Ceramic copper joint, ceramic copper circuit substrate, and method for manufacturing ceramic copper joint

Abstract

This invention provides a ceramic-copper bonding agent, a ceramic-copper circuit board, and a method for manufacturing the ceramic-copper bonding agent, all capable of further improving heat dissipation. The ceramic-copper bonding agent according to the embodiments includes a ceramic substrate and a copper layer stack bonded to a first surface of the ceramic substrate. The copper layer stack includes: a first copper plate bonded to the first surface via a first bonding layer; and a second copper plate bonded to the first copper plate via a second bonding layer. The thickness of the second bonding layer is in the range of 5 μm or more and 50 μm or less. The second bonding layer contains one or more selected from Ag, Cu, and Ti. The first copper plate includes a first portion having a thickness T1 of 0.05 mm or more. The second copper plate includes a second portion having a thickness T2 of 0.3 mm or more. The thickness T1 of the first portion and the thickness T2 of the second portion satisfy 1.1 ≤ T2 / T1.

Description

Technical Field

[0001] The embodiments described below generally relate to ceramic-copper bonding agents, ceramic-copper circuit boards, and methods for manufacturing ceramic-copper bonding agents. Background Technology

[0002] Ceramic-copper bonding pads are used in semiconductor devices that mount semiconductor components. In recent years, with the increasing performance of semiconductor components, the requirements for the TCT (thermal cycling test) characteristics of ceramic-copper bonding pads have become more stringent.

[0003] For example, Japanese Patent No. 6789955 (Patent Document 1) discloses a ceramic circuit board in which the hardness and size of the bonding layer protrusion extending from the end of a metal plate are controlled. The ceramic circuit board of Patent Document 1 exhibits good TCT characteristics and improved heat dissipation. On the other hand, the ceramic circuit board of Patent Document 1 controls the size of the exposed bonding layer and the side shape of the metal plate through an etching process. Etching is difficult to apply when the metal plate is thick.

[0004] For example, Japanese Patent No. 6430382 (Patent Document 2) discloses a ceramic circuit board with a thick copper plate bonded without using an etching process. In Patent Document 2, the TCT characteristics are improved by making the bonding layer rise to the side of the copper plate.

[0005] On the other hand, in order to improve the heat dissipation of ceramic circuit boards, attempts have been made to thicken them by stacking metal plates. For example, Japanese Patent No. 7024331 (Patent Document 3) discloses a ceramic circuit board in which titanium material is stacked between an aluminum plate and a copper plate.

[0006] Existing technical documents Patent documents Patent Document 1: Japanese Patent No. 6789955 Patent Document 2: Japanese Patent No. 6430382 Patent Document 3: Japanese Patent No. 7024331 Summary of the Invention

[0007] The problem that the invention aims to solve In Patent Document 3, a ceramic circuit board with stacked metal plates is obtained by using titanium. In the ceramic circuit board of Patent Document 3, an aluminum plate is used as the metal plate bonded to the ceramic substrate. In Patent Document 3, a thick aluminum plate is used. Typically, aluminum has a thermal conductivity of 240 W / m·K and a coefficient of linear expansion of 23.6 × 10⁻⁶. -6 / ℃. On the other hand, copper has a thermal conductivity of 400 W / m·K and a coefficient of linear expansion of 16.2 × 10⁻⁶. -6 / ℃. Aluminum has a lower thermal conductivity and a higher coefficient of linear expansion than copper. In Patent Document 3, the improvement in heat dissipation is limited because the aluminum plate with low thermal conductivity is thickened.

[0008] The embodiments are designed to address such problems, and their purpose is to provide a ceramic-copper bonding agent, a ceramic-copper circuit board, and a method for manufacturing the ceramic-copper bonding agent, which have a laminated structure with metal plates and can further improve heat dissipation.

[0009] Methods for solving problems The ceramic-copper bonding assembly according to the embodiment includes a ceramic substrate and a copper layer stack bonded to a first surface of the ceramic substrate. The copper layer stack includes: a first copper plate bonded to the first surface via a first bonding layer; and a second copper plate bonded to the first copper plate via a second bonding layer. The thickness of the second bonding layer is in the range of 5 μm or more and 50 μm or less. The second bonding layer contains one or more selected from Ag, Cu, and Ti. The first copper plate includes a first portion having a thickness T1 of 0.05 mm or more. The second copper plate includes a second portion having a thickness T2 of 0.3 mm or more. The thickness T1 of the first portion and the thickness T2 of the second portion satisfy 1.1 ≤ T2 / T1. Attached Figure Description

[0010] Figure 1 This is a side view showing an example of a ceramic-copper joint according to an embodiment.

[0011] Figure 2 This is a side view showing another example of the ceramic-copper joint involved in the embodiment.

[0012] Figure 3 This is a side view showing yet another example of the ceramic-copper joint involved in the embodiment.

[0013] Figure 4 This is a side view showing another example of the ceramic-copper joint involved in the embodiment.

[0014] Figure 5 This is an enlarged side view of an example of the ceramic-copper joint involved in the embodiment.

[0015] Figure 6 This is an enlarged side view of another example of the ceramic-copper joint involved in the embodiment.

[0016] Figure 7 This is a side view showing an example of a semiconductor device involved in the embodiment. Detailed Implementation

[0017] The ceramic-copper bonding assembly according to the embodiment includes a ceramic substrate and a copper layer stack bonded to a first surface of the ceramic substrate. The copper layer stack includes: a first copper plate bonded to the first surface via a first bonding layer; and a second copper plate bonded to the first copper plate via a second bonding layer. The thickness of the second bonding layer is in the range of 5 μm or more and 50 μm or less. The second bonding layer contains one or more selected from Ag, Cu, and Ti. The first copper plate includes a first portion having a thickness T1 of 0.05 mm or more. The second copper plate includes a second portion having a thickness T2 of 0.3 mm or more. The thickness T1 of the first portion and the thickness T2 of the second portion satisfy 1.1 ≤ T2 / T1.

[0018] Figure 1 This is a side view showing an example of a ceramic-copper joint according to an embodiment. Figure 1 In the diagram, symbol 1 represents the ceramic-copper bonding body, symbol 2 represents the ceramic substrate, symbol 3 represents the first bonding layer, symbol 4 represents the first copper plate, symbol 5 represents the second bonding layer, symbol 6 represents the second copper plate, and symbol 7 represents the copper layer stack.

[0019] In the ceramic-copper bonding body 1 according to the embodiment, the ceramic substrate 2 has a first surface 2a and a second surface 2b opposite to the first surface 2a. A copper layer stack 7 is bonded to at least one of the first surface 2a and the second surface 2b. The copper layer stack 7 includes a first bonding layer 3, a first copper plate 4, a second bonding layer 5, and a second copper plate 6. The first copper plate 4 is bonded to the ceramic substrate 2 via the first bonding layer 3. The second copper plate 6 is bonded to the first copper plate 4 via the second bonding layer 5. The first copper plate 4 is located between the ceramic substrate 2 and the second copper plate 6.

[0020] exist Figure 1 In the example shown, two first copper plates 4 are joined on the first surface 2a. A second copper plate 6 is joined to one of the first copper plates 4. The second copper plate 6 is not joined to the other first copper plate 4. In addition, another first copper plate 4 is joined on the second surface 2b.

[0021] Figures 2-4 This is a side view illustrating another example of the ceramic-copper joint involved in the embodiment. Figure 2 In the example shown, three copper layer stacks 7-1 to 7-3 are bonded to a ceramic substrate 2. Specifically, two first copper plates 4-1 and 4-2 are bonded to the first surface 2a of the ceramic substrate 2 via two first bonding layers 3-1 and 3-2, respectively. Two second copper plates 6-1 and 6-2 are bonded to the two first copper plates 4-1 and 4-2 via two second bonding layers 5-1 and 5-2, respectively. Furthermore, a first copper plate 4-3 is bonded to the second surface 2b of the ceramic substrate 2 via a first bonding layer 3-3. A second copper plate 6-3 is bonded to the first copper plate 4-3 via a second bonding layer 5-3.

