JP2012109049A - Conductive composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductive composition which is provided on a circuit layer made of aluminum or an aluminum alloy, reacts with an aluminum oxide surface film spontaneously grown on the surface of the circuit layer by burning, and consequently forms a conductive junction layer in electrical connection with the circuit layer.SOLUTION: A conductive composition comprises: silver powder; lead-free glass powder containing ZnO; a resin; and a solvent. The content of powder components consisting of the silver powder and the lead-free glass powder is between 60 and 90 mass% inclusive. The ratio A/G of the weight A of the silver powder to the weight G of the lead-free glass powder in the powder components is set within a range of 80/20 to 99/1. The conductive junction layer produced as a result of burning includes: a lead-free glass layer formed by the softened lead-free glass powder; and an Ag layer made of the silver powder sintered onto the lead-free glass layer. The lead-free glass layer has conductive particles dispersed therein.

Description

  The present invention relates to a conductive composition that is disposed on a circuit layer made of aluminum or an aluminum alloy on which a semiconductor element is mounted, and forms a conductive bonding layer that conducts with the circuit layer by firing.

Examples of the semiconductor device on which the semiconductor element is mounted include a power module for supplying power. Since this power module has a relatively high calorific value, for example, an AlN (aluminum) metal plate is placed on a ceramic substrate made of AlN (aluminum nitride) with an Al-Si brazing material interposed between them. A power module substrate joined together is widely used.
This metal plate is used as a circuit layer, and a semiconductor element as a power element is mounted on the circuit layer via a solder material. It has been proposed that a metal plate such as Al is joined to the lower surface of the ceramic substrate to form a metal layer for heat dissipation, and a cooler is joined via the metal layer.

Here, in the circuit layer made of aluminum or an aluminum alloy, an aluminum oxide film is formed on the surface, so that it is not possible to perform good bonding with the solder material.
Therefore, conventionally, as disclosed in, for example, Patent Document 1, a Ni plating film is formed on the surface of a circuit layer by electroless plating or the like, and a solder material is disposed on the Ni plating film to provide a semiconductor element. It was joined.
Patent Document 2 proposes a technique for joining semiconductor elements using Ag nanopaste without using a solder material.

JP 2004-172378 A JP 2006-202938 A

  By the way, as described in Patent Document 1, in the power module substrate in which the Ni plating film is formed on the surface of the circuit layer, when the cooler is joined to the power module substrate, the Ni plating film is formed on the surface of the circuit layer. When the brazing or the like is performed after forming the Ni plating film, the Ni plating film deteriorates. Therefore, after the power module substrate and the cooler are brazed to form the power module substrate with a cooler, this is put in the plating bath. The whole board | substrate for power modules with a cooler was immersed.

For this reason, the Ni plating film is also formed on portions other than the circuit layer such as a cooler. Here, when the cooler is made of aluminum and an aluminum alloy, there is a possibility that electrolytic corrosion proceeds between the cooler made of aluminum and the Ni plating film. Therefore, in the Ni plating process, it is necessary to perform a masking process so that the Ni plating film is not formed on the cooler portion. As described above, since the plating process is performed after the masking process is performed, a great amount of labor is required to form the Ni plating film on the circuit layer portion, and the manufacturing cost of the power module is greatly increased. There was a problem.
Furthermore, in the process until the semiconductor element is bonded, the surface of the Ni plating film is deteriorated due to oxidation or the like, and there is a possibility that the reliability of bonding with the semiconductor element bonded via the solder material may be lowered.

On the other hand, in the Ag nanopaste disclosed in Patent Document 2, when a semiconductor element is bonded on a circuit layer made of aluminum, an aluminum oxide film is formed on the surface of the circuit layer. It was necessary to form an intervening layer made of Ag or Ni (see paragraph No. 0014 of Patent Document 2).
In view of the above, there has been a demand for a conductive composition that can form a conductive bonding layer that electrically connects a circuit layer made of aluminum or an aluminum alloy and a solder layer without providing a Ni plating film.

  The present invention has been made in view of the above-described circumstances, and is arranged on a circuit layer made of aluminum or an aluminum alloy, and reacts with an aluminum oxide film naturally generated on the surface of the circuit layer by firing to react the circuit. It is an object of the present invention to provide a conductive composition capable of forming a conductive bonding layer that is electrically connected to a layer.

  In order to solve such problems and achieve the above object, the conductive composition of the present invention is disposed on a circuit layer made of aluminum or an aluminum alloy on which a semiconductor element is mounted and fired. A conductive composition for forming a conductive bonding layer that is electrically connected to the circuit layer, comprising silver powder, a lead-free glass powder containing ZnO, a resin, and a solvent, the silver powder and the lead-free The content of the powder component made of glass powder is 60% by mass or more and 90% by mass or less, and the ratio A / G of the weight A of the silver powder and the weight G of the lead-free glass powder in the powder component is 80 / The conductive bonding layer, which is set within a range of 20 to 99/1 and is produced by firing, is composed of a lead-free glass layer formed by softening the lead-free glass powder, and silver on the lead-free glass layer. Powder And sintering have been Ag layer, and wherein the lead-free glass layer inside the conductive particles are characterized by being distributed.

