Insulating circuit board

Abstract

The insulating circuit substrate (10) is one in which aluminum plates (12, 13) composed of aluminum or aluminum alloy are laminated and joined to the surface of a ceramic substrate (11), in the aluminum plates (12, 13), Cu is solid-solubilized at the joining interface with the ceramic substrate (11), and the ratio B / A of the Cu concentration B mass% at a position 100 μm in the thickness direction from the joining interface toward the aluminum plate (12, 13) side to the Cu concentration A mass% at the joining interface is 0.30 or greater and 0.85 or less.

Description

Technical Field

[0001] This invention relates to an insulating circuit board made by bonding a ceramic substrate and an aluminum plate made of aluminum or an aluminum alloy.

[0002] This application claims priority based on Japanese Patent Application No. 2020-047956 filed on March 18, 2020 and Japanese Patent Application No. 2021-040435 filed on March 12, 2021, the contents of which are incorporated herein by reference. Background Technology

[0003] The power module, LED module, and thermoelectric module are configured such that power semiconductor elements, LED elements, and thermoelectric elements are bonded to an insulating circuit board. In the insulating circuit board, a circuit layer composed of conductive material is formed on one side of the insulating layer.

[0004] Furthermore, in the aforementioned insulating circuit board, a substrate with a structure in which a metal plate with excellent conductivity is bonded to one side of a ceramic substrate as a circuit layer, and a metal plate with excellent heat dissipation is bonded to the other side to form a metal layer is also provided.

[0005] Furthermore, in order to effectively dissipate heat generated from components mounted on the circuit layer, an insulating circuit board with a heat sink is also provided, wherein a heat sink is bonded to the metal layer side of the insulating circuit board.

[0006] For example, the insulating circuit board shown in Patent Document 1 is configured to have an insulating circuit board having a circuit layer made of aluminum plate formed on one side of a ceramic substrate and a metal layer made of aluminum plate formed on the other side, and a semiconductor element bonded to the circuit layer by solder.

[0007] Here, Al-Si solder is typically used when bonding ceramic substrates to aluminum plates that serve as circuit and metal layers.

[0008] Here, for the aforementioned insulating circuit board, even under load thermal cycling conditions, it is necessary to fully ensure the reliability of the connection.

[0009] Therefore, Patent Document 2 proposes the following technology: the technology has a process of bonding Cu to at least one side of the bonding surface of the ceramic substrate and the aluminum plate to form a Cu layer, and a process of pressurizing and heating the ceramic substrate and the aluminum plate stacked through the Cu layer in the stacking direction, so as to more firmly bond the ceramic substrate and the aluminum plate.

[0010] In this patent document 2, Cu diffuses to the aluminum plate side, and the Cu concentration within 50 μm from the bonding interface is in the range of 0.05 to 5 wt%. An Al-Cu eutectic phase is formed at the width end of the aluminum plate, and the bonding reliability is excellent.

[0011] However, recently, high-temperature semiconductor devices have been provided, which are made of semiconductor elements such as SiC and operate at higher temperatures than before.

[0012] Therefore, the aforementioned insulating circuit board will be used in more demanding environments than before, requiring it to suppress the cracking of the ceramic substrate and the deformation of the circuit layers even under severe thermal cycling conditions.

[0013] Patent Document 1: Japanese Patent No. 3171234

[0014] Patent Document 2: Japanese Patent No. 5359953 Summary of the Invention

[0015] The present invention was made in view of the above circumstances, and its object is to provide an insulating circuit board that can suppress the cracking of the ceramic substrate and the deformation of the aluminum plate even under severe thermal cycling, and has excellent bonding reliability between the ceramic substrate and the circuit layer.

[0016] To address the aforementioned issues, one aspect of the present invention relates to an insulating circuit substrate comprising an aluminum plate composed of aluminum or an aluminum alloy laminated and bonded to the surface of a ceramic substrate. The invention is characterized in that, in the aluminum plate, Cu is fused at the interface with the ceramic substrate, and the ratio of the Cu concentration B (mass%) at a position 100 μm along the thickness direction from the interface to the aluminum plate to the Cu concentration A (mass%) at the interface, B / A, is 0.30 or more and 0.85 or less.

[0017] The insulating circuit board has a ceramic substrate and an aluminum plate made of aluminum or aluminum alloy, and the aluminum plate is laminated and bonded on the surface of the ceramic substrate.

[0018] According to the insulating circuit board with this configuration, Cu is solidified at the interface between the aluminum plate and the ceramic substrate. The ratio of the Cu concentration B (mass%) at a position 100 μm along the thickness direction from the interface towards the aluminum plate to the Cu concentration A (mass%) at the interface, B / A, is 0.30 or more and 0.85 or less. Therefore, Cu diffuses sufficiently into the interior of the aluminum plate composed of aluminum or aluminum alloy, and a region of Cu supersaturation solidification is formed near the interface of the aluminum plate. Therefore, deformation of the aluminum plate and the formation of cracks within the aluminum plate after thermal cycling can be suppressed.

[0019] Furthermore, Cu is dissolved in the parent phase of Al, so a harder Al-Cu eutectic phase is not formed, which can suppress cracking of the ceramic substrate.