[0022] like Figure 1 and Figure 2 As shown, when multiple first copper plates 4 are bonded to a ceramic substrate 2, the second copper plate 6 can be bonded only on a portion of the multiple first copper plates 4, or the second copper plate 6 can be bonded to all of the first copper plates 4 respectively.

[0023] exist Figure 3 In the example shown, the first copper plate 4-1 is bonded to the first surface 2a via a first bonding layer 3-1. Furthermore, a plurality of second copper plates 6-1 and 6-2 are bonded to the first copper plate 4-1 via second bonding layers 5-1 and 5-2, respectively. Figure 3 As shown, multiple second copper plates 6 can also be joined relative to a first copper plate 4.

[0024] exist Figure 4 In the example shown, the copper laminate 7 is bonded only on the first surface 2a. No copper plate is bonded on the second surface 2b. Figure 4 As shown, the copper stack 7 can also be bonded to only one side of the ceramic substrate 2. The copper stack 7 can be used as a circuit section for mounting semiconductor components, or as a component for heat dissipation.

[0025] Here, for the purpose of illustrating the implementation, the direction perpendicular to the first surface 2a or the second surface 2b is designated as the Z direction. Two directions parallel to and orthogonal to the first surface 2a or the second surface 2b are designated as the X direction and the Y direction. The X direction or the Y direction is an example of the first direction.

[0026] In the ceramic-copper bonding body 1 according to the embodiment, the thickness of the second bonding layer 5 is in the range of 5 μm or more and 50 μm or less. If the thickness of the second bonding layer 5 is in the range of 5 μm or more and 50 μm or less, the bonding strength between the first copper plate 4 and the second copper plate 6 can be improved. If the thickness of the second bonding layer 5 is less than 5 μm, the bonding strength decreases. Even if the thickness of the second bonding layer 5 exceeds 50 μm, not only is the improved bonding strength not achieved, but it also becomes a major cause of increased cost.

[0027] In addition, the second bonding layer 5 contains one or more components selected from Ag (silver), Cu (copper), and Ti (titanium). Preferably, the second bonding layer 5 has Ag, Cu, or Ti as the main component. "Main component" refers to the component that is most abundant in the second bonding layer 5.

[0028] As described below, the second bonding layer 5 is preferably a component formed by heat-treating the bonding material at a temperature of 190°C or higher and 340°C or lower. Bonding using a bonding material with Ag as the main component is called Ag sintering bonding. Bonding using a bonding material with Cu as the main component is called Cu sintering bonding. Bonding using a bonding material with Ti as the main component is called Ti sintering bonding.

[0029] Preferably, the second bonding layer 5 is primarily composed of Ag or Cu. Using a bonding material primarily composed of Ag or Cu facilitates sintering bonding. In addition to Ag or Cu as the main component, the second bonding layer 5 may also contain Ti. Ti is preferably contained in the form of an alloy. For example, the second bonding layer 5 may also use an AgCu alloy, an AgTi alloy, a CuTi alloy, or an AgCuTi alloy. Sintering bonding is a bonding method that utilizes the phenomenon of powders bonding together through heating. The advantage of sintering bonding is that bonding can be performed at temperatures lower than the melting point of the powder. Foil primarily composed of Ag or Cu can also be used instead of powder.

[0030] The second bonding layer 5 may contain components other than Ag, Cu, and Ti, but the content of other components is preferably less than 60% by mass. For example, in addition to Ag, Cu, and Ti, the second bonding layer 5 may also contain one or more components selected from Sn and In. Sn and In have the effect of lowering the melting point of the bonding material. However, if the total content of one or more components selected from Sn and In is 60% by mass or more, the melting point of the bonding material that becomes the second bonding layer 5 may be excessively lowered. Therefore, when bonding semiconductor devices on the copper stack 7, the second bonding layer 5 may melt or soften.

[0031] When the main component of the second bonding layer 5 is Ag or Cu, the melting point of the second bonding layer 5 can be sufficiently reduced even if the second bonding layer 5 does not contain Sn or In. Therefore, when the main component of the second bonding layer 5 is Ag or Cu, the content of Sn or In in the second bonding layer 5 can be less than 1% by mass or 0% by mass.

[0032] Solid-state diffusion bonding can also be used instead of sintering bonding, but the bonding temperature for solid-state diffusion bonding is around 500°C. When the bonding temperature is higher, the surface of the second copper plate 6 may become skewed. Furthermore, if the bonding temperature is higher, the warpage of the ceramic-copper joint 1 may increase.

[0033] Figure 5 and Figure 6 This is an enlarged side view of an example of the ceramic-copper joint involved in the embodiment. Figure 5 and Figure 6 In the figure, reference numeral 4a is the first part, reference numeral T1 is the thickness of the first part 4a, reference numeral 6a is the thickness of the second part 6a, reference numeral T2 is the thickness of the second part 6a, reference numeral L1 is the length of the first copper plate 4, reference numeral L2 is the length of the second copper plate 6, reference numeral 3a is the protrusion, reference numeral L3 is the length of the protrusion, and reference numeral θ is the angle of the lower end of the side of the second copper plate 6 relative to the upper surface of the first copper plate 4.

[0034] In the copper stack 7, the first copper plate 4 includes a first portion 4a having a thickness T1 of 0.05 mm or more. The second copper plate 6 includes a second portion 6a having a thickness T2 of 0.3 mm or more. Furthermore, the thickness T1 of the first portion 4a and the thickness T2 of the second portion 6a satisfy 1.1 ≤ T2 / T1. When the ceramic copper bond 1 includes multiple copper stacks 7, it is sufficient that 1.1 ≤ T2 / T1 is satisfied in at least one copper stack 7.

[0035] The first copper plate 4 and the second copper plate 6 can be as follows Figure 5 It has a flat surface as shown, or it can be like... Figure 6 The surface has an uneven texture, as shown. Alternatively, only one of the first copper plate 4 and the second copper plate 6 may have an uneven surface. Regarding the second copper plate 6, the uneven texture may be formed on its lower surface or its upper surface. Alternatively, the uneven texture may be formed on both the lower and upper surfaces. Figure 6 In the example shown, unevenness is formed on the upper surface of the first copper plate 4 and the lower surface of the second copper plate 6. Additionally, as... Figure 6 As shown, the first copper plate 4 and the second copper plate 6 can be arranged such that the concave portion of the upper surface of the first copper plate 4 and the convex portion of the lower surface of the second copper plate 6 are opposite each other in the Z direction. Alternatively, the first copper plate 4 and the second copper plate 6 can also be arranged such that the convex portion of the upper surface of the first copper plate 4 and the concave portion of the lower surface of the second copper plate 6 are opposite each other in the Z direction.

[0036] When the surface of the first copper plate 4 has irregularities, the thickness of either the portion with the recess or the portion with the protrusion is 0.05 mm or more. When the surface of the second copper plate 6 has irregularities, the thickness of either the portion with the recess or the portion with the protrusion is 0.3 mm or more.

[0037] When the surface of the first copper plate 4 is flat, the thickness of the first copper plate 4 is substantially uniform. The first portion 4a can be any part of the first copper plate 4. Similarly, when the surface of the second copper plate 6 is flat, the thickness of the second copper plate 6 is substantially uniform. The second portion 6a can be any part of the second copper plate 6.

