JP5247293B2 - Brazing and joining structure of steel and aluminum material and brazing method - Google Patents

Description

  The present invention relates to a brazed joint structure obtained by brazing a steel material and an aluminum material, and a brazing method thereof.

  As a method of joining a steel material and an aluminum material, there are a method of mechanically fastening with a bolt / nut or caulking, a method using an adhesive, and a method using brazing. Among these, the joining method by brazing is particularly effective in applications that place importance on heat conduction between a steel material and an aluminum material, such as a radiator member of an automobile. Conventionally, brazing of a steel material and an aluminum material is performed mainly using a brazing material of an Al—Si alloy (for example, Al: 88 atomic%, Si: 12 atomic%).

  However, the conventional brazing has a problem that a brittle Al—Fe alloy layer (reaction layer) is likely to grow at the interface between the steel material and the molten and solidified layer of the brazing material, and sufficient bonding strength cannot always be obtained. It was. Patent Document 1 describes a technique of suppressing the growth of a fragile reaction layer by lowering the brazing temperature using an Al—Si—high Zn brazing material having a lower melting point.

  On the other hand, since general steel materials are inferior in corrosion resistance as compared with aluminum materials, Al-plated steel plates are used as steel materials, and a method of brazing them with aluminum materials has been attempted. Patent Document 2 discloses that, when brazing a hot-dip Al-plated steel plate and an aluminum alloy, steel added with N is used as an original plate of the Al-plated steel plate. N in steel forms an N-enriched layer between the steel substrate and the Al plating layer, which acts as a barrier and inhibits diffusion of Fe in the steel to the brazing material side during brazing, and as a result Growth of a brittle Al—Fe alloy layer (reaction layer) is suppressed.

Japanese Patent Publication No. 7-29202 Japanese Patent Laid-Open No. 9-220692

  Brazing joining of a steel material and an aluminum material is often used for the purpose of cooling the steel material side by utilizing the high thermal conductivity of the aluminum material. Since aluminum material has a higher coefficient of thermal expansion than steel, stress due to the difference in coefficient of thermal expansion is applied to the brazed joint between the two due to temperature rise and fall when used as a member. . As described above, a brittle alloy layer is formed at a brazed joint between a steel material and an aluminum material, and durability at the brazed joint interface may be a problem. The problem of such an alloy layer can be improved to some extent by the techniques of Patent Documents 1 and 2.

  However, depending on the application, it is assumed that stainless steel is used as a steel material from the viewpoint of corrosion resistance. In the case of stainless steel, particularly when the brazing temperature exceeds about 580 ° C., a brittle Al—Fe—Si based alloy layer tends to develop. For this reason, for example, when brazing at a high temperature as in the prior art using a conventional Al-Si brazing material, the thickness of the brittle Al-Fe-Si alloy layer increases and is high. It is difficult to obtain a stable joint strength.

Further, in the case of stainless steel, there is a problem that even if brazing at a low temperature is attempted using a low melting point brazing material as disclosed in Patent Document 1, joining itself is impossible. This is considered that the passive film peculiar to stainless steel has some influence. Furthermore, it was found that the N-added technique as shown in Patent Document 2 is not effective for stainless steel. That is, even if a technique of applying Al plating to stainless steel having a high N content is employed, it is difficult to suppress the growth of a brittle alloy layer. This is probably because stainless steel contains a large amount of Cr having a high affinity with N, so that it is difficult to form an N-enriched layer serving as a barrier under the molten Al plating layer. Is done.
Therefore, even when stainless steel is used as the steel material, establishment of a brazing technique that can sufficiently ensure the durability at the brazed joint interface between the steel material and the aluminum material is strongly demanded.

On the other hand, recently, an attempt has been made to apply an inexpensive and thin steel plate material as a heat sink for a semiconductor substrate such as a power module.
FIG. 1 schematically shows a configuration example of a general power module. A semiconductor substrate 2 on which a semiconductor element 1 is mounted has a copper or aluminum conductor layer 3 bonded to the surface of an insulating substrate 4 made of ceramics such as alumina or aluminum nitride, and the semiconductor element 1 is mounted thereon. A back conductor layer 5 made of copper or aluminum having good thermal conductivity is bonded to the back surface of the insulating substrate 4 (the surface opposite to the semiconductor element 1). The back conductor layer 5 of the semiconductor substrate 2 is joined to the heat sink 6 by brazing. The heat sink 6 is attached to the heat sink 7, for example.

