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 sintering and bonding silver, capable of inexpensively obtaining adhesion between a nickel-plating film and a silver plating film and excellent in heat resistance; a plating film for sintering and bonding silver; a power module substrate including the plating film; a semiconductor element including the plating film; and a semiconductor device including the power module substrate.SOLUTION: A plating method for sintering and bonding silver comprises: a barrier layer formation step of forming an electroless nickel-plating film on a surface to be plated; and an outermost layer formation step of forming an electroless silver plating film as an outermost layer on the surface to be plated on the electroless nickel-plating film using a substitution type electroless silver plating bath.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 such as the substrate for bonding is required, and the film formed by this surface treatment also requires heat resistance.

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

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The substrate has circuits formed from copper or aluminum on the base material. When silver sintering is used to bond semiconductor elements to the circuit, a silver plating film is sometimes used on the outermost layer of the circuit that will be in contact with the silver sintering layer to ensure good bonding strength. Although good initial bonding strength can be obtained with the silver plating film, the silver plating film is permeable to oxygen, and especially under high temperature conditions, it can cause oxidation of the underlying metal such as copper or aluminum, which may reduce bonding strength and tend to have poor heat resistance. To solve this problem, it is necessary to provide an additional oxidation barrier layer for the underlying metal.

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

[0007] The present invention aims to solve the aforementioned problems newly identified by the inventors and to provide a plating method for silver sintering bonding, a plating film for silver sintering bonding, a power module substrate equipped with the plating film, a semiconductor element equipped with the plating film, and a semiconductor device equipped with the power module substrate, which can inexpensively ensure adhesion between a nickel plating film and a silver plating film and have good heat resistance. [Means for solving the problem]

[0008] As a result of diligent research, the inventors of the present invention have found that by using an electroless silver plating film formed using a displacement-type electroless silver plating bath as the silver plating film, 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. In other words, the present invention comprises a barrier layer formation step of forming an electroless nickel plating film on the upper side of the surface to be plated, and an outermost layer formation step of forming an electroless silver plating film on the upper side of the electroless nickel plating film as the outermost layer of the surface to be plated using a displacement type electroless silver plating bath. This relates to a plating method for silver sintering bonding, including silver bonding.

[0009] It is preferable that the substitutional electroless silver plating bath contains at least one complexing agent selected from the group consisting of amide compounds, imide compounds, and sulfur-containing organic compounds.

[0010] It is preferable that the substitution type electroless silver plating bath contains at least one adjusting agent selected from the group consisting of phosphinic acid compounds and nitrogen-containing heterocyclic compounds.

[0011] The displacement-type electroless silver plating bath preferably contains a chelating agent.

[0012] It is preferable that the thickness of the electroless silver plating film is 0.01 to 1.0 μm.

[0013] The present invention also relates to a plated film (plated film laminate) for silver sintering bonding, having an electroless nickel plating film and an electroless silver plating film formed as the outermost layer on top of the electroless nickel plating film using a displacement type electroless silver plating bath.

[0014] It is preferable that the substitutional electroless silver plating bath contains at least one complexing agent selected from the group consisting of amide compounds, imide compounds, and sulfur-containing organic compounds.

[0015] It is preferable that the substitution type electroless silver plating bath contains at least one adjusting agent selected from the group consisting of phosphinic acid compounds and nitrogen-containing heterocyclic compounds.

[0016] The displacement-type electroless silver plating bath preferably contains a chelating agent.

[0017] It is preferable that the thickness of the electroless silver plating film is 0.01 to 1.0 μm.

[0018] The present invention also relates to a substrate for a power module including a base material, a circuit formed on the base material, and the plating film formed on the surface of the circuit.

[0019] It is preferable that the circuit is a circuit made of copper and / or aluminum.

[0020] It is preferable that the surface of the plating film is a silver sintered joint surface.

[0021] The present invention also relates to a semiconductor element having the plating film on its surface.

[0022] The present invention also relates to a semiconductor device including the substrate for a power module and / or a semiconductor element having the plating film on its surface.

[0023] In the semiconductor device, it is preferable that the surface of the plating film of the substrate for a power module and / or the semiconductor element having the plating film on its surface is a silver sintered joint surface.

[0024] The semiconductor device also preferably includes the substrate for a power module and a semiconductor element, and the surface of the plating film of the substrate for a power module and the semiconductor element are silver sintered and joined. In the semiconductor device, it is preferable that the semiconductor element is a semiconductor element having the plating film on its surface.

[0025] The semiconductor device also includes a substrate for a power module and a semiconductor element having the plating film on its surface. It is preferable that the semiconductor device is such that the surface of the plating film of the semiconductor element and the substrate for a power module are silver sintered and joined.

Advantages of the Invention

[0026] According to the present invention, the plating method for silver sintering bonding includes a barrier layer formation step of forming an electroless nickel plating film on the upper side of the surface to be plated, and an outermost layer formation step of forming an electroless silver plating film on the upper side of the electroless nickel plating film as the outermost layer of the surface to be plated using a displacement type electroless silver plating bath. Therefore, adhesion between the nickel plating film and the silver plating film can be ensured inexpensively, and good heat resistance is achieved.

[0027] Furthermore, according to the present invention, since the plating film for silver sintering bonding (plating film laminate) has an electroless nickel plating film and an electroless silver plating film formed as the outermost layer on top of the electroless nickel plating film using a displacement type electroless silver plating bath, adhesion between the nickel plating film and the silver plating film can be ensured inexpensively, and it has good heat resistance.

[0028] Furthermore, according to the present invention, since the power module substrate comprises a base material, a circuit formed on the base material, and a specific plating film (plating film laminate) formed on the surface of the circuit, adhesion between the nickel plating film and the silver plating film can be ensured inexpensively, and it has good heat resistance.

[0029] Furthermore, according to the present invention, since the semiconductor element has a specific plating film (plating film laminate) on its surface, adhesion between the nickel plating film and the silver plating film can be ensured inexpensively, and it has good heat resistance, making it a highly reliable semiconductor element.

[0030] Furthermore, according to the present invention, since the semiconductor device comprises a substrate for a specific power module and / or a specific semiconductor element, adhesion between the nickel plating film and the silver plating film can be ensured inexpensively, and it has good heat resistance, making it a highly reliable semiconductor device. [Brief explanation of the drawing]

[0031] [Figure 1] This is a schematic cross-sectional view showing a plated film according to one embodiment of the present invention. [Figure 2]This is a schematic cross-sectional view of a power module substrate according to one embodiment of the present invention. [Figure 3] This is a schematic cross-sectional view of a semiconductor device relating to one embodiment of the present invention. [Figure 4] This is a cross-sectional view showing a schematic connection between a power module substrate and a semiconductor element according to one embodiment of the present invention. [Figure 5] This is a cross-sectional view showing a schematic connection between a power module substrate and a semiconductor element according to one embodiment of the present invention. [Modes for carrying out the invention]

[0032] The present invention provides a plating method for silver sintering bonding, which includes a barrier layer formation step of forming an electroless nickel plating film on the upper side of the surface to be plated, and a top layer formation step of forming an electroless silver plating film on the upper side of the electroless nickel plating film as the outermost layer of the surface to be plated, using a displacement type electroless silver plating bath. The plating film (plating film laminate) for silver sintering bonding of the present invention comprises an electroless nickel plating film and an electroless silver plating film formed as the outermost layer on top of the electroless nickel plating film using a displacement-type electroless silver plating bath. This allows for inexpensive adhesion between the nickel plating film and the silver plating film, and provides good heat resistance.

