Plating method for silver sintering bonding, plating film for silver sintering bonding, substrate for power module, semiconductor element, and semiconductor device

Abstract

To provide: a plating method for silver sintering bonding which can secure adhesion between a nickel plating film and a silver plating film at low cost and obtains excellent heat resistance; plating films for silver sintering bonding; a substrate for power module which comprises the plating films; a semiconductor element which comprises the plating films; and a semiconductor device which comprises the substrate for power module.SOLUTION: A plating method for silver sintering bonding includes: a barrier layer forming process of forming an electroless nickel plating film on a plated surface; an intermediate layer forming process of forming an electroless strike silver plating film on the electroless nickel plating film; and an outermost surface layer forming process of forming an electroless silver plating film on an outermost surface layer on the plated surface.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a plating method for silver sintering bonding, a plating film for silver sintering bonding, a substrate for a power module, a semiconductor element, and a semiconductor device.

Background Art

[0002] Conventionally, Si (silicon) semiconductors have been used as power semiconductors. In recent years, the use of SiC (silicon carbide) semiconductors and GaN (gallium nitride) semiconductors, which can operate at higher temperatures than Si semiconductors, has been increasing. Therefore, the operating temperature of the semiconductor is expected to increase to 200°C or higher, and the heat resistance of the die bond portion that joins the semiconductor element to the substrate is also becoming necessary. One of the bonding technologies attracting attention is silver sintering bonding. On the other hand, in order to perform silver sintering bonding, surface treatment of members to be joined such as the substrate is required, and the film formed by the surface treatment also requires heat resistance.

[0003] For example, Patent Document 1 discloses that the heat resistance reliability at the die attach portion, which is the joint portion between the semiconductor element and the support, is improved by a film composed of a nickel plating film as an underlayer and a specific alloy plating film formed on the nickel plating film.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The substrate is provided with a circuit formed of copper or aluminum on a base material. When silver sintering bonding is used for bonding a semiconductor element to the circuit, in order to ensure good bonding strength, a silver plating film may be used on the outermost layer of the circuit that will be in contact with the silver sintering layer. Although a good initial bonding strength can be obtained with the silver plating film, the silver plating film easily allows oxygen to pass through, and particularly under high-temperature conditions, it may cause oxidation of the underlying metal such as copper or aluminum, leading to a decrease in bonding strength and tending to be inferior in heat resistance. To solve this problem, it is necessary to further provide a barrier layer for the oxidation of the underlying metal.

[0006] As a result of intensive studies by the present inventors, it has been found that a nickel plating film can be used as a barrier layer to prevent oxidation of the underlying metal, but it has newly been found that sufficient adhesion between the nickel plating film and the silver plating film cannot be ensured. Furthermore, as a result of intensive studies by the present inventors, it has been found that by using a palladium (Pd) plating film, a platinum (Pt) plating film, or the like as an adhesion layer between the nickel plating film and the silver plating film, the adhesion between the nickel plating film and the silver plating film can be ensured, but it has also been found that there is a cost problem because palladium and platinum are expensive.

[0007] The present invention solves the above-mentioned problems newly found by the present inventors, can inexpensively ensure the adhesion between a nickel plating film and a silver plating film, and has good heat resistance, and provides a plating method for silver sintering bonding, a plating film for silver sintering bonding, a substrate for a power module provided with the plating film, a semiconductor element provided with the plating film, and a semiconductor device provided with the substrate for the power module.

Means for Solving the Problems

[0008] As a result of intensive studies, the present inventors have found that by using a strike silver (preferably electroless strike silver) (St-Ag) plating film as an adhesion layer between the nickel plating film and the silver plating film, the adhesion between the nickel plating film and the silver plating film can be ensured inexpensively, and good heat resistance can also be obtained, thus completing the present invention. That is, the present invention relates to a plating method for silver sintering bonding, including a barrier layer forming step of forming an electroless nickel plating film on the upper side of the surface to be plated, an intermediate layer forming step of forming an electroless strike silver plating film on the upper side of the electroless nickel plating film, and a top layer forming step of forming an electroless silver plating film on the outermost layer of the surface to be plated.

[0009] It is preferable that the film thickness of the electroless strike silver plating film is 0.010 to 0.200 μm.

[0010] It is preferable that the intermediate layer forming step is a step of forming an electroless strike silver plating film on the upper side of the electroless nickel plating film using a substitution-type electroless silver plating bath with a pH of 5.0 to 9.0.

[0011] It is preferable that the substitution-type electroless silver plating bath contains at least one complexing agent selected from the group consisting of amide compounds and imide compounds.

[0012] It is preferable that the substitution-type electroless silver plating bath contains at least two complexing agents selected from the group consisting of amide compounds and imide compounds.

[0013] It is preferable that the film thickness of the electroless silver plating film is 0.2 μm or more.

[0014] It is preferable that the top layer forming step is a step of forming an electroless silver plating film on the outermost layer of the surface to be plated using a reducing-type electroless silver plating bath.

[0015] In the plating method for silver sintering bonding, it is preferable that the total film thickness of the plating film is 15 μm or less.

[0016] The present invention also relates to a plating film (plating film laminate) for silver sintering bonding having an electroless nickel plating film, an electroless strike silver plating film on the upper side of the electroless nickel plating film, and an electroless silver plating film on the outermost layer.

[0017] It is preferable that the thickness of the electroless strike silver plating film is 0.010 to 0.200 μm.

[0018] It is preferable that the electroless strike silver plating film is a film formed on the upper side of the electroless nickel plating film using a substitution-type electroless silver plating bath having a pH of 5.0 to 9.0.

[0019] It is preferable that the substitution-type electroless silver plating bath contains at least one complexing agent selected from the group consisting of amide compounds and imide compounds.

[0020] It is preferable that the substitution-type electroless silver plating bath contains at least two complexing agents selected from the group consisting of amide compounds and imide compounds.

[0021] It is preferable that the thickness of the electroless silver plating film is 0.2 μm or more.

[0022] It is preferable that the electroless silver plating film is a film formed on the outermost surface of the surface to be plated using a reducing-type electroless silver plating bath.

[0023] In the plating film, it is preferable that the total film thickness of the plating film is 15 μm or less.

[0024] The present invention also relates to a substrate for a power module including a substrate, a circuit formed on the substrate, and the plating film formed on the surface of the circuit.

[0025] It is preferable that the circuit is a circuit made of copper and / or aluminum.

[0026] It is preferable that the surface of the plating film is a silver sintered joint surface.

[0027] The present invention also relates to a semiconductor device having the plating film on its surface.

[0028] The present invention also relates to a semiconductor device including the substrate for the power module and / or a semiconductor element having the plating film on its surface.

[0029] It is preferable that, in the semiconductor device, the surface of the substrate for the power module and / or the plating film of the semiconductor element having the plating film on its surface is a silver sintering joint surface.

[0030] The semiconductor device also preferably includes the substrate for the power module and a semiconductor element, and the surface of the plating film of the substrate for the power module and the semiconductor element are silver sintering joined. In the semiconductor device, it is preferable that the semiconductor element is a semiconductor element having the plating film on its surface.

[0031] The semiconductor device also includes a substrate for the power module and a semiconductor element having the plating film on its surface. Preferably, the semiconductor device is such that the surface of the plating film of the semiconductor element and the substrate for the power module are silver sintering joined.

Advantages of the Invention

[0032] According to the present invention, since the plating method for silver sintering joint includes a barrier layer forming step of forming an electroless nickel plating film on the upper side of the surface to be plated, an intermediate layer forming step of forming an electroless strike silver plating film on the upper side of the electroless nickel plating film, and a top layer forming step of forming an electroless silver plating film on the outermost layer of the surface to be plated, the adhesion between the nickel plating film and the silver plating film can be ensured at low cost and has good heat resistance.

[0033] Further, according to the present invention, since the plating film (plating film laminate) for silver sintering joint has an electroless nickel plating film, an electroless strike silver plating film on the upper side of the electroless nickel plating film, and an electroless silver plating film on the outermost layer, the adhesion between the nickel plating film and the silver plating film can be ensured at low cost and has good heat resistance.

[0034] Further, according to the present invention, since it is a substrate for a power module including a substrate, a circuit formed on the substrate, and a specific plating film (plating film laminate) formed on the surface of the circuit, the adhesion between the nickel plating film and the silver plating film can be ensured at low cost and has good heat resistance.

[0035] Further, according to the present invention, since it is a semiconductor element having a specific plating film (plating film laminate) on the surface, the adhesion between the nickel plating film and the silver plating film can be ensured at low cost, has good heat resistance, and is a highly reliable semiconductor element.