[0020] In this embodiment of the invention, the insulating circuit board in the aluminum plate has a Cu concentration B at a position 100 μm along the thickness direction from the bonding interface, preferably in the range of 0.04% by mass or more and 0.96% by mass or less.

[0021] At this point, Cu diffuses sufficiently into the interior of the aluminum plate, and a region of Cu supersaturation solid solution is fully formed near the joint interface of the aluminum plate. Therefore, deformation of the aluminum plate and the formation of cracks within the aluminum plate after thermal cycling can be further suppressed.

[0022] Furthermore, preferably, in the insulating circuit substrate according to one aspect of the present invention, after performing 2000 cycles of thermal cycling, in which the temperature is maintained at -65°C for 5 minutes and at 150°C for 5 minutes as one cycle, Al-Cu compound particles containing Al and Cu are precipitated in the grain boundaries and grains of the aluminum plate in the region from the bonding interface to 100 μm in the thickness direction of the aluminum plate.

[0023] At this point, the joint interface of the aluminum plate is strengthened by Al-Cu compound particles, which can reliably suppress the deformation of the aluminum plate after thermal cycling and the generation of cracks within the aluminum plate.

[0024] Furthermore, in the insulating circuit substrate according to one aspect of the present invention, within a thickness direction of 50 μm from the bonding interface toward the aluminum plate side, the number density of the Al-Cu compound particles precipitated after undergoing 2000 cycles of thermal cycling, with each cycle consisting of holding at -65°C for 5 minutes and holding at 150°C for 5 minutes, is preferably 0.50 particles / μm. 2 Above and 8.50 per μm 2 Within the following range.

[0025] At this point, within a 50 μm thickness range from the bonding interface toward the aluminum plate side, after 2000 cycles of thermal cycling (one cycle being held at -65°C for 5 minutes and the other at 150°C for 5 minutes), the number density of the precipitated Al-Cu compound particles is 0.50 particles / μm. 2 Therefore, the deformation resistance of the aluminum plate near the joint interface is increased, which can further suppress the deformation of the aluminum plate. Furthermore, the number density of the Al-Cu compound particles is 8.50 particles / μm. 2 Therefore, the aluminum plate near the bonding interface will not harden excessively, which can further suppress the cracking of the ceramic substrate.

[0026] Furthermore, in the insulating circuit board according to one aspect of the present invention, the average value of the equivalent circular diameter of the Al-Cu compound particles precipitated after performing 2000 cycles of thermal cycling, in which the temperature is maintained at -65°C for 5 minutes and at 150°C for 5 minutes as one cycle, is preferably in the range of 30 nm or more and 130 nm or less.

[0027] At this point, after 2000 cycles of thermal cycling (holding at -65°C for 5 minutes and then at 150°C for 5 minutes as one cycle), the average equivalent circle diameter of the precipitated Al-Cu compound particles is within the aforementioned range. Therefore, it is possible to fully precipitate the aluminum plate near the reinforced interface, further suppressing deformation of the aluminum plate.

[0028] Furthermore, in the insulating circuit board according to one aspect of the present invention, the area ratio of the Al-Cu eutectic phase in a range of 1 mm from the end of the width direction of the interface between the aluminum plate and the ceramic substrate is preferably 30% or less.

[0029] At this point, at the interface between the aluminum plate and the ceramic substrate, the area ratio of the Al-Cu eutectic phase is limited to less than 30%, thus there is less of the harder Al-Cu eutectic phase, which can suppress the cracking of the ceramic substrate.

[0030] According to one aspect of the present invention, an insulating circuit board can be provided that can suppress cracking of the ceramic substrate and deformation of the circuit layer (metal layer) even under severe thermal cycling conditions, and has excellent bonding reliability between the ceramic substrate and the circuit layer (metal layer). Attached Figure Description

[0031] Figure 1 This is a schematic diagram illustrating a power module using an insulating circuit board according to an embodiment of the present invention.

[0032] Figure 2 This is an enlarged illustration of the interface between the circuit layer (metal layer) of the insulating circuit board and the ceramic substrate according to an embodiment of the present invention.

[0033] Figure 3 These are photographs showing the interface between the circuit layer (aluminum plate) and the metal layer (aluminum plate) of the insulating circuit board according to an embodiment of the present invention and the ceramic substrate. Figure 3 (a) is before the heating and cooling cycle load. Figure 3 (b) is after the cooling and heating cycle load.

[0034] Figure 4 yes Figure 3 (b) is an enlarged photograph.

[0035] Figure 5 It is a display Figure 1 The flowchart shows the manufacturing method of the insulating circuit board and power module.

[0036] Figure 6 This is an explanatory diagram showing a method for manufacturing an insulating circuit board according to an embodiment of the present invention. Detailed Implementation

[0037] The embodiments of the present invention will now be described with reference to the accompanying drawings.

[0038] Figure 1 This illustrates an insulating circuit board 10 according to an embodiment of the present invention and a power module 1 using the insulating circuit board 10.

