JP6973674B2 - Insulated circuit board - Google Patents

Description

The present invention relates to an insulating circuit board formed by joining a ceramic substrate and an aluminum plate made of aluminum or an aluminum alloy.

The power module, LED module, and thermoelectric module have a structure in which a power semiconductor element, an LED element, and a thermoelectric element are bonded to an insulating circuit board having a circuit layer made of a conductive material formed on one surface of the insulating layer. ..
Further, in the above-mentioned insulating circuit board, a metal plate having excellent conductivity is bonded to one surface of a ceramic substrate to form a circuit layer, and a metal plate having excellent heat dissipation is bonded to the other surface to form a metal. Layered structures are also provided.
Further, in order to efficiently dissipate heat generated from an element or the like mounted on the circuit layer, an insulated circuit board with a heat sink in which a heat sink is bonded to the metal layer side of the insulated circuit board is also provided.

For example, in the insulating circuit board shown in Patent Document 1, an insulating circuit board in which a circuit layer made of an aluminum plate is formed on one surface of a ceramics substrate and a metal layer made of an aluminum plate is formed on the other surface. The structure is provided with a semiconductor element bonded to the circuit layer via a solder material.
Here, when joining the ceramic substrate and the aluminum plate to be the circuit layer and the metal layer, an Al—Si brazing material is usually used.

Here, it is necessary to sufficiently secure the joining reliability of the above-mentioned insulated circuit board even when a thermal cycle is applied.
Therefore, in Patent Document 2, Cu is fixed to at least one of the joint surfaces of the ceramic substrate and the aluminum plate to form a Cu layer, and the ceramic substrate and the aluminum plate laminated via the Cu layer are added in the stacking direction. A technique has been proposed in which a ceramic substrate and an aluminum plate are more firmly bonded to each other by pressing and heating.
In Patent Document 2, Cu is diffused toward the aluminum plate, and the Cu concentration within the range of 50 μm from the bonding interface is within the range of 0.05 to 5 wt%, and the Cu concentration is set to the widthwise end of the aluminum plate. Has a eutectic phase of Al and Cu, and has excellent bonding reliability.

Japanese Patent No. 3171234 Japanese Patent No. 5359953

By the way, recently, a high-temperature semiconductor device in which a semiconductor element is made of SiC or the like and operates at a higher temperature than before has been provided.
For this reason, the above-mentioned insulated circuit board is used in a harsher environment than before, and even when a harsh thermal cycle is applied, cracking of the ceramic substrate and deformation of the circuit layer are suppressed. Is required to do.

The present invention has been made in view of the above-mentioned circumstances, and can suppress cracking of the ceramic substrate, deformation of the aluminum plate, etc. even when a severe thermal cycle is applied, and the ceramic substrate and the circuit layer can be combined with each other. It is an object of the present invention to provide an insulated circuit board having excellent joining reliability.

In order to solve the above-mentioned problems, the insulating circuit board of the present invention is an insulating circuit board in which an aluminum plate made of aluminum or an aluminum alloy is laminated and bonded to the surface of a ceramics substrate, and the aluminum plate is formed. Cu is solid-dissolved at the bonding interface with the ceramic substrate, and the total concentration (mass%) of Al and Cu is 100 at the bonding interface and at a position 100 μm from the bonding interface in the stacking direction. In this way, the Cu concentration at each of the five points and the average value thereof are obtained, the Cu concentration A (mass%) at the bonding interface and the Cu concentration B (mass%) at a position 100 μm from the bonding interface are calculated, and the Cu concentration B (mass%) at the bonding interface is calculated. It is characterized in that the ratio B / A of the Cu concentration Mass% and the Cu concentration Bmass% at a position 100 μm in the thickness direction from the bonding interface to the aluminum plate side is 0.30 or more and 0.85 or less.

According to the insulating circuit board having this configuration, Cu is solid-dissolved on the bonding interface side of the aluminum plate with the ceramics substrate, and the Cu concentration Mass% at the bonding interface and the thickness from the bonding interface to the aluminum plate side. Since the ratio B / A to the Cu concentration Bmass% at the position of 100 μm in the vertical direction is 0.30 or more and 0.85 or less, Cu is sufficiently diffused into the inside of the aluminum plate made of aluminum or an aluminum alloy. A region in which Cu is oversaturated is formed in the vicinity of the bonding interface of the aluminum plate. Therefore, it is possible to suppress the deformation of the aluminum plate and the occurrence of cracks in the aluminum plate after the load of the thermal cycle.
Further, since Cu is solid-solved in the matrix phase of Al, a hard eutectic phase of Al—Cu is not formed, and the occurrence of cracking of the ceramic substrate can be suppressed.

