WO2024176598A1 - Circuit board and power module - Google Patents

Circuit board and power module Download PDF

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Publication number
WO2024176598A1
WO2024176598A1 PCT/JP2023/045774 JP2023045774W WO2024176598A1 WO 2024176598 A1 WO2024176598 A1 WO 2024176598A1 JP 2023045774 W JP2023045774 W JP 2023045774W WO 2024176598 A1 WO2024176598 A1 WO 2024176598A1
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WO
WIPO (PCT)
Prior art keywords
bonding layer
plate
circuit board
silicon nitride
bonding
Prior art date
Application number
PCT/JP2023/045774
Other languages
French (fr)
Japanese (ja)
Inventor
優太 津川
清治 矢野
良太 青野
Original Assignee
デンカ株式会社
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Publication of WO2024176598A1 publication Critical patent/WO2024176598A1/en

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    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B37/00—Joining burned ceramic articles with other burned ceramic articles or other articles by heating
    • C04B37/02—Joining burned ceramic articles with other burned ceramic articles or other articles by heating with metallic articles
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L23/00—Details of semiconductor or other solid state devices
    • H01L23/12—Mountings, e.g. non-detachable insulating substrates
    • H01L23/13—Mountings, e.g. non-detachable insulating substrates characterised by the shape
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L25/00—Assemblies consisting of a plurality of individual semiconductor or other solid state devices ; Multistep manufacturing processes thereof
    • H01L25/03—Assemblies consisting of a plurality of individual semiconductor or other solid state devices ; Multistep manufacturing processes thereof all the devices being of a type provided for in the same subgroup of groups H01L27/00 - H01L33/00, or in a single subclass of H10K, H10N, e.g. assemblies of rectifier diodes
    • H01L25/04—Assemblies consisting of a plurality of individual semiconductor or other solid state devices ; Multistep manufacturing processes thereof all the devices being of a type provided for in the same subgroup of groups H01L27/00 - H01L33/00, or in a single subclass of H10K, H10N, e.g. assemblies of rectifier diodes the devices not having separate containers
    • H01L25/07—Assemblies consisting of a plurality of individual semiconductor or other solid state devices ; Multistep manufacturing processes thereof all the devices being of a type provided for in the same subgroup of groups H01L27/00 - H01L33/00, or in a single subclass of H10K, H10N, e.g. assemblies of rectifier diodes the devices not having separate containers the devices being of a type provided for in group H01L29/00
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L25/00—Assemblies consisting of a plurality of individual semiconductor or other solid state devices ; Multistep manufacturing processes thereof
    • H01L25/18—Assemblies consisting of a plurality of individual semiconductor or other solid state devices ; Multistep manufacturing processes thereof the devices being of types provided for in two or more different subgroups of the same main group of groups H01L27/00 - H01L33/00, or in a single subclass of H10K, H10N
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K1/00—Printed circuits
    • H05K1/02—Details
    • H05K1/09—Use of materials for the conductive, e.g. metallic pattern
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K3/00—Apparatus or processes for manufacturing printed circuits
    • H05K3/38—Improvement of the adhesion between the insulating substrate and the metal

