JP2015185707A - Method of manufacturing substrate for power module with heat sink - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a substrate for power module with heat sink, capable of preventing a ceramics substrate and a metal layer from peeling, without using a contact prevention material, when bonding the substrate for power module and heat sink by using flux.SOLUTION: In a heat treatment step, impurities existing on the whole aluminum plate while being distributed, e.g., Ce, La and P, are precipitated near the surface layer of the aluminum plate. Subsequently, in an impurity removal step, the impurities containing Ce, La and P precipitated near the surface layer of the aluminum plate are removed from the vicinity of the aluminum plate surface. When applying this aluminum plate to the metal layer 23 and bonding to a ceramic substrate 21, aggregation of Ce and La on the junction interface is suppressed, and peeling can be suppressed at the time of flux intrusion. A substrate 10 for power module with heat sink, where the ceramic substrate 21 and metal layer 23 are bonded rigidly, can thereby be manufactured.

Description

  The present invention uses a power module substrate having a ceramic substrate, a circuit layer formed on one surface of the ceramic substrate, and a metal layer formed on the other surface of the ceramic substrate, and the metal layer and flux. The present invention relates to a method for manufacturing a power module substrate with a heat sink, comprising a heat sink made of aluminum or an aluminum alloy joined together.

  Among various semiconductor elements, for example, a power element for high power control used for controlling an electric vehicle or an electric vehicle has a high current value, and therefore generates a large amount of heat. A power module substrate on which such a power element for high power control is mounted needs to be appropriately cooled in order to prevent malfunction due to heat generation. For this reason, a power module substrate with a heat sink provided with a heat sink for heat dissipation and cooling is used on the power module substrate.

  As a power module substrate with a heat sink, for example, as described in Patent Document 1, an aluminum plate (circuit layer and metal layer) is provided on one surface of a ceramic substrate made of AlN (aluminum nitride) and the other surface. There has been proposed a structure in which a bonded power module substrate and a heat sink made of Al are bonded by brazing.

  For example, in the semiconductor module cooling apparatus disclosed in Patent Document 2, metal plates (upper electrode and lower electrode) made of Al are joined to both surfaces of an insulating substrate made of a ceramic material, and a semiconductor element is joined to the upper electrode. There has been proposed a semiconductor module which is joined to a top plate of a cooler made of aluminum by brazing using a flux.

Here, as the brazing using the flux, there is nocollock brazing using the flux mainly composed of KAlF ₄ . This Nocolok brazing is a technique mainly for joining aluminum plates. For example, an Al—Si brazing foil and a flux mainly composed of KAlF ₄ are disposed between aluminum plates, and this flux is used. Thus, the oxide film formed on the surface of the aluminum plate is removed, and the melting of the brazing material is promoted for bonding.

JP 2007-194256 A JP 2009-105166 A

However, when the power module substrate and the heat sink are joined by Noclock brazing, KAlF ₄ which is a flux component enters the joining surface between the ceramic substrate and the aluminum plate of the power module substrate, and the ceramic substrate and the aluminum plate There was a concern of reducing the bonding reliability between the two.

  The present invention has been made in view of the circumstances described above, and is capable of preventing the ceramic substrate and the metal layer from being peeled off when the power module substrate and the heat sink are bonded using a flux. It aims at providing the manufacturing method of the board | substrate for power modules with an attachment.

  In order to solve the above-mentioned problems, the present inventors have made extensive studies and as a result, obtained the following knowledge. In the power module substrate, when the metal layer to which the heat sink is bonded contains impurities such as Ce and La, when the ceramic substrate and the metal plate are bonded, these Ce and La are bonded to the ceramic substrate and the metal layer. Aggregate. Then, when Ce and La are aggregated at the bonding interface between the ceramic substrate and the metal layer and the heat sink is bonded by brazing using a flux, the flux enters the bonding interface between the ceramic substrate and the metal layer, and peeling occurs. It becomes easy.

  The present invention has been made based on the above knowledge, the manufacturing method of a power module substrate with a heat sink of the present invention is a ceramic substrate, a circuit layer formed on one surface of the ceramic substrate, A power module substrate having a metal layer formed on the other surface of the ceramic substrate, and a heat module substrate with a heat sink comprising a heat sink made of aluminum or an aluminum alloy bonded to the metal layer. A heat treatment step in which an aluminum plate made of aluminum or an aluminum alloy is heat-treated in a non-oxidizing atmosphere in a temperature range of 630 ° C. or more and 660 ° C. or less, and impurities are deposited on the surface; Removing impurities and removing the aluminum plate from the ceramic And the aluminum plate bonding step of forming a metal layer bonded to the other surface of the substrate, and the said metal layer heat sink, characterized by comprising a heat sink bonding step of bonding using a flux, in this order.

