Ceramic-copper bonded body, ceramic-copper circuit board, and method for producing ceramic-copper bonded body

Abstract

Provided are a ceramic-copper bonded body, a ceramic-copper circuit board, and a method for producing a ceramic-copper bonded body, which enable further improvement in heat dissipation. A ceramic-copper bonded body according to an embodiment comprises: a ceramic substrate; and a copper laminate portion bonded to a first surface of the ceramic substrate. The copper laminate portion includes: a first copper plate that is bonded to the first surface via a first bonding layer; and a second copper plate that is bonded to the first copper plate via a second bonding layer. The thickness of the second bonding layer is in a range of 5 μm to 50 μm inclusive. The second bonding layer contains one or more components selected from the group consisting of Ag, Cu, and Ti. The first copper plate includes a first portion that has a thickness T1 of 0.05 mm or more. The second copper plate includes a second portion that has 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 the formula: 1.1 ≤ T2 / T1.

Description

Ceramic-copper bonded body, ceramic-copper circuit board, and method for manufacturing ceramic-copper bonded body

[0001] The embodiments described below generally relate to a ceramic-copper bonded body, a ceramic-copper circuit board, and a method for manufacturing a ceramic-copper bonded body.

[0002] Ceramic-copper joints are used in semiconductor devices incorporating semiconductor elements. In recent years, with the increasing performance of semiconductor elements, there has been an increasing demand for better TCT (thermal cycle test) characteristics of ceramic-copper joints.

[0003] For example, Japanese Patent No. 6789955 (Patent Document 1) discloses a ceramic circuit board in which the hardness and size of the protruding portion of the bonding layer that protrudes from the edge of the metal plate are controlled. The ceramic circuit board of Patent Document 1 has good TCT characteristics and improved heat dissipation. On the other hand, the ceramic circuit board of Patent Document 1 controls the size of the protruding portion of the bonding layer and the side shape of the metal plate through an etching process. The etching process 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 to which a thick copper plate is bonded without using an etching process, and in this patent document, the TCT characteristics are improved by causing a bonding layer to creep up onto the side surface 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 increase their thickness by laminating metal plates. For example, Japanese Patent No. 7024331 (Patent Document 3) discloses a ceramic circuit board in which a titanium material is laminated between an aluminum plate and a copper plate.

[0006] Patent No. 6789955 Patent No. 6430382 Patent No. 7024331

[0007] In Patent Document 3, a ceramic circuit board is obtained by laminating metal plates using a titanium material. 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. Generally, the thermal conductivity of aluminum is 240 W / m·K and the linear expansion coefficient is 23.6×10 －６ On the other hand, the thermal conductivity of copper is 400 W / m K and the linear expansion coefficient is 16.2 × 10 －６ / °C. The thermal conductivity of aluminum is lower than that of copper, and the linear expansion coefficient is higher than that of copper. In Patent Document 3, the aluminum plate, which has low thermal conductivity, is thickened, so there is a limit to the improvement in heat dissipation.

[0008] The embodiments address these problems and provide a ceramic-copper bonded body, a ceramic-copper circuit board, and a method for manufacturing a ceramic-copper bonded body, which have a laminated structure of metal plates and enable further improvement in heat dissipation.

[0009] A ceramic copper joined body according to an embodiment includes a ceramic substrate and a copper laminate portion bonded to a first surface of the ceramic substrate. The copper laminate portion 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 second bonding layer has a thickness of 5 μm to 50 μm. The second bonding layer contains one or more elements selected from the group consisting of 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 the relationship 1.1≦T2 / T1.

[0010] 1 is a side view showing an example of a ceramic-copper joined body according to an embodiment; 2 is a side view showing another example of a ceramic-copper joined body according to an embodiment; 3 is a side view showing another example of a ceramic-copper joined body according to an embodiment; 4 is a side view showing another example of a ceramic-copper joined body according to an embodiment; 5 is an enlarged side view of an example of a ceramic-copper joined body according to an embodiment; 6 is an enlarged side view of another example of a ceramic-copper joined body according to an embodiment; 7 is a side view showing an example of a semiconductor device according to an embodiment;

[0011] A ceramic copper joined body according to an embodiment includes a ceramic substrate and a copper laminate portion bonded to a first surface of the ceramic substrate. The copper laminate portion 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 second bonding layer has a thickness of 5 μm to 50 μm. The second bonding layer contains one or more elements selected from the group consisting of 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 the relationship 1.1≦T2 / T1.

[0012] 1 is a side view showing an example of a ceramic-copper joined body according to an embodiment, in which reference numeral 1 denotes a ceramic-copper joined body, reference numeral 2 denotes a ceramic substrate, reference numeral 3 denotes a first bonding layer, reference numeral 4 denotes a first copper plate, reference numeral 5 denotes a second bonding layer, reference numeral 6 denotes a second copper plate, and reference numeral 7 denotes a copper laminate portion.

[0013] In the ceramic-copper bonded 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. The copper lamination portion 7 is bonded to at least one of the first surface 2a and the second surface 2b. The copper lamination portion 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.

[0014] 1, two first copper plates 4 are bonded to the first surface 2a. A second copper plate 6 is bonded to one of the first copper plates 4. The second copper plate 6 is not bonded to the other first copper plate 4. Another first copper plate 4 is bonded to the second surface 2b.

[0015] 2 to 4 are side views showing another example of a ceramic copper joined body according to an embodiment. In the example shown in FIG. 2, three copper laminations 7-1 to 7-3 are joined to one ceramic substrate 2. Specifically, two first copper plates 4-1 and 4-2 are joined 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 joined to the two first copper plates 4-1 and 4-2 via two second bonding layers 5-1 and 5-2, respectively. Furthermore, the first copper plate 4-3 is joined to the second surface 2b of the ceramic substrate 2 via the first bonding layer 3-3. The second copper plate 6-3 is joined to the first copper plate 4-3 via the second bonding layer 5-3.

[0016] As shown in Figures 1 and 2, when multiple first copper plates 4 are joined to a ceramic substrate 2, the second copper plates 6 may be joined to only some of the multiple first copper plates 4, or the second copper plates 6 may be joined to all of the first copper plates 4.

[0017] In the example shown in Fig. 3, a first copper plate 4-1 is bonded to the first surface 2a via a first bonding layer 3-1. 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. As shown in Fig. 3, a plurality of second copper plates 6 may be bonded to one first copper plate 4.

[0018] In the example shown in Fig. 4, the copper laminate portion 7 is bonded only to the first surface 2a. No copper plate is bonded to the second surface 2b. As shown in Fig. 4, the copper laminate portion 7 may be bonded only to one surface of the ceramic substrate 2. The copper laminate portion 7 may be used as a circuit portion on which a semiconductor element is mounted, or as a member for heat dissipation.