[0033] The reason why the aforementioned effects are obtained with the aforementioned plating method and the aforementioned plating film (plating film laminate) is presumed to be as follows. As mentioned above, the electroless nickel plating film functions effectively as a barrier layer against oxygen, thus providing good heat resistance. Furthermore, by providing an electroless silver plating film formed using a displacement-type electroless silver plating bath on the outermost layer, sufficient initial bonding strength with the silver sintered material can be obtained. Here, the electroless silver plating film formed using a displacement-type electroless silver plating bath has a good film thickness distribution, thus providing stable initial bonding strength with the silver sintered material. Moreover, since the electroless silver plating film formed using a displacement-type electroless silver plating bath has good adhesion with the nickel plating film, adhesion between the nickel plating film and the silver plating film can be ensured inexpensively. As described above, the synergistic effect of the nickel plating film (preferably an electroless nickel plating film) and the electroless silver plating film formed using a displacement-type electroless silver plating bath allows for inexpensive adhesion between the nickel plating film and the silver plating film, and provides good heat resistance. Therefore, the plating method and the plated film laminate have an electroless silver plating film formed as the outermost layer using a displacement-type electroless silver plating bath on the upper side of the electroless nickel plating film. As such, they have good initial bonding strength, and furthermore, adhesion between the nickel plating film and the silver plating film can be ensured inexpensively and have good heat resistance, making them suitably applicable to silver sintering bonding.

[0034] <Plating Method> The present invention provides a plating method for silver sintering bonding, A barrier layer formation step is performed on the upper side of the surface to be plated, forming an electroless nickel plating film. The process involves forming an electroless silver plating film on the upper side of the electroless nickel plating film, using a displacement-type electroless silver plating bath, as the outermost layer of the surface to be plated, as part of the outermost layer formation process. Includes.

[0035] In this specification, the term "plated surface" refers to the surface on which a plating film is formed. For example, when a plating film is formed on a circuit formed on a substrate, the plated surface is the circuit surface.

[0036] In this specification, the "upper side of the plated surface" is not particularly limited as long as it is located above the plated surface, and may be the surface of the plated surface, i.e., the bottom layer of the plating film, or a layer other than the bottom 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 (except for the outermost layer of the plating film), and includes not only the embodiment in which an electroless nickel plating film is formed on the surface of the surface to be plated, i.e., as the bottom layer of the plating film, but also embodiments in which an electroless nickel plating film is formed as a layer other than the bottom layer of the plating film (except for 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. Furthermore, in this specification, other similar expressions, such as "upper side of electroless nickel plating film," have the same meaning. Furthermore, in this specification, the "surface of the plated surface" means "on the plated surface," and other similar expressions, such as the "surface of the electroless nickel plating film," also mean "on the electroless nickel plating film."

[0037] 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.

[0038] <<Barrier layer formation process>> In the barrier layer formation process, an electroless nickel plating film is formed on the upper side of the surface to be plated. This allows for the formation of an electroless nickel plating film that functions sufficiently as a barrier layer against oxygen, resulting in good heat resistance.

[0039] The barrier layer formation process preferably involves forming an electroless nickel plating film on the surface of the plated surface. This provides better heat resistance and is also cost-effective.

[0040] It is important to form an electroless nickel plating film as a barrier layer, and the method of forming the plating film is not particularly limited. Examples of methods for forming the plating film include electroless plating, electroplating, hot-dip plating, vacuum plating (PVD), and vapor deposition (CVD). These may be used individually or in combination of two or more. Among these, electroless plating and electroplating are preferred, with electroless plating being more preferred, due to their low cost, simplicity of equipment, and productivity.

[0041] The electroless plating method is not particularly limited; it is sufficient to deposit metal in the plating bath using a reducing agent, and those skilled in the art can carry it out appropriately according to known methods.

[0042] The reducing agent is not particularly limited as long as it is a water-soluble compound that has the ability to reduce water-soluble metal compounds in the plating bath back to metal. Examples include hydrazine derivatives, formaldehyde compounds, hydroxylamines, sugars, phosphorous acid, formic acid, boron hydride compounds, hypophosphates, dimethylamine borane, and ascorbic acid. These may be used individually or in combination of two or more.

[0043] The thickness of the electroless nickel plating film formed by the barrier layer formation process is preferably 15 μm or less, more preferably 10 μm or less, even more preferably 7 μm or less, preferably 1 μm or more, more preferably 2 μm or more, and even more preferably 3 μm or more. Within the above range, the effect tends to be more favorably obtained.

[0044] The electroless nickel plating film formed by the barrier layer formation process may be an alloy film containing other metals.

[0045] Other metals are not particularly limited and include, for example, transition metal elements of Group 5 or 6 of the periodic table such as tungsten, molybdenum, niobium, tantalum, and vanadium. Other metals may also include phosphorus and boron derived from reducing agents, and carbon, nitrogen, oxygen, and sulfur derived from additives. These other metals may be used individually or in combination of two or more. Among these, phosphorus and boron are preferred because they provide better heat resistance.

[0046] The content of other metals (preferably phosphorus and boron) in the electroless nickel plating film is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, even more preferably 1% by mass or more, preferably 15% by mass or less, more preferably 13% by mass or less, and even more preferably 11% by mass or less. Within the above range, the effect tends to be more favorably obtained. In cases where multiple other metals are present, the aforementioned percentage refers to the total percentage.

[0047] The nickel content in the electroless nickel plating film is preferably 85% by mass or more, more preferably 87% by mass or more, even more preferably 89% by mass or more, preferably 99.9% by mass or less, more preferably 99.5% by mass or less, and even more preferably 99% by mass or less. When the content is within the above range, the effect tends to be more favorably obtained.

[0048] In this specification, the content 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.