According to the conductive composition of this configuration, the lead-free glass powder containing ZnO and the silver powder are provided, and the conductive bonding layer generated by firing is formed by softening the lead-free glass powder. Since the lead-free glass layer and the Ag layer obtained by sintering silver powder on the lead-free glass layer, the lead-free glass layer reacts with the aluminum oxide film on the surface of the circuit layer, It is possible to form a conductive bonding layer bonded directly to the circuit layer surface. Moreover, since electroconductive particle is disperse | distributed inside the said lead-free glass layer, electroconductivity is ensured by this electroconductive particle. Therefore, for example, in the case where a semiconductor element is bonded onto a circuit layer via a solder material, the circuit layer and the semiconductor element can be made conductive by a conductive bonding layer obtained by firing this conductive composition. A semiconductor device such as a power module can be configured. That is, by using this conductive composition, a solder underlayer (conductive bonding layer) can be formed.
In addition, the electrically conductive composition in this invention forms the electroconductive joining layer which has electroconductivity by baking, and the electroconductive composition itself before baking does not need to have electroconductivity.

Moreover, since content of the powder component which consists of the said silver powder and the said lead-free glass powder shall be 60 mass% or more, the above-mentioned conductive joining layer can be formed reliably. Moreover, since content of the powder component which consists of the said silver powder and the said lead-free glass powder shall be 90 mass% or less, fluidity | liquidity is ensured and it becomes possible to apply | coat on a circuit layer.
Furthermore, since the ratio A / G of the weight A of the silver powder and the weight G of the lead-free glass powder is set within the range of 80/20 to 99/1, the lead-free glass layer and the Ag layer can be securely connected. Can be formed.

Here, it is preferable that the lead-free glass powder has a glass transition temperature of 300 ° C. or higher and 450 ° C. or lower.
In this case, the lead-free glass powder containing ZnO reacts satisfactorily with the substrate, and sufficient adhesion can be obtained, so that the conductive bonding layer can be reliably formed even when fired at a relatively low temperature.

Furthermore, it is preferable that the softening temperature of the lead-free glass powder is 600 ° C. or lower and the crystallization temperature is 450 ° C. or higher.
In this case, since the softening temperature of the lead-free glass powder is 600 ° C. or less, the glass flows even when the conductive composition is fired at a relatively low temperature, so that a conductive bonding layer can be formed and It is possible to prevent a circuit layer made of aluminum or an aluminum alloy from being deteriorated when the functional composition is fired.
Further, if the crystallization temperature of the lead-free glass powder is less than 450 ° C., the fluidity inside the conductive composition is deteriorated, the reaction at the interface with the circuit layer becomes insufficient, and the adhesion may be lowered. is there. For this reason, the crystallization temperature of the lead-free glass powder is set to 450 ° C. or higher.

The glass composition of the lead-free glass _powder, Bi ₂ O 3: 68 wt% or more 93 wt% or less, ZnO: 1% by weight to 20% by _weight, B _{2 O} 3: 1 wt% to 11 wt% or less, SiO ₂ : 5 mass% or less, Al ₂ O ₃ : 5 mass% or less, Fe ₂ O ₃ : 5 mass% or less, CuO: 5 mass% or less, CeO ₂ : 5 mass% or less, ZrO ₂ : 5 mass% or less Alkali metal oxides: 2% by mass or less, alkaline earth metal oxides: 7% by mass or less are preferable.
The lead-free glass powder containing these oxides has a relatively low softening temperature, and the firing temperature can be set low. In addition, the crystallization temperature becomes relatively high, the fluidity inside the conductive composition is ensured, and the adhesion with the circuit layer is improved.
Here, the content of the alkali metal oxide is the total amount of alkali metal oxides such as Li ₂ O, Na ₂ O, and K ₂ O.
The content of the alkaline earth metal oxide is the total amount of alkaline earth metal oxides such as MgO, CaO, BaO, and SrO.

Moreover, it is preferable that the particle size of the said silver powder shall be 0.05 micrometer or more and 1.0 micrometer or less.
In this case, since the particle size of the silver powder is 0.05 μm or more and 1.0 μm or less, the conductive particles are uniformly dispersed when this conductive composition is applied on the circuit layer, By firing this conductive composition, a uniform conductive bonding layer can be formed, and the semiconductor element and the circuit layer can be reliably conducted through the conductive bonding layer.

