HK1153850A - Substrate for power module, power module, and method for producing substrate for power module - Google Patents
Substrate for power module, power module, and method for producing substrate for power module Download PDFInfo
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- HK1153850A HK1153850A HK11108235.5A HK11108235A HK1153850A HK 1153850 A HK1153850 A HK 1153850A HK 11108235 A HK11108235 A HK 11108235A HK 1153850 A HK1153850 A HK 1153850A
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Description
Technical Field
The present invention relates to a power module (power module) substrate used in a semiconductor device for controlling a large current and a high voltage, a power module provided with the power module substrate, and a method for manufacturing the power module substrate.
The present application claims priority based on japanese patent application 2008-.
Background
Conventionally, a power module is used in a semiconductor device for supplying power. The heat generation amount of the power module is high. Therefore, as a substrate on which the power module is mounted, for example, AlN (aluminum nitride) or Si is used3N4(silicon nitride) or Al2O3A power module substrate is provided in which an Al (aluminum) metal plate is bonded to a ceramic substrate made of (aluminum oxide) via an Al-Si-based brazing material.
The metal plate is formed as a circuit layer, and a semiconductor chip as a power element is mounted on the metal plate via a solder.
In order to improve heat dissipation efficiency, a structure has been proposed in which a metal plate of Al or the like is bonded to the lower surface of a ceramic substrate to form a metal layer, and the entire power module substrate is bonded to the heat dissipation plate via the metal layer.
Conventionally, for example, as disclosed in patent document 1, a technique is known in which the surface roughness of a ceramic substrate is made less than 0.5 μm to obtain a good bonding strength between a metal plate functioning as the circuit layer and the metal layer and the ceramic substrate.
Documents of the prior art
Patent document
Patent document 1: japanese laid-open patent publication No. 3-234045
Disclosure of Invention
Problems to be solved by the invention
However, when a metal plate is bonded to a ceramic substrate, a sufficiently high bonding strength cannot be obtained by merely reducing the surface roughness of the ceramic substrate, and there is a problem that reliability cannot be improved.
For example, with respect to the surface of the ceramic substrate, even if Al is used2O3The particles were subjected to dry honing treatment to have a surface roughness Ra of 0.2 μm, and interfacial peeling was sometimes caused in a peeling test.
Even when the ceramic substrate is polished by a polishing method so that the surface roughness Ra is 0.1 μm or less, interfacial peeling may occur in the same manner.
It is also known that when a thermal cycle is applied to the power module substrate, not only the bonding interface is peeled off but also the ceramic substrate is cracked.
Especially, recently, miniaturization of the power module and thickness reduction of the power module are required, and the use environment thereof becomes severe. For example, the power module is used in a use environment where thermal stress is repeatedly generated.
In recent years, the amount of heat generated from electronic components tends to increase, and it is necessary to dispose the power module substrate on the heat radiation plate as described above.
In this case, since the power module substrate is restrained by the heat radiation plate, a large shearing force acts on the joint interface between the metal plate and the ceramic substrate during a thermal cycle under load. Therefore, further improvement in bonding strength and improvement in reliability are required.
The present invention has been made in view of the above circumstances, and an object thereof is to provide a power module substrate in which a metal plate and a ceramic substrate are reliably joined and which has high thermal cycle reliability, a power module including the power module substrate, and a method for manufacturing the power module substrate.
Means for solving the problems
In order to solve the above problems and achieve the above object, a power module substrate according to claim 1 of the present invention includes a ceramic substrate having a surface, and a metal plate bonded to the surface of the ceramic substrate, made of aluminum, and containing Cu at a bonding interface with the ceramic substrate; the Cu concentration in the bonding interface is set to be in the range of 0.05 to 5 wt%.
In the power module substrate having the above configuration, since Cu is diffused in the metal plate and the Cu concentration at the bonding interface is set to be in the range of 0.05 to 5 wt%, the bonding interface of the metal plate is subjected to solid solution strengthening.
Therefore, the occurrence and development of cracks in the metal plate can be prevented during a thermal cycle under load, and the bonding reliability can be improved.
In the power module substrate according to claim 1 of the present invention, it is preferable that an aluminum phase containing Cu in aluminum and a eutectic phase composed of a 2-membered eutectic structure of Al and Cu are formed at the end of the metal plate in the width direction.
In this case, since the eutectic phase composed of the 2-membered eutectic structure of Al and Cu is formed at the end portion of the metal plate in the width direction, the end portion of the metal plate in the width direction can be further strengthened.
This prevents the occurrence and development of cracks from the widthwise end of the metal plate, thereby improving the bonding reliability.
In the power module substrate according to claim 1 of the present invention, preferably, the eutectic phase is precipitated with precipitated particles made of a Cu-containing compound.
In this case, since the precipitation particles composed of the Cu-containing compound precipitate in the eutectic phase formed at the widthwise end portion of the metal plate, the widthwise end portion of the metal plate can be further precipitation-strengthened.
This can reliably prevent the occurrence and development of cracks from the widthwise end of the metal plate, and can improve the bonding reliability.
In the power module substrate according to claim 1 of the present invention, the metal plate preferably includes: a concentration inclined portion in which the Cu concentration gradually decreases as the metal plate is separated from the bonding interface in the direction in which the metal plate and the ceramic substrate are laminated, and a soft layer having a lower hardness than the vicinity of the bonding interface and formed on the opposite side of the concentration inclined portion from the ceramic substrate.
At this time, in the vicinity of the bonding interface in the metal plate, the Cu concentration is set high, and thus the metal plate is hardened by solid solution strengthening.
On the other hand, in the softer layer, the Cu concentration is set low, so that the hardness is low and the strain resistance is small.
Therefore, the soft layer can absorb thermal deformation (thermal stress) caused by the difference between the thermal expansion coefficients of the metal plate and the ceramic substrate, and the thermal cycle reliability can be greatly improved.
The power module according to claim 2 of the present invention includes: the power module substrate according to claim 1, and an electronic component mounted on the power module substrate.
In the power module having such a configuration, since the bonding strength between the ceramic substrate and the metal plate is high, the reliability thereof can be remarkably improved even in a case where the use environment is severe, for example, even in a case where the power module is used in a manner such that thermal stress is repeatedly generated.
A method for manufacturing a power module substrate according to claim 3 of the present invention is a method for manufacturing a power module substrate, including preparing a ceramic substrate, a metal plate made of aluminum, and a Cu layer having a thickness of 0.15 μm or more and 3 μm or less, laminating the ceramic substrate and the metal plate with the Cu layer interposed therebetween (laminating step), heating the laminated ceramic substrate, Cu layer, and metal plate while applying pressure in the laminating direction to form a molten metal layer at an interface between the ceramic substrate and the metal plate (melting step), solidifying the molten metal layer by cooling the molten metal layer (solidification step), and in the melting step and the solidification step, containing Cu so that a Cu concentration is in a range of 0.05 to 5 wt% in a vicinity of a bonding interface between the ceramic substrate and the metal plate among the metal plates.
The method for manufacturing the power module substrate having this configuration includes laminating a ceramic substrate and a metal plate with a Cu layer interposed therebetween, and heating the laminated ceramic substrate and metal plate while applying pressure in the laminating direction. Thus, the melting point in the vicinity of the bonding interface is lowered by the eutectic reaction between Cu of the Cu layer and Al of the metal plate, and a molten metal layer can be formed at the interface between the ceramic substrate and the metal plate even at a relatively low temperature, whereby the ceramic substrate and the metal plate can be bonded to each other.
That is, the ceramic substrate and the metal plate may be joined without using a brazing material made of an Al — Si alloy or the like.
In this way, since the bonding is performed without using the brazing material, the brazing material does not seep out to the surface of the circuit layer, and the Ni plating layer can be formed well on the surface of the circuit layer.
If the thickness of the Cu layer is less than 0.15 μm, the molten metal layer may not be sufficiently formed at the interface between the ceramic substrate and the metal plate.
When the thickness of the Cu layer exceeds 3 μm, the reactant of Cu and Al is excessively generated at the bonding interface, and the vicinity of the bonding interface of the metal plate is excessively strengthened, so that cracking may occur on the ceramic substrate during thermal cycling under load.
Therefore, the thickness of the Cu layer is preferably 0.15 μm or more and 3 μm or less.
In order to reliably obtain the above effects, the thickness of the Cu layer is preferably 0.5 μm or more and 2.5 μm or less.
In the method for manufacturing a power module substrate according to claim 3 of the present invention, it is preferable that the Cu layer is fastened to at least one of the ceramic substrate and the metal plate before the ceramic substrate, the Cu layer, and the metal plate are laminated.
In this case, Cu is firmly bonded to the surface (bonding surface) of the metal plate facing the ceramic substrate or the surface (bonding surface) of the ceramic substrate facing the metal plate, and therefore the ceramic substrate and the metal plate can be reliably laminated via the Cu layer, and the ceramic substrate and the metal plate can be reliably bonded.
In the method for manufacturing a power module substrate according to claim 3 of the present invention, when the Cu is bonded to at least one of the ceramic substrate and the metal plate, it is preferable that the Cu is bonded to at least one of the ceramic substrate and the metal plate by a method selected from any one of a vapor deposition method, a sputtering method, a plating method, and a coating method of a Cu paste.
In this case, the Cu layer can be reliably formed by any method selected from a vapor deposition method, a sputtering method, a plating method, and a coating method of a Cu paste, and the ceramic substrate and the metal plate can be bonded to each other.
In the method for manufacturing a power module substrate according to claim 3 of the present invention, when the ceramic substrate and the metal plate are laminated via the Cu layer, the Cu layer is preferably disposed by interposing a copper foil between the ceramic substrate and the metal plate.
In this case, the Cu foil is interposed, whereby a Cu layer can be formed on a surface (bonding surface) of the metal plate facing the ceramic substrate or a surface (bonding surface) of the ceramic substrate facing the metal plate.
Therefore, the ceramic substrate and the metal plate can be firmly joined.
The power module substrate according to claim 4 of the present invention includes: from AlN or Si3N4A ceramic substrate having a surface; a metal plate bonded to the surface of the ceramic substrate and made of pure aluminum, and a Cu high concentration portion formed at a bonding interface between the metal plate and the ceramic substrate and having a Cu concentration 2 times or more higher than a Cu concentration in the metal plate.
In the power module substrate having the above-mentioned structure, AlN or Si is used3N4Since the joint interface between the ceramic substrate and the metal plate made of pure aluminum has a Cu high concentration portion having a Cu concentration 2 times or more higher than the Cu concentration in the metal plate, the joint strength between the ceramic substrate and the metal plate can be improved by Cu atoms present in the vicinity of the interface.
The Cu concentration in the metal plate means the Cu concentration in a portion of the metal plate which is a predetermined distance (for example, 50nm or more) from the bonding interface.
In the power module substrate according to claim 4 of the present invention, the oxygen concentration in the Cu high concentration portion is preferably higher than the oxygen concentration in the metal plate and the oxygen concentration in the ceramic substrate.
In this case, the presence of oxygen in the junction interface can further improve the bonding strength of AlN or Si3N4The bonding strength between the ceramic substrate and the metal plate made of pure aluminum.
It is considered that oxygen present at a high concentration at the bonding interface is oxygen derived from oxygen present on the surface of the ceramic substrate and an oxide film formed on the surface of the metal plate.
Here, the oxygen concentration is present at a high concentration in the junction interface, meaning that these oxide films and the like are sufficiently heated to be reliably removed. Therefore, the ceramic substrate and the metal plate can be firmly joined.
In the substrate for a power module according to claim 4 of the present invention, it is preferable that the ceramic substrate is composed of AlN, and a mass ratio of Al, Cu, O, and N is 50 to 90 wt% to 1 to 10 wt% to 2 to 20 wt% to 25 wt% or less when the bonding interface including the Cu high concentration portion is analyzed by energy dispersive X-ray analysis.
In the power module substrate according to claim 4 of the present invention, the Si for ceramic substrate is preferable3N4And the mass ratio of Al, Si, Cu, O and N is 15 to 45 wt%, 1 to 10 wt%, 2 to 20 wt% and 25 wt% or less when the bonding interface containing the Cu high concentration portion is analyzed by energy dispersive X-ray analysis.
When the mass ratio of Cu atoms present at the bonding interface exceeds 10 wt%, a reactant of Al and Cu is excessively generated, and the reactant may inhibit bonding.
In addition, the vicinity of the bonding interface of the metal plates is excessively strengthened by the reactant, and stress acts on the ceramic substrate during thermal cycling under load, which may cause cracking of the ceramic substrate.
On the other hand, if the mass ratio of Cu atoms is less than 1 wt%, there is a possibility that the bonding strength by Cu atoms cannot be sufficiently improved.
Therefore, the mass ratio of Cu atoms in the bonding interface is preferably in the range of 1 to 10 wt%.
When the mass ratio of oxygen atoms present in the bonding interface containing the Cu high concentration portion exceeds 20 wt%, the thickness of the portion having a high oxygen concentration increases, and cracks are generated in the high concentration portion during thermal cycles under load. Thus, the bonding reliability may be lowered. Therefore, the oxygen concentration is preferably 2 to 20 wt%.
Since the point diameter is extremely small when the analysis is performed by the energy dispersive X-ray analysis method, a plurality of points (for example, 10 to 100 points) of the junction interface are measured and an average value thereof is calculated.
In the measurement, the bonding interface between the grain boundary of the metal plate and the ceramic substrate is not measured, but only the bonding interface between the crystal grain and the ceramic substrate is measured.
The analysis value by energy dispersive X-ray analysis in the present specification can be obtained under the condition of an acceleration voltage of 200kV using a NORAN System7, an energy dispersive fluorescent X-ray elemental analyzer manufactured by Thermo Fisher Scientific co.
The power module according to claim 5 of the present invention includes: the power module substrate according to claim 4, and an electronic component mounted on the power module substrate.
According to the power module having this configuration, the bonding strength between the ceramic substrate and the metal plate is high, and the reliability thereof can be significantly improved even in a case where the use environment is severe, for example, even in a case where the power module is used in which thermal stress is repeatedly generated.
The method for manufacturing a power module substrate according to claim 6 of the present invention comprises: preparing a ceramic substrate made of AlN, a metal plate made of pure aluminum, and a Cu layer having a thickness of 0.15 μm to 3 μm, laminating the ceramic substrate and the metal plate with the Cu layer interposed therebetween (laminating step), heating the laminated ceramic substrate, Cu layer, and metal plate while pressing them in the laminating direction to form a molten aluminum layer at an interface between the ceramic substrate and the metal plate (melting step), and cooling the molten aluminum layer to solidify the molten aluminum layer (solidification step), wherein a Cu high concentration portion having a Cu concentration 2 times or more the Cu concentration in the metal plate is formed at a junction interface between the ceramic substrate and the metal plate in the melting step and the solidification step.
The method for manufacturing the power module substrate having this configuration includes laminating a ceramic substrate and a metal plate with a Cu layer interposed therebetween, and heating the laminated ceramic substrate and metal plate while pressing them in a laminating direction. Thus, the melting point in the vicinity of the bonding interface is lowered by the eutectic reaction between Cu of the Cu layer and Al of the metal plate, and a molten aluminum layer can be formed at the interface between the ceramic substrate and the metal plate even at a relatively low temperature, whereby the ceramic substrate and the metal plate can be bonded to each other.
That is, the ceramic substrate and the metal plate can be joined without using a brazing material made of an Al — Si alloy or the like.
If the Cu layer has a thickness of less than 0.15 μm, a molten aluminum layer may not be sufficiently formed at the interface between the ceramic substrate and the metal plate.
