Metal substrate

Abstract

Metal-based surface mount substrates are used for mounting semiconductor devices and the like due to their excellent heat dissipation and processability. However, conventional technology requires the application of brazing paste material onto the plating layer, which presents challenges in terms of manufacturing costs. [Solution] The above problem is solved by a metal substrate in which a plating layer is formed on part or the entire surface of the substrate, the plating layer has a structure in which intermetallic compound crystals containing Sn and Cu are dispersed in a matrix phase containing Sn, a Sn-Cu alloy, Ni or Al or Cr, and the plating layer has a concentration gradient in which the concentrations of Sn and Cu change from the contact point between the substrate and the plating layer toward the surface of the metal substrate.

Description

Technical Field

[0001] The present invention relates to a metal substrate.

Background Art

[0002] Metal-based substrates for surface mounting are used for substrates for mounting semiconductor elements and the like because they are excellent in heat dissipation, workability, etc. For example, in Patent Document 1, a thin plate-shaped core material made of Mo is centered, and Au plating surface layers of Au or an Au alloy are formed on both sides so as to be vertically symmetric, and at least a Cu plating layer for complementing and maintaining it is provided between the core material and the Au plating surface layer. A wafer for an LED characterized by forming a composite base layer is disclosed. Further, Patent Document 2 includes a metal substrate for an LED in which adjustment plating layers having high brightness and high heat dissipation and hardness and the like are provided on both upper and lower surfaces of a core material, and an LED chip mounted thereon. The metal substrate has an adhesive plating layer of metal plating serving as an adhesive material formed by melting on the adjustment plating layer. On the LED chip, an adhesive sputter film by a sputter device is formed via an epitaxial layer corresponding to the adhesive plating layer, and the adhesive plating layer and the adhesive sputter film are fused to form an adhesive material layer by melting between the adjustment plating layer and the epitaxial layer. A metal substrate with an LED chip is disclosed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the conventional technology described above requires the application of a brazing paste material onto the plated layer, which presents challenges in terms of manufacturing costs. Therefore, the object of the present invention is to provide a metal substrate having a plating layer formed on a substrate, which eliminates the need to use brazing paste material when surface mounting is performed, thereby reducing manufacturing costs and providing a bonding function. [Means for solving the problem]

[0005] The present invention relates to a metal substrate in which a plating layer is formed on part or all of the substrate, The aforementioned plating layer has a structure in which intermetallic compound crystals containing Sn and Cu are dispersed in a matrix phase containing Sn, a Sn-Cu alloy, Ni, Al, or Cr. The plating layer has a concentration gradient in which the concentrations of Cu and Sn change from the contact point between the substrate and the plating layer toward the surface of the metal substrate. This provides... [Effects of the Invention]

[0006] According to the present invention, a metal substrate having a plating layer formed on a substrate can be provided, which eliminates the need to use brazing paste material when surface mounting is performed, thereby reducing manufacturing costs and providing a metal substrate with bonding functionality. [Brief explanation of the drawing]

[0007] [Figure 1] This figure illustrates an example of a manufacturing apparatus suitable for producing metal particles according to the present invention. [Figure 2] This is a cross-sectional SEM image of bulk 1 from Example 1. [Figure 3] This figure shows the results of elemental mapping analysis by EDS on one cross-section of bulk 1 of Example 1. [Figure 4A] This is a photograph of a cross-section of the metal substrate obtained in Example 1. [Figure 4B] This is an SEM image of a cross-section of the substrate surface of the metal substrate obtained in Example 1. [Figure 5] This photograph shows the cross-sections of a metal substrate and a Si chip, after which the polished surfaces were examined using a microscope (500x magnification). [Modes for carrying out the invention]

[0008] The embodiments of the present invention will be described in more detail below. In this specification, unless otherwise specified, the following terms shall apply: (1) When we refer to metals, we may include not only individual metal elements but also alloys containing multiple metal elements and intermetallic compound crystals. (2) When referring to a particular elemental metal, it does not mean only a substance consisting entirely of that element, but also includes substances containing trace amounts of other substances. That is, it does not mean excluding substances containing trace amounts of impurities that have little effect on the properties of the element, nor does it mean excluding, for example, in the case of a matrix, substances in which some atoms in the Sn crystal are replaced by other elements (e.g., Cu). For example, the aforementioned other substances or other elements may be present in the terminals described below at a concentration of 0 to 0.1 mass%.

