Joined body, and ceramic circuit board and semiconductor device using the same

Abstract

To control Ag distribution in a bonding layer.SOLUTION: In a joined body in which a metal plate and a ceramic substrate are joined via a joining layer containing Ag, an Ag-rich region having an Ag concentration of 60at% or more is present at an area ratio of 70% or less with respect to an Ag-poor region having an Ag concentration of 50at% or less in a measuring region formed by a length in a thickness direction of the joining layer * a length in an orthogonal direction of 200 μm in a cross section formed by the thickness direction of the joining layer and the orthogonal direction thereof. In addition, the length of the bonding layer in the thickness direction is preferably in a range of 10 μm to 60 μm. The ceramic substrate is preferably a silicon nitride substrate.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The embodiments described below generally relate to a bonded body, and a ceramic circuit board and a semiconductor device using the bonded body. [Background technology]

[0002] Ceramic copper circuit boards, in which a ceramic substrate and a copper plate are bonded together, are used as circuit boards for mounting semiconductor elements and the like. The ceramic copper circuit board described in International Publication No. 2017 / 056360 (Patent Document 1) is an improved version of a bonded body in which a ceramic substrate and a copper plate are bonded together via a bonding layer. In Patent Document 1, a protruding portion is provided in which the bonding layer protrudes from the edge of the copper plate. The TCT characteristics are improved by controlling the size of this protruding portion of the bonding layer.

[0003] In Patent Document 1, an etching process is used to control the size of the protruding portion of the bonding layer. The etching process is a process of removing the copper plate and bonding layer of the bonded body. The bonding layer in Patent Document 1 contains Ag, Cu, and Ti. The bonding layer containing Ag, Cu, and Ti is formed by an active metal bonding method. The bonded body in Patent Document 1 did not necessarily have a good yield when the size of the protruding portion was controlled in the etching process.

[0004] For example, Japanese Patent No. 3302714 (Patent Document 2) shows a conceptual diagram of a bonding layer structure containing Ag, Cu, and Ti. The bonding layer structure of Patent Document 2 contains Ag, Cu, and Ag-Cu eutectic. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2017 / 056360 [Patent Document 2] Patent No. 3302714 [Patent Document 3] International Publication No. 2019 / 054294 Summary of the Invention [Problem to be solved by the invention]

[0006] The bonding layer formed by the active metal bonding method has a structure in which Ag and Cu are mixed. In this mixed structure, the removal effect of the etching solution varies. This is because the etching effect differs between areas with a high Ag content and areas with a low Ag content. As a result, the size of the protruding part of the bonding layer varies.

[0007] The bonded structure according to the embodiment is intended to address such problems, and is characterized by controlling the Ag distribution in the bonding layer. [Means for solving the problem]

[0008] The bonded body of the embodiment is a bonded body in which a metal plate and a ceramic substrate are bonded via a bonding layer containing Ag, and is characterized in that in a measurement area formed by a cross section formed in the thickness direction of the bonding layer and in the direction perpendicular to the thickness direction of the bonding layer, the length in the thickness direction of the bonding layer x the length in the direction perpendicular to the thickness direction is 200 μm, and an Ag-rich area with an Ag concentration of 60 at% or more exists in an area ratio of 70% or less to an Ag-poor area with an Ag concentration of 50 at% or less. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a side view showing an example of a bonded body according to the embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing an example of an Ag-rich region and an Ag-poor region in a bonding layer. [Figure 3] FIG. 2 is a side view showing an example of a ceramic copper circuit substrate according to an embodiment. [Figure 4] FIG. 1 is a side view showing an example of a semiconductor device according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] The bonded body according to the embodiment is a bonded body in which a metal plate and a ceramic substrate are bonded via a bonding layer containing Ag, The test is characterized in that, in a measurement area formed by the thickness direction of the bonding layer and the direction perpendicular to it, which is 200 μm in length in the thickness direction of the bonding layer x the length in the direction perpendicular to it, an Ag-rich region with an Ag concentration of 60 at% or more exists at an area ratio of 70% or less to an Ag-poor region with an Ag concentration of 50 at% or less.

[0011] FIG. 1 shows an example of a bonded structure. In FIG. 1, 1 denotes a bonded structure, 2 denotes a ceramic substrate, 3 denotes a metal plate, and 4 denotes a bonding layer. FIG. 1 shows a bonded structure 1 in which metal plates 3 are disposed on both sides of a ceramic substrate 2 via a bonding layer 4. The ceramic substrate 2 and the copper plate 3 are shown as having the same metal plate size. The bonded structure according to the embodiment is not limited to this configuration and may have a structure in which a metal plate is provided on one side. In FIG. 1, the thickness direction of the ceramic substrate 2, the copper plate 3, and the bonding layer 4 is defined as the Z-axis direction, the vertical direction is defined as the X-axis direction, and the horizontal direction is defined as the Y-axis direction. The length and width of the ceramic substrate 2 (the length in the X-axis direction and the length in the Y-axis direction) may be different, and the length and width of the metal plate 3 may be different.