When the thickness of the Cu layer exceeds 3 μm, the reaction product of Cu and Al may be excessively generated at the junction interface, and the vicinity of the junction interface of the metal plate may be excessively strengthened, thereby causing cracking in the ceramic substrate made of AlN during thermal cycling.
Therefore, in the case of a ceramic substrate composed of AlN, the thickness of the Cu layer is preferably 0.15 μm or more and 3 μm or less.
A method for manufacturing a power module substrate according to claim 7 of the present invention is a method for manufacturing a power module substrate made of Si3N4The ceramic substrate, the metal plate made of pure aluminum, and the Cu layer with the thickness of 0.15-3 μm are laminated (laminating step) by the Cu layer, the laminated ceramic substrate, the Cu layer, and the metal plate are heated while being pressed in the laminating direction, a molten aluminum layer is formed at the interface between the ceramic substrate and the metal plate (melting step), the molten aluminum layer is solidified by cooling the molten aluminum layer (solidification step), and in the melting step and the solidification step, a Cu high concentration portion having a Cu concentration of 2 times or more of the Cu concentration in the metal plate is formed at the bonding interface between the ceramic substrate and the metal plate.
The method for manufacturing the power module substrate having this configuration includes laminating a ceramic substrate and a metal plate with a Cu layer interposed therebetween, and heating the laminated ceramic substrate and metal plate while pressing them in a laminating direction. Thus, the melting point in the vicinity of the bonding interface is lowered by the eutectic reaction between Cu of the Cu layer and Al of the metal plate, and a molten aluminum layer can be formed at the interface between the ceramic substrate and the metal plate even at a relatively low temperature, whereby the ceramic substrate and the metal plate can be bonded to each other.
That is, the ceramic substrate and the metal plate can be joined without using a brazing material made of an Al — Si alloy or the like.
If the Cu layer has a thickness of less than 0.15 μm, a molten aluminum layer may not be sufficiently formed at the interface between the ceramic substrate and the metal plate.
When the thickness of the Cu layer exceeds 3 μm, a reactant of Cu and Al may be excessively generated at the bonding interface to inhibit bonding.
Therefore, in the presence of Si3N4In the case of the structured ceramic substrate, the thickness of the Cu layer is preferably 0.15 μmAbove and below 3 μm.
In the method for manufacturing a power module substrate according to claim 6 or 7 of the present invention, it is preferable that, when the ceramic substrate and the metal plate are laminated with the Cu layer interposed therebetween, the Cu layer is disposed by interposing a copper foil between the ceramic substrate and the metal plate.
In the method for manufacturing a power module substrate according to claim 6 or 7 of the present invention, it is preferable that the Cu layer is fastened to at least one of the ceramic substrate and the metal plate before the ceramic substrate, the Cu layer, and the metal plate are laminated.
In the method for manufacturing a power module substrate according to claim 6 or 7 of the present invention, when the Cu is bonded to at least one of the ceramic substrate and the metal plate, it is preferable that the Cu is bonded to at least one of the ceramic substrate and the metal plate by a method selected from any one of a vapor deposition method, a sputtering method, a plating method, and a coating method of a Cu paste.
According to these methods, a Cu layer having a desired thickness can be formed between the ceramic substrate and the metal plate, and the ceramic substrate and the metal plate can be reliably joined.
The power module substrate according to claim 8 of the present invention includes: from Al2O3The ceramic substrate is provided with a ceramic substrate having a surface, a metal plate bonded to the surface of the ceramic substrate and made of pure aluminum, and a Cu high concentration section formed at a bonding interface between the metal plate and the ceramic substrate and having a Cu concentration 2 times or more higher than the Cu concentration in the metal plate.
In the power module substrate having the above structure, Al is used2O3Since the joint interface between the ceramic substrate and the metal plate made of pure aluminum has a Cu high concentration portion having a Cu concentration 2 times or more higher than the Cu concentration in the metal plate, the joint strength between the ceramic substrate and the metal plate can be improved by Cu atoms present in the vicinity of the interface.
The Cu concentration in the metal plate means the Cu concentration in a portion of the metal plate which is a predetermined distance (for example, 50nm or more) from the bonding interface.
In the substrate for a power module according to claim 8 of the present invention, when the bonding interface including the Cu high concentration portion is analyzed by energy dispersive X-ray analysis, the mass ratio of Al, Cu, and O is preferably 50 to 90 wt%, 1 to 10 wt%, and 0 to 45 wt%.
When the mass ratio of Cu atoms present at the bonding interface exceeds 10 wt%, a reactant of Al and Cu is excessively generated, and the reactant may inhibit bonding.
On the other hand, if the mass ratio of Cu atoms is less than 1 wt%, there is a possibility that the bonding strength by Cu atoms cannot be sufficiently improved.
Therefore, the mass ratio of Cu atoms in the bonding interface is preferably in the range of 1 to 10 wt%.
Here, since the point diameter when performing analysis by the energy dispersive X-ray analysis method is extremely small, the average value is calculated by measuring at a plurality of points (for example, 10 to 100 points) of the junction interface.
In the measurement, the bonding interface between the grain boundary of the metal plate and the ceramic substrate is not measured, but only the bonding interface between the crystal grain and the ceramic substrate is measured.
A power module according to claim 9 of the present invention includes: the power module substrate according to claim 8, and an electronic component mounted on the power module substrate.
According to the power module having this configuration, the bonding strength between the ceramic substrate and the metal plate is increased, and the reliability thereof can be significantly improved even in a case where the use environment is severe, for example, even in a case where the power module is used in which thermal stress is repeatedly generated.
Power module of the 10 th aspect of the present inventionThe method for manufacturing the substrate for the block is to prepare Al2O3The ceramic substrate, the metal plate made of pure aluminum, and the Cu layer with the thickness of 0.15-3 μm are laminated (laminating step) by the Cu layer, the laminated ceramic substrate, the Cu layer, and the metal plate are heated while being pressed in the laminating direction, a molten aluminum layer is formed at the interface between the ceramic substrate and the metal plate (melting step), the molten aluminum layer is solidified by cooling the molten aluminum layer (solidification step), and in the melting step and the solidification step, a Cu high concentration portion having a Cu concentration of 2 times or more of the Cu concentration in the metal plate is formed at the bonding interface between the ceramic substrate and the metal plate.
The method for manufacturing the power module substrate having this configuration includes laminating a ceramic substrate and a metal plate with a Cu layer interposed therebetween, and heating the laminated ceramic substrate and metal plate while pressing them in a laminating direction. Thus, the melting point in the vicinity of the bonding interface is lowered by the eutectic reaction between Cu of the Cu layer and Al of the metal plate, and a molten aluminum layer can be formed at the interface between the ceramic substrate and the metal plate even at a relatively low temperature, whereby the ceramic substrate and the metal plate can be bonded to each other.
That is, the ceramic substrate and the metal plate can be joined without using a brazing material made of an Al — Si alloy or the like.
If the Cu layer has a thickness of less than 0.15 μm, a molten aluminum layer may not be sufficiently formed at the interface between the ceramic substrate and the metal plate.
When the thickness of the Cu layer exceeds 3 μm, the reaction product of Cu and Al is excessively generated at the bonding interface, and the vicinity of the bonding interface of the metal plate is excessively strengthened, and Al is excessively generated during thermal cycle under load2O3Cracks are generated in the constituted ceramic substrate.
Therefore, in the presence of Al2O3In the case of the ceramic substrate having the above structure, the thickness of the Cu layer is preferably 0.15 μm or more and 3 μm or less.
In the method for manufacturing a power module substrate according to claim 10 of the present invention, when the ceramic substrate and the metal plate are laminated via the Cu layer, the Cu layer is preferably disposed by interposing a copper foil between the ceramic substrate and the metal plate.
In the method for manufacturing a power module substrate according to claim 10 of the present invention, it is preferable that the Cu layer is fastened to at least one of the ceramic substrate and the metal plate before the ceramic substrate, the Cu layer, and the metal plate are laminated.
In the method for manufacturing a power module substrate according to claim 10 of the present invention, when the Cu is bonded to at least one of the ceramic substrate and the metal plate, it is preferable that the Cu is bonded to at least one of the ceramic substrate and the metal plate by a method selected from any one of a vapor deposition method, a sputtering method, a plating method, and a coating method of a Cu paste.
According to these methods, a Cu layer having a desired thickness can be formed between the ceramic substrate and the metal plate, and the ceramic substrate and the metal plate can be reliably joined.
A power module substrate according to claim 11 of the present invention includes a ceramic substrate having a surface, a metal plate made of aluminum bonded to the surface of the ceramic substrate via a Si-containing brazing material, and Cu added to a bonding interface between the ceramic substrate and the metal plate; the metal plate contains Si and Cu, and the Si concentration in a portion adjacent to the bonding interface of the metal plate is set to be in the range of 0.05 to 0.5 wt%, and the Cu concentration is set to be in the range of 0.05 to 1.0 wt%.
In the power module substrate having this configuration, a ceramic substrate and a metal plate made of aluminum are joined using a brazing material containing Si, and Cu is added to a joint interface between the metal plate and the ceramic substrate.
Here, Cu is an element having high reactivity with Al, and therefore the surface of the metal plate made of aluminum is activated by the presence of Cu at the bonding interface.
Therefore, even when a general Al — Si-based brazing material is used and the joining is performed under a joining condition of a relatively low temperature and a short time, the ceramic substrate and the metal plate can be firmly joined.
As a method of adding Cu to the bonding interface, Cu may be secured to the surfaces of the ceramic substrate and the brazing material by a vapor deposition method, a sputtering method, a plating method, or the like, or may be contained in an Al — Si-based brazing material.
Further, Cu is diffused to the metal plate, and a Cu concentration of a portion adjacent to the bonding interface is set in a range of 0.05 to 1.0 wt%, so that the portion adjacent to the bonding interface of the metal plate is subjected to solid solution strengthening.
Thereby, breakage in the metal plate portion can be prevented, and the bonding reliability can be improved.
Further, the ceramic substrate and the metal plate made of aluminum are joined by using a brazing material containing Si, Si diffuses into the metal plate, and the Si concentration in a portion adjacent to the joining interface is set to be in the range of 0.05 to 0.5 wt%. Thus, the brazing material is reliably melted to be in a solid solution state, Si is sufficiently diffused into the metal plate, and the ceramic substrate and the metal plate are firmly joined.
In the power module substrate according to claim 11 of the present invention, it is preferable that the ceramic substrate has a width wider than that of the metal plate, and an aluminum phase containing Si and Cu in aluminum, an Si phase having a Si content of 98 wt% or more, and a eutectic phase composed of a 3-membered eutectic structure of Al, Cu, and Si are formed at an end of the metal plate in the width direction.
In this case, the end portion of the metal plate in the width direction is reinforced because an Si phase having a Si content of 98 wt% or more and a eutectic phase composed of a 3-membered eutectic structure of Al, Cu and Si are formed in addition to an aluminum phase in which Si and Cu are diffused in aluminum.
In the power module substrate according to claim 11 of the present invention, preferably, the eutectic phase is precipitated with precipitated particles made of a Cu-containing compound.
In this case, since the precipitated particles composed of the Cu-containing compound are precipitated in the eutectic phase formed at the widthwise end portion of the metal plate, the widthwise end portion of the metal plate can be precipitation-strengthened.
This prevents the metal plate from being broken at the end in the width direction, thereby improving the bonding reliability.
The power module substrate according to claim 11 of the present invention includes: an Si high concentration portion formed at a junction interface between the metal plate and the ceramic substrate and having an Si concentration 5 times or more that of the metal plate, wherein the ceramic substrate may be made of AlN or Al2O3And (4) forming.
In this case, the junction interface between the metal plate and the ceramic substrate is formed with an Si high concentration portion having an Si concentration 5 times or more higher than the Si concentration in the metal plate, and thus is composed of AlN or Al2O3The bonding strength between the ceramic substrate and the metal plate made of aluminum is improved by the Si atoms present at the bonding interface.
Here, the Si concentration in the metal plate means the Si concentration in a portion of the metal plate that is a predetermined distance (for example, 50nm or more) from the bonding interface.
It is considered that Si present at a high concentration at the joining interface is mainly Si contained in the brazing filler metal.
At the time of bonding, Si diffuses into aluminum (metal plate) and the amount thereof in the bonding interface decreases, but the interface portion between the ceramic and aluminum (metal plate) becomes a site where non-uniform nuclei are generated, and Si atoms remain in the interface portion, forming a Si high concentration portion having a Si concentration 5 times or more the Si concentration in the metal plate.
The power module substrate according to claim 11 of the present invention includes a metal plate formed between the metal plate and the ceramic substrateAnd an oxygen-rich portion having a thickness of 4nm or less and having an oxygen concentration higher than the oxygen concentration in the metal plate and the oxygen concentration in the ceramic substrate, wherein the ceramic substrate may be made of AlN or Si3N4And (4) forming.
In this case, from AlN or Si3N4The junction interface between the ceramic substrate and the metal plate made of aluminum is formed with an oxygen high concentration portion having an oxygen concentration higher than oxygen concentrations in the metal plate and the ceramic substrate, and is made of AlN or Si3N4The bonding strength between the ceramic substrate and the metal plate made of aluminum is improved by oxygen present at the bonding interface.
Further, since the thickness of the oxygen high concentration portion is 4nm or less, cracks generated in the oxygen high concentration portion due to stress during thermal cycles under load are suppressed.
Here, the oxygen concentration in the metal plate and the ceramic substrate means the oxygen concentration in a portion of the metal plate and the ceramic substrate which is a predetermined distance (for example, 50nm or more) from the bonding interface.
It is considered that oxygen present at a high concentration in the joining interface is oxygen derived from oxygen present on the surface of the ceramic substrate and an oxide film formed on the surface of the brazing material.
Here, the oxygen concentration is present at a high concentration in the junction interface, meaning that these oxide films and the like are sufficiently heated to be reliably removed. Therefore, the ceramic substrate and the metal plate can be firmly joined.
A power module according to claim 12 of the present invention includes: the power module substrate according to claim 11, and an electronic component mounted on the power module substrate.
According to the power module of this configuration, the bonding strength between the ceramic substrate and the metal plate is high, and the reliability thereof can be significantly improved even in a case where the use environment is severe, for example, even in a case where the power module is used in which thermal stress is repeatedly generated.
A method for manufacturing a power module substrate according to claim 13 of the present invention includes preparing a ceramic substrate having a joint surface, a metal plate made of aluminum, and a brazing material containing Si, laminating the ceramic substrate and the metal plate by placing the brazing material therebetween (laminating step), heating the laminated ceramic substrate, brazing material, and metal plate in a pressurized state to melt the brazing material and form a molten aluminum layer at an interface between the ceramic substrate and the metal plate (melting step), solidifying the molten aluminum layer (solidifying step), and before placing the brazing material between the ceramic substrate and the metal plate and laminating, fastening Cu to at least one of the joint surface of the ceramic substrate and a surface of the brazing material facing the ceramic substrate (fastening step).
The method for manufacturing the power module substrate having the above configuration includes: and a Cu fastening step of fastening Cu to at least one of a bonding surface of the ceramic substrate and a surface of the brazing material facing the ceramic substrate, prior to the laminating step of placing the brazing material containing Si between the ceramic substrate and the metal plate and laminating the substrates. Thus, Cu is reliably added to the bonding interface between the ceramic substrate and the metal plate, the surface of the metal plate is activated by the Cu, and the ceramic substrate and the metal plate can be firmly bonded even if a general Al — Si based brazing material is used and bonded under a bonding condition at a relatively low temperature in a short time.