  According to the present invention, the lead-free conductive bonding layer disposed on the circuit layer made of aluminum or an aluminum alloy and reacting with the aluminum oxide film naturally generated on the surface of the circuit layer by firing is electrically connected to the circuit layer. An electrically conductive composition that can be formed can be provided.

It is a flowchart which shows the manufacturing method of the electroconductive composition which is embodiment of this invention. It is a schematic explanatory drawing of the power module using the electroconductive composition which is embodiment of this invention. It is. It is explanatory drawing which shows the board | substrate for power modules which is embodiment of this invention. It is an expansion explanatory view of the conductive junction layer formed in the circuit layer surface. In embodiment of this invention, it is upper surface explanatory drawing which shows the measuring method of the electrical resistance value P of the thickness direction of a conductive joining layer. In embodiment of this invention, it is side explanatory drawing which shows the measuring method of the electrical resistance value P of the thickness direction of a conductive joining layer. It is a flowchart which shows the manufacturing method of the power module of FIG.

  Hereinafter, a conductive composition according to an embodiment of the present invention, a power module substrate using the conductive composition, and a power module will be described with reference to the accompanying drawings.

First, the electroconductive composition which is this embodiment is demonstrated. This conductive composition contains silver powder, lead-free glass powder containing ZnO, a resin, a solvent, and a dispersant, and the content of a powder component consisting of silver powder and lead-free glass powder However, it is 60 mass% or more and 90 mass% or less of the whole electrically conductive composition, and the remainder is made into resin, a solvent, and a dispersing agent. In addition, in this embodiment, content of the powder component which consists of silver powder and a lead-free glass powder is 85 mass% of the whole electrically conductive composition.
In the present embodiment, the viscosity of the conductive composition is adjusted to 10 Pa · s to 500 Pa · s, more preferably 50 Pa · s to 300 Pa · s.

The silver powder has a particle size of 0.05 μm or more and 1.0 μm or less. In this embodiment, the silver powder having an average particle size of 0.8 μm was used.
The lead-free glass powder contains Bi ₂ O ₃ , ZnO, and B ₂ O ₃ as main components, and has a glass transition temperature of 300 ° C. or higher and 450 ° C. or lower, a softening temperature of 600 ° C. or lower, and a crystallization temperature. 450 ° C. or higher.
The weight ratio A / G between the weight A of the silver powder and the weight G of the lead-free glass powder is adjusted within the range of 80/20 to 99/1. In this embodiment, A / G = 80 / It was set to 5.

As the solvent, those having a boiling point of 200 ° C. or more are suitable, and for example, α-terpineol, butyl carbitol acetate, diethylene glycol dibutyl ether and the like can be applied. In the present embodiment, diethylene glycol dibutyl ether is used.
The resin is used to adjust the viscosity of the conductive composition, and is suitably decomposed at 500 ° C. or higher. For example, an acrylic resin, an alkyd resin, or the like can be applied. In this embodiment, ethyl cellulose is used.
In this embodiment, a dicarboxylic acid-based dispersant is added. In addition, you may comprise a conductive composition, without adding a dispersing agent.

Here, the lead-free glass powder used in the present embodiment will be described in detail. The glass composition of the lead-free glass powder in this embodiment is
Bi ₂ O ₃ : 68 mass% or more and 93 mass% or less,
ZnO: 1% by mass or more and 20% by mass or less,
B ₂ O ₃ : 1% by mass or more and 11% by mass or less,
SiO ₂ : 5% by mass or less,
Al ₂ O ₃ : 5% by mass or less,
Fe ₂ O ₃ : 5% by mass or less,
CuO: 5 mass% or less,
CeO ₂ : 5% by mass or less,
ZrO ₂ : 5% by mass or less,
Alkali metal oxide: 2% by mass or less,
Alkaline earth metal oxide: 7% by mass or less,
It is said that.

That is, Bi ₂ O ₃ , ZnO, B ₂ O ₃ is an essential component, and this includes SiO ₂ , Al ₂ O ₃ , Fe ₂ O ₃ , CuO, CeO ₂ , ZrO ₂ , Li ₂ O, Na ₂ O, Alkali metal oxides such as K ₂ O and alkaline earth metal oxides such as MgO, CaO, BaO and SrO are appropriately added as necessary. Here, the reason why these oxides are within the above-mentioned range is shown below.

(Bi ₂ O ₃ )
Bi ₂ O ₃ is a main raw material of the lead-free glass powder, and is an essential component for lowering the melting point. When the content of Bi ₂ O ₃ is less than 68 wt%, the softening temperature becomes high. On the other hand, when the content of Bi ₂ O ₃ exceeds 93% by mass, the crystallization temperature is lowered. For this reason, the content of _Bi 2 _{O 3} and 68 wt% or more 93 wt% or less.