[0012] Examples of the ceramic substrate 2 include a silicon nitride substrate, an aluminum nitride substrate, an aluminum oxide substrate, and an alu-zir substrate. The length of the ceramic substrate 2 in its thickness direction (i.e., in the Z-axis direction) (hereinafter simply referred to as "thickness") is preferably 0.1 mm or more and 1 mm or less. This is because a thickness of the ceramic substrate 2 less than 0.1 mm may result in a decrease in strength. Also, if the thickness of the ceramic substrate 2 is greater than 1 mm, the ceramic substrate 2 may become a thermal resistor, which may reduce the heat dissipation performance of the bonded body 1.

[0013] Furthermore, when the ceramic substrate 2 is a silicon nitride substrate, the silicon nitride substrate preferably has a three-point bending strength of 600 MPa or more. Furthermore, the thermal conductivity is preferably 80 W / m·K or more. By increasing the strength of the silicon nitride substrate, the substrate thickness can be reduced. Therefore, the silicon nitride substrate preferably has a three-point bending strength of 600 MPa or more, and more preferably 700 MPa or more. The silicon nitride substrate can be reduced in thickness to 0.40 mm or less, and even 0.30 mm or less.

[0014] Furthermore, when the ceramic substrate 2 is an aluminum nitride substrate, the three-point bending strength of the aluminum nitride substrate is approximately 300 to 450 MPa. On the other hand, the thermal conductivity of the aluminum nitride substrate is 160 W / m·K or more. Because the aluminum nitride substrate has low strength, the substrate thickness is preferably 0.60 mm or more.

[0015] Furthermore, when the ceramic substrate 2 is an aluminum oxide substrate, aluminum oxide substrates have a three-point bending strength of approximately 300 to 450 MPa, but are inexpensive. Alternatively, the ceramic substrate 2 may be an aridil substrate. An aridil substrate has a high three-point bending strength of approximately 550 MPa, but a thermal conductivity of approximately 30 to 50 W / m·K. An aridil substrate is a substrate made of a sintered body made of a mixture of aluminum oxide and zirconium oxide.

[0016] The ceramic substrate 2 is preferably either a silicon nitride substrate or an aluminum nitride substrate. The silicon nitride substrate and the aluminum nitride substrate are nitride ceramic substrates. Nitride ceramics react with an active metal brazing material containing Ti to form titanium nitride. Oxide ceramics react with an active metal brazing material containing Ti to form titanium oxide.

[0017] Furthermore, the metal plate 3 is preferably one selected from a copper plate, a copper alloy plate, an aluminum plate, and an aluminum alloy plate. Furthermore, the metal plate 3 is preferably a copper plate or a copper alloy plate. Generally, the thermal conductivity of copper is approximately 400 W / m·K, and the thermal conductivity of aluminum is approximately 240 W / m·K. Because copper plate has high thermal conductivity, it can improve the heat dissipation of the circuit board. Furthermore, the thickness of the metal plate 3 may be 0.3 mm or more, or even 0.6 mm or more. By increasing the thickness of the metal plate 3, the heat dissipation of the assembly can be improved.

[0018] The copper plate is preferably oxygen-free copper, which has a copper purity of 99.96 mass % (wt %) or more as specified in JIS-H-3100.

[0019] Here, a cross section is set in the thickness direction of the bonding layer 4 and in a direction perpendicular to the thickness direction. In a measurement region of the cross section of the bonded body 1, which is formed by the thickness of the bonding layer 4 and a length of 200 μm in the perpendicular direction, an Ag-rich region with an Ag concentration of 60 at% or more exists at an area ratio of 70% or less to an Ag-poor region with an Ag concentration of 50 at% or less. The thickness direction of the bonding layer 4 corresponds to the Z-axis direction. Meanwhile, the direction perpendicular to the thickness direction corresponds to a direction that can be obtained in a plane including the X-axis and Y-axis (i.e., the XY plane), such as the X-axis direction or the Y-axis direction.

[0020] The bonding layer 4 contains Ag (silver), Cu (copper), and Ti (titanium). Ti is an active metal and easily reacts with the ceramic substrate 2. The bonding method using a brazing filler metal containing Ti is called the active metal bonding method. In the active metal bonding method, a Ti reaction layer 5 (shown in Figure 2) is formed on the surface of the ceramic substrate 2. The formation of the Ti reaction layer 5 improves the bonding strength. For example, when the ceramic substrate 2 is a nitride-based ceramic substrate, a layer mainly composed of titanium nitride (TiN) is formed on the surface of the ceramic substrate 2. When the ceramic substrate 2 is an oxide-based ceramic substrate, a layer mainly composed of titanium oxide (TiO2) is formed. The layer mainly composed of titanium nitride or titanium oxide formed on the surface of the ceramic substrate 2 becomes the Ti reaction layer 5.

[0021] The bonding layer 4 is provided between the ceramic substrate 2 and the metal plate 3. The boundary between the ceramic substrate 2 and the bonding layer 4 is the boundary between the ceramic substrate 2 and the Ti reaction layer 5 (shown in Figure 2). If nitrogen is detected by EDX area analysis, the layer containing titanium as its main component is considered to be Ti nitride. Furthermore, if it is difficult to distinguish the boundary between the ceramic substrate 2 and the bonding layer 4, TEM (transmission electron microscope) analysis should be used. Based on the results of the TEM analysis, it is effective to perform EDX point analysis of the bonding layer 4 to detect Ti and N. Oxygen can also be measured using a similar method.