In the method for manufacturing a power module substrate according to claim 13 of the present invention, it is preferable that Cu is fixed to at least one of the bonding surface of the ceramic substrate and the surface of the brazing material facing the ceramic substrate by a vapor deposition method or a sputtering method when the Cu is fixed.
In this case, Cu can be securely fixed to at least one of the bonding surface of the ceramic substrate and the surface of the brazing material by the vapor deposition method or the sputtering method, and Cu can be securely present at the bonding interface between the ceramic substrate and the metal plate.
This activates the surface of the metal plate with Cu, and the ceramic substrate and the metal plate can be firmly bonded to each other.
Effects of the invention
According to the present invention, it is possible to provide a power module substrate in which a metal plate and a ceramic substrate are reliably joined and which has high thermal cycle reliability, a power module including the power module substrate, and a method for manufacturing the power module substrate.
Drawings
Fig. 1 is a schematic cross-sectional view of a power module using a power module substrate according to embodiment 1 of the present invention.
Fig. 2 is an explanatory view showing Cu concentration distributions of a circuit layer and a metal layer of a power module substrate according to embodiment 1 of the present invention.
Fig. 3 is an explanatory view showing the end portions in the width direction of the circuit layer and the metal layer (metal plate) of the power module substrate according to embodiment 1 of the present invention.
Fig. 4 is a sectional view showing a method for manufacturing a power module substrate according to embodiment 1 of the present invention.
FIG. 5 is a cross-sectional view of the vicinity of the bonding interface between the metal plate and the ceramic substrate in FIG. 4.
FIG. 6 is a graph showing the evaluation results of the bonding reliability in example 1.
FIG. 7 is a graph showing the evaluation results of the bonding reliability in example 1.
Fig. 8 is a schematic cross-sectional view of a power module using a power module substrate according to embodiment 2 of the present invention.
Fig. 9 is a schematic cross-sectional view of a circuit layer and a bonding interface between a metal layer (metal plate) and a ceramic substrate of a power module substrate according to embodiment 2 of the present invention.
Fig. 10 is a sectional view showing a method for manufacturing a power module substrate according to embodiment 2 of the present invention.
FIG. 11 is a cross-sectional view of the vicinity of the bonding interface between the metal plate and the ceramic substrate in FIG. 10.
Fig. 12 is a schematic cross-sectional view of a power module using a power module substrate according to embodiment 3 of the present invention.
Fig. 13 is a schematic cross-sectional view of a circuit layer and a bonding interface between a metal layer (metal plate) and a ceramic substrate of a power module substrate according to embodiment 3 of the present invention.
Fig. 14 is a sectional view showing a method for manufacturing a power module substrate according to embodiment 3 of the present invention.
FIG. 15 is a cross-sectional view showing a vicinity of a bonding interface between the metal plate and the ceramic substrate in FIG. 14.
FIG. 16 is a graph showing the results of evaluation of cracking of the ceramic substrate in example 2.
FIG. 17 is a graph showing the evaluation results of the bonding reliability in example 2.
FIG. 18 is a graph showing the results of evaluation of cracking of the ceramic substrate in example 3.
FIG. 19 is a graph showing the evaluation results of the bonding reliability in example 3.
Fig. 20 is a schematic cross-sectional view of a power module using a power module substrate according to embodiment 4 of the present invention.
Fig. 21 is a schematic cross-sectional view of a circuit layer and a bonding interface between a metal layer (metal plate) and a ceramic substrate of a power module substrate according to embodiment 4 of the present invention.
Fig. 22 is a sectional view showing a method of manufacturing a power module substrate according to embodiment 4 of the present invention.
FIG. 23 is a cross-sectional view of the vicinity of the bonding interface between the metal plate and the ceramic substrate in FIG. 22.
FIG. 24 is a graph showing the results of evaluation of cracking of the ceramic substrate in example 4.
FIG. 25 is a graph showing the evaluation results of the bonding reliability in example 4.
Fig. 26 is a schematic cross-sectional view of a power module using a power module substrate according to embodiment 5 of the present invention.
Fig. 27 is an explanatory view showing an Si concentration distribution and a Cu concentration distribution of a circuit layer and a metal layer of a power module substrate according to embodiment 5 of the present invention.
Fig. 28 is an explanatory view showing an end portion in a width direction of a bonding interface between a circuit layer and a metal layer (metal plate) of a power module substrate according to embodiment 5 of the present invention and a ceramic substrate.
Fig. 29 is a schematic cross-sectional view of a circuit layer and a bonding interface between a metal layer (metal plate) and a ceramic substrate of a power module substrate according to embodiment 5 of the present invention.
Fig. 30 is a sectional view showing a method for manufacturing a power module substrate according to embodiment 5 of the present invention.
FIG. 31 is a sectional view of the vicinity of the bonding interface between the metal plate and the ceramic substrate in FIG. 29.
Fig. 32 is a schematic cross-sectional view of a power module using a power module substrate according to embodiment 6 of the present invention.
Fig. 33 is a schematic cross-sectional view of a circuit layer and a bonding interface between a metal layer (metal plate) and a ceramic substrate of a power module substrate according to embodiment 6 of the present invention.
Fig. 34 is a cross-sectional view of a power module substrate used in a comparative test.
Detailed Description
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(embodiment 1)
Fig. 1 shows a power module substrate and a power module according to embodiment 1 of the present invention.
The power module 1 includes: a power module substrate 10 provided with a circuit layer 12, a semiconductor chip 3 bonded to the surface of the circuit layer 12 via a solder layer 2, and a heat sink 4.
The solder layer 2 is, for example, Sn-Ag based, Sn-In based, or Sn-Ag-Cu based solder.
In embodiment 1, a Ni plating layer (not shown) is provided between circuit layer 12 and solder layer 2.
The power module substrate 10 includes: a ceramic substrate 11, a circuit layer 12 disposed on the 1 st surface (upper surface in fig. 1) of the ceramic substrate 11, and a metal layer 13 disposed on the 2 nd surface (lower surface in fig. 1) of the ceramic substrate 11.
The ceramic substrate 11 is a substrate for preventing electrical connection between the circuit layer 12 and the metal layer 13, and is made of AlN (aluminum nitride) having high insulation properties.
The thickness of the ceramic substrate 11 is set to be in the range of 0.2 to 1.5mm, and 0.635mm in embodiment 1.
In embodiment 1, as shown in fig. 1, the width of the ceramic substrate 11 is set to be larger than the widths of the circuit layer 12 and the metal layer 13.
The circuit layer 12 is formed by bonding a metal plate 22 having conductivity to the 1 st surface of the ceramic substrate 11.
In embodiment 1, the circuit layer 12 is formed by bonding a metal plate 22 made of a rolled plate of aluminum having a purity of 99.99% or more (so-called 4N aluminum) to the ceramic substrate 11.
The metal layer 13 is formed by bonding a metal plate 23 to the 2 nd surface of the ceramic substrate 11.
In embodiment 1, the metal layer 13 is formed by bonding a metal plate 23, which is a rolled plate of aluminum having a purity of 99.99% or more (so-called 4N aluminum), to the ceramic substrate 11, as in the case of the circuit layer 12.
The heat sink 4 is a member for cooling the power module board 10, and includes a top plate portion 5 joined to the power module board 10, and a flow path 6 for flowing a cooling medium (e.g., cooling water).
The heat sink 4 (top plate 5) is preferably made of a material having good thermal conductivity, and in embodiment 1, is made of a6063 (aluminum alloy).
In embodiment 1, a buffer layer 15 made of aluminum, an aluminum alloy, or a composite material containing aluminum (for example, AlSiC) is provided between the top plate 5 and the metal layer 13 of the heat sink 4.
As shown in fig. 1 and 2, in the central portion in the width direction of the bonding interface 30 between the ceramic substrate 11 and the circuit layer 12 (metal plate 22) and the central portion in the width direction (portion a in fig. 1) of the bonding interface 30 between the ceramic substrate 11 and the metal layer 13 (metal plate 23), Cu diffuses to the circuit layer 12 (metal plate 22) and the metal layer 13 (metal plate 23), and a concentration gradient layer 33 (concentration gradient portion) in which the concentration of Cu gradually decreases as it is separated from the bonding interface 30 in the stacking direction is formed.
In the present specification, the "lamination direction" refers to a direction in which the ceramic, the substrate 11, the circuit layer 12, and the metal layer 13 are laminated.
Here, the Cu concentration of the portion of the concentration gradient layer 33 adjacent to the junction interface 30 is set in the range of 0.05 to 5 wt%.
Note that the Cu concentration in the portion of the concentration-gradient layer 33 adjacent to the junction interface 30 is an average value obtained by measuring 5 points in a range from the junction interface 30 to 50 μm by EPMA analysis (spot diameter 30 μm).
On the opposite side (lower side in fig. 2) of the concentration gradient layer 33 from the ceramic substrate 11, a soft layer 34 having a lower Cu concentration and a lower hardness is formed in the vicinity of the bonding interface 30.
Further, as shown in fig. 3, at the end in the width direction of the bonding interface 30 between the ceramic substrate 11 and the circuit layer 12 (metal plate 22) and at the end in the width direction of the bonding interface 30 between the ceramic substrate 11 and the metal layer 13 (metal plate 23) (portion B in fig. 1): an aluminum phase 41 in which Cu diffuses into aluminum so as to be in a solid solution state, and a eutectic phase 42 composed of a 2-membered eutectic structure of Al and Cu.
Further, in the eutectic phase 42, a compound containing Cu (e.g., CuAl) is precipitated2) And precipitate particles formed.
Such a power module substrate 10 is manufactured as follows.
First, as shown in fig. 4 a and 5 a, a ceramic substrate 11 made of AlN, a metal plate 22 (rolled plate of 4N aluminum) as the circuit layer 12, and a metal plate 23 (rolled plate of 4N aluminum) as the metal layer 13 were prepared.
Then, Cu is fixed to both surfaces of the ceramic substrate 11 by sputtering, thereby forming Cu layers 24 and 25 having a film thickness of 0.15 μm to 3 μm (Cu fixing step). Thereby, the ceramic substrate 11, the metal plates 22 and 23, and the Cu layers 24 and 25 are prepared.
Next, as shown in fig. 4(b), a metal plate 22 is laminated on the 1 st surface of the ceramic substrate 11, and a metal plate 23 is laminated on the 2 nd surface of the ceramic substrate 11 (laminating step). Thereby forming the laminated body 20.
Then, the laminate 20 thus formed is pressed in the laminating direction (pressure 1 to 5 kgf/cm)2) Then, the mixture was charged into a vacuum furnace and heated.
The degree of vacuum in the vacuum furnace here was 10-3Pa～10-5Pa, and the heating temperature is 610-650 ℃.
In the pressurizing and heating step, as shown in fig. 5 b, the surface layers of the metal plates 22 and 23, which are the circuit layer 12 and the metal layer 13, and the Cu layers 24 and 25 are melted, and molten metal layers 26 and 27 are formed on the surface of the ceramic substrate 11 (melting step).
Next, as shown in fig. 4 c and 5c, the molten metal layers 26 and 27 are solidified by cooling the stacked body 20 (solidification step).
By the melting step and the solidification step, Cu is diffused in the vicinity of the bonding interface between the metal plate 22 as the circuit layer 12 and the ceramic substrate 11 or in the vicinity of the bonding interface between the metal plate 23 as the metal layer 13 and the ceramic substrate 11 so that the Cu concentration is in the range of 0.05 to 5 wt%.
In this way, the metal plates 22 and 23 as the circuit layer 12 and the metal layer 13 are bonded to the ceramic substrate 11, and the power module substrate 10 as embodiment 1 is manufactured.
In the power module substrate 10 and the power module 1 according to embodiment 1 having the above-described configurations, Cu diffuses in a solid solution state in the circuit layer 12 (metal plate 22) and the metal layer 13 (metal plate 23). Further, since the Cu concentration in the joining interface 30 between the circuit layer 12 and the ceramic substrate 11 or the joining interface 30 between the metal layer 13 and the ceramic substrate 11 is set to be in the range of 0.05 to 5 wt%, the joining interface 30 between the circuit layer 12 (metal plate 22) and the metal layer 13 (metal plate 23) is subjected to solid solution strengthening. Therefore, cracks can be prevented from occurring in the circuit layer 12 (metal plate 22) and the metal layer 13 (metal plate 23) during thermal cycles under load, and the reliability of the power module substrate 10 and the power module 1 can be greatly improved.
Further, since the aluminum phase 41 in which Cu diffuses into aluminum and the eutectic phase 42 composed of a 2-membered eutectic structure of Al and Cu are formed in the end portions in the width direction of the circuit layer 12 (metal plate 22) and the metal layer 13 (metal plate 23), the end portions in the width direction of the circuit layer 12 (metal plate 22) and the metal layer 13 (metal plate 23) can be further strengthened.
This prevents the circuit layer 12 (metal plate 22) and the metal layer 13 (metal plate 23) from being broken at the ends in the width direction, thereby improving the reliability of the bonding of the power module substrate 10.
In embodiment 1, a compound containing Cu (e.g., CuAl) is precipitated in the eutectic phase 422) The precipitate particles thus constituted can precipitate and strengthen the end portions in the width direction of the circuit layer 12 (metal plate 22) and the metal layer 13 (metal plate 23), and can reliably prevent the development of cracks from the end portions in the width direction of the circuit layer 12 (metal plate 22) and the metal layer 13 (metal plate 23).
Further, in the central portion in the width direction of the bonding interface 30 between the ceramic substrate 11 and the circuit layer 12 (metal plate 22) and the central portion in the width direction (portion a in fig. 1) of the bonding interface 30 between the ceramic substrate 11 and the metal layer 13 (metal plate 23), Cu diffuses in a solid solution state in the circuit layer 12 (metal plate 22) and the metal layer 13 (metal plate 23), a concentration gradient layer 33 in which the concentration of Cu gradually decreases as it is separated from the bonding interface 30 in the stacking direction is formed, and a soft layer 34 having a lower Cu concentration, a lower hardness, and a lower strain resistance than those in the vicinity of the bonding interface 30 is formed on the opposite side (lower side in fig. 2) of the concentration gradient layer 33 from the ceramic substrate 11. In this configuration, the soft layer 34 can absorb thermal deformation (thermal stress) caused by the difference between the thermal expansion coefficients of the circuit layer 12 (metal plate 22) and the ceramic substrate 11 and the difference between the thermal expansion coefficients of the metal layer 13 (metal plate 23) and the ceramic substrate 11, thereby greatly improving the thermal cycle reliability of the power module substrate 10.
According to the method for manufacturing a power module substrate of embodiment 1, since the ceramic substrate 11, the metal plate 22 as the circuit layer 12, and the metal plate 23 as the metal layer 13 are laminated via the Cu layers 24 and 25, and the laminated ceramic substrate 11 and the metal plates 22 and 23 are heated while being pressed in the laminating direction, the melting point in the vicinity of the bonding interface 30 is lowered by the eutectic reaction between Cu of the Cu layers 24 and 25 and Al of the metal plates 22 and 23, and the molten metal layers 26 and 27 can be formed at the interfaces of the ceramic substrate 11 and the metal plates 22 and 23 even at a relatively low temperature, whereby the ceramic substrate 11 and the metal plates 22 and 23 can be bonded.
In this way, since the ceramic substrate 11 and the metal plates 22 and 23 can be joined without using a brazing material made of an Al — Si alloy or the like, there is no possibility that the brazing material oozes out to the surface of the circuit layer 12, and peeling or the like of the Ni plating layer formed on the surface of the circuit layer 12 can be prevented.
This makes it possible to favorably form the solder layer 2 on the circuit layer 12 via the Ni plating layer.