[0049] <<<Outermost layer formation process>>> In the outermost layer formation process, an electroless silver plating film is formed on the upper side of the electroless nickel plating film as the outermost layer of the surface to be plated, using a displacement-type electroless silver plating bath. In other words, in the outermost layer formation process, an electroless silver plating film formed using a displacement-type electroless silver plating bath is formed as the outermost layer of the plating film (plating film laminate) provided on the surface to be plated. This allows for the formation of a silver plating film on the upper outermost layer of the plating film laminate, and sufficient initial bonding strength with the silver sintered material is obtained. Here, the electroless silver plating film formed using the displacement-type electroless silver plating bath has a good film thickness distribution, thus providing stable initial bonding strength with the silver sintered material. Furthermore, since the electroless silver plating film formed using the displacement-type electroless silver plating bath has good adhesion to the nickel plating film, adhesion between the nickel plating film and the silver plating film can be ensured inexpensively.

[0050] The outermost layer formation step preferably involves forming an electroless silver plating film on the surface of the electroless nickel plating film using a displacement-type electroless silver plating bath as the outermost layer of the plated surface. This tends to provide better adhesion between the nickel plating film and the silver plating film, as well as being cost-effective.

[0051] It is important to form an electroless silver plating film on the upper side of the aforementioned electroless nickel plating film using a displacement-type electroless silver plating bath, and the method of forming the plating film is not particularly limited except for the use of a displacement-type electroless silver plating bath. The method of forming the plating film is the same as the barrier layer formation process, except for the use of a displacement-type electroless silver plating bath. In particular, it is preferable to use a displacement-type electroless silver plating bath with a pH of 6.0 to 12.0 because it is possible to suitably form an electroless silver plating film on the surface of the electroless nickel plating film using a displacement-type electroless silver plating bath.

[0052] The displacement-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 include, for instance, silver chloride, silver nitrate, silver oxide, silver sulfate, silver sulfite, silver carbonate, silver acetate, silver lactate, silver sulfosuccinate, silver sulfamate, silver sulfadiazine, silver oxalate, silver cyanide, silver ethanesulfonate, silver phenolsulfonate, silver chloride, and silver methanesulfonate. These may be used individually or in combination of two or more. Among these, silver nitrate and silver oxide are preferred, with silver nitrate being more preferred.

[0053] The displacement-type electroless silver plating bath preferably contains a silver compound at a silver (metallic silver (Ag)) concentration of 0.1 to 3.0 g / L, and more preferably 0.5 to 1.5 g / L. Below 0.1 g / L, it may cause uneven appearance and deterioration of film thickness distribution, and sufficient adhesion tends not to be ensured. Above 3.0 g / L, it may cause uneven appearance and deterioration of film thickness distribution, and sufficient adhesion tends not to be ensured. In this specification, the concentration of metals such as silver (metallic silver (Ag)) in the plating bath is measured by ICP (manufactured by Horiba, Ltd.).

[0054] The displacement-type electroless silver plating bath preferably contains a complexing agent. As a result, the electroless silver plating film formed using the displacement-type electroless silver plating bath tends to have better adhesion to the nickel plating film. The complexing agent is not particularly limited as long as it is a compound capable of stably dissolving silver ions. Specific examples include amide compounds, imide compounds, sulfur-containing organic compounds, and nitrogen-containing compounds (nitrogen-containing compounds other than amide compounds and imide compounds). These may be used individually or in combination of two or more. Among these, amide compounds, imide compounds, and sulfur-containing organic compounds are preferred, with amide compounds and imide compounds being more preferred.

[0055] The amide compounds are not particularly limited and include, for example, cyclic amide compounds such as benzamide, N-methylpyrrolidone, N-ethylpyrrolidone, N-vinylpyrrolidone, pyrrolidone, N-butylpyrrolidone, 5-methylpyrrolidone, N-methylpiperidinone, N-ethylpiperidinone, N-butylpiperidinone, N-benzoylglycine, salicylamide, and nicotinamide; and chain-like 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, oxamic acid, and acrylamide. These may be used alone or in combination of two or more.

[0056] The imide compounds are not particularly limited and include, for example, cyclic imide compounds such as hydantoin, 5,5-dimethylhydantoin, 1-methylhydantoin, 1,3-dimethylhydantoin, 5,5'-diphenylhydantoin, glutarimide, succinimide, barbituric acid, phthalimide, and maleimide; and 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, and (trifluoromethanesulfonyl)(nonafluorobutanesulfonyl)imide salt. These may be used alone or in combination of two or more.

[0057] The sulfur-containing organic compounds are not particularly limited, and examples include thiol-based sulfur-containing organic compounds such as methanethiol, ethanethiol, thiophenol, cysteine, glutathione, 4-mercaptobenzoic acid, and thioglycolic acid; sulfide-based sulfur-containing organic compounds such as dimethyl sulfide, methionine, acetylmethionine, 3,6-dithiaoctanediol, and thiodiglycolic acid; and thiourea-based sulfur-containing organic compounds such as thiourea, 1,3-diethyl-2-thiourea, tetramethylthiourea, and allylthiourea. These may be used individually or in combination of two or more.

[0058] The displacement-type electroless silver plating bath preferably contains 1 to 50 g / L of 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. Below 1 g / L, sufficient adhesion cannot be ensured, and Ag turbidity tends to occur. Above 50 g / L, sufficient adhesion cannot be ensured, dissolution is difficult, and it tends to be disadvantageous in terms of cost. In cases where multiple types of complexing agents are included, the aforementioned concentration refers to the total concentration, and the same applies to the concentrations of other components.

[0059] The displacement-type electroless silver plating bath preferably contains a chelating agent. The chelating agent is not particularly limited as long as it is a compound capable of forming a complex with the underlying metal (e.g., nickel) and stably dissolving the underlying metal ions (e.g., nickel ions) as the substitution reaction progresses and the amount of underlying metal (e.g., nickel) dissolved in the plating bath increases. Specific examples include, for example, ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), ethylenediaminetetramethylenephosphonic acid (EDTMP), hydroxyethylethylenediaminetriacetic acid (HEDTA), diethylenetriaminepentaacetic acid (DTPA), triethylenetetraminehexaacetic acid (TTHA), methylethylenediaminetetraacetic acid (PDTA), N,N-bis(2-hydroxyethyl)glycine (DHEG), etidronic acid (HEDP), Examples of chelating agents include nitrogen-containing and phosphorus-based chelating agents such as ethylenediaminetetramethylenephosphonic acid (HDTMP); organic acid-based chelating agents such as citric acid, malic acid, gluconic acid, lactic acid, malonic acid, fumaric acid, maleic acid, tartaric acid, acetic acid, succinic acid, oxalic acid, glycolic acid, and formic acid; and amino acid-based chelating agents such as glycine, alanine, aspartic acid, glutamic acid, iminodiacetic acid, leucine, isoleucine, lysine, tryptophan, valine, histidine, arginine, serine, and tyrosine. These may be used individually or in combination of two or more.

[0060] The displacement type electroless silver plating bath preferably contains 1 to 50 g / L of chelating agent, more preferably 3 to 40 g / L, even more preferably 5 to 20 g / L, and particularly preferably 5 to 15 g / L. Below 1 g / L, sufficient adhesion (especially during aging (Ni dissolution)) tends not to be ensured. Above 50 g / L, sufficient adhesion cannot be ensured, dissolution is difficult, and it tends to be disadvantageous in terms of cost.