[0022] The boundary between the bonding layer 4 and the metal plate 3 is the farthest point (the point farthest from the ceramic substrate 2) among the areas within the measurement region where the components of the bonding layer 4 are connected and in contact with the metal plate 3. The "connected" components of the bonding layer 4 refer to an area where the components of the bonding layer 4 are 5 at % or more. For example, when the metal plate 3 is a copper plate, the boundary between the bonding layer 4 and the metal plate 3 is the farthest point among the areas where the Ag component is 5 at % or more and is connected.

[0023] The amount of Ag in the bonding layer 4 is measured by EDX (energy dispersive X-ray) analysis. The measurement area formed by the thickness of the bonding layer 4 x a length of 200 μm in the direction perpendicular to the thickness direction is analyzed by EDX, and the area within the unit area defined as the measurement area is analyzed. EDX is sometimes called EDS.

[0024] The EDX measurement is performed using SEM-EDX. As the SEM, a FE-SEM (Field Emission SEM) may also be used. The FE-SEM used is a JEOL JSM-7200F or a device with equivalent performance, and the EDX used is a JEOL EX-74600U4L2Q or a device with equivalent performance.

[0025] First, an area analysis is performed using EDX over a range of 200 μm in length, which is the thickness of the bonding layer 4 and the direction perpendicular to the thickness direction. The unit area for area analysis is set to 200 μm in length, which is the thickness of the bonding layer 4 and the direction perpendicular to the thickness direction, because this is a range suitable for examining the distribution of bonding layer components. In addition, it is preferable to use the mapping function for area analysis using SEM-EDX. Ag color mapping is used to select areas with high Ag concentration and areas with low Ag concentration, and concentration analysis is performed. This makes it possible to measure the area ratio (%) of Ag-rich areas to Ag-poor areas. From the color mapping, a 9 μm 2 The area with high Ag concentration above this level is selected and analyzed for Ag concentration. This can be regarded as the Ag concentration in the Ag-rich region. Also, from the color mapping, 2 The above areas with low Ag concentration are selected and analyzed for Ag concentration, which can be regarded as the Ag concentration of the Ag-poor region.

[0026] The bonded body 1 is characterized in that, when the Ag amount in a measurement region of the bonding layer 4 is analyzed, the area ratio of the Ag-rich region to the Ag-poor region in the measurement region of the bonding layer 4 (hereinafter simply referred to as the "area ratio of the Ag-rich region") is 70% or less. In the bonded body 1 according to the embodiment, the area ratio of the Ag-rich region is 70% or less no matter where in the bonding layer 4 is measured. Therefore, the area ratio (%) of the Ag-rich region to the Ag-poor region may be calculated by the following equation: Area ratio (%) of the Ag-rich region to the Ag-poor region = [Area of ​​the Ag-rich region / (Thickness of the bonding layer 4 × Area of ​​200 μm in the direction perpendicular to the thickness direction)] × 100(%).

[0027] FIG. 2 shows a schematic diagram of an example of a partial cross section of the bonded structure 1. In FIG. 2, 2 denotes a ceramic substrate, 3 denotes a metal plate, 4 denotes a bonding layer, 5 denotes a Ti reaction layer, 6 denotes an Ag-rich region, and 7 denotes an Ag-poor region. The cross section shown in FIG. 2 is formed by the Z-axis direction, which is the thickness direction of the bonding layer 4, and a direction perpendicular to that direction (e.g., the Y-axis direction). Within this cross section, a measurement region with a length of 200 μm in the direction perpendicular to the thickness direction of the bonding layer 4 (e.g., the Y-axis direction) and a triple measurement region, in which three measurement regions are connected consecutively in the orthogonal direction (e.g., the Y-axis direction), are set. When the ceramic substrate 2 is a silicon nitride substrate, the Ti reaction layer 5 is a titanium nitride (TiN) layer.

[0028] The titanium nitride in the Ti reaction layer 5 mainly has an atomic ratio of Ti to N of 1:1. However, the titanium nitride in the Ti reaction layer 5 may have an atomic ratio of Ti to N other than 1:1.

[0029] Furthermore, if the ceramic substrate 2 is an oxide ceramic substrate, the Ti reaction layer 5 will be a titanium oxide (TiO2) layer. The titanium oxide layer will mainly consist of Ti and O in an atomic ratio of 1:2. Note that the titanium oxide in the Ti reaction layer 5 may contain Ti and O in an atomic ratio other than 1:2.

[0030] First, there is an Ag-rich region 6 where the Ag concentration is 60 at% or higher. Hereinafter, the Ag-rich region where the Ag concentration is 60 at% or higher may be simply referred to as the Ag-rich region. The presence of the Ag-rich region 6 improves the bonding strength. Furthermore, by reducing the area ratio of the Ag-rich region to 70% or less in the measurement region, the etching property can be improved. As shown in Patent Document 1, the TCT characteristics of the bonded structure are improved by extending the bonding layer from the edge of the metal plate 3. The amount of extension is controlled according to the thickness of the bonding layer 4. The extension is formed by an etching process. The etching process is a process in which unnecessary portions are dissolved using a chemical solution. The chemical solution used for etching has different dissolving rates for Cu and Ag. Generally, Cu is easily etched, while Ag is difficult to etch. Therefore, the Ag-rich region is a difficult-to-etch region. By reducing the area ratio of the Ag-rich region to 70% or less in the measurement region, the area ratio of the difficult-to-etch region can be reduced. This makes it easier to shape the protruding portion when etching is performed. Therefore, the area ratio of the Ag-rich region in the measurement area is preferably 70% or less, and more preferably 50% or less. The lower limit of the area ratio of the Ag-rich region in the measurement area is preferably 20% or more. If the Ag-rich region is less than 20% per unit area, the bonding strength may decrease.

