JP5691901B2 - Power module manufacturing method - Google Patents

Description

  The present invention relates to a method for manufacturing a power module in which a metal film is formed on the surface of a substrate, and particularly suitable for soldering a joining member such as a power element via solder as the metal film. The present invention relates to a method for manufacturing a power module on which a metal film is formed.

  In a power module equipped with a semiconductor element (power element) such as an IGBT (Insulated Gate Bipolar Transistor), the heat generated from the power element is efficiently radiated, and adjustment is made so that the temperature is below the reference temperature even during the heat generation. ing.

  Here, in the conventional power module, a power element is fixed to one side surface of an insulating substrate (also referred to as DBA (Direct Brazed Aluminum)) made of an aluminum nitride (AlN) plate or a pure aluminum plate by soldering. It constitutes a circuit unit. On the other hand, a heat sink (heat sink) for dissipating heat from the power element through the insulating substrate (base material) and a cooler are joined to the other side of the insulating substrate by soldering, brazing, or adhesive. A power module is formed.

  In order to relieve the stress caused by the difference in thermal expansion between the substrate and the member in contact with the substrate, the difference in thermal expansion of the substrate is low, or in a solid state made of a material close to the thermal expansion of the substrate. A metal film is formed by spraying a metal powder together with a carrier gas in a solid state (so-called cold spray method), and these are bonded. By such a cold spray method, a metal film can be formed without damaging the surface of the substrate due to heat (see, for example, Patent Document 1 or 2).

JP 2008-300455 A JP 2009-127086 A

  Here, the surface of the base material described above is coated with a metal film on the surface of the insulating substrate in order to improve the adhesion to the bonding member such as a power element, and the metal film and the bonding member are solder (bonding material). ) Is soldered through. For example, the metal film can be formed by a cold spray method described in Patent Document 1 or 2. However, in the first place, since the cold spray method is performed by spraying a metal powder in a solid state, it is necessary to increase the spray pressure of the carrier gas in order to improve the adhesion of the metal film.

  However, in such a case, as the carrier gas spray pressure is increased, the adhesion of the metal film is improved and the metal film becomes denser (dense), but the carrier gas is included in the metal film. become. As a result, when the joining member is soldered to the surface of the base material via the metal film, the carrier gas included in the metal film causes a large number of solder inside the solder layer (solder). A void (pore) is generated, and the heat transfer property of the power module may be hindered by the void.

  As described above, in consideration of soldering of the joining member, it is desirable to reduce the carrier gas contained in the metal film by lowering the carrier gas spraying pressure described above in order to suppress the generation of voids. However, in this case, the adhesiveness between the base material and the metal film also decreases as the spray pressure decreases.

  Therefore, the surface of the base material is preliminarily subjected to blasting before film formation to create an uneven shape on the surface of the base material, and the adhesion strength of the metal film can be ensured by the anchor effect due to the uneven shape. However, in such a case, the work process becomes complicated due to an increase in the process of blasting, and further, the remaining material due to the blasting remains on the surface of the base material and its periphery, There is also a risk of hindering subsequent soldering.

  The present invention has been made in view of the above points, and the object of the present invention is to form a metal film for soldering a joining member without a pretreatment process and at the time of soldering. A method of manufacturing a power module capable of suppressing the generation of solder voids caused by the carrier gas contained in the metal film and further increasing the adhesion strength between the joining member and the substrate. It is in.

As a result of intensive studies, the inventor formed a metal film for soldering a joining member such as a power element with solder (joining material).
(1) As a first step, the metal powder is sprayed at a spraying pressure so that the carrier gas is encapsulated on the surface of the base material, thereby improving the adhesion between the base material and the metal film to be an undercoat layer without a pretreatment step. Can be increased,
(2) Further, as a second step, the metal film formed at this time is formed by forming a metal film (topcoat layer) on the surface of the metal film (undercoat layer) by lowering the spray pressure. New knowledge that the pressure of the carrier gas contained in the (top coat layer) can be reduced compared to the metal coating (undercoat layer), thereby suppressing the generation of voids in the solder during soldering Got.

  The present invention is based on this new knowledge, and a method for manufacturing a power module according to the present invention is for soldering a joining member by spraying a solid-phase metal powder together with a compressed carrier gas. A power module manufacturing method including at least a film forming step of forming a metal film on a surface of a base material, wherein the film forming step includes a surface pressure of the base material with a spraying pressure such that the carrier gas is included. By spraying the metal powder onto the surface of the substrate, a first film forming step of forming a first metal film made of the metal powder on the surface of the substrate, and a spraying pressure of the metal powder in the first film forming step A second metal film made of the metal powder is formed on the surface of the first metal film by spraying the metal powder onto the surface of the first metal film with a lower spray pressure. Characterized in that it comprises at least a second film forming step.