According to the method for manufacturing a power module substrate with a heat sink of the present invention, impurities contained in an aluminum plate for forming a metal layer are deposited in the vicinity of the surface by a heat treatment process, and further, the impurities are removed by an impurity removal process. . By joining the pre-treated aluminum plate to the ceramic substrate to form a metal layer, impurities are agglomerated at the bonding interface between the metal layer and the ceramic substrate even if the metal layer and the heat sink are bonded using a flux. Therefore, it is possible to manufacture a power module substrate with a heat sink that suppresses peeling between the metal layer and the ceramic substrate when the flux enters.
Here, when the temperature of the heat treatment is less than 630 ° C., impurities contained in the aluminum plate cannot be deposited on the surface. Moreover, when the temperature of heat processing exceeds 660 degreeC, there exists a possibility that an aluminum plate may fuse | melt. Therefore, the heat treatment temperature is set in the range of 630 ° C. or more and 660 ° C. or less.

According to the present invention, the impurity removal step is preferably a step of removing the impurities by etching.
By etching the aluminum surface layer, impurities deposited in the heat treatment step can be reliably removed without remaining in the vicinity of the surface of the aluminum plate.

According to the present invention, the aluminum plate preferably has an Al purity of 99.99% by mass or more.
By using Al with a purity of 99.99% by mass or more as the aluminum plate, the thermal strain due to the difference in thermal expansion coefficient between the heat sink and the ceramic substrate can be sufficiently absorbed by the metal layer, and the ceramic substrate can be damaged. Can be suppressed.

According to the present invention, it is preferable that the circuit layer is formed using the aluminum plate from which the impurities are removed.
Thus, by forming the circuit layer using the aluminum plate from which the impurities have been removed, the aggregation of impurities at the bonding interface between the circuit layer and the ceramic substrate is suppressed, and peeling at the time of flux entry can be suppressed. Therefore, it is possible to firmly bond the circuit layer and the ceramic substrate.

According to the present invention, the heating time in the heat treatment step is preferably 12 minutes or more and 180 minutes or less.
By setting the heating time in the heat treatment step to 12 minutes or more, impurities existing inside the aluminum plate can be sufficiently precipitated in the vicinity of the surface. Moreover, the deformation of the aluminum plate due to excessive heating can be prevented by setting the heating time to 180 minutes or less.

According to the present invention, it is preferable that the impurities to be removed in the impurity removal step include at least Ce and La.
When Ce and La are contained in the aluminum plate, when the flux enters between the ceramic substrate and the metal layer, it may cause the ceramic substrate and the metal layer to peel off. By including at least Ce and La as impurities to be removed from the aluminum plate, Ce and La may aggregate at the bonding interface between the aluminum plate (metal layer) and the ceramic substrate when the aluminum plate and the ceramic substrate are bonded. A power module substrate with a heat sink that suppresses separation between the metal layer and the ceramic substrate even if the flux enters the bonding interface between the metal layer and the ceramic substrate when the metal layer and the heat sink are bonded using a flux. It becomes possible to manufacture.

According to the present invention, it is preferable that the impurities removed in the impurity removal step further include P.
P contained in the aluminum plate can also cause the ceramic substrate and the metal layer to peel off when flux enters between the ceramic substrate and the metal layer. Therefore, it is possible to bond the ceramic substrate and the metal layer more firmly by removing P, which is likely to peel off the bond between the ceramic substrate and the metal layer by the flux component, like Ce and La. .

  ADVANTAGE OF THE INVENTION According to this invention, when joining the power module board | substrate and a heat sink using a flux, the manufacturing method of the power module board | substrate with a heat sink which can prevent peeling with a ceramic substrate and a metal layer is provided. be able to.

It is sectional drawing which shows the board | substrate for power modules with a heat sink. It is sectional drawing which showed the manufacturing method of the board | substrate for power modules with a heat sink of this invention in steps. It is sectional drawing which showed the manufacturing method of the board | substrate for power modules with a heat sink of this invention in steps. It is sectional drawing which showed the manufacturing method of the board | substrate for power modules with a heat sink of this invention in steps.

