (mm<NUM>) and yield stress of the metal layer is σ2 (MPa), a thickness of the metal layer is t2 (mm), and a bonding area between the metal layer and the ceramic board is A2 (mm<NUM>): in the power-module substrate with heat-sink, the thickness t1 is formed to be not less than <NUM> and not more than <NUM>, the thickness t2 is formed to be not less than <NUM> and not more than <NUM> and the thickness t2 is formed to be larger than the thickness t1, and a ratio {(σ2 × t2 × A2) / (σ1 × t1 × A1)} is in a range not less than <NUM> and not more than <NUM>.

The aluminum-impregnated silicon carbide porous body forming the heat sink has coefficient of linear expansion which is near to the ceramic board: there is a slight difference in the coefficient of linear expansion. Accordingly, if the metal layer is thin, a warp arises resulting from the difference of linear expansion between the ceramic board and the heat sink.

In the power-module substrate with heat-sink of the present invention, the thickness t2 of the metal layer made of copper or a copper alloy having high rigidity is larger (thicker) than the thickness t1 of the circuit layer; so that resistance force of the metal layer is dominant in stress difference along the front and back surfaces of the metal layer. Therefore, it is possible to reduce the warp resulting from the difference of linear expansion between the ceramic board and the heat sink, and it is possible to further reduce the warp arisen in the power-module substrate with heat-sink.

However, if the thickness t2 of the metal layer is too large, the ceramic board may be broken (cracked) resulting from thermal expansion of the metal layer while hot-cold cycles. Moreover, if the thickness t1 of the circuit layer is larger than the thickness t2 of the metal layer, influence of thermal expansion of the circuit layer is increased, so that a warp arises. Accordingly, the circuit layer and the metal layer are formed in a range of prescribed thicknesses, and a relation between the circuit layer and the metal layer is adjusted in a range of a ratio {(σ2 × t2 × A2) / (σ1 × t1 × A1)} not less than <NUM> and not more than <NUM>. Thereby reducing the warp of the whole of the power-module substrate with heat-sink, and it is possible to form the power-module substrate with heat-sink having high reliability against the power cycles and the hot-cold cycles.

In addition, if the thickness t1 of the circuit layer is less than <NUM>, bonding material used for bonding the ceramic board and the circuit layer may exude on a surface of the circuit layer by heating. Moreover, if the thickness t1 of the circuit layer is more than <NUM>, in a case in which a semiconductor element is bonded or the like for example, when the power-module substrate with heat-sink is heated; the ceramic board may be cracked.

If the thickness t2 of the metal layer is less than <NUM>, an effect of reducing the warp arising in the power-module substrate with heat-sink by increasing the thickness t2 of the metal layer cannot be shown. Moreover, if the thickness t2 of the metal layer is more than <NUM>, when the power-module substrate with heat-sink is heated, for example when bonding the semiconductor element, the ceramic board may be cracked.

According to the present invention, on a lower surface of the heat sink, a center position of a bonding surface between the heat sink and the metal layer is set to be a center of a measuring area, a maximum length of the measuring area is set to L (mm), a deformation amount of the heat sink in the measuring area is set to Z (mm), a value of a warp (Z/L<NUM>) when heated to <NUM> is set to X, and a value of a warp (Z/L<NUM>) when cooled to <NUM> after heated to <NUM> is set to Y: a difference (Y - X) between the warp X and the warp Y is not less than - <NUM> × <NUM>-<NUM> (mm-<NUM>) and not more than <NUM> × <NUM>-<NUM> (mm-<NUM>). Here, the deformation amount Z is positive if the deformation swells toward the circuit layer side; or negative if the deformation swells toward the lower surface side of the heat sink.

In the power-module substrate with heat-sink in which the difference (Y - X) between the warp X when heated <NUM> and the warp Y when cooled <NUM> from <NUM> after the heating is between -<NUM> × <NUM>-<NUM> (nim-<NUM>) and <NUM> × <NUM>-<NUM> (nim-<NUM>) (inclusive), the difference between the warps arising at the low temperature (<NUM>) and the high temperature (<NUM>) is also small. In such a power-module substrate with heat-sink, the warp arising when soldering the electronic part on the circuit layer or wire-bonding or the like and the warp arising when the load of the hot-cold cycles of the power module is placed on are small: it is possible to improve workability in the manufacturing process such as soldering of the electronic part and the like, and to prevent the ceramic board from cracking.