[0036] Further, according to the present invention, since it is a semiconductor device including a specific substrate for a power module and / or a specific semiconductor element, the adhesion between the nickel plating film and the silver plating film can be ensured at low cost, has good heat resistance, and is a highly reliable semiconductor device.

Brief Description of the Drawings

[0037]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0038] The plating method for silver sintering bonding of the present invention includes a barrier layer forming step of forming an electroless nickel plating film on the upper side of the surface to be plated, an intermediate layer forming step of forming an electroless strike silver plating film on the upper side of the electroless nickel plating film, and a outermost layer forming step of forming an electroless silver plating film on the outermost surface of the surface to be plated. The plating film (plating film laminate) for silver sintering bonding of the present invention has an electroless nickel plating film, an electroless strike silver plating film on the upper side of the electroless nickel plating film, and an electroless silver plating film on the outermost layer. Thereby, the adhesion between the nickel plating film and the silver plating film can be ensured at low cost and has good heat resistance.

[0039] The reason why the above-described effects can be obtained with the plating method and the plating film (plating film laminate) is presumed as follows. As described above, since the electroless nickel plating film functions sufficiently as a barrier layer against oxygen, good heat resistance can be obtained. Furthermore, by providing a silver plating film on the outermost layer, sufficient initial bonding strength with the silver sintering material can also be obtained. And, by using a strike silver (preferably electroless strike silver) (St-Ag) plating film as an adhesion layer between the nickel plating film and the silver plating film, the adhesion between the nickel plating film and the silver plating film can be ensured at low cost. As described above, due to the synergistic effect of the nickel plating film (preferably electroless nickel plating film), the strike silver plating film (preferably electroless strike silver plating film), and the silver plating film (preferably electroless silver plating film), the adhesion between the nickel plating film and the silver plating film can be ensured at low cost and has good heat resistance. Therefore, since the plating method and the plating film laminate have a silver plating film on the outermost layer, they have good initial bonding strength, and furthermore, the adhesion between the nickel plating film and the silver plating film can be ensured at low cost and has good heat resistance, so they are suitably applicable to silver sintering bonding.

[0040] <Plating method> The plating method for silver sintering bonding of the present invention is as follows: A barrier layer forming step of forming an electroless nickel plating film on the upper side of the surface to be plated; An intermediate layer forming step of forming an electroless strike silver plating film on the upper side of the electroless nickel plating film; A outermost layer forming step of forming an electroless silver plating film on the outermost layer of the surface to be plated and includes.

[0041] In this specification, the surface to be plated means the surface on which the plating film is formed. For example, when forming a plating film on a circuit formed on a substrate, the surface to be plated is the circuit surface.

[0042] In this specification, the upper side of the surface to be plated is not particularly limited as long as it is located above the surface to be plated, and may be the surface of the surface to be plated, that is, the lowermost layer of the plating film, or a layer other than the lowermost layer of the plating film. Therefore, in this specification, forming an electroless nickel plating film on the upper side of the surface to be plated is not particularly limited as long as an electroless nickel plating film is formed on the upper side of the surface to be plated (however, excluding the outermost layer of the plating film). As the surface of the surface to be plated, that is, the lowermost layer of the plating film, not only the mode of forming an electroless nickel plating film, but also a layer other than the lowermost layer of the plating film (however, excluding the outermost layer of the plating film). For example, after forming one or more plating films on the surface of the surface to be plated, the mode of forming an electroless nickel plating film is also included. Also, in this specification, other similar expressions, for example, the upper side of the electroless nickel plating film also have the same meaning. Also, in this specification, the surface of the surface to be plated means the upper surface of the surface to be plated, and other similar expressions, for example, the surface of the electroless nickel plating film also have the same meaning, meaning the upper surface of the electroless nickel plating film.

[0043] In this specification, forming an electroless silver plating film on the outermost layer of the surface to be plated means forming an electroless silver plating film as the outermost layer of the plating film (plating film laminate) provided on the surface to be plated.

[0044] In this specification, the electroless strike silver plating film means an electroless silver plating film with a thin film thickness.

[0045] <<Barrier layer formation step>> In the barrier layer formation step, an electroless nickel plating film is formed on the upper side of the surface to be plated. Thereby, an electroless nickel plating film that sufficiently functions as a barrier layer against oxygen can be formed, and good heat resistance can be obtained.

[0046] As the barrier layer formation step, it is preferable that an electroless nickel plating film is formed on the surface of the surface to be plated. Thereby, better heat resistance can be obtained and it is also advantageous in terms of cost.

[0047] It is important to form an electroless nickel plating film as the barrier layer, and the method for forming the plating film is not particularly limited. The method for forming the plating film is not particularly limited, and examples include electroless plating, electroplating, fusion plating, physical vapor deposition (PVD), chemical vapor deposition (CVD), etc. These may be used alone or in combination of two or more. Among them, electroless plating and electroplating are preferable, and electroless plating is more preferable, due to reasons such as low cost, simplicity of equipment, and productivity.

[0048] The method of electroless plating is not particularly limited, and it is only necessary to deposit the metal in the plating bath with a reducing agent. A person skilled in the art can appropriately implement it according to a known method.

[0049] The reducing agent is not particularly limited as long as it has the ability to reduce the water-soluble metal compound in the plating bath to metal and is a water-soluble compound. For example, hydrazine derivatives, formaldehyde compounds, hydroxylamines, saccharides, phosphorous acid, formic acid, boron hydride compounds, hypophosphites, dimethylamine borane, ascorbic acid, etc. can be used. These may be used alone or in combination of two or more.

[0050] The thickness of the electroless nickel plating film formed by the barrier layer forming step is preferably 15 μm or less, more preferably 10 μm or less, still more preferably 7 μm or less, and preferably 1 μm or more, more preferably 2 μm or more, still more preferably 3 μm or more. When within the above range, the effect tends to be more preferably obtained.

[0051] The electroless nickel plating film formed by the barrier layer forming step may be an alloy film containing other metals.

[0052] The other metals are not particularly limited, and examples include transition metal elements of Group 5 or Group 6 of the periodic table such as tungsten, molybdenum, niobium, tantalum, and vanadium. Further, as the other metals, phosphorus, boron derived from the reducing agent, and carbon, nitrogen, oxygen, sulfur, etc. derived from the additive may be included. The other metals may be used alone or in combination of two or more. Among them, phosphorus and boron are preferable because better heat resistance can be obtained.

[0053] The content of other metals (preferably phosphorus, boron) in the electroless nickel plating film is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, still more preferably 1% by mass or more, and preferably 15% by mass or less, more preferably 13% by mass or less, still more preferably 11% by mass or less. When within the above range, the effect tends to be more preferably obtained. Here, when containing a plurality of types of other metals, the content means the total content.

[0054] The content of nickel in the electroless nickel plating film is preferably 85% by mass or more, more preferably 87% by mass or more, still more preferably 89% by mass or more, and preferably 99.9% by mass or less, more preferably 99.5% by mass or less, still more preferably 99% by mass or less. When within the above range, the effect tends to be more preferably obtained.

[0055] In this specification, the content rate of each metal in the plating film is measured by an inductively coupled plasma (ICP) emission spectrometer, specifically, by the method described in the examples.

[0056] <<<Intermediate layer formation process>>> In the intermediate layer formation process, an electroless strike silver plating film is formed on the upper side of the electroless nickel plating film. By forming a strike silver (preferably electroless strike silver) (St-Ag) plating film as an adhesion layer between the nickel plating film and the silver plating film, the adhesion between the nickel plating film and the silver plating film can be ensured at low cost.

[0057] As the intermediate layer formation process, it is preferably a process of forming an electroless strike silver plating film on the surface of the electroless nickel plating film. Thereby, better adhesion between the nickel plating film and the silver plating film can be obtained, and it also tends to be advantageous in terms of cost.

[0058] It is important to form an electroless strike silver plating film on the upper side of the electroless nickel plating film, and the method for forming the plating film is not particularly limited. The method for forming the plating film is the same as that in the barrier layer formation process. Among them, it is preferable to use a substitution-type electroless silver plating bath because an electroless strike silver plating film can be preferably formed on the surface of the electroless nickel plating film, and it is more preferable to use a substitution-type electroless silver plating bath with a pH of 5.0 to 9.0. That is, it is preferably that the intermediate layer formation process is a process of forming an electroless strike silver plating film on the upper side (preferably the surface) of the electroless nickel plating film using a substitution-type electroless silver plating bath, and it is more preferable that the intermediate layer formation process is a process of forming an electroless strike silver plating film on the upper side (preferably the surface) of the electroless nickel plating film using a substitution-type electroless silver plating bath with a pH of 5.0 to 9.0.