[0038] When the surface of the first copper plate 4 or the second copper plate 6 has irregularities, the thicknesses of the recessed portions and the convex portions are different. In the first copper plate 4, the first portion 4a can be either a recessed portion or a convex portion. In the second copper plate 6, the second portion 6a can be either a recessed portion or a convex portion. The first portion 4a and the second portion 6a, whose thicknesses T1 and T2 satisfy the relationship 1.1 ≤ T2 / T1, can be respectively contained in the first copper plate 4 and the second copper plate 6.

[0039] 1.1 ≤ T2 / T1 means that the second portion 6a is thicker than the first portion 4a. That is, it means that at least a portion of the second copper plate 6 is thicker than at least a portion of the first copper plate 4. By making the second copper plate 6 thicker, good heat dissipation can be achieved even when high-heat-generating semiconductor devices are mounted on the second copper plate 6. In other words, semiconductor devices are preferably mounted on the second copper plate 6 of the copper layer stack 7 that satisfies 1.1 ≤ T2 / T1. That is, the second copper plate 6 is located at the part where heat dissipation is desired. There is no particular upper limit to T2 / T1, but it is preferably 50 or less. When T2 / T1 exceeds 50, the second copper plate 6 is too thick compared to the first copper plate 4, and the bonding strength between the first copper plate 4 and the second copper plate 6 may decrease.

[0040] Preferably, regardless of which part of the first copper plate 4 is the first part 4a and which part of the second copper plate 6 is the second part 6a, 1.1 ≤ T2 / T1 is satisfied. For example, except for parts where the thickness locally decreases, such as the side of the copper plate, the thickness of any part of the second copper plate 6 is more than 1.1 times the maximum thickness of the first copper plate 4.

[0041] The aforementioned copper layer stack structure can also be applied not to copper plates used to mount semiconductor components, but to copper plates used as heat sinks. For example, as Figure 2 or Figure 4 As shown, a copper layer stack 7 serving as a heat sink can also be provided on the second surface 2b. By providing a copper layer stack 7 on the second surface 2b that satisfies 1.1≤T2 / T1, heat dissipation can be improved when the ceramic copper connector 1 is mounted on a mounting plate or heat sink, etc. When the ceramic copper connector 1 is mounted on a mounting plate or heat sink, the ceramic copper connector 1 can be joined via a coating or bonding layer as needed.

[0042] The thickness of the first copper plate 4 is preferably in the range of 0.05 mm or more and 1.2 mm or less. When the surface of the first copper plate 4 has irregularities, it is preferable that the thickness of both the recesses and protrusions is in the range of 0.05 mm or more and 1.2 mm or less. As described later, sometimes a protrusion is provided in the first bonding layer 3. An etching process is effective for providing the protrusion. If the thickness of the first copper plate 4 is 1.2 mm or less, the size of the protrusion can be easily controlled by the etching process. Therefore, the thickness of the first copper plate 4 is preferably in the range of 0.05 mm or more and 1.2 mm or less, and more preferably in the range of 0.1 mm or more and 0.8 mm or less.

[0043] The upper limit of the thickness of the second copper plate 6 is not particularly limited, but it is preferably 5 mm or less. When the surface of the second copper plate 6 has irregularities, it is preferable that the thickness of both the recesses and protrusions is 5 mm or less. If the thickness of the second copper plate 6 exceeds 5 mm, unevenness is easily generated on the surface of the second copper plate 6. When bonding the second copper plate 6 to the first copper plate 4, a decrease in bonding strength and an increase in porosity may occur. Furthermore, when the surface of the second copper plate 6 is warped, the bonding strength, the stability of the position and orientation of the semiconductor device, and the positioning accuracy may decrease when mounting semiconductor components on the second copper plate 6. Additionally, if the thickness of the second copper plate 6 exceeds 5 mm, the processing load on the second copper plate 6 may increase.

[0044] The thicknesses of the second bonding layers 5 were determined using scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX). First, the copper layer stack 7 was cut along the thickness direction (Z-direction). The cutting position was arbitrary, but preferably through the center of the XY plane of the copper layer stack 7. An arbitrary cross-section of the copper layer stack 7 was observed using SEM. The boundaries between the first copper plate 4 and the second bonding layer 5, and between the second bonding layer 5 and the second copper plate 6, could be determined using SEM images or EDX element mapping. The determined boundaries could also be used to measure the thicknesses of the first copper plate 4 and the second copper plate 6.

[0045] For example, if the second bonding layer 5 contains Ag or Ti, the distribution of Ag or Ti is confirmed in the elemental mapping. The region containing Ag or Ti between the first copper plate 4 and the second copper plate 6 is identified as the second bonding layer 5. If the second bonding layer 5 contains Cu, they are identified in the elemental mapping based on the different elements contained in the first copper plate 4, the second bonding layer 5, and the second copper plate 6, respectively. For example, the first copper plate 4 and the second copper plate 6 are copper plates cut from rolled copper. Phosphorus, silicon, or manganese may be added to the rolled copper. By confirming the distribution of these elements, the first copper plate 4, the second bonding layer 5, and the second copper plate 6 can be identified. Alternatively, if the first copper plate 4, the second bonding layer 5, and the second copper plate 6 all have high copper purity, they can also be identified based on SEM images. For example, the cut surfaces of the first copper plate 4 and the second copper plate 6 are less uneven and flatter than the cut surface of the second bonding layer 5. By increasing the contrast of the SEM image and emphasizing the unevenness and roughness, the first copper plate 4, the second bonding layer 5, and the second copper plate 6 can be identified.

[0046] The density of the second bonding layer 5 can be in the range of 80% or more and 100% or less, preferably in the range of 80% or more and 99.5% or less. If the density of the second bonding layer 5 is less than 80%, the heat dissipation from the second copper plate 6 to the first copper plate 4 may be reduced. If the density is 100%, good heat dissipation can be obtained, but the manufacturing cost may increase. In addition, when the density of the second bonding layer 5 is in the range of 80% or more and 99.5% or less, it also has the effect of mitigating the thermal stress generated in the first copper plate 4 and the second copper plate 6. Therefore, the density of the second bonding layer 5 is preferably in the range of 85% or more and 99.5% or less.

[0047] SEM images were used to determine the density of the second bonding layer 5. In the SEM, a cross-section of the copper layer stack 7 along the Z-direction was observed. The SEM magnification was set to 2000x, and reflectance electron imaging was used for the observation. The size of the measurement area was set to the thickness × width of the second bonding layer 5, 100 μm. The observation area of ​​the SEM could include a copper plate, but in this case, a measurement area of ​​the second bonding layer 5, thickness × width 100 μm, was extracted from the observation area. In the SEM image (reflectance electron imaging), pores appeared as black. The density (%) was set as [(measurement area - total area of ​​black portions) / measurement area] × 100. The density was measured in any three mutually separated measurement areas in the cross-section, and their average value was used as the density of the second bonding layer 5.

[0048] The first bonding layer 3 contains a material suitable for bonding the ceramic substrate 2 and the first copper plate 4 with a solder. The solder composition can be Cu (copper), Ti (titanium), Ag (silver), C (carbon), Sn (tin), In (indium), etc. For example, the solder composition can be Ag-Cu-Ti, Ag-Cu-Sn-Ti, Ag-Cu-Ti-C, Ag-Cu-Sn-Ti-C, Ag-Ti, Cu-Ti, Ag-Sn-Ti, Cu-Sn-Ti, Ag-Ti-C, Cu-Ti-C, Ag-Sn-Ti-C, Cu-Sn-Ti-C, etc. In can also be used instead of Sn. Alternatively, both Sn and In can be used.