[0061] A displacement-type electroless silver plating bath preferably contains a modifier (buffer). The modifier enhances pH buffering, promotes the displacement reaction, and further improves adhesion. The adjusting agent is not particularly limited as long as it is a compound that has pH buffering properties and promotes substitution reactions. Specific examples include phosphinic acid compounds such as phosphoric acid, pyrophosphate, polyphosphate, tripolyphosphate, hypophosphorous acid, phosphorous acid, metaphosphate, dimethylallyl diphosphate, adenosinate phosphate, tetraethyl pyrophosphate, thiamine pyrophosphate, and creatine phosphate (phosphinic acid-based adjusting agents); and nitrogen-containing heterocyclic compounds such as imidazole, imidazoline, thiazole, thiazoline, pyrrole, pyrazoline, pyridine, quinoline, triazole, tetrazole, indole, indidine, and pyrazine (nitrogen-containing heterocyclic compound-based adjusting agents). These may be used alone or in combination of two or more.

[0062] The displacement-type electroless silver plating bath preferably contains 0.1 to 50 g / L of a adjusting agent, more preferably 3 to 40 g / L, even more preferably 5 to 20 g / L, and particularly preferably 5 to 15 g / L. Below 0.1 g / L, pH fluctuations are large, and variations in appearance and adhesion tend to occur. Above 50 g / L, dissolution is difficult, sufficient adhesion cannot be ensured, and it tends to be disadvantageous in terms of cost.

[0063] The pH of the displacement-type electroless silver plating bath is preferably 1.0 to 12.0, more preferably 2.0 to 12.0, and even more preferably 3.0 to 12.0, with a lower limit that is particularly preferably 4.0 or higher, most preferably 5.0 or higher, and most preferably 6.0 or higher. Below 1.0, sufficient adhesion tends not to be ensured. Above 12.0, sufficient adhesion also tends not to be ensured. In this specification, the pH of the plating bath is the value measured at 25°C.

[0064] The pH of the displacement-type electroless silver plating bath can also be adjusted by selecting the types of various components to be added. Alkaline and acidic components may also be added as needed. The alkaline component is not particularly limited, but examples include sodium hydroxide and ammonium. The acidic component is not particularly limited, but examples include sulfuric acid and phosphoric acid. These alkaline and acidic components may be used individually or in combination of two or more.

[0065] The displacement-type electroless silver plating bath may contain, in addition to the above-mentioned components, components commonly used in plating baths, such as surfactants and brighteners. It may also contain water-soluble salts of other metals, such as iron, copper, zinc, nickel, palladium, lead, bismuth, and thallium. These may be used individually or in combination of two or more.

[0066] A displacement-type electroless silver plating bath can be suitably used as a metal replacement treatment solution for forming an electroless silver plating film on the surface of an electroless nickel plating film using the displacement-type electroless silver plating bath.

[0067] In the outermost layer formation process, for example, the surface of the electroless nickel plating film is brought into contact with a displacement-type electroless silver plating bath, and an electroless silver plating film formed using the displacement-type electroless silver plating bath is formed on the surface of the electroless nickel plating film.

[0068] In the outermost layer formation step, the temperature of the displacement-type electroless silver plating bath (bath temperature) is not particularly limited, but is preferably 25 to 80°C, more preferably 30 to 70°C, and even more preferably 40 to 60°C. The processing time with the displacement-type electroless silver plating bath is also not particularly limited, but is preferably 1 to 60 minutes, more preferably 5 to 30 minutes.

[0069] The thickness of the electroless silver plating film formed on the upper side of the electroless nickel plating film by the outermost layer formation process using a displacement-type electroless silver plating bath is preferably 1.0 μm or less, more preferably 0.7 μm or less, even more preferably 0.5 μm or less, preferably 0.01 μm or more, more preferably 0.05 μm or more, and even more preferably 0.1 μm or more. Within this range, better adhesion between the nickel plating film and the silver plating film tends to be obtained.

[0070] The electroless silver plating film formed using a displacement-type electroless silver plating bath in the outermost layer formation step may be an alloy film containing other metals. The other metals, including preferred embodiments, are the same as those used in the electroless nickel plating film formed in the barrier layer formation step.

[0071] The silver content in the electroless silver plating film formed using a displacement-type electroless silver plating bath is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, particularly preferably 95% by mass or more, most preferably 98% by mass or more, and may also be 100% by mass. When the content is within the above range, the effect tends to be more favorably obtained.

[0072] <<Other processes>> The plating method for silver sintering bonding of the present invention may include other steps, as long as it includes the barrier layer formation step and the outermost layer formation step.

[0073] Other processes may include processes for forming other plating films, such as nickel plating films, as well as, if necessary, cleaning, etching, pickling, activating, post-dipping, dismatting, and zincate processes. The chemicals used in the cleaning, etching, pickling, activating, post-dipping, dismatting, and zincate processes can be appropriately selected from known ones.

[0074] The present invention's plating method for silver sintering bonding preferably includes a barrier layer formation step of forming an electroless nickel plating film on the surface of the surface to be plated, and a top layer formation step of forming an electroless silver plating film on the surface of the electroless nickel plating film as the outermost layer of the surface to be plated, using a displacement-type electroless silver plating bath. This tends to yield more favorable results.

[0075] The total thickness of the plated film (plated film laminate) formed by the plating method of the present invention is preferably 15 μm or less, more preferably 10 μm or less, even more preferably 7 μm or less, preferably 1 μm or more, more preferably 2 μm or more, and even more preferably 3 μm or more. When the thickness is within the above range, the effect tends to be more favorably obtained.

[0076] In this specification, the thickness of the plating film and the total thickness are the average values ​​of five measurements taken using an X-ray fluorescence spectrometer, and are specifically measured by the method described in the examples.

[0077] The material of the surface to be plated is not particularly limited and includes, for example, copper, aluminum, iron, nickel, etc. The material of the surface to be plated may also be an alloy of these materials. Among these, copper, aluminum, Fe-Ni alloy, brass and other copper alloys are preferred, and copper and aluminum are more preferred.

[0078] The plating method for silver sintering bonding of the present invention can be applied without particular limitations to any member to be subjected to silver sintering bonding. The member to be subjected to silver sintering bonding is not particularly limited and includes, for example, substrates such as ceramic substrates and printed circuit boards; semiconductor elements, heat sinks, heat dissipation plates, chips, lead frames, copper plates, etc. Among these, members having a base metal, such as substrates (especially ceramic substrates), heat dissipation plates, heat sinks, and chips, are preferred, and substrates (especially ceramic substrates) are more preferred, for the reason that oxidation of the base metal can be prevented and heat resistance can be further improved.