Since the thickness of the Cu layers 24 and 25 is set to 0.15 μm or more and 3 μm or less, the molten metal layers 26 and 27 can be reliably formed at the interfaces between the ceramic substrate 11 and the metal plates 22 and 23, and the ceramic substrate 11 and the metal plates 22 and 23 can be joined together. In addition, excessive generation of a reactant of Cu and Al in the vicinity of the bonding interface 30 can be prevented, and cracking can be prevented from occurring on the ceramic substrate 11 during thermal cycling under load.
Further, since the Cu layers 24 and 25 are formed by a Cu bonding step of bonding Cu to the 1 st and 2 nd surfaces (surfaces facing the bonding surfaces and the metal plates 22 and 23) of the ceramic substrate 11 by sputtering, the ceramic substrate 11 and the metal plates 22 and 23 can be reliably laminated via the Cu layers 24 and 25, the ceramic substrate 11 and the metal plates 22 and 23 can be reliably bonded, and the power module substrate 10 as embodiment 1 can be manufactured.
While embodiment 1 of the present invention has been described above, the present invention is not limited thereto, and can be modified as appropriate within a range not departing from the technical spirit of the present invention.
In embodiment 1 of the present invention, a manufacturing method having a Cu bonding step of bonding Cu to a surface of a ceramic substrate is described, but the present invention is not limited thereto, and Cu may be bonded to a surface (bonding surface) of a metal plate facing the ceramic substrate 11.
Further, in the lamination step, a Cu layer may be formed by interposing a copper foil between the ceramic substrate and the metal plate.
Further, although a method of forming a Cu layer by sputtering has been described, the Cu layer is not limited to this, and may be fixed by an evaporation method, a plating method, a paste coating method, or the like.
(embodiment 2)
Fig. 8 shows a power module substrate 60 and a power module 51 according to embodiment 2 of the present invention.
In embodiment 2, the same members as those in embodiment 1 are given the same reference numerals, and description thereof is omitted or simplified.
The power module 51 includes: a power module substrate 60 provided with a circuit layer 62, a semiconductor chip 3 bonded to the surface of the circuit layer 62 via a solder layer 2, and a heat sink 4.
The power module substrate 60 includes: a ceramic substrate 61, a circuit layer 62 disposed on the 1 st surface (upper surface in fig. 8) of the ceramic substrate 61, and a metal layer 63 disposed on the 2 nd surface (lower surface in fig. 8) of the ceramic substrate 61.
The ceramic substrate 61 is a substrate that prevents electrical connection between the circuit layer 62 and the metal layer 63, and is made of AlN (aluminum nitride) having high insulation properties.
The thickness of the ceramic substrate 61 is set to be in the range of 0.2 to 1.5mm, and 0.635mm in embodiment 2.
The circuit layer 62 is formed by bonding a metal plate 72 having conductivity to the 1 st surface of the ceramic substrate 61.
In embodiment 2, the circuit layer 62 is formed by bonding a metal plate 72 made of a rolled plate of aluminum having a purity of 99.99% or more (so-called 4N aluminum) to the ceramic substrate 61.
The metal layer 63 is formed by bonding a metal plate 73 to the 2 nd surface of the ceramic substrate 61.
In embodiment 2, the metal layer 63 is formed by bonding a metal plate 73, which is a rolled plate of aluminum having a purity of 99.99% or more (so-called 4N aluminum), to the ceramic substrate 61, as in the case of the circuit layer 62.
When the bonding interface 80 between the ceramic substrate 61 and the circuit layer 62 (metal plate 72) and the bonding interface 80 between the ceramic substrate 61 and the metal layer 63 (metal plate 73) are observed by a transmission electron microscope, as shown in fig. 9, a Cu high concentration portion 82 in which Cu is concentrated is formed at the bonding interface 80.
The Cu concentration in the Cu high concentration portion 82 is higher than the Cu concentration in the circuit layer 62 (metal plate 72) and the metal layer 63 (metal plate 73). Specifically, the Cu concentration in the bonding interface 80 is 2 times or more the Cu concentration in the circuit layer 62 and the metal layer 63. In embodiment 2, the thickness H of the Cu high concentration portion 82 is 4nm or less.
Further, in the Cu high concentration portion 82, the oxygen concentration is set higher than the oxygen concentration in the circuit layer 62 and the metal layer 63.
Here, in the bonding interface 80 observed by the transmission electron microscope, as shown in fig. 9, the center between the end of the interface of the lattice image of the circuit layer 62 (metal plate 72) and the metal layer 63 (metal plate 73) and the end of the interface of the lattice image of the ceramic substrate 61 is defined as a reference plane S.
Note that the Cu concentration and the oxygen concentration in the circuit layer 62 (metal plate 72) and the metal layer 63 (metal plate 73) refer to the Cu concentration and the oxygen concentration in a portion of the circuit layer 62 (metal plate 72) and the metal layer 63 (metal plate 73) that is separated from the bonding interface 80 by a certain distance (50 nm or more in embodiment 2).
The mass ratio of Al, Cu, O and N in the bonding interface 80 when analyzed by energy dispersive X-ray spectroscopy (EDS) is set to be 50 to 90 wt% to 1 to 10 wt% to 2 to 20 wt% to 25 wt% or less.
The spot diameter in performing the EDS analysis is 1 to 4nm, and a plurality of spots (for example, 100 spots in embodiment 2) in the joining interface 80 are measured to calculate an average value.
Further, the bonding interface 80 between the grain boundaries of the metal plates 72, 73 constituting the circuit layer 62 and the metal layer 63 and the ceramic substrate 61 is not measured, but only the bonding interface 80 between the crystal grains of the metal plates 72, 73 constituting the circuit layer 62 and the metal layer 63 and the ceramic substrate 61 is measured.
Such a power module substrate 60 is manufactured as follows.
As shown in fig. 10 a and 11 a, a ceramic substrate 61 made of AlN, a metal plate 72 (a rolled plate of 4N aluminum) as the circuit layer 62, a copper foil 74 having a thickness of 0.15 μm or more and 3 μm or less (3 μm in embodiment 2), a metal plate 73 (a rolled plate of 4N aluminum) as the metal layer 63, and a copper foil 75 having a thickness of 0.15 μm or more and 3 μm or less (3 μm in embodiment 2) were prepared.
Next, as shown in fig. 10(b) and 11(b), a metal plate 72 is laminated on the 1 st surface of the ceramic substrate 61 via a copper foil 74, and a metal plate 73 is laminated on the 2 nd surface of the ceramic substrate 61 via a copper foil 75. Thereby forming a laminate 70.
Then, the laminate 70 is pressed in the laminating direction (pressure 1 to 5 kgf/cm)2) And then charged into a vacuum furnace and heated (pressurizing and heating step).
The degree of vacuum in the vacuum furnace here was 10-3Pa～10-5Pa, and the heating temperature is 610-650 ℃.
In the pressing and heating step, as shown in fig. 11(b), the surface layers of the metal plates 72 and 73, which are the circuit layer 62 and the metal layer 63, are melted with the copper foils 74 and 75, and molten aluminum layers 76 and 77 are formed on the surfaces (the 1 st surface and the 2 nd surface) of the ceramic substrate 61.
Next, as shown in fig. 10 c and 11 c, the laminate 70 is cooled to solidify the molten aluminum layers 76 and 77 (solidification step).
By the pressurizing, heating step and the solidifying step, a Cu high concentration portion 82 having a higher Cu concentration and higher oxygen concentration than those of the metal plates 72 and 73 constituting the circuit layer 62 and the metal layer 63 is formed at the bonding interface 80.
Thereby, the power module substrate 60 according to embodiment 2 is manufactured.
In the power module substrate 60 and the sub-power module 51 according to embodiment 2 having the above-described configurations, the Cu high concentration portion 82 having a Cu concentration 2 times or more higher than the Cu concentration in the circuit layer 62 and the metal layer 63 is formed in the bonding interface 80 between the circuit layer 62, the metal layer 63, and the ceramic substrate 61, and the oxygen concentration in the Cu high concentration portion 82 is higher than the oxygen concentration in the circuit layer 62 and the metal layer 63. Thus, the presence of oxygen atoms and Cu atoms at the junction interface 80 can improve the junction strength between the ceramic substrate 61 made of AlN and the circuit layer 62 and the junction strength between the ceramic substrate 61 and the metal layer 63.
In embodiment 2, when the bonding interface 80 is analyzed by energy dispersive X-ray analysis, the mass ratio of Al, Cu, O, and N is 50 to 90 wt%, 1 to 10 wt%, 2 to 20 wt%, and 25 wt% or less. As a result, it is possible to sufficiently obtain the effect of improving the bonding strength by Cu atoms while preventing the reaction product of Al and Cu from being excessively generated at the bonding interface 80 to inhibit bonding.
In addition, in the joining interface 80, an increase in the thickness of a portion having a high oxygen concentration is prevented, and the occurrence of cracks during thermal cycles under load can be suppressed.
Further, on the 1 st surface of the ceramic substrate 61 made of AlN, a metal plate 72 as the circuit layer 62 is laminated via a copper foil 74 having a thickness of 0.15 μm to 3 μm (3 μm in the 2 nd embodiment), and on the 2 nd surface of the ceramic substrate 61, a metal plate 73 (a rolled plate of 4N aluminum) as the metal layer 63 is laminated via a copper foil 75 having a thickness of 0.15 μm to 3 μm (3 μm in the 2 nd embodiment), and the laminate is pressed and heated. As a result, Cu of the copper foils 74 and 75 and Al of the metal plates 72 and 73 are subjected to eutectic reaction, and the melting points of the copper foils 74 and 75 and the surface layer portions of the metal plates 72 and 73 are lowered. Therefore, the molten aluminum layers 76 and 77 can be formed at the interfaces between the ceramic substrate 61 and the metal plates 72 and 73 even at a relatively low temperature (610 ℃ C. to 650 ℃ C.), and the ceramic substrate 61 and the metal plates 72 and 73 can be joined. (embodiment 3)
Next, embodiment 3 of the present invention will be explained.
Fig. 12 shows a power module substrate 110 and a power module 101 according to embodiment 3 of the present invention.
In embodiment 3, the same members as those in embodiments 1 and 2 are given the same reference numerals, and the description thereof will be omitted or simplified.
The power module substrate 110 includes: a ceramic substrate 111, a circuit layer 112 disposed on the 1 st surface (upper surface in fig. 12) of the ceramic substrate 111, and a metal layer 113 disposed on the 2 nd surface (lower surface in fig. 12) of the ceramic substrate 111.
The ceramic substrate 111 is a substrate for preventing electrical connection between the circuit layer 112 and the metal layer 113, and is made of Si having high insulation3N4(silicon nitride).
The thickness of the ceramic substrate 111 is set to be in the range of 0.2 to 1.5mm, and 0.32mm in embodiment 3.
The circuit layer 112 is formed by bonding a conductive metal plate 122 to the 1 st surface of the ceramic substrate 111.
In embodiment 3, the circuit layer 112 is formed by bonding the metal plate 22, which is a rolled plate of aluminum having a purity of 99.99% or more (so-called 4N aluminum), to the ceramic substrate 111.
The metal layer 113 is formed by bonding a metal plate 123 to the 2 nd surface of the ceramic substrate 111.
In embodiment 3, the metal layer 113 is formed by bonding a metal plate 123, which is a rolled plate of aluminum having a purity of 99.99% or more (so-called 4N aluminum), to the ceramic substrate 111, as in the case of the circuit layer 112.
When the bonding interface 130 between the ceramic substrate 111 and the circuit layer 112 (metal plate 122) and the bonding interface 130 between the ceramic substrate 111 and the metal layer 113 (metal plate 123) are observed with a transmission electron microscope, as shown in fig. 13, a Cu high concentration portion 132 in which Cu is concentrated is formed at the bonding interface 130.
The Cu concentration in the Cu high concentration portion 132 is higher than the Cu concentration in the circuit layer 112 (metal plate 122) and the metal layer 113 (metal plate 123). Specifically, the Cu concentration in the bonding interface 130 is 2 times or more the Cu concentration in the circuit layer 112 and the metal layer 113.
Here, in embodiment 3, the thickness H of the Cu high concentration portion 132 is 4nm or less.
Further, in the Cu high concentration portion 132, the oxygen concentration is set higher than the oxygen concentration in the circuit layer 112 and the metal layer 113.
Here, in the bonding interface 130 observed by the transmission electron microscope, as shown in fig. 13, the center between the end on the interface side of the lattice image of the circuit layer 112 (metal plate 122) and the metal layer 113 (metal plate 123) and the end on the interface side of the lattice image of the ceramic substrate 111 is defined as a reference plane S.
Note that the Cu concentration and the oxygen concentration in the circuit layer 112 and the metal layer 113 mean the Cu concentration and the oxygen concentration in a portion of the circuit layer 112 and the metal layer 13 which is apart from the bonding interface 130 by a certain distance (50 nm or more in embodiment 3).
The mass ratio of Al, Si, Cu, O and N in the bonding interface 130 is set to 15-45 wt%, 1-10 wt%, 2-20 wt% and 25 wt% or less when analyzed by energy dispersive X-ray spectroscopy (EDS).
The spot diameter in performing the EDS analysis is 1 to 4nm, and a plurality of spots (for example, 100 spots in embodiment 3) in the joining interface 130 are measured to calculate an average value.
Further, the bonding interface 130 between the grain boundaries of the metal plates 122, 123 constituting the circuit layer 112 and the metal layer 113 and the ceramic substrate 111 was not measured, but only the bonding interface 130 between the crystal grains of the metal plates 122, 123 constituting the circuit layer 112 and the metal layer 113 and the ceramic substrate 111 was measured.
Such a power module substrate 110 is manufactured as follows.
First, as shown in FIG. 14(a), Si is added3N4Both surfaces of the ceramic substrate 111 thus formed were fastened with Cu by vacuum deposition to form Cu fastening layers 124 and 125 having a thickness of 0.15 to 3 μm (Cu fastening step).
Next, as shown in fig. 14(b) and (c) and fig. 15(a) and (b), the metal plate 122 (rolled plate of 4N aluminum) as the circuit layer 112 is laminated on the 1 st surface of the ceramic substrate 111 on which the Cu clad layers 124 and 125 are formed, and the metal plate 123 (rolled plate of 4N aluminum) as the metal layer 113 is laminated on the 2 nd surface of the ceramic substrate 111 (laminating step).
The laminate 120 thus formed is pressed in the laminating direction (pressure 1 to 5 kgf/cm)2) Then, the resultant mixture was charged into a vacuum furnace and heated (pressurizing/heating step).
The degree of vacuum in the vacuum furnace here was 10-3Pa～10-5Pa, and the heating temperature is 610-650 ℃.
Through the pressing and heating steps, as shown in fig. 15, the surface layers of the metal plates 122 and 123, which are the circuit layer 112 and the metal layer 113, and the Cu clad layers 124 and 125 are melted, and molten aluminum layers 126 and 127 are formed on the surface of the ceramic substrate 111.
Next, as shown in fig. 14(d) and 15(c), the molten aluminum layers 126 and 127 are solidified by cooling the laminate 120 (solidification step).
By the pressurizing, heating step and the solidifying step, a Cu high concentration portion 132 having a higher Cu concentration and higher oxygen concentration than those of the metal plates 122 and 123 constituting the circuit layer 112 and the metal layer 113 is formed at the bonding interface 130.
Thereby, the power module substrate 110 according to embodiment 3 is manufactured.