  According to the present invention, the first metal film (undercoat layer) formed on the surface of the substrate has a higher spraying pressure than the second metal film (topcoat layer) (the carrier gas). Therefore, the first metal film becomes a dense film having higher adhesion than the second metal film, and the base material and the first metal film Can be ensured.

  Furthermore, since the second metal film is formed as a topcoat layer on the surface of the first metal film at a lower pressure than the pressure of the metal powder in the first film formation step, the second metal film The pressure of the carrier gas contained (encapsulated) in the film can be reduced as compared with the first metal film. Thereby, when soldering a joining member, generation | occurrence | production of a void can be suppressed.

  That is, the second metal film is a porous film having a higher porosity than the first metal film, and the gas pressure inside the second metal film is the pressure (atmospheric pressure) in the soldering environment. Therefore, it is possible to effectively suppress the generation of the above-described voids, thereby improving the wettability of the solder.

  In addition, the above-described metal film formation is not particularly limited as long as the metal film adhesion and the generation of voids can be reduced. However, as a more preferable aspect, the method further includes a heat treatment step of heat treating the first and second metal films in an atmosphere containing a reducing gas.

  According to this aspect, the bonding strength between the first metal film and the second metal film can be increased by performing the heat treatment step. Moreover, by performing this heat treatment in an atmosphere containing a reducing gas, the oxide film (oxide) on the surface of the second metal film during the heat treatment can be reduced, and the surface oxide can be reduced. Thereby, the wettability of the 2nd metal film with respect to a joining member can be improved at the time of the soldering which is a post process.

  Here, the “reducing gas” referred to in the present invention refers to a gas for reducing at least the metal oxide contained in the second metal film and reducing the ratio of the metal oxide. Here, the atmosphere containing the reducing gas may be a gas atmosphere in which the reducing gas is mixed with the atmosphere. However, more preferably, it is desirable to be in a gas atmosphere in which a reducing gas is mixed with an inert gas. Thereby, the oxidation of the second metal film during heat treatment is suppressed. For example, the reducing gas can include hydrogen gas, and the inert gas can include helium gas, argon gas, nitrogen, and the like. Also good.

  Further, examples of the carrier gas (compressed gas) suitable for the first and second film forming steps according to the present invention include an inert gas such as nitrogen gas, helium gas, and argon gas, or air (atmosphere). As long as the metal powder can be deposited in the solid phase and deposited to form a metal film, the type of the carrier gas is not particularly limited. However, in order to increase the wettability of the solder in the soldering process, it is desirable that the surface of the metal film has less oxide, so it is preferable to use the inert gas described above as the carrier gas described above.

  In addition, the form of the metal powder is not particularly limited as long as the first and second metal films can be formed, and the metal powder may be a gas atomized powder or a water atomized powder. An atomized powder, an electrolytic powder produced by depositing metal on an electrode using electrolysis, or a granulated powder obtained by granulating these powders can be used.

  However, as a more preferable aspect, water atomized powder is used as the metal powder in the first film forming step, and electrolytic powder is used as the metal powder in the second film forming step.

  According to the present invention, in the first film forming step, by using the water atomized powder, the water atomized powder has a shape close to a sphere, so that the dense first metal film having high adhesion is formed. Can do.

  On the other hand, the electrolytic powder is in the form of a tuft-like powder (cocoon-like powder) and a tree-like powder (dendritic powder (dent-like powder)), compared to other powders. The surface has a lot of irregularities. Therefore, in the second film forming step, the use of the electrolytic powder makes it possible to form the second metal film more easily at a lower pressure than when other powders are used. In addition, the second metal film can be easily made into a porous film, and the carrier gas contained in the second metal film can be easily released.

  In addition, the metal powder is not particularly limited as long as the formed metal film is a material that can ensure the adhesion and thermal conductivity between the joining member and the base material. For example, a powder containing at least one material selected from aluminum, chromium, nickel, copper, iron, and alloys thereof can be used.