(ZnO)
ZnO has the effect of suppressing crystallization of lead-free glass containing Bi ₂ O ₃ . When the content of ZnO is less than 1% by mass, the effect of suppressing crystallization cannot be sufficiently achieved. On the other hand, when the content of ZnO exceeds 20% by mass, the softening temperature becomes high. For this reason, content of ZnO was made into 1 mass% or more and 20 mass% or less.

(B ₂ O ₃ )
B ₂ O ₃ is an essential component for vitrification. If the content of B ₂ O ₃ is less than 1% by mass, vitrification becomes insufficient and crystallization occurs easily. On the other hand, when the content of B ₂ O ₃ exceeds 11% by mass, the softening temperature is increased. For this _reason, the content of B 2 _{O 3} and 1 wt% to 11 wt% or less.

(SiO ₂ )
SiO ₂ has an effect of suppressing chemical durability and crystallization of glass. When the content of SiO ₂ exceeds 5% by mass, the glass transition temperature becomes high and firing at a low temperature cannot be performed. Therefore, the content of SiO ₂ was 5 mass% or less.

(Al ₂ O ₃ , ZrO ₂ )
Al ₂ O ₃ and ZrO ₂ have the effect of suppressing the chemical durability and crystallization of glass. When the content of Al ₂ O ₃ or the content of ZrO ₂ exceeds 5% by mass, the glass transition temperature becomes high and vitrification becomes difficult. Therefore, content of _Al 2 _{O 3,} and ZrO ₂ content of 5 wt% or less, respectively.

(Fe ₂ O ₃ , CuO, CeO ₂ )
Fe ₂ O ₃ , CuO, and CeO ₂ have an effect of suppressing crystallization of lead-free glass containing Bi ₂ O ₃ . When the content of Fe ₂ O _3, the content of CuO, and the content of CeO ₂ exceed 5% by mass, the glass transition temperature becomes high and vitrification becomes difficult. For this reason, the content of Fe ₂ O _3, the content of CuO, and the content of CeO ₂ were each 5% by mass or less.

(Alkali metal oxide)
The alkali metal oxide is contained as a raw material-derived component. When the total content of the alkali metal oxides exceeds 2% by mass, crystallization becomes easy and vitrification becomes difficult. For this reason, the sum total of content of the alkali metal oxide was made into 2 mass% or less.

(Alkaline earth metal oxide)
The alkaline earth metal oxide is contained in order to finely adjust the physical properties of the glass. When the total content of the alkaline earth metal oxides exceeds 7% by mass, the glass transition temperature becomes high and vitrification becomes difficult. For this reason, the total content of alkaline earth metal oxides was set to 7% by mass or less.

Such a lead-free glass powder containing ZnO is produced as follows. The above-mentioned various oxides, carbonates or ammonium salts are used as raw materials. This raw material is charged into a platinum crucible, an alumina crucible, a quartz crucible or the like and melted in a melting furnace. Although there is no restriction | limiting in particular in melting conditions, It is preferable to set it as the range of 900 degreeC or more and 1300 degrees C or less and 30 minutes or more and 120 minutes or less so that all the raw materials may be mixed uniformly by a liquid phase.
The obtained melt is dropped on carbon, steel, copper plate, twin rolls, water, etc., and rapidly cooled to produce a uniform glass lump.
The glass lump is pulverized with a ball mill, a jet mill or the like, and coarse particles are classified to obtain a lead-free glass powder. Here, in this embodiment, the center particle diameter d50 of the lead-free glass powder is set in the range of 0.1 μm or more and 5.0 μm or less.

Next, the manufacturing method of the electroconductive composition which is this embodiment is demonstrated with reference to the flowchart shown in FIG.
First, the above-mentioned silver powder and lead-free glass powder are mixed to produce a mixed powder (mixed powder forming step S1). Moreover, a solvent and resin are mixed and an organic mixture is produced | generated (organic substance mixing process S2).
And the mixed powder obtained by mixed powder formation process S1, the organic mixture obtained by organic substance mixing process S2, and a dispersing agent are premixed with a mixer (preliminary mixing process S3).
Next, the preliminary mixture is mixed while kneading using a roll mill having a plurality of rolls (kneading step S4).
The kneaded material obtained by kneading process S4 is filtered with a paste filter (filtration process S5).
Thus, the electroconductive composition which is this embodiment is produced.

Next, the power module comprised using the electroconductive composition which is this embodiment is demonstrated using FIG.
The power module 1 includes a power module substrate 10 on which a circuit layer 12 is disposed, a semiconductor chip 3 bonded to the surface of the circuit layer 12 via a solder layer 2, and a cooler 40.