[0059] The pH of the substitution-type electroless silver plating bath is preferably from 5.0 to 9.0, more preferably from 5.5 to 8.5, and still more preferably from 6.0 to 8.0. Thereby, better adhesion between the nickel plating film and the silver plating film can be ensured at low cost, and there is a tendency to have better heat resistance. In addition, in this specification, the pH of the plating bath is a value measured at 25°C.

[0060] The substitution-type electroless silver plating bath contains a silver compound. The silver compound is not particularly limited as long as it is a water-soluble silver compound. Specific examples thereof include, for example, silver nitrate, silver oxide, silver sulfate, silver chloride, silver methanesulfonate, etc. These may be used alone or in combination of two or more. Among them, silver nitrate and silver oxide are preferred, and silver nitrate is more preferred.

[0061] The substitution-type electroless silver plating bath preferably contains the silver compound in a concentration of 0.1 to 3.0 g / L as silver (metallic silver (Ag)), and more preferably 0.5 to 1.5 g / L. If it is less than 0.1 g / L, sufficient adhesion tends not to be ensured. If it exceeds 3.0 g / L, there is a risk of causing uneven appearance and deterioration of the film thickness distribution, and sufficient adhesion tends not to be ensured. In addition, in this specification, the metal concentration such as silver (metallic silver (Ag)) in the plating bath is measured by ICP (manufactured by Horiba, Ltd.).

[0062] The substitution-type electroless silver plating bath preferably contains a complexing agent. The complexing agent is not particularly limited as long as it is a compound capable of stably dissolving silver ions. Specific examples thereof include, for example, amide compounds, imide compounds, thiosulfate compounds, sulfite compounds, sulfur-containing compounds (sulfur-containing compounds other than thiosulfate compounds and sulfite compounds), nitrogen-containing compounds (nitrogen-containing compounds other than amide compounds and imide compounds), and the like. These may be used alone or in combination of two or more. Among them, amide compounds and imide compounds are preferable, and it is more preferable to use in combination two or more compounds selected from the group consisting of amide compounds and imide compounds. That is, it is preferable that the substitution-type electroless silver plating bath contains at least one complexing agent selected from the group consisting of amide compounds and imide compounds, and it is more preferable that the substitution-type electroless silver plating bath contains at least two complexing agents selected from the group consisting of amide compounds and imide compounds. By the substitution-type electroless silver plating bath containing at least two compounds selected from the group consisting of amide compounds and imide compounds, there is a tendency to obtain better adhesion between the nickel plating film and the silver plating film.

[0063] The amide compound is not particularly limited. For example, cyclic amide compounds such as benzamide, N-methylpyrrolidone, N-ethylpyrrolidone, N-vinylpyrrolidone, pyrrolidone, N-butylpyrrolidone, 5-methylpyrrolidone, N-methylpiperidinone, N-ethylpiperidinone, and N-butylpiperidinone; chain amide compounds such as acetamide, formamide, N,N-dimethylformamide, N-methyl-N-phenylformamide, N,N-diphenylformamide, N,N-dimethylacetamide, N-methyl-N-phenylacetamide, N,N-diphenylacetamide, N,N-diethylformamide, N-ethyl-N-phenylformamide, N,N-diethylacetamide, N-ethyl-N-phenylacetamide, and oxamic acid can be mentioned. These may be used alone or in combination of two or more. Among them, chain amide compounds are preferable, acetamide and formamide are more preferable, and acetamide is even more preferable.

[0064] The imide compound is not particularly limited. For example, cyclic imide compounds such as hydantoin, 5,5-dimethylhydantoin, 1-methylhydantoin, 1,3-dimethylhydantoin, glutarimide, and succinimide; chain imide compounds such as bis(fluorosulfonyl)imide salt, bis(trifluoromethanesulfonyl)imide salt, bis(pentafluoroethanesulfonyl)imide salt, (trifluoromethanesulfonyl)(pentafluoroethanesulfonyl)imide salt, (trifluoromethanesulfonyl)(heptafluoropropanesulfonyl)imide salt, (trifluoromethanesulfonyl)(nonafluorobutanesulfonyl)imide salt, etc. These may be used alone or in combination of two or more. Among them, cyclic imide compounds are preferred, and hydantoin, 5,5-dimethylhydantoin, 1-methylhydantoin, succinimide, 1,3-dimethylhydantoin, and glutarimide are more preferred, and hydantoin, 5,5-dimethylhydantoin, 1-methylhydantoin, and succinimide are even more preferred.

[0065] As the complexing agent, as described above, it preferably contains at least two complexing agents selected from the group consisting of amide compounds and imide compounds. More preferably, it contains two complexing agents selected from the group consisting of amide compounds and imide compounds. Even more preferably, it is a combination of acetamide and hydantoin, a combination of succinimide and hydantoin, a combination of succinimide and 5,5-dimethylhydantoin, or a combination of succinimide and 1-methylhydantoin.

[0066] The substitution-type electroless silver plating bath preferably contains 1 to 50 g / L of the complexing agent, more preferably 5 to 45 g / L, even more preferably 10 to 40 g / L, and particularly preferably 20 to 40 g / L. If it is less than 1 g / L, sufficient adhesion cannot be ensured, and Ag turbidity tends to occur. If it exceeds 50 g / L, sufficient adhesion cannot be ensured, and it is difficult to dissolve, which tends to be disadvantageous in terms of cost. Here, when containing a plurality of types of complexing agents, the above concentration means the total concentration, and the same applies to the concentrations of other components.

[0067] The displacement electroless silver plating bath preferably contains a chelating agent. As the chelating agent increases the base metal (for example, nickel) dissolved in the plating bath due to the progress of the substitution reaction, it is not particularly limited as long as it is a compound capable of forming a complex with this base metal (for example, nickel) and stably dissolving base metal ions (for example, nickel ions). Specific examples thereof include, for example, ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid, citric acid, ethylenediaminetetramethylenephosphonic acid (EDTMP), hydroxyethylethylenediaminetriacetic acid (HEDTA), and the like. These may be used alone or in combination of two or more. Among them, EDTA and HEDTA are preferable, and EDTA is more preferable.

[0068] The displacement electroless silver plating bath preferably contains 1 to 50 g / L of a chelating agent, more preferably 3 to 40 g / L, still more preferably 5 to 20 g / L, and particularly preferably 5 to 15 g / L. If it is less than 1 g / L, sufficient adhesion tends not to be ensured. If it exceeds 50 g / L, sufficient adhesion cannot be ensured, and it also tends to be difficult to dissolve, which is disadvantageous in terms of cost.

[0069] The displacement electroless silver plating bath may contain a buffering agent in order to enhance the pH buffering property. The buffering agent is not particularly limited as long as it has buffering properties, and examples thereof include disodium phosphate, imidazole, glycine, citric acid, sodium aspartate, tripolyphosphoric acid, and the like. These may be used alone or in combination of two or more.

[0070] The displacement electroless silver plating bath preferably contains 1 to 50 g / L of a buffering agent, more preferably 3 to 40 g / L, still more preferably 5 to 20 g / L, and particularly preferably 5 to 15 g / L. If it is less than 1 g / L, the pH fluctuation is large and the adhesion tends to vary. If it exceeds 50 g / L, it tends to be difficult to dissolve, which is disadvantageous in terms of cost.

[0071] The pH of the substitution-type electroless silver plating bath can also be adjusted by selecting the types of various components to be compounded. Further, an alkali component and an acid component may be added as necessary. The alkali component is not particularly limited, and examples thereof include sodium hydroxide and ammonium. The acid component is not particularly limited, and examples thereof include sulfuric acid and phosphoric acid. These alkali components and acid components may be used alone or in combination of two or more.

[0072] The substitution-type electroless silver plating bath may contain components commonly used in plating baths, such as surfactants and brighteners, together with the above components. Further, it may contain water-soluble salts of metals other than the above, such as iron, copper, zinc, nickel, palladium, lead, bismuth, and thallium. These may be used alone or in combination of two or more.

[0073] The substitution-type electroless silver plating bath can be suitably used as a metal substitution treatment liquid for forming an electroless strike silver plating film on the surface of an electroless nickel plating film.

[0074] In the intermediate layer forming step, for example, the surface of the electroless nickel plating film is brought into contact with the substitution-type electroless silver plating bath to form an electroless strike silver plating film on the surface of the electroless nickel plating film.