[0009] The plating layer of the present invention has a structure in which intermetallic compound crystals containing Sn and Cu are dispersed in a matrix phase containing Sn, a Sn-Cu alloy, Ni, Al, or Cr, and has a concentration gradient in which the concentrations of Cu and Sn change from the contact point between the substrate and the plating layer toward the surface of the metal substrate.

[0010] The plating for providing the aforementioned plating layer may be either electrolytic plating or electroless plating, but below we will describe a plating method using an electroless plating solution.

[0011] The electroless plating solution in the present invention contains a metal ion source in which intermetallic compound crystals containing Sn and Cu are dispersed in a matrix phase containing Sn, a Sn-Cu alloy, and Ni, Al, or Cr.

[0012] The metal ion source in the present invention can be manufactured as follows. First, metal particles described below (hereinafter sometimes referred to as the metal particles of the present invention) are manufactured. Subsequently, the obtained metal particles of the present invention are melted by high-frequency induction heating under vacuum, and this is subjected to die casting under atmospheric pressure in a nitrogen gas atmosphere, cooled and solidified to form a rolled sheet, and if necessary, a plurality of these are laminated (hereinafter sometimes referred to as a bulk), and pulverized to obtain the metal ion source.

[0013] The metal particles of the present invention can be manufactured from a raw material having a composition of, for example, 8% by mass of Cu, 1% by mass of Ni or Al or Cr, and the balance being Sn.

[0014] For example, the raw material is melted, supplied onto a dish-shaped disk that rotates at high speed in a nitrogen gas atmosphere, and the molten metal is scattered as droplets by centrifugal force and cooled and solidified under reduced pressure to obtain the metal particles of the present invention.

[0015] An example of a manufacturing apparatus suitable for producing metal particles of the present invention will be described with reference to Figure 1. Figure 1 is a diagram illustrating an example of a manufacturing apparatus suitable for producing metal particles of the present invention. The granulation chamber 1 has a cylindrical upper part and a cone-shaped lower part, and has a lid 2 at the top. A nozzle 3 is inserted vertically into the center of the lid 2, and a dish-shaped rotating disk 4 is provided directly below the nozzle 3. Reference numeral 5 denotes a mechanism that supports the dish-shaped rotating disk 4 so that it can move up and down. A discharge pipe 6 for the generated particles is connected to the lower end of the cone portion of the granulation chamber 1. The upper part of the nozzle 3 is connected to an electric furnace (high-frequency furnace: conventionally a ceramic crucible was used, but in the present invention a carbon crucible is used) 7 for melting the metal to be granulated. Atmospheric gas adjusted to a predetermined composition in a mixed gas tank 8 is supplied to the inside of the granulation chamber 1 and the top of the electric furnace 7, respectively, by pipes 9 and 10. The pressure inside the granulation chamber 1 is controlled by a valve 11 and an exhaust device 12, and the pressure inside the electric furnace 7 is controlled by a valve 13 and an exhaust device 14, respectively. Molten metal supplied from nozzle 3 onto dish-shaped rotating disk 4 is dispersed in the form of fine droplets by centrifugal force from the dish-shaped rotating disk 4, and then cooled under reduced pressure to become solid particles. The generated solid particles are supplied from discharge pipe 6 to automatic filter 15 for separation. Reference numeral 16 denotes a particulate matter recovery device.

[0016] The process of melting the molten metal at high temperatures and then cooling and solidifying it is important for forming the metal particles of the present invention. For example, the following conditions can be cited. The melting temperature of the metal in the electric furnace 7 is set to 800°C to 1000°C, and while maintaining that temperature, the molten metal is supplied from the nozzle 3 onto the dish-shaped rotating disk 4. As the disc-shaped rotating disk 4, a disc-shaped disk with an inner diameter of 35 mm and a rotating body thickness of 5 mm is used, and it is set to rotate at 80,000 to 100,000 revolutions per minute. Granulation chamber 1 is 9 × 10 -2 Using a vacuum chamber capable of reducing pressure to approximately Pa, the pressure is reduced, and simultaneously, nitrogen gas at 15-50°C is supplied while the chamber is evacuated, resulting in a pressure of 1 × 10⁻¹⁶ in the granulation chamber 1. -1 It should be Pa or less.

[0017] The metal particles of the present invention are obtained as described above. The particle size of the metal particles of the present invention is approximately 5 μm, but the particle size of the metal particles of the present invention is preferably in the range of 1 μm to 50 μm.