[0039] Figure 1 The power module 1 shown includes: an insulating circuit board 10, and a solder layer 2 bonded to one side of the insulating circuit board 10 (in... Figure 1 The semiconductor element 3 (located on the upper side) and the semiconductor element 3 disposed on the other side of the insulating circuit board 10 (in the middle). Figure 1 Heat sink 31 (located on the lower side).

[0040] The solder layer 2 is, for example, a Sn-Ag, Sn-Cu, Sn-In, or Sn-Ag-Cu solder material (so-called lead-free solder material).

[0041] Semiconductor element 3 is an electronic component that has semiconductors, and various semiconductor elements can be selected according to the required functions.

[0042] like Figure 1 As shown, the insulating circuit board 10 includes: a ceramic substrate 11, and a side disposed on the ceramic substrate 11 (in... Figure 1 The circuit layer 12 (top) and the circuit layer formed on the other side of the ceramic substrate 11 (on the top). Figure 1 The metal layer 13 (with the middle layer below) is located below.

[0043] The ceramic substrate 11 prevents electrical connections between the circuit layer 12 and the metal layer 13, and is made of highly insulating Si3N4 (silicon nitride). Furthermore, the thickness of the ceramic substrate 11 is set within the range of 0.2 mm or more and 1.5 mm or less; in this embodiment, it is set to 0.32 mm.

[0044] The circuit layer 12 is formed by bonding an aluminum plate 22, which is made of aluminum or an aluminum alloy, to one side of the ceramic substrate 11.

[0045] In this embodiment, the circuit layer 12 is formed by bonding an aluminum plate 22, made of an aluminum plate with a purity of 99.99% by mass or higher (so-called 4N aluminum), to a ceramic substrate 11.

[0046] The metal layer 13 is formed by bonding an aluminum plate 23 to the other side of the ceramic substrate 11.

[0047] In this embodiment, similar to the circuit layer 12, the metal layer 13 is formed by bonding an aluminum plate 23, made of an aluminum plate with a purity of 99.99% by mass or more (so-called 4N aluminum), to the ceramic substrate 11.

[0048] The heat sink 31 is used to dissipate heat from the insulating circuit board 10 side. The heat sink 31 is made of aluminum or an aluminum alloy with good thermal conductivity; in this embodiment, it is made of A6063 alloy. The thickness of the heat sink 31 is set in the range of 3 mm or more and 10 mm or less.

[0049] In addition, the heat sink 31 is bonded to the metal layer 13 of the insulating circuit board 10 using solder.

[0050] Moreover, in this embodiment, such as Figure 2 As shown, in the circuit layer 12 and the metal layer 13, Cu is solidified at the interface with the ceramic substrate 11. The ratio of the Cu concentration B (mass%) at a position 100 μm along the thickness direction from the interface to the circuit layer 12 and the metal layer 13 to the Cu concentration A (mass%) at the interface is B / A, which is 0.30 or more and 0.85 or less.

[0051] That is, Cu is also present at a position 100 μm along the thickness direction from the bonding interface toward the circuit layer 12 and the metal layer 13.

[0052] If the B / A ratio is less than 0.30, the bonding interface may harden and the bonding reliability may deteriorate, or Cu may not diffuse sufficiently into the circuit layer 12 (metal layer 13), resulting in deformation and cracking in the circuit layer 12 (metal layer 13).

[0053] If the B / A ratio exceeds 0.85, Cu may diffuse excessively, causing the circuit layer 12 (metal layer 13) to harden as a whole, which will be unable to alleviate the stress on the circuit layer during temperature cycling and may lead to cracking.

[0054] Furthermore, the upper limit of the ratio B / A of the Cu concentration B mass% at a position 100 μm along the thickness direction from the bonding interface toward the circuit layer 12 and the metal layer 13 to the Cu concentration A mass% at the bonding interface is preferably 0.70 or less, and more preferably 0.50 or less.

[0055] In this embodiment, the Cu concentration B at a position 100 μm along the thickness direction from the bonding interface in the circuit layer 12 and the metal layer 13 is preferably in the range of 0.04% by mass or more and 0.96% by mass or less.

[0056] Furthermore, the lower limit of the Cu concentration B at a position 100 μm along the thickness direction from the bonding interface is more preferably 0.10% by mass or more, and even more preferably 0.14% by mass or more. On the other hand, the upper limit of the Cu concentration B at a position 100 μm along the thickness direction from the bonding interface is more preferably 0.50% by mass or less, and even more preferably 0.45% by mass or less.

[0057] Furthermore, in this embodiment, the area ratio of the Al-Cu eutectic phase within a range of 1 mm from the end of the interface between the circuit layer 12 and the metal layer 13 and the ceramic substrate 11 in the width direction toward the center is preferably limited to 30% or less.

[0058] Furthermore, the area fraction of the Al-Cu eutectic phase at the interface between the circuit layer 12 and the metal layer 13 and the ceramic substrate 11 is more preferably 20% or less, and even more preferably 17% or less. The lower limit of the area fraction of the Al-Cu eutectic phase can be 0%, and the area fraction of the Al-Cu eutectic phase can also be 6.2% or more.