[0049] Preferably, the first bonding layer 3 contains Cu and Ti as essential components, and also contains one or more selected from Ag, C, Sn, and In. Cu is a component that forms the base material for the solder. Ti is an active metal. The first bonding layer 3 containing Ti is formed by an active metal bonding method. Ag, Sn, and In have the effect of improving the bonding strength and lowering the melting point of the solder. The decrease in the melting point of the solder leads to a decrease in the bonding temperature. C (carbon) has the effect of controlling the flowability of the solder or reacting with other components to control the microstructure of the bonding layer.

[0050] In the active metal bonding method, an active metal solder is applied between the ceramic substrate 2 and the first copper plate 4, and the ceramic substrate 2 and the first copper plate 4 are bonded by heating. The active metal solder preferably contains 15% by mass or more and 85% by mass of Cu (copper), and 1% by mass or more and 15% by mass of Ti (titanium) or TiH2 (titanium hydride). When using both Ti and TiH2, it is preferable that their combined content is in the range of 1% by mass or more and 15% by mass or less.

[0051] When using Ag, its content is preferably in the range of 5% by mass or more and 60% by mass or less. When using at least one of Sn or In, their overall content is preferably in the range of 1% by mass or more and 50% by mass or less. C (carbon) may be added as needed, in the range of 0.1% by mass or more and 2% by mass or less.

[0052] The composition ratio of the active metal solder is calculated by setting the total amount of the mixed raw materials to 100% by mass. For example, when the active metal solder is composed of three elements (Ag, Cu, and Ti), the total amount of Ag, Cu, and Ti is set to 100% by mass. Similarly, when the active metal solder is composed of four elements (Ag, Cu, TiH2, and In), the total amount of Ag, Cu, TiH2, and In is set to 100% by mass. Finally, when the active metal solder is composed of five elements (Ag, Cu, Ti, Sn, and C), the total amount of Ag, Cu, Ti, Sn, and C is set to 100% by mass.

[0053] The active metal solder may contain one or more elements selected from tungsten (W), molybdenum (Mo), and rhenium (Re) in a range of 0.1% to 10% by mass. The flowability of the active metal solder can be controlled by adding tungsten, molybdenum, or rhenium. Additionally, magnesium (Mg) may be added to the active metal solder.

[0054] When multiple copper layer stacks 7 are provided on one side of the ceramic substrate 2, the sum of the maximum thickness of the first copper plate 4 and the maximum thickness of the second copper plate 6 in one copper layer stack 7 may differ from the sum of the maximum thickness of the first copper plate 4 and the maximum thickness of the second copper plate 6 in another copper layer stack 7. Figure 2 In the example shown, copper laminates 7-1 and 7-2 are provided on the first surface 2a. The maximum thickness of the second copper plate 6-1 included in copper laminate 7-1 is greater than the maximum thickness of the second copper plate 6-2 included in copper laminate 7-2. Therefore, the sum of the maximum thickness of the first copper plate 4-1 and the maximum thickness of the second copper plate 6-1 in copper laminate 7-1 is different from the sum of the maximum thickness of the first copper plate 4-2 and the maximum thickness of the second copper plate 6-2 in copper laminate 7-2. For example, the thickness of each second copper plate 6 can be different depending on the need for heat dissipation. It should be noted that if heat dissipation is required for any copper laminate 7, the sum of the maximum thickness of the first copper plate 4 and the maximum thickness of the second copper plate 6 between copper laminate 7-1 and copper laminate 7-2 can also be the same.

[0055] like Figure 2 As shown, a copper layer stack 7-3 can also be provided on the second surface 2b. For example, the surface of the copper plate provided on the second surface 2b can be used as a mounting surface for a heat sink or mounting plate. By providing the copper layer stack 7-3 on the second surface 2b, heat dissipation to the heat sink or mounting plate can be improved.

[0056] The angle θ between the lower end of the side surface of the second copper plate 6 and the upper surface of the first copper plate 4 is preferably in the range of 50° or more and 110° or less. More specifically, the angle θ is the angle between a straight line parallel to the lower end of the side surface of the second copper plate 6 and the first bonding surface of the first copper plate 4. The first bonding surface is the upper surface of the first copper plate 4, which is the surface that is bonded to the second copper plate 6 via the second bonding layer 5. By making the angle θ in the range of 50° or more and 110° or less, the surface of the second copper plate 6 can be used as a mounting surface for semiconductor devices, etc.

[0057] The second copper plate 6 can be formed by etching the first copper plate 4 after a larger copper plate is joined to it. Alternatively, a pre-processed second copper plate 6 can be joined to the first copper plate 4. The smaller the angle θ, the greater the difference between the dimensions of the lower surface and the upper surface of the second copper plate 6. When the angle θ is small, the size of the upper surface of the second copper plate 6, which can be used for mounting semiconductor components, becomes smaller compared to the size of the first copper plate 4 required for joining the second copper plate 6. When the angle θ is less than 50°, it is preferable to etch the second copper plate 6 to make the angle θ 50° or greater. If the angle θ is 50° or greater, the etching process of the second copper plate 6 can be omitted, thus shortening the manufacturing process time. In addition, since both the first copper plate 4 and the second copper plate 6 are made of copper, they have substantially the same coefficient of thermal expansion. When joining components with different coefficients of thermal expansion, it is preferable to tilt the side of one component to mitigate thermal stress. However, since the first copper plate 4 and the second copper plate 6 have the same coefficient of thermal expansion, it is not necessary to increase the angle θ to mitigate thermal stress. Therefore, the angle θ is preferably 50° or more and 110° or less.

[0058] Furthermore, by keeping the angle θ within the range of 50° to 110°, position detection via a camera becomes easier. The camera can be, for example, a CCD camera or a CMOS camera. If the angle θ is within the range of 50° to 110°, the deviation between the contour of the lower surface of the second copper plate 6 and the contour of the upper surface of the second copper plate 6 is small when viewed from above, thus improving the accuracy of position detection of the second copper plate 6. This, in turn, improves the positional accuracy of the mounted semiconductor element. To improve the position detection capability of the camera, it is preferable that the angle θ is close to a right angle. Therefore, the angle θ is preferably within the range of 70° to 110°, and more preferably within the range of 85° to 95°.

[0059] In the angle measurement, a camera or SEM is used to observe the cross-section of the copper layer stack 7 along the Z-direction, with the entire upper surface of the first copper plate 4 and the thickness direction of the second copper plate 6 entering the field of view at magnification. On the observed image, a straight line parallel to the portion slightly below the center in the thickness direction is drawn on the side surface of the second copper plate 6. In the portion slightly below the center in the thickness direction, the straight line that best approximates the side surface is drawn, taking into account variations in the side's inclination. The straight line extends beyond the second bonding layer 5 to the upper surface of the first copper plate 4. The angle θ between this straight line and the upper surface of the first copper plate 4 is measured. Without intersecting the upper surface of the first copper plate 4, the angle between the straight line and a surface parallel to the upper surface of the first copper plate 4 is measured.

[0060] When the length of the first copper plate 4 is set as L1 and the length of the second copper plate 6 is set as L2, the ratio of length L2 to length L1 is preferably in the range of 0.1 or more and 2 or less. That is, it is preferable to satisfy 0.1 ≤ L2 / L1 ≤ 2. The length is measured in a direction parallel to the first surface 2a or the second surface 2b. The length L1 is measured so as to pass through the center of the first copper plate 4 in the Z direction. The length L2 of the second copper plate 6 is measured so as to pass through the center of the second copper plate 6 in the Z direction. The lengths L1 and L2 are measured when the copper layer stack 7 is viewed from the same side direction. Alternatively, the lengths L1 and L2 can also be measured using a section parallel to the Z direction.