Definitions

  • This disclosure relates to a circuit board and a power module.
  • the circuit boards mounted on electronic devices are manufactured by joining ceramic and metal plates with a brazing material. Furthermore, the multi-layer structure allows the circuit board to be endowed with a variety of properties.
  • Patent Document 1 discloses a circuit board that can suppress the deterioration of electrical properties due to heat generation and cooling by making the ceramic base material and metal base material into multiple layers.
  • Patent Document 2 discloses a circuit board that has high durability against heat cycles by laminating a metal layer and a sprayed layer on a ceramic plate.
  • the present disclosure provides a circuit board with high bonding strength.
  • the present disclosure also provides a power module that includes such a circuit board.
  • One aspect of the present disclosure provides the following circuit board:
  • a circuit board comprising a silicon nitride plate, a copper plate, and a bonding layer bonding the silicon nitride plate and the copper plate, the bonding layer having, from the silicon nitride plate side, a first bonding layer containing titanium nitride, a second bonding layer having a higher silicon content than the first bonding layer, and a third bonding layer having a higher silver content than the first bonding layer and the second bonding layer, the second bonding layer being interposed between the first bonding layer and the third bonding layer so as to isolate the first bonding layer from the third bonding layer.
  • the bonding layer of the circuit board has a second bonding layer interposed between the first bonding layer and the third bonding layer so as to isolate the first bonding layer and the third bonding layer.
  • the circuit board of [1] above may be any one of [2] to [6] below.
  • the difference between the maximum and minimum thicknesses of the first bonding layer is 70 nm or less.
  • the first bonding layer having such a thickness, the first bonding layer is sufficiently formed without variation over a wide range, and the bonding strength between the silicon nitride plate and the copper plate can be sufficiently high.
  • the second bonding layer has a thickness of 50 nm or more. In such a circuit board, the second bonding layer is formed with a sufficient thickness, and the bonding strength between the silicon nitride plate and the copper plate can be sufficiently high.
  • t1/t2 is 5 or less.
  • One aspect of the present disclosure provides the following power module:
  • a power module comprising a circuit board described in any one of [1] to [6] above and a semiconductor element electrically connected to the copper plate of the circuit board.
  • the power module has high bonding strength between the silicon nitride plate and the copper plate of the circuit board. Therefore, the power module has excellent durability.
  • the present disclosure can provide a circuit board with high bonding strength.
  • the present disclosure can also provide a power module that includes such a circuit board.
  • FIG. 5A to 5C are cross-sectional views of an example of a laminate for explaining a process in a method for manufacturing a circuit board.
  • FIG. FIG. 2 is a plan view of the structure with a portion of the pressing jig cut away.
  • FIG. 2 is a front view of the structure with a portion of the pressing jig cut away.
  • FIG. 2 is a side view of the structure with a portion of the pressing jig cut away.
  • 7 is a cross-sectional view of the structure shown in FIG. 4 taken along line VII-VII.
  • 13 is a cross-sectional view of the structure showing a state in which the pressure plate is raised and the spring washer is restored to its original state.
  • 1A is an STEM image of a cross section of a circuit board in Example 1.
  • FIG. 1B is an STEM image of a cross section of a circuit board in Comparative Example 1.
  • 1A is a diagram showing the distribution of titanium elements by EDX analysis of a cross section of the circuit board in Example 1.
  • FIG. 1B is a diagram showing the distribution of silicon elements by EDX analysis of a cross section of the circuit board in Example 1.
  • 1A is a diagram showing the distribution of silver and copper elements by EDX analysis of a cross section of the circuit board in Example 1; FIG.
  • 1B is a diagram showing the distribution of silver and copper elements by EDX analysis of a cross section of the circuit board in Example 1;
  • 1A is a diagram showing the distribution of titanium elements by EDX analysis of a cross section of the circuit board in Comparative Example 1.
  • FIG. 1B is a diagram showing the distribution of silicon elements by EDX analysis of a cross section of the circuit board in Comparative Example 1.
  • 1A is a diagram showing the distribution of silver and copper elements by EDX analysis of a cross section of the circuit board in Comparative Example 1; 1 is an EDX line profile in Example 1.
  • 1A is a photograph showing the state when the copper plate is peeled off from the circuit board in Example 1.
  • 1B is a photograph showing the state when the copper plate is peeled off from the circuit board in Comparative Example 1.
  • 1A is an SEM image of the peeled surface after the copper plate is peeled off from the circuit board in Example 1.
  • FIG. 1B is an SEM image of the peeled surface after the copper plate is peeled off from the circuit board in Comparative Example 1.
  • 1A is a diagram showing the distribution of silicon elements by EDX analysis of the peeled surface after peeling the copper plate from the circuit board in Example 1.
  • FIG. 1B is a diagram showing the distribution of silicon elements by EDX analysis of the peeled surface after peeling the copper plate from the circuit board in Comparative Example 1.
  • FIG. 1 is a schematic cross-sectional view of a circuit board according to one embodiment.
  • the circuit board 100 has a pair of copper plates 50 on both sides of a silicon nitride plate 10, and a bonding layer 20 that bonds each main surface of the silicon nitride plate 10 to the main surface of the copper plate 50.
  • the bonding layer 20 has, from the silicon nitride plate 10 side, a first bonding layer 21, a second bonding layer 22, and a third bonding layer 23, in this order.
  • the shape of the circuit board 100 is not particularly limited, and it may be an aggregate board, or an individual board obtained by dividing an aggregate board.
  • the thickness of the circuit board may be 0.9 to 2.7 mm, or 1.3 to 2.2 mm.
  • the silicon nitride plate 10 may be made of a silicon nitride sintered body obtained by sintering silicon nitride powder. There are no particular limitations on the shape of the silicon nitride plate 10 as long as it is plate-like.
  • the thickness of the silicon nitride plate 10 may be, for example, 0.2 to 2.0 mm, or 0.32 to 1.1 mm.
  • the copper plate 50 is not particularly limited in shape as long as it can be bonded to the main surface of the silicon nitride plate 10.
  • the thickness of the copper plate 50 may be, for example, 0.1 to 1.2 mm, or may be 0.2 to 1.0 mm.
  • the copper plate 50 may have a plating film on its surface.
  • the bonding layer 20 has, from the silicon nitride plate 10 side, a first bonding layer 21 containing titanium nitride, a second bonding layer 22 having a higher concentration of silicon element than the first bonding layer 21, and a third bonding layer 23 having a higher concentration of silver element than the first bonding layer 21 and the second bonding layer 22.
  • the second bonding layer 22 is interposed between the first bonding layer 21 and the third bonding layer 23 so as to isolate the first bonding layer 21 and the third bonding layer 23.
  • a circuit board 100 having such a bonding layer 20 can increase the bonding strength between the silicon nitride plate 10 and the copper plate 50.
  • the bonding layer 20 is a layer having a first bonding layer 21, a second bonding layer 22, and a third bonding layer 23.
  • the bonding layer 20 contains titanium, silver, and silicon elements.
  • the bonding layer 20 may further contain one or two metals selected from the group consisting of copper, tin, and an active metal.
  • the two or more metals may be an alloy.
  • the active metal may contain one or two or more metals selected from the group consisting of titanium, hafnium, zirconium, and niobium.
  • the silver contained in the bonding layer 20 may be contained in the bonding layer 20 as an alloy, such as an Ag-Cu eutectic alloy.
  • the silver content in the bonding layer 20 may be 60-95 mass% in Ag equivalent.
  • the silver and copper contents in the bonding layer 20 may be 75-100 mass%, 85-99 mass%, or 90-98 mass% in Ag and Cu equivalent, respectively. This makes it possible to sufficiently reduce the residual stress in the bonding layer 20 while improving the density of the bonding layer 20.
  • the content of the active metal in the bonding layer 20 may be 0.5 to 5 parts by mass per 100 parts by mass of Ag and Cu combined. By making the content of the active metal 0.5 parts by mass or more, it is possible to improve the bond between the silicon nitride plate 10 and the bonding layer 20. On the other hand, by making the content of the active metal 5 parts by mass or less, it is possible to suppress the formation of a brittle alloy layer at the bonding interface.
  • the metal contained in the bonding layer 20 may be contained as a nitride, oxide, carbide or hydride.
  • the bonding layer 20 may contain titanium nitride and/or titanium hydride (TiH 2 ). This allows the silicon nitride plate 10 and the bonding layer 20 to react sufficiently to form the first bonding layer 21, the second bonding layer 22, and the third bonding layer 23. This allows the bonding strength between the silicon nitride plate 10 and the copper plate 50 to be sufficiently high.
  • the content of TiH 2 relative to a total of 100 parts by mass of Ag and Cu may be, for example, 1 to 8 parts by mass.
  • the elements contained in the bonding layer 20 can be identified and quantified by the following procedure.
  • a cross section of the circuit board is observed, for example, with a scanning transmission electron microscope (STEM).
  • STEM scanning transmission electron microscope
  • EDX energy dispersive X-ray analyzer
  • the cross section in this disclosure refers to a cross section perpendicular to the main surface of the silicon nitride plate 10 on which the bonding layer 20 is provided, and passing through the bonding layer 20.
  • the first bonding layer 21 is a layer containing titanium nitride.
  • the titanium nitride content may be 50 to 90 atomic %, 55 to 85 atomic %, or 60 to 80 atomic %.
  • the titanium element and the nitrogen element may be detected in the first bonding layer 21 in greater amounts than the second bonding layer 22 and the third bonding layer 23. That is, the first bonding layer 21 may have a higher titanium nitride content than the second bonding layer 22 and the third bonding layer 23.
  • the titanium nitride phase contained in the first bonding layer 21 may be formed in a layer along the contact surface between the silicon nitride plate 10 and the first bonding layer 21.
  • the bonding strength between the silicon nitride plate 10 and the copper plate 50 can be further increased.
  • the fact that the titanium nitride phase is formed in a layer along the contact surface between the silicon nitride plate 10 and the first bonding layer 21 can be confirmed by analyzing a cross section, for example, with an electron beam microanalyzer (EPMA).
  • EPMA electron beam microanalyzer
  • the thickness of the first bonding layer 21 can be determined as the length of the line at which titanium and nitrogen elements are detected with a content of 10 atomic % or more.
  • the titanium and nitrogen elements contained in the first bonding layer 21 may be 10 to 45 atomic %, or 20 to 40 atomic %.
  • the thickness of the first bonding layer 21 may be 100 to 300 nm, or 150 to 250 nm.
  • the difference between the maximum and minimum thicknesses of the first bonding layer 21 may be 70 nm or less, 50 nm or less, or 45 nm or less.
  • the first bonding layer 21 contains a sufficient amount of titanium nitride, and the bonding strength between the silicon nitride plate 10 and the copper plate 50 can be improved.
  • the average thickness t1 of the first bonding layer 21 can be calculated as the average thickness value measured at five or more lines.
  • the average thickness t1 of the first bonding layer 21 may be 175 to 235 nm, 180 to 230 nm, or 190 to 220 nm.
  • the second bonding layer 22 is a layer with a higher silicon element content than the first bonding layer 21.
  • the silicon element originates from the silicon nitride plate 10, and when the silicon nitride plate 10 and the copper plate 50 are heat-bonded via the brazing material layer, it is believed that the silicon nitride reacts with the titanium of the brazing material layer due to heating, forming the second bonding layer 22 as a layer containing titanium silicide.
  • the silicon element content of the second bonding layer 22 may be 10-40 atomic %, or 20-30 atomic %.
  • the second bonding layer 22 with a silicon element content in this range is formed by a sufficient reaction between the silicon nitride plate 10 and the titanium in the brazing material layer. This allows the bonding strength between the silicon nitride plate 10 and the copper plate 50 to be sufficiently improved.
  • the second bonding layer 22 is formed so as to isolate the first bonding layer 21 from the third bonding layer 23. That is, the second bonding layer 22 is formed over the entire area between the first bonding layer 21 and the third bonding layer 23.
  • Such a second bonding layer 22 is formed by the sufficient reaction between the silicon nitride and the titanium in the brazing material layer when the silicon nitride plate 10 and the copper plate 50 are heat-bonded via the brazing material layer. Therefore, the bonding strength between the silicon nitride plate 10 and the copper plate 50 of the circuit board 100 can be improved.
  • the thickness of the second bonding layer 22 can be determined as the length of the line at which the silicon element content is 10 atomic % or more.
  • the thickness of the second bonding layer 22 may be 50 nm or more, 50 to 120 nm, 60 to 110 nm, or 80 to 100 nm.
  • the average thickness t2 of the second bonding layer 22 can be determined by calculating the average thickness measured at five or more lines.
  • the average thickness t2 of the second bonding layer 22 may be 60 to 100 nm, or 70 to 90 nm.
  • a second bonding layer 22 with an average thickness t2 in this range is formed by the reaction between the silicon nitride plate 10 and the brazing material layer progressing sufficiently. Such a second bonding layer 22 can sufficiently increase the bonding strength between the silicon nitride plate 10 and the copper plate 50.
  • the ratio (t1/t2) of the average thickness t1 of the first bonding layer 21 to the average thickness t2 of the second bonding layer 22 may be 5 or less, 4 or less, or 3 or less. By having (t1/t2) within this range, the first bonding layer 21 and the second bonding layer 22 are formed in a balanced manner, and the bonding strength between the silicon nitride plate 10 and the copper plate 50 can be sufficiently high.
  • the lower limit of the above ratio may be 1.0 or 1.5.
  • the third bonding layer 23 is a layer having a higher silver element content than the first bonding layer 21 and the second bonding layer 22.
  • the silver element content in the third bonding layer 23 may be 20 to 90 atomic %, or may be 30 to 80 atomic %.
  • the thickness of the third bonding layer 23 may be 1.0 to 2.0 ⁇ m, or may be 1.2 to 1.7 ⁇ m.
  • Titanium elements do not have to be present at the interface between the third bonding layer 23 and the copper plate 50.
  • the reaction between the silicon nitride plate 10 and the titanium in the brazing material layer has progressed sufficiently, so that the titanium elements tend to remain in the first bonding layer 21 and the second bonding layer 22 near the silicon nitride plate 10 side.
  • the absence of titanium elements at the interface between the third bonding layer 23 and the copper plate 50 results in a circuit board 100 in which the reaction between the silicon nitride plate 10 and the titanium in the brazing material layer has progressed sufficiently.
  • the bonding strength between the silicon nitride plate 10 and the copper plate 50 can be made sufficiently high.
  • the bonding layer 20 may contain carbon derived from the organic binder.
  • the carbon may be contained in the third bonding layer 23.
  • the average value of the ratio (C1/C3) of the carbon content (C1) contained in the first bonding layer 21 to the carbon content (C3) contained in the third bonding layer 23 may be 0.5 or less, 0.45 or less, or 0.4 or less.
  • the lower limit of the above ratio may be 0.2 or 0.3.
  • the average value of (C1/C3) is obtained as follows.
  • (C3) and (C1) are measured on five or more lines, and (C1/C3) is calculated from each measurement value.
  • the above average value is obtained from five or more (C1/C3) values.
  • each of the five or more (C1/C3) values may be 0.5 or less, 0.45 or less, or 0.4 or less.
  • the bond strength between the silicon nitride plate 10 and the copper plate 50 can be determined in accordance with JIS K 6854-1:1999 "Adhesives - Peel Adhesion Strength Test Method” by peeling the copper plate 50 vertically upward at 90° from the circuit board 100 and measuring the strength at the time of peeling.
  • the bond strength may be 500 to 800 N/cm, or 600 to 700 N/cm.
  • a circuit board 100 having such bond strength reduces variation in bond strength on the circuit board 100, and the quality of the circuit board 100 can be stabilized.
  • the manufacturing method in this example includes a step (a) of producing a plurality of composites 40 each including a silicon nitride plate 10, a copper plate 50, and a brazing material layer 30 that bonds them together, a step (b) of placing a spacer 70 between a pair of composites 40 to produce a laminate 80, a step (c) of heating the laminate 80 to bond the silicon nitride plate 10 and the copper plate 50 with the brazing material layer 30, and a step (d) of producing a circuit board from the bonded assembly.
  • a partition line may be formed on the main surface of the silicon nitride plate 10 used in step (a).
  • a laser beam may be irradiated onto the main surface of the silicon nitride plate 10 to provide a scribe line as the partition line.
  • the laser beam to be irradiated include a carbon dioxide laser and a YAG laser.
  • the brazing material applied to the main surface of the silicon nitride plate 10 contains, for example, silver, copper, tin, active metals, and metal compounds containing these as constituent elements, an organic solvent, and an organic binder.
  • the viscosity of the brazing material may be, for example, 5 to 20 Pa ⁇ s.
  • the organic solvent content in the brazing material may be, for example, 5 to 25 mass %, and the organic binder content may be, for example, 2 to 15 mass %.
  • the brazing filler metal may contain silver in the form of a metal element or a metal compound (alloy), and may contain, in addition to silver, one or more metals selected from the group consisting of copper, tin, and active metals.
  • the two or more metals may be in the form of an alloy.
  • the active metal may contain one or more metals selected from the group consisting of titanium, hafnium, zirconium, and niobium.
  • the silver content in the brazing filler metal may be 45 to 95 mass% or 50 to 95 mass% in terms of Ag.
  • the total silver and copper content in the brazing filler metal may be 65 to 100 mass%, 70 to 99 mass%, or 90 to 98 mass% in terms of Ag and Cu, respectively.
  • the content of the active metal in the brazing filler metal may be 0.5 to 8 parts by mass per 100 parts by mass of the total of Ag and Cu. By making the content of the active metal 0.5 parts by mass or more, it is possible to improve the bond between the silicon nitride plate and the brazing filler metal. On the other hand, by making the content of the active metal 8 parts by mass or less, it is possible to suppress the formation of a brittle alloy layer at the bonded interface.
  • the above metals contained in the brazing material may be contained as nitrides, oxides, carbides, or hydrides.
  • the brazing material may contain titanium nitride and/or titanium hydride (TiH 2 ). This allows the bonding strength between the silicon nitride plate 10 and the copper plate 50 to be sufficiently high.
  • TiH 2 titanium nitride and/or titanium hydride
  • the content of TiH 2 relative to a total of 100 parts by mass of Ag and Cu may be, for example, 1 to 8 parts by mass.
  • the tin content in the brazing material may be 0.5 to 6 parts by mass per 100 parts by mass of the total of Ag and Cu. By making the tin content 0.5 parts by mass or more, it is possible to improve the bond between the silicon nitride plate 10 and the bonding layer 20. On the other hand, by making the tin content 5 parts by mass or less, it is possible to suppress the formation of a brittle alloy layer at the bonding interface.
  • a brazing material is applied to both main surfaces of the silicon nitride plate 10 by a roll coater method, a screen printing method, a transfer method, or the like, and then dried to provide one or more brazing material layers 30.
  • the brazing material layers 30 may be provided at positions where the copper plates 50 are to be joined to the silicon nitride plate 10. Once the brazing material layers 30 are formed, the silicon nitride plates 10 and the copper plates 50 are stacked with the brazing material layer 30 sandwiched between them to produce multiple composites 40.
  • step (b) a pair of composites 40 are laminated so as to sandwich a spacer 70, to produce a laminate 80.
  • a commercially available carbon plate may be used as the spacer 70.
  • the density of the carbon plate may be 1.6 to 1.9 g/cm 3.
  • the thickness of the carbon plate may be 0.5 to 1.0 mm.
  • the surface roughness Ra may be 5 to 10 ⁇ m.
  • the spacers 70 and composites 40 used in the laminate 80 may be repeatedly laminated in any number.
  • the number of composites 40 and spacers 70 to be laminated is not particularly limited, and may be adjusted depending on the size of the heating furnace to be used. By laminating in this manner, a plurality of composites 40 can be heated at once, and a bonded body can be efficiently produced.
  • the laminate 80 may be heated in step (c) while being pressurized in the stacking direction.
  • An example of a method for pressurizing the laminate 80 is described below with reference to Figures 3, 4, 5, 6, 7, and 8.
  • the structure 90 in Figure 3 includes a pressurizing jig 1 and a laminate 80 sandwiched between a base plate 2 and a cover plate 3 of the pressurizing jig 1.
  • the laminate 80 is formed by alternately stacking a plurality of spacers 70 and a plurality of composites 40.
  • the laminate 80 is rectangular in plan view, but may have other shapes.
  • a spacer 70 is disposed between the laminate 80 and the pressurizing jig 1.
  • the spacer 70 also has the function of preventing bonding between the composites 40 and bonding between the composites 40 and the pressurizing jig 1.
  • the pressing jig 1 comprises a plate-shaped base plate 2 (foundation portion) on which the laminate 80 is placed, and a cover plate 3 (cover portion) arranged opposite the base plate 2.
  • the cover plate 3 and the base plate 2 sandwich the laminate 80.
  • the pressing jig 1 comprises a plurality of spring washers 4 arranged on the cover plate 3, and a pressing plate 5 (pressing portion) arranged on the spring washers 4.
  • the pressing jig 1 has a pressing structure 6 that compresses the spring washers 4 with the pressing plate 5 to pressurize the laminate 80.
  • the base plate 2 is, for example, rectangular, and has an area that extends beyond the laminate 80 in a plan view, i.e., a protruding area 2a that does not overlap the laminate 80.
  • a protruding area 2a of the base plate 2 multiple (for example, two) pillars 8 (pillar portions) are erected along the short sides of the base plate 2.
  • the pillars 8 are also arranged opposite each other on both sides of the longitudinal direction (left-right direction) of the base plate 2, and the laminate 80 is arranged between a pair of pillars 8 facing each other on the left and right.
  • An engagement hole 8a is formed in the upper part of the pillar 8, through which a locking claw 9 is inserted.
  • the cover plate 3 has a rectangular shape corresponding to the shape of the laminate 80, and has one surface 3a (hereinafter referred to as the "lower surface”) and the other surface 3b (hereinafter referred to as the "upper surface”) as shown in Figs. 5 and 7.
  • the lower surface 3a is flat and abuts against the spacer 70 arranged closer to the cover plate 3.
  • the upper surface 3b has a plurality of counterbores 3c formed therein, and the spring washer 4 is housed in each counterbores 3c.
  • the depth of the counterbores 3c may be a dimension such that the entire spring washer 4 is housed therein when the helical spring washer 4 is compressed and flattened.
  • the counterbores 3c are donut-shaped (annular) in plan view, and the annular spring washer 4 is housed therein, preventing the spring washer 4 from shifting out of position.
  • the counterbores 3c function as positioning portions for the spring washer 4.
  • the pressure plate 5 has a surplus area 5a that faces the protruding area 2a of the base plate 2 in a plan view.
  • a post through hole 5b through which the post 8 passes is formed in the surplus area 5a.
  • a storage groove 5c is provided on the upper surface of the surplus area 5a so as to pass through the post through hole 5b.
  • the locking claw 9 fits into the storage groove 5c.
  • the pressure plate 5 is placed so as to overlap the cover plate 3, and is further pressed down so as to abut against the spring washer 4.
  • a support 8 is passed through the support through hole 5b provided in the excess area 5a of the pressure plate 5.
  • the upper part of the support 8 protrudes above the support through hole 5b.
  • An engagement hole 8a is provided in the upper part of the support 8, and a locking claw 9 (locking portion) is inserted into the engagement hole 8a.
  • the locking claw 9 passes through the engagement hole 8a from the lateral direction and locks the pressure plate 5 by abutting against the surface (upper surface) of the pressure plate 5 opposite the surface (lower surface) that abuts against the spring washer 4.
  • a storage groove 5c corresponding to the outer shape of the locking claw 9 is formed in the upper surface of the pressure plate 5, and the locking claw 9 slides along the storage groove 5c.
  • the pressure structure 6 in this embodiment is configured to include at least the pressure plate 5, the support 8, the engagement hole 8a, and the locking claw 9.
  • the spring washer 4 is formed of, for example, an alloy such as Inconel 750 or Inconel 718, silicon nitride, or a carbon composite.
  • the spring washer 4 is in an uncompressed state when it is not in contact with the cover plate 3 (see FIG. 8).
  • the spring washer 4 is an example of a compression spring that is wound in a spiral shape without overlapping and has both ends 4a and 4b spaced apart. More specifically, the spring washer 4 has a C-shape, and both ends 4a and 4b are spaced apart from each other and are offset in the axial direction (for example, vertical direction) assuming a spiral shape.
  • one end that is in contact with the bottom of the countersink 3c is the lower end 4a, and the other end on the opposite side is the upper end 4b.
  • the spring washer 4 is compressed by the pressure structure 6 through the cover plate 3, the lower end 4a and the upper end 4b approach each other, the spiral shape of the spring washer 4 is eliminated, and the spring washer 4 becomes substantially flat (see Figure 7).
  • the multiple spring washers 4 are arranged so as to fit inside the outer edge 3x of the cover plate 3 without protruding beyond the outer edge 3x of the cover plate 3.
  • the multiple spring washers 4 are also arranged along the outer edge 3x of the cover plate 3.
  • the outer edge 3x of the cover plate 3 according to this embodiment is rectangular.
  • Three spring washers 4 are arranged in a row along each short side of the outer edge 3x, and five spring washers 4 are arranged in a row along each long side.
  • the multiple spring washers 4 are arranged at equal intervals. Specifically, a total of 15 spring washers 4 are arranged in three rows and five columns (multiple rows and multiple columns), and all of the spring washers 4 are arranged at equal intervals. By arranging the spring washers 4 at equal intervals, it becomes easier for the cover plate 3 to apply uniform pressure to the laminate 80. Note that only the multiple spring washers 4 arranged along the outer edge 3x of the cover plate 3 may be arranged at equal intervals. Furthermore, when the center of the cover plate 3 is defined in a plan view, the multiple spring washers 4 may be arranged so as to be point symmetrical with respect to this center.
  • a separation region 4x is formed between the lower end 4a and upper end 4b of the spring washer 4 (between both ends).
  • the multiple spring washers 4 are arranged so that the separation region 4x faces the outer edge 3x of the cover plate 3.
  • the spring washer 4 is assumed to be ring-shaped in a plan view, the spring washer 4 is arranged so that the separation region 4x is closer to the outer edge 3x of the cover plate 3 than the center point of the ring.
  • a line is assumed to connect the separation regions 4x of the multiple spring washers 4, this line is arranged to run along the outer edge 3x of the cover plate 3.
  • FIG. 9 shows an enlarged cross section of the laminated structure of the composite 40 and the spacer 70 in FIG. 8 along the lamination direction.
  • the spacer 70, the laminate 80, and the spacer 70 are laminated in this order from the base plate 2 toward the cover plate 3.
  • the laminate 80 is formed by laminating a pair of composites 40 so as to sandwich the spacer 70.
  • the composite 40 is formed by laminating a pair of copper plates 50 so as to sandwich the silicon nitride plate 10 with the brazing material layer 30 between them.
  • the laminate 80 may be formed by repeatedly laminating any number of composites 40 and spacers 70. This laminated structure makes it possible to suppress the variation in reaction during heating in step (c) and obtain a joint having high joint strength.
  • the number of spacers 70 and composites 40 constituting the laminate 80 is not particularly limited.
  • step (c) the laminate 80 is heated in a heating furnace while still under pressure to cause a reaction between the silicon nitride plate 10 and the copper plate 50 and the brazing material layer 30, thereby obtaining a bonded body in which the silicon nitride plate 10 and the copper plate 50 are bonded.
  • the brazing material layer 30 becomes the bonding layer 20 described above. Therefore, the bonding layer 20 may contain a reaction product between the silicon nitride plate 10 and the copper plate 50 and the brazing material layer 30.
  • Step (c) may include a step of degreasing the carbon in the brazing material layer 30.
  • the heating temperature in the degreasing step may be 370 to 420°C, 380 to 415°C, or 390 to 410°C.
  • the heating time at the above heating temperature may be 3.5 hours or more, or 3.75 hours or more. In order to shorten the time required for the entire manufacturing process, the heating time may be 5 hours or less, or 4.5 hours or less.
  • the degreasing step can remove excess carbon derived from the organic binder contained in the brazing material layer 30 by thermal decomposition, so that carbon and titanium do not react when heated at 700 to 900°C, and the generation of titanium nitride and titanium silicide can be sufficiently promoted.
  • the atmosphere in the heating furnace may be an inert gas such as nitrogen, and may be performed under reduced pressure below atmospheric pressure, or may be performed under vacuum.
  • the heating furnace may be a continuous type that continuously produces a plurality of composites 40, or may be a batch type that produces one or a plurality of composites 40.
  • the heating temperature may be 700 to 900°C or 750 to 850°C from the viewpoint of promoting the reaction.
  • the heating time may be 3 hours or less, or 2 hours or less.
  • the pressure in the furnace during heating may be any of normal pressure, reduced pressure, and vacuum. From the viewpoint of promoting the reaction, the pressure in the furnace may be 10 -2 to 10 -7 Pa.
  • the heating rate in the heating furnace in step (c) may be 70 to 120°C/min, or may be 80 to 110°C/min. By keeping the heating rate in this range, the time required for the entire manufacturing process can be sufficiently shortened. In addition, the temperature reduction rate after heating may also be in the same range as the above heating rate.
  • an annealing step may be performed.
  • the annealing temperature in the annealing step may be 400 to 650°C, or 500 to 600°C.
  • the annealing time at the annealing temperature may be 1.5 to 3.0 hours, or 2.0 to 2.5 hours.
  • the bonded body may be removed from the pressure jig.
  • step (d) resist printing and etching are performed on the resulting bonded body to obtain the circuit board 100. Since the carbon in the brazing material layer 30 has been sufficiently removed from the circuit board 100, the bonding layer 20 has a first bonding layer 21, a second bonding layer 22, and a third bonding layer 23. Therefore, the bonding strength between the silicon nitride plate 10 and the copper plate 50 in the circuit board 100 can be made sufficiently high.
  • the circuit board 100 may be used to manufacture a power module.
  • the power module can be manufactured by mounting a semiconductor element electrically connected to the copper plate of the circuit board using solder and wire bonding, etc., and housing the circuit board and the semiconductor element in the housing space of the housing, and then sealing with resin.
  • the present disclosure is not limited to the above-described embodiments.
  • the structures and shapes of the metal plates and joints joined to each of the pair of main surfaces of the silicon nitride plate may be different from each other.
  • the present disclosure may be a circuit board in which a joining layer and a copper plate are provided on only one main surface of the silicon nitride plate.
  • the brazing material contained Ag, Cu, TiH 2 , and Sn.
  • the mass ratio of Ag to Cu was 9: 1.
  • the brazing material contained 5 parts by mass of Sn and 3.5 parts by mass of TiH 2 with respect to 100 parts by mass of Ag and Cu in total.
  • the brazing filler metal was applied to the main surface of the silicon nitride plate by screen printing (mesh number: 150) and dried to form a brazing filler metal layer.
  • the application area of the brazing filler metal layer was the same as the area of the main surface of the copper plate to be joined to the silicon nitride plate.
  • the thickness of the applied brazing filler metal layer was 0.03 mm.
  • the copper plate was placed on top of the silicon nitride plate so that the brazing material layer was in contact with the main surface of the copper plate, creating a composite. In this way, 20 composites of silicon nitride plate, brazing material layer, and copper plate were created.
  • a pair of carbon plates (thickness: 0.5 mm, density: 1.8 g/cm 3 ) were placed between adjacent composites to produce a laminate as shown in Fig. 2. As shown in Fig. 9, spacers were placed on both main surfaces of the laminate and fixed in place by a pressing jig.
  • the laminate While being fixed by the pressure tool, the laminate was heated to 400°C in a vacuum ( 10-3 Pa) at a heating rate of 100°C/min, and degreasing was performed at 400°C for 3.5 hours. Thereafter, the laminate was heated from 400°C to 750°C at a heating rate of 100°C/min in an atmosphere of 10-3 Pa, and heated at 750°C for 3 hours. Thereafter, the laminate was cooled to 600°C at a cooling rate of 100°C/min, and an annealing step was performed in which the laminate was held at 600°C for 2 hours. After cooling, the bonded body was removed from the pressure tool. In this way, a bonded body was produced in which a silicon nitride plate and a copper plate were bonded via a bonding layer. A circuit board was produced using the bonded body produced.
  • circuit board evaluation ⁇ Elemental mapping of the layer state of a cross section of a circuit board>
  • the cross section of the obtained circuit board was observed at a magnification of 25,000 times using a scanning transmission electron microscope (STEM, Hitachi High-Tech Corporation, product name: HD-2700).
  • the observed cross section was subjected to elemental mapping of Ti, Si, Ag, and Cu at an acceleration voltage of 200 kV using an energy dispersive X-ray analyzer (EDX, Oxford, product name: XMAXN 100TLE).
  • the STEM image of Example 1 is shown in FIG. 10(A), and the results of elemental mapping are shown in FIG. 11(A), FIG. 11(B), FIG. 12(A), and FIG. 12(B).
  • FIG. 10(B) The STEM image of Comparative Example 1 is shown in FIG. 10(B), and the results of elemental mapping are shown in FIG. 13(A), FIG. 13(B), FIG. 14(A), and FIG. 14(B).
  • FIG. 11(A) and FIG. 13(A) show the distribution of titanium element
  • FIG. 11(B) and FIG. 13(B) show the distribution of silicon element
  • FIG. 12(A) and FIG. 14(A) show the distribution of silver element
  • FIG. 12(B) and FIG. 14(B) show the distribution of copper element.
  • Example 1 The results of the STEM images and element mapping showed that in Example 1, the second bonding layer 22 was interposed between the first bonding layer 21 and the third bonding layer 23 so as to isolate them (see Figures 11(A), 11(B), and 12(A)).
  • Comparative Example 1 the second bonding layer 22A was confirmed, but unlike the second bonding layer 22, the second bonding layer 22A was a discontinuous layer, and there were portions where the first bonding layer 21 and the third bonding layer 23 were in direct contact (see Figures 13(A), 13(B), and 14(A)).
  • Example 1 As shown in Figures 13(A), 14(A), and 14(B), titanium elements were scattered at the interface between the copper plate 50 and the third bonding layer 23. On the other hand, in Example 1, as shown in Figures 11(A), 12(A), and 12(B), titanium elements were not present at the interface between the copper plate 50 and the third bonding layer 23.
  • the line profile was performed at five arbitrary points in each STEM image, and the thicknesses of the first bonding layer 21 and the second bonding layer 22 were measured in the same manner.
  • five arbitrary points were selected from the portion where the second bonding layer 22A was formed and measured.
  • the average value t1 of the thickness of the first bonding layer 21 and the average value t2 of the thickness of the second bonding layer at the five measured points were calculated, and t1/t2 was calculated.
  • Table 1 also shows the maximum value, minimum value, and difference between the measured thicknesses of the bonding layers.
  • Example 1 showed a thicker second bonding layer than Comparative Example 1. This indicates that the reaction between the silicon nitride plate and the brazing material layer caused by heating has progressed sufficiently.
  • the atomic % of C (carbon) (C1) of the first bonding layer 21 was measured at a position 100 nm away from the position where titanium element was first detected at 10 atomic % or more along the line toward the copper plate 50 side, measured from the silicon nitride plate 10 side.
  • the atomic % of C (carbon) (C3) of the third bonding layer 23 was measured at a position 1000 nm away from the position where it was first detected along the line toward the copper plate 50 side, measured from the position where it was first detected.
  • Example 1 It was confirmed that in Example 1, the amount of carbon detected in the first bonding layer relative to the third bonding layer was less than in Comparative Example 1. Therefore, it was shown that in Example 1, the carbon derived from the binder in the first bonding layer was reduced by degreasing for a long time at high temperature. Therefore, it is considered that the reaction between carbon and titanium was suppressed, and the reaction between nitrogen derived from silicon nitride and titanium progressed sufficiently.
  • Example 1 and Comparative Example 1 the copper plate bonded to the silicon nitride plate was pulled vertically upward using a tensile tester, and the bonding strength was measured at the time when the copper plate peeled off from the silicon nitride plate as shown in Figures 16(A) and 16(B).
  • the stage of the tensile tester used was FGS-100VC manufactured by Nidec-Shimpo Corporation.
  • the force gauge used was FGP-20 manufactured by Nidec-Shimpo Corporation.
  • the peeling speed was 50 mm/min.
  • the results were 650 N/cm in Example 1 and 450 N/cm in Comparative Example 1.
  • SEM images of the peeled surface and elemental analysis by EDX of the fractured cross section were performed. The elemental analysis conditions were the same as those described above.
  • FIG. 16(A) shows a photograph of the appearance of the copper plate of Example 1 when peeled off
  • FIG. 17(A) shows the results of SEM image observation of the peeled surface of Example 1
  • FIG. 18(A) shows the results of elemental analysis by EDX of Example 1.
  • FIG. 16(B) shows a photograph of the appearance of the copper plate of Comparative Example 1 when peeled off
  • FIG. 17(B) shows the results of SEM image observation of the peeled surface of Comparative Example 1
  • FIG. 18(B) shows the results of elemental analysis by EDX of Comparative Example 1.
  • the black parts 101 in FIG. 17(A) and FIG. 17(B) represent parts containing silicon elements
  • the gray parts 105 represent parts containing silver elements.
  • each dot of the dotted pattern parts 102 in FIG. 18(A) and FIG. 18(B) represents parts containing silicon elements
  • the black parts 106 represent parts containing silver elements.
  • Example 1 From Figures 17(A), 17(B), 18(A), and 18(B), in Example 1, a large amount of silicon element was attached to the peeled surface, causing fracture near the silicon nitride plate 10. In contrast, in Comparative Example 1, the amount of silicon element attached to the peeled surface was less than in Example 1, and it was confirmed that interfacial peeling occurred between the third bonding layer 23 and the copper plate 50. In Example 1, more silicon element was attached to the peeled surface than in Comparative Example 1, and the bonding strength was also higher as described above. From these results, it was found that in the circuit board of Example 1, the first bonding layer and second bonding layer were sufficiently formed, and therefore the silicon nitride plate 10 and bonding layer 20 were bonded more firmly than in Comparative Example 1.
  • the present disclosure provides a circuit board with high bonding strength. It also provides a power module using such a circuit board.