[0075] In the intermediate layer forming step, the temperature (bath temperature) of the substitution-type electroless silver plating bath is not particularly limited, but is preferably 25 to 80°C, more preferably 30 to 50°C, and still more preferably 35 to 45°C. The treatment time with the substitution-type electroless silver plating bath is also not particularly limited, but is preferably 1 to 10 minutes, more preferably 3 to 7 minutes.

[0076] On the upper side of the electroless nickel plating film, the film thickness of the electroless strike silver plating film formed by the intermediate layer forming process is preferably 0.200 μm or less, more preferably 0.150 μm or less, still more preferably 0.100 μm or less, particularly preferably 0.090 μm or less, most preferably 0.080 μm or less, even most preferably 0.070 μm or less, still most preferably 0.060 μm or less, and particularly most preferably 0.050 μm or less, and is preferably 0.010 μm or more, more preferably 0.020 μm or more, still more preferably 0.025 μm or more. When within the above range, there is a tendency to obtain better adhesion between the nickel plating film and the silver plating film.

[0077] The electroless strike silver plating film formed by the intermediate layer forming process may be an alloy film containing other metals. The other metals are the same as those of the electroless nickel plating film formed by the barrier layer forming process, including preferred embodiments.

[0078] The silver content in the electroless strike silver plating film is preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, particularly preferably 95% by mass or more, most preferably 98% by mass or more, and may be 100% by mass. When within the above range, there is a tendency to more suitably obtain the effect.

[0079] <<Outermost layer forming process>> In the outermost layer forming process, an electroless silver plating film is formed on the outermost layer of the surface to be plated. That is, in the outermost layer forming process, an electroless silver plating film is formed as the outermost layer of the plating film (plating film laminate) provided on the surface to be plated. Thereby, a silver plating film can be formed on the upper outermost layer of the plating film laminate, and sufficient initial bonding strength with the silver sintered material can be obtained.

[0080] In the outermost layer forming step, an electroless silver plating film is formed on the outermost layer of the surface to be plated. It is preferable to form the electroless silver plating film on the surface of the electroless strike silver plating film formed by the intermediate layer forming step. This can obtain better adhesion between the nickel plating film and the silver plating film and tends to be advantageous in terms of cost.

[0081] It is important to form a silver plating film as the outermost layer of the surface to be plated (the outermost layer of the plating film provided on the surface to be plated), and the method for forming the plating film is not particularly limited. The method for forming the plating film is the same as that of the barrier layer forming step including preferred embodiments. Among them, it is preferable to use a reducing type electroless silver plating bath because an electroless silver plating film with a sufficient film thickness can be obtained. That is, it is preferable that the outermost layer forming step is a step of forming an electroless silver plating film on the outermost layer of the surface to be plated using a reducing type electroless silver plating bath.

[0082] The reducing type electroless silver plating bath is the same as the displacement type electroless silver plating bath including preferred embodiments. On the other hand, different from the displacement type electroless silver plating bath that performs plating by a displacement reaction, the reducing type electroless silver plating bath performs plating by a reduction reaction. Therefore, the reducing type electroless silver plating bath contains a reducing agent.

[0083] The reducing agent has the ability to reduce the water-soluble metal compound in the plating bath to a metal and is not particularly limited as long as it is a water-soluble compound. Specific examples thereof include, for example, the reducing agents described in the barrier layer forming step. These may be used alone or in combination of two or more. Among them, hydrazine derivatives, hydroxylamines, dimethylamine borane, and boron hydride compounds are preferable.

[0084] As the reducing type electroless silver plating bath, for example, those with a silver concentration of 0.1 to 10 g / L, a pH of 2.0 to 12.0, and a reducing agent concentration of 0.1 to 20 g / L can be used.

[0085] The film thickness of the electroless silver plating film formed by the outermost layer forming step is preferably 3.0 μm or less, more preferably 2.5 μm or less, still more preferably 2.0 μm or less, particularly preferably 1.5 μm or less, and preferably 0.2 μm or more, more preferably 0.3 μm or more, still more preferably 0.4 μm or more. When it is within the above range, the effect tends to be more preferably obtained.

[0086] The silver plating film formed by the outermost layer forming step may be an alloy film containing other metals. Examples of the other metals include the same metals as described above, and they may be used alone or in combination of two or more.

[0087] The silver content in the silver plating film formed by the outermost layer forming step is preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, particularly preferably 95% by mass or more, most preferably 98% by mass or more, and may be 100% by mass. When it is within the above range, the effect is more preferably obtained, and the initial bonding strength also tends to be excellent.

[0088] <<Other steps>> The plating method for silver sintering bonding of the present invention may include other steps as long as it includes the barrier layer forming step, the intermediate layer forming step, and the outermost layer forming step.

[0089] Examples of other steps include steps for forming other plating films such as a nickel plating film. In addition, if necessary, a cleaner step, an etching step, a pickling step, an activator step, a post-dip step, a dismut step, a zincate step, etc. may be performed. The chemical solutions used in the cleaner step, etching step, pickling step, activator step, post-dip step, dismut step, and zincate step can be appropriately selected from known ones.

[0090] The plating method for silver sintering bonding of the present invention preferably includes a barrier layer forming step of forming an electroless nickel plating film on the surface of the surface to be plated, an intermediate layer forming step of forming an electroless strike silver plating film on the surface of the electroless nickel plating film, and a top layer forming step of forming an electroless silver plating film on the surface of the electroless strike silver plating film as the outermost layer of the surface to be plated. Thereby, the effect tends to be obtained more preferably.

[0091] The total film thickness of the plating film (plating film laminate) formed by the plating method of the present invention is preferably 15 μm or less, more preferably 10 μm or less, still more preferably 7 μm or less, particularly preferably 6 μm or less, preferably 0.1 μm or more, more preferably 0.2 μm or more, still more preferably 0.4 μm or more, particularly preferably 0.6 μm or more, most preferably 1 μm or more, even most preferably 2 μm or more, still most preferably 3 μm or more, particularly most preferably 4 μm or more. When it is within the above range, the effect tends to be obtained more preferably.

[0092] In this specification, the film thickness and total film thickness of the plating film are the average values of the measurement values at five locations measured by a fluorescent X-ray spectroscopic analyzer, and specifically, they are measured by the method described in the examples.

[0093] The material of the surface to be plated is not particularly limited, and examples thereof include copper, aluminum, iron, nickel, etc. The material of the surface to be plated may be these alloys. Among them, copper, aluminum, Fe-Ni alloys, copper alloys such as brass are preferable, and copper and aluminum are more preferable.

[0094] The plating method for silver sintering bonding of the present invention can be applied without particular limitation to any member for which silver sintering bonding is to be performed. The member for which silver sintering bonding is to be performed is not particularly limited, and examples thereof include substrates such as ceramic substrates and printed circuit boards; semiconductor elements, heat sinks, heat spreaders, chips, lead frames, copper plates, and the like. Among these, substrates (particularly ceramic substrates), heat sinks, heat spreaders, and chips, which are members having a base metal, are preferable, and substrates (particularly ceramic substrates) are more preferable, because they can prevent oxidation of the base metal and further improve heat resistance.

[0095] <plating film (plating film laminate)> The plating film (plating film laminate) for silver sintering bonding of the present invention is a electroless nickel plating film, and on the upper side of the electroless nickel plating film, an electroless strike silver plating film, and on the outermost surface, an electroless silver plating film and has them. The plating film of the present invention is, for example, a plating film provided on the surface to be plated formed by the plating method of the present invention. Therefore, each film of the plating film of the present invention is the same as each film described in the plating method of the present invention, including preferable aspects and the like. Also, other descriptions are the same including preferable aspects and the like.

[0096] The plating film (plating film laminate) of the present invention only needs to have an electroless nickel plating film, an electroless strike silver plating film on the upper side of the electroless nickel plating film, and an electroless silver plating film on the outermost surface, and may have films other than the electroless nickel plating film, the electroless strike silver plating film, and the electroless silver plating film.

[0097] <<Barrier layer>> The plating film (plating film laminate) of the present invention has an electroless nickel plating film as a barrier layer on the upper side of the surface to be plated. The barrier layer only needs to be located on the upper side of the surface to be plated, but is preferably formed on the surface of the surface to be plated. The electroless nickel plating film functions sufficiently as a barrier layer against oxygen, so good heat resistance can be obtained.