Here, in the insulating circuit board of the present invention, in the aluminum plate, the Cu concentration B at a position 100 μm in the thickness direction from the bonding interface is within the range of 0.04 mass% or more and 0.96 mass% or less. Is preferable.
In this case, Cu is sufficiently diffused toward the inside of the aluminum plate, and a region in which Cu is supersaturated and solid-solved is sufficiently formed in the vicinity of the bonding interface of the aluminum plate. Therefore, it is possible to further suppress the deformation of the aluminum plate and the occurrence of cracks in the aluminum plate after the load of the cold cycle.

Further, in the insulating circuit substrate of the present invention, after 2000 times of a thermal cycle in which holding at −65 ° C. for 5 minutes and holding at 150 ° C. for 5 minutes as one cycle is performed 2000 times, the thickness direction from the bonding interface of the aluminum plate. It is preferable that Al—Cu compound particles containing Al and Cu are precipitated in the crystal grain boundaries and crystal grains of the aluminum plate in a region of up to 100 μm.
In this case, the vicinity of the joint interface of the aluminum plate is reinforced by the Al—Cu compound particles, and it is possible to reliably suppress the deformation of the aluminum plate and the occurrence of cracks in the aluminum plate after the cold cycle load.

Further, in the insulating circuit substrate of the present invention, a cold cycle in which holding at −65 ° C. for 5 minutes and holding at 150 ° C. for 5 minutes is one cycle within a range of 50 μm in the thickness direction from the bonding interface to the aluminum plate side. The number density of the Al—Cu compound particles precipitated after 2000 times is preferably in the range of ^{0.50 / μm 2} or more and 8.50 / μm ^{2 or less.}
In this case, it precipitates after 2000 times of a thermal cycle in which holding at −65 ° C. for 5 minutes and holding at 150 ° C. for 5 minutes as one cycle within a range of 50 μm in the thickness direction from the bonding interface to the aluminum plate side. Since the number density of the Al—Cu compound particles is 0.50 / μm ² or more, the deformation resistance of the aluminum plate near the bonding interface increases, and the deformation of the aluminum plate can be further suppressed. Further, since the number density of the Al—Cu compound particles is 8.50 particles / μm ² or less, the aluminum plate near the bonding interface does not become harder than necessary, and cracking of the ceramic substrate can be further suppressed. can.

Further, in the insulating circuit board of the present invention, the circle-equivalent diameter of the Al-Cu compound particles precipitated after 2000 times of a cold heat cycle in which holding at −65 ° C. for 5 minutes and holding at 150 ° C. for 5 minutes as one cycle is performed 2000 times. It is preferable that the average of the particles is in the range of 30 nm or more and 130 nm or less.
In this case, the average circle-equivalent diameter of the Al-Cu compound particles precipitated after 2000 times of a cold heat cycle in which holding at −65 ° C. for 5 minutes and holding at 150 ° C. for 5 minutes is within the above range. Therefore, the aluminum plate in the vicinity of the bonding interface can be sufficiently precipitated and strengthened, and the deformation of the aluminum plate can be further suppressed.

Further, in the insulating circuit board of the present invention, at the bonding interface between the aluminum plate and the ceramics substrate, the Al—Cu eutectic phase within a range of 1 mm from the end in the width direction of the bonding interface toward the center. The area ratio is preferably 30% or less.
In this case, since the area ratio of the Al—Cu eutectic phase is limited to 30% or less at the bonding interface between the aluminum plate and the ceramic substrate, there are few hard Al—Cu eutectic phases and the ceramic substrate is cracked. Occurrence can be suppressed.

According to the present invention, cracking of the ceramic substrate and deformation of the circuit layer (metal layer) can be suppressed even when a severe cold heat cycle is applied, and the bonding reliability between the ceramic substrate and the circuit layer (metal layer) can be suppressed. It is possible to provide an excellent insulated circuit board.

It is a schematic explanatory drawing of the power module using the insulation circuit board which is an embodiment of this invention. It is an enlarged explanatory view of the bonding interface of a circuit layer (metal layer) and a ceramics substrate in an insulating circuit board which is an embodiment of this invention. It is an observation photograph of the junction interface between a circuit layer (aluminum plate) and a metal layer (aluminum plate) of an insulating circuit board which is an embodiment of this invention, and a ceramics substrate. (A) is before the cold cycle load, and (b) is after the cold cycle load. It is an enlarged photograph of FIG. 3 (b). It is a flow chart which shows the manufacturing method of the insulation circuit board and a power module shown in FIG. It is explanatory drawing which shows the manufacturing method of the insulation circuit board which is an embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows an insulated circuit board 10 according to an embodiment of the present invention and a power module 1 using the insulated circuit board 10.
The power module 1 shown in FIG. 1 has an insulating circuit board 10, a semiconductor element 3 bonded to one side (upper side in FIG. 1) of the insulating circuit board 10 via a solder layer 2, and the other side of the insulating circuit board 10. It is provided with a heat sink 31 arranged (lower side in FIG. 1).