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Abstract

This circuit board comprises a silicon nitride plate, a copper plate, and a bonding layer that bonds the silicon nitride plate and the copper plate. The bonding layer includes, from the silicon nitride plate side, a first bonding layer containing titanium nitride, a second bonding layer having a higher elemental silicon content than the first bonding layer, and a third bonding layer having a higher elemental silver content than the first bonding layer and the second bonding layer, and the second bonding layer is interposed between the first bonding layer and the third bonding layer so as to partition the first bonding layer from the third bonding layer.

Description

回路基板、及びパワーモジュールCircuit boards and power modules
　本開示は、回路基板、及びパワーモジュールに関する。 This disclosure relates to a circuit board and a power module.
　電子デバイスに搭載される回路基板は、セラミック板と金属板をろう材を介して接合することで製造される。また、多層構造であることで、回路基板に様々な特性を付与することができる。例えば、特許文献１には、セラミックス基材及び金属基材を多層にすることで、発熱及び冷却による電気特性の低下を抑制できる回路基板が開示されている。また、特許文献２には、セラミックス板上に金属層と溶射層を積層することで、ヒートサイクルに対する高い耐久性を有する回路基板が開示されている。 The circuit boards mounted on electronic devices are manufactured by joining ceramic and metal plates with a brazing material. Furthermore, the multi-layer structure allows the circuit board to be endowed with a variety of properties. For example, Patent Document 1 discloses a circuit board that can suppress the deterioration of electrical properties due to heat generation and cooling by making the ceramic base material and metal base material into multiple layers. Furthermore, Patent Document 2 discloses a circuit board that has high durability against heat cycles by laminating a metal layer and a sprayed layer on a ceramic plate.
特開２０１９－０６７８０５号公報JP 2019-067805 A 特開２０２１－０８０５３７号公報JP 2021-080537 A
　集合基板や個片基板では、窒化ケイ素板に銅板を接合した場合に、窒化ケイ素板と銅板間の接合層の接合強度が十分ではないことがわかった。そこで本開示は、高い接合強度を有する回路基板を提供する。また、本開示は、そのような回路基板を有するパワーモジュールを提供する。 It has been found that when a copper plate is bonded to a silicon nitride plate in an assembly board or individual board, the bonding strength of the bonding layer between the silicon nitride plate and the copper plate is insufficient. Therefore, the present disclosure provides a circuit board with high bonding strength. The present disclosure also provides a power module that includes such a circuit board.
　本開示の一側面は、以下の回路基板を提供する。 One aspect of the present disclosure provides the following circuit board:
［１］窒化ケイ素板と、銅板と、前記窒化ケイ素板と前記銅板とを接合する接合層と、を備える回路基板であって、前記接合層は、前記窒化ケイ素板側から、窒化チタンを含む第１接合層と、前記第１接合層よりもケイ素元素の含有量が高い第２接合層と、前記第１接合層及び前記第２接合層よりも銀元素の含有量が高い第３接合層と、を有し、前記第２接合層は、前記第１接合層と前記第３接合層とを遮断するように、前記第１接合層と前記第３接合層との間に介在している、回路基板。 [1] A circuit board comprising a silicon nitride plate, a copper plate, and a bonding layer bonding the silicon nitride plate and the copper plate, the bonding layer having, from the silicon nitride plate side, a first bonding layer containing titanium nitride, a second bonding layer having a higher silicon content than the first bonding layer, and a third bonding layer having a higher silver content than the first bonding layer and the second bonding layer, the second bonding layer being interposed between the first bonding layer and the third bonding layer so as to isolate the first bonding layer from the third bonding layer.
　上記回路基板の接合層は、上記第１接合層と上記第３接合層とを遮断するように、上記第１接合層と上記第３接合層との間に介在する第２接合層を有する。回路基板がこのような接合層を備えることで、回路基板における窒化ケイ素板と銅板との接合強度を向上することができる。 The bonding layer of the circuit board has a second bonding layer interposed between the first bonding layer and the third bonding layer so as to isolate the first bonding layer and the third bonding layer. By providing such a bonding layer on the circuit board, the bonding strength between the silicon nitride plate and the copper plate in the circuit board can be improved.
　上記［１］の回路基板は、以下の［２］～［６］のいずれか一つであってもよい。 The circuit board of [1] above may be any one of [2] to [6] below.
［２］前記銅板と前記接合層との界面にチタン元素が存在しない、［１］に記載の回路基板。
［３］前記第１接合層における炭素の含有量をＣ１原子％、前記第３接合層における炭素の含有量をＣ３原子％としたときに、Ｃ１／Ｃ３の平均値が０．５以下である、［１］又は［２］に記載の回路基板。
［４］前記第１接合層の厚さの最大値と最小値の差が７０ｎｍ以下である［１］～［３］のいずれか一つに記載の回路基板。
［５］前記第２接合層の厚さが５０ｎｍ以上である、［１］～［４］のいずれか一つに記載の回路基板。
［６］前記第１接合層の厚さの平均値をｔ１、前記第２接合層の厚さの平均値をｔ２としたときに、ｔ１／ｔ２が５以下である、［１］～［５］のいずれか一つに記載の回路基板。 [2] The circuit board according to [1], wherein titanium elements are not present at the interface between the copper plate and the bonding layer.
[3] The circuit board according to [1] or [2], wherein when the carbon content in the first bonding layer is C1 atomic % and the carbon content in the third bonding layer is C3 atomic %, the average value of C1/C3 is 0.5 or less.
[4] The circuit board according to any one of [1] to [3], wherein the difference between the maximum and minimum thicknesses of the first bonding layer is 70 nm or less.
[5] The circuit board according to any one of [1] to [4], wherein the second bonding layer has a thickness of 50 nm or more.
[6] The circuit board according to any one of [1] to [5], wherein t1/t2 is 5 or less, when the average thickness of the first bonding layer is t1 and the average thickness of the second bonding layer is t2.
　上記［２］の回路基板は、銅板と接合層との界面にチタン元素が存在しない。チタン元素が銅板と接合層との界面に存在しないことで、第１接合層及び第２接合層が十分に形成され、窒化ケイ素板と銅板との接合強度を十分に向上することができる。上記［３］の回路基板は、接合層中のバインダ由来の炭素を十分に除去できており、第１接合層、第２接合層、及び第３接合層が十分に形成され、窒化ケイ素板と銅板との接合強度を十分に高くすることができる。 In the circuit board of [2] above, no titanium element is present at the interface between the copper plate and the bonding layer. As no titanium element is present at the interface between the copper plate and the bonding layer, the first bonding layer and the second bonding layer are sufficiently formed, and the bonding strength between the silicon nitride plate and the copper plate can be sufficiently improved. In the circuit board of [3] above, carbon derived from the binder in the bonding layer can be sufficiently removed, and the first bonding layer, the second bonding layer, and the third bonding layer are sufficiently formed, and the bonding strength between the silicon nitride plate and the copper plate can be sufficiently increased.
　上記［４］の回路基板は、第１接合層の厚さの最大値と最小値の差が７０ｎｍ以下である。第１接合層がこのような厚さであることによって、第１接合層が広い範囲でばらつきなく十分に形成されており、窒化ケイ素板と銅板との接合強度を十分に高くすることができる。上記［５］の回路基板は、第２接合層の厚さが５０ｎｍ以上である。このような回路基板では、第２接合層が十分な厚さで形成されているため、窒化ケイ素板と銅板との接合強度を十分に高くすることができる。 In the circuit board of [4] above, the difference between the maximum and minimum thicknesses of the first bonding layer is 70 nm or less. With the first bonding layer having such a thickness, the first bonding layer is sufficiently formed without variation over a wide range, and the bonding strength between the silicon nitride plate and the copper plate can be sufficiently high. In the circuit board of [5] above, the second bonding layer has a thickness of 50 nm or more. In such a circuit board, the second bonding layer is formed with a sufficient thickness, and the bonding strength between the silicon nitride plate and the copper plate can be sufficiently high.
　上記［６］の回路基板は、第１接合層の厚さの平均値ｔ１、第２接合層の厚さの平均値をｔ２としたときに、ｔ１／ｔ２が５以下である。第１接合層の厚さの平均値及び第２接合層の厚さの平均値がこの範囲であることによって、第１接合層と第２接合層とをバランスよく有しており、窒化ケイ素板と銅板の接合強度を十分に高くすることができる。 In the circuit board of [6] above, when the average thickness of the first bonding layer is t1 and the average thickness of the second bonding layer is t2, t1/t2 is 5 or less. By having the average thickness of the first bonding layer and the average thickness of the second bonding layer in this range, the first bonding layer and the second bonding layer are well balanced, and the bonding strength between the silicon nitride plate and the copper plate can be sufficiently increased.
　本開示の一側面は、以下のパワーモジュールを提供する。 One aspect of the present disclosure provides the following power module:
［７］上記［１］～［６］のいずれか一項に記載の回路基板と、前記回路基板の前記銅板に電気的に接続された半導体素子と、を備える、パワーモジュール。 [7] A power module comprising a circuit board described in any one of [1] to [6] above and a semiconductor element electrically connected to the copper plate of the circuit board.
　上記パワーモジュールは、回路基板の窒化ケイ素板と銅板の接合強度が高い。したがって、上記パワーモジュールは耐久性に優れる。 The power module has high bonding strength between the silicon nitride plate and the copper plate of the circuit board. Therefore, the power module has excellent durability.
　本開示は、高い接合強度を有する回路基板を提供することができる。また、本開示は、そのような回路基板を備えるパワーモジュールを提供することができる。 The present disclosure can provide a circuit board with high bonding strength. The present disclosure can also provide a power module that includes such a circuit board.
回路基板の断面図である。FIG. 回路基板の製造方法における工程を説明するための積層体の断面図の一例である。5A to 5C are cross-sectional views of an example of a laminate for explaining a process in a method for manufacturing a circuit board. 加圧治具の斜視図である。FIG. 加圧治具の一部を切り欠いて示す構造体の平面図である。FIG. 2 is a plan view of the structure with a portion of the pressing jig cut away. 加圧治具の一部を切り欠いて示す構造体の正面図である。FIG. 2 is a front view of the structure with a portion of the pressing jig cut away. 加圧治具の一部を切り欠いて示す構造体の側面図である。FIG. 2 is a side view of the structure with a portion of the pressing jig cut away. 図４に示す構造体のＶＩＩ-ＶＩＩ線断面図である。7 is a cross-sectional view of the structure shown in FIG. 4 taken along line VII-VII. 加圧プレートを上昇させてスプリングワッシャを復元させた状態を示す構造体の断面図である。13 is a cross-sectional view of the structure showing a state in which the pressure plate is raised and the spring washer is restored to its original state. FIG. 図８の複合体及びスペーサの一部を拡大して示す断面図である。FIG. 9 is an enlarged cross-sectional view showing a portion of the composite body and the spacer of FIG. 8 . （Ａ）は、実施例１における回路基板の断面のＳＴＥＭ画像である。（Ｂ）は比較例１における回路基板の断面のＳＴＥＭ画像である。1A is an STEM image of a cross section of a circuit board in Example 1. FIG. 1B is an STEM image of a cross section of a circuit board in Comparative Example 1. （Ａ）は、実施例１における回路基板の断面のＥＤＸ分析によるチタン元素の分布を示す図である。（Ｂ）は、実施例１における回路基板の断面のＥＤＸ分析によるケイ素元素の分布を示す図である。1A is a diagram showing the distribution of titanium elements by EDX analysis of a cross section of the circuit board in Example 1. FIG. 1B is a diagram showing the distribution of silicon elements by EDX analysis of a cross section of the circuit board in Example 1. （Ａ）は、実施例１における回路基板の断面のＥＤＸ分析による銀元素の分布を示す図である。（Ｂ）は、実施例１における回路基板の断面のＥＤＸ分析による銅元素の分布を示す図である。1A is a diagram showing the distribution of silver and copper elements by EDX analysis of a cross section of the circuit board in Example 1; FIG. 1B is a diagram showing the distribution of silver and copper elements by EDX analysis of a cross section of the circuit board in Example 1; （Ａ）は、比較例１における回路基板の断面のＥＤＸ分析によるチタン元素の分布を示す図である。（Ｂ）は、比較例１における回路基板の断面のＥＤＸ分析によるケイ素元素の分布を示す図である。1A is a diagram showing the distribution of titanium elements by EDX analysis of a cross section of the circuit board in Comparative Example 1. FIG. 1B is a diagram showing the distribution of silicon elements by EDX analysis of a cross section of the circuit board in Comparative Example 1. （Ａ）は、比較例１における回路基板の断面のＥＤＸ分析による銀元素の分布を示す図である。（Ｂ）は、比較例１における回路基板の断面のＥＤＸ分析による銅元素の分布を示す図である。1A is a diagram showing the distribution of silver and copper elements by EDX analysis of a cross section of the circuit board in Comparative Example 1; 実施例１におけるＥＤＸのラインプロファイルである。1 is an EDX line profile in Example 1. （Ａ）は、実施例１において、回路基板から銅板を剥離した際の状態を示す写真である。（Ｂ）は、比較例１において、回路基板から銅板を剥離した際の状態を示す写真である。1A is a photograph showing the state when the copper plate is peeled off from the circuit board in Example 1. FIG. 1B is a photograph showing the state when the copper plate is peeled off from the circuit board in Comparative Example 1. （Ａ）は、実施例１において、回路基板から銅板を剥離した後の剥離面のＳＥＭ画像である。（Ｂ）は、比較例１において、回路基板から銅板を剥離した後の剥離面のＳＥＭ画像である。1A is an SEM image of the peeled surface after the copper plate is peeled off from the circuit board in Example 1. FIG. 1B is an SEM image of the peeled surface after the copper plate is peeled off from the circuit board in Comparative Example 1. （Ａ）は、実施例１において、回路基板から銅板を剥離した後の剥離面のＥＤＸ分析により、ケイ素元素の分布を示す図である。（Ｂ）は、比較例１において、回路基板から銅板を剥離した後の剥離面のＥＤＸ分析により、ケイ素元素の分布を示す図である。1A is a diagram showing the distribution of silicon elements by EDX analysis of the peeled surface after peeling the copper plate from the circuit board in Example 1. FIG. 1B is a diagram showing the distribution of silicon elements by EDX analysis of the peeled surface after peeling the copper plate from the circuit board in Comparative Example 1.
　以下、本開示の実施形態を説明する。ただし、以下の実施形態は、本開示を説明するための例示であり、本開示を以下の内容に限定する趣旨ではない。本開示に明示される数値範囲の上限値又は下限値は、実施例に示されるいずれかの値に置き換えてもよい。また、個別に記載した上限値及び下限値は任意に組み合わせてもよい。本開示において例示する材料又は成分は特に断らない限り、１種を単独で又は２種以上を組み合わせて用いることができる。説明において、同一要素又は同一機能を有する要素には同一の符号を付し、重複する説明を省略する。また、説明に使用される上下左右等の位置関係は、特に断らない限り、図面に示す位置関係に基づくものとする。 Below, an embodiment of the present disclosure will be described. However, the following embodiment is an example for explaining the present disclosure, and is not intended to limit the present disclosure to the following content. The upper or lower limit of the numerical range specified in this disclosure may be replaced with any value shown in the examples. Furthermore, the upper and lower limit values described individually may be combined in any combination. Unless otherwise specified, the materials or components exemplified in this disclosure may be used alone or in combination of two or more types. In the description, the same elements or elements having the same functions are given the same reference numerals, and duplicate descriptions are omitted. Furthermore, the positional relationships such as up, down, left, and right used in the description shall be based on the positional relationships shown in the drawings, unless otherwise specified.
　図１は、一実施形態に係る回路基板の模式断面図である。回路基板１００は、窒化ケイ素板１０の両方の面上に一対の銅板５０を有し、窒化ケイ素板１０の各主面と銅板５０の主面とを接合する接合層２０を有する。接合層２０は、窒化ケイ素板１０側から、第１接合層２１と、第２接合層２２と、第３接合層２３とをこの順に有する。 Figure 1 is a schematic cross-sectional view of a circuit board according to one embodiment. The circuit board 100 has a pair of copper plates 50 on both sides of a silicon nitride plate 10, and a bonding layer 20 that bonds each main surface of the silicon nitride plate 10 to the main surface of the copper plate 50. The bonding layer 20 has, from the silicon nitride plate 10 side, a first bonding layer 21, a second bonding layer 22, and a third bonding layer 23, in this order.
　回路基板１００の形状は特に限定されず、集合基板であってもよく、集合基板を分割することにより得られる個片基板であってもよい。回路基板の厚さは０．９～２．７ｍｍであってよく、１．３～２．２ｍｍであってもよい。 The shape of the circuit board 100 is not particularly limited, and it may be an aggregate board, or an individual board obtained by dividing an aggregate board. The thickness of the circuit board may be 0.9 to 2.7 mm, or 1.3 to 2.2 mm.
