Ceramic Copper Circuit Board and Semiconductor Device Using the Same

Abstract

Provided are: a ceramic copper circuit board in which the average length RSm of the roughness curve element on the surface of a copper member is controlled; and a semiconductor device using same. A ceramic copper circuit board according to an embodiment of the present invention comprises a ceramic substrate and a copper member bonded to one surface of the ceramic substrate. When the average length RSm of the roughness curve element is measured at each of five arbitrary points selected from the surface of the copper member, the average value of the five average lengths RSm is 40-250 μm.

Description

Technical Field

[0001] The embodiments described below generally relate to a ceramic copper circuit board and a semiconductor device using the same.

Background Art

[0002] A ceramic copper circuit board in which a ceramic substrate and a copper plate are joined is used as a circuit board for mounting semiconductor elements and the like. Further, with the improvement in performance of semiconductor elements, it is expected that the junction temperature will increase. Along with this, joining using Ag nanoparticles for mounting semiconductor elements has been studied. In performing joining using Ag nanoparticles, providing an Ag layer on the surface of a metal plate has been studied. For example, the ceramic circuit board described in Japanese Patent No. 6262968 (Patent Document 1) improves the surface roughness (arithmetic mean roughness Ra) of a circuit board in which a ceramic substrate and an aluminum plate are joined via a joining layer. In addition, an Ag paste is used for mounting semiconductor elements and the like. In order to improve the adhesion to the silver layer, plating a copper plate surface has also been carried out. A Ni-P plating film is used for the plating film. For example, Japanese Unexamined Patent Application Publication No. 2019-41108 (Patent Document 2) shows providing recesses on the copper surface.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] As described above, in order to improve the bondability with semiconductor elements, silver (Ag) paste has been used. On the other hand, when a silver (Ag) layer was provided on a copper member of a ceramic copper circuit board, a phenomenon of decreased bond strength occurred. When investigating the cause, it was found that the cause was the average length RSm of the roughness curve elements on the surface of the copper member. The present invention is for addressing such problems, and an object thereof is to provide a ceramic copper circuit board in which the average length RSm of the roughness curve elements on the surface of the copper member is controlled.

Means for Solving the Problems

[0005] The ceramic copper circuit board according to the embodiment includes a ceramic substrate and a copper member joined to one surface of the ceramic substrate. When the average length RSm of the roughness curve elements is measured at each of any five locations selected from the surface of the copper member, the average value of the five average lengths RSm is characterized by being 40 μm or more and 250 μm or less.

Brief Description of the Drawings

[0006]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0007] The ceramic copper circuit board according to the embodiment includes a ceramic substrate and a copper member joined to one surface of the ceramic substrate. When the average length RSm of the roughness curve elements is measured at each of any five locations selected from the surface of the copper member, the average value of the five average lengths RSm is characterized by being 40 μm or more and 250 μm or less.

[0008] A description will be given of the drawings of this application. FIG. 1 is a schematic diagram showing an example of a ceramic copper circuit board according to an embodiment of the present invention. FIG. 1 shows an example in which two copper plates are joined to both sides of a ceramic substrate. The copper plate is an example of a copper member. In FIG. 1, 1 is a ceramic copper circuit board, 2 is a ceramic substrate, 3 is a copper plate (front copper plate), 4 is a copper plate (back copper plate), and 5 is a brazing material layer (active metal brazing material layer).

[0009] In the ceramic copper circuit board 1 shown in FIG. 1, the copper plate 3 and the copper plate 4 are arranged on both sides of the ceramic substrate 2 via the brazing material layer 5, respectively. In the structure shown in FIG. 1, a circuit shape is imparted to the copper plate 3, and the copper plate 4 is used as a heat sink. For convenience, the copper plate 3 is called the front copper plate, and the copper plate 4 is called the back copper plate. Also, two copper plates 3 are arranged. The ceramic copper circuit board 1 according to the embodiment is not limited to such a form. Three or more front copper plates 3 may be provided on the ceramic substrate 2, or only one front copper plate 3 may be provided. Further, the ceramic copper circuit board 1 may have a structure in which a circuit shape is imparted to the back copper plate 4. Or, the ceramic copper circuit board 1 may have a structure in which only the front copper plate 3 is provided without providing the back copper plate 4. FIG. 1 shows an example in which copper plates are joined to both sides of the ceramic substrate 2. When the back copper plate 4 is used as a heat dissipation member, an aluminum plate may be used as a heat sink instead of the back copper plate 4.