In the power module substrate 110 according to embodiment 3 having the above configuration, the Cu high concentration portion 132 having a Cu concentration 2 times or more higher than the Cu concentration in the circuit layer 112 and the metal layer 113 is formed at the bonding interface 130 between the circuit layer 112 and the metal layer 113 and the ceramic substrate 111. Further, the oxygen concentration in the Cu high concentration portion 132 is set higher than the oxygen concentration in the circuit layer 112 and the metal layer 113. Thus, the presence of oxygen atoms and Cu atoms in the bonding interface 130 can improve the bonding strength by Si3N4The ceramic substrate 111, the circuit layer 112, and the metal layer 113 are bonded together with high strength.
Further, in embodiment 3, the mass ratio of Al, Si, Cu, O, and N when the bonding interface 130 is analyzed by energy dispersive X-ray analysis (EDS) is set in the range of 15 to 45 wt% of Al, Si, Cu, O, and N, 15 to 45 wt% of 1 to 10 wt% of 2 to 20 wt% of 25 wt% or less, so that it is possible to prevent excessive generation of a reactant of Al and Cu at the bonding interface 130 to inhibit bonding, and to sufficiently obtain an effect of improving the bonding strength by Cu atoms.
In addition, in the joint interface 130, the increase in the thickness of the portion having a high oxygen concentration is prevented, and the occurrence of cracks during thermal cycles under load can be suppressed.
In addition, in the presence of Si3N4Both surfaces of the ceramic substrate 111 thus constituted are bonded with Cu by vacuum deposition, and a metal plate 122 (rolled plate of 4N aluminum) as the circuit layer 112 is laminated on the 1 st surface of the ceramic substrate 111 on which the Cu bonding layers 124 and 125 are formed, and a metal plate 123 (rolled plate of 4N aluminum) as the metal layer 113 is laminated on the 2 nd surface of the ceramic substrate 111, and the laminated body is pressed and heated. As a result, the Cu of the Cu clad layers 124 and 125 and the Al of the metal plates 122 and 123 cause eutectic reaction, thereby lowering the melting point of the surface layer portions of the metal plates 122 and 123, and enabling the ceramic substrate 111 and the metal to be formed even at a relatively low temperature (610 to 650 ℃)The interface between the plates 122, 123 forms molten aluminum layers 126, 127, which can bond the ceramic substrate 111 and the metal plates 122, 123.
While the embodiments 2 and 3 of the present invention have been described above, the present invention is not limited thereto, and can be modified as appropriate within a range not departing from the technical spirit of the present invention.
In embodiment 3, although the method of fastening Cu to both surfaces of the ceramic substrate has been described, the method is not limited to this, and Cu may be fastened to a surface (bonding surface) of the metal plate facing the ceramic substrate 11, or Cu may be fastened to both the metal plate and the ceramic substrate.
Further, although the method of fastening Cu by vacuum deposition has been described, the method is not limited to this, and Cu may be fastened by a method such as sputtering, plating, or coating with a copper paste.
(embodiment 4)
Fig. 20 shows a power module substrate 160 and a power module 151 according to embodiment 4 of the present invention.
In embodiment 4, the same members as those in embodiments 1 to 3 are given the same reference numerals, and the description thereof will be omitted or simplified.
The power module 151 includes: a power module board 160 provided with a circuit layer 162, a semiconductor chip 3 bonded to the surface of the circuit layer 162 via a solder layer 2, and a heat sink 4.
The power module substrate 160 includes: a ceramic substrate 161, a circuit layer 162 disposed on the 1 st surface (upper surface in fig. 20) of the ceramic substrate 161, and a metal layer 163 disposed on the 2 nd surface (lower surface in fig. 20) of the ceramic substrate 161.
The ceramic substrate 161 is a substrate for preventing electrical connection between the circuit layer 162 and the metal layer 163, and is made of Al having high insulation property2O3(alumina).
The thickness of the ceramic substrate 161 is set to be in the range of 0.2 to 1.5mm, and 0.635mm in embodiment 4.
The circuit layer 162 is formed by bonding a conductive metal plate 172 to the 1 st surface of the ceramic substrate 161.
In embodiment 4, the circuit layer 162 is formed by joining a metal plate 172 made of a rolled plate of aluminum having a purity of 99.99% or more (so-called 4N aluminum) to the ceramic substrate 161.
The metal layer 163 is formed by bonding a metal plate 173 to the 2 nd surface of the ceramic substrate 161.
In embodiment 4, the metal layer 163 is formed by bonding a metal plate 173 made of a rolled plate of aluminum having a purity of 99.99% or more (so-called 4N aluminum) to the ceramic substrate 161, similarly to the circuit layer 162.
When the bonding interface 180 between the ceramic substrate 161 and the circuit layer 162 (metal plate 172) and the bonding interface 180 between the ceramic substrate 161 and the metal layer 163 (metal plate 173) are observed with a transmission electron microscope, as shown in fig. 21, a Cu high concentration portion 182 in which Cu is concentrated is formed at the bonding interface 180.
The Cu concentration in the Cu high concentration portion 182 is higher than the Cu concentration in the circuit layer 162 (metal plate 172) and the metal layer 163 (metal plate 173). Specifically, the Cu concentration in the bonding interface 180 is 2 times or more the Cu concentration in the circuit layer 162 and the metal layer 163. Here, in embodiment 4, the thickness H of the Cu high concentration portion 182 is 4nm or less.
Here, in the bonding interface 180 observed by a transmission electron microscope, as shown in fig. 21, the center between the end on the interface side of the lattice image of the circuit layer 162 (metal plate 172) and the metal layer 163 (metal plate 173) and the end on the interface side of the lattice image of the ceramic substrate 161 is defined as a reference plane S.
Note that the Cu concentration in the circuit layer 162 (metal plate 172) and the metal layer 163 (metal plate 173) means the Cu concentration in a portion of the circuit layer 162 (metal plate 172) and the metal layer 163 (metal plate 173) which is separated from the bonding interface 180 by a predetermined distance (50 nm or more in embodiment 4).
The mass ratio of Al, Cu and O in the bonding interface 180 is set in the range of 50 to 90 wt%: 1 to 10 wt%: 0 to 45 wt% when analyzed by energy dispersive X-ray analysis (EDS).
The spot diameter in performing the EDS analysis is 1 to 4nm, and a plurality of spots (for example, 100 spots in embodiment 4) in the joining interface 180 are measured to calculate an average value.
In addition, the bonding interface 180 between the grain boundaries of the metal plates 172 and 173 constituting the circuit layer 162 and the metal layer 163 and the ceramic substrate 161 is not measured, and only the bonding interface 180 between the crystal grains of the metal plates 172 and 173 constituting the circuit layer 162 and the metal layer 163 and the ceramic substrate 161 is measured.
Such a power module substrate 160 is manufactured as follows.
As shown in FIGS. 22(a) and 23(a), Al is prepared2O3The ceramic substrate 161 thus constituted, a metal plate 172 (a rolled plate of 4N aluminum) as the circuit layer 162, a copper foil 174 having a thickness of 0.15 μm to 3 μm (3 μm in embodiment 2), a metal plate 173 (a rolled plate of 4N aluminum) as the metal layer 163, and a copper foil 175 having a thickness of 0.15 μm to 3 μm (3 μm in embodiment 2).
Next, as shown in fig. 22(b) and 23(b), a metal plate 172 is laminated on the 1 st surface of the ceramic substrate 161 via a copper foil 174, and a metal plate 173 is laminated on the 2 nd surface of the ceramic substrate 161 via a copper foil 175. Thereby forming a laminate 170.
Then, the laminate 170 is pressed in the laminating direction (pressure 1 to 5 kgf/cm)2) And then charged into a vacuum furnace in this state and heated (pressurizing and heating step).
The degree of vacuum in the vacuum furnace here was 10-3Pa～10-5Pa, and the heating temperature is 610-650 ℃.
By the pressing and heating steps, as shown in fig. 23, the surface layers of the metal plates 172 and 173, which are the circuit layer 162 and the metal layer 163, are melted with the copper foils 174 and 175, and melted aluminum layers 176 and 177 are formed on the surface of the ceramic substrate 161.
Next, as shown in fig. 22 c and 23 c, the laminate 170 is cooled to solidify the molten aluminum layers 176 and 177 (solidification step).
By the pressurizing, heating step and solidifying step, a Cu high concentration portion 182 having a Cu concentration higher than the Cu concentration in the metal plates 172 and 173 constituting the circuit layer 162 and the metal layer 163 is formed at the bonding interface 180.
Thereby, the power module substrate 160 according to embodiment 4 is manufactured.
In the power module substrate 160 and the sub-power module 151 according to embodiment 4 having the above-described configurations, the Cu high concentration portion 182 having a Cu concentration 2 times or more the Cu concentration in the circuit layer 162 and the metal layer 163 is formed at the bonding interface 180 between the circuit layer 162 and the metal layer 163 and the ceramic substrate 161. Thus, Cu atoms are present in the bonding interface 180, and Al atoms are increased2O3The bonding strength between the ceramic substrate 161 and the circuit layer 162, and the bonding strength between the ceramic substrate 161 and the metal layer 163.
Further, in embodiment 4, when the bonding interface 180 is analyzed by energy dispersive X-ray analysis, the mass ratio of Al, Cu, and O is 50 to 90 wt%, 1 to 10 wt%, and 0 to 45 wt%. As a result, it is possible to prevent excessive generation of a reactant of Al and Cu at the bonding interface 180 to inhibit bonding, and at the same time, it is possible to sufficiently obtain an effect of improving the bonding strength by Cu atoms.
In addition, in the case of Al2O3A metal plate 172 as a circuit layer 162 is laminated on the 1 st surface of the ceramic substrate 161 via a copper foil 174 having a thickness of 0.15 to 3 μm (3 μm in the 4 th embodiment), and a metal is formed on the 2 nd surface of the ceramic substrate 161The metal plate 173 (rolled plate of 4N aluminum) of the layer 163 is laminated via a copper foil 175 having a thickness of 0.15 μm to 3 μm (3 μm in embodiment 4), and the laminate is pressed and heated. As a result, Cu of the copper foils 174 and 175 and Al of the metal plates 172 and 173 are subjected to eutectic reaction, and the melting points of the copper foils 174 and 175 and the surface layer portions of the metal plates 172 and 173 are lowered. Therefore, the molten aluminum layers 176 and 177 can be formed at the interfaces between the ceramic substrate 161 and the metal plates 172 and 173 even at a relatively low temperature (610 ℃ C. to 650 ℃ C.), and the ceramic substrate 161 and the metal plates 172 and 173 can be bonded to each other.
While embodiment 4 of the present invention has been described above, the present invention is not limited thereto, and can be modified as appropriate within a range not departing from the technical spirit of the present invention.
In embodiment 4 of the present invention, a method of interposing a copper foil between a ceramic substrate and a metal plate in a lamination step is described, but the method is not limited thereto, and a Cu layer may be formed by a Cu fastening step of fastening Cu to at least one of a surface (bonding surface) of the metal plate facing the ceramic substrate and a surface (bonding surface) of the ceramic substrate facing the metal plate before the lamination step.
Examples of a method for fastening Cu include: vacuum deposition, sputtering, plating, and coating with copper paste.
(embodiment 5)
Fig. 26 shows a power module substrate and a power module according to embodiment 5 of the present invention.
In embodiment 5, the same members as those in embodiments 1 to 4 are given the same reference numerals, and the description thereof will be omitted or simplified.
The power module 201 includes: a power module substrate 210 on which a circuit layer 212 is disposed, a semiconductor chip 3 bonded to the surface of the circuit layer 212 via a solder layer 2, and a heat sink 4.
The power module substrate 210 includes: a ceramic substrate 211, a circuit layer 212 disposed on the 1 st surface (upper surface in fig. 26) of the ceramic substrate 211, and a metal layer 213 disposed on the 2 nd surface (lower surface in fig. 26) of the ceramic substrate 211.
The ceramic substrate 211 is a substrate for preventing electrical connection between the circuit layer 212 and the metal layer 213, and is made of AlN (aluminum nitride) having high insulation properties.
The thickness of the ceramic substrate 211 is set to be in the range of 0.2 to 1.5mm, and 0.635mm in embodiment 5.
In embodiment 5, as shown in fig. 26, the width of the ceramic substrate 211 is set to be larger than the widths of the circuit layer 212 and the metal layer 213.
The circuit layer 212 is formed by bonding a conductive metal plate 222 to the 1 st surface of the ceramic substrate 211.
In embodiment 5, the circuit layer 212 is formed by bonding a metal plate 222 made of a rolled plate of aluminum having a purity of 99.99% or more (so-called 4N aluminum) to the ceramic substrate 211.
Here, an Al — Si based brazing material containing Si, which is a melting point lowering element, is used for bonding the ceramic substrate 211 and the metal plate 222.
The metal layer 213 is formed by bonding a metal plate 223 to the 2 nd surface of the ceramic substrate 211.
In embodiment 5, the metal layer 213 is formed by bonding a metal plate 223, which is a rolled plate of aluminum having a purity of 99.99% or more (so-called 4N aluminum), to the ceramic substrate 211, as in the case of the circuit layer 212.
Here, for joining the ceramic substrate 211 and the metal plate 223, an Al — Si-based brazing material containing Si, which is a melting point lowering element, is used.
As shown in fig. 27, in the central portion in the width direction of the bonding interface 230 between the ceramic substrate 211 and the circuit layer 212 (metal plate 222) and the central portion in the width direction (portion a in fig. 26) of the bonding interface 230 between the ceramic substrate 211 and the metal layer 213 (metal plate 223), Si and Cu diffuse into the circuit layer 212 (metal plate 222) and the metal layer 213 (metal plate 223), and a concentration gradient layer 233 in which the concentration of Si and Cu gradually decreases as it is separated from the bonding interface 230 in the stacking direction is formed.
Here, in a portion of the concentration-sloped layer 233 adjacent to the bonding interface 230, the Si concentration is set within a range of 0.05 to 0.5 wt%, and the Cu concentration is set within a range of 0.05 to 1.0 wt%.
The Si concentration and the Cu concentration in the portion of the concentration-gradient layer 233 adjacent to the junction interface 230 were average values obtained by measuring 5 points in the range from the junction interface 230 to 50 μm by EPMA analysis (point diameter: 30 μm).
Further, as shown in fig. 28, an aluminum phase 241 in which Si and Cu are diffused in solid solution in aluminum, an Si phase 242 in which the content of Si is 98 wt% or more, and a eutectic phase 243 composed of a 3-membered eutectic structure of Al, Cu, and Si are formed in the end 235 in the width direction of the bonding interface 230 between the ceramic substrate 211 and the circuit layer 212 (metal plate 222) and the end 235 in the width direction of the bonding interface 230 between the ceramic substrate 211 and the metal layer 213 (metal plate 223) (portion B in fig. 26).
Further, in the eutectic phase 243, a compound containing Cu (e.g., CuAl) is precipitated2) And precipitate particles formed.
When the bonding interface 230 between the ceramic substrate 211 and the circuit layer 212 (metal plate 222) and the bonding interface 230 between the ceramic substrate 211 and the metal layer 213 (metal plate 223) are observed with a transmission electron microscope, as shown in fig. 29, a Si high concentration portion 232 in which Si is concentrated is formed at the bonding interface 230.
The Si concentration in the Si high concentration portion 232 is 5 times or more higher than the Si concentration in the circuit layer 212 (metal plate 222) and the metal layer 213 (metal plate 223). The thickness H of the Si high concentration portion 232 is 4nm or less.
Here, in the bonding interface 230 observed by a transmission electron microscope, as shown in fig. 29, the center between the end on the interface side of the lattice image of the circuit layer 212 (metal plate 222) and the metal layer 213 (metal plate 223) and the end on the interface side of the lattice image of the ceramic substrate 211 is defined as a reference plane S.