　窒化ケイ素板１０は、窒化ケイ素粉末を焼結した窒化ケイ素焼結体により構成されるものであってよい。窒化ケイ素板１０の形状は板状であれば特に制限されない。窒化ケイ素板１０の厚さは、例えば０．２～２．０ｍｍであってよく、０．３２～１．１ｍｍであってもよい。 The silicon nitride plate 10 may be made of a silicon nitride sintered body obtained by sintering silicon nitride powder. There are no particular limitations on the shape of the silicon nitride plate 10 as long as it is plate-like. The thickness of the silicon nitride plate 10 may be, for example, 0.2 to 2.0 mm, or 0.32 to 1.1 mm.
　銅板５０は、窒化ケイ素板１０の主面に接合できる形状であれば特に制限されない。銅板５０の厚さは、例えば０．１～１．２ｍｍであってよく、０．２～１．０ｍｍであってもよい。銅板５０は表面にめっき膜を有していてもよい。 The copper plate 50 is not particularly limited in shape as long as it can be bonded to the main surface of the silicon nitride plate 10. The thickness of the copper plate 50 may be, for example, 0.1 to 1.2 mm, or may be 0.2 to 1.0 mm. The copper plate 50 may have a plating film on its surface.
　接合層２０は、窒化ケイ素板１０側から、窒化チタンを含む第１接合層２１と、第１接合層２１よりもケイ素元素の濃度が高い第２接合層２２と、第１接合層２１及び第２接合層２２よりも銀元素の濃度が高い第３接合層２３と、を有する。第２接合層２２は、第１接合層２１と第３接合層２３とを遮断するように、第１接合層２１と第３接合層２３との間に介在している。このような接合層２０を有する回路基板１００は、窒化ケイ素板１０と、銅板５０との接合強度を高くすることができる。 The bonding layer 20 has, from the silicon nitride plate 10 side, a first bonding layer 21 containing titanium nitride, a second bonding layer 22 having a higher concentration of silicon element than the first bonding layer 21, and a third bonding layer 23 having a higher concentration of silver element than the first bonding layer 21 and the second bonding layer 22. The second bonding layer 22 is interposed between the first bonding layer 21 and the third bonding layer 23 so as to isolate the first bonding layer 21 and the third bonding layer 23. A circuit board 100 having such a bonding layer 20 can increase the bonding strength between the silicon nitride plate 10 and the copper plate 50.
　接合層２０は、第１接合層２１、第２接合層２２、及び第３接合層２３を有する層である。接合層２０は、チタン元素、銀元素、及びケイ素元素を含む。接合層２０は、さらに銅、錫、及び活性金属からなる群より選ばれる一種又は二種を含有してよい。二種以上の金属は合金となっていてもよい。活性金属は、チタン、ハフニウム、ジルコニウム、及びニオブからなる群より選ばれる一種又は二種以上含んでいてよい。 The bonding layer 20 is a layer having a first bonding layer 21, a second bonding layer 22, and a third bonding layer 23. The bonding layer 20 contains titanium, silver, and silicon elements. The bonding layer 20 may further contain one or two metals selected from the group consisting of copper, tin, and an active metal. The two or more metals may be an alloy. The active metal may contain one or two or more metals selected from the group consisting of titanium, hafnium, zirconium, and niobium.
　接合層２０に含まれる銀は、例えばＡｇ－Ｃｕ共晶合金等の合金として接合層２０に含まれていてもよい。接合層２０における銀の含有量は、Ａｇ換算で６０～９５質量％であってよい。接合層２０における銀及び銅の含有量は、それぞれＡｇ及びＣｕに換算して７５～１００質量％であってよく、８５～９９質量％であってよく、９０～９８質量％であってもよい。これによって、接合層２０における残留応力を十分に低減しつつ、接合層２０の緻密性を向上することができる。 The silver contained in the bonding layer 20 may be contained in the bonding layer 20 as an alloy, such as an Ag-Cu eutectic alloy. The silver content in the bonding layer 20 may be 60-95 mass% in Ag equivalent. The silver and copper contents in the bonding layer 20 may be 75-100 mass%, 85-99 mass%, or 90-98 mass% in Ag and Cu equivalent, respectively. This makes it possible to sufficiently reduce the residual stress in the bonding layer 20 while improving the density of the bonding layer 20.
　接合層２０における活性金属の含有量は、Ａｇ及びＣｕの合計１００質量部に対して、０．５～５質量部であってよい。活性金属の含有量を０．５質量部以上とすることで、窒化ケイ素板１０と接合層２０との接合性を向上することができる。一方、活性金属の含有量を５質量部以下とすることで、接合界面に脆弱な合金層が形成されることを抑制できる。 The content of the active metal in the bonding layer 20 may be 0.5 to 5 parts by mass per 100 parts by mass of Ag and Cu combined. By making the content of the active metal 0.5 parts by mass or more, it is possible to improve the bond between the silicon nitride plate 10 and the bonding layer 20. On the other hand, by making the content of the active metal 5 parts by mass or less, it is possible to suppress the formation of a brittle alloy layer at the bonding interface.
　接合層２０に含有される上記金属は、窒化物、酸化物、炭化物又は水素化物として含まれていてもよい。一例として、接合層２０は、窒化チタン及び／又は水素化チタン（ＴｉＨ２）を含んでいてよい。これによって、窒化ケイ素板１０と接合層２０を十分に反応させて、第１接合層２１、第２接合層２２、及び第３接合層２３を形成することができる。これによって、窒化ケイ素板１０と銅板５０との接合強度を十分に高くすることができる。接合層２０において、ＡｇとＣｕの合計１００質量部に対するＴｉＨ２の含有量は例えば１～８質量部であってよい。 The metal contained in the bonding layer 20 may be contained as a nitride, oxide, carbide or hydride. As an example, the bonding layer 20 may contain titanium nitride and/or titanium hydride (TiH 2 ). This allows the silicon nitride plate 10 and the bonding layer 20 to react sufficiently to form the first bonding layer 21, the second bonding layer 22, and the third bonding layer 23. This allows the bonding strength between the silicon nitride plate 10 and the copper plate 50 to be sufficiently high. In the bonding layer 20, the content of TiH 2 relative to a total of 100 parts by mass of Ag and Cu may be, for example, 1 to 8 parts by mass.
　接合層２０に含まれる元素は、以下の手順で同定、及び定量を行うことができる。まず、回路基板の断面を、例えば走査型透過電子顕微鏡（ＳＴＥＭ）により観察する。断面の画像において、窒化ケイ素板１０から銅板５０側に向かい、窒化ケイ素板１０の主面に直交するラインに沿って、エネルギー分散型Ｘ線分析装置（ＥＤＸ）による分析を行う。これによって各元素の分布をラインプロファイルとして検出し、定量することができる。ここで、本開示における断面とは、接合層２０が設けられる窒化ケイ素板１０の主面に直交し、接合層２０を通る断面である。 The elements contained in the bonding layer 20 can be identified and quantified by the following procedure. First, a cross section of the circuit board is observed, for example, with a scanning transmission electron microscope (STEM). In the image of the cross section, analysis is performed with an energy dispersive X-ray analyzer (EDX) along a line perpendicular to the main surface of the silicon nitride plate 10, from the silicon nitride plate 10 toward the copper plate 50. This allows the distribution of each element to be detected as a line profile and quantified. Here, the cross section in this disclosure refers to a cross section perpendicular to the main surface of the silicon nitride plate 10 on which the bonding layer 20 is provided, and passing through the bonding layer 20.
　第１接合層２１は、窒化チタンを含む層である。窒化チタンの含有量は５０～９０原子％であってよく、５５～８５原子％であってよく、６０～８０原子％であってよい。第１接合層２１中のチタン元素及び窒素元素は、第２接合層２２及び第３接合層２３よりも多く検出されてもよい。すなわち、第１接合層２１は、第２接合層２２及び第３接合層２３よりも窒化チタンの含有量が高くてもよい。 The first bonding layer 21 is a layer containing titanium nitride. The titanium nitride content may be 50 to 90 atomic %, 55 to 85 atomic %, or 60 to 80 atomic %. The titanium element and the nitrogen element may be detected in the first bonding layer 21 in greater amounts than the second bonding layer 22 and the third bonding layer 23. That is, the first bonding layer 21 may have a higher titanium nitride content than the second bonding layer 22 and the third bonding layer 23.
　第１接合層２１に含まれる窒化チタン相は、窒化ケイ素板１０と第１接合層２１との接触面に沿って層状に形成されていてもよい。窒化チタン相が窒化ケイ素板１０と第１接合層２１との接触面に層状に連なって形成されることによって、窒化ケイ素板１０と銅板５０との接合強度を一層高くすることができる。窒化チタン相が窒化ケイ素板１０と第１接合層２１との接触面に沿って層状に形成されていることは、例えば電子線マイクロアナライザ（ＥＰＭＡ）によって断面を分析することで確認することができる。 The titanium nitride phase contained in the first bonding layer 21 may be formed in a layer along the contact surface between the silicon nitride plate 10 and the first bonding layer 21. By forming the titanium nitride phase in a continuous layer along the contact surface between the silicon nitride plate 10 and the first bonding layer 21, the bonding strength between the silicon nitride plate 10 and the copper plate 50 can be further increased. The fact that the titanium nitride phase is formed in a layer along the contact surface between the silicon nitride plate 10 and the first bonding layer 21 can be confirmed by analyzing a cross section, for example, with an electron beam microanalyzer (EPMA).
　第１接合層２１の厚さは、チタン元素及び窒素元素が含有量１０原子％以上で検出されるラインの長さとして求めることができる。第１接合層２１に含まれるチタン元素及び窒素元素の含有量は、１０～４５原子％であってもよく、２０～４０原子％であってよい。 The thickness of the first bonding layer 21 can be determined as the length of the line at which titanium and nitrogen elements are detected with a content of 10 atomic % or more. The titanium and nitrogen elements contained in the first bonding layer 21 may be 10 to 45 atomic %, or 20 to 40 atomic %.
　第１接合層２１の厚さは、１００～３００ｎｍであってよく、１５０～２５０ｎｍであってよい。第１接合層２１の厚さの最大値と最小値の差は、７０ｎｍ以下であってよく、５０ｎｍ以下であってもよく、４５ｎｍ以下であってもよい。第１接合層２１の厚さの最大値と最小値の差がこの範囲であることによって、第１接合層２１に窒化チタンが十分に含まれ、窒化ケイ素板１０と銅板５０との接合強度を向上させることができる。第１接合層２１の厚さの平均値ｔ１は、５つ以上のラインで測定した厚さの平均値として求めることができる。第１接合層２１の厚さの平均値ｔ１は、１７５～２３５ｎｍであってよく、１８０～２３０ｎｍであってよく、１９０～２２０ｎｍであってよい。 The thickness of the first bonding layer 21 may be 100 to 300 nm, or 150 to 250 nm. The difference between the maximum and minimum thicknesses of the first bonding layer 21 may be 70 nm or less, 50 nm or less, or 45 nm or less. When the difference between the maximum and minimum thicknesses of the first bonding layer 21 is within this range, the first bonding layer 21 contains a sufficient amount of titanium nitride, and the bonding strength between the silicon nitride plate 10 and the copper plate 50 can be improved. The average thickness t1 of the first bonding layer 21 can be calculated as the average thickness value measured at five or more lines. The average thickness t1 of the first bonding layer 21 may be 175 to 235 nm, 180 to 230 nm, or 190 to 220 nm.
　第２接合層２２は、第１接合層２１よりもケイ素元素の含有量が高い層である。ケイ素元素は、窒化ケイ素板１０由来であり、窒化ケイ素板１０と銅板５０を、ろう材層を介して加熱接着させる際、加熱により窒化ケイ素とろう材層のチタンが反応し、ケイ化チタンを含む層として第２接合層２２を形成すると考えられる。 The second bonding layer 22 is a layer with a higher silicon element content than the first bonding layer 21. The silicon element originates from the silicon nitride plate 10, and when the silicon nitride plate 10 and the copper plate 50 are heat-bonded via the brazing material layer, it is believed that the silicon nitride reacts with the titanium of the brazing material layer due to heating, forming the second bonding layer 22 as a layer containing titanium silicide.
　第２接合層２２のケイ素元素の含有量は、１０～４０原子％であってよく、２０～３０原子％であってよい。ケイ素元素の含有量がこの範囲である第２接合層２２は、窒化ケイ素板１０と、ろう材層中のチタンとの反応が十分に進行して形成されたものである。このため、窒化ケイ素板１０と銅板５０の接合強度を十分に向上することができる。 The silicon element content of the second bonding layer 22 may be 10-40 atomic %, or 20-30 atomic %. The second bonding layer 22 with a silicon element content in this range is formed by a sufficient reaction between the silicon nitride plate 10 and the titanium in the brazing material layer. This allows the bonding strength between the silicon nitride plate 10 and the copper plate 50 to be sufficiently improved.
　第２接合層２２は、第１接合層２１と第３接合層２３の間を遮断するように形成されている。すなわち、第２接合層２２は、第１接合層２１と第３接合層２３との間の全体にわたって形成されている。このような第２接合層２２は、窒化ケイ素板１０と銅板５０を、ろう材層を介して加熱接着させる際に、窒化ケイ素とろう材層中のチタンとの反応が十分に進行することによって形成されている。したがって、回路基板１００の窒化ケイ素板１０と銅板５０との接合強度を向上することができる。 The second bonding layer 22 is formed so as to isolate the first bonding layer 21 from the third bonding layer 23. That is, the second bonding layer 22 is formed over the entire area between the first bonding layer 21 and the third bonding layer 23. Such a second bonding layer 22 is formed by the sufficient reaction between the silicon nitride and the titanium in the brazing material layer when the silicon nitride plate 10 and the copper plate 50 are heat-bonded via the brazing material layer. Therefore, the bonding strength between the silicon nitride plate 10 and the copper plate 50 of the circuit board 100 can be improved.
　第２接合層２２の厚さは、ケイ素元素が含有量１０原子％以上で検出されるラインの長さとして求めることができる。第２接合層２２の厚さは、５０ｎｍ以上であってよく、５０～１２０ｎｍであってよく、６０～１１０ｎｍであってよく、８０～１００ｎｍであってもよい。第２接合層２２の厚さがこのような範囲であることによって、窒化ケイ素と接合層中のチタンとの反応が十分に進行し、窒化ケイ素板と銅板の接合強度を向上させることができる。 The thickness of the second bonding layer 22 can be determined as the length of the line at which the silicon element content is 10 atomic % or more. The thickness of the second bonding layer 22 may be 50 nm or more, 50 to 120 nm, 60 to 110 nm, or 80 to 100 nm. By having the thickness of the second bonding layer 22 in such a range, the reaction between the silicon nitride and the titanium in the bonding layer can proceed sufficiently, improving the bonding strength between the silicon nitride plate and the copper plate.
　第２接合層２２の厚さの平均値ｔ２は、５つ以上のラインで測定した厚さの平均値を計算して求めることができる。第２接合層２２の厚さの平均値ｔ２は、６０～１００ｎｍであってよく、７０～９０ｎｍであってよい。厚さの平均値ｔ２がこの範囲にある第２接合層２２は、窒化ケイ素板１０とろう材層との反応が十分に進行することによって形成される。このような第２接合層２２は、窒化ケイ素板１０と銅板５０との接合強度を十分に高くすることができる。 The average thickness t2 of the second bonding layer 22 can be determined by calculating the average thickness measured at five or more lines. The average thickness t2 of the second bonding layer 22 may be 60 to 100 nm, or 70 to 90 nm. A second bonding layer 22 with an average thickness t2 in this range is formed by the reaction between the silicon nitride plate 10 and the brazing material layer progressing sufficiently. Such a second bonding layer 22 can sufficiently increase the bonding strength between the silicon nitride plate 10 and the copper plate 50.
　第２接合層２２の厚さの平均値ｔ２に対する、第１接合層２１の厚さの平均値ｔ１の比（ｔ１／ｔ２）は、５以下であってよく、４以下であってよく、３以下であってもよい。（ｔ１／ｔ２）がこの範囲内であることによって、第１接合層２１と第２接合層２２がバランスよく形成され、窒化ケイ素板１０と銅板５０の接合強度を十分に高くすることができる。上記比の下限は、１．０であってよく、１．５であってよい。 The ratio (t1/t2) of the average thickness t1 of the first bonding layer 21 to the average thickness t2 of the second bonding layer 22 may be 5 or less, 4 or less, or 3 or less. By having (t1/t2) within this range, the first bonding layer 21 and the second bonding layer 22 are formed in a balanced manner, and the bonding strength between the silicon nitride plate 10 and the copper plate 50 can be sufficiently high. The lower limit of the above ratio may be 1.0 or 1.5.
　第３接合層２３は、第１接合層２１及び第２接合層２２よりも、銀元素の含有量が高い層である。第３接合層２３中の銀元素は、２０～９０原子％であってもよく、３０～８０原子％であってよい。第３接合層２３の厚さは、１．０～２．０μｍであってよく、１．２～１．７μｍであってよい。 The third bonding layer 23 is a layer having a higher silver element content than the first bonding layer 21 and the second bonding layer 22. The silver element content in the third bonding layer 23 may be 20 to 90 atomic %, or may be 30 to 80 atomic %. The thickness of the third bonding layer 23 may be 1.0 to 2.0 μm, or may be 1.2 to 1.7 μm.
　第３接合層２３と銅板５０との界面にチタン元素は存在しなくてもよい。回路基板１００は、窒化ケイ素板１０とろう材層中のチタンとの反応が十分に進行しているため、チタン元素は窒化ケイ素板１０側に近い第１接合層２１及び第２接合層２２内に留まる傾向にある。第３接合層２３と銅板５０との界面にチタン元素が存在しないことで、窒化ケイ素板１０とろう材層中のチタンとの反応が十分に進行した回路基板１００が得られる。その結果、窒化ケイ素板１０と銅板５０との接合強度を十分に高くすることができる。 Titanium elements do not have to be present at the interface between the third bonding layer 23 and the copper plate 50. In the circuit board 100, the reaction between the silicon nitride plate 10 and the titanium in the brazing material layer has progressed sufficiently, so that the titanium elements tend to remain in the first bonding layer 21 and the second bonding layer 22 near the silicon nitride plate 10 side. The absence of titanium elements at the interface between the third bonding layer 23 and the copper plate 50 results in a circuit board 100 in which the reaction between the silicon nitride plate 10 and the titanium in the brazing material layer has progressed sufficiently. As a result, the bonding strength between the silicon nitride plate 10 and the copper plate 50 can be made sufficiently high.