[0010] Figure 2 is a schematic diagram showing the method of the bonding strength (peel strength) test in the embodiment of the present invention. In Figure 2, 1 is a ceramic copper circuit board, 6 is a bonding layer, and 7 is a silver ribbon. As shown in Figure 2, the peel strength test was conducted using a silver ribbon. Figure 3 is a schematic diagram showing an example of a semiconductor device according to an embodiment of the present invention. In Figure 3, 6 is a bonding layer, 8 is a semiconductor element, and 9 is a semiconductor device. In the semiconductor device 9 described in Figure 3, one semiconductor element 8 is mounted on the surface copper plate 3. In the semiconductor device 9, a plurality of semiconductor elements 8 may be provided. A plurality of semiconductor elements 8 may be mounted on one surface copper plate 3. Further, in the example shown in Figure 3, the semiconductor device 9 includes a bonding layer 6 (solder layer), but the bonding layer 6 may not be provided, and the surface copper plate 3 and the semiconductor element 8 may be directly bonded.

[0011] The ceramic substrate 2 is a silicon nitride substrate, an aluminum nitride substrate, an aluminum oxide substrate, an aludur substrate, etc. The thickness of the ceramic substrate 2 is preferably 0.1 mm or more and 3 mm or less. If the thickness of the substrate is less than 0.1 mm, there is a possibility of causing a decrease in strength. If the thickness of the substrate is thicker than 3 mm, the ceramic substrate 2 becomes a heat resistor, and there is a possibility that the heat dissipation property of the ceramic copper circuit board 1 may decrease. A more preferable range of the thickness of the ceramic substrate 2 is 0.2 mm or more and 2 mm or less.

[0012] The three-point bending strength of the silicon nitride substrate is preferably 600 MPa or more. The thermal conductivity is preferably 80 W / m·K or more. If the thermal conductivity is 80 W / m·K or more, the thermal conductivity of the silicon nitride substrate may be 90 W / m·K or more, or 130 W / m·K or more. By increasing the strength of the substrate, the substrate thickness can be reduced. For this reason, the three-point bending strength of the silicon nitride substrate is preferably 600 MPa or more, and more preferably 700 MPa or more. By using the silicon nitride substrate, the substrate thickness can be reduced to 0.40 mm or less, and further to 0.30 mm or less.

[0013] The three-point bending strength of the aluminum nitride substrate is about 300 to 450 MPa. On the other hand, the thermal conductivity of the aluminum nitride substrate is 160 W / m·K or more. Since the strength of the aluminum nitride substrate is low, the substrate thickness is preferably 0.60 mm or more. The three-point bending strength of the aluminum oxide substrate is about 300 to 450 MPa, but the aluminum oxide substrate is inexpensive. The three-point bending strength of the aldyl substrate is as high as about 550 MPa, but the thermal conductivity is about 30 to 50 W / m·K. The aldyl substrate is a substrate made of a sintered body obtained by mixing aluminum oxide and zirconium oxide.

[0014] The ceramic substrate 2 is preferably either a silicon nitride substrate or an aluminum nitride substrate. The silicon nitride substrate and the aluminum nitride substrate are nitride-based ceramic substrates. The nitride-based ceramics react with an active metal brazing material containing Ti to form titanium nitride. The oxide-based ceramics react with an active metal brazing material containing Ti to form titanium oxide. The nitride-based ceramics can improve the bonding strength with a copper member (especially a copper plate) by using the active metal bonding method.

[0015] The copper member is oxygen-free copper, a copper alloy, etc. Generally, since the thermal conductivity of copper is as high as about 400 W / m·K, the heat dissipation performance of the ceramic copper circuit board 1 can be improved. Also, the thickness of the copper plate 3 and the thickness of the copper plate 4 may be 0.3 mm or more, and further 0.6 mm or more. The copper plate of 0.6 mm or more includes, for example, a 1 mm copper plate, a 2 mm copper plate, etc.

[0016] By increasing the thickness of the copper plate, the heat dissipation performance of the bonded body (ceramic copper circuit board 1) can be improved. Also, the thickness of the front copper plate 3 and the thickness of the back copper plate 4 may be the same or different from each other. The copper member is preferably a member made of oxygen-free copper or a member in which a graphite layer exists in the copper layer. As shown in JIS-H-3100 (such as ISO1337), oxygen-free copper has a copper purity of 99.96 wt% or more. The copper member may be directly bonded to the ceramic substrate 2 or may be bonded to the ceramic substrate 2 via a brazing material layer. A copper member in which a circuit shape has been previously imparted by punching or the like to the copper plate may be bonded to the ceramic substrate. After bonding the copper plate to the ceramic substrate, a circuit shape may be imparted to the copper plate by etching. The heat dissipation member may have a shape protruding from the ceramic substrate (for example, a shape in which a heat sink and a lead frame are integrated). A groove shape may be provided in the heat dissipation member.