  Since the ceramic of the insulating substrate 4 has a smaller coefficient of thermal expansion than the metal material of the heat sink 6, the apparent thermal expansion coefficient of the back conductor layer 5 constrained by the insulating substrate 4 is smaller than that of the heat sink 6. Yes. Therefore, the stress at the joint interface 10 is repeatedly applied to the joint interface 10 due to repeated temperature rise and fall when used as an electronic component, and durability at the joint interface 10 becomes a problem. There is. In order to relieve such stress generated at the joint interface 10, it is advantageous to configure the heat sink 6 with a metal material having a thermal expansion coefficient as small as possible. For this reason, for example, a heat sink material having a structure in which a Cu—Mo alloy plate having a small thermal expansion coefficient and relatively good thermal conductivity is sandwiched between two copper plates may be employed. However, this type of heat sink material has the disadvantage of being very expensive.

  As an inexpensive metal material having a low coefficient of thermal expansion, a steel material whose matrix is a ferrite phase can be given. Steel materials are inferior in thermal conductivity compared to copper and aluminum, but according to the study by the inventors, it is considered that thermal conductivity characteristics required for a heat sink can be satisfied by reducing the plate thickness. However, for example, when the back conductor layer 5 is made of an aluminum material, there is a concern that if a steel material is used for the heat radiating plate 6, durability at the joint interface 10 becomes insufficient due to a brittle alloy layer generated at the joint interface 10. When applying a steel material to a heat sink application, it is assumed that stainless steel having good corrosion resistance is adopted. As described above, it is more difficult to improve the durability at the brazed joint interface with the aluminum material when stainless steel is used.

  In view of such a current situation, the present invention provides a stable and durable durability at the joint interface when the temperature rise and fall are repeated even when the steel material is stainless steel in the brazing of the steel material and the aluminum material. This is to provide a technique that can be improved.

The purpose is to join Al-plated steel material and aluminum material by brazing using a brazing material having an Al-Cu-Si alloy composition with an Mg content of 0.3 to 4% by mass and a melting point of less than 550 ° C. a structure, in order from the steel material side, the steel basis material, Al-Fe-Si alloy layer, the more configured Al-containing fabric, Cu concentrated from crystallized Desho or that of Cu-Al alloy in the Al matrix reduction phase, Si concentrated phase, and there is Mg concentrated phase, brazing conditions are met der Ru steel and aluminum material of the Al-Fe-Si-based alloy layer (1) and (2) below Achieved by the joint structure.
(1) The average thickness of the Al—Fe—Si alloy layer is 15 μm or less. (2) The Al—Fe—Si alloy layer is a phase of two types of Al—Fe—Si alloys having different Cu concentrations. Have a mixed configuration

The brazed joint structure described above can be applied, for example, to joining a semiconductor substrate and a heat sink. That is, in the present invention, the brazing joint structure is provided in which the aluminum material is a member constituting the surface opposite to the element mounting surface of the semiconductor substrate, and the steel material is a heat radiating plate joined to the semiconductor substrate. .

As a method for constructing such a brazed joint structure, in the present invention, a steel material having a molten Al plating layer containing Si: 5 to 13% by mass on the surface and an aluminum material are interposed between the two materials. A furnace having a temperature not lower than 530 ° C. and not lower than the melting point of the brazing material and not higher than 580 ° C. with an Al—Cu—Si brazing material containing Mg in the range of 0.3 to 4% by mass and having a melting point of less than 550 ° C. The brazing material was melted by inserting into the brazing material, and the holding in the above temperature range was terminated so that the average thickness of the Al—Fe—Si based alloy layer growing on the steel base surface of the brazed joint became 15 μm or less. A method of vacuum brazing of steel and aluminum material is provided that transitions to a cooling process . Referred to here "vacuum brazing" is brazed to perform the pressure of the atmosphere in the holding temperature of less 1 × 10 ^-2 Pa. “The average thickness of the Al—Fe—Si based alloy layer” is the average thickness of the Al—Fe—Si based alloy layer after the brazing heat treatment is completed (when the temperature is cooled from the holding temperature to room temperature), that is, the brazing It is the average thickness of the Al—Fe—Si based alloy layer observed in the material after being attached.