The solder layer 2 is, for example, a Sn-Ag-based, Sn-Cu-based, Sn-In-based, or Sn-Ag-Cu-based solder material (so-called lead-free solder material).
The semiconductor element 3 is an electronic component provided with a semiconductor, and various semiconductor elements are selected according to a required function.

As shown in FIG. 1, the insulating circuit board 10 includes a ceramic substrate 11, a circuit layer 12 disposed on one surface of the ceramic substrate 11 (upper surface in FIG. 1), and the other surface of the ceramic substrate 11 (the other surface of the ceramic substrate 11). A metal layer 13 formed on the lower surface in FIG. 1) is provided.

Ceramic substrate 11 is for preventing an electrical connection between the circuit layer 12 and the metal layer 13, and a high insulating property Si 3 _N 4 _(silicon nitride). Further, the thickness of the ceramic substrate 11 is set within the range of 0.2 mm or more and 1.5 mm or less, and in this embodiment, it is set to 0.32 mm.

The circuit layer 12 is formed by joining an aluminum plate 22 made of aluminum or an aluminum alloy to one surface of the ceramic substrate 11.
In the present embodiment, the circuit layer 12 is formed by joining an aluminum plate 22 made of a rolled aluminum plate having a purity of 99.99 mass% or more (so-called 4N aluminum) to a ceramic substrate 11.

The metal layer 13 is formed by joining an aluminum plate 23 to the other surface of the ceramic substrate 11.
In the present embodiment, the metal layer 13 is formed by joining an aluminum plate 23 made of a rolled aluminum plate having a purity of 99.99 mass% or more (so-called 4N aluminum) to the ceramic substrate 11, similarly to the circuit layer 12. It is formed.

The heat sink 31 is for dissipating heat on the insulating circuit board 10 side. The heat sink 31 is made of aluminum or an aluminum alloy having good thermal conductivity, and in this embodiment, it is made of an A6063 alloy. The thickness of the heat sink 31 is set within the range of 3 mm or more and 10 mm or less.
The heat sink 31 and the metal layer 13 of the insulating circuit board 10 are joined by using a brazing material.

Then, in the present embodiment, as shown in FIG. 2, in the circuit layer 12 and the metal layer 13, Cu is solid-dissolved at the bonding interface with the ceramic substrate 11, and the Cu concentration is mass% at the bonding interface. The ratio B / A to the Cu concentration Bmass% at a position of 100 μm in the thickness direction from the interface to the circuit layer 12 and the metal layer 13 side is 0.30 or more and 0.85 or less.
That is, Cu is sufficiently present even at a position of 100 μm in the thickness direction from the bonding interface to the circuit layer 12 and the metal layer 13 side.
When the ratio B / A is less than 0.30, the bonding interface becomes hard and the bonding reliability deteriorates, or Cu does not sufficiently diffuse into the circuit layer 12 (metal layer 13), and the circuit layer 12 (metal layer 13). ) May be deformed or cracked.
When the ratio B / A exceeds 0.85, Cu diffuses too much, the entire circuit layer 12 (metal layer 13) becomes hard, and the stress that the circuit layer receives in the temperature cycle cannot be relaxed, resulting in cracking. There is a risk.
The upper limit of the ratio B / A between the Cu concentration Mass% at the bonding interface and the Cu concentration B mass% at a position 100 μm in the thickness direction from the bonding interface to the circuit layer 12 and the metal layer 13 is 0.70 or less. It is preferably 0.50 or less, and more preferably 0.50 or less.

Here, in the present embodiment, in the circuit layer 12 and the metal layer 13, the Cu concentration B at a position 100 μm in the thickness direction from the bonding interface is within the range of 0.04 mass% or more and 0.96 mass% or less. Is preferable.
The lower limit of the Cu concentration B at a position 100 μm in the thickness direction from the bonding interface is more preferably 0.10 mass% or more, and further preferably 0.14 mass% or more. On the other hand, the upper limit of the Cu concentration B at a position 100 μm in the thickness direction from the bonding interface is more preferably 0.50 mass% or less, and further preferably 0.45 mass% or less.

Further, in the present embodiment, the area ratio of the Al—Cu eutectic phase within a range of 1 mm from the end in the width direction of the bonding interface between the circuit layer 12 and the metal layer 13 and the ceramic substrate 11 toward the center is 30. It is preferably limited to% or less.
The area ratio of the Al—Cu eutectic phase at the junction 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 ratio of the Al—Cu eutectic phase may be 0% or 6.2% or more.