  Hereinafter, with reference to drawings, the manufacturing method of the board for power modules with a heat sink of the present invention is explained. Each embodiment described below is specifically described for better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified. In addition, in the drawings used in the following description, in order to make the features of the present invention easier to understand, there is a case where a main part is shown in an enlarged manner for convenience, and the dimensional ratio of each component is the same as the actual one. Not necessarily.

(Power module substrate with heat sink)
First, a configuration of a power module substrate with a heat sink obtained by the method for manufacturing a power module substrate with a heat sink of the present invention will be described with reference to FIG.
FIG. 1 is a cross-sectional view showing a power module substrate with a heat sink.
The power module substrate 10 with a heat sink includes a power module substrate 11 and a heat sink 12 bonded to the power module substrate 11.

  The power module substrate 11 includes a ceramic substrate 21, a circuit layer 22 bonded to one surface (21a side) of the ceramic substrate 21, and a metal layer 23 bonded to the other surface (21b side). Has been.

  The ceramic substrate 21, the circuit layer 22, and the metal layer 23 are joined by a brazing material. As this brazing material, for example, an Al-Si brazing material is joined. The Al—Si brazing material has a melting point of about 550 ° C. to 620 ° C.

As the ceramic substrate 21, a substrate made of ceramics having high insulation and heat resistance is preferably used. Examples of the ceramic constituting the ceramic substrate 21 include AlN (aluminum nitride), Al ₂ O ₃ (aluminum oxide), Si ₃ N ₄ (silicon nitride), Zr—Al ₂ O ₃ (zirconium-aluminum oxide), and the like. It is done. In this embodiment, AlN is used as the ceramic substrate 21. The thickness of such a ceramic board should just be about 0.1-1.0 mm, for example. As an example, in this embodiment, it is set to 0.635 mm.

  The circuit layer 22 is formed by joining a circuit layer aluminum plate 52 made of aluminum or an aluminum alloy. The metal layer 23 is formed by joining a metal layer aluminum plate 53 made of aluminum or an aluminum alloy. In the present embodiment, these aluminum plates are made of a high purity aluminum material, for example, a rolled plate of aluminum (so-called 4N aluminum) having a purity of 99.99% by mass or more.

A semiconductor element is bonded to one surface (the upper surface in FIG. 1) of the circuit layer 22 via a solder layer. The sheet sink 12 is joined to one surface (the lower surface in FIG. 1) of the metal layer 23 by brazing using a flux.
The metal layer 23 is used as a buffer layer, for example. The buffer layer can absorb the thermal stress generated in the ceramic substrate 21 when the cooling module is loaded on the power module substrate 10 with a heat sink by the buffer layer (metal layer 23), and the ceramic substrate 21 is cracked. Can be suppressed.

  Of the circuit layer 22 and the metal layer 23, the metal layer aluminum plate 53 for forming at least the metal layer 23 to be joined to the heat sink 12 is at least Ce (cerium) and La which are trace elements contained in Al. A material from which impurities including (lanthanum) are removed is used. Such removal of impurities from the aluminum plate will be described in detail in the manufacturing method.

  Such impurities such as Ce and La may cause the circuit layer 22, the metal layer 23, and the ceramic substrate 21 to be peeled off when the power module substrate 11 and the heat sink 12 are bonded using a flux. Therefore, the Ce or La having a very low concentration is used, and the peeling of the joint portion between the circuit layer 22 and the metal layer 23 and the ceramic substrate 21 is suppressed.

  For the circuit layer 22, it is preferable to use an aluminum plate for circuit layer from which impurities including Ce (cerium) and La (lanthanum) are removed in order to form the circuit layer 22.

  The metal layer aluminum plate 53 and the circuit layer aluminum plate used to form the metal layer 23 and the circuit layer 22 are preferably used after further removing P (phosphorus) which is a trace element contained in Al. . Such impurities such as P can also cause the circuit layer 22, the metal layer 23, and the ceramic substrate 21 to be peeled off when the power module substrate 11 and the heat sink 12 are bonded using a flux. Therefore, the P having an extremely low concentration is used to suppress the peeling of the joint portion between the circuit layer 22 and the metal layer 23 and the ceramic substrate 21.