  Stainless steel can be adopted as the steel material.

  According to the present invention, in the brazing of a steel material and an aluminum material, even when stress due to the difference in thermal expansion coefficient between the two materials is repeatedly applied to the joint interface, a joint structure having high durability can be stably obtained. It came to be able to. As the steel material, stainless steel can be used, and vacuum brazing can be supported. Therefore, the present invention can be widely applied to various members that transfer heat between a steel material and an aluminum material.

[Steel]
In the present invention, “Al plated steel” is used as the steel. The presence of the Al plating layer on the surface of the steel material improves the reactivity with the brazing material and makes it possible to reduce the brazing temperature.
The Al plating layer is preferably a molten Al plating layer obtained by immersing a steel material in an Al—Si alloy bath containing 5 to 13 mass% of Si.

  In FIG. 2, the SEM photograph of the cross section containing the plating layer of hot-dip Al plating steel materials is illustrated. In this example, SUH409 having a thickness of 0.8 mm is used as a base material. The plating bath composition is Al-9 mass% Si, and the balance of Si is Al and inevitable impurities. A reaction layer is formed in the vicinity of the steel substrate of the plating layer. This reaction layer is formed by the reaction of Al and Si of the plating bath with Fe of the base material. When the base material is stainless steel, this reaction layer tends to grow easily. However, it has been confirmed that the composition of the plating layer is almost the same as the bath composition. When brazing is performed, the Al plating layer and the reaction layer react with the molten brazing material, and a new reaction layer (an Al—Fe—Si alloy layer described later) is formed in the vicinity of the steel base.

By containing Si in the molten Al plating bath, the melting point is lowered, and the plating bath temperature can be lowered. In addition, since the melting point of the formed Al plating layer is also lowered, the reactivity with the brazing material is improved during brazing. In order to sufficiently obtain such an effect, the Si content in the Al plating layer is preferably 5 to 13% by mass, and may be managed in the range of 7 to 11% by mass. When using a “steel plate” as a base material, a hot-dip Al-plated steel plate manufactured using a general continuous hot-dip plating line is a suitable target. The Al plating adhesion amount may be, for example, 15 to 150 g / m ² per one surface of the steel sheet, and more preferably 30 to 100 g / m ² .

  As the base steel, various steel types that can be subjected to hot-dip Al plating can be applied, and may be selected according to the intended use. For applications where corrosion resistance is required, it is desirable to use stainless steel. “Stainless steel” is a steel having a Cr content of 10.5% by mass or more as shown in the number 4201 of JIS G0203: 2000, but considering the manufacturability and cost, the Cr content is in the range of 32% by mass or less. It is desirable to do. Since the ferritic steel type has a smaller coefficient of thermal expansion than the austenitic steel type, it is desirable to use ferritic stainless steel, for example, in the application of a heat sink for joining semiconductor substrates. When it is desired to apply a steel material that is as close as possible to the thermal expansion coefficient of the aluminum material itself, austenitic stainless steel is advantageous.

  Examples of the composition of ferritic stainless steel include C: 0.12% or less, Si: 1% or less, Mn: 1% or less, P: 0.04% or less, S: 0.03% or less, Cr: 10 0.5 to 32%, particularly 11 to 20%, and Mo: 3% or less, Cu: 1% or less, Ti + Nb + Zr total: 0.8% or less, Ni: 0.6% or less, B: 0 as necessary 1% or less, V: 1% or less, Ca: 0.1% or less, Mg: 0.1% or less, Y: 0.1% or less, REM (rare earth element): 0.1% or less And a composition comprising the balance Fe and inevitable impurities. As existing standard steel types, for example, ferritic steel types described in Table 4 of JIS 4305: 2005 and Table 3 of JIS G4312-1991 can be adopted.