[0098] The film thickness of the electroless nickel plating film is preferably 15 μm or less, more preferably 10 μm or less, still more preferably 7 μm or less, and preferably 1 μm or more, more preferably 2 μm or more, still more preferably 3 μm or more. When it is within the above range, the effect tends to be more preferably obtained.

[0099] The electroless nickel plating film may be an alloy film containing other metals. As other metals, including preferred embodiments, they are the same as the electroless nickel plating film formed by the barrier layer forming step. Also, the content of other metals in the electroless nickel plating film is the same as that of the electroless nickel plating film formed by the barrier layer forming step. Furthermore, the nickel content in the electroless nickel plating film is the same as that of the electroless nickel plating film formed by the barrier layer forming step.

[0100] <<Intermediate layer (adhesion layer)>> The plating film (plating film laminate) of the present invention has an electroless strike silver plating film on the upper side of the electroless nickel plating film as an intermediate layer (adhesion layer). By having a strike silver (preferably electroless strike silver) (St-Ag) plating film as the adhesion layer between the nickel plating film and the silver plating film, the adhesion between the nickel plating film and the silver plating film can be ensured at low cost.

[0101] The plating film (plating film laminate) of the present invention preferably has an electroless strike silver plating film on the surface of the electroless nickel plating film. Thereby, better adhesion between the nickel plating film and the silver plating film can be obtained, and it also tends to be advantageous in terms of cost.

[0102] It is preferable that the electroless strike silver plating film is a film formed on the upper side of the electroless nickel plating film using a substitution-type electroless silver plating bath, and it is more preferable that the electroless strike silver plating film is a film formed on the upper side of the electroless nickel plating film using a substitution-type electroless silver plating bath with a pH of 5.0 to 9.0.

[0103] The substitution-type electroless silver plating bath is the same as the substitution-type electroless silver plating bath described in the intermediate layer formation step, including preferred embodiments.

[0104] The substitution-type electroless silver plating bath preferably contains at least one complexing agent selected from the group consisting of amide compounds and imide compounds, more preferably contains at least two complexing agents selected from the group consisting of amide compounds and imide compounds, still more preferably contains two complexing agents selected from the group consisting of amide compounds and imide compounds, and the combined use of acetamide and hydantoin, the combined use of succinimide and hydantoin, the combined use of succinimide and 5,5-dimethylhydantoin, and the combined use of succinimide and 1-methylhydantoin are particularly preferred.

[0105] The film thickness of the electroless strike silver plating film is preferably 0.200 μm or less, more preferably 0.150 μm or less, still more preferably 0.100 μm or less, particularly preferably 0.090 μm or less, most preferably 0.080 μm or less, even most preferably 0.070 μm or less, and particularly most preferably 0.050 μm or less, and is preferably 0.010 μm or more, more preferably 0.020 μm or more, and still more preferably 0.025 μm or more. Within this range, there is a tendency to obtain better adhesion between the nickel plating film and the silver plating film.

[0106] The electroless strike silver plating film may be an alloy film containing other metals. Examples of the other metals include the same metals as described above, and they may be used alone or in combination of two or more. Also, the silver content in the electroless strike silver plating film is the same as that of the electroless strike silver plating film formed in the intermediate layer formation step.

[0107] <<Outermost layer>> The plating film (plating film laminate) of the present invention has an electroless silver plating film as the outermost layer of the plating film provided on the surface to be plated. Since the outermost layer has a silver plating film, sufficient initial bonding strength with the silver sintered material can be obtained.

[0108] The plating film (plating film laminate) of the present invention has an electroless silver plating film on the outermost layer of the surface to be plated. However, as the outermost layer of the surface to be plated, it is preferable to have an electroless silver plating film on the surface of the electroless strike silver plating film. Thereby, better adhesion between the nickel plating film and the silver plating film can be obtained, and it also tends to be advantageous in terms of cost.

[0109] It is preferable that the electroless silver plating film is a film formed on the outermost layer of the surface to be plated using a reducing type electroless silver plating bath. Thereby, an electroless silver plating film with a sufficient film thickness can be obtained, and the initial bonding strength with the silver sintered material tends to be more sufficiently obtained.

[0110] The reducing type electroless silver plating bath is the same as the reducing type electroless silver plating bath described in the outermost layer formation step, including preferred embodiments.

[0111] The film thickness of the electroless silver plating film is preferably 3.0 μm or less, more preferably 2.5 μm or less, still more preferably 2.0 μm or less, and particularly preferably 1.5 μm or less, and is preferably 0.2 μm or more, more preferably 0.3 μm or more, still more preferably 0.4 μm or more. When within the above range, the effect tends to be more suitably obtained.

[0112] The electroless silver plating film may be an alloy film containing other metals. Examples of the other metals include the same metals as described above, and they may be used alone or in combination of two or more. Also, the silver content in the silver plating film is the same as that of the silver plating film formed in the outermost layer forming step.

[0113] <<Other layer>> The plating film of the present invention may have an electroless nickel plating film, an electroless strike silver plating film, and an electroless silver plating film, and may also have other layers.

[0114] The other layers are not particularly limited, and examples include a platinum plating film, a palladium plating film, a gold plating film, a cobalt plating film, and the like.

[0115] The plating film (plating film laminate) of the present invention preferably has an electroless nickel plating film formed on the surface of the surface to be plated, an electroless strike silver plating film formed on the surface of the electroless nickel plating film, and an electroless silver plating film formed on the surface of the electroless strike silver plating film as the outermost layer of the surface to be plated. Thereby, the effect tends to be obtained more preferably.

[0116] The total film thickness of the plating film (plating film laminate) of the present invention is preferably 15 μm or less, more preferably 10 μm or less, still more preferably 7 μm or less, particularly preferably 6 μm or less, preferably 0.1 μm or more, more preferably 0.2 μm or more, still more preferably 0.4 μm or more, particularly preferably 0.6 μm or more, most preferably 1 μm or more, even most preferably 2 μm or more, still most preferably 3 μm or more, particularly most preferably 4 μm or more. When within the above range, the effect tends to be obtained more preferably.

[0117] As shown in Fig. 1, the plating film 1 according to an embodiment of the present invention includes an electroless nickel plating film 2 formed on the surface of the surface to be plated 6, an electroless strike silver plating film 4 formed on the surface of the electroless nickel plating film 2, and an electroless silver plating film 3 formed on the surface of the electroless strike silver plating film 4 as the outermost layer of the surface to be plated 6.

[0118] The plating film (plating film laminate) for silver sintering bonding of the present invention can be applied without particular limitation to any member for silver sintering bonding. The members for silver sintering bonding are the same as those described in the plating method of the present invention, including preferred embodiments and the like. Also, the material of the surface to be plated is the same as that described in the plating method of the present invention, including preferred embodiments and the like.

[0119] <Substrate for power module> As described above, the plating film (plating film laminate) of the present invention can be suitably applied to a substrate. Hereinafter, as an example of a substrate using the plating film of the present invention, a substrate for a power module will be described. The substrate for a power module of the present invention includes a base material, a circuit formed on the base material, and a plating film formed on the surface of the circuit, wherein the plating film is the plating film (plating film laminate) of the present invention. In this specification, the substrate for a power module means a substrate used for a power module, specifically, the substrates exemplified below. In this specification, the substrate for a power module is a concept including lead frames and spacers used for power semiconductors.

[0120] The substrate including a base material and a circuit formed on the base material is not particularly limited, and examples thereof include a DBC substrate, a DBA substrate, an AMB substrate, etc. Here, DBC is an abbreviation for Direct Bonded Copper, DBA is an abbreviation for Direct Bonded Aluminum, and AMB is an abbreviation for Active Metal Brazing.

[0121] Hereinafter, with reference to the drawings, a substrate for a heat-resistant power module according to an embodiment of the present invention will be described. A substrate 100 for a power module according to an embodiment of the present invention is a substrate for mounting a power semiconductor that generates high heat. And, as shown in FIG. 2, the substrate 100 for a power module according to an embodiment of the invention includes a base material 10, a circuit 20 formed directly or via a brazing material on the base material, and a plating film (plating film laminate) 1 formed on the surface of the circuit.

[0122] The base material 10 used for the substrate 100 for a power module according to an embodiment of the present invention is not particularly limited, and examples thereof include aluminum oxide, aluminum nitride, silicon nitride, etc. These may be used alone or in combination of two or more. Among them, aluminum oxide, aluminum nitride, and silicon nitride are preferable because they are excellent in terms of cost, heat dissipation, strength, etc.