[0018] Next, the obtained metal particles of the present invention are melted by high-frequency induction heating under vacuum, and then cast into a mold in a nitrogen gas atmosphere under atmospheric pressure, cooled and solidified to form a rolled sheet. Multiple sheets of this sheet are then stacked as needed to obtain a bulk material. Examples of the aforementioned high-frequency induction heating and cooling solidification conditions include the following: High-frequency induction heating: 9 × 10 -2 A high-frequency induction melting crucible is placed in a vacuum chamber capable of reducing the pressure to approximately Pa. The metal particles of the present invention are introduced into the crucible, and high-frequency induction heating is performed on the metal particles of the present invention while the pressure is reduced to approximately the aforementioned degree of reduced pressure. The heating temperature is set to 800°C to 1000°C to melt the metal particles of the present invention, and this temperature is maintained for 5 to 15 minutes. Cooling and solidification: Next, while flowing nitrogen gas at 15-50°C into the tank, the heating temperature is set to approximately 400°C or higher under atmospheric pressure, the material is poured into the mold, and then cooled and solidified at 30°C or lower.

[0019] The bulk in the present invention, for example, has the following composition: Cu7~15% by mass, Ni or Al or Cr 1-0.2% by mass, The remainder is Sn. However, it may contain unavoidable impurities in amounts of 0.1% by mass or less. Furthermore, the composition is the same as that of the metal particles of the present invention.

[0020] Furthermore, the composition of the bulk matrix in the present invention is Cu0.001~5% by mass, Ni or Al or Cr 0.001~1% by mass, The remainder can be Sn. The composition of the matrix phase is the same as that of the metal particles of the present invention.

[0021] Furthermore, the composition of the bulk intermetallic compound crystal in the present invention is, Cu10~40% by mass, Ni or Al 10.1-6% by mass, The remainder may be Sn. If Cr is present, it is located at the interface (endotaxial phase) between the matrix phase and the intermetallic compound, and the Cr content at this interface is 0.1 to 6% by mass. The composition of the intermetallic compound crystal is the same as that of the metal particles of the present invention.

[0022] Furthermore, in the bulk material, the proportion of intermetallic compound crystals is, for example, 20 to 60% by mass, and preferably 30 to 40% by mass. The intermetallic compound crystal is contained within the matrix phase.

[0023] The composition and proportions of the matrix phase and intermetallic compound crystals in the present invention can be achieved by following the manufacturing conditions of the bulk material. The inventors have confirmed that the structure of the bulk material and the metal particles of the present invention are the same.

[0024] Furthermore, in the electroless plating method according to the present invention, intermetallic compound crystals and matrix contained in the crushed bulk dissolve in the plating bath as metal ion sources, and these are plated onto the substrate surface to form a plating layer. The formed plating layer has a structure in which intermetallic compound crystals containing Sn and Cu are dispersed in a matrix containing Sn, a Sn-Cu alloy, Ni, Al, or Cr.

[0025] The electroless plating solution in the present invention may contain, for example, various additives that have been conventionally known as a reducing plating solution. For example, reducing agents include hypophosphate, formaldehyde, paraformaldehyde, ammonium boro hydroxide, and dimethylamine borane. Examples of complexing agents include acetic acid, lactic acid, glycine, citric acid, malonic acid, malic acid, oxalic acid, succinic acid, tartaric acid, thioglycolic acid, ammonia, alanine, glutamic acid, and ethylenediamine. As pH adjusters, alkalis such as sodium hydroxide, potassium hydroxide, sodium carbonate, and hydroxide solutions of alkali metals or alkaline earth metals such as ammonia water can be used. As acids, hydrochloric acid, sulfuric acid, nitric acid, etc. can be used. Examples of stabilizers include nitrates of lead, bismuth, thallium, etc.

[0026] In the electroless plating solution of the present invention, the metal ion source concentration is preferably, for example, 10 to 200 g / liter, and the plating temperature is preferably 25 to 65°C.

[0027] The composition of the matrix phase and intermetallic compound crystals contained in the obtained plating layer is the same as that of the bulk material used. Furthermore, the amount of intermetallic compound crystals contained in the plating layer is, for example, 20 to 60% by mass. The composition of the matrix phase is the same as that of the bulk material used. The composition and structure of the entire plating layer, the matrix phase, and the intermetallic compound can be formed by the plating conditions.

[0028] Through the above procedure, a plating layer is formed on the substrate. The thickness of the plating layer is, for example, 1 μm to 10 μm.

[0029] Examples of substrates include metals such as aluminum alloys, copper, copper alloys, or stainless steel. Organic substrates and ceramic substrates can also be used, and these can be selected without particular limitation from among known materials. For example, examples of copper alloys include brass and phosphor bronze.