  The component composition of austenitic stainless steel is exemplified by mass%, C: 0.12% or less, Si: 4% or less, particularly 1% or less, Mn: 5% or less, particularly 2% or less, P: 0.045% or less. , S: 0.03% or less, Ni: 6-28%, especially 8-14%, Cr: 15-32%, especially 16-26%, N: 0.3% or less, and Mo: 7 if necessary % Or less, particularly 3% or less, Cu: 4% or less, particularly 2% or less, Ti + Nb + Zr: 0.8% or less, B: 0.1% or less, V: 1% or less, Ca: 0.1% or less, Mg A composition comprising one or more of: 0.1% or less, Y: 0.1% or less, REM (rare earth element): 0.1% or less, the balance being Fe and inevitable impurities can be given. As existing standard steel types, for example, austenitic steel types described in Table 2 of JIS 4305: 2005 and Table 2 of JIS G4312-1991 can be adopted.

[Aluminum material]
As the aluminum material, pure Al and various Al alloys whose matrix is an Al phase (Al content of 80 mass% or more, preferably 85 mass% or more) are applicable. As existing standard materials, various materials (1000 series to 8000 series) defined in JIS H4000 can be adopted.

[Brazing material]
A brazing material having a melting point of less than 550 ° C. is used. The thing below 540 degreeC is more preferable. Conventionally known brazing materials for aluminum alloys are Al-Si based materials, for example, Si: a composition containing about 12 atomic% is the mainstream. However, the Al—Si system has a high melting point exceeding 570 ° C. and cannot be used in the present invention where it is important to make the thickness of the Al—Fe—Si alloy layer as thin as possible.

  As a result of various studies, in the present invention, an Al—Cu—Si based alloy containing Cu and a brazing material having a melting point of less than 550 ° C. is used. Specifically, Al-26.7 mass% Cu-5.3 mass% Si composition (eutectic point temperature; about 524 ° C.) of Al—Cu—Si ternary eutectic point or a composition close to this melting point Is employed in a range of less than 550 ° C., preferably less than 540 ° C. However, in the case of subjecting to vacuum brazing without using a flux, it is preferable to apply a composition in which Mg is added to the Al—Cu—Si based alloy in a range of 4 mass% or less. The surfaces of the Al-plated steel material and the aluminum material that are the materials to be joined are covered with stable Al oxide. Mg mixed in the brazing material acts as a reducing agent for the Al oxide when the brazing material is melted, and can ensure the reactivity with the Al-plated steel material and the aluminum material without using a flux. In order to sufficiently bring out such an action, the Mg content in the brazing material is desirably 0.3% by mass or more, and more preferably 0.5% by mass or more. However, it is not necessary to contain Mg in a large amount, and it may be adjusted within a range of 4% by mass or less. For example, you may manage in the range of 2.5 mass% or less. By containing Mg, the melting point of the brazing material may vary slightly, but if the blending ratio of Al, Cu, Si is the above eutectic composition or a composition close thereto, the melting point is less than 550 ° C., preferably 540 ° C. It is sufficiently possible to obtain an Mg-containing Al—Cu—Si brazing material that is less than the above.