As a preferred aspect of the power-module substrate with heat-sink of the present invention, it is preferable that the warp X be not less than -<NUM> × <NUM>-<NUM> (mm-<NUM>) and not more than <NUM> × <NUM>-<NUM> (nim-<NUM>) and the warp Y be not less than -<NUM> × <NUM>-<NUM> (mm-<NUM>) and not more than <NUM> × <NUM>-<NUM> (mm-<NUM>).

In a case in which the warps X and Y are more than <NUM> × <NUM>-<NUM> (mm-<NUM>), when the power-module substrate with heat-sink is installed on a water-cooling cooler or the like, a large amount of grease is necessary to be used between the heat sink and the water-cooling cooler, and thermal resistance may be increased. In a case in which the warps X and Y are less than -<NUM> × <NUM>-<NUM> (mm-<NUM>), when the power-module substrate with heat-sink is installed on the water-cooling cooler or the like, a load is placed on the ceramic board and cracks or the like may arise.

As a preferred aspect of the power-module substrate with heat-sink of the present invention, it is preferable that a diffusion layer having an intermetallic compound of aluminum and copper be formed between the metal layer and the heat sink.

Between the metal layer of the power-module substrate and the heat sink, the diffusion layer having the intermetallic compound of aluminum and copper is formed and the metal layer and the heat sink are bonded with the diffusion layer therebetween; so that the metal layer and the heat sink are closely adhered to each other and can be firmly bonded.

According to the power-module substrate with heat-sink of the present invention, it is possible to prevent the ceramic board from cracking resulting from the temperature variation and the reliability against the power cycles and the hot-cold cycles can be improved.

Below, an embodiment of the present invention will be explained with referring the drawings. A power-module substrate with heat-sink <NUM> of the present embodiment is shown in <FIG>. The power-module substrate with heat-sink <NUM> is provided with a power-module substrate <NUM> and a heat sink <NUM> bonded on the power-module substrate <NUM>.

As shown in <FIG>, the power-module substrate <NUM> is provided with a ceramic board <NUM> structuring an insulating layer, a circuit layer <NUM> disposed on one surface (an upper surface in <FIG>) of the ceramic board <NUM>, and a metal layer <NUM> disposed on the other surface (a lower surface in <FIG>) of the ceramic board <NUM>.

The ceramic board <NUM> is for preventing electric connection between the circuit layer <NUM> and the metal layer <NUM>. The ceramic board <NUM> is formed from ceramics having high insulation, for instance, such as AlN (aluminum nitride), Si<NUM>N<NUM> (silicon nitride), Al<NUM>O<NUM> (alumina), SiC (silicon carbide), to have a thickness t3 in a range of not less than <NUM> and not more than <NUM>.

The circuit layer <NUM> is formed by bonding a copper board made of copper or a copper alloy (preferably oxygen-free copper: OFC) on one surface of the ceramic board <NUM>. The circuit layer <NUM> has a prescribed circuit pattern formed by etching or the like. The circuit layer <NUM> (a thickness of the copper board) has the thickness t1 in a range of not less than <NUM> and not more than <NUM>.

The metal layer <NUM> is formed by bonding a copper board made of copper or a copper alloy (preferably oxygen-free copper: OFC) on the other surface of the ceramic board <NUM>. A thickness t2 of the metal layer <NUM> (a thickness of the copper board) is formed in a range not less than <NUM> and not more than <NUM>.

In the power-module substrate <NUM>, as shown in <FIG>, where yield strength of the circuit layer <NUM> is σ1 (MPa), the thickness of the circuit layer <NUM> is t1 (mm), a bonding area between the circuit layer <NUM> and the ceramic board <NUM> is A1 (mm<NUM>); and yield strength of the metal layer <NUM> is σ2 (MPa), the thickness of the metal layer <NUM> is t2 (mm), a bonding area between the metal layer <NUM> and the ceramic board <NUM> is A2 (mm<NUM>); the thickness t2 of the metal layer <NUM> is formed to be larger (thicker) than the thickness t1 of the circuit layer, and the circuit layer <NUM> and the metal layer <NUM> are adjusted to have a relation in which a ratio {(σ2 × t2 × A2) / (σ1 × t1 × A1)} is in a range between <NUM> and <NUM> inclusive.