[0030] The metal substrate is subsequently subjected to heat treatment. The heat treatment conditions are, for example, a temperature of 170°C to 220°C in an inert gas atmosphere, and a heating time of, for example, 30 to 120 minutes. This heat treatment causes the intermetallic compound crystals to diffuse in the matrix phase, resulting in a concentration gradient in which the concentrations of Cu and Sn change from the contact point between the substrate and the plating layer toward the surface of the metal substrate. This concentration gradient further enhances the effects of the present invention.

[0031] Furthermore, the heat treatment results in a solid-phase diffusion layer of Sn extending from the contact point between the substrate and the plating layer toward the interior of the substrate, in a range of 0.2 μm to 2 μm. This solid-phase diffusion layer further enhances the effects of the present invention.

[0032] The resulting metal substrate of the present invention, when surface mounted, has a plating layer that functions as a bonding material, eliminating the need for conventional brazing paste materials to be used on the substrate. This can reduce manufacturing costs. [Examples]

[0033] The present invention will be further described below with reference to examples and comparative examples, but the present invention is not limited to the following examples. Example 1 Using raw materials with a composition of 8% by mass of Cu, 1% by mass of Ni, and the remainder being Sn, metal particles 1 with a diameter of approximately 3 to 50 μm were produced using the manufacturing apparatus shown in Figure 1. The following conditions were adopted at that time. A molten metal crucible was placed in the electric furnace 7, the above raw materials were placed inside, and the mixture was melted at 900°C. While maintaining that temperature, the molten metal was supplied from the nozzle 3 onto the dish-shaped rotating disc 4. As the disc-shaped rotating disc 4, a disc-shaped disc with a diameter of 35 mm and a rotating surface thickness of 3 to 5 mm was used, and the rotation speed was set to 80,000 to 100,000 revolutions per minute. Granulation chamber 1 is 9 × 10 -2 Using a vacuum chamber capable of reducing pressure to approximately Pa, the pressure is reduced, and simultaneously, nitrogen gas at 15-50°C is supplied while the chamber is evacuated, resulting in a pressure of 1 × 10⁻¹⁶ in the granulation chamber 1. -1It was set to Pa or less. A bulk material was prepared using the obtained metal powder 1. The following conditions were adopted at that time. High-frequency induction heating: 9 × 10 -2 A high-frequency induction melting crucible was placed in a vacuum chamber capable of reducing the pressure to approximately Pa. The metal particles 1 were introduced into the crucible, and high-frequency induction heating was performed on the metal particles 1 while maintaining the reduced pressure to approximately the aforementioned degree. The heating temperature was set to 900°C to melt the metal particles 1, and this temperature was maintained for 5 minutes. Cooling and solidification: Next, while circulating nitrogen gas at 15-50°C into the tank for 10 minutes, the raw material was heated to approximately 400°C under atmospheric pressure, cast into a mold, and then cooled and solidified at room temperature. The obtained material was rolled into sheets, and multiple sheets were stacked together to produce bulk material 1.

[0034] Figure 2 shows a cross-sectional SEM image of bulk 1 from Example 1. As can be seen in Figure 2, it was confirmed that intermetallic compound crystals (dark color) are embedded within the matrix phase (light color). Furthermore, elemental mapping analysis of one cross-section of bulk 1 by EDS (see Figure 3) revealed that its composition was 7.7 mass% Cu, 0.4 mass% Ni, and the remainder being Sn. It was also confirmed that bulk 1 has a structure in which intermetallic compound crystals containing Sn, Cu, and Ni are dispersed in a matrix phase containing Sn, a Sn-Cu alloy, and Ni. Furthermore, elemental mapping analysis of the matrix phase of bulk 1 using EDS revealed that its composition was 0.96 mass% Cu, 0.12 mass% Ni, and the remainder Sn. Furthermore, elemental mapping analysis of the intermetallic compound crystal using EDS revealed that its composition was 27.30 mass% Cu, 2.74 mass% Ni, and the remainder Sn. Furthermore, intermetallic compound crystals accounted for 30-35% by mass in bulk 1.

[0035] Next, bulk material 1 was heated to 150°C and crushed into small pieces, and the resulting pulverized material was placed in the plating bath described below. A copper substrate was used as the substrate, and electroless plating was performed on its surface. The details of the electroless plating bath are as follows.