[0031] Furthermore, it is preferable that the Ag-rich region 6 is on the Ti reaction layer 5, that is, in contact with the Ti reaction layer 5. The etching process is performed from the metal plate 3 side. This is because if there is an Ag-rich region 6 on the metal plate 3 side, the etching efficiency of the bonding layer 4 may decrease. When there are multiple Ag-rich regions 6 in the measurement area, it is preferable that 80% to 100% of the total area of ​​the Ag-rich regions 6 is present on the Ti reaction layer 5.

[0032] In addition, a triple measurement region is set, in which three measurement regions are continuously connected in the direction perpendicular to the thickness direction. When measuring the Ag distribution in the triple measurement region, it is preferable that there is at least one region in the thickness direction of the bonding layer 4 where Ag-poor regions with an Ag concentration of 50 at% or less are connected in the thickness direction. Herein, the measurement region refers to a range of 200 μm in length in the direction perpendicular to the thickness direction of the bonding layer 4 by the thickness of the bonding layer 4. Measuring a triple measurement region means measuring three regions of 200 μm in length in the direction perpendicular to the thickness direction of the bonding layer 4 by the thickness of the bonding layer 4. Hereinafter, the Ag-poor region 7 with an Ag concentration of 50 at% or less will sometimes be simply referred to as Ag-poor region 7.

[0033] The Ag concentration of the Ag-poor region 7 being 50% or less indicates that there are many elements other than Ag. The Ag concentration of the Ag-poor region is preferably 50 at% or less, and more preferably 40 at% or less. The Ag-poor region is a region that is easier to etch than the Ag-rich region. The presence of at least one Ag-poor region in the triple measurement region can improve the etching properties of the bonding layer 4. The presence or absence of an Ag-poor region in the triple measurement region can be measured using EDX color mapping. Furthermore, regardless of which triple measurement region of the bonding layer 4 is measured, it is preferable that there is a region in which the Ag-poor regions are connected in the thickness direction.

[0034] Note that there may be regions where the Ag concentration is greater than 50 at% but less than 60 at%. The region where the Ag concentration is greater than 50 at% but less than 60 at% is called the Ag intermediate region. The Ag intermediate region preferably has an area ratio of 0% or more and 20% or less. If the Ag intermediate region has an area ratio of more than 20%, the effect of increasing the Ag-poor region may be insufficient. For this reason, the Ag intermediate region preferably has an area ratio of 0% or more and 20% or less, and more preferably 0% or more and 10% or less. The most preferable Ag intermediate region is 0%.

[0035] Furthermore, the thickness of bonding layer 4 is preferably within a range of 10 μm to 60 μm. The thickness of bonding layer 4 is the length from the boundary between ceramic substrate 2 and bonding layer 4 to the boundary between bonding layer 4 and metal plate 3. When the thickness of bonding layer 4 is 10 μm to 60 μm, both bonding strength and etchability can be achieved.

[0036] If the thickness of the bonding layer 4 is less than 10 μm, the bonding layer 4 may be too thin, making it difficult to control the area ratio of the Ag-rich region to 70% or less. Furthermore, if the thickness of the bonding layer 4 exceeds 60 μm, the amount of etching increases, which may result in increased costs. Therefore, the thickness of the bonding layer 4 is preferably 10 μm or more and 60 μm or less, and more preferably 15 μm or more and 40 μm or less.

[0037] The boundary between the ceramic substrate 2 and the bonding layer 4 is the boundary between the ceramic substrate 2 and the Ti reaction layer 5. As described above, the boundary between the bonding layer 4 and the metal plate 3 is the farthest point among the regions connected to the bonding layer 4 where the Ag concentration is 5 at% or more.

[0038] The bonding layer 4 preferably contains Sn or In, and the Sn or In concentration in the measurement region is preferably in the range of 1 at% to 6 at%. The measurement region here is formed within a cross section of the bonding layer 4 in the thickness direction and the direction perpendicular to the thickness direction, and refers to a rectangular (square or oblong) region with a length of 200 μm in the thickness direction of the bonding layer 4 and the direction perpendicular to the thickness direction. By including Sn (tin) or In (indium) in the bonding layer 4, the melting point of the brazing material constituting the bonding layer 4 can be lowered. Furthermore, including Sn or In facilitates the formation of Ag-rich and Ag-poor regions. The bonding layer 4 contains Ag, Cu, and Ti. Ag and Cu are elements that readily form a eutectic. The AgCu eutectic is stable at an atomic ratio of approximately Ag:Cu = 7:3. This results in a bonding layer with many Ag-rich regions. The inclusion of Sn or In facilitates the formation of Ag-poor regions by forming compounds with Ag and Cu.