[0079] <Plating film (plating film laminate)> The present invention provides a plated film (plated film laminate) for silver sintering bonding, Electroless nickel plating film and On top of the electroless nickel plating film, as the outermost layer, there is an electroless silver plating film formed using a displacement-type electroless silver plating bath, It holds. The plating film of the present invention is, for example, a plating film provided on a surface to be plated 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 preferred embodiments. The other descriptions are also the same, including preferred embodiments.

[0080] The plated film (plated film laminate) of the present invention may have an electroless nickel plating film and an electroless silver plating film formed on the upper side of the electroless nickel plating film as the outermost layer using a displacement-type electroless silver plating bath, but it may also have films other than the electroless nickel plating film and the electroless silver plating film formed using a displacement-type electroless silver plating bath.

[0081] <<Barrier layer>> The plated film (plated 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 may be located on the upper side of the surface to be plated, but it is preferable that it be formed on the surface of the surface to be plated. Electroless nickel plating provides excellent heat resistance because it functions effectively as a barrier layer against oxygen.

[0082] The thickness of the electroless nickel plating film is preferably 15 μm or less, more preferably 10 μm or less, even more preferably 7 μm or less, preferably 1 μm or more, more preferably 2 μm or more, and even more preferably 3 μm or more. Within this range, the effect tends to be more favorably obtained.

[0083] The electroless nickel plating film may be an alloy film containing other metals. The other metals, including preferred embodiments, are the same as those formed by the barrier layer formation process in the electroless nickel plating film. Furthermore, the content of other metals in the electroless nickel plating film is the same as that formed by the barrier layer formation process in the electroless nickel plating film. Moreover, the nickel content in the electroless nickel plating film is the same as that formed by the barrier layer formation process in the electroless nickel plating film.

[0084] <<Top layer>> The plated film (plated film laminate) of the present invention has an electroless silver plating film formed using a displacement-type electroless silver plating bath on the upper side of an electroless nickel plating film as the outermost layer of the plated film provided on the surface to be plated. This ensures sufficient initial bonding strength with the silver sintered material. Here, the electroless silver plating film formed using a displacement-type electroless silver plating bath has a good film thickness distribution, thus providing stable initial bonding strength with the silver sintered material. Furthermore, since the electroless silver plating film formed using a displacement-type electroless silver plating bath has good adhesion to the nickel plating film, adhesion between the nickel plating film and the silver plating film can be ensured inexpensively.

[0085] The plated film (plated film laminate) of the present invention preferably has an electroless silver plating film formed on the surface of an electroless nickel plating film using a displacement-type electroless silver plating bath. This tends to provide better adhesion between the nickel plating film and the silver plating film, as well as cost advantages.

[0086] The displacement-type electroless silver plating bath is the same as the displacement-type electroless silver plating bath described in the outermost layer formation process, including preferred embodiments.

[0087] The thickness of the electroless silver plating film formed using a displacement-type electroless silver plating bath is preferably 1.0 μm or less, more preferably 0.7 μm or less, even more preferably 0.5 μm or less, preferably 0.01 μm or more, more preferably 0.05 μm or more, and even more preferably 0.1 μm or more. Within this range, better adhesion between the nickel plating film and the silver plating film tends to be obtained.

[0088] The electroless silver plating film formed using a displacement-type electroless silver plating bath may be an alloy film containing other metals. Examples of other metals include those mentioned above, which may be used alone or in combination of two or more. Furthermore, the silver content in the electroless silver plating film formed using the displacement-type electroless silver plating bath is the same as that of the electroless silver plating film formed using the displacement-type electroless silver plating bath in the outermost layer formation process.

[0089] <<Other layers>> The plating film of the present invention may have an electroless nickel plating film and an electroless silver plating film formed using a displacement-type electroless silver plating bath, but may also have other layers.

[0090] Other layers are not particularly limited and include, for example, platinum plating, palladium plating, gold plating, and cobalt plating.

[0091] The plated film (plated film laminate) of the present invention preferably has an electroless nickel plating film formed on the surface of the surface to be plated, and an electroless silver plating film formed using a displacement-type electroless silver plating bath, which is formed on the surface of the electroless nickel plating film as the outermost layer of the surface to be plated. This tends to result in a more favorable effect.

[0092] The total thickness of the plating film (plating film laminate) of the present invention is preferably 15 μm or less, more preferably 10 μm or less, even more preferably 7 μm or less, preferably 1 μm or more, more preferably 2 μm or more, and even more preferably 3 μm or more. When the thickness is within the above range, the effect tends to be more favorably obtained.

[0093] As shown in Figure 1, the plating film 1 according to one embodiment of the present invention has an electroless nickel plating film 2 formed on the surface of the surface to be plated 6, and an electroless silver plating film 3 formed on the surface of the electroless nickel plating film 2 as the outermost layer of the surface to be plated 6, using a displacement type electroless silver plating bath.

[0094] The plating film (plating film laminate) for silver sintering bonding of the present invention can be applied without particular limitations to any member to be silver sintered. The member to be silver sintered is the same as the member described in the plating method of the present invention, including preferred embodiments. The material of the surface to be plated is also the same as the material described in the plating method of the present invention, including preferred embodiments.

[0095] <Power module circuit board> As described above, the plating film (plating film laminate) of the present invention is suitably applicable to substrates, and below, a power module substrate will be described as an example of a substrate using the plating film of the present invention. The power module substrate of the present invention is Substrate and A circuit formed on the substrate, The circuit comprises a plated film formed on the surface of the circuit, The aforementioned plating film is the plating film (plating film laminate) of the present invention. In this specification, "power module substrate" refers to a substrate used in a power module, and specifically refers to the substrates exemplified below. In this specification, the concept of a power module substrate also includes lead frames and spacers used in power semiconductors.

[0096] The substrate comprising a base material and a circuit formed on the base material is not particularly limited, and examples include DBC substrates, DBA substrates, AMB substrates, 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.

[0097] A heat-resistant power module substrate according to one embodiment of the present invention will be described below with reference to the drawings. A power module substrate 100 according to one embodiment of the present invention is a substrate for mounting a power semiconductor that generates high heat. As shown in Figure 2, the power module substrate 100 according to one embodiment of the invention comprises a base material 10, a circuit 20 formed directly on the base material or via a brazing material, and a plating film (plating film laminate) 1 formed on the surface of the circuit.

[0098] The substrate 10 used in the power module substrate 100 according to one embodiment of the present invention is not particularly limited, and examples include aluminum oxide, aluminum nitride, silicon nitride, etc. These may be used individually or in combination of two or more. Among these, aluminum oxide, aluminum nitride, and silicon nitride are preferred for their superior cost, heat dissipation, strength, etc.