[Brazed joint structure]
When the Al-plated steel material and the aluminum material are brazed and joined using the Al-Cu-Si-based brazing material, the structure of the brazed portion is, in order from the steel material side, "steel base", "Al-Fe-Si-based alloy layer "," Al substrate ". The Al substrate consists of a region where the aluminum material originally existed and a region formed by the reaction of the Al plating layer of the steel material, the brazing material and the aluminum material, but the boundary between these two regions is not always clear. . In many cases, in the brazed joint structure of the present invention, a crystallized phase of a Cu-Al alloy or a Cu-concentrated phase derived from it usually remains in a portion close to the Al-Fe-Si-based alloy layer. In addition, there are Si concentrated phase and Mg concentrated phase. In the present specification, such a “phase that is not an Al phase and not an Al—Fe—Si alloy phase” is referred to as a “different phase”. Even in a region where a heterogeneous phase exists in the brazed joint, that is, a region that is clearly melted and solidified during brazing, the substrate is the Al phase, and the Al phase originally contains the aluminum material. In this specification, the region where these different phases exist is also included in the “Al substrate” (see SEM images in FIGS. 4 to 6 described later). In particular, when the amount of brazing material used is relatively small or when the brazing time is relatively long, most of the heterogeneous phase originating from the solidified structure has disappeared due to diffusion, and it is possible to grasp the melted and solidified part. It becomes even more difficult. Note that the concentration of Cu derived from the brazing filler metal dissolved in the Al phase tends to gradually decrease as the distance from the Al—Fe—Si alloy layer increases.

  According to the study by the inventors, in the brazed joint between the steel material and the aluminum material constituted by the “steel base”, “Al—Fe—Si alloy layer”, and “Al base” as described above, Al— It has been found that the Fe—Si based alloy layer is brittle compared to other portions, and the breakage at the brazed joint is caused by a crack generated in the Al—Fe—Si based alloy layer. As a result of further detailed study, the inventors have made the average thickness of the Al—Fe—Si alloy layer 15 μm or less, and the durability at the brazed joint when the temperature rise / fall is repeated is remarkable. I found it to be improved. It is more effective to set the average thickness of the Al—Fe—Si based alloy layer to 10 μm or less.

  FIG. 3 illustrates an SEM photograph of a cross section in the brazed joint structure of the present invention. This is an example of Test No. 6 in Examples described later. A layer in which the A phase indicated as (A) and the B phase indicated as (B) (a phase that looks darker than A) is formed on the surface of the steel substrate. As a result of the analysis, both the A phase and the B phase are Al—Fe—Si based alloy layers, but more Cu exists in the A phase than in the B phase. Further, when the steel material is stainless steel, there is more Cr in the A phase than in the B phase. A whitish phase is observed in the vicinity of these phases, which is a crystallized phase of Cu-Al alloy or a Cu concentrated phase derived therefrom. The average thickness of the Al—Fe—Si alloy layer is observed in the observation region of a certain distance L in the direction along the steel substrate surface (lateral direction in the photograph of FIG. 3) by observing the structure of the cross section as shown in FIG. The total area of the A phase and the B phase to be calculated can be calculated and divided by the distance L. In this case, the crystallization phase of the Cu-Al alloy in contact with the A phase or the B phase, or the Cu concentrated phase derived therefrom, and other different phases are not constituent elements of the Al-Fe-Si alloy layer. Ignored in measuring the average thickness of the Al-Fe-Si alloy layer. Whether the observed phase is the A phase, the B phase, or another phase can be specified by microscopic analysis using EDX or the like. The areas of the A phase and the B phase can be determined by image processing.

  When the average thickness of the Al—Fe—Si-based alloy layer is as thin as 15 μm or less, in many cases, a structural state in which the A phase and the B phase are mixed is obtained. The interface between the Al-Fe-Si-based alloy layer and the Al phase in the Al substrate exhibits a concavo-convex form mainly reflecting the crystallization form of the B phase. It is considered that the occurrence and propagation of cracks in the Al—Fe—Si based alloy layer is greatly reduced only by the fact that the average thickness of the Al—Fe—Si based alloy layer is as thin as 15 μm or less, preferably 10 μm or less. . In addition, the Al—Fe—Si based alloy layer has a multiphase structure of different types of A phase and B phase, and the interface with the Al phase exhibits an uneven shape, whereby the Al—Fe—Si based alloy layer Is further strengthened, and it is considered that durability against repeated heating and cooling is further improved.