[0059] Furthermore, in this embodiment, after performing 2000 cycles of hot and cold cycling, with each cycle consisting of holding at -65°C for 5 minutes and holding at 150°C for 5 minutes, Al-Cu compound particles 15 containing Al and Cu are preferably precipitated in the grain boundaries and grains of the circuit layer 12 and the metal layer 13 in the region extending 100 μm along the thickness direction from the interface between the circuit layer 12 and the metal layer 13.

[0060] Here, Figure 3 and Figure 4 The image shows the observation results of the bonding interface between the circuit layer 12 and the metal layer 13 of the insulating circuit board 10 of this embodiment and the ceramic substrate 11.

[0061] like Figure 3 As shown in (a), in the state before the load cooling and heating cycle, there are no Al-Cu compound particles 15 in the circuit layer 12 and the metal layer 13, and the structure is composed of Cu solidified in the Al parent phase.

[0062] After performing 2000 cycles of hot and cold cycling, with each cycle consisting of holding the temperature at -65°C for 5 minutes and holding it at 150°C for 5 minutes, as... Figure 3 (b) and Figure 4 As shown, the grains are refined, and Al-Cu compound particles containing Al and Cu were identified at the grain boundaries and within the grains 15.

[0063] In this embodiment, within a thickness direction of 50 μm from the bonding interface toward the circuit layer 12 and the metal layer 13, the number density of Al-Cu compound particles 15 precipitated after 2000 cycles of thermal cycling (holding at -65°C for 5 minutes and at 150°C for 5 minutes as one cycle) is preferably 0.50 particles / μm. 2 Above and 8.50 per μm 2 Within the following range.

[0064] Furthermore, the number density of Al-Cu compound particles 15 is more preferably 0.60 particles / μm. 2 The above is further preferred to be 0.75 particles / μm. 2 That's all. Furthermore, the number density of Al-Cu compound particles 15 is more preferably 8.30 particles / μm. 2 The following is a further preferred value of 8.10 particles / μm. 2 In this embodiment, Al-Cu compound particles with a particle size of 0.01 μm or more and 2 μm or less are used as the target, and the number density is calculated. Furthermore, in the calculation of the number density, if the particle shape is not spherical, the shortest portion (minor axis) is determined as the particle size.

[0065] Furthermore, in this embodiment, the average equivalent circle diameter of the Al-Cu compound particles 15 precipitated after 2000 cycles of hot and cold cycling, in which the temperature is maintained at -65°C for 5 minutes and at 150°C for 5 minutes as one cycle, is preferably in the range of 30 nm or more and 130 nm or less.

[0066] Furthermore, the average equivalent circular diameter of the Al-Cu compound particles 15 is more preferably 37 μm or more, and even more preferably 45 μm or more. The average equivalent circular diameter of the Al-Cu compound particles 15 is more preferably 125 μm or less, and even more preferably 120 μm or less.

[0067] Next, use Figure 5 and Figure 6 The method for manufacturing the insulating circuit board 10 and the power module 1 of this embodiment will be described.

[0068] (Cu layer formation process S01)

[0069] First, such as Figure 5 and Figure 6 As shown, a Cu layer 26 is formed on at least one of the bonding surfaces of the aluminum plate 22 (serving as circuit layer 12) and the aluminum plate 23 (serving as metal layer 13) with the ceramic substrate 11. In this embodiment, as... Figure 6As shown, Cu layers 26 are formed on both sides of the ceramic substrate 11. In addition, there are no particular restrictions on the method of forming Cu layers 26, and existing methods such as sputtering, evaporation, CVD, electroplating, paste, and foil can be used appropriately.

[0070] Here, the Cu bonding amount in Cu layer 26 is preferably set at 0.08 mg / cm³. 2 Above and 2.0 mg / cm 2 Within the following range.

[0071] (Lamination process S02)

[0072] Next, an aluminum plate 22, which serves as a circuit layer 12, is stacked on one side of the ceramic substrate 11 through a Cu layer 26, and an aluminum plate 23, which serves as a metal layer 13, is stacked on the other side of the ceramic substrate 11 through a Cu layer 26.

[0073] (Jointing process S03)

[0074] Next, the stack of aluminum plate 22 (as circuit layer 12), ceramic substrate 11, and aluminum plate 23 (as metal layer 13) is placed into a vacuum heating furnace under pressure in the stacking direction using a pressurizing device. The aluminum plate 22 is bonded to the ceramic substrate 11 to form the circuit layer 12, and the aluminum plate 23 is bonded to the ceramic substrate 11 to form the metal layer 13.

[0075] Here, in the bonding process S03, the pressure load in the lamination direction is set within the range of 0.098 MPa or more and 2.94 MPa or less.

[0076] Furthermore, the bonding temperature is set within the range of 600°C to 650°C, and the holding time at the bonding temperature is set to 180 minutes or less.

[0077] Furthermore, the heating rate from the eutectic temperature of Al and Cu (548°C) to the bonding temperature is set to a range of 5°C / min or more and 20°C / min or less.

[0078] Through the above processes, the insulating circuit board 10 of this embodiment is manufactured.