In addition, a circuit pattern is formed in the circuit layer <NUM>: in a case in which it has a plurality of separated pattern forms, the bonding area A1 (mm<NUM>) is a total sum of bonding areas of the respective pattern forms: the bonding area A1 of the circuit layer <NUM> is normally an area of about <NUM>% of the bonding area A2 of the metal layer <NUM>. The yield strength σ1 of the circuit layer <NUM> and the yield strength σ2 of the metal layer <NUM> are yield strengths at <NUM> of a conditioning (temper) designation "O".

The heat sink <NUM> is for cooling the power-module substrate <NUM>. The heat sink <NUM> is bonded on a lower surface of the metal layer <NUM>, as shown in <FIG>. As shown in <FIG>, the heat sink <NUM> is formed from an aluminum-impregnated silicon carbide porous body in which aluminum (Al) or an aluminum alloy is impregnated in a porous body <NUM> made of silicon carbide (SiC); and coating layers <NUM> of aluminum or the aluminum alloy which is impregnated inside are formed on a surface of the porous body <NUM>: and the heat sink <NUM> is formed as a flat board shape.

For the aluminum which is impregnated in the porous body <NUM> of the heat sink <NUM>, pure aluminum as exemplified by aluminum (2N-Al) of purity <NUM>% or higher by mass and aluminum (4N-Al) of purity <NUM>% by mass, or an aluminum alloy having composition below can be used: Al: between <NUM>% by mass and <NUM>% by mass inclusive, Si: between <NUM>% by mass and <NUM>% by mass inclusive, Mg: between <NUM>% by mass and <NUM>% by mass inclusive, and the remainder: impurity. Aluminum alloys such as ADC <NUM>, A356 and the like can be also used.

A thickness t4 of the heat sink <NUM> can be <NUM> to <NUM> inclusive. The thickness t4 of the heat sink <NUM> is a thickness including a thickness t141 of the coating layers <NUM> coating both the surfaces of the porous body <NUM>. The thickness t141 per one surface of the coating layers <NUM> is preferably <NUM>-fold to <NUM>-fold (inclusive) of the thickness t4 of the heat sink <NUM>.

The heat sink <NUM> in which the coating layers <NUM> are formed on the surfaces of the porous body <NUM> is manufactured by, for example, disposing the porous body <NUM> in a mold which is provided so as to have a prescribed clearance on a periphery thereof in advance, press-injecting heated and melted aluminum or the aluminum alloy in the mold, and cooling them in a pressurized state. As described above, by press-injecting aluminum or the like, the aluminum alloy can be impregnated in the porous body <NUM> which has bad wettability with aluminum and the like; furthermore, aluminum or the like is filled in the clearance around the porous body <NUM> so that the coating layers <NUM> having the prescribed thickness can be formed on the surface of the porous body <NUM>. In addition, the thickness t141 of the coating layers <NUM> may be adjusted by cutting of the coating layers <NUM> which are already formed.

Between the metal layer <NUM> of the power-module substrate <NUM> and the heat sink <NUM>, a diffusion layer <NUM> having an intermetallic compound consisting of copper and aluminum is formed by mutually diffusion of copper atoms in the metal layer <NUM> and aluminum atoms in the heat sink <NUM>. It is preferable to form a thickness t131 of the diffusion layer <NUM> be in a range between <NUM> and <NUM> (inclusive) in a range of the thickness t141 of the coating layers <NUM>.

In addition, as a preferable example of combination of the power-module substrate with heat-sink <NUM> of the present embodiment, respective members of the power-module substrate <NUM> are structured from, for example, the ceramic board <NUM> is AlN (aluminum nitride) with the thickness t3 = <NUM>, and the metal layer <NUM> is OFC (oxygen-free copper, the yield strength σ1: <NUM> MPa) with the thickness t2 = <NUM>. In a case in which the bonding area A1 is <NUM><NUM> and the bonding area A2 is <NUM><NUM>, the ratio {(σ2 × t2 × A2) / (σ1 × t1 × A1)} = <NUM>. In the heat sink <NUM>, the aluminum or the like which is impregnated is structured from an Al-Si based alloy, the whole thickness t4 is <NUM>, and the coating layers <NUM> is structured with the thickness t141 about <NUM>. The thickness t131 of the diffusion layer <NUM> is about <NUM>.

In addition, coefficients of linear expansion of the respective members are as follows: <NUM> × <NUM>-<NUM> K-<NUM> for the ceramic board <NUM> made of AlN; <NUM> × <NUM>-<NUM> K-<NUM> for the circuit layer <NUM> and the metal layer <NUM> made of OFC; and <NUM> × <NUM>-<NUM> K-<NUM> for the heat sink <NUM> made of the aluminum-impregnated silicon carbide porous body into which an Al-Si based alloy is impregnated.