The heat sink 12 includes, for example, a top plate portion 31 and a plurality of fins 32, 32... Formed on the top plate portion 31. The fins 32, 32... Are plate-like members arranged at a predetermined interval from each other. The heat sink 12 is a so-called air-cooled heat sink that dissipates heat propagated from the power module substrate 11 joined to the heat sink 12 when air as a refrigerant flows between the fins 32, 32. 12.
The heat sink 12 may be, for example, a so-called water-cooled heat sink 12 in which a plurality of channels for circulating cooling water, for example, are integrally formed on the top plate portion 31.

  The top plate portion 31 and the fins 32, 32... Constituting the heat sink 12 are made of, for example, aluminum or an aluminum alloy. Specifically, A3003, A1050, 4N-Al, A6063, etc. are mentioned. In this embodiment, a rolled plate of A1050 was used.

  In addition, even if the top plate portion 31 and the fins 32, 32... Are formed as an integral member, the plurality of fins 32, 32. There may be. When the top plate portion 31 and the plurality of fins 32, 32... Are configured as separate members, the top plate portion 31 and the plurality of fins 32, 32.

Such a heat sink 12 is a Nocolok brazing that uses an Al—Si brazing material and a flux containing F (fluorine), for example, a flux mainly composed of KAlF ₄ for the metal layer 23 of the power module substrate 11. It is joined by attaching.

(Method for manufacturing power module substrate with heat sink)
A method for manufacturing a power module substrate with a heat sink according to the present invention will be described with reference to FIG. 2, FIG. 3, and FIG.
2, 3 and 4 are cross-sectional views showing a method for manufacturing a power module substrate with a heat sink according to the present invention step by step.

  Prepared are a circuit layer 22 to be bonded to one surface 21a and the other surface 21b of the ceramic substrate 21, an aluminum plate 52 for circuit layer for forming the metal layer 23, and an aluminum plate 53 for metal layer (both aluminum plates 51). To do. First, both the aluminum plates 51 are heat-treated (heat treatment process). Both aluminum plates 51 can use an aluminum material with a purity of 99% or more, an aluminum material with a purity of 99.9% or more, and an aluminum material with a purity of 99.99% or more. The thickness is set to 0.2 mm to 2.5 mm. In this embodiment, aluminum (so-called 4N aluminum) having a purity of 99.99 mass% or more is used, the circuit layer aluminum 52 is 0.5 mm thick, and the metal layer aluminum 53 is 1.5 mm thick. Is used.

  As shown in FIG. 2A, in the heat treatment step, both aluminum plates 51 are heated to 630 ° C. using a heating furnace 50 in a non-oxidizing atmosphere, for example, an inert gas atmosphere such as vacuum or nitrogen or argon. As mentioned above, it heats in the temperature range below 660 degreeC. In the present embodiment, a vacuum heating furnace is used as the heating furnace 42 and both the aluminum plates 51 are heated.

  The holding time in the heat treatment step can be 12 minutes or more and 180 minutes or less.

  By such a heat treatment process, impurities, such as Ce, La, and P, dispersed in the entire aluminum plates 51, for example, can be deposited in the vicinity of the surface layers of the both aluminum plates 51. That is, the mobility of these Ce, La, and P is increased by heating both aluminum plates 51, and these Ce, La, and P existing inside both aluminum plates 51 move toward the surface layer of both aluminum plates 51, and the surface layer It is thought that it precipitates in the vicinity.

  Next, impurities including Ce, La, and P deposited in the vicinity of the surface layers of both aluminum plates 51 in the heat treatment step are removed from the vicinity of the surfaces of both aluminum plates 51 (impurity removing step). As shown in FIG. 2B, in the impurity removal step, both the aluminum plates 51 that have been subjected to the heat treatment step are immersed in an etching solution 53. As the etching solution 53, an alkali metal hydroxide, which is an aqueous solution of NaOH (sodium hydroxide) in this embodiment, is used. The NaOH concentration of the NaOH aqueous solution may be in the range of 2 to 10% by mass, for example, and is 5% by weight in this embodiment. Further, the temperature of the etching solution 53 may be, for example, in the range of room temperature to 70 ° C., and in this embodiment, the temperature of the etching solution 53 is 50 ° C.