[0019] For the purpose of explaining the embodiment, the direction perpendicular to the first surface 2 a or the second surface 2 b is referred to as the Z direction. Two directions parallel to the first surface 2 a or the second surface 2 b and perpendicular to each other are referred to as the X direction and the Y direction. The X direction or the Y direction is an example of the first direction.

[0020] In the ceramic copper bonded body 1 according to the embodiment, the thickness of the second bonding layer 5 is in the range of 5 μm to 50 μm. When the thickness of the second bonding layer 5 is in the range of 5 μm to 50 μm, the bonding strength between the first copper plate 4 and the second copper plate 6 can be increased. When the thickness of the second bonding layer 5 is less than 5 μm, the bonding strength decreases. When the thickness of the second bonding layer 5 exceeds 50 μm, not only is the effect of further improving the bonding strength not obtained, but it also causes an increase in costs.

[0021] Second bonding layer 5 also contains one or more elements selected from the group consisting of Ag (silver), Cu (copper), and Ti (titanium). Preferably, second bonding layer 5 contains one of Ag, Cu, and Ti as a main component. The "main component" refers to the component contained in the largest amount in second bonding layer 5.

[0022] As will be described later, the second bonding layer 5 is preferably a member produced by heat treating a bonding material at 190°C or higher and 340°C or lower. Bonding using a bonding material containing Ag as the main component is called Ag sinter bonding. Bonding using a bonding material containing Cu as the main component is called Cu sinter bonding. Bonding using a bonding material containing Ti as the main component is called Ti sinter bonding.

[0023] Preferably, the second bonding layer 5 is primarily composed of Ag or Cu. Using a bonding material primarily composed of Ag or Cu facilitates sinter bonding. The second bonding layer 5 may contain Ti in addition to Ag or Cu as its primary component. Ti is preferably contained as an alloy. For example, the second bonding layer 5 may be made of an AgCu alloy, an AgTi alloy, a CuTi alloy, or an AgCuTi alloy. Sinter bonding is a bonding method that utilizes the phenomenon in which powders bond together due to heating. The advantage of sinter bonding is that bonding can be achieved at a temperature lower than the melting point of the powder. Instead of powder, a foil primarily composed of Ag or Cu may be used.

[0024] The second bonding layer 5 may contain components other than Ag, Cu, and Ti, but the content of these other components is preferably less than 60% by mass. For example, the second bonding layer 5 may contain one or more elements selected from Sn and In in addition to Ag, Cu, and Ti. Sn and In have the effect of lowering the melting point of the bonding material. However, if the total content of one or more elements 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 a semiconductor element is bonded to the copper stack portion 7, the second bonding layer 5 may melt or soften.

[0025] When second bonding layer 5 is mainly composed of Ag or Cu, the melting point of second bonding layer 5 can be sufficiently lowered even if second bonding layer 5 does not contain Sn or In. Therefore, when second bonding layer 5 is mainly composed of Ag or Cu, the content of Sn or In in second bonding layer 5 may be 1 mass % or less, or may be 0 mass %.

[0026] Solid-phase diffusion bonding may be used instead of sinter bonding, but the bonding temperature for solid-phase diffusion bonding is about 500° C. If the bonding temperature is too high, the surface of the second copper plate 6 may be distorted. Also, if the bonding temperature is too high, the ceramic-copper bonded body 1 may be significantly warped.

[0027] 5 and 6 are enlarged side views of an example of a ceramic-copper bonded body according to an embodiment. In Fig. 5 and Fig. 6, reference numeral 4a denotes the first portion, reference numeral T1 denotes the thickness of the first portion 4a, reference numeral 6a denotes the second portion 6a, reference numeral T2 denotes the thickness of the second portion 6a, reference numeral L1 denotes the length of the first copper plate 4, reference numeral L2 denotes the length of the second copper plate 6, reference numeral 3a denotes the protruding portion, reference numeral L3 denotes the length of the protruding portion, and reference numeral θ denotes the angle of the lower end of the side surface of the second copper plate 6 relative to the upper surface of the first copper plate 4.

[0028] In the copper laminated portion 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. The thickness T1 of the first portion 4a and the thickness T2 of the second portion 6a satisfy the relationship 1.1≦T2 / T1. When the ceramic-copper bonded body 1 includes multiple copper laminated portions 7, it is sufficient that at least one copper laminated portion 7 satisfies the relationship 1.1≦T2 / T1.

[0029] The first copper plate 4 and the second copper plate 6 may have flat surfaces as shown in FIG. 5 , or may have textured surfaces as shown in FIG. 6 . Only one of the first copper plate 4 and the second copper plate 6 may have a textured surface. The second copper plate 6 may have textured surfaces on either the lower surface or the upper surface. Textured surfaces may also be formed on both the lower and upper surfaces. In the example shown in FIG. 6 , textured surfaces are formed on the upper surface of the first copper plate 4 and the lower surface of the second copper plate 6. Alternatively, as shown in FIG. 6 , the first copper plate 4 and the second copper plate 6 may be arranged so that the recessed portions on the upper surface of the first copper plate 4 and the recessed portions on the lower surface of the second copper plate 6 face each other in the Z direction. Alternatively, the first copper plate 4 and the second copper plate 6 may be arranged so that the protruding portions on the upper surface of the first copper plate 4 and the recessed portions on the lower surface of the second copper plate 6 face each other in the Z direction.

[0030] When the first copper plate 4 has an uneven surface, the thickness is 0.05 mm or more in both the recessed and protruding portions. When the second copper plate 6 has an uneven surface, the thickness is 0.3 mm or more in both the recessed and protruding portions.

[0031] 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 may be any portion 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 may be any portion of the second copper plate 6.

[0032] When the surface of the first copper plate 4 or the second copper plate 6 is uneven, the thickness of the portions where the recesses are formed differs from the thickness of the portions where the protrusions are formed. The first portion 4a may be the portion of the first copper plate 4 where the recesses are formed, or the portion of the second copper plate 6 where the protrusions are formed. The second portion 6a may be the portion of the second copper plate 6 where the recesses are formed, or the portion of the second copper plate 6 where the protrusions are formed. It is sufficient that the first copper plate 4 and the second copper plate 6 each include a first portion 4a and a second portion 6a such that the thickness T1 of the first portion 4a and the thickness T2 of the second portion 6a satisfy the relationship 1.1≦T2 / T1.