[0039] The Sn or In concentration in the measurement region is preferably 1 at% or more and 6 at% or less. If the Sn or In concentration is less than 1 at%, the effect of including it may be insufficient. If the Sn or In concentration is higher than 6 at%, the amount of Ag-rich region formed may be insufficient.

[0040] Furthermore, regardless of where in the bonding layer 4 the measurement is made, it is preferable that the Sn or In concentration in the measurement region be in the range of 1 at% to 6 at%. This indicates that even if Ag-rich regions and Ag-poor regions are formed, the distribution of Sn or In does not vary greatly. In other words, Sn or In plays a role in controlling the area ratio of the Ag-rich region.

[0041] The bonding layer 4 may also contain carbon (C), which has the effect of suppressing the wetting and spreading of the bonding brazing material.

[0042] The bonded body 1 described above is suitable for use as a ceramic circuit substrate. FIG. 3 shows an example of a ceramic circuit substrate. In FIG. 3, 10 denotes a ceramic circuit substrate, 8 denotes a circuit portion, and 9 denotes a heat sink. Also in FIG. 3, 1 denotes a bonded body, 2 denotes a ceramic substrate, 3 denotes a metal plate, and 4 denotes a bonding layer. FIG. 3 shows a circuit portion 8 formed by applying a pattern to the metal plate 3 on the front side (upper side in FIG. 3) of the bonded body 1. Methods for forming the circuit portion 8 include a method of bonding metal plates using a brazing material and a metallization method using a metal paste. In addition, in FIG. 3, a heat sink is bonded to the metal plate 3 on the back side (lower side in FIG. 3) of the bonded body 1, but the circuit portions 8 may be bonded to both the front and back sides. The number and size of the circuit portions 8 can be changed as needed.

[0043] The ceramic circuit substrate 10 needs to be formed into a pattern shape according to the purpose. Etching is an effective method for forming the pattern shape. The bonded body 1 according to the embodiment is suitable for use in an etching process. It is also suitable for a ceramic circuit substrate 10 having a protruding portion where the bonding layer 4 protrudes from the end of the metal plate 3. The side surface of the metal plate 3 may also be provided with an inclined structure.

[0044] Furthermore, the bonding strength of the metal plate 3 can be made 16 kN / mm or more. The bonding strength is measured by a peel test. The specimen for the peel test is a ceramic substrate to which a rectangular metal plate is bonded. It is preferable that the metal plate 3 is bonded so that one end of the metal plate protrudes from the ceramic substrate 2. The peel strength can be measured by pulling the protruding metal plate 3 vertically.

[0045] When no protruding metal plate 3 is formed, the edge of the metal plate 3 is pulled so as to peel off. When multiple metal plates 3 are joined, the peel test is performed using the metal plate 3 closest to the surface of the ceramic substrate 2.

[0046] Furthermore, the ceramic circuit board 10 according to the embodiment can be applied to a semiconductor device having a semiconductor element mounted thereon. FIG. 4 shows an example of a semiconductor device according to the embodiment. In FIG. 4, 8 denotes a circuit section, 9 denotes a heat sink, 10 denotes a ceramic circuit board, 20 denotes a semiconductor element, and 30 denotes a semiconductor device. The semiconductor element 20 is bonded to the surface of the circuit section 8 of the ceramic circuit board 10 (the upper side in FIG. 4) via a bonding layer. Although FIG. 4 shows an example in which one semiconductor element 20 is mounted, multiple semiconductor elements 20 may also be mounted. Furthermore, in addition to the semiconductor element 20, a lead frame, metal terminals, wire bonding, and the like (not shown) may also be bonded to the circuit section 8.

[0047] Next, a method for manufacturing the bonded body 1 according to the embodiment will be described. The method for manufacturing the bonded body 1 according to the embodiment is not limited as long as it has the above-described configuration, but the following method is used to manufacture the bonded body 1 with a high yield.

[0048] First, prepare the ceramic substrate 2. Examples of the ceramic substrate 2 include a silicon nitride substrate, an aluminum nitride substrate, an aluminum oxide substrate, and an alu- zirconium substrate. The thickness of the ceramic substrate 2 is preferably 0.1 mm or more and 1 mm or less.

[0049] Furthermore, when the ceramic substrate 2 is a silicon nitride substrate, the ceramic substrate 2 preferably has a three-point bending strength of 600 MPa or more. Furthermore, the thermal conductivity is preferably 80 W / m·K or more. By increasing the strength of the silicon nitride substrate, the substrate thickness can be reduced. Therefore, the three-point bending strength of the silicon nitride substrate is preferably 600 MPa or more, and more preferably 700 MPa or more. The silicon nitride substrate can be thinned to a thickness of 0.40 mm or less, and even 0.30 mm or less. Furthermore, the length and width of the ceramic substrate 2 may be a large substrate for producing multiple pieces. Furthermore, the length and width of the ceramic substrate 2 may be the same size as that used for the ceramic circuit substrate 10.