[0079] (Heat sink bonding process S04)

[0080] Next, on the other side of the metal layer 13 of the insulating circuit board 10, a heat sink 31 is laminated with solder, and the insulating circuit board 10 and the heat sink 31 are placed in a vacuum heating furnace under pressure in the lamination direction to join the metal layer 13 and the heat sink 31.

[0081] (Semiconductor device bonding process S05)

[0082] Next, on one side of the circuit layer 12, the semiconductor element 3 is stacked with solder material (solder layer 2) and soldered in a heating furnace.

[0083] As described above, manufactured Figure 1 The power module 1 shown.

[0084] According to the insulating circuit board 10 of this embodiment configured as described above, Cu is solidified at the interface between the circuit layer 12 and the metal layer 13 and the ceramic substrate 11. The ratio of the Cu concentration B (mass%) at a position 100 μm along the thickness direction from the interface towards the circuit layer 12 and the metal layer 13 to the Cu concentration A (mass%) at the interface, B / A, is 0.30 or more and 0.85 or less. Therefore, Cu sufficiently diffuses into the interior of the aluminum-based circuit layer 12 and the metal layer 13, forming a region of Cu supersaturation near the interface between the circuit layer 12 and the metal layer 13. Consequently, the circuit layer 12 and the metal layer 13 are strengthened, and deformation of the circuit layer 12 and the metal layer 13 and the formation of cracks within the circuit layer 12 and the metal layer 13 after thermal cycling are suppressed.

[0085] Furthermore, Cu is dissolved in the parent phase of Al, so a harder Al-Cu eutectic phase will not be formed, thereby suppressing the cracking of the ceramic substrate 11.

[0086] Furthermore, in this embodiment, when the area ratio of the Al-Cu eutectic phase in the range of 1 mm from the end of the interface between the circuit layer 12 and the metal layer 13 and the ceramic substrate 11 in the width direction toward the center is 30% or less, there is less hard Al-Cu eutectic phase, which can suppress the cracking of the ceramic substrate 11.

[0087] In this embodiment, when the Cu concentration B at a position 100 μm along the thickness direction from the interface between the circuit layer 12 and the metal layer 13 and the ceramic substrate 11 is in the range of 0.04% by mass or more and 0.96% by mass or less, Cu diffuses sufficiently into the interior of the circuit layer 12 and the metal layer 13, which can further suppress the deformation of the circuit layer 12 and the metal layer 13 after thermal cycling and the generation of cracks in the circuit layer 12 and the metal layer 13.

[0088] In this embodiment, after 2000 cycles of thermal cycling, with each cycle consisting of holding at -65°C for 5 minutes and holding at 150°C for 5 minutes, Al-Cu compound particles 15, comprising Al and Cu, precipitate at the grain boundaries and within the grains of the circuit layer 12 and metal layer 13 in the region extending 100 μm along the thickness direction from the interface between the circuit layer 12 and metal layer 13 and the ceramic substrate 11. Therefore, the area near the interface between the circuit layer 12 and metal layer 13 and the ceramic substrate 11 is strengthened by the Al-Cu compound particles 15. Thus, deformation of the circuit layer 12 and metal layer 13 and the formation of cracks within the circuit layer 12 and metal layer 13 after thermal cycling can be reliably suppressed.

[0089] In this embodiment, within a thickness direction of 50 μm from the bonding interface toward the circuit layer 12 and the metal layer 13, after undergoing 2000 cycles of thermal cycling (one cycle being holding at -65°C for 5 minutes and the other at 150°C for 5 minutes), the number density of Al-Cu compound particles precipitated is 0.50 particles / μm. 2 Above and 8.50 per μm 2 Within the following ranges, the deformation resistance near the interface between the circuit layer 12 and the metal layer 13 is increased, which can further suppress the deformation of the circuit layer 12 and the metal layer 13. Furthermore, the area near the interface between the circuit layer 12 and the metal layer 13 will not become excessively hardened, which can further suppress the cracking of the ceramic substrate 11.

[0090] In this embodiment, when the average equivalent circle diameter of the Al-Cu compound particles 15 is in the range of 30 nm or more and 130 nm or less, sufficient precipitation can be made to strengthen the portion near the bonding interface between the circuit layer 12 and the metal layer 13, thereby further suppressing the deformation of the circuit layer 12 and the metal layer 13.

[0091] The embodiments of the present invention have been described above, but the present invention is not limited thereto. Appropriate modifications can be made without departing from the technical requirements of the present invention.

[0092] For example, in this embodiment, the case where the ceramic substrate is made of silicon nitride has been described, but it is not limited to this. It can be made of aluminum oxide or aluminum nitride.

[0093] Furthermore, this embodiment describes the case where a power module is constructed by mounting power semiconductor elements on the circuit layer of an insulating circuit board, but it is not limited to this. For example, an LED module can be constructed by mounting LED elements on an insulating circuit board, or a thermoelectric module can be constructed by mounting thermoelectric elements on the circuit layer of an insulating circuit board.

[0094] Furthermore, in this embodiment, the case of joining the insulating circuit board (metal layer) and the heat sink by brazing has been described, but it is not limited to this, and other joining methods such as solid-phase diffusion bonding and transient liquid-phase diffusion bonding (TLP) can also be applied.