[0017] In the ceramic copper circuit board 1 according to the embodiment, when the average length RSm of the roughness curve elements is measured at each of any five locations selected from the surface of the copper member, the average value of the five average lengths RSm is preferably 40 μm or more and 250 μm or less. More preferably, the average value of the five average lengths RSm is 50 μm or more and 200 μm or less. Most preferably, the average value of the five average lengths RSm is 60 μm or more and 150 μm or less. When the average length RSm of the roughness curve elements is within the above range, the bonding material can easily enter the minute recesses on the surface of the copper plate 4 moderately. Therefore, the bonding between the copper plate 4 and the bonding layer 6 can be made stronger.

[0018] Note that the any five locations are selected from regions that do not overlap with each other and are separated from each other by 500 μm or more. Also, the "surface" refers to the region excluding the side surface. The average length RSm of the roughness curve elements on the side surface may be within or outside the above preferred range.

[0019] The measurement length per time is set to 4 mm. When the measurement length cannot be measured at a value of 4 mm, it is substituted by measurements at a plurality of locations (3 locations or less). Each measurement length is set so that the total value of the measurement lengths at the plurality of locations becomes 4 mm, and the average length RSm measured at each location is averaged according to the ratio of the measurement lengths.

[0020] For example, the value of RSm measured at a measurement length of 3 mm at the first location is A μm, and the value of RSm measured at a measurement length of 1 mm at the second location is B μm. In this case, RSm is calculated by the following formula. RSm = (3A + B) / 4

[0021] JIS B0601:2013 is referred to for the calculation of surface roughness such as the average length RSm. JIS-B-0601 corresponds to ISO4287. For the measurement of surface roughness, an apparatus having a measurement accuracy equal to or higher than that of SURFCOM 2000DX-23 manufactured by Tokyo Seimitsu Co., Ltd. is used.

[0022] The minimum value of the five average lengths RSm is preferably 30 μm or more. Therefore, each numerical value (absolute value) of the five average lengths RSm is more preferably 30 μm or more and 250 μm or less. More preferably, each numerical value of the five average lengths RSm is 35 μm or more and 150 μm or less. Most preferably, each numerical value of the five average lengths RSm is 40 μm or more and 140 μm or less. The fact that the value of each individual average length RSm is within the above range indicates that the difference in the average length RSm for each measurement location is small and its variation is controlled. Therefore, the variation in the bonding strength can be reduced, and a more user-friendly ceramic copper circuit board 1 can be obtained.

[0023] In addition to the average length RSm, it is preferable that the arithmetic mean roughness Ra is also controlled. When the arithmetic mean roughness Ra is measured at each of any five locations selected from the surface of the copper member, it is preferable that the average value of the five arithmetic mean roughnesses Ra is 0.1 μm or more and 0.7 μm or less. More preferably, the average value of the five arithmetic mean roughnesses Ra is 0.2 μm or more and 0.6 μm or less. Also, it is preferable that each of the five arithmetic mean roughnesses Ra is greater than 0 μm and 1.5 μm or less. More preferably, each arithmetic mean roughness Ra is 0.05 μm or more and 1.0 μm or less.

[0024] It is preferable that the maximum valley depth Rv of the roughness curve is also controlled. When the maximum valley depth Rv of the roughness curve is measured at each of any five locations selected from the surface of the copper member, it is preferable that the average value of the five maximum valley depths Rv is 0.4 μm or more and 2.5 μm or less. More preferably, the average value of the five maximum valley depths Rv is 0.5 μm or more and 2.0 μm or less. Even more preferably, the average value of the five maximum valley depths Rv is 0.6 μm or more and 1.8 μm or less.

[0025] It is preferable that the surface roughness is controlled such that the minimum value of the five maximum valley depths Rv is 0.25 μm or more and 2.5 μm or less. It is more preferable that the surface roughness is controlled such that the minimum value of the five maximum valley depths Rv is 0.3 μm or more and 2.4 μm or less. It is even more preferable that the surface roughness is controlled such that the minimum value of the five maximum valley depths Rv is 0.4 μm or more and 2.3 μm or less.

[0026] It is also preferable that the maximum height roughness Rz is controlled. When the maximum height roughness Rz of the roughness curve is measured at each of any five locations selected from the surface of the copper member, it is preferable that the average value of the five maximum height roughnesses Rz is 10 μm or less.

[0027] When measuring the average length RSm, arithmetic mean roughness Ra, maximum valley depth Rv, and maximum height roughness Rz, all the measurement locations are the same. That is, the five locations where the average length RSm is measured, the five locations where the arithmetic mean roughness Ra is measured, the five locations where the maximum valley depth Rv is measured, and the five locations where the maximum height roughness Rz is measured are the same as each other.