[0050] Next, a metal plate 3 is prepared. The metal plate 3 is preferably one selected from a copper plate, a copper alloy plate, an aluminum plate, and an aluminum alloy plate. The thickness of the metal plate 3 is preferably 0.3 mm or more, and more preferably 0.6 mm or more. There is no particular upper limit to the thickness of the metal plate 3, but it is preferably 2 mm or less. If the metal plate 3 is thicker than 2 mm, it may be difficult to perform the etching process. The length and width of the metal plate 3 may be the same as those of the ceramic substrate 2. Alternatively, a metal plate pre-processed into a pattern shape may be used.

[0051] Next, a brazing filler metal is prepared. The brazing filler metal contains Ag (silver), Cu (copper), and Ti (titanium) as essential components. If necessary, one or more elements selected from Sn (tin), In (indium), and C (carbon) may be added.

[0052] Ag and Cu are components that form the base of the bonding layer 4. Ti is a component that reacts with the ceramic substrate 2 to form the Ti reaction layer 5. Ti may be used as simple Ti or titanium hydride (TiH2). Sn or In has the effect of lowering the melting point of the brazing material. C (carbon) can control the fluidity of the brazing material.

[0053] Furthermore, Ag is preferably in the range of 20% by mass to 60% by mass, and Cu is preferably in the range of 15% by mass to 40% by mass. One or both of Ti and TiH2 is preferably in the range of 1% by mass to 15% by mass. One or both of Sn (tin) and In (indium) is preferably in the range of 1% by mass to 50% by mass. C (carbon) is preferably in the range of 0.01% by mass to 2% by mass.

[0054] The ratio of the brazing filler metal composition is calculated by taking the total of the mixed raw materials as 100% by mass. For example, if the brazing filler metal is composed of three elements, Ag, Cu, and Ti, then Ag + Cu + Ti = 100% by mass. If the brazing filler metal is composed of four elements, Ag, Cu, TiH2, and In, then Ag + Cu + TiH2 + In = 100% by mass. If the brazing filler metal is composed of five elements, Ag, Cu, Ti, Sn, and C, then Ag + Cu + Ti + Sn + C = 100% by mass. The particle size of the raw material powder of the brazing material is preferably as follows.

[0055] The average particle size of Ag powder is D 50 It is preferable that the average particle diameter D of the Cu powder is 3.0 μm or less. 50 The average particle diameter D of the Ti powder or TiH2 powder is preferably 12.0 μm or less, and more preferably 10.0 μm or less. 50 The average particle size D of the Sn powder or the In powder is preferably 6.0 μm or less. 50 The average particle diameter D of the carbon powder is preferably 16.0 μm or less, and more preferably 14.0 μm or less. 50 It is preferable that the thickness is 3.0 μm or less. In addition, Ag particle size D 50is preferably 1.5 μm or more and 3.0 μm or less, and more preferably 1.8 μm or more and 2.8 μm or less. In addition, the particle size D of the Ag powder 10 It is preferable that the particle diameter D of the Ag powder is 1.0 μm or more. 90 The average particle size D of the Ag powder is preferably 3.5 μm or less. 50 is 3.0 μm or less, and the particle size D 10 is 1.0 μm or more, and the particle size D 90 It is preferable that the thickness is 3.5 μm or less. 10 , D 50 , D 90 By controlling the above, Ag powder with uniform particle size can be obtained. Ag powder with uniform particle size has a sharp particle size distribution. This makes it easier for the Ag powder to aggregate and form Ag-rich regions.

[0056] The tap density of Ag powder is 4.5 g / cm 3 It is preferable that the tap density is equal to or greater than this. The tap density is the value obtained by dividing the mass of a powder sample by the tap volume. The tap volume is measured by lifting a container containing a powder sample a certain distance and then dropping it, thereby measuring the voids between particles. The tap density is measured in accordance with JIS-Z-2512 (2012). The ISO corresponding to JIS-Z-2512 is ISO3953 (2011).

[0057] The tap density indicates the fluidity of the powder. The higher the tap density, the better the fluidity of the powder. By improving the fluidity, the Ag powder can be applied while maintaining its aggregated state. This makes it easier to form the Ag-rich region 6. For this reason, the tap density of the Ag powder is 4.5 g / cm. 3 Above 4.8g / cm 3 The upper limit of the tap density of the Ag powder is not particularly limited, but is preferably 6.2 g / cm. 3 Preferably less than 6.2 g / cm 3 If it is larger than this, it may cause an increase in costs.

[0058] Furthermore, the Ag powder preferably contains 0.005 mass% or less of Na (sodium), K (potassium), and Cl (chlorine) in total. Each of these elements is preferably 0.002 mass% or less. Na, K, and Cl are impurities. High levels of these elements may reduce reactivity during the thermal bonding process. With the above-described configuration, the Ag-rich region 6 can be easily formed in the bonding layer 4.

[0059] The powders of the components of the brazing material are mixed to prepare a uniformly dispersed mixed powder. The mixing step of the powder components is preferably carried out for 10 hours or more.

[0060] Next, the mixed powder is mixed with a binder and a solvent to prepare a brazing paste. It is also preferable that the mixing step of the mixed powder with the binder, etc., is carried out for 10 hours or more.