Further, in the present embodiment, after 2000 times of a thermal cycle in which holding at −65 ° C. for 5 minutes and holding at 150 ° C. for 5 minutes as one cycle is performed 2000 times, the thickness direction from the bonding interface of the circuit layer 12 and the metal layer 13 It is preferable that Al—Cu compound particles containing Al and Cu are precipitated in the crystal grain boundaries of the circuit layer 12 and the metal layer 13 and in the crystal grains in a region up to 100 μm.

Here, FIGS. 3 and 4 show the observation results of the bonding interface between the circuit layer 12 and the metal layer 13 of the insulating circuit board 10 and the ceramic substrate 11 according to the present embodiment.
As shown in FIG. 3A, in the state before loading the cold cycle, Al—Cu compound particles are not present in the circuit layer 12 and the metal layer 13, and Cu is contained in the matrix phase of Al. It is said to be a solid solution structure.
After 2000 times of cold and heat cycles with holding at −65 ° C. for 5 minutes and holding at 150 ° C. for 5 minutes as one cycle, the crystal grains are refined as shown in FIGS. 3 (b) and 4. , Al—Cu compound particles 15 containing Al and Cu are confirmed at the crystal grain boundaries and in the crystal grains.

In the present embodiment, a thermal cycle in which holding at −65 ° C. for 5 minutes and holding at 150 ° C. for 5 minutes is one cycle within a range of 50 μm in the thickness direction from the bonding interface to the circuit layer 12 and the metal layer 13 side is performed. It is preferable that the number density of the Al—Cu compound particles 15 precipitated after 2000 times is in the range of 0.50 / μm ² or more and 8.50 / μm ^{2 or less.}
The number density of the Al—Cu compound particles ^{is more preferably 0.60 / μm 2} or more, and more preferably 0.75 / μm ² or more. Further, the number density of the Al—Cu compound particles ^{is more preferably 8.30 particles / μm 2} or less, and more preferably 8.10 ^{particles / μm 2} or less. In the present embodiment, the number density is calculated for Al—Cu compound particles having a particle size in the range of 0.01 μm or more and 2 μm or less. In the calculation of the number density, if the particle shape is not circular, the shortest portion (minor diameter) is used for judgment.

Further, in the present embodiment, the average circle-equivalent diameter of the Al-Cu compound particles precipitated after 2000 cold cycles with holding at −65 ° C. for 5 minutes and holding at 150 ° C. for 5 minutes as one cycle is 30 nm. It is preferably in the range of 130 nm or less.
The average circle-equivalent 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 circle-equivalent diameter of the Al—Cu compound particles 15 is more preferably 125 μm or less, and even more preferably 120 μm or less.

Next, a method of manufacturing the insulated circuit board 10 and the power module 1 according to the present embodiment will be described with reference to FIGS. 5 and 6.

(Cu layer forming step S01)
First, as shown in FIGS. 5 and 6, a Cu layer 26 is formed on at least one of the joint surfaces of the aluminum plate 22 which is the circuit layer 12 and the aluminum plate 23 which is the metal layer 13 and the ceramic substrate 11. In this embodiment, as shown in FIG. 6, Cu layers 26 are formed on both surfaces of the ceramic substrate 11. The method for forming the Cu layer 26 is not particularly limited, and existing means such as sputtering, vapor deposition, CVD, plating, paste, and foil material can be appropriately used.
Here, the amount of Cu adhered to the Cu layer 26 is preferably in the range of ^{0.08 mg / cm 2} or more and 2.0 mg / cm ^{2 or less.}

(Laminating step S02)
Next, the aluminum plate 22 to be the circuit layer 12 is laminated on one surface of the ceramic substrate 11 via the Cu layer 26, and the aluminum plate to be the metal layer 13 is laminated on the other surface of the ceramic substrate 11 via the Cu layer 26. 23 are laminated.

(Joining step S03)
Next, the laminated body of the aluminum plate 22 to be the circuit layer 12, the ceramic substrate 11, and the aluminum plate 23 to be the metal layer 13 is charged into a vacuum heating furnace in a state of being pressurized in the stacking direction using a pressurizing device. The aluminum plate 22 and the ceramic substrate 11 are joined to form the circuit layer 12, and the aluminum plate 23 and the ceramic substrate 11 are joined to form the metal layer 13.