  However, a more preferable metal powder is a powder made of copper or a copper alloy. According to the present invention, by using a powder made of copper or a copper alloy as the metal powder, the adhesion to the substrate can be improved, and the thermal conductivity and electrical conductivity of the coating can be improved. Examples of the substrate include aluminum, copper, silver, or alloys thereof, and ceramics mainly composed of aluminum such as aluminum nitride. Preferred embodiments include aluminum and aluminum alloys as the substrate. Alternatively, ceramics mainly composed of aluminum can be used.

  And when the material of such a preferable aspect is selected, an Al-Cu alloy phase is generated between the base material and the first metal film in the heat treatment step. It is more preferable to heat the first and second metal films under heating conditions of 300 ° C. to 550 ° C. so that the thickness of the Cu alloy phase is 20 μm or less. According to this aspect, since the heat treatment step is performed so that the Al—Cu alloy phase has a thickness of 20 μm or less, the adhesion strength of the metal film to the substrate can be ensured.

  That is, when the Al—Cu alloy phase exceeds 20 μm, the adhesion strength of the metal film to the substrate decreases after the heat treatment. In addition, in the case of heating conditions of less than 300 ° C. in this heat treatment, a long heat treatment time is required to sufficiently reduce the second metal film. An Al—Cu alloy phase that causes a decrease is easily formed.

  According to the present invention, a metal film for soldering a joining member such as a power element can be formed without a pretreatment step, and the carrier gas included in the metal film is caused at the time of soldering. The generation of voids in the solder (layer) can be suppressed, and the adhesion strength between the joining member and the substrate can be increased.

It is a schematic diagram for demonstrating the manufacturing method of the power module which concerns on embodiment of this invention, (a) is a figure for demonstrating a masking process, (b) is for demonstrating a 1st film-forming process. (C) The figure for demonstrating a 2nd film-forming process, (d) is a figure for demonstrating a heat treatment process, (e) is a figure for demonstrating a soldering process. The typical conceptual diagram of the film-forming apparatus used for FIG.1 (b) and (c). FIG. 3 is a schematic conceptual diagram for explaining a method for measuring the adhesion strength of a test specimen according to Example 1. The figure which showed the adhesion strength of the test body which concerns on Examples 1, 2 and Comparative Examples 1, 2, and the result of a fracture | rupture position. It is a photograph figure of the X-ray transmission image of the solder after soldering of the power module concerning Example 1 and Comparative Example 2, (a) is an X-ray transmission image of the solder after soldering of Example 1, (B) is an X-ray transmission image of the solder after soldering of Comparative Example 2. It is the photograph which observed the interface vicinity of the base material (Al base material) which concerns on Example 3 and Comparative Example 3, and the 1st metal membrane | film | coat (Cu layer) with the microscope, (a) concerns on Example 3. It is the photograph which observed the interface vicinity with the microscope, (b) is the photograph figure which observed the interface vicinity which concerns on the comparative example 3 with the microscope. The table | surface figure which showed the result of having observed the interface vicinity of the base material (Al base material) which concerns on Example 3 and the comparative example 3, and a 1st metal membrane | film | coat (Cu layer) with the microscope. The figure which showed the adhesive strength of the test body which concerns on Example 1, and Comparative Example 3, and the result of the fracture | rupture position.

Embodiments of a method for manufacturing a power module according to the present invention will be described below.
1A and 1B are schematic views for explaining a method for manufacturing a power module according to an embodiment of the present invention. FIG. 1A is a diagram for explaining a masking process, and FIG. 1B is a first film forming process. (C) The figure for demonstrating a 2nd film-forming process, (d) is a figure for demonstrating a heat treatment process, (e) is a figure for demonstrating a soldering process. It is. FIG. 2 is a schematic conceptual diagram of the film forming apparatus used in FIGS. 1B and 1C.

[1. Masking process)
As shown in FIG. 1A, a base 11 such as pure aluminum or aluminum nitride is prepared as a substrate to which a power element (joining member) constituting the power module according to this embodiment is soldered.

  Next, the masking material 31 masks the surface other than the surface 11b covering the metal film among the surface 11a of the substrate 11. The masking material may be any material as long as the masking material 31 does not peel off by a cold spray method described later, and examples thereof include a metal material or a resin material.

[2. Film formation process]
Next, a metal film forming step is performed. The metal film deposition process includes first and second film deposition processes. Specifically, the film is formed using the film forming apparatus 20 shown in FIG. The film forming apparatus 20 includes at least a compressed gas supply unit 21, a metal powder supply unit 22, a spray gun 23, and a spray gun moving unit 24.