[0061] The brazing paste is applied to at least one of a ceramic substrate or a copper plate. The thickness of the brazing paste layer is preferably 5 μm or more and 60 μm or less. The thickness of the brazing paste layer is the thickness after the applied paste has dried. If the thickness is less than 5 μm, the bonding strength may decrease. If the thickness is more than 60 μm, the bonding layer 4 may become thick and the etching load may increase. For this reason, the thickness of the brazing paste layer is preferably 5 μm or more and 60 μm or less, and more preferably 10 μm or more and 50 μm or less.

[0062] After the step of applying the brazing paste, a step of placing the side without the paste is performed. For example, after applying the brazing paste to the ceramic substrate, a step of placing a copper plate is performed. Alternatively, the brazing paste may be applied to both sides of the ceramic substrate, and copper plates may be placed on both sides. Alternatively, the brazing paste may be applied to the copper plate, and the ceramic substrate may be placed on it.

[0063] Next, a heat bonding step is carried out. The heating temperature is preferably 720°C or more and 920°C or less. The atmosphere in the heat bonding step is 10 -3It is preferable to carry out the process in a vacuum of 100 Pa or less.

[0064] The bonded body 1 can be manufactured through the above steps. Furthermore, the ceramic circuit substrate 10 can be manufactured by etching the bonded body 1. Any etching method can be applied. An example of an etching method is described in International Publication No. 2019 / 054294 (Patent Document 3). The etching process for the bonded body 1 manufactured by the active metal bonding method requires the steps of etching the metal plate 3, the bonding layer 4, and the Ti reaction layer 5. Since the distribution of the Ag-rich region 6 is controlled in the bonded body 1 according to the embodiment, the processing speed of the etching process for the bonding layer 4 can be increased. Furthermore, the etching rate in the etching process for the bonding layer 4 can be stabilized. This can reduce the variation in size of the protruding portion of the bonding layer 4. As described above, the ceramic circuit substrate 10 according to the embodiment can improve the bonding strength of the metal plate 3. In other words, the etching property can be improved while maintaining the bonding strength.

[0065] After the etching process, a scribing process is carried out as necessary to obtain multiple pieces.

[0066] (Example) (Examples 1 to 10, Comparative Example 1) Silicon nitride substrates, aluminum nitride substrates, and Arsil substrates were prepared as ceramic substrates. The silicon nitride substrates were 200mm long x 160mm wide x 0.32mm thick and had a thermal conductivity of 90W / m·K. The aluminum nitride substrates were 200mm long x 160mm wide x 0.635mm thick and had a thermal conductivity of 170W / m·K. The Arsil substrates were 200mm long x 160mm wide x 0.635mm thick and had a thermal conductivity of 20W / m·K.

[0067] Copper plates were prepared as metal plates. The first copper plate was 200 mm long, 160 mm wide, and 0.8 mm thick. The second copper plate was 200 mm long, 160 mm wide, and 0.3 mm thick.

[0068] Next, a brazing filler metal was prepared. The brazing filler metal composition is shown in Table 1. The particle sizes of the components of the brazing filler metal are shown in Tables 2 and 3.

[0069] [Table 1]

[0070] [Table 2]

[0071] [Table 3]

[0072] As shown in Table 3, brazing filler metals 1 to 3 and 5 are Ag powder D 10 , D 50 , D 90 As shown in Table 3, the brazing filler metal 4 has a tap density of 4.5 g / cm3. 3 The tap density was measured in accordance with JIS-Z-2512 (2012).

[0073] Next, the mixing process of the component powders of the brazing material was carried out for 10 hours or more. After that, the mixed powder was mixed with a binder and a solvent to prepare a brazing material paste. The mixing process of the mixed powder with the binder, etc. was also carried out for 10 hours or more.

[0074] Next, the brazing paste was applied to both sides of the ceramic substrate, and the metal plates were placed on top of it. -3 The process was carried out in a vacuum of 100 Pa or less. The combinations of ceramic substrates, metal plates, and brazing materials are as shown in Table 4. By this process, bonded bodies according to the examples and comparative examples were produced.

[0075] [Table 4]

[0076] For the bonded structures obtained in Examples 1 to 10 and Comparative Example 1 in Table 4, the thickness of the bonding layer and the bonding strength of the metal plates were measured. The thickness of the bonding layer was observed at a cross section formed in the thickness direction and in a direction perpendicular to the thickness direction. The bonding strength of the metal plates was also measured by a peel test. The results are shown in Table 5.

[0077] The thickness of the bonding layer was measured using the method described above. For the peel test, samples were prepared using the bonding conditions of each example and comparative example. The samples were prepared by bonding a rectangular copper plate to a ceramic substrate. One end of the copper plate was bonded so that it protruded from the ceramic substrate. The protruding copper plate was pulled vertically to measure the peel strength.

[0078] [Table 5]

[0079] As can be seen from Table 5, the thickness of the bonding layer was within the range of 10 μm or more and 60 μm or less in Examples 1 to 10 and Comparative Example 1. Furthermore, in all of Examples 1 to 9, a titanium nitride layer was formed as the Ti reaction layer. Furthermore, in Example 10, a titanium oxide layer was formed as the Ti reaction layer.