[0095] Furthermore, in this embodiment, the case where the heat sink is made of aluminum has been described, but it is not limited to this; it can be made of copper or the like, and may also have internal flow paths for the cooling medium. Additionally, a buffer layer, for example, made of 4N aluminum, may be provided between the heat sink and the insulating circuit board.

[0096] Example

[0097] The results of the confirmation experiments conducted to verify the effectiveness of the present invention will be described below.

[0098] (Example 1)

[0099] Prepare a ceramic substrate (40mm × 40mm) as shown in Table 1. Form Cu layers on one and the other sides of the ceramic substrate by sputtering. The Cu adhesion amount is shown in Table 1.

[0100] Furthermore, an aluminum plate (37mm×37mm×thickness(t)0.4mm) composed of 4N aluminum is laminated on one side of the ceramic substrate through a Cu layer, and an aluminum plate (37mm×37mm×thickness(t)0.4mm) composed of 4N aluminum is laminated on the other side of the ceramic substrate through a Cu layer.

[0101] Furthermore, under the conditions shown in Table 1, an insulating circuit board was manufactured by bonding an aluminum plate and a ceramic substrate. Additionally, the heating rates listed in Table 1 are the rates of increase from the eutectic temperature of Al and Cu (548°C) to the bonding temperature.

[0102] A heat sink (a 50mm × 60mm, 5mm thick aluminum plate (A6063)) is bonded to the metal layer of the resulting insulating circuit board using a 4N aluminum (0.9mm thick) buffer layer, thereby obtaining an insulating circuit board with a heat sink. Furthermore, the bonding between the metal layer and the buffer layer, and between the buffer layer and the heat sink, is performed using Al-Si foil brazing.

[0103] Regarding the obtained insulating circuit board with heat sink, the Cu concentration A at the bonding interface of the aluminum plate, the Cu concentration B at a position 100 μm inside the aluminum plate from the bonding interface, the initial bonding rate, the presence of Al-Cu compound particles after the thermal cycling test, the bonding rate after the thermal cycling test, and the presence of cracks in the substrate after the thermal cycling test were evaluated.

[0104] (Cu concentration A, Cu concentration B)

[0105] An insulating circuit board with heat sinks was cut along the stacking direction to form a cross-section. Using an electron probe microanalyzer (JXA-8530F, manufactured by JEOL Ltd.), at a magnification of 500x and an accelerating voltage of 15kV, Cu was quantitatively analyzed at the bonding interface and at a position 100μm from the bonding interface along the stacking direction within the observation area. In the observation region, the Cu concentration and its average were calculated at five points: the bonding interface and the position 100μm from the bonding interface. This yielded the Cu concentration A (mass%) at the bonding interface and the Cu concentration B (mass%) at the position 100μm from the bonding interface. The Cu concentration was calculated by setting the total Al and Cu concentrations (mass%) at these points to 100.

[0106] (Initial bonding rate)

[0107] The bonding rate between the aluminum plate and the ceramic substrate was evaluated. Specifically, in an insulated circuit board with a heat sink, the bonding rate at the interface between the aluminum plate and the ceramic substrate was evaluated using an ultrasonic flaw detector (FineSAT200 manufactured by Hitachi Power Solutions Co., Ltd.) and calculated using the following formula. Here, the initial bonding area refers to the area that should be bonded before bonding, i.e., the area of ​​the circuit layer. In the image after binarizing the ultrasonic flaw detector image, the peeling is represented by the white area within the bonding region; therefore, the area of ​​this white area is taken as the peeling area (non-bonding region area).

[0108] (Joint ratio) = {((Initial joint area) – (Non-joint area)) / (Initial joint area)} × 100

[0109] (Cold and hot cycling test)

[0110] Using a TSB-51 thermal shock tester manufactured by ESPEC Corp., an insulated circuit board with heat sink was subjected to 2000 cycles of -65°C for 5 minutes and then 150°C for 5 minutes in a fluid bath.

[0111] (Are Al-Cu compound particles present after the thermal cycling test?)

[0112] The insulating circuit board with heat sink, after the above-mentioned thermal cycling, was cut along the stacking direction. Then, in the cross-section at the center of the width direction of the board, the region containing the interface between the aluminum plate and the ceramic substrate (17μm×23μm) was observed using a scanning electron microscope (Gemini SEM 500 manufactured by Carl Zeiss) at a magnification of 5000x and an accelerating voltage of 5.0kV.

[0113] In this observation, SEM images and elemental maps (MAPs) of Cu and Al were obtained. In the SEM images, granular regions observed as white were identified, and the presence of Cu and Al in these regions was assessed as "present" (having) Al-Cu compound particles.

[0114] Furthermore, the presence or absence of Al-Cu compound particles was evaluated by observing the region extending 100 μm along the thickness direction from the interface of the aluminum plates.

[0115] (Bonding rate after thermal cycling test)

[0116] As described above, the heat sink-equipped insulating circuit board after thermal cycling test was evaluated using an ultrasonic flaw detector (FineSAT200 manufactured by Hitachi Power Solutions Co., Ltd.), and the bonding rate was calculated.