[0123] As shown in FIG. 2, a circuit 20 is formed on the base material 10. At this time, the circuit 20 may be formed directly on the base material 10, or the circuit 20 may be formed via a brazing material (not shown). The circuit 20 is usually made of copper and / or aluminum. Here, copper and aluminum may be alloys.

[0124] For the method of forming the circuit 20, a known method may be used and is not particularly limited. In the direct method, one side of a copper plate, which is a circuit member, may be oxidized, joined to the base material 10, and unnecessary portions other than the circuit may be etched. Aluminum has excellent ductility, and copper has excellent heat dissipation. Also, in terms of cost, these metals are superior to other metals and are thus used for power module substrates.

[0125] The plating film 1 formed on the surface of the circuit 20 is the plating film of the present invention. Then, the surface of the plating film and, for example, a semiconductor element are silver-sintered and joined, so that the surface of the plating film forms a silver-sintered joint surface, and has good adhesion, initial joint strength, and heat resistance between the nickel plating film and the silver plating film. In FIG. 4, the surface of the plating film 1 formed on the surface of the circuit 20 and the semiconductor element 30 are silver-sintered and joined. That is, the surface of the plating film 1 and the semiconductor element 30 are joined via the silver sintered body layer 40.

[0126] In the present invention, the method of silver-sintered joining is not particularly limited, and those skilled in the art can appropriately implement it according to known methods. For example, a paste in which silver particles are dispersed in an organic solvent can be used as a silver-sintered material, and the organic solvent can be volatilized by heating or the like to bring the silver particles into contact with each other, and a joint layer can be formed by sintering.

[0127] <Semiconductor element> The plating film (plating film laminate) of the present invention can be suitably applied to a semiconductor element. Hereinafter, an example of a semiconductor element using the plating film of the present invention will be described. The semiconductor element of the present invention has a plating film on its surface, and the plating film is the plating film (plating film laminate) of the present invention. Since the semiconductor element of the present invention is excellent in the adhesion and heat resistance between the nickel plating film and the silver plating film, it can be suitably used as a semiconductor element for a power module.

[0128] Hereinafter, with reference to the drawings, a semiconductor element according to an embodiment of the present invention will be described. The semiconductor element 30 according to an embodiment of the present invention is a semiconductor element used for a substrate of a power module. And, as shown in FIG. 3, the semiconductor element 30 according to an embodiment of the invention includes a plating film (plating film laminate) 1 formed on the surface of the semiconductor element 30 on the semiconductor element 30.

[0129] The semiconductor element is not particularly limited, and examples thereof include power semiconductor elements such as Si (silicon) semiconductor elements, SiC (silicon carbide) semiconductor elements, and GaN (gallium nitride) semiconductor elements. These may be used alone or in combination of two or more. Among them, power semiconductor elements are preferred, and SiC semiconductor elements and GaN semiconductor elements are more preferred because of the particularly required heat resistance.

[0130] The plating film 1 formed on the surface of the semiconductor element 30 is the plating film of the present invention. Then, the surface of the plating film and, for example, the substrate are silver-sintered and joined, so that the surface of the plating film forms a silver-sintered joint surface, and has good adhesion between the nickel plating film and the silver plating film, initial joint strength, and heat resistance. In FIG. 5, the surface of the plating film 1 formed on the surface of the semiconductor element 30 and the surface of the plating film 1 formed on the surface of the circuit 20 are silver-sintered and joined. That is, the circuit 20 and the semiconductor element 30 are joined via the silver sintered body layer 40.

[0131] In the present invention, the method of silver-sintered joining is not particularly limited, and those skilled in the art can appropriately implement it according to known methods. For example, a paste in which silver particles are dispersed in an organic solvent may be used as a silver-sintered material, the organic solvent may be volatilized by heating or the like to bring the silver particles into contact with each other, and a joint layer may be formed by sintering.

[0132] <Semiconductor device> The substrate for a power module of the present invention and the semiconductor element of the present invention can be suitably applied to a semiconductor device. Therefore, the semiconductor device of the present invention is a semiconductor device including the substrate for a power module of the present invention and / or the semiconductor element of the present invention, and preferably, the surface of the plating film of the present invention possessed by the substrate for a power module of the present invention and / or the semiconductor element of the present invention is a silver-sintered joint surface. Such a semiconductor device of the present application can inexpensively ensure the adhesion between the nickel plating film and the silver plating film, has good heat resistance, and is a highly reliable semiconductor device.

[0133] Hereinafter, an example of a semiconductor device using the substrate for a power module of the present invention will be described. The semiconductor device of the present invention includes the substrate for a power module of the present invention and semiconductor elements, and it is preferable that the semiconductor elements are silver-sintered and joined to the surface of the plating film of the substrate for a power module. Since it is a semiconductor device including a specific substrate for a power module and semiconductor elements, and the semiconductor elements are silver-sintered and joined to the surface of the plating film of the substrate for a power module, the adhesion between the nickel plating film and the silver plating film can be ensured at low cost, and it has good heat resistance and is a highly reliable semiconductor device.

[0134] In this specification, the fact that the semiconductor elements are silver-sintered and joined to the surface of the plating film of the substrate for a power module means that the semiconductor elements may be silver-sintered and joined over the entire surface of the plating film, or may be silver-sintered and joined to a part of the surface of the plating film. For example, when the plating film is formed on both the front and back surfaces of the substrate, the semiconductor elements may be silver-sintered and joined only to the surface of the plating film formed on either one of the surfaces. In this case, the surface to which the semiconductor elements are silver-sintered and joined may be the entire surface of the plating film or only a part of the surface. That is, the semiconductor elements may be silver-sintered and joined only to a part of the surface of the plating film formed on one of the surfaces. Also, in this specification, among the semiconductor elements included in the substrate, it is sufficient that at least one semiconductor element is silver-sintered and joined to the surface of the plating film of the substrate for a power module, and all the semiconductor elements may be silver-sintered and joined to the surface of the plating film of the substrate for a power module. In addition, in this specification, the statement that the surface of the plating film of the substrate for the power module and the semiconductor element are silver sintered and joined means that the surface of the plating film of the substrate for the power module and the surface of the semiconductor element may be silver sintered and joined, or the surface of the plating film of the substrate for the power module and the surface of the plating film applied to the surface of the semiconductor element may be silver sintered and joined.

[0135] In the semiconductor device of the present invention, since the surface of the plating film of the present invention and the semiconductor element are silver sintered and joined, the surface of the plating film forms a silver sintered joint surface, and it has good adhesion between the nickel plating film and the silver plating film, initial joint strength, and heat resistance, and is a highly reliable semiconductor device.

[0136] The semiconductor element is not particularly limited, and examples include power semiconductor elements such as Si (silicon) semiconductor elements, SiC (silicon carbide) semiconductor elements, and GaN (gallium nitride) semiconductor elements. These may be used alone or in combination of two or more. Among them, power semiconductor elements are preferred, and SiC semiconductor elements and GaN semiconductor elements are more preferred because of the particular requirement for heat resistance.

[0137] The semiconductor element preferably has a plating film on its surface, and the plating film is the plating film (plating film laminate) of the present invention. Thereby, better adhesion between the nickel plating film and the silver plating film can be ensured at low cost, and it has better initial joint strength and heat resistance, and becomes a more reliable semiconductor element and semiconductor device.

[0138] Hereinafter, an example of a semiconductor device using the semiconductor element of the present invention will be described. The semiconductor device of the present invention comprises a substrate for a power module and the semiconductor element of the present invention. It is preferable that the surface of the plating film of the semiconductor element and the substrate for the power module are silver-sintered and joined. Since the semiconductor device includes a substrate for a power module and a specific semiconductor element, and the surface of the plating film of the semiconductor element and the substrate for the power module are silver-sintered and joined, the adhesion between the nickel plating film and the silver plating film can be ensured at low cost, and it has good heat resistance and is a highly reliable semiconductor device.

[0139] In this specification, the statement that the surface of the plating film of the semiconductor element and the substrate for the power module are silver-sintered and joined means that they may be silver-sintered and joined with the substrate for the power module over the entire surface of the plating film, or they may be silver-sintered and joined with the substrate for the power module on a part of the surface of the plating film. For example, when the plating film is formed on the front and back surfaces of the semiconductor element, they may be silver-sintered and joined with the substrate for the power module only on the surface of the plating film formed on either one of the surfaces. In this case, the surface that is silver-sintered and joined with the substrate for the power module may be the entire surface of the plating film or only a part of the surface. That is, they may be silver-sintered and joined with the substrate for the power module only on a part of the surface of the plating film formed on one of the surfaces. Also, in this specification, among the semiconductor elements included in the substrate, it is sufficient that the surface of the plating film of at least one semiconductor element of the present invention and the substrate for the power module are silver-sintered and joined, and the surface of the plating film of all the semiconductor elements of the present invention and the substrate for the power module may be silver-sintered and joined. Also, in this specification, the statement that the surface of the plating film of the semiconductor element and the substrate for the power module are silver-sintered and joined means that the surface of the plating film of the semiconductor element and the surface of the substrate for the power module may be silver-sintered and joined, or the surface of the plating film of the semiconductor element and the surface of the plating film applied to the surface of the substrate for the power module may be silver-sintered and joined.