　接合層２０は、有機バインダ由来の炭素を含有してもよい。炭素は、第３接合層２３に含まれてもよい。第３接合層２３に含まれる炭素の含有量（Ｃ３）に対する、第１接合層２１に含まれる炭素の含有量（Ｃ１）の比（Ｃ１／Ｃ３）の平均値は、０．５以下であってよく、０．４５以下であってよく、０．４以下であってもよい。（Ｃ１／Ｃ３）の平均値がこの範囲であることによって、第１接合層２１の厚さが十分に大きくなる。その結果、窒化ケイ素板１０と銅板５０との接合強度を十分に高くすることができる。上記比の下限は、０．２であってよく、０．３であってよい。（Ｃ１／Ｃ３）の平均値は、次のようにして求める。５つ以上のラインで（Ｃ３）及び（Ｃ１）を測定し、各測定値から（Ｃ１／Ｃ３）を計算する。５つ以上の（Ｃ１／Ｃ３）の値から上記平均値を求める。なお、５つ以上の（Ｃ１／Ｃ３）の各値が０．５以下であってよく、０．４５以下であってよく、０．４以下であってもよい。 The bonding layer 20 may contain carbon derived from the organic binder. The carbon may be contained in the third bonding layer 23. The average value of the ratio (C1/C3) of the carbon content (C1) contained in the first bonding layer 21 to the carbon content (C3) contained in the third bonding layer 23 may be 0.5 or less, 0.45 or less, or 0.4 or less. When the average value of (C1/C3) is in this range, the thickness of the first bonding layer 21 becomes sufficiently large. As a result, the bonding strength between the silicon nitride plate 10 and the copper plate 50 can be sufficiently high. The lower limit of the above ratio may be 0.2 or 0.3. The average value of (C1/C3) is obtained as follows. (C3) and (C1) are measured on five or more lines, and (C1/C3) is calculated from each measurement value. The above average value is obtained from five or more (C1/C3) values. In addition, each of the five or more (C1/C3) values may be 0.5 or less, 0.45 or less, or 0.4 or less.
　窒化ケイ素板１０と銅板５０の接合強度は、ＪＩＳ　Ｋ　６８５４－１：１９９９「接着剤－はく離接着強さ試験方法」に準拠して、銅板５０を回路基板１００から９０°鉛直上方向に引きはがし、剥離した際の強度を測定して求めることができる。接合強度は、５００～８００Ｎ／ｃｍであってよく、６００～７００Ｎ／ｃｍであってよい。このような接合強度を有する回路基板１００は、回路基板１００上での接合強度のばらつきが抑えられ、回路基板１００の品質を安定させることができる。 The bond strength between the silicon nitride plate 10 and the copper plate 50 can be determined in accordance with JIS K 6854-1:1999 "Adhesives - Peel Adhesion Strength Test Method" by peeling the copper plate 50 vertically upward at 90° from the circuit board 100 and measuring the strength at the time of peeling. The bond strength may be 500 to 800 N/cm, or 600 to 700 N/cm. A circuit board 100 having such bond strength reduces variation in bond strength on the circuit board 100, and the quality of the circuit board 100 can be stabilized.
　回路基板１００の製造方法の一例を図２～９を参照にしながら以下に説明する。この例の製造方法は、窒化ケイ素板１０と、銅板５０と、これらを接着するろう材層３０とを備える複数の複合体４０を作製する工程（ａ）と、一対の複合体４０の間に、スペーサ７０を配置して積層体８０を作製する工程（ｂ）と、積層体８０を加熱して窒化ケイ素板１０と銅板５０とをろう材層３０で接合する工程（ｃ）と接合体から回路基板を作製する工程（ｄ）を有する。 An example of a manufacturing method for a circuit board 100 is described below with reference to Figures 2 to 9. The manufacturing method in this example includes a step (a) of producing a plurality of composites 40 each including a silicon nitride plate 10, a copper plate 50, and a brazing material layer 30 that bonds them together, a step (b) of placing a spacer 70 between a pair of composites 40 to produce a laminate 80, a step (c) of heating the laminate 80 to bond the silicon nitride plate 10 and the copper plate 50 with the brazing material layer 30, and a step (d) of producing a circuit board from the bonded assembly.
　工程（ａ）で用いる窒化ケイ素板１０の主面には区画線を形成してもよい。例えば、窒化ケイ素板１０の主面にレーザー光を照射して、区画線としてスクライブラインを設けてもよい。照射するレーザー光としては、例えば、炭酸ガスレーザー及びＹＡＧレーザー等が挙げられる。このようなレーザー源からレーザー光を間欠的に照射することによって、区画線となるスクライブラインを形成する。このような区画線は、接合体を分割する際の切断線として利用することができる。 A partition line may be formed on the main surface of the silicon nitride plate 10 used in step (a). For example, a laser beam may be irradiated onto the main surface of the silicon nitride plate 10 to provide a scribe line as the partition line. Examples of the laser beam to be irradiated include a carbon dioxide laser and a YAG laser. By intermittently irradiating the laser beam from such a laser source, a scribe line that serves as the partition line is formed. Such a partition line can be used as a cutting line when dividing the bonded body.
　窒化ケイ素板１０の主面に塗布するろう材は、例えば、銀、銅、錫、活性金属、及びこれらを構成元素とする金属化合物、有機溶媒、並びに有機バインダ等を含有する。ろう材の粘度は、例えば５～２０Ｐａ・ｓであってよい。ろう材における有機溶媒の含有量は、例えば、５～２５質量％、有機バインダ量の含有量は、例えば、２～１５質量％であってよい。 The brazing material applied to the main surface of the silicon nitride plate 10 contains, for example, silver, copper, tin, active metals, and metal compounds containing these as constituent elements, an organic solvent, and an organic binder. The viscosity of the brazing material may be, for example, 5 to 20 Pa·s. The organic solvent content in the brazing material may be, for example, 5 to 25 mass %, and the organic binder content may be, for example, 2 to 15 mass %.
　ろう材は、金属単体又は金属化合物（合金）の形態で、銀を含んでよく、銀に加えて、銅、錫、及び活性金属からなる群より選ばれる一種又は二種以上の金属を含有してよい。二種以上の金属は合金となっていてもよい。活性金属は、チタン、ハフニウム、ジルコニウム、及びニオブからなる群より選ばれる一種又は二種以上を含んでいてよい。ろう材における銀の含有量は、Ａｇ換算で４５～９５質量％であってよく、５０～９５質量％であってもよい。ろう材における銀及び銅の合計含有量は、それぞれＡｇ及びＣｕに換算して６５～１００質量％であってよく、７０～９９質量％であってよく、９０～９８質量％であってもよい。 The brazing filler metal may contain silver in the form of a metal element or a metal compound (alloy), and may contain, in addition to silver, one or more metals selected from the group consisting of copper, tin, and active metals. The two or more metals may be in the form of an alloy. The active metal may contain one or more metals selected from the group consisting of titanium, hafnium, zirconium, and niobium. The silver content in the brazing filler metal may be 45 to 95 mass% or 50 to 95 mass% in terms of Ag. The total silver and copper content in the brazing filler metal may be 65 to 100 mass%, 70 to 99 mass%, or 90 to 98 mass% in terms of Ag and Cu, respectively.
　ろう材における活性金属の含有量は、Ａｇ及びＣｕの合計１００質量部に対して、０．５～８質量部であってよい。活性金属の含有量を０．５質量部以上とすることで、窒化ケイ素板とろう材との接合性を向上することができる。一方、活性金属の含有量を８質量部以下とすることで、接合界面に脆弱な合金層が形成されることを抑制できる。 The content of the active metal in the brazing filler metal may be 0.5 to 8 parts by mass per 100 parts by mass of the total of Ag and Cu. By making the content of the active metal 0.5 parts by mass or more, it is possible to improve the bond between the silicon nitride plate and the brazing filler metal. On the other hand, by making the content of the active metal 8 parts by mass or less, it is possible to suppress the formation of a brittle alloy layer at the bonded interface.
　ろう材に含有される上記金属は、窒化物、酸化物、炭化物又は水素化物として含まれていてもよい。一例として、ろう材は、窒化チタン及び／又は水素化チタン（ＴｉＨ２）を含んでいてよい。これによって、窒化ケイ素板１０と銅板５０との接合強度を十分に高くすることができる。ＡｇとＣｕの合計１００質量部に対するＴｉＨ２の含有量は例えば１～８質量部であってよい。 The above metals contained in the brazing material may be contained as nitrides, oxides, carbides, or hydrides. As an example, the brazing material may contain titanium nitride and/or titanium hydride (TiH 2 ). This allows the bonding strength between the silicon nitride plate 10 and the copper plate 50 to be sufficiently high. The content of TiH 2 relative to a total of 100 parts by mass of Ag and Cu may be, for example, 1 to 8 parts by mass.
　ろう材における錫の含有量は、Ａｇ及びＣｕの合計１００質量部に対して、０．５～６質量部であってよい。錫の含有量を０．５質量部以上とすることで、窒化ケイ素板１０と接合層２０との接合性を向上することができる。一方、錫の含有量を５質量部以下とすることで、接合界面に脆弱な合金層が形成されることを抑制できる。 The tin content in the brazing material may be 0.5 to 6 parts by mass per 100 parts by mass of the total of Ag and Cu. By making the tin content 0.5 parts by mass or more, it is possible to improve the bond between the silicon nitride plate 10 and the bonding layer 20. On the other hand, by making the tin content 5 parts by mass or less, it is possible to suppress the formation of a brittle alloy layer at the bonding interface.
　窒化ケイ素板１０の両主面に、ロールコーター法、スクリーン印刷法、又は転写法等の方法によってろう材を塗布及び乾燥して一つ又は複数のろう材層３０を設ける。ろう材層３０は、窒化ケイ素板１０に銅板５０が接合される位置に設ければよい。ろう材層３０を形成したら、ろう材層３０を挟むようにして窒化ケイ素板１０と銅板５０とを積層して複数の複合体４０を作製する。 A brazing material is applied to both main surfaces of the silicon nitride plate 10 by a roll coater method, a screen printing method, a transfer method, or the like, and then dried to provide one or more brazing material layers 30. The brazing material layers 30 may be provided at positions where the copper plates 50 are to be joined to the silicon nitride plate 10. Once the brazing material layers 30 are formed, the silicon nitride plates 10 and the copper plates 50 are stacked with the brazing material layer 30 sandwiched between them to produce multiple composites 40.
　工程（ｂ）では、図２に示すように一対の複合体４０でスペーサ７０を挟むように積層し、積層体８０を作製する。スペーサ７０には市販の炭素製プレートを使用してもよい。炭素製プレートの密度は１．６～１．９ｇ／ｃｍ３であってもよい。炭素製プレートの厚さは０．５～１．０ｍｍであってもよい。面粗度Ｒａは５～１０μｍであってもよい。積層体８０に使用するスペーサ７０及び複合体４０は任意の個数を繰り返して積層してもよい。積層する複合体４０及びスペーサ７０の個数は特に制限されず、使用する加熱炉のサイズによって調節してもよい。このように積層することで、複数の複合体４０を一度に加熱でき、効率的に接合体を作製することができる。 In step (b), as shown in FIG. 2, a pair of composites 40 are laminated so as to sandwich a spacer 70, to produce a laminate 80. A commercially available carbon plate may be used as the spacer 70. The density of the carbon plate may be 1.6 to 1.9 g/cm 3. The thickness of the carbon plate may be 0.5 to 1.0 mm. The surface roughness Ra may be 5 to 10 μm. The spacers 70 and composites 40 used in the laminate 80 may be repeatedly laminated in any number. The number of composites 40 and spacers 70 to be laminated is not particularly limited, and may be adjusted depending on the size of the heating furnace to be used. By laminating in this manner, a plurality of composites 40 can be heated at once, and a bonded body can be efficiently produced.
　積層体８０は、積層方向に加圧されながら工程（ｃ）で加熱されてもよい。積層体８０を加圧する方法の一例を、図３、図４、図５、図６、図７、及び図８を参照して以下に説明する。図３の構造体９０は、加圧治具１と、加圧治具１のベースプレート２とカバープレート３の間に挟まれた積層体８０とを備える。積層体８０は、複数のスペーサ７０及び複数の複合体４０が交互に重ねられて構成される。積層体８０は平面視で矩形であるが、他の形状であってもよい。積層体８０と加圧治具１との間にはスペーサ７０が配置されている。スペーサ７０は、複合体４０同士の接合及び複合体４０と加圧治具１との接合を阻止する機能も有する。 The laminate 80 may be heated in step (c) while being pressurized in the stacking direction. An example of a method for pressurizing the laminate 80 is described below with reference to Figures 3, 4, 5, 6, 7, and 8. The structure 90 in Figure 3 includes a pressurizing jig 1 and a laminate 80 sandwiched between a base plate 2 and a cover plate 3 of the pressurizing jig 1. The laminate 80 is formed by alternately stacking a plurality of spacers 70 and a plurality of composites 40. The laminate 80 is rectangular in plan view, but may have other shapes. A spacer 70 is disposed between the laminate 80 and the pressurizing jig 1. The spacer 70 also has the function of preventing bonding between the composites 40 and bonding between the composites 40 and the pressurizing jig 1.
　図３に示すように、加圧治具１は、積層体８０が載置される板状のベースプレート２（土台部）と、ベースプレート２に対向して配置されたカバープレート３（カバー部）とを備えている。カバープレート３とベースプレート２は、積層体８０を挟持する。加圧治具１は、カバープレート３上に配置された複数のスプリングワッシャ４と、スプリングワッシャ４上に配置された加圧プレート５（加圧部）とを備えている。加圧治具１は、加圧プレート５によってスプリングワッシャ４を圧縮して積層体８０を加圧する加圧構造６を有する。 As shown in FIG. 3, the pressing jig 1 comprises a plate-shaped base plate 2 (foundation portion) on which the laminate 80 is placed, and a cover plate 3 (cover portion) arranged opposite the base plate 2. The cover plate 3 and the base plate 2 sandwich the laminate 80. The pressing jig 1 comprises a plurality of spring washers 4 arranged on the cover plate 3, and a pressing plate 5 (pressing portion) arranged on the spring washers 4. The pressing jig 1 has a pressing structure 6 that compresses the spring washers 4 with the pressing plate 5 to pressurize the laminate 80.
　ベースプレート２は、例えば矩形状であり、平面視で積層体８０からはみ出た領域、つまり積層体８０に重なっていない張出領域２ａを有する。ベースプレート２の張出領域２ａには、ベースプレート２の短辺に沿うように複数（例えば、二本）の支柱８（支柱部）が立設されている。また、支柱８は、ベースプレート２の長手方向（左右方向）の両側で対向して配置されており、左右で対向する一対の支柱８同士の間に積層体８０が配置されている。支柱８の上部には、係止爪９が挿通される係合孔８ａが形成されている。 The base plate 2 is, for example, rectangular, and has an area that extends beyond the laminate 80 in a plan view, i.e., a protruding area 2a that does not overlap the laminate 80. In the protruding area 2a of the base plate 2, multiple (for example, two) pillars 8 (pillar portions) are erected along the short sides of the base plate 2. The pillars 8 are also arranged opposite each other on both sides of the longitudinal direction (left-right direction) of the base plate 2, and the laminate 80 is arranged between a pair of pillars 8 facing each other on the left and right. An engagement hole 8a is formed in the upper part of the pillar 8, through which a locking claw 9 is inserted.
　カバープレート３は、積層体８０の形状に対応した矩形状であり、図５及び図７に示すように、一方の表面３ａ（以下、「下面」と称する）と他方の表面３ｂ（以下、「上面」と称する）とを有する。下面３ａは平坦面であり、カバープレート３寄りに配置されるスペーサ７０に当接する。図３に示すように、上面３ｂには、複数の座ぐり３ｃが形成されており、各座ぐり３ｃ内にはスプリングワッシャ４が収納される。座ぐり３ｃの深さは、例えば螺旋状のスプリングワッシャ４が圧縮されて平坦になった際に、スプリングワッシャ４の全体が収まる程度の寸法であってよい。座ぐり３ｃは、平面視でドーナツ状（環状）を呈し、平面視で環状のスプリングワッシャ４が収まり、スプリングワッシャ４の位置ずれを防止する。座ぐり３ｃは、スプリングワッシャ４の位置決め部として機能する。 The cover plate 3 has a rectangular shape corresponding to the shape of the laminate 80, and has one surface 3a (hereinafter referred to as the "lower surface") and the other surface 3b (hereinafter referred to as the "upper surface") as shown in Figs. 5 and 7. The lower surface 3a is flat and abuts against the spacer 70 arranged closer to the cover plate 3. As shown in Fig. 3, the upper surface 3b has a plurality of counterbores 3c formed therein, and the spring washer 4 is housed in each counterbores 3c. The depth of the counterbores 3c may be a dimension such that the entire spring washer 4 is housed therein when the helical spring washer 4 is compressed and flattened. The counterbores 3c are donut-shaped (annular) in plan view, and the annular spring washer 4 is housed therein, preventing the spring washer 4 from shifting out of position. The counterbores 3c function as positioning portions for the spring washer 4.
　図５に示すように、加圧プレート５は、平面視でベースプレート２の張出領域２ａに対向する余剰領域５ａを有する。余剰領域５ａには、図３及び図４に示すように、支柱８が貫通する支柱貫通孔５ｂが形成されている。余剰領域５ａの上面には、支柱貫通孔５ｂを通るように収納溝５ｃが設けられている。収納溝５ｃには、係止爪９が収まる。 As shown in FIG. 5, the pressure plate 5 has a surplus area 5a that faces the protruding area 2a of the base plate 2 in a plan view. As shown in FIG. 3 and FIG. 4, a post through hole 5b through which the post 8 passes is formed in the surplus area 5a. A storage groove 5c is provided on the upper surface of the surplus area 5a so as to pass through the post through hole 5b. The locking claw 9 fits into the storage groove 5c.