  The compressed gas supply means 21 is a means for supplying compressed gas to a spray gun 23 which will be described later, and is connected to the spray gun 23 via a pressure adjusting valve 21a for adjusting the pressure of the compressed gas. The compressed gas supply means 21 can include a cylinder filled with air, an inert gas, etc., a compressor that compresses the atmosphere, and the like, and is sprayed as a compressed gas (carrier gas) under a pressure condition of 0.3 to 5 MPa. What can supply to the gun 23 is preferable. This is because it is difficult to form a film if the pressure of the carrier gas is less than 0.3 MPa, and when the pressure of the carrier gas is greater than 5 MPa, not only a film-forming facility having pressure resistance is required, but also described later. It cannot be expected that the adhesion of the first metal film 12 to be formed is further secured.

  Further, a heating unit 21 b for heating the carrier gas is further provided downstream of the compressed gas supply unit 21. The carrier gas is heated by the heating means 21b, and the metal powder p, which will be described later, can be sprayed onto the substrate 11 under a desired temperature condition. The heating means 21b is for indirectly heating the metal powder p with the compressed gas, and may be arranged inside the compressed gas supply means 21. If it can be heated to a temperature, it is not particularly necessary.

  The metal powder supply means 22 is connected to the spray gun 23 so that the metal powder sprayed on the base material 11 is accommodated in the hopper 22a, and the metal powder p can be supplied to the spray gun 23 with a predetermined supply amount. Yes. As the metal powder p accommodated in the metal powder supply means 22, a water atomized powder having an average particle diameter of preferably an average particle diameter of 25 μm or less is used in the first film forming process, and an average is used in the second film forming process. Electrolytic powder having an average particle diameter of preferably 25 μm or less is used.

  Here, the electrolytic powder is a powder produced by depositing a metal on an electrode using electrolysis, and the shape of the water atomized powder is more spherical than that of the water atomized powder. Has a surface shape close to, for example, a dendrite shape, which includes more irregularities than gas atomized powder.

  Further, the spray gun 23 is connected to the spray gun moving means 24. By driving the spray gun moving means 24, the spray gun 23 can be moved to a predetermined route. Furthermore, a heater 23 a for heating the supplied metal powder p is provided inside the spray gun 23. Using such a film forming apparatus 20, the following first and second film forming steps are performed.

[2-1. First film forming step]
Specifically, as shown in FIG. 1B, first, a first film forming step is performed. In the first film forming step, a metal powder (for example, copper or copper alloy powder) is sprayed on the surface 11b of the base material 11 together with the transport gas at a spraying pressure so that the transport gas is included, whereby the surface 11b of the base material 11 Then, a first metal film (undercoat layer) 12 made of metal powder is formed.

  The carrier gas in the first film forming step is preferably nitrogen gas. Thereby, compared with the case where air | atmosphere is used for carrier gas, the oxidation of a 1st metal membrane | film | coat (copper membrane | film | coat) can be suppressed.

  In addition, the blowing pressure is performed by adjusting the pressure of the carrier gas, for example, the carrier gas supplied from the compressed gas supply means 21 with the pressure regulating valve 21a, and the temperature of the carrier gas is adjusted by the heating means 21b and the heater 23a. To do. Here, the gas temperature of the carrier gas is preferably 200 ° C. to 500 ° C., and the spraying pressure to the base material 11 (pressure in the pressure regulating valve 21a) is preferably 2 to 5 MPa.

  Here, when the temperature of the carrier gas is less than 200 ° C. or the spraying pressure is less than 2 MPa, the adhesion (adhesiveness of the metal powder) of the first metal film 12 to the substrate 11 may be reduced. If the temperature of the carrier gas exceeds 500 ° C, the metal powder may be oxidized. Moreover, even if the spraying pressure exceeds 5 MPa, it is not expected to improve the adhesion of the first metal film 12 any more.

  Further, as described above, in the first film forming process, water atomized powder is used as the metal powder. Thereby, unlike the gas atomized powder and the electrolytic powder, the water atomized powder has a nearly spherical shape, so that the dense first metal film 12 with high adhesion can be formed.

  Here, in this embodiment, it is preferable that the film thickness of a 1st metal film exists in the range of 5-500 micrometers. If the film thickness of the first metal film is less than 5 μm, the first metal film may not function sufficiently as an underlayer for soldering. If the film thickness of the first metal film exceeds 500 μm, The above effects cannot be expected.