[0117] (Whether the substrate cracked after the thermal cycling test)

[0118] The presence of cracks in the heat-insulating circuit board with heat sink was evaluated using an ultrasonic flaw detector (FineSAT200 manufactured by Hitachi Power Solutions Co., Ltd.) after thermal cycling testing. Any crack found in the circuit layer, metal layer, or ceramic substrate was evaluated as "present" (cracked).

[0119] [Table 1]

[0120]

[0121] [Table 2]

[0122]

[0123] In Comparative Examples 1-4, the ratio of Cu concentration B (mass%) at a position 100 μm along the thickness direction from the bonding interface to Cu concentration A (mass%) at the bonding interface was less than 0.30 or greater than 0.85. In Comparative Examples 1-4, the bonding rate was low after the thermal cycling test, and cracks were found on the substrate after the thermal cycling test.

[0124] In contrast, in Examples 1-8 of the present invention, the ratio of Cu concentration B (mass%) at a position 100 μm along the thickness direction from the bonding interface to Cu concentration A (mass%) at the bonding interface, B / A, is 0.30 or more and 0.85 or less. In Examples 1-8 of the present invention, the bonding rate is sufficiently high even after thermal cycling tests, and no cracking is confirmed on the substrate.

[0125] (Example 2)

[0126] Prepare a ceramic substrate (40mm × 40mm) as shown in Table 3. Form Cu layers on one and the other sides of the ceramic substrate by sputtering. The Cu adhesion amount is shown in Table 3.

[0127] Furthermore, an aluminum plate (37mm×37mm×thickness(t)0.4mm) composed of 4N aluminum is laminated on one side of the ceramic substrate through a Cu layer, and an aluminum plate (37mm×37mm×thickness(t)0.4mm) composed of 4N aluminum is laminated on the other side of the ceramic substrate through a Cu layer.

[0128] Furthermore, under the conditions shown in Table 3, an insulating circuit board was manufactured by bonding an aluminum plate and a ceramic substrate.

[0129] Regarding the obtained insulating circuit board, the Cu concentration A at the bonding interface of the aluminum plate, the Cu concentration B at a position 100 μm inside the aluminum plate from the bonding interface, the initial bonding rate, the bonding rate after the thermal cycling test, and whether the substrate cracked after the thermal cycling test were evaluated in the same order as in Example 1.

[0130] Furthermore, the area ratio of the Al-Cu eutectic phase at the interface, the number density of Al-Cu compound particles after thermal cycling tests, and the average equivalent circle diameter of Al-Cu compound particles were evaluated in the following manner.

[0131] (Area fraction of Al-Cu eutectic phase at the interface)

[0132] At the bonding interface, a backscattered electron (BSE) image of the region extending 1 mm from the end in the width direction towards the center was obtained using a scanning electron microscope (Gemini SEM 500, manufactured by Carl Zeiss). This BSE image was then binarized. The area of ​​the Al-Cu eutectic phase and the area extending 1 mm from the end of the bonding interface were determined, and the area fraction of the Al-Cu eutectic phase at the bonding interface was calculated using the following formula.

[0133] (Area fraction of Al-Cu eutectic phase) = {(Area of ​​Al-Cu eutectic phase / (Area from the end to 1 mm towards the center)} × 100

[0134] (Number density of Al-Cu compound particles after thermal cycling test)

[0135] The insulating circuit board after the above-mentioned thermal cycling test was cut along the stacking direction. Then, the presence or absence of Al-Cu compound particles was confirmed in the cross-section at the center of the board's width direction using the method described above. In the area where Al-Cu compound particles were confirmed (within a 50 μm thickness range from the bonding interface towards the aluminum plate side), an angle-selective backscattered electron (ASB) image at 1000x magnification was obtained using a scanning electron microscope (Carl Zeiss Gemini SEM 500). The ASB image was then binarized to make the Al-Cu compound particles appear white.

[0136] Furthermore, the number density is calculated by measuring the number of Al-Cu compound particles and dividing by the area of ​​the measurement range. The number density is calculated for Al-Cu compound particles with a diameter of 0.01 μm or more and 2 μm or less. In cases where the particle shape is not spherical, the shortest portion (minor axis) is determined as the particle diameter. Additionally, if the shape of a particle is unclear due to factors such as some particles being outside the measurement range, that particle is excluded before further measurement.

[0137] (Average equivalent circle diameter of Al-Cu compound particles after thermal cycling test)

[0138] The ASB image was binarized using the same method as for the number density determination. Next, the area of ​​each Al-Cu compound particle within the measurement region was calculated, and the equivalent circle diameter was calculated from this area. The average equivalent circle diameter was then determined. This average value is shown in Table 4. Furthermore, when calculating the area, particles whose areas could not be calculated due to reasons such as some particles being outside the measurement range were excluded.