　加圧プレート５は、カバープレート３に重ねるように配置され、更に、スプリングワッシャ４に当接するように押し下げられる。加圧プレート５を押し下げる際、加圧プレート５の余剰領域５ａに設けられた支柱貫通孔５ｂには支柱８が通される。支柱８の上部は支柱貫通孔５ｂの上方に突き出る。支柱８の上部には、係合孔８ａが設けられており、係合孔８ａには係止爪９（係止部）が挿通される。係止爪９は、横方向から係合孔８ａを貫通すると共に、加圧プレート５のスプリングワッシャ４に当接する側の表面（下面）とは反対側の表面（上面）に当接して加圧プレート５を係止する。加圧プレート５の上面には、係止爪９の外形に対応する収納溝５ｃが形成されており、係止爪９は収納溝５ｃに沿ってスライドする。 The pressure plate 5 is placed so as to overlap the cover plate 3, and is further pressed down so as to abut against the spring washer 4. When the pressure plate 5 is pressed down, a support 8 is passed through the support through hole 5b provided in the excess area 5a of the pressure plate 5. The upper part of the support 8 protrudes above the support through hole 5b. An engagement hole 8a is provided in the upper part of the support 8, and a locking claw 9 (locking portion) is inserted into the engagement hole 8a. The locking claw 9 passes through the engagement hole 8a from the lateral direction and locks the pressure plate 5 by abutting against the surface (upper surface) of the pressure plate 5 opposite the surface (lower surface) that abuts against the spring washer 4. A storage groove 5c corresponding to the outer shape of the locking claw 9 is formed in the upper surface of the pressure plate 5, and the locking claw 9 slides along the storage groove 5c.
　係止爪９が加圧プレート５を係止すると、加圧プレート５は上方への移動を規制される。加圧プレート５の移動の規制により、スプリングワッシャ４の復元が阻止され、スプリングワッシャ４は圧縮状態で保持される。本実施形態に係る加圧構造６は、少なくとも加圧プレート５、支柱８、係合孔８ａ及び係止爪９を備えて構成されている。 When the locking claw 9 locks the pressure plate 5, the pressure plate 5 is restricted from moving upward. By restricting the movement of the pressure plate 5, the spring washer 4 is prevented from returning to its original position, and the spring washer 4 is held in a compressed state. The pressure structure 6 in this embodiment is configured to include at least the pressure plate 5, the support 8, the engagement hole 8a, and the locking claw 9.
　スプリングワッシャ４は、例えば、インコネル７５０又はインコネル７１８等の合金、窒化ケイ素、或いはカーボンコンポジット等によって形成されている。スプリングワッシャ４は、例えば、カバープレート３に当接していない状態で非圧縮状態である（図８参照）。スプリングワッシャ４は、重なることなく螺旋状に巻かれ、且つ両端部４ａ、４ｂが離隔している圧縮バネの一例である。より具体的に説明すると、スプリングワッシャ４はＣ字状の形状を呈し、両端部４ａ、４ｂは、互いに離隔すると共に、螺旋状を仮定した場合の軸線方向（例えば上下方向）にずれている。ここで、カバープレート３の座ぐり３ｃ内で、座ぐり３ｃの底に当接している一方の端部を下端部４ａとし、反対側の他方の端部を上端部４ｂとする。スプリングワッシャ４は、カバープレート３を介し、加圧構造６によって圧縮されると下端部４ａと上端部４ｂは近接し、スプリングワッシャ４の螺旋状は解消され、実質的に平坦な形状になる（図７参照）。 The spring washer 4 is formed of, for example, an alloy such as Inconel 750 or Inconel 718, silicon nitride, or a carbon composite. The spring washer 4 is in an uncompressed state when it is not in contact with the cover plate 3 (see FIG. 8). The spring washer 4 is an example of a compression spring that is wound in a spiral shape without overlapping and has both ends 4a and 4b spaced apart. More specifically, the spring washer 4 has a C-shape, and both ends 4a and 4b are spaced apart from each other and are offset in the axial direction (for example, vertical direction) assuming a spiral shape. Here, within the countersink 3c of the cover plate 3, one end that is in contact with the bottom of the countersink 3c is the lower end 4a, and the other end on the opposite side is the upper end 4b. When the spring washer 4 is compressed by the pressure structure 6 through the cover plate 3, the lower end 4a and the upper end 4b approach each other, the spiral shape of the spring washer 4 is eliminated, and the spring washer 4 becomes substantially flat (see Figure 7).
　複数のスプリングワッシャ４は、カバープレート３の外縁３ｘからはみ出すことなく、カバープレート３の外縁３ｘよりも内側に収まるように配置されている。また、複数のスプリングワッシャ４は、カバープレート３の外縁３ｘに沿って配置されている。例えば、本実施形態に係るカバープレート３の外縁３ｘは矩形状である。スプリングワッシャ４は、外縁３ｘの各短辺に沿って３個が並んで配置されており、各長辺に沿って５個のスプリングワッシャ４が並んで配置されている。複数のスプリングワッシャ４をカバープレート３の外縁３ｘに沿って配置することにより、カバープレート３を介して積層体８０を均一に加圧し易くなる。 The multiple spring washers 4 are arranged so as to fit inside the outer edge 3x of the cover plate 3 without protruding beyond the outer edge 3x of the cover plate 3. The multiple spring washers 4 are also arranged along the outer edge 3x of the cover plate 3. For example, the outer edge 3x of the cover plate 3 according to this embodiment is rectangular. Three spring washers 4 are arranged in a row along each short side of the outer edge 3x, and five spring washers 4 are arranged in a row along each long side. By arranging the multiple spring washers 4 along the outer edge 3x of the cover plate 3, it becomes easier to apply uniform pressure to the laminate 80 via the cover plate 3.
　複数のスプリングワッシャ４は、等間隔で配置されている。具体的には、複数のスプリングワッシャ４は、３行、５列（複数行、複数列）となるように計１５個が配置されており、全てのスプリングワッシャ４は等間隔で配置されている。スプリングワッシャ４を等間隔で配置することにより、カバープレート３によって積層体８０を均一に加圧し易くなる。なお、カバープレート３の外縁３ｘに沿って配置されている複数のスプリングワッシャ４のみを等間隔で配置するようにしてもよい。また、平面視でカバープレート３の中心を規定した場合に、この中心を基準にして点対称となるように複数のスプリングワッシャ４を配置するようにしてもよい。 The multiple spring washers 4 are arranged at equal intervals. Specifically, a total of 15 spring washers 4 are arranged in three rows and five columns (multiple rows and multiple columns), and all of the spring washers 4 are arranged at equal intervals. By arranging the spring washers 4 at equal intervals, it becomes easier for the cover plate 3 to apply uniform pressure to the laminate 80. Note that only the multiple spring washers 4 arranged along the outer edge 3x of the cover plate 3 may be arranged at equal intervals. Furthermore, when the center of the cover plate 3 is defined in a plan view, the multiple spring washers 4 may be arranged so as to be point symmetrical with respect to this center.
　スプリングワッシャ４の下端部４ａと上端部４ｂとの間（両端部同士の間）には離隔領域４ｘが形成されている。複数のスプリングワッシャ４は、離隔領域４ｘがカバープレート３の外縁３ｘに面するように配置されている。つまり、スプリングワッシャ４を平面視でリング状と仮定した場合に、スプリングワッシャ４は、離隔領域４ｘがリング状の中心点よりもカバープレート３の外縁３ｘに近い位置となるように配置されている。更に補足すると、複数のスプリングワッシャ４の各離隔領域４ｘを結ぶような線を仮定した場合に、この線は、カバープレート３の外縁３ｘに沿うように配置されている。 A separation region 4x is formed between the lower end 4a and upper end 4b of the spring washer 4 (between both ends). The multiple spring washers 4 are arranged so that the separation region 4x faces the outer edge 3x of the cover plate 3. In other words, if the spring washer 4 is assumed to be ring-shaped in a plan view, the spring washer 4 is arranged so that the separation region 4x is closer to the outer edge 3x of the cover plate 3 than the center point of the ring. To further add, if a line is assumed to connect the separation regions 4x of the multiple spring washers 4, this line is arranged to run along the outer edge 3x of the cover plate 3.
　スプリングワッシャ４が圧縮された際、スプリングワッシャ４は、離隔領域４ｘを挟んで対向する下端部４ａと上端部４ｂとにおける反発力（加圧力）が最も大きくなる。この離隔領域４ｘがカバープレート３の外縁３ｘに面するように配置することで、カバープレート３の外縁３ｘに沿った部分を確実に抑え込みやすくなり、カバープレート３を介して積層体８０を均一に加圧し易くなる。 When the spring washer 4 is compressed, the repulsive force (pressure) is greatest at the lower end 4a and upper end 4b, which face each other across the separation area 4x. By arranging this separation area 4x to face the outer edge 3x of the cover plate 3, it becomes easier to reliably hold down the portion along the outer edge 3x of the cover plate 3, and it becomes easier to apply uniform pressure to the laminate 80 via the cover plate 3.
　図９は、図８の複合体４０及びスペーサ７０の積層構造の積層方向に沿う断面の一部を拡大して示している。図９では、ベースプレート２からカバープレート３に向かって、スペーサ７０、積層体８０、スペーサ７０がこの順に積層されている。積層体８０は一対の複合体４０でスペーサ７０を挟むように積層したものである。複合体４０は、一対の銅板５０がろう材層３０を介して、窒化ケイ素板１０を挟むように積層したものである。積層体８０は、複合体４０とスペーサ７０を任意の個数を繰り返し積層して構成されてもよい。このような積層構造であることによって、工程（ｃ）で加熱する際に、反応のばらつきを抑え、高い接合強度を有する接合体を得ることができる。なお、積層体８０を構成するスペーサ７０及び複合体４０の個数は特に限定されない。 9 shows an enlarged cross section of the laminated structure of the composite 40 and the spacer 70 in FIG. 8 along the lamination direction. In FIG. 9, the spacer 70, the laminate 80, and the spacer 70 are laminated in this order from the base plate 2 toward the cover plate 3. The laminate 80 is formed by laminating a pair of composites 40 so as to sandwich the spacer 70. The composite 40 is formed by laminating a pair of copper plates 50 so as to sandwich the silicon nitride plate 10 with the brazing material layer 30 between them. The laminate 80 may be formed by repeatedly laminating any number of composites 40 and spacers 70. This laminated structure makes it possible to suppress the variation in reaction during heating in step (c) and obtain a joint having high joint strength. The number of spacers 70 and composites 40 constituting the laminate 80 is not particularly limited.
　工程（ｃ）では、加圧したまま加熱炉内で積層体８０を加熱して、窒化ケイ素板１０及び銅板５０と、ろう材層３０とを反応させ、窒化ケイ素板１０と銅板５０を接合させた接合体を得る。加熱により、ろう材層３０は上述した接合層２０となる。したがって、接合層２０は、窒化ケイ素板１０及び銅板５０と、ろう材層３０との反応生成物を含んでよい。 In step (c), the laminate 80 is heated in a heating furnace while still under pressure to cause a reaction between the silicon nitride plate 10 and the copper plate 50 and the brazing material layer 30, thereby obtaining a bonded body in which the silicon nitride plate 10 and the copper plate 50 are bonded. By heating, the brazing material layer 30 becomes the bonding layer 20 described above. Therefore, the bonding layer 20 may contain a reaction product between the silicon nitride plate 10 and the copper plate 50 and the brazing material layer 30.
　工程（ｃ）は、ろう材層３０中の炭素を脱脂する工程を含んでよい。脱脂する工程の加熱温度は、３７０～４２０℃であってもよく、３８０～４１５℃であってもよく、３９０～４１０℃であってもよい。また、上記加熱温度における加熱時間は３．５時間以上であってよく、３．７５時間以上であってよい。また、全体の製造工程にかかる時間を短縮する観点から上記加熱時間は５時間以下であってもよく、４．５時間以下であってもよい。脱脂する工程により、ろう材層３０に含まれる有機バインダ由来の余分な炭素を熱分解で除去することができるため、７００～９００℃での加熱時に炭素とチタンが反応せず、窒化チタン及びケイ化チタンの生成を十分に進行させることができる。 Step (c) may include a step of degreasing the carbon in the brazing material layer 30. The heating temperature in the degreasing step may be 370 to 420°C, 380 to 415°C, or 390 to 410°C. The heating time at the above heating temperature may be 3.5 hours or more, or 3.75 hours or more. In order to shorten the time required for the entire manufacturing process, the heating time may be 5 hours or less, or 4.5 hours or less. The degreasing step can remove excess carbon derived from the organic binder contained in the brazing material layer 30 by thermal decomposition, so that carbon and titanium do not react when heated at 700 to 900°C, and the generation of titanium nitride and titanium silicide can be sufficiently promoted.
　加熱炉内の雰囲気は窒素等の不活性ガスであってよく、大気圧未満の減圧下で行ってもよく、真空下で行ってもよい。加熱炉は、複数の複合体４０を連続的に製造する連続式のものであってもよいし、一つ又は複数の複合体４０をバッチ式で製造するものであってもよい。加熱温度は、反応を促進する観点から、７００～９００℃であってもよく、７５０～８５０℃であってもよい。加熱時間は３時間以下であってもよく、２時間以下であってもよい。加熱時の炉内の圧力は、常圧、減圧、真空のいずれであってもよい。反応を促進する観点から、炉内の圧力は１０－２～１０－７Ｐａであってもよい。 The atmosphere in the heating furnace may be an inert gas such as nitrogen, and may be performed under reduced pressure below atmospheric pressure, or may be performed under vacuum. The heating furnace may be a continuous type that continuously produces a plurality of composites 40, or may be a batch type that produces one or a plurality of composites 40. The heating temperature may be 700 to 900°C or 750 to 850°C from the viewpoint of promoting the reaction. The heating time may be 3 hours or less, or 2 hours or less. The pressure in the furnace during heating may be any of normal pressure, reduced pressure, and vacuum. From the viewpoint of promoting the reaction, the pressure in the furnace may be 10 -2 to 10 -7 Pa.
　工程（ｃ）での加熱炉内の昇温速度は７０～１２０℃／ｍｉｎであってよく、８０～１１０℃／ｍｉｎであってもよい。昇温速度がこの範囲であることにより、全体の製造工程にかかる時間を十分に短縮することができる。また、加熱後の降温速度についても上記昇温速度と同様の範囲であってよい。 The heating rate in the heating furnace in step (c) may be 70 to 120°C/min, or may be 80 to 110°C/min. By keeping the heating rate in this range, the time required for the entire manufacturing process can be sufficiently shortened. In addition, the temperature reduction rate after heating may also be in the same range as the above heating rate.
　工程（ｃ）の後、アニール工程を行ってよい。アニール工程におけるアニール温度は４００～６５０℃であってよく、５００～６００℃であってよい。アニール温度におけるアニール時間は、１．５～３．０時間であってもよく、２．０～２．５時間であってよい。冷却後、加圧治具から接合体を取り外してもよい。アニール工程を行うことで、積層体８０の加熱による歪みを軽減し、ヒートサイクル特性に十分に優れる回路基板を作製することができる。 After step (c), an annealing step may be performed. The annealing temperature in the annealing step may be 400 to 650°C, or 500 to 600°C. The annealing time at the annealing temperature may be 1.5 to 3.0 hours, or 2.0 to 2.5 hours. After cooling, the bonded body may be removed from the pressure jig. By performing the annealing step, it is possible to reduce distortion of the laminate 80 due to heating, and to produce a circuit board with sufficiently excellent heat cycle characteristics.
　工程（ｄ）では、得られた接合体にレジスト印刷及びエッチングを行い、回路基板１００を得る。回路基板１００は、ろう材層３０の炭素を十分に除去していることから、接合層２０が第１接合層２１、第２接合層２２、及び第３接合層２３を有する。したがって、回路基板１００における窒化ケイ素板１０と銅板５０との接合強度を十分に高くすることができる。 In step (d), resist printing and etching are performed on the resulting bonded body to obtain the circuit board 100. Since the carbon in the brazing material layer 30 has been sufficiently removed from the circuit board 100, the bonding layer 20 has a first bonding layer 21, a second bonding layer 22, and a third bonding layer 23. Therefore, the bonding strength between the silicon nitride plate 10 and the copper plate 50 in the circuit board 100 can be made sufficiently high.
　回路基板１００を用いて、パワーモジュールを製造してもよい。パワーモジュールは、回路基板の銅板上に、ハンダとワイヤボンディング等を用いて電気的に接続された半導体素子を搭載し、回路基板及び半導体素子を筐体の収容空間内に収容したうえで樹脂封止を行って製造することができる。 The circuit board 100 may be used to manufacture a power module. The power module can be manufactured by mounting a semiconductor element electrically connected to the copper plate of the circuit board using solder and wire bonding, etc., and housing the circuit board and the semiconductor element in the housing space of the housing, and then sealing with resin.
　以上、本開示の実施形態を説明したが、本開示は上記実施形態に何ら限定されるものではない。例えば、窒化ケイ素板の一対の主面のそれぞれに接合される金属板及び接合部の構造及び形状は、互いに異なっていてもよい。また、窒化ケイ素板の一方の主面のみに接合層及び銅板が設けられた回路基板であってもよい。 Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments. For example, the structures and shapes of the metal plates and joints joined to each of the pair of main surfaces of the silicon nitride plate may be different from each other. Also, the present disclosure may be a circuit board in which a joining layer and a copper plate are provided on only one main surface of the silicon nitride plate.
　実施例及び比較例を参照して本開示の内容をより詳細に説明するが、本開示は下記の実施例に限定されるものではない。 The contents of this disclosure will be explained in more detail with reference to examples and comparative examples, but this disclosure is not limited to the following examples.
（実施例１）
［回路基板の作製］
　厚さ０．３２ｍｍの窒化ケイ素板、銅板（サイズ：縦×横×厚さ＝１７０ｍｍ×１２０ｍｍ×０．８ｍｍ）及びろう材を準備した。銅板は打ち抜き加工によって得た。 Example 1
[Preparation of circuit board]