When both the aluminum plates 51 are immersed in the etching solution 53, the etching solution 53 may be either in a stationary state or in a state of being stirred at a predetermined flow rate.
The time (etching time) for immersing both aluminum plates 51 in the etching solution 53 may be in the range of 30 seconds to 5 minutes, for example, and in this embodiment, the etching time is 80 seconds.

  By such an impurity removal step, the range from the surfaces of both aluminum plates 51 to a predetermined depth is removed by the etching solution 53. Thereby, impurities including Ce, La, and P deposited on the surfaces of both aluminum plates 51 in the heat treatment process are also removed by the etching solution 53.

  In this impurity removal step, in addition to removing the surface regions of both aluminum plates 51 uniformly with the etchant 53 such as NaOH as described above, for example, an etchant that can selectively dissolve impurities is used. It is also preferable to selectively dissolve only impurities from the surfaces of both aluminum plates 51.

In the impurity removal step, it is preferable that both the aluminum plates 51 are etched with the etching solution 53 and then washed with pure water 54 and then pickled with the pickling solution 55. As the pickling solution 55, an inorganic acid solution, in this embodiment, HNO ₃ (nitric acid) is used. The concentration of HNO ₃ is, for example, about 30% by mass. Moreover, as a liquid temperature of the pickling liquid 55, it is set as room temperature (20 degreeC), for example.

When both the aluminum plates 51 are immersed in the pickling solution 55, the etching solution 53 may be either in a stationary state or in a state of being stirred at a predetermined flow rate.
The time for pickling both the aluminum plates 51 with the pickling solution 55 may be about 20 seconds, for example.
In the impurity removal step, by performing the above-described pickling after etching both the aluminum plates 51, the residue after etching can be dissolved and removed more reliably than when only washing with water is performed.

After pickling both the aluminum plates 51, both the aluminum plates 51 are washed again with pure water 54 to wash away the pickling solution 55, and the impurity removal step is completed.
Both the aluminum plates 51 after removing the impurities obtained as described above contain impurities such as Ce, La, and P only at a very low concentration. As an example, both the aluminum plates 51 after removing impurities have a total concentration of Ce and La of 2.6 ppm or less and a concentration of P of 4 ppm or less.

  Both aluminum plates 51 from which impurities such as Ce, La, and P obtained by the heat treatment step and the impurity removal step are removed are used to form the circuit layer 22 and the metal layer 23, respectively. As shown in FIG. 3A, a circuit layer aluminum plate 52 is laminated on one surface (21 a side) of the ceramic substrate 21 with a brazing filler metal foil 41 interposed therebetween. A metal layer aluminum plate 53 is laminated on the other surface (21b side) of the ceramic substrate 21 with a brazing filler metal foil 41 interposed therebetween. As the ceramic substrate 21, AlN is used. Further, as the brazing material foil 41, Al-5.0 mass% Si to Al-10 mass% Si brazing material is used. The thickness of the brazing foil 41 is set within a range of 10 μm to 30 μm. In this embodiment, an Al-7 mass% Si brazing foil having a thickness of 15 μm was used as the brazing foil 41.

Next, as shown in FIG. 3B, vacuum heating is performed in a state where the circuit layer aluminum plate 52, the ceramic substrate 21, and the metal layer aluminum plate 53 are pressurized (pressure 1 to 5 kgf / cm ² ) in the stacking direction. It is introduced into the furnace 40 and heated to the melting temperature of the brazing material foil 41. Then, the brazing filler metal foil 41, the circuit layer aluminum plate 52, and a part of the metal layer aluminum plate 53 are melted, and the circuit layer 22 is formed on one surface (21a side) of the ceramic substrate 21 and the ceramic substrate 21. The metal layers 23 are respectively formed on the other surface (21b side) (aluminum plate joining step). In addition, the heating temperature at the time of vacuum heating is 550 degreeC or more and 650 degrees C or less, for example, and heating time is 30 minutes or more and 180 minutes or less. In this embodiment, heating was performed at 630 ° C. for 90 minutes.

  3C, the circuit layer 22 is formed on one surface (21a side) of the ceramic substrate 21, and the metal layer 23 is formed on the other surface (21b side) of the ceramic substrate 21. Thus, the power module substrate 11 bonded with the Al—Si brazing material is obtained.