[0080] Next, in Examples 1 to 10 and Comparative Example 1, the Ag-rich regions and Ag-poor regions in a measurement area of ​​200 μm (thickness of the bonding layer × length in the direction perpendicular to the thickness direction) were measured using EDX analysis, and the area ratio of the Ag-rich regions was calculated. In Comparative Example 1, the area ratio of the Ag-rich regions was the largest (85%) in the measurement area (thickness 18 μm × length 200 μm in the direction perpendicular to the thickness direction). Furthermore, in Comparative Example 1, the Ag concentration was the highest (48 at%) among the Ag-poor regions in the measurement area. Furthermore, in Examples 1 to 10 and Comparative Example 1, it was confirmed whether there were one or more regions in which the Ag-poor regions were connected in the thickness direction among the three consecutive measurement areas. The results are shown in Table 6.

[0081] [Table 6]

[0082] As can be seen from Table 6, in the joined bodies according to Examples 1 to 10, the area ratio of the Ag-rich region in the measurement region was 70% or less. Furthermore, in the joined bodies according to Examples 1 to 10, even the smallest value of the area ratio of the Ag-rich region in the measurement region was always 20% or more. Furthermore, in the joined bodies according to Examples 1 to 10, 80% or more of the Ag-rich region was formed on the titanium nitride layer. In the joined bodies according to Examples 1 to 10, the Ag concentration in the Ag-poor region was 50 at% or less at its maximum. In addition, it was confirmed that in the joined bodies according to Examples 1 to 10, there was a region in which the Ag-poor regions were connected in the thickness direction among the three measurement regions.

[0083] In contrast, the area ratio of Ag-rich regions in the measurement region was 85% in Comparative Example 1. Furthermore, in Comparative Example 1, no region where Ag-poor regions were connected in the thickness direction was confirmed among the three consecutive measurement regions.

[0084] Next, the etching properties of each bonded structure were examined. The etching process first involved applying a pattern to the copper plate. Multiple locations were created with a pattern spacing of 2 mm. This process resulted in a bonded structure with the bonding layer exposed.

[0085] Next, a step of etching the bonding layer and titanium nitride layer was performed. To etch the bonding layer and titanium nitride layer, an etching solution containing hydrogen peroxide (H2O2) and ammonium fluoride (NH4F) was prepared. The ratio of the etching time required for the ceramic substrate surface of the bonded body according to the example to that required for the ceramic substrate surface of the bonded body according to Comparative Example 1 to become visible was determined. The results are shown in Table 7.

[0086] [Table 7]

[0087] As can be seen from Table 7, under the same etching conditions, the joined bodies according to Examples 1 to 10 can shorten the etching time by about 20 to 30% compared to Comparative Example 1. In other words, Comparative Example 1, which has many Ag-rich regions, has a slow etching rate.

[0088] In addition, an etching process was performed to form an overhanging portion in which the bonding layer protruded from the edge of the metal plate. The target amount of overhang was set. The amount of overhang after etching was measured at 10 random locations. The minimum and maximum values ​​of the amount of overhang were shown. The results are shown in Table 8.

[0089] [Table 8]

[0090] As can be seen from Table 8, the bonded structures according to Examples 1 to 10 had deviations between the minimum and maximum values ​​(maximum value - minimum value, or minimum value - maximum value) of ±28 μm relative to the target protrusion amount. In contrast, Comparative Example 1 had portions with deviations of 30 μm or more. It was found that the bonded structures according to Examples 1 to 10 were able to maintain their shape when subjected to an etching treatment. This shows that the bonded structure 1 according to the embodiment is suitable for use in etching treatment.

[0091] Although several embodiments of the present invention have been described above, these embodiments are presented by way of example only and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, modifications, etc. can be made without departing from the spirit of the invention. Modifications of these embodiments are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as set forth in the claims. Furthermore, the above-described embodiments can be implemented in combination with each other.

Claims

1. A method for manufacturing a ceramic circuit board, comprising: etching a bonded body in which a metal plate and a ceramic substrate are bonded via a bonding layer containing Ag, to form a protruding portion of the bonding layer, In a measurement region formed by a length in the thickness direction of the bonding layer multiplied by a length of 200 μm in the orthogonal direction of the cross section formed in the thickness direction of the bonding layer, an Ag-rich region having an Ag concentration of 60 at% or more exists in an area ratio of 20% to 70% relative to an Ag-poor region having an Ag concentration of 50 at% or less, the bonding layer contains Sn or In, and the concentration of Sn or In in the measurement region is within a range of 1 at % or more and 6 at % or less; A method for manufacturing a ceramic circuit board, characterized in that there is at least one region in which the Ag-poor regions are connected in the thickness direction of the bonding layer among three consecutive measurement regions in which the measurement regions are connected in the orthogonal direction.

2. 2. The method for manufacturing a ceramic circuit board according to claim 1, wherein the length of the bonding layer in the thickness direction is within a range of 10 μm to 60 μm.

3. 3. The method for manufacturing a ceramic circuit board according to claim 1, wherein the ceramic substrate is a silicon nitride substrate, and the metal plate is a copper plate.

4. 4. The method for manufacturing a ceramic circuit board according to claim 1, wherein the ceramic substrate is a silicon nitride substrate having a thickness of 0.4 mm or less, and the metal plate is a copper plate having a thickness of 0.5 mm or more.

5. 5. The method for manufacturing a ceramic circuit board according to claim 1, wherein the difference between the maximum and minimum protrusion amounts of the protruding portion of the bonding layer is within 28 [mu]m.

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