In the case of this embodiment, since copper powder was used as the metal powder, the density of the first metal film 12 is 8.0 kg / m ³ or more, preferably 8.56 to 8.73 kg / m. It is in the range of ³ . The density of copper itself (copper bulk material) is 8.92 kg / m ³ . In addition, the density shown in this specification is a value based on “4. Measuring method for weighing in liquid” of JIS Z8807 “Method for measuring solid specific gravity”.

  Thus, since the 1st metal membrane | film | coat 12 sprays metal powder (copper powder) on the base material 11 with high energy, it becomes close to the density of a copper bulk material, and carrier gas is contained in the 1st metal membrane | film | coat 12. It will be included. Therefore, when a bonding member such as a power element is soldered to the surface of the first metal film 12 via a bonding material (solder), the contained carrier gas is released and voids (pores) are generated in the solder. Will be. Therefore, in the present embodiment, the generation of this void is suppressed by performing the following second film forming step.

[2-2. Second film forming step]
The second film forming step is a step of forming the second metal film 13 as shown in FIG. Specifically, in the second film-forming step, the metal powder is sprayed onto the surface of the first metal film 12 at a spraying pressure lower than the spraying pressure of the metal powder in the first film-forming step. A second metal film (topcoat layer) 13 made of metal powder is formed on the surface of the metal film 12.

  The carrier gas in the second film forming step is preferably nitrogen gas. Thereby, compared with the case where air | atmosphere is used for carrier gas, the oxidation of the 2nd metal membrane | film | coat (copper membrane | film | coat) 13 is suppressed, and the wettability of solder can be improved.

  For example, the carrier gas supplied from the compressed gas supply means 21 is adjusted by adjusting the pressure of the compressed gas with the pressure adjusting valve 21a, and the temperature of the carrier gas is adjusted by the heating means 21b and the heater 23a. To do. Here, the gas temperature of the carrier gas is preferably about 400 ° C. to 600 ° C., and the spray pressure to the base material 11 (pressure in the pressure adjusting valve 21a) is preferably 0.3 to 1 MPa.

  Here, when the temperature of the carrier gas is less than 400 ° C. or the spraying pressure is less than 0.3 MPa, the adhesion (adhesion of the metal powder) of the second metal film 13 to the first metal film 12 is high. When the temperature of the carrier gas exceeds 600 ° C., the metal powder may be oxidized. Further, when the spray pressure of the carrier gas exceeds 1 MPa, the carrier gas that causes voids generated in the solder is included in the metal powder.

  Further, as described above, in the second film forming step, electrolytic powder is used as the metal powder. Thereby, unlike the atomized powder, since the shape is far from spherical (a shape close to a dendrite), the dense second metal film 13 having a high porosity can be formed.

  Here, in this embodiment, it is preferable that the film thickness of a 2nd metal film exists in the range of 10-500 micrometers. If the thickness of the second metal film is less than 10 μm, the first metal film may not function sufficiently as an underlayer for soldering. If the film thickness of the second metal film exceeds 500 μm, The above effects cannot be expected.

In the present embodiment, since copper powder is used as the metal powder, the density of the second metal film 13 is in the range of 6.0 kg / m ^{3 to} less than 8.0 kg / m ³ , preferably 7 It is in the range of 0.0 to 7.8 kg / m ³ .

  Thus, since the second metal film 13 is formed as a topcoat layer on the surface of the first metal film 12 at a spraying pressure lower than the spraying pressure of the metal powder in the first film forming step, The pressure of the carrier gas contained (enclosed) in the second metal film 13 can be reduced as compared with the first metal film 12. Thereby, generation | occurrence | production of a void can be suppressed when soldering a power element. In particular, since the second metal film is porous with a high porosity in the above-described density range, the solder wettability can be improved in the soldering process described later.

[3. Heat treatment process]
Next, the masking material 31 is removed from the base material 11, and the base material 11 on which the first and second metal films 12 and 13 are formed is put into the heating furnace 32 as shown in FIG. To do. And the inside of the heating furnace 32 is made into the atmosphere containing the non-oxidizing gas whose hydrogen gas density | concentration becomes 3-50 volume% specifically with respect to air | atmosphere, The heat source 33 is used in this oxidizing gas atmosphere. Then, the first and second metal films 12 and 13 are heat-treated.

  In the present embodiment, in the heat treatment step, the heating condition is 300 ° C. to 550 ° C. so that the thickness of the Al—Cu alloy phase is 20 μm or less between the base material 11 and the first metal film 12. The first and second metal films 12 and 13 are heated.