  During the holding at the brazing temperature, the molten brazing material reacts with the surrounding solid phase, so that the composition of the liquid phase deviates from the ternary eutectic composition and the melting point increases, and the holding time at the brazing temperature is increased. When it is long to some extent, it is considered that the liquid phase disappears during the holding time. The longer the holding time, the more the atom diffuses and the solidified structure loses its shape. According to the study by the inventors, the thickness of the Al—Fe—Si alloy layer increases with the diffusion of the atoms, the A phase having a relatively high Cu concentration absorbs the B phase, and eventually Al. The -Fe-Si alloy layer is almost composed of only the A phase. In such a state, coarse cracks are likely to occur inside the Al—Fe—Si based alloy layer. As a result of detailed investigation, coarse cracking occurs when the holding at the brazing temperature is terminated before the average thickness of the Al—Fe—Si alloy layer exceeds 15 μm and the process proceeds to the cooling process. Easy formation of an Al-Fe-Si alloy layer is avoided. It is more preferable to shift to the cooling process before the average thickness of the Al—Fe—Si based alloy layer exceeds 10 μm. The proportion of the B phase in the Al—Fe—Si based alloy layer is preferably about 3 to 70% by volume. The time until the liquid phase disappears is considered to depend on the holding temperature and the amount of brazing material used (the amount of the liquid phase to be generated), but data corresponding to the brazing conditions is collected by preliminary experiments. Thus, the average thickness of the Al—Fe—Si based alloy layer can be controlled to 15 μm or less, preferably 10 μm or less.

[Brazing method]
The method of brazing is
(I) the brazing temperature is 530 ° C. or higher and the melting point of the brazing material is 580 ° C. or lower;
(Ii) ending the holding at the brazing temperature in a short time so that the average thickness of the Al—Fe—Si based alloy layer is 15 μm or less, preferably 10 μm or less, and shifting to the cooling process;
Except for the above, conventional general methods may be followed. It is more preferable to control the brazing temperature to 570 ° C. or lower or lower than 570 ° C. In the case of vacuum brazing, a conventionally known vacuum brazing technique may be used after applying the brazing material containing Mg and adopting the above conditions (i) and (ii).

As a steel material, a hot-dip Al-plated steel plate using ferritic stainless steel SUH409 as a plating base plate was prepared. The plate thickness is 0.8 mm, the plating adhesion amount per side is 120 g / m ² , and the plating layer composition is Al-9 mass% Si.
As an aluminum material, an aluminum alloy plate material of Al: 99.5 mass% or more corresponding to JIS H4000 and alloy number 1050 was prepared. The plate thickness is 5 mm.
As a brazing material, an alloy sheet having an Al-27 mass% Cu-4.5 mass% Si-2 mass% Mg composition was prepared. The sheet thickness is 0.1 mm and the melting point is about 535 ° C.

Samples of 25 mm × 25 mm are cut out from the steel, aluminum material and brazing material, and the steel material (0.8 mm thickness), brazing material (0.1 mm thickness), aluminum material (5 mm thickness) are placed on a horizontal tray made of stainless steel. ) To obtain a laminate. The laminated body was placed in a horizontal state with the tray placed in a furnace at 550 ° C. and subjected to vacuum brazing at an atmospheric pressure of 1 × 10 ⁻³ Pa. The material temperature was monitored by a thermocouple attached to the surface of the laminate, and the in-furnace time from when the material temperature reached 530 ° C. was defined as “brazing holding time”. The brazing holding time was set at various stages of 2 to 20 minutes, and when the predetermined brazing holding time had elapsed, the laminate was taken out of the furnace and shifted to the cooling process. In this way, various “brazed joints” having different brazing holding times were obtained.

  For the brazed joint of each holding time, observe the cross-sectional structure of the brazed joint, and calculate the total area of the A phase and B phase observed in the observation region of a certain distance L in the direction along the steel substrate surface. Then, by dividing this by the distance L, the average thickness of the Al—Fe—Si based alloy layer was determined. Further, the proportion of the B phase in the Al—Fe—Si based alloy layer (the total area of the A phase and the B phase) is calculated, and the proportion of the B phase is 3 to 70% by volume is less than 3% by volume. Was rated as x. O The thing of evaluation is thought to be effective for the durability improvement of the Al-Fe-Si type alloy layer by the double phase structure of A phase + B phase.