[0140] In the semiconductor device of the present invention, since the surface of the plating film of the present invention and the substrate for the power module are silver-sintered and joined, the surface of the plating film forms a silver-sintered joint surface, and it has good adhesion between the nickel plating film and the silver plating film, initial joint strength, and heat resistance, and is a highly reliable semiconductor device.

[0141] The substrate for the power module is not particularly limited, and examples thereof include a DBC substrate, a DBA substrate, an AMB substrate, etc. These may be used alone or in combination of two or more.

[0142] The substrate for the power module is preferably the substrate for the power module of the present invention. Thereby, better adhesion between the nickel plating film and the silver plating film can be ensured at low cost, and it has better initial joint strength and heat resistance, and becomes a more reliable semiconductor device.

[0143] As described above, in FIG. 4, the surface of the plating film 1 formed on the surface of the circuit 20 and the semiconductor element 30 are silver-sintered and joined. That is, the surface of the plating film 1 and the surface of the semiconductor element 30 are joined via the silver sintered body layer 40. Similarly, in FIG. 5, the surface of the plating film 1 formed on the surface of the semiconductor element 30 and the surface of the plating film 1 formed on the surface of the circuit 20 are silver-sintered and joined.

[0144] Here, as described above, in the present invention, as shown in FIG. 4, the surface of the plating film of the substrate for the power module and the surface of the semiconductor element (without the plating film) may be silver-sintered and joined. As shown in FIG. 5, the surface of the plating film of the substrate for the power module and the surface of the plating film applied to the surface of the semiconductor element may be silver-sintered and joined. Here, the plating film applied to the surface of the semiconductor element is not particularly limited. For example, in addition to the plating film of the present invention (the plating film 1 in FIG. 5), there are also sputtered Ag (Ti / Ag, Ta / Ag, TaN / Ag, Ni / Au, Ni / Ag, etc.) films and Ni / Au, Ni / Pd / Au films by electroplating and / or electroless plating. Among them, the plating film of the present invention is preferable. The material of the surface of the semiconductor element without the plating film is, for example, titanium, tantalum, tantalum nitride, etc.

[0145] Also, as described above, in the present invention, although not shown, the surface of the plating film of the semiconductor element and the surface of the substrate for the power module (without the plating film) may be silver-sintered and joined. As shown in FIG. 5, the surface of the plating film of the semiconductor element and the surface of the plating film applied to the surface of the substrate for the power module may be silver-sintered and joined. Here, the plating film applied to the surface of the substrate for the power module is not particularly limited. For example, in addition to the plating film of the present invention (the plating film 1 in FIG. 5), there are also Ni / Au, Ni / Pd / Au films by electroplating and / or electroless plating. Among them, the plating film of the present invention is preferable. The material of the surface of the substrate for the power module without the plating film is, for example, copper, aluminum, etc.

[0146] The semiconductor device of the present invention can be used in various electronic components. Examples of the electronic components include electronic components used in home appliances, in-vehicle devices, power transmission systems, transportation devices, communication devices, etc. Specifically, there are power modules such as air conditioners, elevators, electric vehicles, hybrid vehicles, trains, and power control units for power generation devices, general home appliances, personal computers, etc. Among them, power modules are preferable because heat resistance is particularly required.

Example

[0147] Based on the examples, the present invention will be specifically described, but the present invention is not limited only to these.

[0148] According to the conditions shown in Tables 1 to 3, each plating was applied to the substrate to form a plating film laminate. Here, as the base substrate to be plated, a Cu bulk material (25×60×3 mm) was used. The obtained plating film laminate and the substrate provided with the plating film laminate were evaluated by the following method. The evaluation results are shown in Tables 1 and 2. In Table 2, the concentrations of silver nitrate and silver oxide are the concentrations in terms of silver element (g / L). In Table 1, Argent RSD-4 manufactured by Uemura Kogyo Co., Ltd. is a reducing electroless silver plating bath with a silver concentration of 1.0 g / L, a pH of 8.5, and a concentration of reducing agent (hydrazine derivative, hydroxylamine, dimethylamine borane, boron hydride compound) of 1.0 g / L.

[0149] <Measurement of the Thickness of the Plating Film> The thickness of the plating film was calculated as the average value of the measured values at 5 locations by a fluorescent X-ray spectroscopic analyzer (manufactured by Hitachi High-Technologies Corporation, product name: SFT-9550).

[0150] <Analysis of the Composition of the Plating Film> After the formation of the plating film, the composition was analyzed. Specifically, the plating film was dissolved in nitric acid, and this solution was quantitatively analyzed for each element using an inductively coupled plasma (ICP) optical emission spectrometer (manufactured by HORIBA, product name: Ultima Expert), and the content ratio of each component in the film was calculated from the mass of the dissolved plating film.

[0151] <Adhesion Evaluation (Cross-Cut Test)> A blade was applied perpendicular to the plating film and six parallel cuts were made. Next, six cuts perpendicular to the six cuts already made were made. Cellophane tape was attached to the cut portions in a grid pattern and rubbed firmly with a finger. The tape was forcefully peeled off to check for peeling of the plating film, and the adhesion (adhesion between the nickel plating film and the silver plating film) was evaluated according to the following criteria. ◎: No peeling 〇: Slight peeling at a very small part △: Partial peeling ×: Complete peeling

[0152] <Heat resistance evaluation> (Preparation of evaluation samples) For the substrate to be plated (base substrate (Cu bulk material; 25×60×3 mm) and simulated chip (Cu bulk material processed to chip size; 5×5×1 mm)), according to the conditions shown in Tables 1 to 3, after applying each plating, the base substrate and the simulated chip (both forming the same film laminate) were connected to each other using a silver sintering material (MAX102: manufactured by Nihon Handa Co., Ltd.), heat-treated at 250 °C under atmospheric pressure for 10 minutes without pressure to perform silver sintering bonding, and further heat-treated at 300 °C for 500 hours to cause thermal degradation, and evaluation samples were prepared. (Measurement of bonding strength) For the evaluation samples, the silver-sintered bonded chip was sheared horizontally, and the strength at the time of fracture was measured using a bond tester (manufactured by Nordson DAGE, product name: 4000Plus) as the bonding strength (bonding strength after heat treatment). Then, based on the bonding strength after heat treatment, the heat resistance was evaluated according to the following criteria. ◎: No problem (bonding strength after heat treatment: 30 Mpa or more) 〇: Slight decrease in strength due to heat treatment (bonding strength after heat treatment: less than 20 - 30 MPa) △: Decrease in strength by heat treatment (bonding strength after heat treatment: less than 20 MPa)

[0153] <Cost> Pd: Average retail price ￥8218 / g (average in October 2021) Pt: Average retail price ￥4142 / g (average in October 2021) Ag: Average retail price: ¥98 / g (average in October 2021) Ni: Average retail price: ¥2.2 / g (average in October 2021) Based on the above retail prices, calculate the prices of the metals in each film composition (assuming 100% of each metal). Ni / Pd / Ag (4.5 / 0.1 / 0.5 μm): ¥104 / dm 2 Ni / Pt / Ag (4.5 / 0.1 / 0.5 μm): ¥95 / dm 2 Ni / St / Ag / Ag (4.5 / 0.05 / 0.5 μm): ¥5.5 / dm 2 The cost was evaluated according to the following criteria. High: Ni / Pd / Ag, Ni / Pt / Ag Low: Ni / St-Ag / Ag

[0154] Hereinafter, the manufacturing methods of the plating film laminate and the substrate provided with the plating film laminate in each example and comparative example will be described in detail.

[0155] (Comparative Example 1) An electroless NiP plating film was formed on the surface of the Cu bulk material, which is the surface to be plated, using Nimmden KSL-2 manufactured by Uemura Kogyo Co., Ltd., and an electroless Ag plating film was formed on the surface thereof using Argent RSD-4 manufactured by Uemura Kogyo Co., Ltd.