Next, as shown in FIG. 4A, the heat sink 12 is bonded to the metal layer 23 of the power module substrate 11 (heat sink bonding step).
Specifically, between the metal layer 23 of the power module substrate 11 and the top plate portion 31 of the heat sink 12, an Al—Si based brazing material foil 42 and a fluoride such as KAlF ₄ are used as main components. A flux 43 is interposed. As the Al—Si based brazing material foil 42, Al-10 mass% Si to Al-12 mass% Si brazing material is used. The thickness of the brazing foil 42 is set within a range of 30 μm to 150 μm. In the present embodiment, an Al-10 mass% Si brazing foil having a thickness of 100 μm was used as the brazing foil 42.

  Next, the stacked power module substrate 11 and heat sink 12 are introduced into the heating furnace 44 and heated. In this embodiment, the inside of the heating furnace 44 is a nitrogen gas atmosphere, and the heating temperature is set to 610 to 625 ° C. In this embodiment, the temperature is 625 ° C. for 5 minutes.

  During heating in the heating furnace 44, the natural oxide film of Al formed on the surface of the metal layer 23 and the surface of the top plate portion 31 of the heat sink 12 is removed by the flux 43. Then, the brazing material foil 42 and a part of the metal layer 23 are melted, and the metal layer 23 of the power module substrate 11 and the heat sink 12 are firmly bonded with the natural oxide film removed.

  At the time of joining the power module substrate 11 and the heat sink 12 as described above, the flux component may be liquefied and vaporized and move to the ceramic substrate 21 side. However, the circuit layer 22 and the metal layer 23 are made of an aluminum plate in which impurities such as Ce, La, and P are removed by the heat treatment process and the impurity removal process in the previous process, and Ce, La, and P are extremely low in concentration. The flux component penetrates into the bonding interface between the ceramic substrate 21 and the metal layer 23 and the bonding interface between the ceramic substrate 21 and the circuit layer 22 when the metal layer 23 and the top plate 31 of the heat sink are bonded. Even in this case, it is possible to suppress the ceramic substrate 21 and the circuit layer 22 and the ceramic substrate 21 and the metal layer 23 that are bonded to each other by the Al—Si brazing material in the previous step from being separated.

  Through the above-described steps, as shown in FIG. 4B, the power module substrate 10 with a heat sink having the power module substrate 11 in which the ceramic substrate 21 and the circuit layer 22 and the metal layer 23 are firmly bonded is manufactured. be able to.

As mentioned above, although embodiment of this invention was described, this invention is not limited to this, It can change suitably in the range which does not deviate from the technical idea of the invention.
In this embodiment, the heat treatment step and the impurity removal step are performed on both the circuit layer aluminum plate 52 and the metal layer aluminum plate 53, but the circuit layer aluminum plate 52 is not necessarily subjected to the heat treatment step and impurities. There is no need to apply a removal step. Since the flux penetrates most into the bonding interface between the ceramic substrate and the metal layer, the effect of the present invention can be obtained by performing the above-described treatment only on the metal layer aluminum plate 53.
For example, in addition to chemically dissolving the surfaces of the aluminum plates 51 as described above, the surfaces of both the aluminum plates 51 are physically ground and polished, so that they are deposited on the surfaces of both the aluminum plates 51 in the heat treatment step. Impurities including Ce, La, and P thus made can be removed.
Further, the flux component is not limited to KAlF ₄ , and any flux that is effective for removing the natural oxide film on the aluminum plate can be preferably used.

Hereinafter, the result of the Example which verified the effect of the board | substrate for power modules with a heat sink of this invention is described.
First, samples of Invention Example 1-5 and Comparative Example 1-3 were prepared. First, an aluminum plate for forming the metal layer of the power module substrate was prepared. The aluminum plate was a rolled plate of aluminum having a purity of 99.99% by mass or more (so-called 4N aluminum) with a thickness of 1.5 mm. Using this aluminum plate, a heat treatment step was performed at the temperature shown in Table 1. The heat treatment process was performed in vacuum for 60 minutes.
Next, the impurity removal process was implemented by the etching with respect to the aluminum plate which performed the heat processing process. A 5% NaOH aqueous solution was used as an etching solution, and the solution temperature was 50 ° C. and immersion was performed for the time shown in Table 1 for etching treatment. Thereafter, pickling and water washing described in the above embodiment were performed. In Comparative Example 1, the heat treatment process and the impurity removal process were not performed. In Comparative Example 3, the impurity removal step was not performed.