Such a power module substrate 210 is manufactured as follows.
First, Cu is fixed to both surfaces of the ceramic substrate 211 made of AlN by sputtering (Cu fixing step).
Next, as shown in fig. 30 a and 31 a, a ceramic substrate 211 of AlN to which Cu is fastened, a metal plate 222 (a rolled plate of 4N aluminum) as a circuit layer 212, a solder foil 224 having a thickness of 10 to 30 μm (20 μm in embodiment 5), a metal plate 223 (a rolled plate of 4N aluminum) as a metal layer 213, and a solder foil 225 having a thickness of 10 to 30 μm (20 μm in embodiment 5) are prepared.
Next, as shown in fig. 30(b) and 31(b), the metal plate 222 is laminated on the 1 st surface of the ceramic substrate 211 via the brazing filler metal foil 224, and the metal plate 223 is laminated on the 2 nd surface of the ceramic substrate 211 via the brazing filler metal foil 225 (laminating step). Thereby forming a laminate 220.
Then, the laminate 220 is pressed in the laminating direction (pressure 1 to 5 kgf/cm)2) Then, the solder foil 224 and 225 are placed in a vacuum furnace and heated in this state to melt (melting step).
The degree of vacuum in the vacuum furnace here was 10-3Pa～10-5Pa. In this melting step, as shown in fig. 31(b), part of the metal plates 222 and 223 as the circuit layer 212 and the metal layer 213 is melted with the solder foils 224 and 225, and molten aluminum layers 226 and 227 are formed on the surface of the ceramic substrate 211.
Next, as shown in fig. 30(c) and 31(c), the molten aluminum layers 226 and 227 are solidified by cooling the stacked body 220 (solidification step).
In this way, the metal plates 222 and 223 as the circuit layer 212 and the metal layer 213 are joined to the ceramic substrate 211, and the power module substrate 210 as embodiment 5 is manufactured.
In the power module substrate 210 and the power module 201 according to embodiment 5 having the above configurations, the ceramic substrate 211, the circuit layer 212 (metal plate 222) and the metal layer 213 (metal plate 223) are bonded using an Al — Si-based brazing material, and Cu is added to the bonding interface 230 between the circuit layer 212 (metal plate 222) and the metal layer 213 (metal plate 223) and the ceramic substrate 211. Thus, Cu and Al present at the bonding interface 230 are melted and reacted, and even when the ceramic substrate 211 is bonded under a bonding condition of a low temperature and a short time, the circuit layer 212 (metal plate 222) and the metal layer 213 (metal plate 223) can be firmly bonded, and the bonding reliability can be greatly improved.
In addition, in the central portion in the width direction of the bonding interface 230 between the ceramic substrate 211 and the circuit layer 212 (metal plate 222) and the central portion in the width direction (portion a in fig. 26) of the bonding interface 230 between the ceramic substrate 211 and the metal layer 213 (metal plate 223), Si and Cu diffuse to the circuit layer 212 (metal plate 222) and the metal layer 213 (metal plate 223), and a concentration gradient layer 233 in which the concentrations of Si and Cu gradually decrease as it is separated from the bonding interface 230 in the stacking direction is formed. In addition, since the Cu concentration of the portion of the concentration-gradient layer 233 adjacent to the bonding interface 230 is set in the range of 0.05 to 1.0 wt%, the portions of the circuit layer 212 (metal plate 222) and the metal layer 213 (metal plate 223) adjacent to the bonding interface 230 are subjected to solid solution strengthening, and occurrence of cracks in the circuit layer 212 (metal plate 222) and the metal layer 213 (metal plate 223) can be prevented.
Further, the Si concentration of the portion of the concentration-sloped layer 233 adjacent to the bonding interface 230 is set in the range of 0.05 to 0.5 wt%, so that Si is sufficiently diffused into the return layer 212 (metal plate 222) and the metal layer 213 (metal plate 223). Thus, the brazing material is reliably melted and solidified, whereby the ceramic substrate 211 and the circuit layer 212 (metal plate 222), and the ceramic substrate 211 and the metal layer 213 (metal plate 223) can be firmly joined.
Further, the width of the ceramic substrate 211 is set to be wider than the widths of the circuit layer 212 (metal plate 222) and the metal layer 213 (metal plate 223), and an aluminum phase 241 in which Si and Cu are diffused into aluminum, an Si phase 242 having a Si content of 98 wt% or more, and a eutectic phase 243 composed of a 3-membered eutectic structure of Al, Cu, and Si are formed at the end 235 in the width direction of the circuit layer 212 (metal plate 222) and the metal layer 213 (metal plate 223). This improves the strength of the end portions 235 of the circuit layer 212 (metal plate 222) and the metal layer 213 (metal plate 223) in the width direction.
Further, in the eutectic phase 243, a compound containing Cu (e.g., CuAl) is precipitated2) The precipitate particles thus constituted can precipitate and strengthen the widthwise end portion 235.
This prevents the circuit layer 212 (metal plate 222) and the metal layer 213 (metal plate 223) from being broken at the widthwise end 235.
In embodiment 5, the ceramic substrate 211 is made of AlN, and the Si high concentration portion 232 having an Si concentration 5 times or more higher than the Si concentration in the circuit layer 212 (metal plate 222) and the metal layer 213 (metal plate 223) is formed at the junction interface 230 between the metal plates 222 and 223 and the ceramic substrate 211. This can improve the bonding strength between the ceramic substrate 211 and the metal plates 222 and 223 by Si present at the bonding interface 230.
(embodiment 6)
Next, embodiment 6 of the present invention will be described with reference to fig. 32 and 33.
In embodiment 6, the same members as those in embodiments 1 to 5 are given the same reference numerals, and the description thereof will be omitted or simplified.
In the power module substrate 260 according to embodiment 6, the ceramic substrate 261 is made of Si3N4This point is different from embodiment 5.
When the bonding interface 280 between the ceramic substrate 261 and the circuit layer 262 (metal plate 272) and the bonding interface 280 between the ceramic substrate 261 and the metal layer 263 (metal plate 273) are observed by a transmission electron microscope, as shown in fig. 33, it is observed that the oxygen high concentration portion 282 in which oxygen is concentrated is formed at the bonding interface 280.
The oxygen concentration in the oxygen high concentration portion 282 is higher than the oxygen concentration in the circuit layer 262 (metal plate 272) and the metal layer 263 (metal plate 273).
The thickness H of the oxygen high concentration portion 282 is 4nm or less.
Here, in the bonding interface 280 observed by the transmission electron microscope, as shown in fig. 33, the center between the end on the interface side of the lattice images of the circuit layer 262 (metal plate 272) and the metal layer 263 (metal plate 273) and the end on the bonding interface side of the lattice image of the ceramic substrate 261 is defined as a reference plane S.
In the power module substrate 260 according to embodiment 6 having the above configuration, the oxygen high concentration portion 282 having a higher oxygen concentration than the oxygen concentration in the metal plates 272 and 273 constituting the circuit layer 262 and the metal layer 263 is formed at the bonding interface 280 between the metal plates 272 and 273 constituting the circuit layer 262 and the metal layer 263 and the ceramic substrate 261, and therefore the bonding strength between the ceramic substrate 261 and the metal plates 272 and 273 can be improved by this oxygen.
Since the thickness of the oxygen high concentration portion 282 is 4nm or less, cracks generated in the oxygen high concentration portion 282 due to stress during thermal cycles are suppressed.
Although embodiments 1 to 6 of the present invention have been described above, the present invention is not limited thereto, and can be modified as appropriate within a range not departing from the technical spirit of the present invention.
For example, although the case where a rolled sheet of pure aluminum having a purity of 99.99% is used as the metal sheet constituting the circuit layer and the metal layer has been described, the present invention is not limited thereto, and aluminum having a purity of 99% (2N aluminum) may be used.
Further, the case where the buffer layer made of aluminum or an aluminum alloy or a composite material containing aluminum (for example, AlSiC or the like) is provided between the top plate portion and the metal layer of the heat sink has been described, but the buffer layer may not be provided.
Further, although the structure in which the heat sink is formed of aluminum has been described, a structure in which the heat sink is formed of an aluminum alloy, a composite material containing aluminum, copper, a copper alloy, or the like may be employed.
Further, as the heat radiating fins, a structure having a flow path for the cooling medium has been described, but the structure of the heat radiating fins is not particularly limited.
In embodiment 5, a case where a ceramic substrate made of AlN is used has been described, but the present invention is not limited thereto, and Al may be used2O3And the like.
Further, although the manufacturing method having the Cu bonding step of bonding Cu to the surface of the ceramic substrate has been described, Cu may be bonded to the surface of the solder foil without being limited thereto.
Note that Cu may be fixed by an evaporation method, a plating method, or the like instead of the sputtering method.
Further, Cu may be added to the Al — Si based brazing filler metal.
Examples
Next, in order to confirm the effectiveness of the power module substrate (power module) according to embodiments 1 to 6, a confirmation test is performed, and the results thereof will be described.
(example 1)
In example 1 described below, the results of a confirmation test performed to confirm the effectiveness of the power module substrate according to embodiment 1 will be described with reference to fig. 6 and 7.
First, as a power module substrate used in the test, a power module substrate was manufactured by the following manufacturing method.
Specifically, a 40mm square thick 0.635mm thick AlN plate was preparedThe ceramic substrate obtained was 2 metal plates made of 4N aluminum having a thickness of 0.6 mm. Then, Cu was secured to both surfaces of the ceramic substrate by vacuum deposition, and metal plates were laminated on both surfaces of the ceramic substrate, respectively, to form a laminated body. A pressure of 1 to 5kgf/cm in the laminating direction2The laminate was placed in a vacuum furnace (degree of vacuum 10) under pressure-3Pa～10-5Pa) to manufacture a substrate for a power module comprising a ceramic substrate, a circuit layer and a metal layer.
Similarly, a ceramic substrate of AlN of 40mm square and 0.635mm in thickness and 2 metal plates of 4N aluminum of 0.6mm in thickness were prepared. Then, Cu was secured to one surface of each metal plate by vacuum deposition, and the metal plates were laminated on both surfaces of the ceramic substrate so that the deposition surfaces of the metal plates faced the ceramic substrate, thereby forming a laminate. A pressure of 1 to 5kgf/cm in the laminating direction2The laminate was placed in a vacuum furnace (degree of vacuum 10) under pressure-3Pa～10-5Pa) to manufacture a substrate for a power module comprising a ceramic substrate, a circuit layer and a metal layer.
As described above, in example 1, 2 kinds of substrates for power modules were used.
Here, the fastening amount (Cu thickness) of Cu by vacuum deposition was varied to 5 parameters (5 levels) of 0.1. mu.m, 0.5. mu.m, 1.0. mu.m, 2.0. mu.m, and 3.0. mu.m. The heating temperature was varied to 3 parameters (3 levels) of 610 ℃, 630 ℃ and 650 ℃. Thus, a total of 30 kinds of power module substrates were prepared.
An aluminum plate (a6063) having a thickness of 50mm × 60mm and 5mm corresponding to the top plate of the heat sink was bonded to the metal layer of the power module substrate formed in this manner via a buffer layer made of AlSiC and having a thickness of 0.9 mm. Thus, a total of 30 test pieces were prepared.
Next, before the thermal cycle test was performed on the total of 30 kinds of test pieces, the bonding area ratio (bonding ratio) at the bonding interface between the ceramic substrate and the metal plate was determined. Specifically, the bonding interface between the ceramic substrate and the metal plate was imaged using an ultrasonic imaging device (probe frequency 15MHz), and the data obtained by imaging was binarized to obtain the area occupied by the bonding portion in the entire bonding interface, thereby calculating the bonding ratio. Before the thermal cycle test, the bonding ratio between the ceramic substrate and the metal plate was 100%.
Then, the total of 30 kinds of test pieces were subjected to 3000 thermal cycles at-40 ℃ to 105 ℃ to apply a load. Then, the bonding ratio of the ceramic substrate and the metal plate, that is, the bonding ratio after the heat cycle was performed 3000 times was determined by the same method as described above using the ultrasonic imaging apparatus. Thus, the evaluation results of the power module substrate were obtained.
Fig. 6 shows the evaluation results of the power module substrate obtained by depositing Cu on the ceramic substrate.
Fig. 7 shows the evaluation results of the power module substrate obtained by depositing Cu on the metal plate.
In fig. 6 and 7, a power module substrate having a bonding ratio of 85% or more after 3000 heat cycles as a load is indicated by a symbol "o", a power module substrate having a bonding ratio of 70% or more and less than 85% after 3000 heat cycles as a load is indicated by a symbol "Δ", and a power module substrate having a bonding ratio of less than 70% after 3000 heat cycles as a load is indicated by a symbol "x".
As shown in fig. 6 and 7, the higher the heating temperature, the higher the bonding reliability tends to be.
Furthermore, it was confirmed that when the Cu layer thickness is about 1.0 μm to 2.0. mu.m, the bonding reliability is improved even at a low heating temperature.
Further, fig. 6 and 7 show the same tendency, and there is no difference between the case of depositing Cu on the ceramic substrate and the case of depositing Cu on the metal plate.
(example 2)
In example 2 described below, the results of a confirmation test performed to confirm the effectiveness of the power module substrate according to embodiment 2 are described with reference to fig. 16(a) and (b) and fig. 17(a) and (b).
First, as a power module substrate used in the test, a power module substrate was manufactured by the following manufacturing method.
Specifically, a ceramic substrate of AlN of 40mm square and 0.635mm in thickness and 2 metal plates of 4N aluminum of 0.6mm in thickness were prepared. Then, Cu was secured to both surfaces of the ceramic substrate by vacuum deposition, and metal plates were laminated on both surfaces of the ceramic substrate, respectively, to form a laminated body. A pressure of 1 to 5kgf/cm in the laminating direction2The laminate was placed in a vacuum furnace (degree of vacuum 10) under pressure-3Pa～10-5Pa) to manufacture a substrate for a power module comprising a ceramic substrate, a circuit layer and a metal layer.
Similarly, a ceramic substrate of AlN of 40mm square and 0.635mm in thickness and 2 metal plates of 4N aluminum of 0.6mm in thickness were prepared. Then, Cu was secured to one surface of each metal plate by vacuum deposition, and the metal plates were laminated on both surfaces of the ceramic substrate so that the deposition surfaces of the metal plates faced the ceramic substrate, thereby forming a laminate. A pressure of 1 to 5kgf/cm in the laminating direction2The laminate was placed in a vacuum furnace (degree of vacuum 10) under pressure-3Pa～10-5Pa) to manufacture a substrate for a power module comprising a ceramic substrate, a circuit layer and a metal layer.
As described above, in example 2, 2 kinds of substrates for power modules were used.
Here, the fastening amount (Cu thickness) of Cu by vacuum deposition was varied to 5 parameters (5 levels) of 0.1. mu.m, 0.5. mu.m, 1.0. mu.m, 2.0. mu.m, and 3.0. mu.m. The heating temperature was varied to 3 parameters (3 levels) of 610 ℃, 630 ℃ and 650 ℃. Thereby, a total of 30 kinds of power module substrates were formed.
On the metal layer of the power module substrate thus formed, an aluminum plate (a6063) having a thickness of 50mm × 60mm and 5mm corresponding to the top plate of the heat sink was bonded via a buffer layer made of 4N aluminum and having a thickness of 0.9 mm.
Thus, a total of 30 test pieces were prepared.