[0033] 1.1≦T2 / T1 means that the second portion 6a is thicker than the first portion 4a. That is, at least a portion of the second copper plate 6 is thicker than at least a portion of the first copper plate 4. By increasing the thickness of the second copper plate 6, good heat dissipation can be achieved even when a semiconductor element that generates a large amount of heat is mounted on the second copper plate 6. In other words, it is preferable that the semiconductor element be mounted on the second copper plate 6 of the copper laminate portion 7 that satisfies 1.1≦T2 / T1. That is, the second copper plate 6 is provided in a location where improved heat dissipation is desired. While there is no particular upper limit for T2 / T1, it is preferably 50 or less. If T2 / T1 exceeds 50, the second copper plate 6 will be excessively thick compared to the first copper plate 4, which may reduce the bonding strength between the first copper plate 4 and the second copper plate 6.

[0034] Preferably, 1.1≦T2 / T1 is satisfied 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. For example, the thickness of every part of the second copper plate 6 is 1.1 times or more the maximum thickness of the first copper plate 4, except for parts where the thickness is locally reduced, such as the side surfaces of the copper plate.

[0035] The above-described copper laminate structure may be applied to a copper plate used as a heat sink, rather than a copper plate on which a semiconductor element is mounted. For example, as shown in FIG. 2 or FIG. 4, a copper laminate 7 serving as a heat sink may be provided on the second surface 2b. By providing the copper laminate 7 satisfying 1.1≦T2 / T1 on the second surface 2b, heat dissipation can be improved when the ceramic-copper joined body 1 is mounted on a mounting board, a heat sink, or the like. When the ceramic-copper joined body 1 is mounted on a mounting board, a heat sink, or the like, the ceramic-copper joined body 1 may be joined via a plating film or a bonding layer, as necessary.

[0036] The thickness of the first copper plate 4 is preferably in the range of 0.05 mm to 1.2 mm. When concaves and convexes are provided on the surface of the first copper plate 4, the thickness of both the concaves and convexities is preferably in the range of 0.05 mm to 1.2 mm. As will be described later, a protruding portion may be provided in the first bonding layer 3. An etching process is effective for providing the protruding portion. When the thickness of the first copper plate 4 is 1.2 mm or less, the size of the protruding portion can be easily controlled by the etching process. For this reason, the thickness of the first copper plate 4 is preferably in the range of 0.05 mm to 1.2 mm, and more preferably in the range of 0.1 mm to 0.8 mm.

[0037] The upper limit of the thickness of the second copper plate 6 is not particularly limited, but is preferably 5 mm or less. When the surface of the second copper plate 6 is provided with irregularities, it is preferable that the thickness of both the concave and convex portions be 5 mm or less. If the thickness of the second copper plate 6 exceeds 5 mm, undulations are likely to occur on the surface of the second copper plate 6. When the second copper plate 6 is bonded to the first copper plate 4, a decrease in bonding strength and an increase in void rate may occur. Furthermore, if the surface of the second copper plate 6 is distorted, when mounting a semiconductor element on the second copper plate 6, the bonding strength, stability of the position and orientation of the semiconductor element, positioning accuracy, etc. may decrease. Furthermore, if the thickness of the second copper plate 6 exceeds 5 mm, the load of processing the second copper plate 6 may increase.

[0038] The thickness of each second bonding layer 5 is measured using scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX). First, the copper laminate 7 is cut along the thickness direction (Z direction). The cutting position is arbitrary, but it is preferable to cut through the center of the copper laminate 7 in the XY plane. An arbitrary cross section of the copper laminate 7 is observed using an SEM. The boundary between the first copper plate 4 and the second bonding layer 5 and the boundary between the second bonding layer 5 and the second copper plate 6 can be identified using SEM photographs or EDX element mapping. The thickness of the first copper plate 4 and the thickness of the second copper plate 6 can also be measured using the identified boundaries.

[0039] For example, if the second bonding layer 5 contains Ag or Ti, the distribution of Ag or Ti is confirmed by elemental mapping. In the region between the first copper plate 4 and the second copper plate 6, the region containing Ag or Ti is identified as the second bonding layer 5. If the second bonding layer 5 is made of Cu, the first copper plate 4, the second bonding layer 5, and the second copper plate 6 are identified by elemental mapping based on the differences in the elements contained therein. For example, the first copper plate 4 and the second copper plate 6 are copper plates cut from rolled copper. Phosphorus, silicon, manganese, or the like 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, the first copper plate 4, the second bonding layer 5, and the second copper plate 6 may be identified from SEM photographs. For example, the cut surfaces of the first copper plate 4 and the second copper plate 6 are flatter and have fewer irregularities than the cut surface of the second bonding layer 5. By increasing the contrast of the SEM photograph and emphasizing the irregularities and roughness, the first copper plate 4, the second bonding layer 5, and the second copper plate 6 can be distinguished.

[0040] The density of the second bonding layer 5 may be in the range of 80% to 100% and preferably in the range of 80% to 99.5%. 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 is obtained, but the manufacturing cost may increase. Furthermore, if the density of the second bonding layer 5 is in the range of 80% to 99.5%, it also has the effect of alleviating 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% to 99.5%.

[0041] SEM photographs are used to measure the density of the second bonding layer 5. The cross section of the copper laminate portion 7 along the Z direction is observed using the SEM. The SEM magnification is set to 2000x, and a backscattered electron image is used for observation. The size of the measurement area is set to the thickness of the second bonding layer 5 x 100 μm in width. The SEM observation area may include the copper plate, in which case a measurement area of ​​the thickness of the second bonding layer 5 x 100 μm in width is extracted from the observation area. In the SEM photograph (backscattered electron image), pores appear black. [(area of ​​measurement area - total area of ​​black parts) / area of ​​measurement area] x 100 = density (%). Density is measured in any three measurement areas spaced apart from each other on the cross section, and the average value is used as the density of the second bonding layer 5.

[0042] The first bonding layer 3 contains a material that can be used as a brazing filler metal for bonding the ceramic substrate 2 and the first copper plate 4. The brazing filler metal may be composed of Cu (copper), Ti (titanium), Ag (silver), C (carbon), Sn (tin), In (indium), or the like. For example, the brazing filler metal may be composed of 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, or the like. In may be used instead of Sn. Both Sn and In may be used.

[0043] Preferably, the first bonding layer 3 contains Cu and Ti as essential components, and further contains one or more selected from the group consisting of Ag, C, Sn, and In. Cu is a component that serves as the base material of the brazing material. 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 effects of improving bonding strength and lowering the melting point of the brazing material. A lower melting point of the brazing material leads to a lower bonding temperature. C (carbon) has the effects of controlling the fluidity of the brazing material and controlling the structure of the bonding layer by reacting with other components.

[0044] In the active metal bonding method, an active metal brazing material 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 thermally bonded together. The active metal brazing material contains 15% by mass or more and 85% by mass or less of Cu (copper), Ti (titanium), or TiH ２ It is preferable that the titanium hydride is contained in an amount of 1 mass % or more and 15 mass % or less. ２ When both of these are used, the total amount thereof is preferably in the range of 1% by mass to 15% by mass.