[0028] In the ceramic copper circuit board 1, it is preferable that the ceramic substrate 2 and the copper plate 3 are joined via a brazing material layer 5. Furthermore, the brazing material layer 5 preferably contains silver (Ag), copper (Cu), or an active metal. Specific examples include a brazing material layer containing Ag, Cu, and an active metal, a brazing material layer substantially free of Ag and containing copper and an active metal, a brazing material layer containing Cu and magnesium (Mg), and the like. Substantially free of Ag means that Ag is not intentionally added, including cases where Ag is inevitably contained as an impurity. If necessary, Sn or In may be added. The brazing material layer 5 may also contain one or more selected from carbon (C), tungsten (W), molybdenum (Mo), and rhenium (Re) in an amount of 0.1% by mass or more and 10% by mass or less. By adding carbon, tungsten, molybdenum, and rhenium, the fluidity of the active metal brazing material can be controlled. Also, manganese (Mn) may be added to the brazing material layer 5 as necessary.

[0029] For the joining of the ceramic substrate 2 and the copper plate 4, it is preferable to use an active metal brazing material containing an active metal. The active metal is preferably at least one selected from Ti (titanium), Nb (niobium), Zr (zirconium), and Hf (hafnium). The active metal brazing material preferably contains at least Ti. Also, the thickness of the joining layer is preferably 5 μm or more. More preferably, the thickness of the brazing material layer 5 is 10 μm or more and 200 μm or less. Even more preferably, the thickness of the brazing material layer 5 is 15 μm or more and 150 μm or less. If the brazing material layer 5 is thinner than 5 μm, sufficient joining strength may not be maintained. On the other hand, if the brazing material layer 5 is thicker than 200 μm, it may be a factor in increasing costs.

[0030] Next, the composition of each brazing material component and the joining method will be described. The content of Ag contained in the brazing material is preferably in the range of 0 mass% or more and 95 mass% or less. The content of Cu is preferably in the range of 3 mass% or more and 90 mass% or less. The total content of the active metal or active metal hydride is preferably in the range of 1 mass% or more and 15 mass% or less. The total content of Sn or In is preferably in the range of 1 mass% or more and 30 mass% or less. More preferably, the total content of Sn or In is in the range of 2 mass% or more and 15 mass% or less.

[0031] Ag or Cu is a component that becomes the main component of the brazing material layer 5. The active metal or active metal hydride is a component for reacting with the ceramic substrate 2 to obtain a strong joint. Sn or In has the effect of lowering the melting point of the active metal brazing material. The brazing material may also contain other inevitable impurities.

[0032] Carbon (C) may be added to the active metal brazing material in an amount of 0.1 mass% or more and 2 mass% or less. Also, one or more selected from tungsten (W), molybdenum (Mo), and rhenium (Re) may be added to the active metal brazing material in an amount of 0.1 mass% or more and 10 mass% or less. By adding carbon, tungsten, molybdenum, and rhenium, the fluidity of the active metal brazing material can be controlled. Manganese (Mn) may be added to the brazing material as needed.

[0033] The component ratio of the above active metal brazing material is the ratio when the total of each metal component is 100 mass%. For example, when titanium nitride powder is used, it is the mass% of titanium. Note that the mass of organic substances such as binders is not counted. In the joining method according to the embodiment, a brazing material paste having the above-described composition may be prepared and applied to the ceramic substrate, or a metal foil having the above-described composition may be used instead of the brazing material paste. Here, the method using the brazing material paste will be described. Each brazing material component is mixed, a binder and the like are added, and an active metal brazing material paste is prepared.

[0034] A variety of substrates can be applied to the ceramic substrate 2. Examples of the ceramic substrate include a silicon nitride substrate, an aluminum nitride substrate, an alumina substrate, a zirconia substrate, and an aldyl (a mixture of alumina and zirconia) substrate. The types of the substrates can also be classified into oxide-based ceramic substrates or nitride-based ceramic substrates. It is also possible to classify the types of the substrates according to metal components, such as a silicon-containing ceramic substrate, an aluminum-containing ceramic substrate, and a zirconium-containing ceramic.

[0035] The silicon nitride substrate and the aluminum nitride substrate are called nitride-based ceramic substrates. When a nitride-based ceramic and a copper plate are joined by an active metal bonding method, the active metal reacts with the nitride-based ceramic substrate to form an active metal nitride layer. When Ti is used as the active metal, a titanium nitride (TiN) layer is formed. The formation of this active metal nitride layer can improve the bonding strength between the ceramic substrate 2 and the copper plate 3.