The power module substrate 10 includes a ceramic substrate 11 constituting an insulating layer, a circuit layer 12 disposed on one surface of the ceramic substrate 11 (upper surface in FIG. 2), and the other surface of the ceramic substrate 11 (FIG. 2 and a metal layer 13 disposed on the lower surface.
The ceramic substrate 11 prevents electrical connection between the circuit layer 12 and the metal layer 13, and is made of highly insulating AlN (aluminum nitride). In addition, the thickness of the ceramic substrate 11 is set within a range of 0.2 to 1.5 mm, and in this embodiment is set to 0.635 mm.

  The circuit layer 12 is formed by bonding a conductive metal plate to one surface of the ceramic substrate 11. In the present embodiment, the circuit layer 12 is formed by joining an aluminum plate made of a rolled plate of aluminum (so-called 4N aluminum) having a purity of 99.99% or more to the ceramic substrate 11.

  The metal layer 13 is formed by bonding a metal plate to the other surface of the ceramic substrate 11. In the present embodiment, the metal layer 13 is formed by joining an aluminum plate made of a rolled plate of aluminum (so-called 4N aluminum) having a purity of 99.99% or more, like the circuit layer 12, to the ceramic substrate 11. Has been.

  The cooler 40 is for cooling the power module substrate 10 described above. The top plate portion 41 joined to the power module substrate 10 and the top plate portion 41 are suspended downward. The heat radiation fin 42 and the flow path 43 for distribute | circulating a cooling medium (for example, cooling water) are provided. The cooler 40 (top plate portion 41) is preferably made of a material having good thermal conductivity, and in this embodiment, is made of A6063 (aluminum alloy).

  In the present embodiment, a buffer layer 15 made of aluminum, an aluminum alloy, or a composite material containing aluminum (for example, AlSiC) is provided between the top plate portion 41 of the cooler 40 and the metal layer 13. Yes.

In the power module 1 shown in FIG. 2, a conductive bonding layer 30 formed by firing the above-described conductive composition is formed on the surface of the circuit layer 12 (upper surface in FIG. 2). The semiconductor chip 3 is bonded to the surface of the conductive bonding layer 30 via the solder layer 2. Here, examples of the solder material for forming the solder layer 2 include Sn—Ag, Sn—In, and Sn—Ag—Cu.
As shown in FIG. 2, the conductive bonding layer 30 is not formed on the entire surface of the circuit layer 12 but is selectively formed only on a portion where the semiconductor chip 3 is disposed.

3 and 4 show the power module substrate 10 before the semiconductor chip 3 is joined via the solder layer 2.
In the power module substrate 10, the conductive bonding layer 30 described above is formed on the surface of the circuit layer 12 (upper surface in FIGS. 3 and 4). In the state before the semiconductor chip 3 is bonded via the solder layer 2, the conductive bonding layer 30 includes a lead-free glass layer 31 formed on the circuit layer 12 side and the lead-free glass layer 31 as shown in FIG. And an Ag layer 32 formed thereon. In the lead-free glass layer 31, fine conductive particles 33 having a particle size of about several nanometers are dispersed. In the present embodiment, the conductive particles 33 are crystalline particles containing at least one of Ag and Al. The conductive particles 33 in the lead-free glass layer 31 are observed by using, for example, a transmission electron microscope (TEM).

  The electric resistance value P in the thickness direction of the conductive bonding layer 30 is set to 0.5Ω or less, more preferably 0.2Ω or less. Here, the electric resistance value P in the thickness direction of the conductive bonding layer 30 is an electric resistance between the upper surface of the conductive bonding layer 30 and the upper surface of the circuit layer 12. This is because the electrical resistance of 4N aluminum constituting the circuit layer 12 is much smaller than the electrical resistance in the thickness direction of the conductive bonding layer 30. When measuring the electrical resistance, as shown in FIGS. 5 and 6, the upper surface center point of the conductive bonding layer 30 and the distance from the upper surface center point of the conductive bonding layer 30 to the end of the conductive bonding layer 30. The electrical resistance between a point on the circuit layer 12 that is separated from the end of the conductive bonding layer 30 by H by H was measured.

  In the present embodiment, since the circuit layer 12 is made of aluminum having a purity of 99.99%, the aluminum oxide film 12A naturally generated in the atmosphere is formed on the surface of the circuit layer 12 (the upper surface in FIG. 4). However, the aluminum oxide film 12A is removed from the portion where the conductive bonding layer 30 is formed, and the conductive bonding layer 30 is formed directly on the circuit layer 12. That is, the aluminum constituting the circuit layer 12 and the lead-free glass layer 31 are directly joined.

  Here, the thickness to of the aluminum oxide film 12A that naturally occurs on the circuit layer 12 is set to 4 nm ≦ to ≦ 6 nm. Further, in the present embodiment, the thickness tg of the lead-free glass layer 31 is 0.01 μm ≦ tg ≦ 5 μm, the thickness ta of the Ag layer 32 is 1 μm ≦ ta ≦ 100 μm, and the total thickness tg + ta of the conductive bonding layer 30 is 1. .01 μm ≦ tg + ta ≦ 105 μm.