On an upper surface of the circuit layer <NUM> in the power-module substrate with heat-sink <NUM> structured as above, an electronic part <NUM> such as a semiconductor element or the like is mounted so that a power module <NUM> is manufactured as shown in <FIG>. The electronic part <NUM> is solder-bonded on the upper surface of the circuit layer <NUM> by solder material such as Sn-Cu, Sn-Cu-Ni or the like: a solder-bonding part with a thickness about <NUM> to <NUM> is formed between the electronic part <NUM> and the circuit layer <NUM>, though the illustration is omitted.

Below, a manufacturing process of the power-module substrate with heat-sink <NUM> of the present embodiment will be explained.

First, a copper board which will be the circuit layer <NUM> and the ceramic board <NUM>, and a copper board which will be the metal layer <NUM> and the ceramic board <NUM>, are bonded. The bonding of the copper boards which will be the circuit layer <NUM> and the metal layer <NUM> to the ceramic board <NUM> is performed by a so-called active-metal brazing method.

In detail, the copper board which will be the circuit layer <NUM> is layered on the upper surface of the ceramic board <NUM> with interposing the active metal brazing material of Ag-Cu-Ti, Ag-Ti or the like (not illustrated): and the copper board which will be the metal layer <NUM> is layered on the lower surface of the ceramic board <NUM> with interposing the same active metal brazing material. Then, a layered body in which these copper boards, the active metal brazing material, and the ceramic board <NUM> is heated in a pressured state in a layering direction thereof in a range between <NUM> MPa and <NUM> MPa (inclusive) as shown in <FIG>, so that the copper board which will be the circuit layer <NUM> is bonded to the ceramic board <NUM>, and the copper board which will be the metal layer <NUM> is bonded to the ceramic board <NUM>: then, the power-module substrate <NUM> is manufactured. Heating condition for this, heating temperature is <NUM> and heating time is <NUM> minutes, for example.

Next, the heat sink <NUM> is bonded on the lower surface of the metal layer <NUM> of the power-module substrate <NUM>. For bonding the power-module substrate <NUM> and the heat sink <NUM>, as shown in <FIG>, it is preferable to use a pressurizing tool <NUM> having a pressurizing board <NUM> having a pressurizing surface 51a of a swelling-curved surface shape and a pressurizing board <NUM> having a pressurizing surface 52a of a sunk-curved surface shape. For the two pressurizing boards <NUM> and <NUM>, it is desirable that the pressurizing surfaces 51a and 52a facing to each other be formed in a sunk surface or a swelled surface having a curved surface with a radius of curvature R <NUM> to <NUM>. In this case, as shown in <FIG>, the pressurizing surface 52a of the pressurizing board <NUM> pressing a lower surface of the heat sink <NUM> in the layering direction is formed by a sunk surface, and the pressing surface 51a of the pressurizing board <NUM> pressing an upper surface of the power-module substrate <NUM> (the upper surface of the circuit layer <NUM>) in the layering direction is formed by a swelled surface. The pressurizing tool <NUM> is provided with an urging device such as a spring or the like giving a pressurizing force by urging the pressurizing boards <NUM> and <NUM> in the layering direction, though the illustration is omitted. In addition, flat boards can be also used for the pressurizing boards <NUM> and <NUM>.

Between the pressurizing board <NUM> and the pressurizing board <NUM> of the pressurizing tool <NUM> structured as above, the power-module substrate <NUM> and the heat sink <NUM> are disposed in a layered manner so that these are interposed in the layering direction. At this time, a layered body of the power-module substrate <NUM> and the heat sink <NUM> is pressurized in the layering direction (a thickness direction) by the pressurizing surface 51a of the pressurizing board <NUM> and the pressurizing surface 52a of the pressurizing board <NUM>, and held in a state of deformation (a warp) swelling the lower surface of the heat sink <NUM> downward. The layered body of the power-module substrate <NUM> and the heat sink <NUM> is heated in the pressurized state by the pressurizing tool <NUM> so that the lower surface of the metal layer <NUM> of the power-module substrate <NUM> and an upper surface of the heat sink <NUM> (the coating layer <NUM>) are bonded by solid-diffusion bonding.