[0036] The aluminum oxide substrate, the zirconium oxide substrate, and the aldyl substrate are called oxide-based ceramic substrates. When an oxide-based ceramic substrate and a copper plate are joined by an active metal bonding method, the active metal reacts with the oxide-based ceramic substrate to form an active metal oxide layer. When Ti is used as the active metal, a titanium oxide (TiO2) layer is formed. The formation of this active metal oxide layer can improve the bonding strength between the ceramic substrate 2 and the copper plate 3.

[0037] The joined body in which the ceramic substrate 2 and the copper plate 3 are joined may be an assembly substrate for taking out a plurality of divided parts, with two or more divided parts. By dividing the assembly substrate into a plurality of parts, individual joined bodies can be obtained. The joined body may further have a notch shape or a through hole for screwing or the like. That is, the shape of the ceramic copper circuit board 1 is not limited to a short shape as shown in the figure. Also, after producing a joined body by installing copper plates on both sides of the ceramic substrate and heating at 850 °C, it is preferable to obtain the ceramic copper circuit board 1 as shown in FIG. 1 by etching the surface copper plate.

[0038] The thickness of the copper member is preferably 0.3 mm or more. By increasing the thickness of the copper plate 3, the heat dissipation performance can be improved. Also, the current-carrying capacity can be increased. Therefore, the thickness of the copper plate is preferably 0.3 mm or more, more preferably 0.6 mm or more. The upper limit of the thickness of the copper plate is not particularly limited, but is preferably 5 mm or less. If it exceeds 5 mm, it may be difficult to impart a circuit shape by etching. It is preferable that both the thickness of the front copper plate 3 and the thickness of the back copper plate 4 are 0.3 mm or more.

[0039] Here, the "copper plate" includes copper alloy plates. The copper plate is preferably an oxygen-free copper plate. Oxygen-free copper has a copper purity of 99.96 wt% or more, as shown in JIS-H-3100. A film may be provided on the surface of the copper member, or a rust preventive agent may be applied. The rust preventive agent and the film may be provided partially or over the entire surface of the copper member. The copper plate may be given a predetermined shape such as a circuit shape before joining by punching or the like. Further, a rust preventive agent may be applied to the surface of the copper plate.

[0040] FIG. 1 shows an example in which the ceramic copper circuit board 1 has a three-layer structure of copper-ceramics-copper. The structure of the ceramic copper circuit board 1 is not limited to the illustrated example. For example, the ceramic copper circuit board 1 may have a structure of five layers or more, such as copper-ceramics-copper-ceramics-copper.

[0041] In the joining of a copper plate and a semiconductor element, it is preferable to use a paste containing one or more selected from silver and copper. More preferably, at least one of silver or copper is made the main component among the solid components. Here, the main component refers to a component occupying 50 wt% or more. A joining material containing 50 wt% or more of silver or copper is distinguished from general SnAg solder and SnCu solder. The paste used for joining to a semiconductor element preferably contains metal components other than copper or silver not exceeding the impurity level. More preferably, it is to use a silver paste or a copper paste. Even more preferably, it is to use a silver paste. Although the silver paste may cause ion migration, it is less likely to oxidize than copper. It is preferable because the reliability of the joining can be maintained. The copper paste is easily oxidized but ion migration is less likely to occur. Therefore, depending on the use of the ceramic copper circuit board 1, the paste may be used appropriately.

[0042] Here, the copper member - ceramic substrate - copper member has been described as an example of an embodiment of the present invention, but the structure of the ceramic copper circuit board 1 is not particularly limited. The ceramic copper circuit board 1 may have a structure such as copper member - ceramic substrate - copper member - ceramic substrate - copper member. The heat sink may be made of aluminum, such as in the case of copper member - ceramic substrate - aluminum member. The thickness of the heat sink and the thickness of the circuit portion (surface copper plate 3) may be different. The heat sink may have a shape integrated with the lead. That is, the copper member may protrude with respect to the ceramic substrate 2.

[0043] Next, a method for controlling the surface roughness will be described. First, prepare a ceramic copper circuit board 1. Next, measure the surface roughness of the copper member (copper surface plate 3) and check whether its surface roughness is within a preferable range. In general copper members, their surfaces are often smooth, and the average value of the average length RSm is less than 40 μm. In the process of preparing the ceramic copper circuit board 1, the surface roughness may be controlled by methods other than those exemplified below. For example, the resist removal process or the bonding process provided on the surface of the copper member may be devised so that the surface roughness is controlled to be within a preferable range. When the surface roughness is not within the preferable range, it is preferable to perform a process for controlling the surface property. The surface property control process may be performed without measuring the surface property. Examples of the method for controlling the surface property include abrasive paper, plasma treatment, etc.