[0061] When the ratio L2 / L1 is less than 0.1, the effect of setting the second copper plate 6 may be insufficient. In particular, if the second copper plate 6 is too small, the mounting area for semiconductor components, etc., may be insufficient. If the ratio L2 / L1 exceeds 2, the flatness of the second copper plate 6 may not be maintained. For example, the side of the second copper plate 6 may protrude from the first copper plate 4 and droop. Therefore, the ratio L2 / L1 is preferably in the range of 0.1 or more and 1.5 or less, and more preferably in the range of 0.5 or more and 1 or less.

[0062] The first bonding layer 3 existing between the ceramic substrate 2 and the first copper plate 4 preferably includes a protrusion 3a. The protrusion 3a is a portion of the first bonding layer 3 that extends from the side of the first copper plate 4. The length L3 of the protrusion 3a is preferably in the range of 10 μm or more and 300 μm or less. By having a protrusion 3a in the first bonding layer 3, the TCT characteristics can be improved. When the length L3 is less than 10 μm, the stress relief effect becomes lower, and the TCT characteristics may decrease. When the length L3 exceeds 300 μm, the ceramic-copper bond becomes larger, and the manufacturing cost may increase. Therefore, the length L3 of the protrusion 3a is preferably in the range of 10 μm or more and 300 μm or less.

[0063] The coefficient of thermal expansion of the copper plate is greater than that of the ceramic substrate. Therefore, when the temperature rises and both the ceramic substrate and the copper plate thermally expand, the amount of thermal expansion of the copper plate is greater than that of the ceramic substrate. The thicker the copper plate bonded to the ceramic substrate, the greater the amount of thermal expansion of the copper plate when the temperature rises. The greater the amount of thermal expansion of the copper plate, the greater the stress applied between the ceramic substrate and the copper plate. Due to the stress, cracks may occur in the ceramic substrate or the bonding layer, or the copper plate may peel off from the ceramic substrate. Therefore, the thicker the copper plate bonded to the ceramic substrate, the better the heat dissipation of the ceramic-copper joint, but the lower the TCT characteristics. According to the embodiment, instead of providing a single thick copper plate, a copper layer stack 7 including a first copper plate 4 and a second copper plate 6 is provided. When the copper layer stack 7 is provided, the stress caused by the thermal expansion of the second copper plate 6 is applied to the first copper plate 4 and the second bonding layer 5. The stress caused by the thermal expansion of the first copper plate 4 is mainly applied to the first bonding layer 3. That is, by stacking multiple copper plates through the second bonding layer 5, the stress applied to the ceramic substrate 2 and the first bonding layer 3 can be mitigated. According to the implementation method, compared with the case where a single thick copper plate is provided, the TCT characteristics can be improved while maintaining the heat dissipation of the ceramic copper joint 1.

[0064] Furthermore, according to the embodiment, the copper laminate 7, in which the first copper plate 4 and the second copper plate 6 are stacked, is bonded to the ceramic substrate 2. The thermal conductivity of copper is greater than that of titanium, aluminum, etc. Therefore, according to the embodiment, compared to the case where titanium or aluminum is stacked, the heat dissipation of the ceramic-copper joint 1 can be further improved.

[0065] Along any straight line parallel to the Z direction passing through the copper layer stack 7, the sum of the thickness of the first copper plate 4 and the thickness of the second copper plate 6 is preferably 0.8 mm or more. If the sum of the thicknesses is less than 0.8 mm, it is difficult to improve heat dissipation. The first bonding layer 3 and the second bonding layer 5 are sufficiently thin compared to the first copper plate 4 and the second copper plate 6, so the sum of their thicknesses can be substantially considered as the thickness of the copper layer stack 7. By thickening the copper layer stack 7, heat dissipation can be improved. There is no particular upper limit to the sum of the thicknesses, but it is preferably 6.2 mm or less. The thickness of the first copper plate 4 is preferably 1.2 mm or less. When the upper limit of the thickness of the first copper plate 4 is set to 1.2 mm, the larger the sum of the thicknesses, the thicker the second copper plate 6, and the greater the difference in thickness between the first copper plate 4 and the second copper plate 6. The thicker the second copper plate 6 is compared to the first copper plate 4, the greater the difference in thermal expansion between the first copper plate 4 and the second copper plate 6 when the temperature rises. When the sum of the thicknesses exceeds 6.2 mm, the difference in thermal expansion may cause cracks in the second bonding layer 5 between the first copper plate 4 and the second copper plate 6, or cause peeling of the second copper plate 6. Therefore, the sum of the thicknesses is more preferably in the range of 0.8 mm or more and 6.2 mm or less.

[0066] When multiple copper layer stacks 7 are bonded to one side of the ceramic substrate 2, preferably at least one of the following among at least one group of adjacent copper layer stacks 7—the shortest distance between the first copper plates 4, the shortest distance between the first copper plate 4 and the second copper plate 6, and the shortest distance between the second copper plates 6—is within the range of 0.2 mm or more and 2 mm or less. Here, "shortest distance" refers to the minimum distance between components in a direction perpendicular to the Z direction when the ceramic copper bonding body 1 is viewed from the Z direction.

[0067] By ensuring that at least one of the shortest distances is 2 mm or less, the proportion of the bonding area of ​​the copper layer stack 7 within the surface of the ceramic substrate 2 can be increased. For example, when the bonding area of ​​the copper layer stack 7 is constant, increasing the proportion of the bonding area can reduce the size of the substrate, thus achieving weight reduction. Alternatively, when the size of the substrate is constant, the size of the XY plane of the copper layer stack 7 can be increased, thereby increasing the area available for mounting semiconductor devices. On the other hand, when any of the shortest distances is 0.2 mm or less, the insulation between the copper plates may decrease. Therefore, it is preferable that at least one of the shortest distances is in the range of 0.2 mm or more and 2 mm or less. It should be noted that the shortest distance between the first copper plates 4, the shortest distance between the first copper plate 4 and the second copper plate 6, and the shortest distance between the second copper plates 6 can all be 0.2 mm or more and 2 mm or less, and some of the shortest distances may exceed 2 mm. However, from the viewpoint of insulation, any shortest distance is preferably 0.2 mm or more.

[0068] When multiple copper layer stacks 7 are bonded to one side of the ceramic substrate 2, greater stress is applied to the ceramic substrate 2 during thermal deformation in the areas where the copper layer stacks 7 have a higher density. This stress becomes even greater when any of the shortest distances is 2 mm or less. According to the embodiment, as described above, by stacking multiple copper plates via the second bonding layer 5, the stress applied to the ceramic substrate 2 is mitigated. Therefore, even when thick copper layer stacks 7 are arranged close to each other, the generation of stress-induced cracks in the ceramic substrate 2 and the peeling of the first copper plate 4 can be suppressed. In other words, according to the embodiment, even when thick copper layer stacks 7 are provided, the shortest distance can be designed to be 2 mm or less.

[0069] The ceramic substrate 2 is preferably selected from silicon nitride substrate, aluminum nitride substrate, alumina substrate, and zirconium oxide substrate. The thermal conductivity of the silicon nitride substrate is 50 W / m·K or higher, and more specifically, 80 W / m·K or higher. The three-point bending strength of the silicon nitride substrate is 600 MPa or higher, and more specifically, 700 MPa or higher. The thermal conductivity of the aluminum nitride substrate is 150 W / m·K or higher, and more specifically, 200 W / m·K or higher. The three-point bending strength of the aluminum nitride substrate is approximately 300 to 450 MPa. The three-point bending strength of the alumina substrate is approximately 300 to 450 MPa, but alumina substrates are less expensive than other substrates. Furthermore, the thermal conductivity of the alumina substrate is approximately 20 to 30 W / m·K. The three-point bending strength of the zirconium oxide substrate is as high as approximately 550 MPa, but its thermal conductivity is approximately 30 to 50 W / m·K.