[0099] As shown in Figure 2, a circuit 20 is formed on a substrate 10. The circuit 20 may be formed directly on the substrate 10, or it may be formed via a brazing material (not shown). The circuit 20 is typically made of copper and / or aluminum. Here, copper and aluminum may be alloys.

[0100] The method for forming the circuit 20 can be any known method and is not particularly limited, but in the direct method, one side of the copper plate which is the circuit component may be oxidized and bonded to the base material 10, and any unnecessary parts other than the circuit may be etched. Aluminum has excellent malleability and ductility, and copper has excellent heat dissipation. In addition, these metals are superior to other metals in terms of cost, so they are used in power module substrates.

[0101] The plating film 1 formed on the surface of the circuit 20 is the plating film of the present invention. When the surface of the plating film and, for example, a semiconductor element are silver-sintered together, the surface of the plating film forms a silver-sintered bonding surface, resulting in good adhesion between the nickel-plated film and the silver-plated film, as well as good initial bonding strength and heat resistance. In Figure 4, the surface of the plating film 1 formed on the surface of the circuit 20 and the semiconductor element 30 are silver-sintered together. That is, the surface of the plating film 1 and the semiconductor element 30 are bonded via a silver-sintered layer 40.

[0102] In the present invention, the method of silver sintering bonding is not particularly limited, and those skilled in the art can carry it out as appropriate according to known methods. For example, a paste in which silver particles are dispersed in an organic solvent can be used as the silver sintering material, and the organic solvent can be evaporated by heating or the like to bring the silver particles into contact with each other, thereby forming a bonding layer by sintering.

[0103] <Semiconductor elements> The plating film (plating film laminate) of the present invention is suitably applicable to semiconductor devices, and an example of a semiconductor device using the plating film of the present invention will be described below. The semiconductor element of the present invention is Having a plated film on the surface, The aforementioned plating film is the plating film (plating film laminate) of the present invention. The semiconductor element of the present invention is suitable for use as a semiconductor element for power modules because it has excellent adhesion between the nickel plating film and the silver plating film, as well as excellent heat resistance.

[0104] A semiconductor device according to one embodiment of the present invention will be described below with reference to the drawings. A semiconductor element 30 according to one embodiment of the present invention is a semiconductor element used in a power module substrate. As shown in Figure 3, the semiconductor element 30 according to one embodiment of the invention includes a plating film (plating film laminate) 1 formed on the surface of the semiconductor element 30.

[0105] The semiconductor elements are 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 individually or in combination of two or more types. Among these, power semiconductor elements are preferred, and SiC semiconductor elements and GaN semiconductor elements are more preferred, due to the particular requirement for heat resistance.

[0106] The plating film 1 formed on the surface of the semiconductor element 30 is the plating film of the present invention. When the surface of the plating film and, for example, the substrate are silver-sintered, the surface of the plating film forms a silver-sintered bonding surface, resulting in good adhesion between the nickel-plated film and the silver-plated film, initial bonding strength, and heat resistance. In Figure 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. That is, the circuit 20 and the semiconductor element 30 are bonded via the silver-sintered body layer 40.

[0107] In the present invention, the method of silver sintering bonding is not particularly limited, and those skilled in the art can carry it out as appropriate according to known methods. For example, a paste in which silver particles are dispersed in an organic solvent can be used as the silver sintering material, and the organic solvent can be evaporated by heating or the like to bring the silver particles into contact with each other, thereby forming a bonding layer by sintering.

[0108] <Semiconductor device> The power module substrate and semiconductor element of the present invention are suitably applicable to semiconductor devices. Therefore, the semiconductor device of the present invention is a semiconductor device comprising the power module substrate and / or the semiconductor element of the present invention, and preferably, the surface of the plating film of the present invention on the power module substrate and / or the semiconductor element of the present invention is a silver sintered bonding surface. Such a semiconductor device of the present invention can inexpensively ensure adhesion between the nickel plating film and the silver plating film, has good heat resistance, and is a highly reliable semiconductor device.

[0109] An example of a semiconductor device using the power module substrate of the present invention will be described below. The semiconductor device of the present invention is The present invention comprises a power module substrate and semiconductor elements, Preferably, the surface of the plating film on the power module substrate and the semiconductor element are silver sintered together. Since the semiconductor device comprises a specific power module substrate and a semiconductor element, and the surface of the plating film on the power module substrate and the semiconductor element are silver sintered together, adhesion between the nickel plating film and the silver plating film can be ensured inexpensively, and it has good heat resistance, making it a highly reliable semiconductor device.

[0110] In this specification, when we say that the surface of the plating film on the power module substrate and the semiconductor element are silver-sintered, it means that the entire surface of the plating film and the semiconductor element are silver-sintered, or that only a portion of the surface of the plating film and the semiconductor element are silver-sintered. For example, if the plating film is formed on both the front and back surfaces of the substrate, the surface of the plating film formed on one of the surfaces may be silver-sintered to the semiconductor element. In this case, the surface that is silver-sintered to the semiconductor element may be the entire surface of the plating film or only a portion of the surface. That is, the surface of the plating film formed on one of the surfaces may be silver-sintered to the semiconductor element. Furthermore, in this specification, it is sufficient that at least one of the semiconductor elements provided on the substrate is silver-sintered bonded to the surface of the plating film on the power module substrate, and all of the semiconductor elements may be silver-sintered bonded to the surface of the plating film on the power module substrate. Furthermore, in this specification, when we say that the surface of the plating film on the power module substrate and the semiconductor element are silver sintered bonded, it is also possible that the surface of the plating film on the power module substrate and the surface of the semiconductor element are silver sintered bonded, or that the surface of the plating film on the power module substrate and the surface of the plating film applied to the surface of the semiconductor element are silver sintered bonded.

[0111] In the semiconductor device of the present invention, the surface of the plating film and the semiconductor element are bonded by silver sintering. As a result, the surface of the plating film forms a silver sintering bonding surface, providing good adhesion between the nickel plating film and the silver plating film, as well as excellent initial bonding strength and heat resistance, making it a highly reliable semiconductor device.

[0112] The semiconductor elements are 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 individually or in combination of two or more types. Among these, power semiconductor elements are preferred, and SiC semiconductor elements and GaN semiconductor elements are more preferred, due to the particular requirement for heat resistance.

[0113] The semiconductor device preferably has a plating film on its surface, and the plating film is preferably the plating film (plating film laminate) of the present invention. This allows for better adhesion between the nickel plating film and the silver plating film at a lower cost, resulting in better initial bonding strength and heat resistance, and a more reliable semiconductor device and semiconductor device.

[0114] An example of a semiconductor device using the semiconductor element of the present invention will be described below. The semiconductor device of the present invention is The power module comprises a substrate and the semiconductor element of the present invention. Preferably, the surface of the plating film on the semiconductor element and the power module substrate are silver sintered together. Since the semiconductor device comprises a power module substrate and a specific semiconductor element, and the surface of the plating film on the semiconductor element and the power module substrate are silver sintered together, adhesion between the nickel plating film and the silver plating film can be ensured inexpensively, and it has good heat resistance, making it a highly reliable semiconductor device.