A silicon nitride plate having a thickness of 0.32 mm, a copper plate (size: length×width×thickness=170 mm×120 mm×0.8 mm), and a brazing material were prepared. The copper plate was obtained by punching.
　ろう材は、Ａｇ、Ｃｕ、ＴｉＨ２、Ｓｎを含んでいた。ＡｇとＣｕの質量比は９：１であった。ろう材は、ＡｇとＣｕの合計１００質量部に対し、Ｓｎを５質量部、及びＴｉＨ２を３．５質量部含んでいた。 The brazing material contained Ag, Cu, TiH 2 , and Sn. The mass ratio of Ag to Cu was 9: 1. The brazing material contained 5 parts by mass of Sn and 3.5 parts by mass of TiH 2 with respect to 100 parts by mass of Ag and Cu in total.
　窒化ケイ素板の主面に、スクリーン印刷（メッシュ数：１５０）でろう材を塗布して乾燥しろう材層を形成した。ろう材層の塗布面積は、窒化ケイ素板と接合される銅板の主面の面積と同じとした。塗布したろう材層の厚さは０．０３ｍｍとした。 The brazing filler metal was applied to the main surface of the silicon nitride plate by screen printing (mesh number: 150) and dried to form a brazing filler metal layer. The application area of the brazing filler metal layer was the same as the area of the main surface of the copper plate to be joined to the silicon nitride plate. The thickness of the applied brazing filler metal layer was 0.03 mm.
　ろう材層を形成した後、窒化ケイ素板の上に、ろう材層と銅板の主面とが接するようにして銅板を重ね、複合体を作製した。このようにして、窒化ケイ素板、ろう材層、及び銅板の複合体を２０枚作製した。 After forming the brazing material layer, the copper plate was placed on top of the silicon nitride plate so that the brazing material layer was in contact with the main surface of the copper plate, creating a composite. In this way, 20 composites of silicon nitride plate, brazing material layer, and copper plate were created.
　一対の炭素製プレート（厚さ：０．５ｍｍ、密度：１．８ｇ／ｃｍ３）を隣り合う上記複合体の間に１枚ずつ配置して図２に示すような積層体を作製した。図９に示すように積層体の両主面上にスペーサを配置し、加圧治具によって固定した。 A pair of carbon plates (thickness: 0.5 mm, density: 1.8 g/cm 3 ) were placed between adjacent composites to produce a laminate as shown in Fig. 2. As shown in Fig. 9, spacers were placed on both main surfaces of the laminate and fixed in place by a pressing jig.
　加圧治具で固定したまま、上記積層体を真空中（１０－３Ｐａ）で、１００℃／ｍｉｎの昇温速度で４００℃まで昇温させ、４００℃で３．５時間の脱脂を行った。その後、１０－３Ｐａの雰囲気下で４００℃から１００℃／ｍｉｎの昇温速度で７５０℃まで昇温し、７５０℃で３時間の加熱を行った。その後、１００℃／ｍｉｎの降温速度で６００℃まで降温し、６００℃で２時間保持するアニール工程を行った。冷却後、加圧治具から接合体を取り外した。このようにして、窒化ケイ素板と銅板が、接合層を介して接合した接合体を作製した。作製した接合体を用いて回路基板を作製した。 While being fixed by the pressure tool, the laminate was heated to 400°C in a vacuum ( 10-3 Pa) at a heating rate of 100°C/min, and degreasing was performed at 400°C for 3.5 hours. Thereafter, the laminate was heated from 400°C to 750°C at a heating rate of 100°C/min in an atmosphere of 10-3 Pa, and heated at 750°C for 3 hours. Thereafter, the laminate was cooled to 600°C at a cooling rate of 100°C/min, and an annealing step was performed in which the laminate was held at 600°C for 2 hours. After cooling, the bonded body was removed from the pressure tool. In this way, a bonded body was produced in which a silicon nitride plate and a copper plate were bonded via a bonding layer. A circuit board was produced using the bonded body produced.
（比較例１）
　脱脂を３５０℃、３時間で行ったこと以外は、実施例１と同一の手順で回路基板を作製した。 (Comparative Example 1)
A circuit board was produced in the same manner as in Example 1, except that degreasing was carried out at 350° C. for 3 hours.
［回路基板の評価］
＜回路基板の断面の層状態の元素マッピング＞
　得られた回路基板の断面を走査型透過電子顕微鏡（ＳＴＥＭ、株式会社日立ハイテク製、商品名：ＨＤ－２７００）を用いて２５０００倍の倍率で観察した。観察した断面に対して、エネルギー分散型Ｘ線分析装置（ＥＤＸ、Ｏｘｆｏｒｄ製、商品名：ＸＭＡＸＮ　１００ＴＬＥ）を用いて、加速電圧２００ｋＶでＴｉ、Ｓｉ、Ａｇ、及びＣｕの元素マッピングを行った。実施例１のＳＴＥＭ像を図１０（Ａ）に示し、元素マッピングの結果を図１１（Ａ）、図１１（Ｂ）、図１２（Ａ）、図１２（Ｂ）に示した。比較例１のＳＴＥＭ像を図１０（Ｂ）に示し、元素マッピングの結果を図１３（Ａ）、図１３（Ｂ）、図１４（Ａ）、図１４（Ｂ）に示した。図１１（Ａ）及び図１３（Ａ）はチタン元素の分布を示し、図１１（Ｂ）及び図１３（Ｂ）はケイ素元素の分布を示している。また、図１２（Ａ）及び図１４（Ａ）は銀元素の分布を示し、図１２（Ｂ）及び図１４（Ｂ）は銅元素の分布を示している。 [Circuit board evaluation]
<Elemental mapping of the layer state of a cross section of a circuit board>
The cross section of the obtained circuit board was observed at a magnification of 25,000 times using a scanning transmission electron microscope (STEM, Hitachi High-Tech Corporation, product name: HD-2700). The observed cross section was subjected to elemental mapping of Ti, Si, Ag, and Cu at an acceleration voltage of 200 kV using an energy dispersive X-ray analyzer (EDX, Oxford, product name: XMAXN 100TLE). The STEM image of Example 1 is shown in FIG. 10(A), and the results of elemental mapping are shown in FIG. 11(A), FIG. 11(B), FIG. 12(A), and FIG. 12(B). The STEM image of Comparative Example 1 is shown in FIG. 10(B), and the results of elemental mapping are shown in FIG. 13(A), FIG. 13(B), FIG. 14(A), and FIG. 14(B). FIG. 11(A) and FIG. 13(A) show the distribution of titanium element, and FIG. 11(B) and FIG. 13(B) show the distribution of silicon element. Moreover, FIG. 12(A) and FIG. 14(A) show the distribution of silver element, and FIG. 12(B) and FIG. 14(B) show the distribution of copper element.
　ＳＴＥＭ像と元素マッピングの結果、実施例１では第２接合層２２は第１接合層２１と第３接合層２３を遮断するように介在していた（図１１（Ａ）、図１１（Ｂ）、図１２（Ａ）参照）。一方、比較例１では、第２接合層２２Ａが確認されたが、第２接合層２２と異なり、第２接合層２２Ａは不連続な層であり、第１接合層２１と第３接合層２３が直接接していた部分があった（図１３（Ａ）、図１３（Ｂ）、図１４（Ａ）参照）。 The results of the STEM images and element mapping showed that in Example 1, the second bonding layer 22 was interposed between the first bonding layer 21 and the third bonding layer 23 so as to isolate them (see Figures 11(A), 11(B), and 12(A)). On the other hand, in Comparative Example 1, the second bonding layer 22A was confirmed, but unlike the second bonding layer 22, the second bonding layer 22A was a discontinuous layer, and there were portions where the first bonding layer 21 and the third bonding layer 23 were in direct contact (see Figures 13(A), 13(B), and 14(A)).
　比較例１では、図１３（Ａ）、図１４（Ａ）、及び図１４（Ｂ）に示されるように、銅板５０と第３接合層２３の界面にチタン元素が点在していた。一方、実施例１では、図１１（Ａ）、図１２（Ａ）、及び図１２（Ｂ）に示されるように、銅板５０と第３接合層２３との界面にチタン元素は存在していなかった。 In Comparative Example 1, as shown in Figures 13(A), 14(A), and 14(B), titanium elements were scattered at the interface between the copper plate 50 and the third bonding layer 23. On the other hand, in Example 1, as shown in Figures 11(A), 12(A), and 12(B), titanium elements were not present at the interface between the copper plate 50 and the third bonding layer 23.
＜第１接合層２１と第２接合層２２の厚さ測定＞
　上記の各ＳＴＥＭ像において、窒化ケイ素板から銅板へ向かうラインに沿ってＥＤＸ分析による各元素のラインプロファイルを測定した。実施例１におけるＥＤＸ分析の結果を図１５に示した。図１５において、チタン元素及び窒素元素がそれぞれ１０原子％以上検出されるラインの長さを第１接合層２１の厚さとした。また、チタン元素及びケイ素元素が１０原子％以上検出されるラインの長さを第２接合層２２の厚さとした。ラインプロファイルは各ＳＴＥＭ像において任意の５箇所で行い、それぞれ同様の方法で第１接合層２１及び第２接合層２２の厚さを測定した。比較例１では第２接合層２２Ａが形成される部分から任意の５箇所を選択して測定した。測定した５箇所における第１接合層２１の厚さの平均値ｔ１及び第２接合層の厚さの平均値ｔ２を算出し、ｔ１／ｔ２を算出した。測定結果を表１に示した。また、表１には、測定した接合層の厚さの最大値、最小値、及びこれらの差も示した。 <Measurement of Thickness of First Bonding Layer 21 and Second Bonding Layer 22>
In each of the above STEM images, the line profile of each element was measured by EDX analysis along the line from the silicon nitride plate to the copper plate. The result of the EDX analysis in Example 1 is shown in FIG. 15. In FIG. 15, the length of the line where titanium element and nitrogen element are detected at 10 atomic % or more was defined as the thickness of the first bonding layer 21. In addition, the length of the line where titanium element and silicon element are detected at 10 atomic % or more was defined as the thickness of the second bonding layer 22. The line profile was performed at five arbitrary points in each STEM image, and the thicknesses of the first bonding layer 21 and the second bonding layer 22 were measured in the same manner. In Comparative Example 1, five arbitrary points were selected from the portion where the second bonding layer 22A was formed and measured. The average value t1 of the thickness of the first bonding layer 21 and the average value t2 of the thickness of the second bonding layer at the five measured points were calculated, and t1/t2 was calculated. The measurement results are shown in Table 1. Table 1 also shows the maximum value, minimum value, and difference between the measured thicknesses of the bonding layers.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　実施例１は、比較例１よりも第２接合層の厚さが大きいことが示された。したがって、加熱による窒化ケイ素板とろう材層との反応が十分に進行していることが示された。 Example 1 showed a thicker second bonding layer than Comparative Example 1. This indicates that the reaction between the silicon nitride plate and the brazing material layer caused by heating has progressed sufficiently.
＜第１接合層２１と第３接合層２３に含まれるＣ（炭素）の比率＞
　上記のラインプロファイルにおいて、銀元素が４０原子％以上検出される部分を第３接合層２３とした。窒化ケイ素板１０側から測定してチタン元素が１０原子％以上最初に検出された位置から上記ラインに沿って銅板５０側に１００ｎｍ離れた位置の第１接合層２１のＣ（炭素）（Ｃ１）の原子％を測定した。また、上記の最初に検出された位置から上記ラインに沿って銅板５０側に１０００ｎｍ離れた位置の第３接合層２３のＣ（炭素）（Ｃ３）の原子％を測定した。さらにそれぞれの測定値からＣ（炭素）の比（Ｃ１／Ｃ３）を算出した。炭素の原子％の測定は、互いに異なる５箇所のラインを任意に選択してライン毎に行った。結果を表２に示した。また、表２には、測定した炭素の原子％及び算出した（Ｃ１）／（Ｃ３）の平均値、最大値、最小値、及び最大値と最小値との差も示した。 <Ratio of C (carbon) contained in first bonding layer 21 and third bonding layer 23>
In the above line profile, the portion where silver element is detected at 40 atomic % or more was determined as the third bonding layer 23. The atomic % of C (carbon) (C1) of the first bonding layer 21 was measured at a position 100 nm away from the position where titanium element was first detected at 10 atomic % or more along the line toward the copper plate 50 side, measured from the silicon nitride plate 10 side. In addition, the atomic % of C (carbon) (C3) of the third bonding layer 23 was measured at a position 1000 nm away from the position where it was first detected along the line toward the copper plate 50 side, measured from the position where it was first detected. Furthermore, the ratio of C (carbon) (C1/C3) was calculated from each measured value. The measurement of the atomic % of carbon was performed for each line by arbitrarily selecting five different lines. The results are shown in Table 2. Table 2 also shows the measured atomic % of carbon and the average value, maximum value, minimum value, and difference between the maximum value and the minimum value of the calculated (C1)/(C3).
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
　実施例１は、比較例１よりも第３接合層に対する第１接合層中の炭素の検出量が少ないことが確認された。したがって、実施例１では長時間、且つ高温での脱脂により、第１接合層中のバインダ由来の炭素が低減されていることが示された。したがって、炭素とチタンの反応が抑制され、窒化ケイ素由来の窒素とチタンの反応が十分に進行していると考えられる。 It was confirmed that in Example 1, the amount of carbon detected in the first bonding layer relative to the third bonding layer was less than in Comparative Example 1. Therefore, it was shown that in Example 1, the carbon derived from the binder in the first bonding layer was reduced by degreasing for a long time at high temperature. Therefore, it is considered that the reaction between carbon and titanium was suppressed, and the reaction between nitrogen derived from silicon nitride and titanium progressed sufficiently.
＜銅板の接合強度及び接合状態＞
　実施例１及び比較例１において、窒化ケイ素板に接合した銅板を、引張試験機を用いて、鉛直上方に引っ張り、図１６（Ａ）及び図１６（Ｂ）に示すように銅板が窒化ケイ素板から剥離した時点での接合強度を測定した。引張試験機のステージは日本電産シンポ株式会社のＦＧＳ―１００ＶＣを用いた。フォースゲージは日本電産シンポ株式会社のＦＧＰ－２０を用いた。剥離速度は５０ｍｍ／分で実施した。その結果、実施例１では６５０Ｎ／ｃｍ、比較例１では４５０Ｎ／ｃｍであった。さらに、剥離面のＳＥＭ像観察と、破断断面のＥＤＸによる元素分析を行った。元素分析の条件は上述の条件と同じである。 <Bonding strength and bonding state of copper plates>
In Example 1 and Comparative Example 1, the copper plate bonded to the silicon nitride plate was pulled vertically upward using a tensile tester, and the bonding strength was measured at the time when the copper plate peeled off from the silicon nitride plate as shown in Figures 16(A) and 16(B). The stage of the tensile tester used was FGS-100VC manufactured by Nidec-Shimpo Corporation. The force gauge used was FGP-20 manufactured by Nidec-Shimpo Corporation. The peeling speed was 50 mm/min. The results were 650 N/cm in Example 1 and 450 N/cm in Comparative Example 1. Furthermore, SEM images of the peeled surface and elemental analysis by EDX of the fractured cross section were performed. The elemental analysis conditions were the same as those described above.
　実施例１の銅板の剥離時の外観写真を図１６（Ａ）に示し、実施例１の剥離面のＳＥＭ像観察の結果を図１７（Ａ）に示し、実施例１のＥＤＸによる元素分析の結果を図１８（Ａ）にそれぞれ示した。同様に、比較例１の銅板の剥離時の外観写真を図１６（Ｂ）に示し、比較例１の剥離面のＳＥＭ像観察の結果を図１７（Ｂ）に示し、比較例１のＥＤＸによる元素分析の結果を図１８（Ｂ）にそれぞれ示した。図１７（Ａ）及び図１７（Ｂ）の黒色部１０１は、ケイ素元素が含まれている部分を表し、灰色部１０５は銀元素が含まれている部分を表している。一方、図１８（Ａ）及び図１８（Ｂ）の点状模様部１０２の各点はケイ素元素が含まれている部分を表し、黒色部１０６は銀元素が含まれている部分を表している。 　FIG. 16(A) shows a photograph of the appearance of the copper plate of Example 1 when peeled off, FIG. 17(A) shows the results of SEM image observation of the peeled surface of Example 1, and FIG. 18(A) shows the results of elemental analysis by EDX of Example 1. Similarly, FIG. 16(B) shows a photograph of the appearance of the copper plate of Comparative Example 1 when peeled off, FIG. 17(B) shows the results of SEM image observation of the peeled surface of Comparative Example 1, and FIG. 18(B) shows the results of elemental analysis by EDX of Comparative Example 1. The black parts 101 in FIG. 17(A) and FIG. 17(B) represent parts containing silicon elements, and the gray parts 105 represent parts containing silver elements. Meanwhile, each dot of the dotted pattern parts 102 in FIG. 18(A) and FIG. 18(B) represents parts containing silicon elements, and the black parts 106 represent parts containing silver elements.
　図１７（Ａ）、図１７（Ｂ）、図１８（Ａ）、及び図１８（Ｂ）より、実施例１では、剥離面にケイ素元素が多く付着していることから、窒化ケイ素板１０付近での破断が起こっていた。これに対し、比較例１では剥離面に付着するケイ素元素が実施例１よりも少なく、第３接合層２３と銅板５０との間での界面剥離が起こっていることが確認された。実施例１は比較例１よりも剥離面にケイ素元素が多く付着し、上述のとおり接合強度も高くなっていた。これらの結果から、実施例１の回路基板は、第１接合層及び第２接合層が十分に形成されていることで、窒化ケイ素板１０と接合層２０とが比較例１よりも強固に接合していることがわかった。 From Figures 17(A), 17(B), 18(A), and 18(B), in Example 1, a large amount of silicon element was attached to the peeled surface, causing fracture near the silicon nitride plate 10. In contrast, in Comparative Example 1, the amount of silicon element attached to the peeled surface was less than in Example 1, and it was confirmed that interfacial peeling occurred between the third bonding layer 23 and the copper plate 50. In Example 1, more silicon element was attached to the peeled surface than in Comparative Example 1, and the bonding strength was also higher as described above. From these results, it was found that in the circuit board of Example 1, the first bonding layer and second bonding layer were sufficiently formed, and therefore the silicon nitride plate 10 and bonding layer 20 were bonded more firmly than in Comparative Example 1.
　本開示によれば、高い接合強度を有する回路基板が提供される。また、このような回路基板を用いたパワーモジュールが提供される。 The present disclosure provides a circuit board with high bonding strength. It also provides a power module using such a circuit board.
１００…回路基板、１…加圧治具、２…ベースプレート、３…カバープレート、３ｘ…外縁、４…スプリングワッシャ、４ａ…下端部、４ｂ…上端部、４ｘ…離隔領域、５…加圧プレート、５ｂ…支柱貫通孔、６…加圧構造、８…支柱部（支柱）９…係止爪（係止部）、８ａ…係合孔、１０…窒化ケイ素板、２０…接合層、２１…第１接合層、２２…第２接合層、２３…第３接合層、５０…銅板、３０…ろう材層、４０…複合体、７０…スペーサ、８０…積層体、１０１，１０６…黒色部、１０５…灰色部、１０２…点状模様部。