[0070] The thickness of the ceramic substrate 2 is preferably in the range of 0.2 mm or more and 3 mm or less, more preferably in the range of 0.2 mm or more and 1 mm or less. If the thickness of the ceramic substrate 2 is less than 0.2 mm, there is a possibility of insufficient strength. If the thickness of the ceramic substrate 2 exceeds 3 mm, the ceramic substrate 2 becomes a thermal resistor, and the heat dissipation performance may be reduced.

[0071] Because silicon nitride substrates have high strength, their thickness can be designed to be between 0.2 mm and 0.5 mm. From the viewpoint of substrate thinning, silicon nitride substrates are preferred.

[0072] The ceramic-copper bonding agent described in the embodiments can be used in ceramic-copper circuit boards. The ceramic-copper circuit board includes a copper layer stack 7 in the shape of a circuit. For example, a second copper plate 6 in the shape of a circuit is bonded to a first copper plate 4, or the second copper plate 6 bonded to the first copper plate 4 is processed into a circuit shape, thereby obtaining a ceramic-copper circuit board.

[0073] A ceramic copper circuit board can be used as a semiconductor device by mounting semiconductor components. A semiconductor device is obtained by mounting semiconductor components on a second copper plate 6.

[0074] Figure 7 This is a side view illustrating an example of a semiconductor device according to an embodiment. Figure 7 In the diagram, symbol 10 represents a semiconductor device, symbol 11 represents a bonding layer, and symbol 12 represents a semiconductor element. In the semiconductor device 10, the semiconductor element 12 is mounted on the second copper plate 6 via the bonding layer 11.

[0075] When multiple second copper plates 6 are provided, semiconductor components can be mounted on only a portion of the second copper plates 6, or the semiconductor components can be mounted on all the second copper plates 6. Multiple semiconductor components can be mounted on a single second copper plate 6. If necessary, semiconductor components can be mounted on a first copper plate 4 without second copper plates 6. The semiconductor components can be mounted using solder, Ag sintering, Cu sintering, etc. A plating layer can also be applied to the surface of the copper plate on which the semiconductor components are mounted. In addition to semiconductor components, lead frames, wire bonding, etc., can also be bonded to the copper plates.

[0076] Next, the manufacturing method of the ceramic-copper joint 1 according to the embodiment will be described. The manufacturing method of the ceramic-copper joint 1 according to the embodiment is not particularly limited as long as it has the above-described structure. Here, an example of a method for obtaining the ceramic-copper joint 1 with good yield will be described.

[0077] First, prepare ceramic substrate 2. Ceramic substrate 2 is selected from one of silicon nitride substrate, aluminum nitride substrate, alumina substrate, or zirconium oxide substrate. The characteristics and thickness of ceramic substrate 2 are as described above.

[0078] Next, prepare the copper plate to be used as the first copper plate 4. The size of the copper plate used can be larger than that of the first copper plate 4, or a copper plate pre-processed to the size of the first copper plate 4 can be used.

[0079] Next, an active metal solder is prepared. The composition of the active metal solder is as described above. An active metal solder paste is prepared by adding a binder or the like to the active metal solder. The active metal solder is applied to a ceramic substrate 2, and a copper plate for the first copper plate 4 is placed on it. When bonding copper plates to both sides of the ceramic substrate 2, active metal solder paste is applied to both sides, and copper plates are placed on both sides. Through this process, a laminate with a ceramic substrate / active metal solder layer / copper plate stack structure is obtained. When copper plates are placed on both sides of the ceramic substrate 2, a laminate with a copper plate / active metal solder layer / ceramic substrate / active metal solder layer / copper plate stack structure can be obtained.

[0080] It can also be used instead of active metal solder paste, and active metal solder foil can be used. The active metal solder foil has the above composition, and its thickness is preferably in the range of 5 μm or more and 50 μm or less.

[0081] Next, the laminate is heated to perform heat bonding. The heat bonding temperature is preferably in the range of 650°C or higher and 950°C or lower. Heat bonding is preferably performed in a vacuum or a nitrogen atmosphere. In a vacuum (10... -3 For heat bonding (below Pa), a vacuum furnace (intermittent furnace) can be used. For heat bonding in a nitrogen atmosphere, a continuous furnace can be used. By heat bonding, the copper plate is bonded to the ceramic substrate 2 to obtain a bonded body.

[0082] Next, an etching process is performed. When using a large copper plate, the etching process processes the copper plate to the size of the first copper plate 4. Multiple first copper plates 4 can also be formed from a single copper plate. Additionally, the etching process can impart an inclined shape to the sides of the first copper plate 4. A portion of the first bonding layer 3 can also be removed by etching to form a protrusion 3a. Thus, a ceramic copper plate with the first copper plate 4 bonded to the ceramic substrate 2 is obtained.

[0083] Next, a metal layer containing one or more elements selected from the group consisting of Ag, Cu, and Ti is formed on the first copper plate 4. This metal layer is then heat-treated to become the second bonding layer 5. The metal layer is formed using powder containing one or more elements selected from the group consisting of Ag, Cu, and Ti. Examples of powders include Ag powder, Cu powder, Ti powder, AgCu alloy powder, AgTi alloy powder, CuTi alloy powder, and AgCuTi alloy powder. Composite metal powders containing both metal and organic matter can also be used.

[0084] A paste is prepared using powder and then applied to the first copper plate 4. The coating thickness is preferably in the range of 10 μm or more and 100 μm or less. This allows the thickness of the second bonding layer 5 after heat treatment to be in the range of 5 μm or more and 50 μm or less.

[0085] Bonding using metal layers with Ag as the main component is called Ag sintering. Bonding using metal layers with Cu as the main component is called Cu sintering. Bonding using metal layers with Ti as the main component is called Ti sintering. Ag sintering, Cu sintering, or Ti sintering are bonding methods that use metal powder or metal oxide powder.

[0086] The average particle size of the powder used in sintering bonding is preferably 10 μm or less. The smaller the average particle size, the easier it is to sinter bond. Therefore, the average particle size of the powder is preferably 10 μm or less, more preferably 20 nm or less. Sintering bonding using nanoparticles with an average particle size of 20 nm or less is sometimes referred to as nanoparticle bonding. In particular, sintering bonding with Ag or Cu as the main component exhibits good bonding properties.

[0087] Alternatively, foils with Ag or Cu as the main components can be used instead of sintering. When using foils, the thickness is preferably in the range of 5 μm or more and 50 μm or less.

[0088] Next, a second copper plate 6 is disposed on the metal layer. The thickness of the second copper plate 6 is 0.3 mm or more. Preferably, the second copper plate 6 is pre-processed to the required size. For example, a second copper plate 6 of a specified size is formed by etching, wire cutting, or stamping a strip of copper. By performing wire cutting or stamping, the angle θ of the lower end of the side of the second copper plate 6 relative to the upper surface of the first copper plate 4 can be easily controlled within the range of 50° or more and 110° or less.

[0089] Next, the first copper plate 4 and the second copper plate 6 are bonded by heating the laminate containing the second copper plate 6 in a nitrogen atmosphere. The nitrogen concentration in the nitrogen atmosphere is in the range of 95 vol% or more and 100 vol% or less. The heat treatment temperature is set in the range of 190°C or more and 340°C or less. If necessary, heat treatment can also be performed while under pressure. For example, the pressure is preferably in the range of 2 MPa or more and 30 MPa or less. Hot pressing can also be used for pressurization.