[0115] In this specification, when we say that the surface of the plating film of the semiconductor element and the power module substrate are silver-sintered, it means that the entire surface of the plating film is silver-sintered with the power module substrate, or that only a portion of the surface of the plating film is silver-sintered with the power module substrate. For example, if the plating film is formed on both the front and back surfaces of the semiconductor element, the silver-sintered bond may be formed only on the surface of the plating film formed on one of the surfaces. In this case, the surface that is silver-sintered with the power module substrate may be the entire surface of the plating film, or only a portion of the surface. That is, the silver-sintered bond may be formed only on a portion of the surface of the plating film formed on one of the surfaces. Furthermore, in this specification, it is sufficient that the surface of the plating film of the present invention of at least one semiconductor element among the semiconductor elements provided on the substrate is silver-sintered bonded to the power module substrate, or the surfaces of the plating film of the present invention of all semiconductor elements are silver-sintered bonded to the power module substrate. Furthermore, in this specification, when we say that the surface of the plating film of the semiconductor element and the power module substrate are silver sintered bonded, it is also possible that the surface of the plating film of the semiconductor element and the surface of the power module substrate are silver sintered bonded, or that the surface of the plating film of the semiconductor element and the surface of the plating film applied to the surface of the power module substrate are silver sintered bonded.

[0116] In the semiconductor device of the present invention, the surface of the plated film of the present invention and the power module substrate are bonded by silver sintering. As a result, the surface of the plated film forms a silver sintering bonding surface, providing good adhesion between the nickel plating film and the silver plating film, as well as excellent initial bonding strength and heat resistance, making it a highly reliable semiconductor device.

[0117] The power module substrate is not particularly limited and examples include DBC substrates, DBA substrates, AMB substrates, etc. These may be used individually or in combination of two or more types.

[0118] The power module substrate is preferably the power module substrate of the present invention. This allows for better adhesion between the nickel plating film and the silver plating film at a lower cost, resulting in better initial bonding strength and heat resistance, and a more reliable semiconductor device.

[0119] As described above, in Figure 4, the surface of the plating film 1 formed on the surface of the circuit 20 and the semiconductor element 30 are joined by silver sintering. 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 Figure 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 joined by silver sintering.

[0120] As described above, in the present invention, as shown in Figure 4, the surface of the plating film on the power module substrate and the surface of the semiconductor element (without the plating film) may be silver sintered and bonded, and as shown in Figure 5, the surface of the plating film on the power module substrate and the surface of the plating film applied to the semiconductor element surface may be silver sintered and bonded. The plating film applied to the semiconductor element surface is not particularly limited, but examples include, in addition to the plating film of the present invention (plating film 1 in Figure 5), sputtered Ag (Ti / Ag, Ta / Ag, TaN / Ag, Ni / Au, Ni / Ag, etc.) films, electroplated and / or electroless plated Ni / Au, Ni / Pd / Au films, etc. Among these, the plating film of the present invention is preferred. The material of the semiconductor element surface without the plating film is, for example, titanium, tantalum, tantalum nitride, etc.

[0121] Furthermore, as described above, in the present invention, although not shown in the figures, the surface of the plating film on the semiconductor element and the surface of the power module substrate (without the plating film) may be silver sintered and bonded, and as shown in Figure 5, the surface of the plating film on the semiconductor element and the surface of the plating film applied to the power module substrate may be silver sintered and bonded. Here, the plating film applied to the surface of the power module substrate is not particularly limited, but for example, in addition to the plating film of the present invention (plating film 1 in Figure 5), examples include Ni / Au, Ni / Pd / Au films by electroplating and / or electroless plating. Among these, the plating film of the present invention is preferred. The material of the power module substrate surface without the plating film is, for example, copper, aluminum, etc.

[0122] The semiconductor device of the present invention can be used in a variety of electronic components. Examples of electronic components include those used in home appliances, in-vehicle equipment, power transmission systems, transportation equipment, and communication equipment. Specifically, these include air conditioners, elevators, electric vehicles, hybrid vehicles, trains, power modules such as power control units for power generation equipment, general home appliances, and personal computers. Among these, power modules are preferred because heat resistance is particularly required. [Examples]

[0123] The present invention will be specifically described based on the examples provided, but the present invention is not limited to these examples.

[0124] A plated film laminate was formed by applying each plating to a substrate according to the conditions shown in Tables 1 to 8. A Cu bulk material (25 × 60 × 3 mm) was used as the base substrate to be plated. The obtained plated film laminate and the substrate on which the plated film laminate was applied were evaluated using the following method. The evaluation results are shown in Tables 1 to 7. Note that in Tables 2-7, the silver salt concentrations are expressed as silver element equivalent concentrations (g / L). Furthermore, as shown 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, pH 8.5, and a reducing agent (hydrazine derivative, hydroxylamines, dimethylamine borane, boron hydride compound) concentration of 1.0 g / L.

[0125] <Measurement of plating film thickness> The thickness of the plating film was calculated as the average value of five measurements taken using an X-ray fluorescence spectrometer (Hitachi High-Tech Science Corporation, product name: SFT-9550).

[0126] <Analysis of the composition of the plated film> The composition was analyzed after the plating film was formed. Specifically, the plating film was dissolved in nitric acid, and this solution was quantitatively analyzed for each element using an inductively coupled plasma (ICP) emission spectrometer (HORIBA, product name: Ultima Expert). The content of each component in the film was calculated from the mass of the dissolved plating film.

[0127] <Adhesion evaluation (cross-cut test)> Six parallel cuts were made by applying a blade perpendicular to the plating film. Next, six more cuts were made perpendicular to the first six cuts. Cellophane tape was applied to the grid-like cut areas and rubbed firmly with a finger. The tape was quickly 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 △: Partially peeled off ×: Completely peeled off

[0128] <Heat resistance evaluation> (Preparation of evaluation samples) For the base substrate (Cu bulk material; 25 × 60 × 3 mm) and simulated chip (Cu bulk material processed to chip size; 5 × 5 × 1 mm), plating was applied according to the conditions shown in Tables 1 to 8. Then, the base substrate and simulated chip (both forming the same film laminate) were joined to each other using silver sintering material (MAX102: manufactured by Nihon Handa Co., Ltd.) and heat-treated at 250°C without pressure for 10 minutes under air to perform silver sintering bonding. Furthermore, to induce thermal degradation, the substrate was heat-treated at 300°C for 500 hours to prepare evaluation samples. (Measurement of joint strength) For the evaluation samples, the silver-sintered chips were splintered from the side, and the strength at which they fractured was measured using a bond tester (Nordson DAGE, product name: 4000Plus), and this was defined as the bond strength (bond strength after heat treatment). Based on the bond strength after heat treatment, the heat resistance was evaluated according to the following criteria. ○: No problem (Joint strength after heat treatment: 30 MPa or higher) △: Slight decrease in strength due to heat treatment (Joint strength after heat treatment: less than 20-30 MPa) ×: Strength decreases due to heat treatment (Joint strength after heat treatment: less than 20 MPa)