  100...circuit board, 1...pressure jig, 2...base plate, 3...cover plate, 3x...outer edge, 4...spring washer, 4a...lower end, 4b...upper end, 4x...separation area, 5...pressure plate, 5b...post through hole, 6...pressure structure, 8...post portion (post) 9...locking claw (locking portion), 8a...engagement hole, 10...silicon nitride plate, 20...bonding layer, 21...first bonding layer, 22...second bonding layer, 23...third bonding layer, 50...copper plate, 30...brazing material layer, 40...composite, 70...spacer, 80...laminated body, 101, 106...black portion, 105...gray portion, 102...dot pattern portion.

Claims (7)

  1. 　窒化ケイ素板と、銅板と、前記窒化ケイ素板と前記銅板とを接合する接合層と、を備える回路基板であって、
    　前記接合層は、前記窒化ケイ素板側から、窒化チタンを含む第１接合層と、前記第１接合層よりもケイ素元素の含有量が高い第２接合層と、前記第１接合層及び前記第２接合層よりも銀元素の含有量が高い第３接合層と、を有し、
    　前記第２接合層は、前記第１接合層と前記第３接合層とを遮断するように、前記第１接合層と前記第３接合層との間に介在している、回路基板。     A circuit board comprising a silicon nitride plate, a copper plate, and a bonding layer that bonds the silicon nitride plate and the copper plate,
    The bonding layer includes, from the silicon nitride plate side, a first bonding layer containing titanium nitride, a second bonding layer having a higher silicon element content than the first bonding layer, and a third bonding layer having a higher silver element content than the first bonding layer and the second bonding layer,
    A circuit board, wherein the second bonding layer is interposed between the first bonding layer and the third bonding layer so as to isolate the first bonding layer from the third bonding layer.
  2. 　前記銅板と前記接合層との界面にチタン元素が存在しない、請求項１に記載の回路基板。 The circuit board according to claim 1, wherein no titanium element is present at the interface between the copper plate and the bonding layer.
  3. 　前記第１接合層における炭素の含有量をＣ１原子％、前記第３接合層における炭素の含有量をＣ３原子％としたときに、Ｃ１／Ｃ３の平均値が０．５以下である、請求項１に記載の回路基板。 The circuit board according to claim 1, in which the average value of C1/C3 is 0.5 or less when the carbon content in the first bonding layer is C1 atomic % and the carbon content in the third bonding layer is C3 atomic %.
  4. 　前記第１接合層の厚さの最大値と最小値の差が７０ｎｍ以下である、請求項１に記載の回路基板。 The circuit board according to claim 1, wherein the difference between the maximum and minimum thicknesses of the first bonding layer is 70 nm or less.
  5. 　前記第２接合層の厚さが５０ｎｍ以上である、請求項１に記載の回路基板。 The circuit board according to claim 1, wherein the second bonding layer has a thickness of 50 nm or more.
  6. 　前記第１接合層の厚さの平均値をｔ１、前記第２接合層の厚さの平均値をｔ２としたときに、ｔ１／ｔ２が５以下である、請求項１に記載の回路基板。 The circuit board according to claim 1, in which t1/t2 is 5 or less, where t1 is the average thickness of the first bonding layer and t2 is the average thickness of the second bonding layer.
  7. 　請求項１～６のいずれか一項に記載の回路基板と、前記回路基板の前記銅板に電気的に接続された半導体素子と、を備える、パワーモジュール。

          A power module comprising: the circuit board according to any one of claims 1 to 6; and a semiconductor element electrically connected to the copper plate of the circuit board.
PCT/JP2023/045774 2023-02-24 2023-12-20 Circuit board and power module WO2024176598A1 (en)

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Publication number Priority date Publication date Assignee Title
JPH09283671A (en) * 1996-04-12 1997-10-31 Dowa Mining Co Ltd Ceramics-metal composite circuit board
JP2009170930A (en) * 2009-03-12 2009-07-30 Hitachi Metals Ltd Ceramic circuit board and power semiconductor module using the same
WO2013002407A1 (en) * 2011-06-30 2013-01-03 日立金属株式会社 Brazing filler metal, brazing filler metal paste, ceramic circuit substrate, ceramic master circuit substrate, and power semiconductor module
JP2018008869A (en) * 2016-06-30 2018-01-18 三菱マテリアル株式会社 Copper-ceramic bonded body and insulation circuit board
WO2018180965A1 (en) * 2017-03-30 2018-10-04 株式会社 東芝 Ceramic-copper circuit substrate and semiconductor device using same
JP2021143120A (en) * 2020-03-10 2021-09-24 日立金属株式会社 Ceramic circuit board and its manufacturing method

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH09283671A (en) * 1996-04-12 1997-10-31 Dowa Mining Co Ltd Ceramics-metal composite circuit board
JP2009170930A (en) * 2009-03-12 2009-07-30 Hitachi Metals Ltd Ceramic circuit board and power semiconductor module using the same
WO2013002407A1 (en) * 2011-06-30 2013-01-03 日立金属株式会社 Brazing filler metal, brazing filler metal paste, ceramic circuit substrate, ceramic master circuit substrate, and power semiconductor module
JP2018008869A (en) * 2016-06-30 2018-01-18 三菱マテリアル株式会社 Copper-ceramic bonded body and insulation circuit board
WO2018180965A1 (en) * 2017-03-30 2018-10-04 株式会社 東芝 Ceramic-copper circuit substrate and semiconductor device using same
JP2021143120A (en) * 2020-03-10 2021-09-24 日立金属株式会社 Ceramic circuit board and its manufacturing method

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