In this case, the solid-phase diffusion bonding is performed by maintaining in vacuum atmosphere, <NUM> MPa to <NUM> MPa of a pressurizing load (a pressurizing force), <NUM> to <NUM> (inclusive) of heating temperature for <NUM> minutes to <NUM> minutes. Accordingly, between the metal layer <NUM> of the power-module substrate <NUM> and the heat sink <NUM> (the coating layer <NUM>), the copper atoms in the metal layer <NUM> and the aluminum atoms in the heat sink <NUM> (the coating layer <NUM>) are mutually diffused. Thereby forming the diffusion layer <NUM> having the intermetallic compound of copper and aluminum between the metal layer <NUM> and the heat sink <NUM>, the power-module substrate <NUM> and the heat sink <NUM> are bonded with interposing the diffusion layer <NUM>. In addition, the thickness t131 of the diffusion layer <NUM> is increased in accordance with bonding time.

The diffusion layer <NUM> has a structure in which intermetallic compounds with a plurality of composition in accordance with an existence ration of the aluminum atoms and the copper atoms are layered along a boundary surface between the metal layer <NUM> and the heat sink <NUM>. That is to say, in an area at the heat sink <NUM> side of the diffusion layer <NUM>, the existence ratio of the aluminum atoms is high, and an intermetallic compound phase with large content of aluminum is formed. On the other hand, in an area at the metal layer <NUM> side of the diffusion layer <NUM>, the existence ratio of the copper atoms is high, and an intermetallic compound phase with large content of copper is formed. Accordingly, the metal layer <NUM> and the heat sink <NUM> can be adhered to each other and firmly bonded.

The diffusion layer <NUM> is a part in which aluminum (Al) density is less than <NUM> atm% and copper (Cu) density is less than <NUM> atm% in a bonding boundary between the metal layer <NUM> and the heat sink <NUM>. For instance, a vertical section of the power-module substrate with heat-sink <NUM> can be measured in the thickness direction of the bonding boundary between the metal layer <NUM> and the heat sink <NUM> by performing line analysis by EPMA (JXA-8530F made by JEOL Ltd. : an accelerating voltage <NUM> kV, a spot diameter not more than <NUM>, magnification <NUM>-power, an interval <NUM>). A thickness of a part in which the aluminum density is less than <NUM> atm% and the copper (Cu) density is less than <NUM> atm% in the line analysis is the thickness t131 of the diffusion layer.

Next, a bonded body of the power-module substrate <NUM> and the heat sink <NUM> is cooled to <NUM> in a state of being installed on the pressurizing tool <NUM>, that is, in a state of being pressurized. In this case, the bonded body of the power-module substrate <NUM> and the heat sink <NUM> is pressurized in the thickness direction by the pressurizing tool <NUM> so as to be bound in a state of deformation of a warp in which the lower surface of the heat sink <NUM> swells downward. Therefore, a shape of the bonded body appears not to change while the cooling: however, the bonded body is restricted by being pressurized against stress into a state in which deformation as a warp by cooling cannot be accepted: as a result, plastic deformation arises. Then, after cooling to <NUM>, the pressurization of the pressurizing tool <NUM> is released, so that the power-module substrate with heat-sink <NUM> is manufactured.

In the power-module substrate with heat-sink <NUM>, since the thickness t2 of the metal layer <NUM> made of copper or a copper alloy having high rigidity is larger (thicker) than the thickness t1 of the circuit layer <NUM>, resistance force of the metal layer <NUM> is dominant in the stress difference between the front and back (the upper and lower) surfaces of the metal layer <NUM>. Therefore, although there is a slightly difference of the coefficient of linear expansion between the ceramic board <NUM> and the aluminum-impregnated silicon carbide porous body forming the heat sink <NUM> though, it is possible to reduce the warp resulting from the difference of the linear expansion between the ceramic board <NUM> and the heat sink <NUM>. Accordingly, it is possible to reduce the warp arising in the whole body of the power-module substrate with heat-sink <NUM>.

However, if the thickness t2 of the metal layer <NUM> is too large, when the power-module substrate with heat-sink <NUM> is heated, for example, when the semiconductor element and the like is bonded, the ceramic board <NUM> may be broken (crack) by the thermal expansion of the metal layer <NUM>. If the thickness t1 of the circuit layer <NUM> is larger than the thickness t2 of the metal layer <NUM>, the warp may arise because influence of the thermal expansion of the circuit layer <NUM> is large.