[0044] Examples of the abrasive paper include sandpaper. When using sandpaper, it is preferable that its grain size (particle size) is 20 μm or more and 50 μm or less. Not only the grain size is controlled, but the surface roughness may be adjusted by changing the number of rubbing times in the same direction. The number of rubbing times is preferably 2 or more and 30 or less. The surface roughness can be controlled by rubbing the surface of the copper member with sandpaper. The surface becomes rougher by increasing the number of rubbing times or increasing the rubbing strength. Also, the larger the grain size, the rougher the surface after rubbing.

[0045] When performing plasma treatment, it is preferable to use argon (Ar) gas. Specifically, place the ceramic copper circuit board 1 in the treatment space and generate plasma of Ar gas. The surface of the copper member is exposed to the plasma, so that the surface becomes rougher. The plasma treatment may be performed at normal pressure or in a reduced-pressure atmosphere. Using plasma treatment is preferable because it may be possible to remove elements other than copper adhering to the surface of the copper member.

[0046] The surface properties of the copper member may be controlled by etching or chemical polishing. At this time, it is preferable to use a chemical solution with a controlled dissolution rate for the copper member. By using a chemical solution with a controlled dissolution rate and controlling the time for which the copper member is in contact with the chemical solution, the surface of the copper member can be more effectively controlled. The surface property control method is preferably any one selected from the methods described above, or two or more methods may be combined.

[0047] When joining semiconductor elements, the holding time for pressure sintering is preferably 100 seconds or more and 280 seconds or less. More preferably, the holding time is 120 seconds or more and 200 seconds or less. It is preferable that the holding time is within the above-mentioned range because it can reduce the variation in joining. Also, a reducing agent may be added to the joining layer between the copper member and the semiconductor element. The difference between the average length RSm of the roughness curve elements of the front copper plate 3 and the average length RSm of the roughness curve elements of the back copper plate 4 is preferably 100 μm or less.

[0048] Examples of semiconductor elements include Si elements, SiC elements, or GaN elements. Among these, either a SiC element or a GaN element is preferable. These semiconductor elements may be elements processed by a dicing saw.

[0049] (Examples) Examples of the present invention are shown below. First, copper plates are respectively disposed on both surfaces of a ceramic substrate via an active metal brazing material layer. The laminate is heated to join the copper plates to the ceramic substrate, thereby obtaining a ceramic copper circuit board. Among the ceramic copper circuit boards, the ceramic substrate is a silicon nitride substrate or an aluminum nitride substrate. The thickness of the copper plate was set to 0.3 mm or more and 1.0 mm or less. The thickness of the brazing material layer was set to 30 μm or more and 50 μm or less. The types of ceramic substrates, the thicknesses of the copper plates, and the thicknesses of the brazing material layers in the examples and comparative examples are as shown in Table 1.

[0050]

Table 1

[0051] In Examples 1-11 and Comparative Examples 1-2, the surface of the copper plate of the obtained bonded body was treated using sandpaper. The grain size of the sandpaper used in the examples was 20 μm to 50 μm. The surface of the copper plate was rubbed 2 to 30 times in substantially the same direction to roughen the surface of the copper plate. On the other hand, in Comparative Example 1, the surface of the copper member was rubbed 10 times using sandpaper with a grain size of 5 μm or less. In Comparative Example 2, the surface of the copper member was rubbed 20 times using sandpaper with a grain size of 100 μm or more.

[0052] In Examples 1-11 and Comparative Examples 1-2, the surface roughness of the copper (Cu) member was measured. The results obtained by measuring the surface roughness are shown in Table 2. SURFCOM 2000DX-23 manufactured by Tokyo Seimitsu Co., Ltd. was used for measuring the surface roughness. The surface roughness at five locations selected from the surface of the copper plate was measured. Each measurement location was separated from each other by 500 μm or more. Also, from the results of the five measurements, the values of RSm, Ra, Rv, and Rz were measured simultaneously. That is, four parameters of RSm, Ra, Rv, and Rz were measured simultaneously from one measurement location.

[0053] Table 2 shows the average value of RSm at five locations, the minimum value among the five RSm values, the average value of Ra at five locations, and the average value of Rv at five locations. Also, in the column of the minimum value of RSm, the value farthest from 145 μm (the average value of 40 μm and 250 μm within the range described in claim 1) is described in parentheses. In any of the examples, the measurement length was unified to 4.0 mm.