Next, an aluminum plate for a circuit layer (purity 99.99% or more, thickness 0.5 mm) is laminated on one surface of a ceramic substrate made of AlN via an Al—Si brazing material, and metal is deposited on the other surface. Each aluminum plate of Invention Example 1-5 and Comparative Example 1-3 was laminated as an aluminum plate for layers through an Al—Si brazing material, and joined at 640 ° C. while pressing in the laminating direction, and a power module substrate It was created.
Then, a heat sink was laminated on each of the metal layers of these power module substrates on both surfaces of the Al—Si brazing material and the brazing material foil via a flux containing KAlF ₄ as a main component, and Noclock brazing was performed. As the heat sink, an A1050 aluminum plate was used.

  With respect to the power module substrate with a heat sink of Invention Examples 1-5 and Comparative Example 1-3 obtained in this manner, the peeling rate of the joint surface between the metal layer and the heat sink was evaluated.

The “peeling rate” was evaluated by evaluating the joint between the ceramic substrate and the metal layer using an ultrasonic deep flaw device, and was calculated from the formula: peeling rate = peeling area / joining area × 100.
Here, the peeled area is obtained by measuring the area of the white portion because peeling is indicated by a white portion in the joined portion in an ultrasonic deep wound image obtained by photographing the joint surface. The bonding area was the area of the bonding surface of the metal layer, which is the area to be bonded before bonding.
Those having a peel rate of 3% or more were evaluated as x, those having a peel rate of 2% or more and less than 3% were evaluated as ◯, and those having a peel rate of less than 2% were evaluated as ◎.
The evaluation results are shown in Table 1.

  In Comparative Example 1 in which heat treatment and impurity removal were not performed, in Comparative Example 2 in which the heat treatment temperature was less than 630 ° C., and in Comparative Example 3 in which impurity removal was not performed, the peel rate was 3% or more, which is not preferable as a product. It was in a state.

  A substrate for a power module with a heat sink, in which a metal layer is formed using the aluminum plate of Invention Example 1-5, in which impurities are removed by etching after heat treatment in a temperature range of 630 ° C. or more and 660 ° C. or less, has a peeling rate. It was less than 3%, and it was confirmed that peeling of the metal layer and the heat sink was suppressed. In particular, the power module substrate with a heat sink using the aluminum of Invention Example 1-4 having an etching time of 80 seconds could have a peeling rate of less than 2%.

DESCRIPTION OF SYMBOLS 10 Power module substrate with heat sink 11 Power module substrate 12 Heat sink 21 Ceramic substrate 22 Circuit layer 23 Metal layer 51 Aluminum plate

Claims (7)

A power module substrate having a ceramic substrate, a circuit layer formed on one surface of the ceramic substrate, and a metal layer formed on the other surface of the ceramic substrate, and aluminum bonded to the metal layer or A method of manufacturing a power module substrate with a heat sink comprising a heat sink made of an aluminum alloy,
A heat treatment step in which an aluminum plate made of aluminum or an aluminum alloy is heat-treated in a non-oxidizing atmosphere in a temperature range of 630 ° C. or more and 660 ° C. or less, and impurities are deposited on the surface;
An impurity removing step of removing the impurities from the surface of the aluminum plate;
An aluminum plate joining step of joining the aluminum plate to the other surface of the ceramic substrate and forming a metal layer;
A heat sink joining step for joining the metal layer and the heat sink using a flux;
A method of manufacturing a power module substrate with a heat sink, comprising:   2. The method for manufacturing a power module substrate with a heat sink according to claim 1, wherein the impurity removing step is a step of removing the impurities by etching.   The method for manufacturing a power module substrate with a heat sink according to claim 1 or 2, wherein the aluminum plate has an Al purity of 99.99 mass% or more.   The method for manufacturing a power module substrate with a heat sink according to any one of claims 1 to 3, wherein the circuit layer uses the aluminum plate from which the impurities are removed.   5. The method for manufacturing a power module substrate with a heat sink according to claim 1, wherein a heating time in the heat treatment step is 12 minutes or more and 180 minutes or less.   The method for manufacturing a power module substrate with a heat sink according to any one of claims 1 to 5, wherein the impurities to be removed in the impurity removing step include at least Ce and La.   7. The method for manufacturing a power module substrate with a heat sink according to claim 6, wherein the impurities to be removed in the impurity removing step further include P.

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