Accordingly, in the power-module substrate with heat-sink <NUM> of the present embodiment, the warp of the power-module substrate with heat-sink <NUM> is reduced by balancing the power-module substrate with heat-sink <NUM> as a whole, by forming the thickness t1 of the circuit layer <NUM> in the range of <NUM> to <NUM> (inclusive), forming the thickness t2 of the metal layer <NUM> to be larger than the thickness t1 and in the range of <NUM> to <NUM> (inclusive), and adjusting the relation between the circuit layer <NUM> and the metal layer <NUM> to have the ratio {(σ2 × t2 × A2) / (σ1 × t1 × A1)} <NUM> to <NUM> (inclusive).

In the power-module substrate with heat-sink <NUM> structured as above, on the lower surface (the back surface) of the heat sink <NUM>, as shown in <FIG> and <FIG>, where a center C of a bonding surface of the heat sink <NUM> and the metal layer <NUM> is set as a center of a measuring area E, a longest length in the measuring area E is set to L, a deformation amount of the warp of the heat sink <NUM> in the measuring area E is set to Z, and where a value of a warp (Z/L<NUM>) when it is heated to <NUM> is X and a value of a warp (Z/L<NUM>) when it is cooled after heated to <NUM> is Y; a difference (Y - X) between the warp X and the warp Y is not less than -<NUM> × <NUM>-<NUM> (mm-<NUM>) and not more than <NUM> × <NUM>-<NUM> (mm-<NUM>): the deformation amount of warp between at high temperature (<NUM>) and low temperature (<NUM>) can be reduced. Here, the deformation amount Z of the heat sink <NUM> is positive if the deformation swells toward the circuit layer side, or negative if the deformation swells toward the lower surface side of the heat sink <NUM>.

In the power-module substrate with heat-sink <NUM>, the value X of the warp (Z/L<NUM>) when it is heated to <NUM> is between -<NUM> × <NUM>-<NUM> (mm-<NUM>) and <NUM> × <NUM>-<NUM> (mm-<NUM>) (inclusive), and the value Y of the warp (Z/L<NUM>) when it is cooled to <NUM> after heating to <NUM> is between -<NUM> × <NUM>-<NUM> (mm-<NUM>) and <NUM> × <NUM>-<NUM> (mm-<NUM>) (inclusive).

In a case in which the warps X and Y exceed <NUM> × <NUM>-<NUM> (mm-<NUM>), when the power-module substrate with heat-sink <NUM> is installed on a water-cooling cooler or the like, a large amount of grease is necessary to be used between the heat sink <NUM> and the water-cooling cooler, and thermal resistance may be increased. If the warps X and Y are less than -<NUM> × <NUM>-<NUM> (mm-<NUM>), when the heat-sink-attached board of for power module <NUM> is installed on the water-cooling cooler or the like, a load is placed on the ceramic board <NUM> and breakages or the like may arise.

As explained above, in the power-module substrate with heat-sink <NUM>, it is possible to reduce the warp arising in manufacturing the power module and reduce the warp deformation in a process of heat treatment: it is possible to improve workability in the manufacturing process such as soldering of the electronic part <NUM> and reliability to the hot-cold cycle load on the power module.

If the thickness t1 of the circuit layer is less than <NUM>, bonding material used for bonding the ceramic board <NUM> and the circuit layer <NUM> may exude to a surface of the circuit layer <NUM> when heated. If the thickness t1 of the circuit layer <NUM> is more than <NUM>, when the power-module substrate with heat-sink <NUM> is heated, for example when bonding the semiconductor element, the ceramic board <NUM> may be broken.

If the thickness t2 of the metal layer <NUM> is less than <NUM>, the effect of reducing the warp arising in the power-module substrate with heat-sink <NUM> by increasing the thickness t2 of the metal layer <NUM> cannot be shown. Moreover, if the thickness t2 of the metal layer <NUM> is more than <NUM>, when the power-module substrate with heat-sink <NUM> is heated, for example when bonding the semiconductor element, the ceramic board <NUM> may be broken.

Below, Examples for confirming the effect of the present invention will be explained. As described in Table <NUM>, manufactured were boards for power module with varying the material of the circuit layer (the yield strength σ1) and the thickness t1 and the bonding area A1 of the circuit layer, and the material of the metal layer (the yield strength σ2) and the thickness t2 and the bonding area A2 of the metal layer for respective Examples. The metal layers of the respective boards for power module and the heat sinks were solid-diffusion phase bonded, so that manufactured were samples of the heat-sink-attached boards for power module in which the diffusion layer was formed between the metal layer and the heat sink.