[0045] When Ag is used, its content is preferably in the range of 5% by mass to 60% by mass. When at least one of Sn and In is used, their total content is preferably in the range of 1% by mass to 50% by mass. If necessary, C (carbon) may be added in the range of 0.1% by mass to 2% by mass.

[0046] The composition ratio of the active metal brazing material is calculated by assuming that the total of the mixed raw materials is 100% by mass. For example, if the active metal brazing material is composed of three elements, Ag, Cu, and Ti, the total of Ag, Cu, and Ti is 100% by mass. ２ When the active metal brazing material is composed of four kinds of Ag, Cu, TiH, and In, ２ When the active metal brazing material is composed of five elements, Ag, Cu, Ti, Sn, and C, the total of Ag, Cu, Ti, Sn, and C is taken as 100 mass %.

[0047] The active metal brazing material may contain at least one element selected from the group consisting of tungsten (W), molybdenum (Mo), and rhenium (Re) in an amount ranging from 0.1% by mass to 10% by mass. The addition of tungsten, molybdenum, or rhenium can control the fluidity of the active metal brazing material. Magnesium (Mg) may also be added to the active metal brazing material.

[0048] When multiple copper laminate sections 7 are provided on one surface 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 laminate section 7 may be different 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 laminate section 7. In the example shown in FIG. 2, copper laminate sections 7-1 and 7-2 are provided on the first surface 2a. The maximum thickness of the second copper plate 6-1 included in the copper laminate section 7-1 is greater than the maximum thickness of the second copper plate 6-2 included in the copper laminate section 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 the copper laminate section 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 the copper laminate section 7-2. For example, the thickness of each second copper plate 6 can be made different depending on the need for heat dissipation. In addition, if heat dissipation properties are required for both copper laminate sections 7, the sum of the maximum thickness of the first copper plate 4 and the maximum thickness of the second copper plate 6 may be the same between copper laminate section 7-1 and copper laminate section 7-2.

[0049] 2, a copper laminate portion 7-3 may be provided on the second surface 2b. For example, the surface of the copper plate provided on the second surface 2b is used as a mounting surface for a heat sink or a mounting board. By providing the copper laminate portion 7-3 on the second surface 2b, heat dissipation to the heat sink or mounting board can be improved.

[0050] The angle θ of the lower end of the side surface of the second copper plate 6 relative to the upper surface of the first copper plate 4 is preferably within a range of 50° to 110°. More specifically, the angle θ is the angle between a 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, and is the surface that is bonded to the second copper plate 6 via the second bonding layer 5. By setting the angle θ within a range of 50° to 110°, the surface of the second copper plate 6 can be used as a mounting surface for a semiconductor element or the like.

[0051] The second copper plate 6 may be formed by joining a larger copper plate to the first copper plate 4 and then etching the copper plate. Alternatively, a pre-processed second copper plate 6 may be joined to the first copper plate 4. The smaller the angle θ, the greater the difference between the size of the bottom surface of the second copper plate 6 and the size of the top surface of the second copper plate 6. A small angle θ reduces the size of the top surface of the second copper plate 6 that can be used to mount semiconductor devices compared to the size of the first copper plate 4 required for joining the second copper plate 6. If 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 for the second copper plate 6 is not necessary, thereby shortening the process time required for manufacturing. Furthermore, since both the first copper plate 4 and the second copper plate 6 are made of copper, the first copper plate 4 and the second copper plate 6 have substantially the same thermal expansion coefficient. When joining members with different thermal expansion coefficients, it is preferable to incline the side of one of the members to relieve thermal stress. However, since the first copper plate 4 and the second copper plate 6 have the same thermal expansion coefficient, it is not necessary to increase the angle θ to relieve thermal stress. Therefore, it is preferable that the angle θ be between 50° and 110°.

[0052] Furthermore, when the angle θ is within the range of 50° to 110°, the position can be easily detected by a camera. The camera is, for example, a CCD camera or a CMOS camera. When the angle θ is within the range of 50° to 110°, the deviation between the outline of the lower surface of the second copper plate 6 and the outline of the upper surface of the second copper plate 6 is small in a plan view, thereby improving the accuracy of position detection of the second copper plate 6. This improves the position accuracy of the mounted semiconductor element. To improve position detection by a camera, it is better for the angle θ to be 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°.

[0053] To measure the angle, a camera or SEM is used to observe the cross section of the copper laminate 7 along the Z direction at a magnification that covers the entire top surface of the first copper plate 4 and the entire thickness direction of the second copper plate 6. On the observed image, a straight line is drawn parallel to the portion from the center to the bottom of the side of the second copper plate 6 in the thickness direction. If the slope of the side changes in the portion from the center to the bottom of the thickness direction, a straight line that best approximates the side is drawn. The straight line is drawn beyond the second bonding layer 5 to the top surface of the first copper plate 4. The angle θ between this line and the top surface of the first copper plate 4 is measured. If the straight line does not intersect with the top surface of the first copper plate 4, the angle between the line and a plane parallel to the top surface of the first copper plate 4 is measured.

[0054] If the length of the first copper plate 4 is L1 and the length of the second copper plate 6 is L2, the ratio of the length L2 to the length L1 is preferably within the range of 0.1 to 2. In other words, it is preferable that 0.1≦L2 / L1≦2 is satisfied. The lengths are 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 laminate portion 7 is viewed from the same side. Alternatively, the lengths L1 and L2 may be measured using a cross section parallel to the Z direction.

[0055] If the ratio L2 / L1 is less than 0.1, the effect of providing the second copper plate 6 may be insufficient. In particular, if the second copper plate 6 is too small, the mounting area for semiconductor elements and the like 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 portions of the second copper plate 6 may protrude from the first copper plate 4 and sag. For this reason, the ratio L2 / L1 is preferably in the range of 0.1 to 1.5, and more preferably in the range of 0.5 to 1.

[0056] The first bonding layer 3 between the ceramic substrate 2 and the first copper plate 4 preferably includes a protruding portion 3a. The protruding portion 3a is a portion of the first bonding layer 3 that protrudes from the side surface of the first copper plate 4. The length L3 of the protruding portion 3a is preferably in the range of 10 μm to 300 μm. The first bonding layer 3 has the protruding portion 3a, which can improve the TCT characteristics. If the length L3 is less than 10 μm, the stress relaxation effect may be reduced, and the TCT characteristics may deteriorate. If the length L3 exceeds 300 μm, the ceramic-copper bonded body may become large, which may increase the manufacturing cost. Therefore, the length L3 of the protruding portion 3a is preferably in the range of 10 μm to 300 μm.