  As described above, by performing the heat treatment step, atoms contained in the first metal film 12 and the second metal film 13 are diffused to each other, and the bonding strength thereof can be increased. Further, by performing this heat treatment in an atmosphere containing a reducing gas, the oxide film (metal oxide) on the surface of the second metal film 13 during the heat treatment is reduced, and the metal oxide on the surface is reduced. Can do. Thereby, the wettability of the 2nd metal film 13 with respect to a power element can be improved at the time of soldering which is a post process.

  Here, when the concentration of hydrogen gas is less than 3% by volume, the reduction treatment of the surface of the second metal film 13 does not proceed (the oxide is not reduced), and the wettability of the solder may be reduced. There is. Moreover, since the heat treatment step is performed so that the Al—Cu alloy phase has a thickness of 20 μm or less, peeling of the metal film from the substrate can be suppressed.

  That is, when the Al—Cu alloy phase exceeds 20 μm, there is a possibility that a gap is formed between the Al—Cu alloy phase and the copper layer due to the heat shrinkage of Al—Cu alloying, and the adhesion strength is reduced. is there. Further, in the case of heating conditions of less than 300 ° C. in this heat treatment, in order to make the reduction treatment of the second metal film 13 sufficiently, a long heat treatment time is required, and when it exceeds 550 ° C., An Al—Cu alloy phase that causes a decrease in adhesion strength is likely to be generated.

  In addition, it is preferable to perform the heat processing time in the heat processing process mentioned above for 1 to 60 minutes. When the treatment time is less than 1 minute, the reduction treatment of the second metal film may not be sufficiently performed. When the treatment time exceeds 60 minutes, an Al—Cu alloy phase that causes a decrease in adhesion strength is easily generated. Become.

[4. Soldering process)
The power element 15 is disposed on the second metal film 13 of the base material 11 after the heat treatment via a solder (joining material) 14 such as Sn—Cu, and the solder material is set to a melting point or higher (for example, 300 ° C. or higher). The power element 15 is soldered to the base material 11 by heating.

  In this way, a metal film for soldering the power element can be formed without a pretreatment step, and further, at the time of soldering, the carrier gas included in the metal film was caused. Generation | occurrence | production of the void of a solder (layer) can be suppressed and it can suppress that thermal conductivity is inhibited by this. Furthermore, the first film forming step and the heat treatment step can enhance the bondability between the base material 11 and the first metal film 12, and the bondability between the first metal film 12 and the second metal film 13 is also improved. Since it can raise, as a result, the adhesiveness of the power element 15 and the base material 11 can be improved.

  And a power module is manufactured by attaching a heat sink member to the base material 11 via a buffer member such as copper-molybdenum (Cu-Mo) or aluminum-silicon carbide (Al-SiC). Is done.

This embodiment will be described by the following examples.
Example 1
A power module in which a copper film was formed on a substrate was manufactured by a cold spray method. Specifically, a DBA substrate having a size of 34 mm × 29 mm × thickness 2 mm was prepared. Next, a part of this surface is masked with a masking material, and as a first film forming step, water atomized powder made of copper and having an average particle diameter of 20 μm is blown together with nitrogen gas (carrier gas) and a spraying pressure of 4 MPa (nitrogen gas). The first metal film (copper film) was formed on the surface of the substrate until the film thickness reached 100 μm at a compressed pressure of 4 MPa) and a nitrogen gas temperature of 400 ° C.

  Next, a part of this surface is masked with a masking material, and as a second film forming step, electrolytic powder made of copper with an average particle diameter of 20 μm is sprayed with nitrogen gas (carrier gas), spraying pressure is 1 MPa, carrier gas A second metal film (copper film) was formed on the surface of the first metal film at a temperature of 400 ° C. until the film thickness reached 100 μm.

  Then, the masking member is removed from the substrate, and the first and second metal films are formed at 400 ° C., 10 ° C. in a heating furnace in a gas atmosphere in which 5% by volume of hydrogen gas is mixed as a reducing gas with respect to the atmosphere. A heat treatment step was performed by heating in minutes. The conditions for this heat treatment step are such that the thickness of the Al—Cu alloy phase generated by the heat treatment is 20 μm or less between the base material and the first metal film.