Next, the manufacturing method of the power module 1 using the electroconductive composition which is this embodiment is demonstrated with reference to the flowchart shown in FIG.
First, an aluminum plate to be the circuit layer 12 and an aluminum plate to be the metal layer 13 are prepared, and these aluminum plates are laminated on one surface and the other surface of the ceramic substrate 11 through brazing materials, respectively, and pressed. -The said aluminum plate and the ceramic substrate 11 are joined by cooling after a heating (circuit layer joining process S11). The brazing temperature is set to 640 ° C to 650 ° C.

  Next, the cooler 40 (top plate portion 41) is joined to the other surface side of the metal layer 13 via the buffer layer 15 via the brazing material (cooler joining step S12). Note that the brazing temperature of the cooler 40 is set to 590 ° C to 610 ° C.

  And the above-mentioned electroconductive composition is apply | coated to the surface of the circuit layer 12 (electroconductive composition application | coating process S13). In addition, when apply | coating a conductive composition, various means, such as a screen printing method, an offset printing method, and a photosensitive process, are employable. In this embodiment, the conductive composition was formed in a pattern by a screen printing method.

In a state where the conductive composition is applied to the surface of the circuit layer 12, the conductive composition is charged into the heating furnace and the conductive composition is fired (firing step S14). The firing temperature at this time is set to 350 ° C. to 645 ° C.
By this firing step S <b> 14, the conductive bonding layer 30 including the lead-free glass layer 31 and the Ag layer 32 is formed. At this time, the lead-free glass layer 31 melts and removes the aluminum oxide film 12 </ b> A naturally generated on the surface of the circuit layer 12, and the lead-free glass layer 31 is formed directly on the circuit layer 12. In addition, fine conductive particles 33 are dispersed inside the lead-free glass layer 31. The conductive particles 33 are crystalline particles containing at least one of Ag and Al, and are presumed to have precipitated in the lead-free glass layer 31 during firing.

  Thus, the power module substrate 10 having the conductive bonding layer 30 formed on the surface of the circuit layer 12 and the power module substrate with a cooler are produced.

Then, the semiconductor chip 3 is placed on the surface of the conductive bonding layer 30 via a solder material, and soldered in a reduction furnace (solder bonding step S15). At this time, a part or all of the Ag layer 32 of the conductive bonding layer 30 is melted in the solder layer 2 formed of the solder material.
As a result, the power module 1 in which the semiconductor chip 3 is bonded onto the circuit layer 12 via the solder layer 2 is produced.

  According to the conductive composition of the present embodiment configured as described above, a lead-free glass powder containing ZnO and a silver powder excellent in conductivity are provided, and the lead-free glass layer 31 is obtained by firing. The lead-free glass layer 31 is allowed to react with an aluminum oxide film naturally generated on the surface of the circuit layer 12 made of aluminum having a purity of 99.99% or more. The lead-free glass layer 31 can be formed so as to be directly bonded to the aluminum constituting the circuit layer 12.

Since the fine conductive particles 33 having a particle size of about several nanometers are dispersed inside the lead-free glass layer 31, the lead-free glass layer 31 can also have conductivity. Specifically, the electrical resistance value P in the thickness direction of the conductive bonding layer 30 including the lead-free glass layer 31 is set to 0.5Ω or less, more preferably 0.2Ω or less.
Therefore, it is possible to reliably conduct electricity between the semiconductor chip 3 and the circuit layer 12 via the conductive bonding layer 30 and the solder layer 2, and the highly reliable power module 1 can be configured. That is, the conductive composition according to the present embodiment can be used as a solder underlayer forming paste.

Moreover, since the glass transition temperature of the lead-free glass powder contained in the conductive composition is 300 ° C. or more and 450 ° C. or less, the lead-free glass powder can react well with the substrate, and sufficient adhesion can be obtained. The conductive bonding layer 30 can be reliably formed even when fired at a relatively low temperature.
Furthermore, since the softening temperature of the lead-free glass powder contained in the conductive composition is set to 600 ° C. or lower, the conductive composition can be fired at a relatively low temperature. Specifically, the firing temperature can be set to 350 ° C. or higher and 645 ° C. or lower. Therefore, it is possible to prevent troubles such as deterioration of the circuit layer 12 and reduction in bonding strength between the circuit layer 12 and the ceramic substrate 11 due to firing of the conductive composition, and the high-quality power module substrate 10 and The power module 1 can be produced.
Moreover, since the crystallization temperature of the lead-free glass powder is set to 450 ° C. or higher, the fluidity inside the conductive composition is ensured, and the adhesion can be improved by the interface reaction with the circuit layer 12.