[0057] The thermal expansion coefficient of the copper plate is greater than that of the ceramic substrate. Therefore, when the temperature rises and the ceramic substrate and 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. This stress can cause cracks in the ceramic substrate or bonding layer, or the copper plate to 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 bonded body, but the worse the TCT characteristics. According to this embodiment, instead of a single thick copper plate, a copper laminate 7 including a first copper plate 4 and a second copper plate 6 is provided. When the copper laminate 7 is provided, stress due to the thermal expansion of the second copper plate 6 is applied to the first copper plate 4 and the second bonding layer 5. Stress caused mainly by thermal expansion of the first copper plate 4 is applied to the first bonding layer 3. That is, by stacking a plurality of copper plates via the second bonding layer 5, the stress applied to the ceramic substrate 2 and the first bonding layer 3 can be alleviated. According to the embodiment, the TCT characteristics can be improved while maintaining the heat dissipation properties of the ceramic-copper bonded body 1, compared to when a single thick copper plate is provided.

[0058] According to the embodiment, a copper laminated portion 7, in which a first copper plate 4 and a second copper plate 6 are laminated, is bonded to the ceramic substrate 2. The thermal conductivity of copper plates is higher than that of titanium, aluminum, etc. Therefore, according to the embodiment, the heat dissipation of the ceramic-copper bonded body 1 can be further improved compared to when titanium or aluminum is laminated.

[0059] On any line parallel to the Z direction passing through the copper laminate portion 7, the sum of the thicknesses of the first copper plate 4 and 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 becomes difficult to improve heat dissipation. Because the first bonding layer 3 and the second bonding layer 5 are sufficiently thinner than the first copper plate 4 and the second copper plate 6, the sum of the thicknesses can be considered to be substantially the thickness of the copper laminate portion 7. By increasing the thickness of the copper laminate portion 7, heat dissipation can be improved. The upper limit of the sum of the thicknesses is not particularly limited, but is preferably 6.2 mm or less. The thickness of the first copper plate 4 is preferably 1.2 mm or less. If the upper limit of the thickness of the first copper plate 4 is 1.2 mm, the larger the sum of the thicknesses, the thicker the second copper plate 6 and the larger the thickness difference 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 between the thermal expansion amounts of the first copper plate 4 and the second copper plate 6 when the temperature rises. If the sum of the thicknesses exceeds 6.2 mm, the difference in the amount of thermal expansion may cause cracks to occur in the second bonding layer 5 between the first copper plate 4 and the second copper plate 6, or peeling of the second copper plate 6. For this reason, it is more preferable that the sum of the thicknesses is within the range of 0.8 mm to 6.2 mm.

[0060] When multiple copper laminates 7 are bonded to one surface of the ceramic substrate 2, it is preferable that at least one of 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 a range of 0.2 mm to 2 mm between at least one pair of adjacent copper laminates 7. Here, the "shortest distance" refers to the smallest distance between the members in a direction perpendicular to the Z direction when the ceramic-copper bonded body 1 is viewed from the Z direction.

[0061] By having at least one of the shortest distances be 2 mm or less, the proportion of the bonding area of ​​the copper laminate portion 7 within the plane of the ceramic substrate 2 can be increased. For example, if the bonding area of ​​the copper laminate portion 7 is constant, increasing the proportion of the bonding area can reduce the size and weight of the substrate. Alternatively, if the size of the substrate is constant, increasing the size of the copper laminate portion 7 in the X-Y plane can increase the area available for mounting semiconductor elements. On the other hand, if any of the shortest distances is 0.2 mm or less, the insulation between the copper plates may be reduced. Therefore, it is preferable that at least one of the shortest distances be within the range of 0.2 mm or more and 2 mm or less. Note 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 may all be 0.2 mm or more and 2 mm or less, or some of the shortest distances may exceed 2 mm. However, from the viewpoint of insulation, it is preferable that all of the shortest distances be 0.2 mm or more.

[0062] When multiple copper lamination sections 7 are bonded to one surface of the ceramic substrate 2, large stress is applied to the ceramic substrate 2 in areas where the copper lamination sections 7 are densely packed, during thermal deformation. In particular, when any of the shortest distances is 2 mm or less, the stress applied to the ceramic substrate 2 becomes even larger. 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 alleviated. Therefore, even when thick copper lamination sections 7 are provided close to each other, the occurrence of cracks in the ceramic substrate 2 and peeling of the first copper plate 4 due to stress can be suppressed. In other words, according to the embodiment, even when thick copper lamination sections 7 are provided, the shortest distance can be designed to be 2 mm or less.

[0063] The ceramic substrate 2 is preferably one selected from a silicon nitride substrate, an aluminum nitride substrate, an aluminum oxide substrate, and a zirconium oxide substrate. The thermal conductivity of the silicon nitride substrate is 50 W / m·K or more, and can even be 80 W / m·K or more. The three-point bending strength of the silicon nitride substrate is 600 MPa or more, and can even be 700 MPa or more. The thermal conductivity of the aluminum nitride substrate is 150 W / m·K or more, and can even be 200 W / m·K or more. The three-point bending strength of the aluminum nitride substrate is approximately 300 to 450 MPa. The three-point bending strength of the aluminum oxide substrate is approximately 300 to 450 MPa, but the aluminum oxide substrate is less expensive than other substrates. The thermal conductivity of the aluminum oxide substrate is approximately 20 to 30 W / m·K. The three-point bending strength of the zirconium oxide substrate is high at about 550 MPa, but its thermal conductivity is about 30 to 50 W / m·K.

[0064] The thickness of the ceramic substrate 2 is preferably in the range of 0.2 mm to 3 mm, and more preferably in the range of 0.2 mm to 1 mm. If the thickness of the ceramic substrate 2 is less than 0.2 mm, the strength may be insufficient. If the thickness of the ceramic substrate 2 exceeds 3 mm, the ceramic substrate 2 may become a thermal resistor, and the heat dissipation performance may be reduced.

[0065] Since silicon nitride substrates have high strength, their thickness can be designed to be in the range of 0.2 mm to 0.5 mm, and from the viewpoint of thinning the substrate, it is preferable to use silicon nitride substrates.

[0066] The ceramic copper bonded body according to the embodiment can be used for a ceramic copper circuit board. The ceramic copper circuit board includes a circuit-shaped copper laminate portion 7. For example, a ceramic copper circuit board can be obtained by bonding a circuit-shaped second copper plate 6 to a first copper plate 4, or by processing the second copper plate 6 bonded to the first copper plate 4 into a circuit shape.

[0067] The ceramic copper circuit board may be used as a semiconductor device by mounting a semiconductor element on the second copper plate 6. By mounting a semiconductor element on the second copper plate 6, a semiconductor device is obtained.