As the copper boards which would be the circuit layer, as shown in Table <NUM>, used were rectangular boards made of OFC (coefficient of linear expansion <NUM> × <NUM>-<NUM> K-<NUM>, the yield stress <NUM> MPa) or ZC (coefficient of linear expansion: <NUM> × <NUM>-<NUM> K-<NUM>, the yield stress <NUM> MPa), with a plane size <NUM> × <NUM>. As the copper boards which would be the metal layer, used were rectangular boards made of OFC (coefficient of linear expansion <NUM> × <NUM>-<NUM> K-<NUM>, the yield stress <NUM> MPa) or ZC (coefficient of linear expansion: <NUM> × <NUM>-<NUM> K-<NUM>, the yield stress <NUM> MPa), with a plane size <NUM> × <NUM>. Rectangular boards with the thickness t3 = <NUM> and a plane size <NUM> × <NUM> made of AlN (coefficient of linear expansion <NUM> × <NUM>-<NUM> K-<NUM>) were used as the ceramic boards.

Ag-Ti based active metal brazing material was used for bonding the respective copper boards and the ceramic board: the copper boards, the active metal brazing material, and the ceramic board were layered and pressurized in the layered direction with pressurizing force <NUM> MPa and heated at heating temperature <NUM> for <NUM> minutes so that the copper board which would be the circuit layer and the ceramic board, the copper board which would be the metal layer and the ceramic board were bonded respectively, and the power-module substrate was manufactured.

The bonding area A1 and the bonding area A2 in Table <NUM> are values respectively calculated from the plane sizes of the copper boards which would be the circuit layer or the metal layer: using these values, the ratio S = {(σ2 × t2 × A2) / (σ1 × t1 × A1)} was calculated.

Used for the heat sink was a rectangular board with the whole thickness t4 =<NUM> and the plane size <NUM> × <NUM> formed from the aluminum-impregnated silicon carbide porous body in which the Al-Si based alloy was impregnated into silicon carbide (SiC), and formed to have the thickness t141 of the coating layers on the front and back surface were <NUM>. Then, the solid-phase diffusion bonding between the power-module substrate and the heat sink was performed as described in Table <NUM>, using the pressurizing board having the pressurizing surface with the radius of curvature R, by pressurizing and heating with the pressurizing load <NUM> MPa and heating temperature <NUM> for <NUM> minutes in vacuum atmosphere. In addition, the radius of curvature R is denoted by "∞" if the pressurizing surface was a flat surface.

Samples of the power-module substrate with heat-sink were obtained, and evaluated regarding the "deformation amount Z", "ceramic breakage", and "element-position displacement" respectively.

The deformation amount Z was measured (<NUM>) when heated to <NUM> and when (<NUM>) cooled to <NUM> after heated to <NUM>. A change of flatness at the lower surface (the back surface) of the heat sink at points of time was measured by moiré interferometry in accordance with JESD22-B112 or JEITAED-<NUM>.

The moiré interferometry is a method such as: by irradiating a measuring light to a measuring surface through a diffraction grating and taking a photo of scattered light scattered at the measuring surface through the diffraction grating with an imaging part so that moiré interference fringes are obtained, and measuring the deformation amount of the measuring surface in accordance with information of moiré interference fringes, a pitch of the diffraction grating and the like. TherMoire PS200 made by Akrometrix was used as a measuring device.

In the present examples, as shown in <FIG>, the deformation amount Z at the lower surface of the heat sink in the measuring area E (refer to <FIG>) was measured with setting the center position C of the bonding surface of the heat sink <NUM> and the metal layer <NUM> as the center of the measuring area E. The deformation amount Z was set to be positive if the deformation projected at the circuit layer side or negative if the deformation projected at the heat sink lower surface side.

The measuring area E is a rectangular area of W <NUM> × H <NUM> as shown in <FIG> and <FIG>: in this case, the maximum length L is a length of a diagonal line of the measuring area E. The deformation amount Z is a difference between a maximum value and a minimum value of measuring values on the diagonal line of the measuring area E, as shown in <FIG>. The warp (Z/L<NUM>) was calculated from the deformation amount Z and the maximum length L.