[0054]

Table 2

[0055] As can be seen from Table 2, in Examples 1-11, the average value of RSm at five locations was within the preferred range. In Examples 2-6, Example 8, and Example 11, the minimum value of RSm was within the preferred range. On the other hand, in Example 1, Example 7, Example 9, and Example 10, the minimum value of RSm was outside the preferred range.

[0056] In Examples 1 - 5, the average value of Ra at five locations was also within a suitable range. In Example 6, the average value of Ra was outside the preferred range. Furthermore, in Examples 1 - 5, the average value of Rv at five locations was also within a suitable range. In Example 6, the average value of Rv was outside the preferred range. Also, in Examples 1 - 5, at any measurement location, Rz was 10 μm or less. On the other hand, in Example 6, there were locations where Rz exceeded 10 μm.

[0057] Silver (Ag) paste was applied to the surface of a copper plate and dried. As shown in Figure 2, a silver (Ag) ribbon was mounted on the surface of the copper plate of the obtained ceramic copper circuit board, and pressure sintering was carried out. The bonding strength of the silver (Ag) ribbon was measured by a peel strength test. In the peel strength test, the silver ribbon was pulled vertically in the surface direction of the ceramic substrate, and the strength when the silver ribbon was peeled off from the copper plate was measured. An example where the peel strength of the silver ribbon was 4.0 or more was designated as "best". An example where the peel strength was 3.0 or more and less than 4 was designated as "better". An example where the peel strength was 2.0 or more and less than 3.0 was designated as "good". An example where the peel strength was less than 2.0 was designated as "bad".

[0058] The peel strength test was carried out using an MX2 series manufactured by IMADA Co., Ltd. (test speed: 60 mm / min), and the electrical signal obtained by the said apparatus was converted into a numerical value using a FGP - 5 (5 kgf) manufactured by Nidec - Shinpo Co., Ltd. The results are shown in Table 3.

[0059]

Table 3

[0060] As can be seen from Table 3, in the examples where the average value of RSm, the average value of Ra, and the average value of Rv were all within the preferred ranges, the peel strength was 4.0 or more in all cases. On the other hand, in Example 1 where the minimum value of RSm was outside the preferred range, the result of the peel strength test was 3.0 or more and less than 4.0. In Example 6 where the average values of Ra and Rv were outside the preferred ranges, the result of the peel strength test was 2.0 or more and less than 3.0. In Comparative Examples 1-2 where the average value of RSm, the average value of Rv, and the minimum value of RSm were outside the preferred ranges, the result of the peel strength test was less than 2.0.

[0061] As can be seen from the results of Table 2 and Table 3, it was found that the value of the surface roughness (especially RSm) greatly affects the peel strength in the bonding with the silver layer.

[0062] This is considered to be due to the following reasons. When the average length RSm of the roughness curve elements is less than 40 μm, the period of the unevenness on the surface of the copper plate is short. The brazing material does not sufficiently penetrate into the unevenness on the copper plate surface, and the bonding strength decreases. On the other hand, when the average length RSm exceeds 250 μm, since the period of the unevenness is long, a sufficient anchor effect does not act on the bonding layer in contact with the copper plate surface, and the bonding strength decreases. By having the average value of the average length RSm be 40 μm or more and 250 μm or less, the anchor effect on the bonding layer can be enhanced, and the bonding strength can be enhanced.

[0063] The control of the surface roughness is particularly useful when a ceramic copper circuit board and a semiconductor element are bonded using a silver paste.

[0064] In the embodiment of the present invention, the bonding layer between the silver ribbon and the copper plate was measured using a silver paste, but it is not limited thereto, and it may be lead-free solder or a copper paste. Further, a reducing agent may be added to the paste as necessary. Also, although the peel strength between the copper plate and the bonding layer was examined, any material bonded through the bonding layer may be used.