  Furthermore, by placing a power element on the second metal film of the base material 11 after the heat treatment via a bonding material (solder) made of Sn—Cu, and heating the bonding material at 300 ° C. for 10 minutes, A power element was soldered to the base material to make a power module. Moreover, in order to measure the following adhesion strength, the test piece as shown in FIG. 3 was produced. Specifically, first and second metal films 12 and 13 are sequentially formed on the surface of the base material 11 under the same conditions, and Ni plating is performed instead of a member corresponding to a power element. A long alloy alloy pin 16 was soldered with a bonding material 14 to obtain a test body.

(Example 2)
A test body was produced in the same manner as in Example 1. The difference from Example 1 is that the heat treatment step is not performed.

(Comparative Example 1)
In the same manner as in Example 1, a power module and a test body were produced. The difference from Example 1 is that the first film formation step is not performed and the second film formation step is performed, that is, the first metal film is not formed, and the metal film is the second film process. This is only a metal film (top coat layer). Specifically, taking the case of a test specimen as an example, as shown in FIG. 4, a second metal film 13 is formed on the surface of the substrate 11, and a long metal film is formed on the surface of the second metal film 13. A long pin 16 was soldered with a bonding material 14.

(Comparative Example 2)
In the same manner as in Example 1, a power module and a test body were produced. The difference from Example 1 is that the first film-forming step is performed and the second film-forming step is not performed. That is, the second metal film is not formed, and the metal film is the first film-forming process. Only a metal film (undercoat layer). Specifically, taking the case of the test body as an example, as shown in FIG. 4, the test body forms the first metal film 12 on the surface of the substrate 11, and the first metal film 12 A long pin 16 was soldered to the surface with a bonding material 14.

[Adhesion strength test]
For the test specimens of Examples 1 and 2 and Comparative Examples 1 to 3, a load was applied in the direction shown in FIG. 3 to measure the load when the test specimen broke, and the breakage of this load and its breaking position was measured. The adhesion strength was measured from the area. The results of the adhesion strength and the fracture position are shown in FIG. Here, for example, the description of “11-13” in Comparative Example 1 shown in FIG. 4 means that there was a fracture position at the interface between the base material 11 and the second metal film 13, and Comparative Example 2 The description of “14” means that the bonding material 14 had a fracture position.

[Confirmation test of solderability]
The state of the solder (joining material) of the power modules (after soldering) of Example 1 and Comparative Examples 1 and 2 was observed with X-rays. The result is shown in FIG. FIG. 5A is an X-ray transmission image of the solder after soldering in Example 1, and FIG. 5B is an X-ray transmission image of the solder after soldering in Comparative Example 2.

[Result 1]
As shown in FIG. 4, the adhesion strengths of the test bodies of Examples 1 and 2 and Comparative Example 2 exceeded 20 MPa. However, the specimen of Comparative Example 1 had a low adhesion strength and could not be measured. Moreover, the fracture position of the test body of Example 1 was in the bonding material 14. The fracture position of the test body of Example 2 was at the interface between the first metal film 12 and the second metal film 13. The fracture position of the specimen of Comparative Example 1 was at the interface between the base material 11 and the first metal film 12. The fracture position of the specimen of Comparative Example 2 was in the bonding material 14.

  Moreover, as shown in FIG.5 (b), in the case of the comparative example 2, the void was produced | generated by the solder. As shown in FIG. 5A, in the case of Example 1, no void was generated in the solder, and the case of Comparative Example 1 was the same.

[Discussion 1]
The reason why the adhesion strengths of the test bodies of Examples 1 and 2 and Comparative Example 2 were higher than that of Comparative Example 1 is considered to be that the adhesion of the first metal film was high. Further, when heat treatment is performed as in Example 1, the adhesion strength is further improved as compared to Example 2, because the adhesion strength (bonding strength) of the first and second metal films is improved by the heat treatment. You can say that.

  Further, the power module of Comparative Example 2 has higher adhesion strength than that of Example 1, but the voids are formed in the solder, which is the bonding material of Comparative Example 2, because the first metal film contains the void. This is considered to be due to the release of the carried carrier gas during soldering. Therefore, it cannot be said that the specimen of Comparative Example 2 has good solder wettability. As a result, it can be said that the power modules of Examples 1 and 2 have better thermal conductivity than the power module of Comparative Example 2 in which voids are generated.

(Example 3)
A test body was produced in the same manner as in Example 1. The test body different from Example 1 is that the heat treatment step is performed by heating the first and second metal films at the heating temperature (heat treatment temperature) and the heat treatment time indicated by the circle in the table of FIG. It is the point that went. And the interface vicinity of a base material (Al base material) and a 1st metal membrane | film | coat (Cu layer) was observed with the microscope. The results are shown in FIG. 6A and FIG. FIG. 6A shows the result of heat treatment conditions of a heat treatment temperature of 360 ° C. and a heat treatment time of 60 minutes.