The ceramic breakage was evaluated by observation of the ceramic board with an ultrasonic flaw detector after the heating test described above: if a crack was generated in the ceramic board, it was rejected; or if the crack was not generated, it was passed. Regarding the element-position displacements, existence of occurrence of position displacement were checked about <NUM> test pieces for respective Examples, by measuring a soldering position after soldering the electronic parts on the circuit layer. If position displacement of not less than <NUM> was occurred, it was rejected; or if the position displacement was less than <NUM>, it was passed.

Thirty test pieces for respective Examples were evaluated, if a rate of being passed was not less than <NUM>%, it was evaluated as "good": or if the rate of being passed was less than <NUM>%, it was evaluated as "poor". Results are shown in Table <NUM>.

As recognized from Tables <NUM> to <NUM>, regarding Examples Nos. <NUM> to <NUM> in which the thickness t1 is between <NUM> and <NUM> (inclusive), the thickness t2 is between <NUM> and <NUM> (inclusive), the thickness t1 is formed to be larger than the thickness t1, and the ratio {(σ2 × t2 × A2) / (σ1 × t1 × A1)} is in a range of <NUM> to <NUM> (inclusive), the difference (Y - X) were between -<NUM> × <NUM>-<NUM> (mm-<NUM>) and <NUM> × <NUM>-<NUM> (mm-<NUM>). In these Examples Nos. <NUM> to <NUM>, both the evaluation of the "ceramic breakage" and the "element-position displacement" showed good results.

On the other hand, regarding Examples Nos. <NUM>, <NUM> and <NUM> in which the ratio {(σ2 × t2 × A2) / (σ1 × t1 × A1)} was out of the above-described range, the difference (Y - X) was deviated from the range between -<NUM> × <NUM>-<NUM> (mm-<NUM>) and <NUM> × <NUM>-<NUM> (nim-<NUM>) (inclusive), the deformation amount of the warp was large, and the "element-position dislocation" arose. Regarding the test pieces of Example No. <NUM> in which the thickness t2 is larger than <NUM>, the deformation amount of the warp was large, and the test pieces in which the breakage of the ceramic board arose after heated to <NUM> was recognized. In Example No. <NUM> in which the thickness t1 is larger than <NUM> and the thickness t2 is larger than <NUM>, although the deformation amount of the warp is small, there was a test piece in which the ceramic board was broken after heated to <NUM>.

Claim 1:
A power-module substrate (<NUM>) with heat-sink (<NUM>), comprising:
a power-module substrate (<NUM>) in which a circuit layer (<NUM>) made of copper or a copper alloy is disposed on one surface of a ceramic board (<NUM>) and a metal layer (<NUM>) is disposed on the other surface of the ceramic board (<NUM>); and
a heat sink (<NUM>) which is bonded on the metal layer (<NUM>) of the power-module substrate (<NUM>) and formed from an aluminum-impregnated silicon carbide porous body (<NUM>) in which aluminum or an aluminum alloy is impregnated in a porous body (<NUM>) made of silicon carbide, wherein
where yield stress of the circuit layer (<NUM>) is σ1 (MPa), a thickness of the circuit layer (<NUM>) is t1 (mm), and a bonding area between the circuit layer (<NUM>) and the ceramic board (<NUM>) is A1 (mm<NUM>) and yield stress of the metal layer is σ2 (MPa), a thickness of the metal layer (<NUM>) is t2 (mm), and a bonding area between the metal layer and the ceramic board (<NUM>) is A2 (mm<NUM>); wherein
the thickness t1 is formed to be not less than <NUM> and not more than <NUM>,
the thickness t2 is formed to be not less than <NUM> and not more than <NUM> and the thickness t2 is formed to be larger than the thickness t1, and characterized in that
the metal layer (<NUM>) is made of copper or a copper alloy; and a ratio {(σ2 × t2 × A2) / (σ1 × t1 × A1)} is in a range not less than <NUM> and not more than <NUM>, wherein, on a lower surface of the heat sink, a center position of a bonding surface between the heat sink (<NUM>) and the metal layer is set to be a center of a measuring area,
a maximum length of the measuring area is set to L (mm),
a deformation amount of the heat sink (<NUM>) in the measuring area is set to Z (mm),
a warp (Z/L<NUM>) when heated to <NUM> is set to X, and
a warp (Z/L<NUM>) when cooled to <NUM> after heating to <NUM> is set to Y, wherein
a difference (Y - X) between the warp X and the warp Y is not less than -<NUM> × <NUM>-<NUM> (mm-<NUM>) and not more than <NUM> × <NUM>-<NUM> (mm-<NUM>) .