Next, before the thermal cycle test was performed on the total of 30 kinds of test pieces, the bonding area ratio (bonding ratio) at the bonding interface between the ceramic substrate and the metal plate was determined. As a method for calculating the bonding ratio, a method for calculating the bonding ratio using an ultrasonic imaging device (probe frequency 15MHz) was employed as described in example 1 above. Before the thermal cycle test, the bonding ratio between the ceramic substrate and the metal plate was 100%.
Then, the total of 30 kinds of test pieces were subjected to 3000 thermal cycles at-40 ℃ to 105 ℃ to apply a load, and the presence or absence of cracking of the ceramic substrate was confirmed.
In this test, 2 test pieces were prepared for each of 30 kinds of test pieces, and the presence or absence of cracking of the ceramic substrate was confirmed. The results are shown in FIGS. 16(a) and (b).
Fig. 16(a) shows the evaluation results of the power module substrate obtained by depositing Cu on the ceramic substrate.
Fig. 16(b) shows the evaluation results of the power module substrate obtained by depositing Cu on the metal plate.
Note that, the power module substrate in which the ceramic substrate was not broken in both of the 2 test pieces is indicated by symbol "o", the power module substrate in which the ceramic substrate was broken in one of the 2 test pieces is indicated by symbol "Δ", and the power module substrate in which the ceramic substrate was broken in both of the 2 test pieces is indicated by symbol "x".
After 3000 times of the thermal cycle, the bonding ratio was determined for a total of 30 types of test pieces.
Specifically, the bonding ratio of the ceramic substrate and the metal plate, that is, the bonding ratio after 3000 thermal cycles was obtained by the same method as described above using the ultrasonic imaging apparatus. Thus, the evaluation results of the power module substrate were obtained.
Fig. 17(a) shows the evaluation results of the power module substrate obtained by depositing Cu on the ceramic substrate.
Fig. 17(b) shows the evaluation results of the power module substrate obtained by depositing Cu on the metal plate.
In fig. 17(a) and (b), a power module substrate having a bonding ratio of 85% or more after 3000 heat cycles as a load is indicated by symbol "o", a power module substrate having a bonding ratio of 70% or more and less than 85% after 3000 heat cycles as a load is indicated by symbol "Δ", and a power module substrate having a bonding ratio of less than 70% after 3000 heat cycles as a load is indicated by symbol "x".
As shown in fig. 16(a) and (b), it was confirmed that cracking of the ceramic substrate made of AlN is more likely to occur as the Cu thickness formed in the Cu bonding step becomes thicker.
In addition, in the test piece having a Cu thickness of 2 μm, it was confirmed that cracking of the ceramic tends to be suppressed as the heating temperature is higher.
As shown in fig. 17(a) and (b), the higher the heating temperature, the higher the bonding reliability tends to be.
Further, it was confirmed that when the Cu thickness was about 2 μm, the bonding reliability was improved even when the heating temperature was low.
From these test results, it was confirmed that, in the ceramic substrate made of AlN, the Cu thickness present at the interface between the metal plate and the ceramic substrate at the time of joining is preferably set to 2.5 μm or less.
(example 3)
In example 3 described below, the results of a confirmation test for confirming the effectiveness of the power module substrate according to embodiment 3 are described with reference to fig. 18(a) and (b) and fig. 19(a) and (b).
First, as a power module substrate used in the test, a power module substrate was manufactured by the following manufacturing method.
Specifically, a 40mm square of Si with a thickness of 0.32mm was prepared3N4A ceramic substrate formed of the above-mentioned composition, and 2 metal plates made of 4N aluminum having a thickness of 0.6 mm. Then, Cu was secured to both surfaces of the ceramic substrate by vacuum deposition, and metal plates were laminated on both surfaces of the ceramic substrate, respectively, to form a laminated body. A pressure of 1 to 5kgf/cm in the laminating direction2The laminate was placed in a vacuum furnace (degree of vacuum 10) under pressure-3Pa～10-5Pa) to manufacture a substrate for a power module comprising a ceramic substrate, a circuit layer and a metal layer.
Similarly, a 40mm square of Si with a thickness of 0.32mm was prepared3N4A ceramic substrate formed of the above-mentioned composition, and 2 metal plates made of 4N aluminum having a thickness of 0.6 mm. Then, Cu was secured to one surface of each metal plate by vacuum deposition, and the metal plates were laminated on both surfaces of the ceramic substrate so that the deposition surfaces of the metal plates faced the ceramic substrate, thereby forming a laminate. A pressure of 1 to 5kgf/cm in the laminating direction2The laminate was placed in a vacuum furnace (degree of vacuum 10) under pressure- 3Pa～10-5Pa) to manufacture a substrate for a power module comprising a ceramic substrate, a circuit layer and a metal layer.
As described above, in example 3, 2 kinds of substrates for power modules were used.
Here, the fastening amount (Cu thickness) of Cu by vacuum deposition was varied to 5 parameters (5 levels) of 0.1. mu.m, 0.5. mu.m, 1.0. mu.m, 2.0. mu.m, and 3.0. mu.m. The heating temperature was varied to 3 parameters (3 levels) of 610 ℃, 630 ℃ and 650 ℃. Thereby, a total of 30 kinds of power module substrates were formed.
On the metal layer of the power module substrate thus formed, an aluminum plate (a6063) having a thickness of 50mm × 60mm and 5mm corresponding to the top plate of the heat sink was bonded via a buffer layer made of 4N aluminum and having a thickness of 0.9 mm.
Thus, a total of 30 test pieces were prepared.
Next, before the thermal cycle test was performed on the total of 30 kinds of test pieces, the bonding area ratio (bonding ratio) at the bonding interface between the ceramic substrate and the metal plate was determined. As a method for calculating the bonding ratio, a method for calculating the bonding ratio using an ultrasonic imaging device (probe frequency 15MHz) was employed as described in example 1 above. Before the thermal cycle test, the bonding ratio between the ceramic substrate and the metal plate was 100%.
Then, the total of 30 kinds of test pieces were subjected to 3000 thermal cycles at-40 ℃ to 105 ℃ to apply a load, and the presence or absence of cracking of the ceramic substrate was confirmed.
In this test, 2 specimens of 30 kinds of test pieces were prepared, and the presence or absence of cracking of the ceramic substrate was confirmed. The results are shown in FIGS. 18(a) and (b).
Fig. 18(a) shows the evaluation results of the power module substrate obtained by depositing Cu on the ceramic substrate.
Fig. 18(b) shows the evaluation results of the power module substrate obtained by depositing Cu on the metal plate.
Note that, the power module substrate in which the ceramic substrate was not broken in both of the 2 test pieces is indicated by symbol "o", the power module substrate in which the ceramic substrate was broken in one of the 2 test pieces is indicated by symbol "Δ", and the power module substrate in which the ceramic substrate was broken in both of the 2 test pieces is indicated by symbol "x".
After 3000 times of the thermal cycle, the bonding ratio was determined for a total of 30 types of test pieces.
Specifically, the bonding ratio of the ceramic substrate and the metal plate, that is, the bonding ratio after 3000 thermal cycles was obtained by the same method as described above using the ultrasonic imaging apparatus. Thus, the evaluation results of the power module substrate were obtained.
Fig. 19(a) shows the evaluation results of the power module substrate obtained by depositing Cu on the ceramic substrate.
Fig. 19(b) shows the evaluation results of the power module substrate obtained by depositing Cu on the metal plate.
In fig. 19(a) and (b), a power module substrate having a bonding ratio of 85% or more after 3000 heat cycles as a load is indicated by symbol "o", a power module substrate having a bonding ratio of 70% or more and less than 85% after 3000 heat cycles as a load is indicated by symbol "Δ", and a power module substrate having a bonding ratio of less than 70% after 3000 heat cycles as a load is indicated by symbol "x".
As shown in FIGS. 18(a) and (b), the silicon-containing alloy is composed of Si3N4In the ceramic substrate having the above structure, no cracking of the ceramic substrate was observed under the present test conditions.
As shown in fig. 19(a) and (b), the higher the heating temperature, the higher the bonding reliability tends to be.
Further, it was confirmed that when the Cu thickness was about 2 μm, the bonding reliability was improved even at a low heating temperature.
From these test results, it was confirmed that3N4In the ceramic substrate having the above structure, the thickness of Cu present at the interface between the metal plate and the ceramic substrate at the time of bonding is preferably set to 0.15 μm or more and 3 μm or less.
(example 4)
In example 4 described below, the results of a confirmation test for confirming the effectiveness of the power module substrate according to embodiment 4 are described with reference to fig. 24(a) and (b) and fig. 25(a) and (b).
First, as a power module substrate used in the test, a power module substrate was manufactured by the following manufacturing method.
Specifically, 40mm square of Al with a thickness of 0.635mm was prepared2O3A ceramic substrate formed of the above-mentioned composition, and 2 metal plates made of 4N aluminum having a thickness of 0.6 mm. Then, Cu was secured to both surfaces of the ceramic substrate by vacuum deposition, and metal plates were laminated on both surfaces of the ceramic substrate, respectively, to form a laminated body. A pressure of 1 to 5kgf/cm in the laminating direction2The laminate was placed in a vacuum furnace (degree of vacuum 10) under pressure-3Pa～10-5Pa) to manufacture a substrate for a power module comprising a ceramic substrate, a circuit layer and a metal layer.
Similarly, 40mm square of Al with a thickness of 0.635mm was prepared2O3A ceramic substrate formed of the above-mentioned composition, and 2 metal plates made of 4N aluminum having a thickness of 0.6 mm. Then, Cu was secured to one surface of each metal plate by vacuum deposition, and the metal plates were laminated on both surfaces of the ceramic substrate so that the deposition surfaces of the metal plates faced the ceramic substrate, thereby forming a laminate. A pressure of 1 to 5kgf/cm in the laminating direction2The laminate was placed in a vacuum furnace (degree of vacuum 10) under pressure-3Pa～10-5Pa) to manufacture a substrate for a power module comprising a ceramic substrate, a circuit layer and a metal layer.
As described above, in example 4, 2 kinds of substrates for power modules were used.
Here, the fastening amount (Cu thickness) of Cu by vacuum deposition was varied to 5 parameters (5 levels) of 0.1. mu.m, 0.5. mu.m, 1.0. mu.m, 2.0. mu.m, and 3.0. mu.m. The heating temperature was varied to 3 parameters (3 levels) of 610 ℃, 630 ℃ and 650 ℃. Thereby, a total of 30 kinds of power module substrates were formed.
On the metal layer of the power module substrate thus formed, an aluminum plate (a6063) having a thickness of 50mm × 60mm and 5mm corresponding to the top plate of the heat sink was bonded via a buffer layer made of 4N aluminum and having a thickness of 0.9 mm.
Thus, a total of 30 test pieces were prepared.
Next, before the thermal cycle test was performed on the total of 30 kinds of test pieces, the bonding area ratio (bonding ratio) at the bonding interface between the ceramic substrate and the metal plate was determined. As a method for calculating the bonding ratio, a method for calculating the bonding ratio using an ultrasonic imaging device (probe frequency 15MHz) was employed as described in example 1 above. Before the thermal cycle test, the bonding ratio between the ceramic substrate and the metal plate was 100%.
Then, the total of 30 kinds of test pieces were subjected to 3000 thermal cycles at-40 ℃ to 105 ℃ to apply a load, and the presence or absence of cracking of the ceramic substrate was confirmed.
In this test, 2 specimens of 30 kinds of test pieces were prepared, and the presence or absence of cracking of the ceramic substrate was confirmed.
Fig. 24(a) shows the evaluation results of the power module substrate obtained by depositing Cu on the ceramic substrate.
Fig. 24(b) shows the evaluation results of the power module substrate obtained by depositing Cu on the metal plate.
Note that, the power module substrate in which the ceramic substrate was not broken in both of the 2 test pieces is indicated by symbol "o", the power module substrate in which the ceramic substrate was broken in one of the 2 test pieces is indicated by symbol "Δ", and the power module substrate in which the ceramic substrate was broken in both of the 2 test pieces is indicated by symbol "x".
After 3000 times of the thermal cycle, the bonding ratio was determined for a total of 30 types of test pieces.
Specifically, the bonding ratio of the ceramic substrate and the metal plate, that is, the bonding ratio after 3000 thermal cycles was obtained by the same method as described above using the ultrasonic imaging apparatus. Thus, the evaluation results of the power module substrate were obtained.
Fig. 25(a) shows the evaluation results of the power module substrate obtained by depositing Cu on the ceramic substrate.
Fig. 25(b) shows the evaluation results of the power module substrate obtained by depositing Cu on the metal plate.
In fig. 25(a) and (b), a power module substrate having a bonding ratio of 85% or more after 3000 heat cycles as a load is indicated by symbol "o", a power module substrate having a bonding ratio of 70% or more and less than 85% after 3000 heat cycles as a load is indicated by symbol "Δ", and a power module substrate having a bonding ratio of less than 70% after 3000 heat cycles as a load is indicated by symbol "x".
As shown in FIGS. 24(a) and (b), the thicker the Cu thickness formed in the Cu bonding step, the greater the thickness of Al2O3The tendency that cracking of the constituted ceramic substrate was more likely to occur was confirmed.
In addition, in the test piece having a Cu thickness of 2 μm, it was confirmed that cracking of the ceramic tends to be suppressed as the heating temperature is higher.
As shown in fig. 25(a) and (b), the higher the heating temperature, the higher the bonding reliability tends to be.
Further, it was confirmed that when the Cu thickness is about 1 μm, the bonding reliability is improved even when the heating temperature is low.
From these test results, it was confirmed that Al is contained in2O3In the ceramic substrate having the above structure, the thickness of Cu present at the interface between the metal plate and the ceramic substrate at the time of bonding is preferably set to 2.5 μm or less.
(example 5)
In examples 5 and 6 described below, the results of the confirmation test performed to confirm the effectiveness of the power module substrates according to embodiments 5 and 6 are described with reference to fig. 34 and table 1.
As shown in fig. 34, in comparative example and example 5, confirmation tests were performed using, as a common substrate for a power module, a substrate for a power module having: a ceramic substrate 211 of AlN with a thickness of 0.635mm, a circuit layer 212 of 4N aluminum with a thickness of 0.6mm, a metal layer 213 of 4N aluminum with a thickness of 0.6mm, a top plate 5 of aluminum alloy (a6063) with a thickness of 5mm, and a buffer layer 15 of 4N aluminum with a thickness of 1.0 mm.
In example 5, Cu was fixed to the surface of the ceramic substrate 211 by sputtering, and then metal plates as the circuit layer 212 and the metal layer 213 were bonded to the ceramic substrate 211 using an Al — Si-based brazing material.
On the other hand, in the comparative example, the metal plates as the circuit layer 212 and the metal layer 213 were joined to the ceramic substrate 211 using an Al — Si based brazing material without adding Cu to the joining interface between the ceramic substrate 211 and the metal plates.
Thus, the test piece of example 5 and the test piece of comparative example were prepared.
Next, before the thermal cycle test was performed on these test pieces, the bonding area ratio (bonding ratio) at the bonding interface between the ceramic substrate and the metal plate was determined. As a method for calculating the bonding ratio, a method for calculating the bonding ratio using an ultrasonic imaging device (probe frequency 15MHz) was employed as described in example 1 above. Before the thermal cycle test, the bonding ratio of the ceramic substrate to the metal plate in the test piece of example 5 was 100%, and the bonding ratio of the ceramic substrate to the metal plate in the test piece of the comparative example was 99.8%.
Then, the bonding reliability was evaluated by using these test pieces.
The evaluation of the bonding reliability was made by comparing the comparative example with example 5, concerning the bonding ratio after repeating the heat cycle (-45 ℃ C. to 125 ℃ C.).