Here, in the joining step S03, the pressure load in the stacking direction is set within the range of 0.098 MPa or more and 2.94 MPa or less.
The joining temperature shall be within the range of 600 ° C. or higher and 650 ° C. or lower, and the holding time at the joining temperature shall be 180 minutes or lower.
Then, the rate of temperature rise from the eutectic temperature (548 ° C.) of Al and Cu to the joining temperature is set within the range of 5 ° C./min or more and 20 ° C./min or less.

The insulated circuit board 10 according to the present embodiment is manufactured by the above steps.

(Heat sink joining step S04)
Next, a heat sink 31 is laminated on the other side of the metal layer 13 of the insulating circuit board 10 via a brazing material, and the insulating circuit board 10 and the heat sink 31 are mounted in a vacuum heating furnace in a state of being pressurized in the stacking direction. Then, the metal layer 13 and the heat sink 31 are joined.

(Semiconductor element joining step S05)
Next, the semiconductor element 3 is laminated on one surface of the circuit layer 12 via a solder material, and solder-bonded in the heating furnace.
As described above, the power module 1 shown in FIG. 1 is manufactured.

According to the insulating circuit board 10 of the present embodiment having the above configuration, Cu is solid-solved on the bonding interface side of the circuit layer 12 and the metal layer 13 with the ceramics substrate 11, and Cu at the bonding interface. Since the ratio B / A of the concentration Amass% to the Cu concentration Bmass% at a position of 100 μm in the thickness direction from the bonding interface to the circuit layer 12 and the metal layer 13 is 0.30 or more and 0.85 or less, aluminum. Cu is sufficiently diffused into the inside of the circuit layer 12 and the metal layer 13 composed of the metal layer 13, and a region in which Cu is solid-solved in a supersaturated state is formed in the vicinity of the bonding interface of the circuit layer 12 and the metal layer 13. .. Therefore, the circuit layer 12 and the metal layer 13 are strengthened, and it is possible to suppress deformation of the circuit layer 12 and the metal layer 13 and generation of cracks in the circuit layer 12 and the metal layer 13 after a thermal cycle load.

Further, since Cu is solid-solved in the matrix phase of Al, a hard eutectic phase of Al—Cu is not formed, and the occurrence of cracks in the ceramic substrate 11 can be suppressed.
Further, in the present embodiment, the area ratio of the Al—Cu eutectic phase within a range of 1 mm from the widthwise end of the bonding interface between the circuit layer 12 and the metal layer 13 and the ceramic substrate 11 toward the center is 30%. In the following cases, the number of hard Al—Cu eutectic phases is small, and the occurrence of cracks in the ceramic substrate 11 can be suppressed.

In the present embodiment, the Cu concentration B at a position 100 μm in the thickness direction from the bonding interface between the circuit layer 12 and the metal layer 13 with the ceramic substrate 11 is within the range of 0.04 mass% or more and 0.96 mass% or less. In this case, Cu is sufficiently diffused toward the inside of the circuit layer 12 and the metal layer 13, and the circuit layer 12 and the metal layer 13 are deformed after the thermal cycle load and the circuit layer 12 and the metal layer 13 are in the same state. The occurrence of cracks can be further suppressed.

In the present embodiment, after 2000 times of a thermal cycle in which holding at −65 ° C. for 5 minutes and holding at 150 ° C. for 5 minutes is performed 2000 times, the thickness is increased from the bonding interface between the circuit layer 12 and the metal layer 13 with the ceramic substrate 11. When Al—Cu compound particles 15 containing Al and Cu are precipitated in the crystal grain boundaries of the circuit layer 12 and the metal layer 13 and in the crystal grains in the region up to 100 μm in the vertical direction, the circuit layer 12 and the metal The vicinity of the bonding interface of the layer 13 with the ceramic substrate 11 is strengthened by the Al—Cu compound particles 15, and the circuit layer 12 and the metal layer 13 are deformed and cracks in the circuit layer 12 and the metal layer 13 after a thermal cycle load. Can be reliably suppressed.

In the present embodiment, 2000 cold cycles are held at −65 ° C. for 5 minutes and at 150 ° C. for 5 minutes within a range of 50 μm in the thickness direction from the bonding interface to the circuit layer 12 and the metal layer 13 side. When the number density of Al-Cu compound particles precipitated after the rotation ^{is within the range of 0.50 / μm 2} or more and 8.50 / μm ² or less, the circuit layer 12 and the metal layer 13 are bonded. Deformation resistance in the vicinity of the interface increases, deformation of the circuit layer 12 and the metal layer 13 can be further suppressed, and the vicinity of the junction interface between the circuit layer 12 and the metal layer 13 does not become harder than necessary, so that the ceramic substrate 11 Cracking can be further suppressed.