[0129] <Cost> Pd: Average retail price ¥8218 / g (average as of October 2021) Pt: Average retail price ¥4142 / g (average as of October 2021) Ag: Average retail price ¥98 / g (average as of October 2021) Ni: Average retail price ¥2.2 / g (average as of October 2021) Based on the above retail prices, calculate the price of each coating component as a metal (assuming each metal is 100%). 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 Cost was evaluated according to the following criteria. High: Ni / Pd / Ag, Ni / Pt / Ag Low: Ni / Ag

[0130] <Ag Appearance> Electroplating was performed on the base substrate (Cu bulk material; 25 × 60 × 3 mm) as the electroplated object according to the conditions shown in Tables 1 to 8, and the appearance of the Ag film was visually confirmed. Ag appearance was evaluated according to the following criteria. 〇: No uneven appearance △: Some uneven appearance ×: Overall uneven appearance

[0131] Hereinafter, the method for producing the electroplated film laminate and the substrate provided with the electroplated film laminate in each example and comparative example will be described in detail.

[0132] (Comparative Example 1) An electroless Ag plating film was formed on the surface of the Cu bulk material, which is the electroplated surface, using Argent RSD-4 manufactured by Uemura Kogyo Co., Ltd.

[0133] (Comparative Example 2) An electroless NiP plating film was formed on the surface of the Cu bulk material, which is the electroplated surface, using Nimden 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.

[0134] (Comparative Example 3) An electroless NiP plating film was formed on the surface of the Cu bulk material, which is the electroplated surface, using Nimden 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.

[0135] (Comparative Example 4) An electroless NiP plating film was formed on the surface of the Cu bulk material, which is the electroplated surface, using Nimden 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.

[0136] (Comparative Example 5) An electroless NiB plating film was formed on the surface of the Cu bulk material to be plated using Nimden BEL-18 manufactured by Uemura Kogyo Co., Ltd., and then an electroless Ag plating film was formed on that surface using Argent RSD-4 manufactured by Uemura Kogyo Co., Ltd.

[0137] (Comparative Example 6) On the surface of the Cu bulk material to be plated, an electroless NiP plating film was formed using Nimden NPR-4 manufactured by Uemura Kogyo Co., Ltd., then an electroless Pd plating film was formed on that surface using Altarea TPD-30 manufactured by Uemura Kogyo Co., Ltd., and finally an electroless Ag plating film was formed on that surface using Argent RSD-4 manufactured by Uemura Kogyo Co., Ltd.

[0138] (Comparative Example 7) On the surface of the Cu bulk material to be plated, an electroless NiP plating film was formed using Nimden NPR-4 manufactured by Uemura Kogyo Co., Ltd., then an electroless Pt plating film was formed on that surface using Altarea TGM-21 manufactured by Uemura Kogyo Co., Ltd., and finally an electroless Ag plating film was formed on that surface using Argent RSD-4 manufactured by Uemura Kogyo Co., Ltd.

[0139] (Example 1) On the surface of the Cu bulk material to be plated, an electroless NiP plating film was formed using Nimden KSL-2 manufactured by Uemura Kogyo Co., Ltd., and on that surface, an electroless silver plating film was formed using a displacement-type electroless silver plating bath with the composition and conditions shown in Tables 1 and 5.

[0140] (Example 2) On the surface of the Cu bulk material to be plated, an electroless NiP plating film was formed using Nimden NPR-4 manufactured by Uemura Kogyo Co., Ltd., and on that surface, an electroless silver plating film was formed using a displacement-type electroless silver plating bath with the composition and conditions shown in Tables 1 and 5.

[0141] (Example 3) On the surface of the Cu bulk material to be plated, an electroless NiP plating film was formed using Nimden DX manufactured by Uemura Kogyo Co., Ltd., and on that surface, an electroless silver plating film was formed using a displacement-type electroless silver plating bath with the composition and conditions shown in Tables 1 and 6.

[0142] (Example 4) On the surface of the Cu bulk material to be plated, an electroless NiB plating film was formed using Nimden BEL-18 manufactured by Uemura Kogyo Co., Ltd., and on that surface, an electroless silver plating film was formed using a displacement-type electroless silver plating bath with the composition and conditions shown in Tables 1 and 7.

[0143] (Examples 5-69) The plating film was formed in the same manner as in Example 2, except that a substitution-type electroless silver plating bath with the composition and conditions shown in Tables 2-7 was used.

[0144] [Table 1]

[0145] [Table 2]

[0146] [Table 3]

[0147] [Table 4]

[0148] [Table 5]

[0149] [Table 6]

[0150] [Table 7]

[0151] [Table 8]

[0152] Tables 1-7 show that in the embodiment having an electroless nickel plating film and an electroless silver plating film formed on the upper side of the electroless nickel plating film as the outermost layer using a displacement-type electroless silver plating bath, adhesion between the nickel plating film and the silver plating film can be ensured inexpensively, and good heat resistance can be obtained. Therefore, the plating method and plating film of the present invention are suitably applicable to silver sintering bonding. Tables 1-7 show the results when a Cu bulk material is used as the base substrate to be plated, but similar results were obtained when an Al bulk material was used as the base substrate to be plated. [Explanation of Symbols]

[0153] 1. Plating film (plating film laminate) 2. Electroless nickel plating film 3. Electroless silver plating film formed using a displacement-type electroless silver plating bath 6. Plating surface 10 Base material 20 circuits 30 Semiconductor elements 40 Silver sintered layer 100 Power Module Circuit Board

Claims

1. A barrier layer formation step is performed on the upper side of the surface to be plated, forming an electroless nickel plating film. The process involves forming an electroless silver plating film on top of the electroless nickel plating film, using a substitution-type electroless silver plating bath containing a sulfur-containing organic compound, as the outermost layer of the surface to be plated, as part of the outermost layer formation step. A plating method for silver sintering bonding, including a silver sintering method.

2. The plating method according to claim 1, wherein the substitution type electroless silver plating bath comprises at least one complexing agent selected from the group consisting of amide compounds and imide compounds.

3. The plating method according to claim 1 or 2, wherein the substitution type electroless silver plating bath comprises at least one adjusting agent selected from the group consisting of phosphinic acid compounds and nitrogen-containing heterocyclic compounds.

4. The plating method according to claim 1 or 2, wherein the displacement type electroless silver plating bath contains a chelating agent.

5. The plating method according to claim 1 or 2, wherein the thickness of the electroless silver plating film is 0.01 to 1.0 μm.

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