[0090] By using a sintering bonding method, the first copper plate 4 and the second copper plate 6 can be bonded at a low temperature of 190°C to 340°C. Bonding at this low temperature suppresses warping of the ceramic-copper joint 1. Furthermore, it suppresses undulations in the second copper plate 6. Warping of the ceramic-copper joint 1 can be suppressed even when adjacent copper layer stacks 7 have different volumes, or when the volume of the copper layer stack 7 bonded to the first surface 2a differs from the volume of the copper layer stack 7 bonded to the second surface 2b. In other words, a ceramic-copper joint 1 with good flatness can be obtained. Additionally, when using foils with Ag or Cu as the main component, the first copper plate 4 and the second copper plate 6 can also be bonded at a low temperature of 190°C to 340°C.

[0091] Alternatively, a copper plate larger than the second copper plate 6 can be joined to the first copper plate 4, and the second copper plate 6 can be processed to the specified size through an etching process. However, to process a thick copper plate through an etching process, it is necessary to increase the number of etching passes or the etching time. In the etching process, a chemical solution is used. If the number of etching passes or the etching time increases, the amount of chemical solution used also increases, as does the amount of waste chemical solution. As described above, by joining the pre-processed second copper plate 6 to the first copper plate 4, an etching process is not required in the processing of the second copper plate 6. Therefore, the generation of waste chemical solution can be suppressed.

[0092] (Examples 1-6, Comparative Examples 1-4) A silicon nitride substrate was prepared as the ceramic substrate. The prepared silicon nitride substrate had a thermal conductivity of 90 W / m·K, a three-point bending strength of 700 MPa, and dimensions of 60 mm (length) × 50 mm (width) × 0.32 mm (thickness).

[0093] A copper plate for a first copper plate is bonded to a silicon nitride substrate using an active metal bonding process. In this process, an active metal solder containing one or more active metals selected from Ag, C, Sn, and In, in addition to Cu and Ti, is used. The copper plate is patterned through an etching process, thereby forming the first copper plate. It should be noted that the copper plate bonded to the side where the semiconductor element is mounted (the first side) is designated as the front copper plate. The copper plate bonded to the opposite side (the second side) is designated as the back copper plate.

[0094] Next, a second copper plate is joined to the first copper plate. The number of first copper plates and the number of second copper plates are shown in Table 1. In Examples 1-3 and 5, multiple first copper plates are joined, and a second copper plate is joined to each of the first copper plates. In Example 4, a second copper plate is joined to each of the three first copper plates, and the thickness of one second copper plate is different from the thickness of the other two second copper plates. In Example 6, a second copper plate is joined to two of the three first copper plates respectively.

[0095] Both the first and second copper plates are quadrilaterals with flat surfaces. The length L1 of the first copper plate was measured in both its longitudinal and transverse directions. Similarly, the length L2 of the second copper plate was measured in both its longitudinal and transverse directions. Furthermore, the thicknesses T1 and T2 of the first and second copper plates were measured respectively. The measurement results are shown in Table 1.

[0096] Furthermore, Table 1 shows the material and thickness of the second bonding layer, as well as its density. In this embodiment, the first copper plate and the second copper plate are bonded using a nanoparticle bonding method (any one of Ag sintering bonding, Cu sintering bonding, or Ti sintering bonding). In the nanoparticle bonding method, a nitrogen atmosphere with a nitrogen concentration of 95 vol% or more and 100 vol% or less is set, and the heating temperature is set in the range of 190°C or more and 340°C or less. The pressure is set in the range of 2 MPa or more and 20 MPa or less.

[0097] In Comparative Example 1, the first copper plate and the second copper plate were bonded using solid-state diffusion bonding with Ti foil. The temperature for Ti solid-state diffusion bonding was set to 500°C. In Comparative Example 2, the first copper plate and the second copper plate were bonded using lead-free solder. The lead-free solder used was a SnAgCu-based solder containing 96.5% by mass Sn, 3% by mass Ag, and 0.5% by mass Cu. The bonding temperature was set to 220°C.

[0098] The density of the second bonding layer was determined using cross-sectional SEM images. The determination method is as described above.

[0099] Next, using the measured thicknesses T1 and T2, it was determined whether 1.1 ≤ T2 / T1 was satisfied. Additionally, using the measured lengths L1 and L2, it was determined whether 0.1 ≤ L2 / L1 ≤ 1.5 was satisfied. The results are shown in Table 2.

[0100] In Table 2, a checkmark is marked when 1.1 ≤ T2 / T1 is satisfied. A hyphen is marked when 1.1 ≤ T2 / T1 is not satisfied. Additionally, a checkmark is marked when the ratio of the length of the second copper plate to the length of the first copper plate is greater than or equal to 0.1 and less than or equal to 1.5. A hyphen is marked when this ratio is less than or equal to 0.1 and less than or equal to 1.5.

[0101] Furthermore, the angle θ between the lower end of the side of the second copper plate and the upper surface of the first copper plate was measured. The length L3 of the protrusion in the first bonding layer was measured. Additionally, the sum of thicknesses T1 and T2 was calculated. Between adjacent copper layer stacks, the shortest distance between the first copper plates, the shortest distance between the first and second copper plates, and the shortest distance between the second copper plates were measured, and it was investigated whether at least one of them was within the range of 0.2 mm or more and 2 mm or less. The measurement results are shown in Table 2. In Table 2, a checkmark is marked if any of the shortest distances is within the range of 0.2 mm or more and 2 mm or less.

[0102] Furthermore, in each embodiment and comparative example, a first copper plate was also bonded to the second side of the silicon nitride substrate. The number of first copper plates and the number of second copper plates on the second side are shown in Table 3. In Embodiments 1 and 3-6, and Comparative Examples 1-4, a second copper plate was bonded to the first copper plate. In Embodiment 2, no second copper plate was bonded to the first copper plate on the second side.

[0103] Regarding the back copper plate, the thickness T1, thickness T2, length L1, and length L2 were measured in the same manner as for the front copper plate. Additionally, the density of the second bonding layer was measured. The material and thickness of the second bonding layer are shown in Table 3.

[0104] For the back copper plate, it was also determined whether 1.1 ≤ T2 / T1 and whether 0.1 ≤ L2 / L1 ≤ 1.5 were satisfied. Additionally, the angle θ and the length L3 of the protruding portion were measured. The sum of the thicknesses T1 and T2 was calculated. These results are shown in Table 4.

[0105] In the ceramic-copper bonding assembly described in the embodiments, a second copper plate is bonded to a first copper plate via a second bonding layer. Furthermore, the second bonding layer contains one or more elements selected from Ag, Cu, and Ti. Additionally, in any embodiment, 1.1 ≤ T2 / T1 is satisfied.

[0106] On the other hand, in Comparative Examples 1 and 4, the first copper plate and the second copper plate were bonded by Ti solid-phase diffusion bonding. Furthermore, in Comparative Example 1, 1.1 ≥ T2 / T1. In Comparative Examples 2 and 3, the first copper plate and the second copper plate were bonded using lead-free solder. Therefore, the thickness of the second bonding layer was 200 μm in Comparative Example 2 and 150 μm in Comparative Example 3. Their thicknesses are greater than those of the second bonding layers in the examples.

[0107] In each embodiment and comparative example, the change in warpage of the ceramic-copper joint and the change in surface undulation of the second copper plate were measured. Specifically, the warpage of the ceramic-copper joint was measured before and after joining the second copper plate. The difference between these warpages was calculated as the change in warpage. Additionally, the surface undulation of the second copper plate was measured before and after joining. The difference between these undulations was calculated as the change in undulation. A three-dimensional shape measuring machine was used for the warpage and undulation measurements. The three-dimensional shape measuring machine can be a One-Shot 3D shape measuring machine manufactured by KEYENCE Corporation or a device with equivalent or superior performance.