[0139] [Table 3]

[0140]

[0141] [Table 4]

[0142]

[0143] In Examples 11, 13, 15, 17, and 18 of this invention, within a 50 μm thickness range from the bonding interface toward the aluminum plate side, after 2000 cycles of thermal cycling (one cycle being held at -65°C for 5 minutes and the other at 150°C for 5 minutes) were performed, the number density of Al-Cu compound particles precipitated was 0.50 particles / μm. 2 Above and 8.50 per μm 2Within the following range: The average equivalent circular diameter of the Al-Cu compound particles is between 30 nm and 130 nm. At the bonding interface between the aluminum plate and the ceramic substrate, the area fraction of the Al-Cu eutectic phase within a 1 mm radius from the end of the bonding interface in the width direction is 30.0% or less. Even after thermal cycling tests, the bonding rate remains sufficiently high, and no cracking has been confirmed on the substrate.

[0144] Furthermore, in Example 12 of the present invention, the area fraction of the Al-Cu eutectic phase was 32.0%. In Example 14 of the present invention, the number density of Al-Cu compound particles after the thermal cycling test was 8.70 particles / μm. 2 Furthermore, the equivalent circle diameter of the Al-Cu compound particles is 27 nm. In Example 16 of this invention, the number density of Al-Cu compound particles after the thermal cycling test is 0.47 particles / μm. 2 Furthermore, the equivalent circle diameter of the Al-Cu compound particles is 133 nm. Compared to Examples 12, 14, and 16 of the present invention, in Examples 11, 13, 15, 17, and 18 of the present invention, the area fraction of the Al-Cu eutectic phase is less than 30.0%, and the number density of Al-Cu compound particles after the thermal cycling test is 0.50 particles / μm. 2 Above and 8.50 per μm 2 Within the following range, and the equivalent circle diameter of the Al-Cu compound particles is 30 nm or more and 130 nm or less. Compared with Examples 12, 14, and 16 of the present invention, in Examples 11, 13, 15, 17, and 18 of the present invention, a more superior bonding rate was confirmed.

[0145] The results of this embodiment confirm that, according to the present invention, an insulating circuit board can be provided that can suppress the cracking of the ceramic substrate or the deformation of the circuit layer (metal layer) even under harsh thermal cycling tests, and has excellent bonding reliability between the ceramic substrate and the circuit layer.

[0146] Industrial availability

[0147] The insulating circuit board of this embodiment is preferably applicable to power modules, LED modules and thermoelectric modules.

[0148] Symbol Explanation

[0149] 1 Power Module

[0150] 3 Semiconductor components

[0151] 10 Insulated circuit board

[0152] 11 Ceramic substrate

[0153] 12 Circuit Layers

[0154] 13 Metal Layers

[0155] 15 Al-Cu compound particles

[0156] 22 and 23 aluminum plates

Claims

1. An insulating circuit board, comprising an aluminum plate composed of aluminum or an aluminum alloy laminated and bonded to the surface of a ceramic substrate, characterized in that, In the aluminum plate, Cu is fused at the interface with the ceramic substrate. At the bonding interface and at a position 100 μm from the bonding interface along the stacking direction, with the sum of Al and Cu concentrations set to 100, the Cu concentration at five points and its average value are calculated. This allows us to calculate the Cu concentration A at the bonding interface and the Cu concentration B at a position 100 μm from the bonding interface. The units for Al concentration, Cu concentration, Cu concentration A, and Cu concentration B are all expressed as mass %. The ratio of Cu concentration B (mass%) at a position 100 μm along the thickness direction from the joint interface towards the aluminum plate side to the Cu concentration A (mass%) at the joint interface, B / A, is 0.30 or more and 0.85 or less. In the interface between the aluminum plate and the ceramic substrate, the area fraction of the Al-Cu eutectic phase within a 1 mm radius from the end of the interface in the width direction toward the center is less than 30%.

2. The insulating circuit board according to claim 1, characterized in that, In the aluminum plate, the Cu concentration B at a position 100 μm along the thickness direction from the joint interface is in the range of 0.04% by mass or more and 0.96% by mass or less.

3. The insulating circuit board according to claim 1 or 2, characterized in that, After performing 2000 cycles of hot and cold cycling, with each cycle consisting of holding at -65°C for 5 minutes and holding at 150°C for 5 minutes, Al-Cu compound particles containing Al and Cu precipitate in the region of the aluminum plate extending 100 μm in the thickness direction from the joint interface into the grain boundaries and grains of the aluminum plate.

4. The insulating circuit board according to claim 3, characterized in that, Within a 50 μm thickness range from the bonding interface toward the aluminum plate side, after 2000 cycles of thermal cycling (one cycle being held at -65°C for 5 minutes and the other at 150°C for 5 minutes), the number density of precipitated Al-Cu compound particles was 0.50 particles / μm. 2 Above and 8.50 per μm 2 Within the following range.

5. The insulating circuit board according to claim 3, characterized in that, After 2000 cycles of thermal cycling, in which the Al-Cu compound particles precipitated were kept at -65°C for 5 minutes and at 150°C for 5 minutes as one cycle, the average equivalent circular diameter of the precipitated particles was greater than 30 nm and less than 130 nm.

6. The insulating circuit board according to claim 4, characterized in that, After 2000 cycles of thermal cycling, in which the Al-Cu compound particles precipitated were kept at -65°C for 5 minutes and at 150°C for 5 minutes as one cycle, the average equivalent circular diameter of the precipitated particles was greater than 30 nm and less than 130 nm.

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