  In addition, the silver powder contained in the conductive composition has a particle size of 0.05 μm or more and 1.0 μm or less. In this embodiment, a silver powder having an average particle size of 0.8 μm is used. When the conductive composition is applied on the circuit layer 12, the silver powder is uniformly dispersed, so that a uniform conductive bonding layer 30 can be formed, and the solder layer 2 and the circuit layer 12 can be securely connected. It can be made conductive.

  Further, since the viscosity of the conductive composition is set to 10 Pa · s or more and 500 Pa · s or less, more preferably 50 Pa · s or more and 300 Pa · s or less, and the paste is in the form of a paste, the conductive composition is formed on the surface of the circuit layer 12. In the conductive composition application step S13 for applying an object, a screen printing method or the like can be applied, and the conductive bonding layer 30 can be selectively formed only on the portion where the semiconductor chip 3 is disposed. Therefore, it becomes possible to reduce the usage-amount of an electroconductive composition, and the manufacturing cost of this board | substrate 10 for power modules and the power module 1 can be reduced significantly.

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.
For example, the thickness ratio between the lead-free glass layer and the Ag layer in the formed conductive bonding layer is not limited to that illustrated in FIG.

Moreover, about the raw material and compounding quantity of an electroconductive composition, it is not limited to what was described in embodiment, You may use another lead-free glass powder, resin, a solvent, and a dispersing agent. The softening temperature should just be below melting | fusing point of aluminum, More preferably, it is 600 degrees C or less.
As the resin, an acrylic resin, an alkyd resin, or the like may be used. Further, α-terpineol, butyl carbitol acetate or the like may be used as the solvent.

  Further, the metal plate constituting the circuit layer and the metal layer has been described as a rolled plate of pure aluminum having a purity of 99.99%, but is not limited thereto, and aluminum having a purity of 99% (2N aluminum) It may be sufficient if it is comprised with aluminum or aluminum alloy.

  Moreover, while brazing the aluminum board used as a circuit layer to a ceramic substrate, and brazing a cooler, it demonstrated as what forms a conductive joining layer on a circuit layer, but it is not limited to this, The conductive bonding layer may be formed before brazing the aluminum plate to the ceramic substrate or before brazing the cooler.

Hereinafter, the results of measuring the electrical resistance value P in the thickness direction of the conductive bonding layer 30 in the power module substrate 10 described in the above embodiment will be described.
The thickness ta of the Ag layer 32 of the conductive bonding layer 30 and the thickness tg of the lead-free glass layer 31 are changed, and the weight ratio A / G between the weight A of the Ag powder and the weight G of the lead-free glass powder is changed. Invention Examples 1 to 5 were produced. As lead-free glass powder of this time, the _Bi 2 _{O 3} 90.6 wt%, the ZnO 2.6 _wt%, the B 2 _{O 3} 6.8 wt%, with lead-free glass powder containing. Further, ethyl cellulose was used as the resin, and diethylene glycol dibutyl ether was used as the solvent. Furthermore, a dicarboxylic acid-based dispersant was added.
In addition, the conductive bonding layer 30 was formed in a square shape having a side length of 15 mm as viewed from above.
The samples of Invention Examples 1 to 5 thus obtained were measured in the thickness direction of the conductive bonding layer 30 using a tester (manufactured by KEITHLEY: 2010 MULTITIMER) by the method described in FIGS. 5 and 6. The electrical resistance value P was measured. The measurement results are shown in Table 1.

  In any of the inventive examples 1 to 5, it was confirmed that the electric resistance value P in the thickness direction of the conductive bonding layer 30 was 0.5Ω or less. Moreover, it was confirmed that the electrical resistance value P in the thickness direction of the conductive bonding layer 30 is reduced by forming the lead-free glass powder in a small ratio and forming the lead-free glass layer 31 with a small thickness tg.

Next, the composition of the lead-free glass powder was changed to adjust the softening temperature, crystallization temperature, and glass transition temperature of the lead-free glass powder. These lead-free glass powders were used to form a conductive composition.
The weight ratio A / G between the weight A of the Ag powder and the weight G of the lead-free glass powder was 97.5 / 2.5. Moreover, Ag powder, lead-free glass powder, resin (ethyl cellulose), and a solvent (diethylene glycol dibutyl ether) were mixed. In this example, the addition amount of the powder component, the resin and the solvent is adjusted so that the content of the powder component composed of Ag powder and lead-free glass powder is 85 mass%, the resin is 3 mass%, and the solvent is 12 mass%. did.