[0156] (Comparative Example 2) An electroless NiP plating film was formed on the surface of the Cu bulk material, which is the surface to be plated, using Nimmden NPR-4 manufactured by Uemura Kogyo Co., Ltd., and an electroless Ag plating film was formed on the surface thereof using Argent RSD-4 manufactured by Uemura Kogyo Co., Ltd.

[0157] (Comparative Example 3) An electroless NiP plating film was formed on the surface of the Cu bulk material, which is the surface to be plated, using Nimmden DX manufactured by Uemura Kogyo Co., Ltd., and an electroless Ag plating film was formed on the surface thereof using Argent RSD-4 manufactured by Uemura Kogyo Co., Ltd.

[0158] (Comparative Example 4) An electroless NiB plating film was formed on the surface of the Cu bulk material, which is the surface to be plated, using Nimden BEL-18 manufactured by Uemura Kogyo Co., Ltd. An electroless Ag plating film was formed on the surface of the electroless NiB plating film using Argent RSD-4 manufactured by Uemura Kogyo Co., Ltd.

[0159] (Comparative Example 5) An electroless NiP plating film was formed on the surface of the Cu bulk material, which is the surface to be plated, using Nimden NPR-4 manufactured by Uemura Kogyo Co., Ltd. An electroless Pd plating film was formed on the surface of the electroless NiP plating film using Altarea TPD-30 manufactured by Uemura Kogyo Co., Ltd. An electroless Ag plating film was formed on the surface of the electroless Pd plating film using Argent RSD-4 manufactured by Uemura Kogyo Co., Ltd.

[0160] (Comparative Example 6) An electroless NiP plating film was formed on the surface of the Cu bulk material, which is the surface to be plated, using Nimden NPR-4 manufactured by Uemura Kogyo Co., Ltd. An electroless Pt plating film was formed on the surface of the electroless NiP plating film using Altarea TGM-21 manufactured by Uemura Kogyo Co., Ltd. An electroless Ag plating film was formed on the surface of the electroless Pt plating film using Argent RSD-4 manufactured by Uemura Kogyo Co., Ltd.

[0161] (Example 1) An electroless NiP plating film was formed on the surface of the Cu bulk material, which is the surface to be plated, using Nimden KSL-2 manufactured by Uemura Kogyo Co., Ltd. An electroless strike silver plating film was formed on the surface of the electroless NiP plating film using a substitution type electroless silver plating bath with the compositions and conditions shown in Tables 1 and 2. An electroless Ag plating film was formed on the surface of the electroless strike silver plating film using Argent RSD-4 manufactured by Uemura Kogyo Co., Ltd.

[0162] (Example 2) An electroless NiP plating film was formed on the surface of the Cu bulk material, which is the surface to be plated, using Nimden NPR-4 manufactured by Uemura Kogyo Co., Ltd. An electroless strike silver plating film was formed on the surface of the electroless NiP plating film using a substitution type electroless silver plating bath with the compositions and conditions shown in Tables 1 and 2. An electroless Ag plating film was formed on the surface of the electroless strike silver plating film using Argent RSD-4 manufactured by Uemura Kogyo Co., Ltd.

[0163] (Example 3) On the surface of the Cu bulk material which is the surface to be plated, an electroless NiP plating film was formed using Nimmden DX manufactured by Uemura Kogyo Co., Ltd. On its surface, an electroless strike silver plating film was formed using a substitution-type electroless silver plating bath with the compositions and conditions shown in Tables 1 and 2. Further, on its surface, an electroless Ag plating film was formed using Argent RSD-4 manufactured by Uemura Kogyo Co., Ltd.

[0164] (Example 4) On the surface of the Cu bulk material which is the surface to be plated, an electroless NiB plating film was formed using Nimmden BEL-18 manufactured by Uemura Kogyo Co., Ltd. On its surface, an electroless strike silver plating film was formed using a substitution-type electroless silver plating bath with the compositions and conditions shown in Tables 1 and 2. Further, on its surface, an electroless Ag plating film was formed using Argent RSD-4 manufactured by Uemura Kogyo Co., Ltd.

[0165] (Examples 5 to 16) A plating film was formed in the same manner as in Example 2, except that a substitution-type electroless silver plating bath with the compositions and conditions shown in Table 2 was used.

[0166]

Table 1

[0167]

Table 2

[0168]

Table 3

[0169] From Tables 1 and 2, it was found that in the examples having an electroless nickel plating film, an electroless strike silver plating film on the upper side of the electroless nickel plating film, and an electroless silver plating film on the outermost layer, the adhesion between the nickel plating film and the silver plating film can be ensured at low cost and has good heat resistance. Therefore, the plating method and the plating film of the present invention can be suitably applied to silver sintering bonding.

Description of Symbols

[0170] 1 Plating film (plating film laminate) 2 Electroless nickel plating film 3 Electroless silver plating film 4 Electroless strike silver plating film 6 Surface to be plated 10 Base material 20 Circuit 30 Semiconductor element 40 Silver sintered body layer 100 Substrate for power module

Claims

1. A barrier layer forming step of forming an electroless nickel plating film on the upper side of the surface to be plated; An intermediate layer forming step of forming an electroless strike silver plating film on the upper side of the electroless nickel plating film; A outermost layer forming step of forming an electroless silver plating film on the outermost surface of the surface to be plated A plating method for silver sintering bonding including these steps.

2. The plating method according to Claim 1, wherein the film thickness of the electroless strike silver plating film is 0.010 to 0.200 μm.

3. The plating method according to Claim 1 or 2, wherein the intermediate layer forming step is a step of forming an electroless strike silver plating film on the upper side of the electroless nickel plating film using a substitution-type electroless silver plating bath having a pH of 5.0 to 9.

0.

4. The plating method according to Claim 3, wherein the substitution-type electroless silver plating bath contains at least one complexing agent selected from the group consisting of amide compounds and imide compounds.

5. The plating method according to Claim 3, wherein the substitution-type electroless silver plating bath contains at least two complexing agents selected from the group consisting of amide compounds and imide compounds.

6. The plating method according to any one of Claims 1 to 5, wherein the film thickness of the electroless silver plating film is 0.2 μm or more.

7. The plating method according to any one of Claims 1 to 6, wherein the outermost layer forming step is a step of forming an electroless silver plating film on the outermost surface of the surface to be plated using a reducing-type electroless silver plating bath.

8. The plating method according to any one of Claims 1 to 7, wherein the total film thickness of the plating film is 15 μm or less.

9. An electroless nickel plating film; An electroless strike silver plating film on the upper side of the electroless nickel plating film; An electroless silver plating film on the outermost layer A plating film for silver sintering bonding having these layers.

10. The plating film according to Claim 9, wherein the film thickness of the electroless strike silver plating film is 0.010 to 0.200 μm.

11. The plating film according to Claim 9 or 10, wherein the electroless strike silver plating film is a film formed on the upper side of the electroless nickel plating film using a substitution-type electroless silver plating bath having a pH of 5.0 to 9.

0.

12. The plating film according to Claim 11, wherein the substitution-type electroless silver plating bath contains at least one complexing agent selected from the group consisting of amide compounds and imide compounds.

13. The plating film according to claim 11, wherein the replacement electroless silver plating bath contains at least two complexing agents selected from the group consisting of amide compounds and imide compounds.

14. The plating film according to any one of claims 9 to 13, wherein the film thickness of the electroless silver plating film is 0.2 μm or more.

15. The plating film according to any one of claims 9 to 14, wherein the electroless silver plating film is a film formed on the outermost surface of the surface to be plated using a reducing electroless silver plating bath.

16. The plating film according to any one of claims 9 to 15, wherein the total film thickness of the plating film is 15 μm or less.

17. A substrate for a power module comprising: a circuit formed on the substrate; and a plating film formed on the surface of the circuit, wherein the plating film is the plating film according to any one of claims 9 to 16.

18. The substrate for a power module according to claim 17, wherein the circuit is a circuit made of copper and / or aluminum.

19. The substrate for a power module according to claim 17 or 18, wherein the surface of the plating film is a silver sintered joint surface.

20. A semiconductor element having the plating film according to any one of claims 9 to 16 on its surface.

21. A semiconductor device comprising the substrate for a power module according to any one of claims 17 to 19 and / or the semiconductor element according to claim 20.

22. The semiconductor device according to claim 21, wherein the surface of the plating film of the substrate for a power module according to any one of claims 17 to 19 and / or the semiconductor element according to claim 20 is a silver sintered joint surface.

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