In the present embodiment, when the average circle-equivalent diameter of the Al—Cu compound particles 15 is within the range of 30 nm or more and 130 nm or less, the portions near the bonding interface of the circuit layer 12 and the metal layer 13 are sufficiently precipitated and strengthened. The deformation of the circuit layer 12 and the metal layer 13 can be further suppressed.

Although the embodiments of the present invention have been described above, the present invention is not limited to this, and can be appropriately changed without departing from the technical idea of the invention.
For example, in the present embodiment, the ceramic substrate has been described as being made of silicon nitride, but the present invention is not limited to this, and it may be made of alumina or aluminum nitride.

Further, in the present embodiment, the power module is described by mounting the power semiconductor element on the circuit layer of the insulated circuit board, but the present invention is not limited to this. For example, an LED element may be mounted on an insulated circuit board to form an LED module, or a thermoelectric element may be mounted on a circuit layer of an insulated circuit board to form a thermoelectric module.

Further, in the present embodiment, the insulation circuit board (metal layer) and the heat sink have been described as being bonded by brazing, but the present invention is not limited to this, and other bonding methods such as solid phase diffusion bonding and TLP are used. May be applied.
Further, in the present embodiment, the heat sink has been described as being made of aluminum, but the heat sink is not limited to this, and may be made of copper or the like, and has a flow path through which a cooling medium is circulated. It may be a heat sink. Further, a cushioning layer made of, for example, 4N-aluminum may be provided between the heat sink and the insulating circuit board.

The results of the confirmation experiment conducted to confirm the effect of the present invention will be described below.

(Example 1)
The ceramic substrate (40 mm × 40 mm) shown in Table 1 was prepared, and a Cu layer was formed on one surface and the other surface of the ceramic substrate by a sputtering method. Table 1 shows the amount of Cu fixed at this time.
Then, an aluminum plate (37 mm × 37 mm × 0.4 mmt) made of 4N aluminum is laminated on one surface of the ceramic substrate via a Cu layer, and aluminum made of 4N aluminum is laminated on the other surface of the ceramic substrate via a Cu layer. Plates (37 mm × 37 mm × 0.4 mmt) were laminated.

Then, under the conditions shown in Table 1, the aluminum plate and the ceramic substrate were joined to manufacture an insulated circuit board. The rate of temperature rise shown in Table 1 indicates the rate of temperature rise from the eutectic temperature (548 ° C.) of Al and Cu to the joining temperature.
A heat sink (50 mm × 60 mm, 5 mm thick aluminum plate (A6063)) is bonded to the metal layer of the obtained insulating circuit board via a buffer layer of 4N-aluminum (thickness 0.9 mm), and an insulating circuit with a heat sink is used. Obtained a substrate. The metal layer and the buffer layer and the buffer layer and the heat sink were joined by brazing using an Al—Si foil.

Regarding the obtained insulated circuit board with heat sink, Cu concentration A at the bonding interface of the aluminum plate, Cu concentration B at a position 100 μm from the bonding interface to the inside of the aluminum plate, initial bonding ratio, and Al-Cu compound particles after the thermal cycle test. The presence or absence of, the bonding rate after the cold cycle test, and the presence or absence of cracks in the substrate after the cold cycle test were evaluated.

(Cu concentration A, Cu concentration B)
Insulated circuit board with heat sink is cut along the stacking direction, and in the center cross section in the width direction of the board, using an electron probe microanalyzer (JXA-8530F manufactured by JEOL Ltd.), the conditions are 500 times magnification and 15 kV acceleration voltage. Then, a quantitative analysis was performed on Cu at a position 100 μm from the bonding interface and the bonding interface in the stacking direction. In the observation region, the Cu concentration at 5 points and their average value were obtained at the junction interface and the position 100 μm from the junction interface in the stacking direction, respectively, and the Cu concentration A (mass%) at the junction interface and Cu at the position 100 μm from the junction interface. A concentration B (mass%) was obtained. At this time, the Cu concentration was calculated so that the total of the concentrations (mass%) of Al and Cu was 100.

(Initial joining rate)
The bonding ratio between the aluminum plate and the ceramic substrate was evaluated. Specifically, in an insulated circuit board with a heat sink, the bonding ratio at the interface between the aluminum plate and the ceramic substrate was evaluated using an ultrasonic flaw detector (FineSAT200 manufactured by Hitachi Power Solutions, Ltd.) and calculated from the following formula. Here, the initial bonding area is the area to be bonded before bonding, that is, the area of the circuit layer. Since the peeling is shown by the white part in the joint portion in the image obtained by binarizing the ultrasonic flaw detection image, the area of this white part is defined as the peeling area (non-joint part area).
(Joining ratio) = {(Initial joining area)-(Non-joining area)} / (Initial joining area) x 100

(Cold heat cycle test)
Using TSB-51 manufactured by ESPEC, a thermal shock tester, a thermal cycle of -65 ° C x 5 minutes ← → 150 ° C x 5 minutes was performed 2000 times on an insulated circuit board with a heat sink in a liquid tank (Fluorinert). bottom.