Specifically, the bonding ratio between the ceramic substrate and the metal plate in comparative example and example 5 was determined by the same method as described above using the ultrasonic imaging apparatus. Further, the respective bonding ratios after 1000, 2000, and 3000 thermal cycles were obtained. Thus, the evaluation results of the power module substrate were obtained. The evaluation results are shown in Table 1.
[ Table 1]
In the comparative example in which the joining was performed using the Al — Si based brazing material without adding Cu to the joining interface, the joining ratio was close to 100% (99.8%) when the heat cycle was performed 1000 times. However, the bonding ratio was reduced (94.2%) when the thermal cycle was carried out 2000 times, and reduced to 91.5% when the thermal cycle was carried out 3000 times.
On the other hand, in example 5 in which Cu was added to the bonding interface, the bonding ratio was not decreased even when the thermal cycle was performed 2000 times. The bonding ratio was 99.2% when the heat cycle was 3000 times.
This confirmation test confirmed that the addition of Cu to the bonding interface improved the thermal cycle reliability.
(example 6)
Next, the results of the composition analysis of the metal layer in the power module substrates according to embodiments 5 and 6 are shown.
A circuit layer 212 made of 4N aluminum having a thickness of 0.6mm and a metal layer 213 made of 4N aluminum having a thickness of 0.6mm were joined to a ceramic substrate 211 made of AlN having a thickness of 0.635mm to fabricate a substrate for a power module.
In examples 6A to 6C, a Cu layer having a thickness of 1.5 μm was formed on the surface of an Al-7.5 wt% Si filler metal, and the circuit layer 212 and the metal layer 213 were bonded to the ceramic substrate 211 using the Al-7.5 wt% Si filler metal.
The bonding temperature was varied to 3 parameters (3 levels) of 610 ℃, 630 ℃ and 650 ℃.
In examples 6D to 6F, a Cu layer having a thickness of 1.5 μm was formed on the surface of the ceramic substrate 211, and the circuit layer 212 and the metal layer 213 were bonded to the ceramic substrate 211 using an Al-7.5 wt% Si brazing filler metal.
The bonding temperature was varied to 3 parameters (3 levels) of 610 ℃, 630 ℃ and 650 ℃.
In examples 6A to 6F, the Cu concentration and the Si concentration in the central portion in the width direction of the interface between the metal layer and the ceramic substrate and the end portions in the width direction of the interface were quantitatively analyzed by using EPMA. The results are shown in Table 2.
[ Table 2]
As a result of the quantitative analysis, it was confirmed that, when the ceramic substrate and the metal plate were joined together using the Al-Si based brazing material while forming the Cu layer, the Si concentration and the Cu concentration were set in the range of 0.05 to 0.5 wt% and 0.05 to 1.0 wt% respectively in the central portion in the width direction in the portion adjacent to the joining interface.
Further, it was confirmed that Si and Cu were present at high concentrations in the end portions in the width direction.
Description of the symbols
1. 51, 101, 151, 201, 251 power module
2 semiconductor chip (electronic component)
10. 60, 110, 160, 210, 260 power module substrate
11. 61, 111, 161, 211, 261 ceramic substrate
12. 62, 112, 162, 212, 262 loop layer
13. 63, 113, 163, 213, 263 metal layer
22. 23, 72, 73, 122, 123, 172, 173, 222, 223, 272, 273 sheet metal
24. 25Cu layer
26. 27 molten metal layer
30. 80, 130, 180, 230, 280 engagement interface
33. 233 concentration gradient layer (concentration gradient part)
34 soft layer
41. 241 phase of aluminum
42. 243 eutectic phase
74. 75, 174, 175 copper foil (Cu layer)
76. 77, 126, 127, 176, 177, 226, 227 molten aluminium layer
82. 132, 182Cu high concentration portion
124. 125Cu fastening layer (Cu layer)
224. 225 brazing filler metal foil (brazing filler metal)
232Si high concentration part
282 oxygen high concentration portion
Claims (37)
1. The substrate for power module is characterized by comprising
A ceramic substrate having a surface, and
a metal plate bonded to the surface of the ceramic substrate, made of aluminum, and containing Cu at a bonding interface with the ceramic substrate;
the Cu concentration in the bonding interface is set to be in the range of 0.05 to 5 wt%.
2. The substrate for power module as set forth in claim 1,
an aluminum phase containing Cu in aluminum and a eutectic phase composed of a 2-membered eutectic structure of Al and Cu are formed at the end of the metal plate in the width direction.
3. The substrate for power module as set forth in claim 2,
in the eutectic phase, precipitated particles composed of a Cu-containing compound are precipitated.
4. The substrate for power module as set forth in claim 1,
the metal plate contains
A concentration gradient portion in which the Cu concentration gradually decreases with distance from the bonding interface in a direction in which the metal plate and the ceramic substrate are laminated, and
a soft layer formed on the opposite side of the concentration inclined portion from the ceramic substrate and having a lower hardness than the vicinity of the bonding interface.
5. A power module is characterized by comprising:
the substrate for power module according to claim 1, and
and an electronic component mounted on the power module substrate.
6. A method for manufacturing a substrate for a power module,
preparing a ceramic substrate, a metal plate made of aluminum, and a Cu layer having a thickness of 0.15 to 3 μm,
the ceramic substrate and the metal plate are laminated via the Cu layer,
heating the laminated ceramic substrate, the Cu layer and the metal plate while pressing them in the laminating direction,
forming a molten metal layer on an interface between the ceramic substrate and the metal plate,
solidifying the molten metal layer by cooling the molten metal layer,
the metal plate contains Cu in the vicinity of the bonding interface between the ceramic substrate and the metal plate so that the Cu concentration is in the range of 0.05 to 5 wt%.
7. The method for manufacturing a substrate for a power module according to claim 6,
before the ceramic substrate, the Cu layer and the metal plate are laminated, the Cu layer is fastened to at least one of the ceramic substrate and the metal plate.
8. The method for manufacturing a substrate for a power module according to claim 7,
in the step of fastening the Cu to at least one of the ceramic substrate and the metal plate, the Cu is fastened to at least one of the ceramic substrate and the metal plate by any one method selected from a vapor deposition method, a sputtering method, a plating method, and a coating method of a Cu paste.
9. The method for manufacturing a substrate for a power module according to claim 6,
when the ceramic substrate and the metal plate are laminated via the Cu layer, the Cu layer is disposed by interposing a copper foil between the ceramic substrate and the metal plate.
10. The substrate for power module is characterized by comprising
From AlN or Si3N4A ceramic substrate having a surface,
a metal plate made of pure aluminum bonded to the surface of the ceramic substrate, and
and a Cu high concentration portion formed at a bonding interface between the metal plate and the ceramic substrate and having a Cu concentration 2 times or more higher than that of the metal plate.
11. The substrate for power module as set forth in claim 10,
the oxygen concentration in the Cu high concentration portion is higher than the oxygen concentration in the metal plate and the ceramic substrate.
12. The substrate for power module as set forth in claim 10,
the ceramic substrate is composed of AlN,
when the bonding interface containing the Cu high concentration portion is analyzed by energy dispersive X-ray analysis, the mass ratio of Al, Cu, O and N is 50-90 wt%, 1-10 wt%, 2-20 wt% and less than 25 wt%.
13. The substrate for power module as set forth in claim 10,
the ceramic substrate is made of Si3N4The structure of the utility model is that the material,
when the bonding interface containing the Cu high concentration portion is analyzed by energy dispersive X-ray analysis, the mass ratio of Al, Si, Cu, O and N is 15-45 wt%, 1-10 wt%, 2-20 wt% and 25 wt% or less.
14. A power module is characterized by comprising
The substrate for power module as set forth in claim 10, and
and an electronic component mounted on the power module substrate.
15. A method for manufacturing a substrate for a power module,
a ceramic substrate made of AlN, a metal plate made of pure aluminum, and a Cu layer having a thickness of 0.15 to 3 μm are prepared,
the ceramic substrate and the metal plate are laminated via the Cu layer,
heating the laminated ceramic substrate, the Cu layer and the metal plate while pressing them in the laminating direction,
forming a molten aluminum layer on an interface between the ceramic substrate and the metal plate,
solidifying the molten aluminum layer by cooling the molten aluminum layer,
a Cu high concentration portion having a Cu concentration 2 times or more the Cu concentration in the metal plate is formed at a bonding interface between the ceramic substrate and the metal plate.
16. The method for manufacturing a substrate for a power module according to claim 15,
when the ceramic substrate and the metal plate are laminated via the Cu layer, the Cu layer is disposed by interposing a copper foil between the ceramic substrate and the metal plate.
17. The method for manufacturing a substrate for a power module according to claim 15,
before the ceramic substrate, the Cu layer and the metal plate are laminated, the Cu layer is fastened to at least one of the ceramic substrate and the metal plate.
18. The method for manufacturing a substrate for a power module according to claim 17,
in the step of fastening the Cu to at least one of the ceramic substrate and the metal plate, the Cu is fastened to at least one of the ceramic substrate and the metal plate by any one method selected from a vapor deposition method, a sputtering method, a plating method, and a coating method of a Cu paste.
19. A method for manufacturing a substrate for a power module,
prepared from Si3N4A ceramic substrate, a metal plate made of pure aluminum, and a Cu layer having a thickness of 0.15 to 3 μm,
the ceramic substrate and the metal plate are laminated via the Cu layer,
heating the laminated ceramic substrate, the Cu layer and the metal plate while pressing them in the laminating direction,
forming a molten aluminum layer on an interface between the ceramic substrate and the metal plate,
solidifying the molten aluminum layer by cooling the molten aluminum layer,
a Cu high concentration portion having a Cu concentration 2 times or more the Cu concentration in the metal plate is formed at a bonding interface between the ceramic substrate and the metal plate.
20. The method for manufacturing a substrate for a power module according to claim 19,
when the ceramic substrate and the metal plate are laminated via the Cu layer, the Cu layer is disposed by interposing a copper foil between the ceramic substrate and the metal plate.
21. The method for manufacturing a substrate for a power module according to claim 19,
before the ceramic substrate, the Cu layer and the metal plate are laminated, the Cu layer is fastened to at least one of the ceramic substrate and the metal plate.
22. The method for manufacturing a substrate for a power module according to claim 21,
in the step of fastening the Cu to at least one of the ceramic substrate and the metal plate, the Cu is fastened to at least one of the ceramic substrate and the metal plate by any one method selected from a vapor deposition method, a sputtering method, a plating method, and a coating method of a Cu paste.
23. The substrate for power module is characterized by comprising
From Al2O3A ceramic substrate having a surface,
a metal plate made of pure aluminum bonded to the surface of the ceramic substrate, and
and a Cu high concentration portion formed at a bonding interface between the metal plate and the ceramic substrate and having a Cu concentration 2 times or more higher than that of the metal plate.
24. The substrate for power module as set forth in claim 23,
when the bonding interface containing the Cu high concentration portion is analyzed by energy dispersive X-ray analysis, the mass ratio of Al, Cu and O is 50-90 wt%, 1-10 wt% and 0-45 wt%.
25. A power module is characterized by comprising
A substrate for a power module as set forth in claim 23, and
and an electronic component mounted on the power module substrate.
26. A method for manufacturing a substrate for a power module,
prepared from Al2O3A ceramic substrate, a metal plate made of pure aluminum, and a Cu layer having a thickness of 0.15 to 3 μm,
the ceramic substrate and the metal plate are laminated via the Cu layer,
heating the laminated ceramic substrate, the Cu layer and the metal plate while pressing them in the laminating direction,
forming a molten aluminum layer on an interface between the ceramic substrate and the metal plate,
solidifying the molten aluminum layer by cooling the molten aluminum layer,
a Cu high concentration portion having a Cu concentration 2 times or more the Cu concentration in the metal plate is formed at a bonding interface between the ceramic substrate and the metal plate.
27. The method for manufacturing a substrate for a power module according to claim 26,
when the ceramic substrate and the metal plate are laminated via the Cu layer, the Cu layer is disposed by interposing a copper foil between the ceramic substrate and the metal plate.
28. The method for manufacturing a substrate for a power module according to claim 26,
before the ceramic substrate, the Cu layer and the metal plate are laminated, the Cu layer is fastened to at least one of the ceramic substrate and the metal plate.
29. The method for manufacturing a substrate for a power module according to claim 28,
in the step of fastening the Cu to at least one of the ceramic substrate and the metal plate, the Cu is fastened to at least one of the ceramic substrate and the metal plate by any one method selected from a vapor deposition method, a sputtering method, a plating method, and a coating method of a Cu paste.
30. The substrate for power module is characterized by comprising
A ceramic substrate having a surface, the ceramic substrate having a surface,
a metal plate made of aluminum bonded to the surface of the ceramic substrate via a brazing material containing Si,
cu added to a bonding interface between the ceramic substrate and the metal plate;
the metal plate contains Si and Cu, the Si concentration in the portion of the metal plate adjacent to the bonding interface is set to be in the range of 0.05 to 0.5 wt%, and the Cu concentration is set to be in the range of 0.05 to 1.0 wt%.
31. The substrate for a power module as set forth in claim 30,
the width of the ceramic substrate is wider than that of the metal plate,
an aluminum phase containing Si and Cu in aluminum, an Si phase having a Si content of 98 wt% or more, and a eutectic phase composed of a 3-membered eutectic structure of Al, Cu and Si are formed in the end portion of the metal plate in the width direction.
32. The substrate for power module as set forth in claim 31,
in the eutectic phase, precipitated particles composed of a Cu-containing compound are precipitated.
33. The substrate for a power module as set forth in claim 30,
a Si high concentration portion which is formed at a bonding interface between the metal plate and the ceramic substrate and has an Si concentration 5 times or more higher than that of the metal plate;
the ceramic substrate is made of AlN or Al2O3And (4) forming.
34. The substrate for a power module as set forth in claim 30,
an oxygen high concentration portion having an oxygen concentration higher than oxygen concentrations in the metal plate and the ceramic substrate and having a thickness of 4nm or less, the oxygen high concentration portion being formed at a bonding interface between the metal plate and the ceramic substrate;
the ceramic substrate is made of AlN or Si3N4And (4) forming.
35. A power module is characterized by comprising
A substrate for a power module as set forth in claim 30, and
and an electronic component mounted on the power module substrate.
36. A method for manufacturing a substrate for a power module,
preparing a ceramic substrate having a bonding surface, a metal plate made of aluminum, and a brazing material containing Si,
the brazing material is filled between the ceramic substrate and the metal plate and laminated,
heating the laminated ceramic substrate, brazing material and metal plate in a state of being pressed,
melting the brazing material to form a molten aluminum layer at the interface between the ceramic substrate and the metal plate,
the molten aluminum layer is solidified, and the molten aluminum layer is solidified,
before the brazing material is interposed between the ceramic substrate and the metal plate and laminated, Cu is bonded to at least one of the bonding surface of the ceramic substrate and a surface of the brazing material facing the ceramic substrate.
37. The method for manufacturing a substrate for a power module as set forth in claim 36,
when the Cu is fastened,
cu is bonded to at least one of the bonding surface of the ceramic substrate and the surface of the brazing material facing the ceramic substrate by vapor deposition or sputtering.
Applications Claiming Priority (5)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2008-149902 | 2008-06-06 | ||
| JP2009-065033 | 2009-03-17 | ||
| JP2009-075315 | 2009-03-26 | ||
| JP2009-086248 | 2009-03-31 | ||
| JP2009-086247 | 2009-03-31 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| HK1153850A true HK1153850A (en) | 2012-04-05 |
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