In addition, with respect to the brazed joint of each holding time, 100 cycles of a thermal shock test in which “holding in a gas phase of −40 ° C. for 30 minutes → holding in a gas phase of 130 ° C. for 30 minutes” is 1 cycle, The cross-sectional structure of the brazed joint after the test was observed. The thermal shock characteristics were evaluated according to the following criteria depending on the degree of cracking generated in the Al—Fe—Si based alloy layer.
◎: No cracking is observed ○: Cracking is recognized, but it is a local minute crack, and it is considered that there is almost no propagation property in the above-mentioned cooling cycle △: The generated microcrack is considered to have propagated and connected It is considered that there is almost no possibility of progressing to continuous cracking in the above-described cooling cycle. ×: The continuous cracking that the generated crack is considered to have propagated and connected is recognized, This crack may lead to material breakage. In the above, if it is more than △ evaluation, it is judged that it can be used in many heat transfer applications with repeated heating and cooling, so it passes △ evaluation or more. It was determined. ○ If it is above evaluation, high reliability can be obtained in many heat transfer applications involving repeated heating and cooling.

  These results are shown in Table 1. For reference, FIGS. 4, 5 and 6 show the SEM image of the brazed joint cross section before the thermal shock test and the element detection results by EPMA for Test No. 6, No. 5 and No. 2, respectively. Show.

  As can be seen from Table 1, the thermal shock characteristics due to repeated temperature increase and decrease are those in which the brazing and holding are finished so that the average thickness of the Al—Fe—Si based alloy layer is 15 μm or less. Is good.

The figure which showed the structural example of the general power module typically. The SEM photograph of the section containing the plating layer of hot-dip Al plating steel materials. The SEM photograph which showed an example of the cross-sectional structure | tissue in the brazing joining structure of this invention. The figure which showed the element detection result by the SEM image and EPMA of a brazing junction cross section about test No. 6 (example of this invention). The figure which showed the element detection result by the SEM image and EPMA of a brazing junction cross section about test No. 5 (example of this invention). The figure which showed the element detection result by the SEM image and EPMA of a brazing junction cross section about test No. 2 (comparative example).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor element 2 Semiconductor substrate 3 Conductor layer 4 Insulating substrate 5 Back surface conductor layer 6 Heat sink 7 Heat sink 10 Bonding interface

Claims (5)

A joining structure in which an Al-plated steel material and an aluminum material are brazed using a brazing material having an Mg content of 0.3 to 4% by mass and a melting point of less than 550 ° C. and having an Al—Cu—Si alloy composition. , in order from the steel material side, the steel basis material, Al-Fe-Si alloy layer, the more configured Al-containing fabric, during the Al matrix Cu enriched phase from crystallization Desho or that of Cu-Al alloy, Si A concentrated phase and a Mg concentrated phase exist, the average thickness of the Al—Fe—Si based alloy layer is 15 μm or less, and the Al—Fe—Si based alloy layer has two types of Al having different Cu concentrations. and it has a structure in which a phase of -fe-Si based alloy are mixed, brazed structure of the steel and the aluminum material. The steel material and the aluminum material brazed joint structure according to claim 1, wherein the steel material is stainless steel. 3. The brazing of a steel material and an aluminum material according to claim 1 or 2 , wherein the aluminum material is a member constituting a surface of the semiconductor substrate opposite to the element mounting surface , and the steel material is a heat radiating plate joined to the semiconductor substrate. Junction structure. Si: 5 to 13 and a steel material having a melting Al coating layer containing mass% on the surface, an aluminum material, mp 550 below ℃ containing material between a range of Mg of 0.3 to 4% by weight thereof both In a state where the Al-Cu-Si brazing filler metal is interposed, the brazing filler metal is melted in a vacuum in a furnace having a temperature of 530 ° C. or higher and a melting point of the brazing filler metal or higher and 580 ° C. or lower. A brazing method for steel and aluminum material, in which the holding in the above temperature range is terminated and the cooling process is started so that the average thickness of the Al—Fe—Si based alloy layer formed in 1 is 15 μm or less. The method for brazing a steel material and an aluminum material according to claim 4 , wherein the steel material is stainless steel.