(Presence / absence of Al-Cu compound particles after cold cycle test)
After cutting the insulated circuit board with a heat sink after the thermal cycle in the stacking direction, a scanning electron microscope (GeminiSEM 500 manufactured by Karlzeis) was used in the cross section in the center of the width direction of the board, and the magnification was 5000 times and the acceleration voltage was 5. A region (17 μm × 23 μm) including the bonding interface between the aluminum plate and the ceramic substrate was observed under the condition of 0.0 kV.
In this observation, when the SEM image and the elemental MAP of Cu and Al are acquired and a granular region observed in white is observed in the SEM image and Cu and Al coexist in this region, Al- The Cu compound particles were evaluated as "Yes". Then, the region from the bonding interface of the aluminum plate to 100 μm in the thickness direction was observed, and the presence or absence of Al—Cu compound particles was evaluated.
Then, the region from the bonding interface of the aluminum plate to 100 μm in the thickness direction was observed, and the presence or absence of Al—Cu compound particles was evaluated.

(Joining rate after cold cycle test)
The insulated circuit board with a heat sink after the thermal cycle test was evaluated using an ultrasonic flaw detector (FineSAT200 manufactured by Hitachi Power Solutions, Ltd.) as described above, and the bonding ratio was calculated.

(Presence / absence of cracks in the substrate after the thermal cycle test)
The presence or absence of cracks in the heat-sink-equipped insulated circuit board after the thermal cycle test was evaluated using an ultrasonic flaw detector (FineSAT200 manufactured by Hitachi Power Solutions, Ltd.). When cracks were confirmed in any of the circuit layer, metal layer, and ceramic substrate, it was evaluated as "Yes".

Comparative Examples 1 to 1 in which the ratio B / A of the Cu concentration Mass% at the bonding interface to the Cu concentration B mass% at a position 100 μm in the thickness direction from the bonding interface to the aluminum plate side was less than 0.30 or over 0.85. In No. 4, the bonding ratio after the cold cycle test was low, and cracks were observed in the substrate after the cold cycle test.

On the other hand, the ratio B / A between the Cu concentration Mass% at the bonding interface and the Cu concentration B mass% at a position 100 μm in the thickness direction from the bonding interface to the aluminum plate side was 0.30 or more and 0.85 or less. In Examples 1 to 8 of the present invention, the bonding ratio was sufficiently high even after the thermal cycle test, and no crack was confirmed in the substrate.

(Example 2)
The ceramic substrate (40 mm × 40 mm) shown in Table 3 was prepared, and a Cu layer was formed on one surface and the other surface of the ceramic substrate by a sputtering method. Table 3 shows the amount of Cu fixed at this time.
Then, an aluminum plate (37 mm × 37 mm × 0.4 mmt) made of 4N aluminum is laminated on one surface of the ceramic substrate via a Cu layer, and aluminum made of 4N aluminum is laminated on the other surface of the ceramic substrate via a Cu layer. Plates (37 mm × 37 mm × 0.4 mmt) were laminated.
Then, under the conditions shown in Table 3, the aluminum plate and the ceramic substrate were joined to manufacture an insulated circuit board.

Regarding the obtained insulated circuit board, Cu concentration A at the bonding interface of the aluminum plate, Cu concentration B at a position 100 μm from the bonding interface to the inside of the aluminum plate, initial bonding rate, bonding rate after the cold cycle test, and after the cold cycle test. The presence or absence of cracks in the substrate was evaluated by the same procedure as in Example 1.
Further, the area ratio of the Al—Cu eutectic phase at the bonding interface, the number density of the Al—Cu compound particles after the thermal cycle test, and the average of the equivalent circle diameters of the Al—Cu compound particles were evaluated as follows.