[0068] 7 is a side view showing an example of a semiconductor device according to an embodiment. In FIG. 7, reference numeral 10 denotes a semiconductor device, reference numeral 11 denotes a bonding layer, and reference numeral 12 denotes 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.

[0069] When multiple second copper plates 6 are provided, semiconductor elements may be mounted on only some of the second copper plates 6, or on all of the second copper plates 6. Multiple semiconductor elements may be mounted on one second copper plate 6. If necessary, semiconductor elements may be mounted on a first copper plate 4 on which no second copper plate 6 is provided. Solder, Ag sinter bonding, Cu sinter bonding, etc. can be used to mount the semiconductor elements. A plating film may be provided on the surface of the copper plate on which the semiconductor elements are mounted. In addition to semiconductor elements, lead frames, wire bonding, etc. may be bonded to the copper plate.

[0070] Next, a method for manufacturing the ceramic-copper bonded body 1 according to the embodiment will be described. The method for manufacturing the ceramic-copper bonded body 1 according to the embodiment is not particularly limited as long as it has the above-described configuration. Here, an example of a method for obtaining the ceramic-copper bonded body 1 with a high yield will be described.

[0071] First, a ceramic substrate 2 is prepared. The ceramic substrate 2 is one selected from a silicon nitride substrate, an aluminum nitride substrate, an aluminum oxide substrate, and a zirconium oxide substrate. The characteristics and thickness of the ceramic substrate 2 are as described above.

[0072] Next, prepare a copper plate to be used as the first copper plate 4. The size of the copper plate to be used may be larger than the first copper plate 4, or a copper plate that has been processed in advance to the size of the first copper plate 4 may be used.

[0073] Next, an active metal brazing material is prepared. The composition of the active metal brazing material is as described above. A binder or the like is added to the active metal brazing material to prepare an active metal brazing material paste. The active metal brazing material is applied to the ceramic substrate 2, and a copper plate for the first copper plate 4 is placed on top of the active metal brazing material. When joining copper plates to both sides of the ceramic substrate 2, the active metal brazing material paste is applied to both sides, and copper plates are placed on both sides. This process results in a laminate having a laminate structure of ceramic substrate / active metal brazing material layer / copper plate. When copper plates are placed on both sides of the ceramic substrate 2, a laminate having a laminate structure of copper plate / active metal brazing material layer / ceramic substrate / active metal brazing material layer / copper plate is obtained.

[0074] Instead of the active brazing paste, an active brazing foil may be used, which preferably has the above-mentioned composition and a thickness in the range of 5 μm to 50 μm.

[0075] Next, the laminate is heated and bonded. The temperature for heat bonding is preferably in the range of 650°C to 950°C. Heat bonding is preferably carried out in a vacuum or a nitrogen atmosphere. －３ For heat bonding at a pressure of 1000 Pa or less, a vacuum furnace (batch 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, and a bonded body is obtained.

[0076] Next, an etching step is performed. When a large copper plate is used, the copper plate is processed to the size of the first copper plate 4 by the etching step. Multiple first copper plates 4 may be formed from one copper plate. Furthermore, an inclined shape may be imparted to the side surface of the first copper plate 4 by the etching step. A part of the first bonding layer 3 may be removed by the etching method, and an overhanging portion 3 a may be formed. In this way, a ceramic copper plate in which the first copper plate 4 is bonded to the ceramic substrate 2 is obtained.

[0077] 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 becomes the second bonding layer 5 by heat treatment. The metal layer is formed using a powder containing one or more elements selected from the group consisting of Ag, Cu, and Ti. Examples of the powder include Ag powder, Cu powder, Ti powder, AgCu alloy powder, AgTi alloy powder, CuTi alloy powder, and AgCuTi alloy powder. A composite metal powder of a metal and an organic substance may also be used.

[0078] A paste is prepared using the powder, and the paste is applied onto the first copper plate 4. The applied thickness is preferably in the range of 10 μm to 100 μm, which allows the thickness of the second bonding layer 5 after heat treatment to be in the range of 5 μm to 50 μm.

[0079] Bonding using a metal layer containing Ag as the main component is called Ag sinter bonding. Bonding using a metal layer containing Cu as the main component is called Cu sinter bonding. Bonding using a metal layer containing Ti as the main component is called Ti sinter bonding. Ag sinter bonding, Cu sinter bonding, and Ti sinter bonding are bonding methods using metal powder or metal oxide powder.

[0080] The average particle size of the powder used for sinter bonding is preferably 10 μm or less. The smaller the average particle size, the easier it is to perform sinter bonding. Therefore, the average particle size of the powder is preferably 10 μm or less, and more preferably 20 nm or less. Sinter bonding using nanoparticles with an average particle size of 20 nm or less is sometimes called nanoparticle bonding. In particular, sinter bonding using Ag or Cu as the main component has good bondability.

[0081] Instead of sinter bonding, a foil containing Ag or Cu as a main component may be used. When a foil is used, the thickness is preferably in the range of 5 μm to 50 μm.

[0082] Next, a second copper plate 6 is placed on the metal layer. The thickness of the second copper plate 6 is 0.3 mm or more. The second copper plate 6 is preferably processed to the required size in advance. For example, a long copper plate is etched, wire-cut, or pressed to form the second copper plate 6 of a predetermined size. By performing wire-cutting or pressing, it becomes easier to control the angle θ of the lower end of the side surface of the second copper plate 6 relative to the upper surface of the first copper plate 4 to within a range of 50° to 110°.

[0083] Next, the laminate with the second copper plate 6 disposed thereon is heated in a nitrogen atmosphere to bond the first copper plate 4 and the second copper plate 6. In the nitrogen atmosphere, the nitrogen concentration is in the range of 95 vol% to 100 vol%. The heat treatment temperature is set in the range of 190°C to 340°C. If necessary, the heat treatment may be performed while applying pressure. For example, the pressure is preferably in the range of 2 MPa to 30 MPa. A hot press may be used for applying pressure.

[0084] According to the sintering bonding method, the first copper plate 4 and the second copper plate 6 can be bonded at a low temperature of 190°C or higher and 340°C or lower. Bonding at a low temperature can suppress the occurrence of warping in the ceramic-copper bonded body 1. Furthermore, waviness of the second copper plate 6 can be suppressed. Even when the volumes of adjacent copper laminated portions 7 are different, or when the volume of the copper laminated portion 7 bonded to the first surface 2a is different from the volume of the copper laminated portion 7 bonded to the second surface 2b, warping of the ceramic-copper bonded body 1 can be suppressed. In other words, a ceramic-copper bonded body 1 with excellent flatness can be obtained. Furthermore, even when a foil containing Ag or Cu as a main component is used, the first copper plate 4 and the second copper plate 6 can be bonded at a low temperature of 190°C or higher and 340°C or lower.