[0036] Electroless plating bath composition (concentration per liter of water): Metal ion source: Intermetallic compound crystals and matrix contained in the bulk 1. Sn concentration=10g / L Cu concentration=1g / L Ni concentration=0.1g / L

[0037] The electroless plating conditions are as follows: Plating temperature: 50℃ Plating time: 120 minutes Heat treatment temperature for the substrate after plating: 200℃ Heat treatment time for substrate after plating: 300 seconds (under nitrogen atmosphere)

[0038] The composition of the plating layer of the metal substrate obtained according to the present invention was confirmed to be the same as that of bulk 1 by elemental mapping analysis using EDS. The thickness of the plating layer was 5 μm.

[0039] Next, the metal substrate was subjected to heat treatment. The heat treatment conditions were, for example, a temperature of 200°C to 220°C in an inert gas atmosphere, and a heating time of, for example, 60 to 120 minutes.

[0040] Figure 4A is a photograph of a cross-section of the obtained metal substrate, with numbers 001 to 006 assigned from the contact point between the substrate and the plating layer toward the surface of the metal substrate. Note that the number 001 on the substrate side is located approximately 2 μm from the substrate surface, and numbers 002 to 006 are spaced at roughly the same intervals. Elemental mapping analysis using EDS was performed at each numbered location, and the Cu and Sn concentrations of the intermetallic compound crystals at numbers 001 to 006 were as follows: the Cu concentration decreased and the Sn concentration increased from number 001 to 004. From these results, it was found that the amount of intermetallic compound crystals decreased from number 001 to 004. Number 001: Cu79.23 mass% Sn11.99 mass% Number 002: Cu58.33 mass% Sn33.32 mass% Number 003: Cu32.24 mass% Sn59.89 mass% Number 004: Cu24.52 mass% Sn68.14 mass% Number 005: Cu28.86 mass% Sn63.80 mass% Number 006: Cu29.37 mass% Sn62.52 mass%

[0041] From the above, it was found that the plating layer has a concentration gradient in which the concentrations of Sn and Cu change from the contact point between the substrate and the plating layer toward the surface of the metal substrate. Furthermore, Figure 4B is an SEM image of a cross-section of the substrate surface of the metal substrate. Elemental mapping analysis using EDS revealed a solid-phase diffusion layer of Sn in the region 003, extending from the contact point 006 between the substrate and the plating layer towards the interior of the substrate. The thickness of the solid-phase diffusion layer was approximately 0.6 μm.

[0042] An experiment was conducted in which a Si chip was mounted as a component on the plated layer of the metal substrate obtained in Example 1. Si chips (5mm square) with a Ti-Ni-Au backside metal treatment were placed on a plated layer, and the Si chips were mounted onto a metal substrate using a formic acid reflow oven. The working conditions were: pressure: glass plate (approx. 2kPa), heating temperature: 220°C, heating time: 5 minutes, heating atmosphere: formic acid / N2. The following checks were performed on the obtained product. Visual inspection: A molten area was observed at the end of the Si chip. X-ray confirmation: Bonding between the metal substrate and the Si chip was confirmed. Die share strength verification: 39.6 MPa, breaking strength 919 N Cross-sectional inspection: The cross-sections of the metal substrate and Si chip were cut out, polished, and then the polished surfaces were inspected with a microscope. The results are shown in Figure 5. No defects such as voids were observed at the bonding surface, confirming a strong bond between the metal substrate and Si chip.

[0043] Although the present invention has been described in detail above with reference to the attached drawings, the present invention is not limited thereto, and it will be obvious to those skilled in the art that various modifications can be conceived based on the basic technical concept and teachings. [Explanation of symbols]

[0044] 1 Granulation chamber 2 lid 3 nozzles 4. Turntable discs 5. Rotating disk support mechanism 6 Particle discharge pipe 7 Electric Furnace 8. Mixed gas tank 9 Piping 10 Piping 11 valves 12 Exhaust system 13 valves 14 Exhaust system 15 Automatic Filter 16. Particulate matter collection device

Claims

1. A metal substrate in which a plating layer is formed on part or all of the substrate, The aforementioned plating layer has a structure in which intermetallic compound crystals containing Sn and Cu are dispersed in a matrix phase containing Sn; a Sn-Cu alloy; Ni or Al or Cr; The plating layer has a concentration gradient in which the Cu concentration decreases, the Sn concentration increases, and the intermetallic compound crystals decrease from the contact point between the substrate and the plating layer toward the surface of the metal substrate.

2. The metal substrate according to claim 1, wherein the substrate has a solid-phase diffusion layer of Sn in the range of 0.2 μm to 2 μm from the contact point between the substrate and the plating layer toward the interior of the substrate.

3. The metal substrate according to claim 1, wherein the thickness of the plating layer is 1 μm to 10 μm.

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