[0065] (Configuration 1) A ceramic substrate, A copper member joined to one surface of the ceramic substrate, and A ceramic copper circuit board, wherein when measuring the average length RSm of roughness curve elements at each of any five locations selected from the surface of the copper member, the average value of the five average lengths RSm is 40 μm or more and 250 μm or less. (Configuration 2) The ceramic copper circuit board according to claim 1, wherein the average value of the five average lengths RSm is 60 μm or more and 150 μm or less. (Configuration 3) The ceramic copper circuit board according to claim 1 or 2, wherein the minimum value of the five average lengths RSm is 30 μm or more. (Configuration 4) The ceramic copper circuit board according to any one of claims 1 to 3, wherein when measuring the arithmetic mean roughness Ra at each of the five locations, the average value of the five arithmetic mean roughnesses Ra is 0.1 μm or more and 0.7 μm or less. (Configuration 5) The ceramic copper circuit board according to any one of claims 1 to 4, wherein when measuring the maximum valley depth Rv of the roughness curve at each of the five locations, the average value of the five maximum valley depths Rv is 0.5 μm or more and 2 μm or less. (Configuration 6) Further comprising a brazing material layer for joining the ceramic substrate and the copper member, The ceramic copper circuit board according to any one of claims 1 to 5, wherein the brazing material layer contains one or more selected from silver, copper, and active metals. (Configuration 7) The ceramic copper circuit board according to any one of claims 1 to 6, wherein the main component of the ceramic substrate is one or more selected from silicon nitride, aluminum nitride, aluminum oxide, or zirconium oxide. (Configuration 8) The ceramic copper circuit board according to any one of claims 1 to 7, wherein the thickness of the copper member is 0.6 mm or more. (Configuration 9) A ceramic copper circuit board according to any one of claims 1 to 8, and A semiconductor element mounted on the copper member, A semiconductor device comprising the same. (Configuration 10) The ceramic copper circuit board according to any one of claims 1 to 8, A semiconductor element mounted on the copper member, A bonding layer for bonding the semiconductor element to the copper member, and a semiconductor device. The bonding layer contains silver or copper.

[0066] According to an embodiment of the present invention, there are provided a ceramic copper circuit board and a semiconductor device in which the average length RSm of the roughness curve elements on the surface of a copper member is controlled.

[0067] As described above, several embodiments of the present invention have been illustrated. However, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, changes, etc. can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the invention described in the claims and its equivalent scope. In addition, the above-described embodiments can be implemented in combination with each other.

Explanation of Reference Numerals

[0068] 1... Circuit board 2... Ceramic substrate 3... Copper member (front copper plate) 4... Copper member (back copper plate) 5... Brazing material layer (active metal brazing material layer) 6... Bonding layer (bonding layer using silver paste or copper paste) 7... Silver ribbon 8... Semiconductor element 9... Semiconductor device

Claims

1. A ceramic substrate, a copper member joined to one surface of the ceramic substrate, and a brazing material layer that joins the ceramic substrate and the copper member, wherein the brazing material layer contains at least an active metal, the thickness of the copper member is 0.3 mm or more and 5 mm or less, when the average length RSm of roughness curve elements is measured at each of any five locations selected from the surface of the copper member, the average value of the five average lengths RSm is 40 μm or more and 250 μm or less, and when the arithmetic mean roughness Ra is measured at each of the five locations, the average value of the five arithmetic mean roughnesses Ra is 0.1 μm or more and 0.7 μm or less, a ceramic copper circuit board.

2. The ceramic copper circuit board according to claim 1, wherein the average value of the five average lengths RSm is 60 μm or more and 150 μm or less.

3. The ceramic copper circuit board according to claim 1, wherein the minimum value of the five average lengths RSm is 30 μm or more.

4. The ceramic copper circuit board according to claim 1, wherein when the maximum valley depth Rv of the roughness curve is measured at each of the five locations, the average value of the five maximum valley depths Rv is 0.5 μm or more and 2 μm or less.

5. The ceramic copper circuit board according to claim 2, wherein the minimum value of the five average lengths RSm is 30 μm or more.

6. The ceramic copper circuit board according to claim 2, wherein when the maximum valley depth Rv of the roughness curve is measured at each of the five locations, the average value of the five maximum valley depths Rv is 0.5 μm or more and 2 μm or less.

7. The ceramic copper circuit board according to claim 5, wherein when the maximum valley depth Rv of the roughness curve is measured at each of the five locations, the average value of the five maximum valley depths Rv is 0.5 μm or more and 2 μm or less.

8. The ceramic copper circuit board according to claim 1, wherein when the arithmetic mean roughness Ra is measured at each of the five locations, any of the arithmetic mean roughnesses Ra is greater than 0 and 1.5 μm or less.

9. The ceramic copper circuit board according to claim 1, wherein the main component of the ceramic substrate is one or more selected from silicon nitride, aluminum nitride, aluminum oxide, or zirconium oxide.

10. The ceramic copper circuit board according to claim 5, wherein the main component of the ceramic substrate is one or more selected from silicon nitride, aluminum nitride, aluminum oxide, or zirconium oxide.

11. The ceramic copper circuit board according to claim 1, wherein the thickness of the copper member is 0.6 mm or more.

12. A ceramic copper circuit board according to any one of claims 1 to 11, a semiconductor element mounted on the copper member, and a semiconductor device comprising the same.

13. A ceramic copper circuit board according to any one of claims 1 to 11, a semiconductor element mounted on the copper member, and a bonding layer for bonding the semiconductor element to the copper member, wherein the bonding layer contains silver or copper, a semiconductor device.

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