[0085] A copper plate larger than the second copper plate 6 may be bonded onto the first copper plate 4, and the second copper plate 6 may be processed to a predetermined size by an etching process. However, to process a thick copper plate by the etching process, the number of etchings or the etching time must be increased. Chemicals are used in the etching process. As the number of etchings or the etching time increases, the amount of chemicals used and the amount of used chemicals discarded also increase. As described above, by bonding the second copper plate 6, which has been processed to a predetermined size in advance, to the first copper plate 4, there is no need to use an etching process to process the second copper plate 6. This reduces the amount of discarded chemicals.

[0086] Examples 1 to 6, Comparative Examples 1 to 4 A silicon nitride substrate was prepared as a ceramic substrate. The 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.

[0087] A copper plate for the first copper plate was bonded to a silicon nitride substrate using an active metal brazing method. In the active metal brazing method, an active metal brazing material containing at least one element selected from the group consisting of Ag, C, Sn, and In in addition to Cu and Ti was used. The first copper plate was formed by imparting a pattern to the copper plate through an etching process. Here, the copper plate bonded to the surface (first surface) on which the semiconductor element is mounted is referred to as the front copper plate. The copper plate bonded to the opposite second surface is referred to as the back copper plate.

[0088] Next, a second copper plate was bonded onto the first copper plate. The number of first copper plates and the number of second copper plates are as shown in Table 1. In Examples 1 to 3 and 5, a plurality of first copper plates were bonded, and a second copper plate was bonded onto each of the first copper plates. In Example 4, a second copper plate was bonded onto each of three first copper plates, and the thickness of one second copper plate was different from the thickness of the other two second copper plates. In Example 6, a second copper plate was bonded to each of two of the three first copper plates.

[0089] The first copper plate and the second copper plate were both rectangular and had flat surfaces. The length L1 of the first copper plate was measured as the length in the vertical direction and the length in the horizontal direction of the first copper plate. The length L2 of the second copper plate was measured as the length in the vertical direction and the length in the horizontal direction of the second copper plate. The thickness T1 of the first copper plate and the thickness T2 of the second copper plate were also measured. The measurement results are shown in Table 1.

[0090] Table 1 shows the material and thickness of the second bonding layer, as well as the density of the second bonding layer. In the examples, the first copper plate and the second copper plate were bonded using a nanoparticle bonding method (one of Ag sinter bonding, Cu sinter bonding, and Ti sinter bonding). In the nanoparticle bonding method, a nitrogen atmosphere with a nitrogen concentration of 95 vol% to 100 vol% was used, and the heating temperature was set to a range of 190°C to 340°C. The pressure was set to a range of 2 MPa to 20 MPa.

[0091] In Comparative Example 1, the first copper plate and the second copper plate were joined by solid-state diffusion bonding using 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 joined using lead-free solder. The lead-free solder used was a SnAgCu-based solder containing 96.5% by mass of Sn, 3% by mass of Ag, and 0.5% by mass of Cu. The joining temperature was set to 220°C.

[0092] The density of the second bonding layer was measured using a cross-sectional SEM photograph as described above.

[0093]

[0094] Next, the measured thicknesses T1 and T2 were used to determine whether 1.1≦T2 / T1 was satisfied. The measured lengths L1 and L2 were also used to determine whether 0.1≦L2 / L1≦1.5 was satisfied. The results are shown in Table 2.

[0095] In Table 2, if 1.1≦T2 / T1 is satisfied, a check mark is entered. If 1.1≦T2 / T1 is not satisfied, a hyphen is entered. Also, if the ratio of the length of the second copper plate to the length of the first copper plate is between 0.1 and 1.5, a check mark is entered. If the ratio is not between 0.1 and 1.5, a hyphen is entered.

[0096] Furthermore, the angle θ of the lower end of the side of the second copper plate relative to the upper surface of the first copper plate was measured. The length L3 of the protruding portion of the first bonding layer was measured. The sum of the thicknesses T1 and T2 was also calculated. Between adjacent copper laminated portions, 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 were measured, and it was checked whether at least any of these 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 check mark is marked if any of the shortest distances was within the range of 0.2 mm or more and 2 mm or less.

[0097]

[0098] In each example and comparative example, a first copper plate was also bonded to the second surface of the silicon nitride substrate. The number of first copper plates and the number of second copper plates on the second surface are as shown in Table 3. In examples 1 and 3 to 6 and comparative examples 1 to 4, a second copper plate was bonded to the first copper plate. In example 2, a second copper plate was not bonded to the first copper plate on the second surface.

[0099] The thickness T1, thickness T2, length L1, and length L2 of the back copper plate were measured in the same manner as the front copper plate. The density of the second bonding layer was also measured. The measurement results, material, and thickness of the second bonding layer are shown in Table 3.

[0100]

[0101] For the back copper plate, it was determined whether 1.1≦T2 / T1 was satisfied, and whether 0.1≦L2 / L1≦1.5 was satisfied. In addition, the angle θ was measured, and the length L3 of the protruding portion was measured. The sum of the thicknesses T1 and T2 was calculated. The results are shown in Table 4.

[0102]

[0103] In the ceramic-copper bonded bodies according to the examples, a second copper plate is bonded to a first copper plate via a second bonding layer. The second bonding layer contains at least one element selected from the group consisting of Ag, Cu, and Ti. In all examples, the relationship T2 / T1 is satisfied.

[0104] On the other hand, in Comparative Examples 1 and 4, the first copper plate and the second copper plate are joined by Ti solid-state 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 are joined with lead-free solder. Therefore, the thickness of the second bonding layer is 200 μm in Comparative Example 2 and 150 μm in Comparative Example 3. These thicknesses are larger than those of the second bonding layer in the Examples.

[0105] In each example and comparative example, the change in warpage of the ceramic-copper bonded body and the change in waviness on the surface of the second copper plate were measured. Specifically, the warpage of the ceramic-copper bonded body was measured before and after bonding the second copper plate. The difference between these warpages was calculated as the change in warpage. In addition, the waviness on the surface of the second copper plate was measured before and after bonding. The difference between these wavinesses was calculated as the change in waviness. A three-dimensional shape measuring device was used to measure the warpage and waviness. The three-dimensional shape measuring device may be a Keyence One-Shot 3D Shape Measuring Machine or a device with equivalent or better performance.

[0106] Here, warpage refers to a state in which the substrate is bent in one direction when viewed as a whole. Waviness refers to a state in which unevenness exists on the surface of the copper plate. For example, when using a Keyence One-Shot 3D Shape Measuring Instrument, the warpage of a ceramic-copper bonded body is measured by setting a reference line or plane and measuring the distance to the farthest point from that reference. The waviness of the surface of the second copper plate is measured by measuring the waviness curve per 5 mm of any copper plate and calculating the maximum and minimum heights.