[0108] It should be noted that, here, warpage refers to the state in which the substrate bends in one direction when observed as a whole. Undulation refers to the presence of unevenness on the surface of the copper plate. For example, using a One-Shot 3D shape measuring machine manufactured by KEYENCE, a straight line or surface is set as a reference, and the distance from that reference to the furthest point is measured, thereby measuring the warpage of the ceramic-copper bond. The waviness curve of any 5mm copper plate is measured, and the maximum and minimum heights are calculated, thereby measuring the waviness of the second copper plate surface.

[0109] Examples with an increase in warpage of less than 100% are classified as "Best". Examples with an increase in warpage exceeding 100% but less than 200% are classified as "Good". Examples with an increase in warpage exceeding 200% are classified as "Poor". Examples with an increase in fluctuation of less than 100% are classified as "Best". Examples with an increase in fluctuation exceeding 100% but less than 200% are classified as "Good". Examples with an increase in fluctuation exceeding 200% are classified as "Poor".

[0110] In addition, the TCT characteristics of the ceramic-copper bonding assembly were measured in each embodiment and comparative example. In the TCT, one cycle was defined as -40°C for 30 minutes → room temperature for 10 minutes → 150°C for 30 minutes → room temperature for 10 minutes, and 1000 cycles were performed. Any defects in the ceramic-copper bonding assembly after TCT were observed. Defects included cracking in the ceramic substrate or the first bonding layer, and delamination of the copper plate. The results are shown in Table 5.

[0111] In the embodiment, the amount of warpage variation in the ceramic-copper joint and the amount of surface undulation variation in the second copper plate were suppressed. This result shows that by using sintering bonding at a temperature above 190°C and below 340°C for heat bonding, the increase in warpage and undulation can be suppressed. Furthermore, the TCT characteristics in the embodiment are also excellent. Therefore, it is evident that bonding the second copper plate to the area where improved heat dissipation is desired is effective in improving TCT characteristics.

[0112] In contrast, in Comparative Example 1, solid-state diffusion bonding was performed at a bonding temperature as high as 500°C. Therefore, the increase in warpage and the increase in surface undulation of the second copper plate were significant. Due to the increased warpage, the TCT properties also decreased.

[0113] In Comparative Example 2, lead-free solder was used for bonding, and the bonding temperature was as low as 220°C. Therefore, the increase in warpage was small. On the other hand, a positional shift of the second copper plate occurred in the TCT. This is because the temperature on the high-temperature side of the TCT was 200°C, close to the bonding temperature.

[0114] In Comparative Example 3, lead-free solder bonding was performed, but the requirement 1.1 ≤ T2 / T1 was not met. Furthermore, the density of the second bonding layer was low, with T1 + T2 less than 0.8 mm. For these reasons, heat dissipation decreased, and warpage increased. Due to the increased warpage, the TCT characteristics also decreased.

[0115] In Comparative Example 4, the bonding temperature was high due to Ti solid-phase diffusion bonding. Furthermore, since L2 / L1 did not satisfy the condition of 0.1 or more and 1.5 or less, heat dissipation was reduced, and warpage increased. Additionally, the length L3 of the protrusion was large, reaching 310 μm, and the angle θ of the second copper plate was small, thus reducing TCT characteristics.

[0116] The above embodiments of the present invention have been illustrated, but these embodiments are merely examples and are not intended to limit the scope of the invention. These new embodiments can be implemented in various other ways, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments or variations thereof are included within the scope or spirit of the invention, and are included within the scope of the invention as described in the claims and its equivalents. Furthermore, the above-described embodiments can be combined with each other.

[0117] Explanation of reference numerals in the attached figures 1…Ceramic-copper joint 2… Ceramic substrate 3…First bonding layer 3a…protruding part 4…First copper coin 4a…Part 1 5…Second bonding layer 6…Second copper coin 6a…Part Two 10… Semiconductor Devices 11… Bonding layer 12… Semiconductor components T1…Thickness of the first copper plate T2…thickness of the second copper plate L1…Length of the first copper plate L2…Length of the second copper plate L3…Length of the protruding part of the bonding layer

Claims

1. A ceramic-copper joint, comprising: Ceramic substrate; and The copper layer stack bonded to the first side of the ceramic substrate The copper stack includes: A first copper plate, which is bonded to the first surface via a first bonding layer; and The second copper plate is bonded to the first copper plate via a second bonding layer. The thickness of the second bonding layer is in the range of 5 μm or more and 50 μm or less. The second bonding layer contains one or more selected from Ag, Cu, and Ti. The first copper plate includes a first portion having a thickness T1 of 0.05 mm or more. The second copper plate includes a second portion having a thickness T2 of 0.3 mm or more. The thickness T1 of the first part and the thickness T2 of the second part satisfy 1.1 ≤ T2 / T1.

2. The ceramic-copper joint according to claim 1, wherein, The first bonding layer contains Cu, Ti, and Selected from one or more of Ag, C, Sn and In.

3. The ceramic-copper joint according to claim 1 or 2, wherein, The density of the second bonding layer is in the range of 80% or more and 99.5% or less.

4. The ceramic-copper joint according to any one of claims 1 to 3, wherein, Multiple copper layer stacks are bonded to the first surface. The sum of the maximum thickness of the first copper plate and the maximum thickness of the second copper plate in one of the plurality of copper stacks is different from the sum of the maximum thickness of the first copper plate and the maximum thickness of the second copper plate in another of the plurality of copper stacks.

5. The ceramic-copper joint according to any one of claims 1 to 4, wherein, The first copper plate has a first mating surface that engages with the second copper plate. The angle between a straight line parallel to the lower end of the side of the second copper plate and the first joint surface is in the range of 50° or more and 110° or less.

6. The ceramic-copper joint according to any one of claims 1 to 5, wherein, Multiple copper layer stacks are bonded to the first surface. Among at least one group of copper layer stacks that are adjacent to each other in the plurality of copper layer stacks, at least any one of the shortest distance between the first copper plates, the shortest distance between the first copper plate and the second copper plate, and the shortest distance between the second copper plates is in the range of more than 0.2 mm and less than 2 mm.

7. The ceramic-copper joint according to any one of claims 1 to 6, wherein, When the length of the first copper plate in the first direction parallel to the first surface is set as L1, and the length of the second copper plate in the first direction is set as L2, the value is 0.1≤L2 / L1≤1.

5.

8. The ceramic-copper joint according to any one of claims 1 to 7, wherein, The first bonding layer includes a protrusion extending from the side of the first copper plate.

9. The ceramic-copper joint according to any one of claims 1 to 8, wherein, The ceramic substrate is a silicon nitride substrate.

10. The ceramic-copper joint according to any one of claims 1 to 9, wherein, On any straight line perpendicular to the first surface, the combined thickness of the first copper plate and the second copper plate is 0.8 mm or more.

11. A ceramic copper circuit board comprising the ceramic copper bonding body as described in any one of claims 1 to 10, The copper stack has a circuit shape.

12. A method for manufacturing a ceramic-copper joint, comprising the following steps: The process of preparing a ceramic copper plate on a ceramic substrate with a first copper plate attached via a first bonding layer. The process of forming a metal layer containing one or more metals selected from Ag, Cu and Ti on the first copper plate; The process of depositing a second copper plate on the metal layer; and The process of bonding the first copper plate and the second copper plate together by heating in a nitrogen atmosphere of 95 vol% or higher within a range of 190°C or higher and 340°C to form a copper layer stack.

13. The method for manufacturing a ceramic-copper joint according to claim 12, wherein, The process of preparing the ceramic copper plate to be bonded with the first copper plate includes the following steps: removing a portion of the first bonding layer by etching, thereby forming a protrusion extending from the first copper plate in the first bonding layer.

14. The method for manufacturing a ceramic-copper joint according to claim 12 or 13, wherein, The process of joining the first copper plate and the second copper plate is carried out by hot pressing.

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