(Comparative Example 3)
A test body was produced in the same manner as in Example 1. The test body different from Example 1 was subjected to the heat treatment process by heating the first and second metal films under the heating conditions (heat treatment temperature) and the heat treatment time indicated by the x mark in the table of FIG. It is the point that went. And the interface of a base material (Al base material) and a 1st metal membrane | film | coat (Cu layer) was observed with the microscope. The result is shown by x in FIG. 6B and FIG. FIG. 6B shows the results of heat treatment conditions at a heating temperature of 550 ° C. and a heat treatment time of 60 minutes. Furthermore, the test body shown in FIG. 3 described above was produced under the heat treatment conditions shown in FIG. The result is shown in FIG. In addition, in FIG. 8, the test result of Example 1 mentioned above was also shown collectively.

[Result 2 and discussion]
As shown in FIG. 6A, FIG. 6B, and FIG. 7, in the case of Example 3, the thickness of the Al—Cu alloy phase generated between the base material and the first metal film. However, in the case of Comparative Example 3, the thickness of the Al—Cu alloy phase generated between the base material and the first metal film exceeded 20 μm. There was a gap between the Al—Cu alloy phase and the copper layer. When the Al—Cu alloy phase grows beyond the thickness of 20 μm, it is considered that a gap is generated between the Al—Cu alloy phase and the copper layer due to thermal shrinkage due to Al—Cu alloying. In addition, in the case of the heat treatment conditions of Example 1 described above, the thickness of the Al—Cu alloy phase generated between the base material and the first metal film is considered to be 20 μm or less. Even if the heating condition is 300 ° C., it is considered that if the heat treatment is performed for more than 1 hour, a suitable heat treatment can be performed as described above.

  Further, as shown in FIG. 8, the adhesion strength of the test body of Comparative Example 3 is lower than that of Example 1, and the fracture position is the interface between the base material 11 and the first metal film 12 ( More precisely, it was between the Al-Cu alloy phase and the copper layer. From the above results, it is considered that when the Al—Cu alloy phase exceeds 20 μm as in Comparative Example 3, the adhesion strength of the metal film to the base material is lowered after the heat treatment due to Al—Cu alloying. .

  As mentioned above, although embodiment and the Example of this invention were explained in full detail, this invention is not limited to the said embodiment, In the range which does not deviate from the mind of this invention described in the claim, Various design changes can be made.

  11: base material, 12: first metal film, 13: second metal film, 14: bonding material (solder), 15: power module, 16: pin, 20: film forming apparatus, 21: compressed gas supply means 21a: pressure adjusting valve, 21b: heating means, 22: metal powder supply means, 22a: hopper, 23: spray gun, 23a: heater, 24: moving means, 31: masking material, 32: heating furnace, 33: heat source

Claims (5)

A method of manufacturing a power module including at least a film forming step of forming a metal film for soldering a joining member on a surface of a base material by spraying a metal powder in a solid state together with a compressed carrier gas. And
Use copper or copper alloy for the metal powder,
In the film forming step, the metal powder is sprayed onto the surface of the base material at a spraying pressure of 2 to 5 MPa so that the carrier gas is contained, whereby the surface of the base material is made of the metal powder. A first film forming step of forming a metal film of
By spraying the metal powder onto the surface of the first metal film at a spraying pressure of 0.3 to 1 MPa lower than the spraying pressure of the metal powder in the first film forming step, A power module manufacturing method comprising at least a second film-forming step of forming a second metal film made of the metal powder on the surface.   The method for manufacturing a power module according to claim 1, further comprising a heat treatment step of heat-treating the first and second metal films in an atmosphere containing a reducing gas.   3. The method of manufacturing a power module according to claim 1, wherein water atomized powder is used as the metal powder in the first film forming step, and electrolytic powder is used as the metal powder in the second film forming step. . Before Kimotozai, aluminum, a manufacturing method for a power module according to claim 1, characterized by using an aluminum alloy or aluminum was mainly made ceramics. In the heat treatment step, between the base material and the first metal film, the first and the first and the first and second under heating conditions of 300 ° C. to 550 ° C. so that the thickness of the Al—Cu alloy phase is 20 μm or less. The method for manufacturing a power module according to claim 2 , wherein the second metal film is heated.

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