[0107] An example in which the increase in warpage was 100% or less was judged to be "best." An example in which the increase in warpage was more than 100% but not more than 200% was judged to be "good." An example in which the increase in warpage was more than 200% was judged to be "poor." An example in which the increase in waviness was 100% or less was judged to be "best." An example in which the increase in waviness was more than 100% but not more than 200% was judged to be "good." An example in which the increase in waviness was more than 200% was judged to be "poor."

[0108] Furthermore, the TCT characteristics of the ceramic-copper bonded bodies were measured for each example and comparative example. The TCT was performed 1,000 times, with one cycle consisting of -40°C for 30 minutes, room temperature for 10 minutes, 150°C for 30 minutes, and room temperature for 10 minutes. The ceramic-copper bonded bodies were then observed for defects after the TCT. Defects included cracks in the ceramic substrate or the first bonding layer, peeling of the copper plate, and the like. The results are shown in Table 5.

[0109]

[0110] In the examples, the change in warpage of the ceramic-copper bonded body and the change in waviness on the surface of the second copper plate were suppressed. These results demonstrate that heat bonding at 190°C or higher and 340°C or lower using sinter bonding can suppress increases in warpage and waviness. Furthermore, the examples also exhibited excellent TCT characteristics. Therefore, it is clear that joining a second copper plate to a location where improved heat dissipation is desired is effective in improving TCT characteristics.

[0111] In contrast, in Comparative Example 1, solid-phase diffusion bonding was performed at a high bonding temperature of 500°C. This resulted in a large increase in the amount of warpage and the amount of waviness on the surface of the second copper plate. As the warpage increased, the TCT characteristics also deteriorated.

[0112] In Comparative Example 2, lead-free solder was used for bonding, and the bonding temperature was low at 220°C. Therefore, the increase in warpage was small. On the other hand, in the TCT, the second copper plate was displaced. This is because the temperature on the high-temperature side of the TCT was 200°C, which is close to the bonding temperature.

[0113] In Comparative Example 3, lead-free soldering was performed, but the condition 1.1≦T2 / T1 was not satisfied. Furthermore, the density of the second bonding layer was low, and T1 + T2 was less than 0.8 mm. These factors resulted in a decrease in heat dissipation and an increase in warpage. The increase in warpage also resulted in a decrease in TCT characteristics.

[0114] In Comparative Example 4, Ti solid-phase diffusion bonding was performed, resulting in a high bonding temperature. Furthermore, the L2 / L1 ratio did not satisfy the range of 0.1 to 1.5, resulting in poor heat dissipation and significant warpage. Furthermore, the protruding portion length L3 was large at 310 μm, and the angle θ of the second copper plate was small, resulting in poor TCT characteristics.

[0115] 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. These embodiments and their modifications 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.

[0116] DESCRIPTION OF SYMBOLS 1...Ceramic copper bonded body 2...Ceramic substrate 3...First bonding layer 3a...Protruding portion 4...First copper plate 4a...First portion 5...Second bonding layer 6...Second copper plate 6a...Second portion 10...Semiconductor device 11...Bonding layer 12...Semiconductor element T1...Thickness of first copper plate T2...Thickness of second copper plate L1...Length of first copper plate L2...Length of second copper plate L3...Length of bonding layer protruding portion

Claims

1. A ceramic copper joined body comprising: a ceramic substrate; and a copper laminate portion bonded to a first surface of the ceramic substrate, wherein the copper laminate portion comprises: 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, wherein the thickness of the second bonding layer is within the range of 5 μm to 50 μm, and the second bonding layer contains one or more elements selected from the group consisting of Ag, Cu, and Ti, the first copper plate includes a first portion having a thickness T1 of 0.05 mm or more, and the second copper plate includes a second portion having a thickness T2 of 0.3 mm or more, and wherein the thickness T1 of the first portion and the thickness T2 of the second portion satisfy the relationship 1.1≦T2 / T1.

2. The ceramic copper joined body according to claim 1, wherein the first joining layer contains Cu, Ti, and one or more elements selected from the group consisting of Ag, C, Sn, and In.

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

4. A ceramic copper joint as described in any one of claims 1 to 3, wherein a plurality of copper laminate sections are joined to the first surface, and 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 laminate sections 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 laminate sections.

5. A ceramic copper joined body according to any one of claims 1 to 4, wherein the first copper plate has a first joining surface joined to the second copper plate, and the angle between a line parallel to the lower end of the side surface of the second copper plate and the first joining surface is within the range of 50° to 110°.

6. A ceramic copper joint as described in any one of claims 1 to 5, wherein a plurality of the copper laminate sections are joined to the first surface, and at least 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 within the range of 0.2 mm or more and 2 mm or less between at least one pair of adjacent copper laminate sections among the plurality of copper laminate sections.

7. A ceramic copper joint body according to any one of claims 1 to 6, wherein, when the length of the first copper plate in a first direction parallel to the first surface is L1 and the length of the second copper plate in the first direction is L2, 0.1≦L2 / L1≦1.

5.

8. A ceramic copper joint according to any one of claims 1 to 7, wherein the first bonding layer includes a protruding portion that protrudes from the side surface of the first copper plate.

9. A ceramic copper bonded body according to any one of claims 1 to 8, wherein the ceramic substrate is a silicon nitride substrate.

10. A ceramic copper joint body as described in any one of claims 1 to 9, wherein the sum of the thickness of the first copper plate and the thickness of the second copper plate is 0.8 mm or more on any straight line perpendicular to the first surface.

11. A ceramic copper circuit board comprising a ceramic copper bonded body according to any one of claims 1 to 10, wherein the copper laminated portion has a circuit shape.

12. A method for manufacturing a ceramic copper joined body, comprising the steps of: preparing a ceramic copper plate in which a first copper plate is joined to a ceramic substrate via a first joining layer; forming a metal layer containing one or more elements selected from the group consisting of Ag, Cu, and Ti on the first copper plate; placing a second copper plate on the metal layer; and heating the first copper plate and the second copper plate at a temperature in the range of 190°C to 340°C in a nitrogen atmosphere of 95 vol% or more to join the first copper plate and the second copper plate to form a copper laminated portion.

13. A method for manufacturing a ceramic copper joint body as described in claim 12, wherein the step of preparing the ceramic copper plate to which the first copper plate is bonded includes a step of removing a portion of the first bonding layer by an etching method to form a protruding portion of the first bonding layer that protrudes from the first copper plate.

14. A method for producing a ceramic copper joined body according to claim 12 or 13, wherein the step of joining the first copper plate and the second copper plate is carried out by hot pressing.

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