Here, the softening temperature, glass transition temperature, and crystallization temperature of the above lead-free glass powder were measured. The measurement results are shown in Tables 2 and 3.
The softening temperature was the temperature of the yield point (deflection point) by performing thermomechanical analysis (TMA) using Thermoflex manufactured by Rigaku Corporation.
The glass transition temperature and the crystallization temperature were measured by performing differential thermal analysis (TG-DTA) using TG-DTA2000S manufactured by BRUKER AXS. The lead-free glass powder is heated at 10 ° C./min, the temperature of the endothermic peak appearing in the calorie change curve is defined as the glass transition temperature, and the temperature of the exothermic peak generated in the temperature region higher than the glass transition temperature is defined as the crystallization temperature. .

  And the conductive joining layer 30 of the board | substrate 10 for power modules disclosed by the above-mentioned embodiment was formed using this electrically conductive composition. In addition, in conductive composition application | coating process S13 which apply | coats a conductive composition to the surface of the circuit layer 12, the application | coating thickness of the conductive composition was 10 micrometers. In the firing step S14, the firing temperature was 575 ° C. and the firing time was 10 minutes. As a result, the conductive bonding layer 30 was formed in which the thickness ta of the Ag layer 32 was about 8 μm and the thickness tg of the lead-free glass layer 31 was about 1 μm.

Then, the semiconductor chip 3 was placed on the surface of the conductive bonding layer 30 via a solder material (Sn—Ag—Cu lead-free solder), and soldered in a reduction furnace.
In this embodiment, the ceramic substrate 11 is 30 mm × 20 mm, the circuit layer 12 is 13 mm × 10 mm, and the semiconductor chip 3 is 12.5 mm × 9.5 mm.

The joining reliability of the power module 1 obtained in this way was evaluated. As an evaluation of the bonding reliability, the bonding rates after 2000 times of the thermal cycle (−45 ° C. to 125 ° C.) were compared. The results are shown in Tables 2 and 3.
In addition, the joining rate was computed with the following formula | equation. Here, the initial bonding area is an area to be bonded before bonding.
Bonding rate = (initial bonding area-peeling area) / initial bonding area When the bonding rate is greater than 85% and 100% or less, “excellent”
"Good" with a joining rate greater than 75% and less than 85%
Bonding rate is greater than 50% and 75% or less
A bonding rate of 50% or less was regarded as “impossible”.

About Examples 1-8, the joining rate after repeating a thermal cycle 2000 times is favorable, and it is confirmed that sufficient joining strength is obtained.
In Samples A to E, although the practicability is satisfactory in the joining rate after 2000 cycles of the cooling and heating cycle, the joining rate is lower than in Examples 1 to 8. In particular, in the samples D and E in which ZnO is not contained in the lead-free glass powder, the crystallization temperatures are lowered to 330 ° C. and 403 ° C., and the joining rate is greatly reduced.

1 Power Module 2 Solder Layer 3 Semiconductor Chip (Semiconductor Element)
DESCRIPTION OF SYMBOLS 10 Power module substrate 12 Circuit layer 12A Aluminum oxide film 30 Conductive joining layer 31 Lead-free glass layer 32 Ag layer 33 Conductive particles

Claims (5)

A conductive composition that is disposed on a circuit layer made of aluminum or an aluminum alloy on which a semiconductor element is mounted, and forms a conductive bonding layer that is electrically connected to the circuit layer by firing,
Containing silver powder, lead-free glass powder containing ZnO, resin, and solvent,
The content of the powder component consisting of the silver powder and the lead-free glass powder is 60 mass% or more and 90 mass% or less,
The ratio A / G of the weight A of the silver powder and the weight G of the lead-free glass powder in the powder component is set within a range of 80/20 to 99/1,
The conductive bonding layer generated by firing includes a lead-free glass layer formed by softening the lead-free glass powder, and an Ag layer in which silver powder is sintered on the lead-free glass layer. A conductive composition in which conductive particles are dispersed inside the lead-free glass layer.   The conductive composition according to claim 1, wherein the lead-free glass powder has a glass transition temperature of 300 ° C. or higher and 450 ° C. or lower.   The conductive composition according to claim 1 or 2, wherein the lead-free glass powder has a softening temperature of 600 ° C or lower and a crystallization temperature of 450 ° C or higher. The glass composition of the lead-free glass powder is
Bi ₂ O ₃ : 68 mass% or more and 93 mass% or less,
ZnO: 1% by mass or more and 20% by mass or less,
B ₂ O ₃ : 1% by mass or more and 11% by mass or less,
SiO ₂ : 5% by mass or less,
Al ₂ O ₃ : 5% by mass or less,
Fe ₂ O ₃ : 5% by mass or less,
CuO: 5 mass% or less,
CeO ₂ : 5% by mass or less,
ZrO ₂ : 5% by mass or less,
Alkali metal oxide: 2% by mass or less,
Alkaline earth metal oxide: 7% by mass or less,
The electrically conductive composition according to any one of claims 1 to 3, wherein   The conductive composition according to any one of claims 1 to 4, wherein a particle size of the silver powder is 0.05 µm or more and 1.0 µm or less.

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