(Area ratio of Al-Cu eutectic phase at the junction interface)
At the bonding interface, a BSE image in a range of 1 mm from the edge in the width direction toward the center was obtained by a scanning electron microscope (GeminiSEM 500 manufactured by Carl Zeiss), and this BSE image was binarized. The area of the Al—Cu eutectic phase and the area in the range from the end of the junction interface to 1 mm were determined, and the area ratio of the Al—Cu eutectic phase at the junction interface was calculated by the following formula.
(Area ratio of Al-Cu eutectic phase) = (Area of Al-Cu eutectic phase) / (Area from edge to center 1 mm) x 100

(Number density of Al-Cu compound particles after cold cycle test)
After cutting the insulated circuit board after the thermal cycle test in the stacking direction, the presence or absence of Al—Cu compound particles was confirmed in the cross section at the center in the width direction of the board by the above method. In the region where Al-Cu compound particles were confirmed (within a range of 50 μm in the thickness direction from the bonding interface to the aluminum plate side), an ASB image 1000 times larger than that of a scanning electron microscope (GeminiSEM 500 manufactured by Karlzeis) was obtained. , The ASB image was binarized so that the Al—Cu compound particles became white.
Then, the number of Al—Cu compound particles was measured and divided by the area of the measurement range to calculate the number density. The number density is calculated for Al—Cu compound particles having a particle size in the range of 0.01 μm or more and 2 μm or less. Further, the particle size when the particle shape is not circular is determined by the shortest portion (minor diameter). Furthermore, when the shape of the particles is unknown, such as when a part of the particles is out of the measurement range, the particles are excluded from the measurement.

(Average of equivalent circle diameters of Al-Cu compound particles after cold cycle test)
The ASB image was binarized in the same manner as when the number density was obtained. Then, the area of each Al—Cu compound particle in the measurement region was obtained, and the radius corresponding to the circle was calculated from this area to obtain the average value. This average value is shown in the table. When determining the area, if the area could not be determined because some of the particles were out of the measurement range, these particles were excluded.

In Examples 11, 13, 15, 17, and 18 of the present invention, holding at −65 ° C. for 5 minutes and holding at 150 ° C. for 5 minutes within a range of 50 μm in the thickness direction from the bonding interface to the aluminum plate side is defined as one cycle. The number density of Al—Cu compound particles precipitated after 2000 times of the cooling and heating cycle was within the range of ^{0.50 / μm 2} or more and 8.50 / μm ^{2 or less.} The average circle-equivalent diameter of the Al—Cu compound particles was in the range of 30 nm or more and 130 nm or less. At the bonding interface between the aluminum plate and the ceramic substrate, the area ratio of the Al—Cu eutectic phase within a range of 1 mm from the end in the width direction of the bonding interface toward the center was 30.0% or less. Even after the thermal cycle test, the bonding ratio was sufficiently high, and no cracks were confirmed on the substrate.

Further, in Example 12 of the present invention, the area ratio of the Al—Cu eutectic phase was 32.0%. In Example 14 of the present invention, the number density of the Al—Cu compound particles after the thermal cycle test was 8.70 particles / μm ² , and the equivalent circle diameter of the Al—Cu compound particles was 27 nm. In Example 16 of the present invention, the number density of the Al—Cu compound particles after the thermal cycle test was 0.47 / μm ² , and the equivalent circle diameter of the Al—Cu compound particles was 133 nm. Compared with these Examples 12, 14, 16 of the present invention, in Examples 11, 13, 15, 17, 18 of the present invention, the area ratio of the Al—Cu eutectic phase was 30.0% or less, and after the thermal cycle test, the area ratio was 30.0% or less. The number density of Al-Cu compound particles ^{is within the range of 0.50 / μm 2} or more and 8.50 / μm ² or less, and the equivalent circle diameter of Al-Cu compound particles is within the range of 30 nm or more and 130 nm or less. there were. It was confirmed that the bonding ratio was further excellent in Examples 11, 13, 15, 17 and 18 of the present invention as compared with Examples 12, 14 and 16 of the present invention.

From the results of this embodiment, according to the example of the present invention, cracking of the ceramic substrate, deformation of the circuit layer (metal layer), etc. can be suppressed even when a severe thermal cycle is applied, and the ceramic substrate and the circuit layer can be used. It was confirmed that it is possible to provide an insulated circuit board with excellent bonding reliability.

1 Power module 3 Semiconductor element 10 Insulation circuit board 11 Ceramic substrate 12 Circuit layer 13 Metal layer 15 Al-Cu compound particles 22,23 Aluminum plate

Claims (6)

An insulating circuit board in which an aluminum plate made of aluminum or an aluminum alloy is laminated and joined to the surface of a ceramic substrate.
Cu is solid-solved in the aluminum plate at the bonding interface with the ceramic substrate.
The Cu concentration at 5 points and the average value thereof were obtained so that the total concentration (mass%) of Al and Cu was 100 at the bonding interface and the position 100 μm from the bonding interface in the stacking direction. Calculate the Cu concentration A (mass%) at the bonding interface and the Cu concentration B (mass%) at a position 100 μm from the bonding interface.
The ratio B / A between the Cu concentration Mass% at the bonding interface and the Cu concentration B mass% at a position 100 μm in the thickness direction from the bonding interface to the aluminum plate side is 0.30 or more and 0.85 or less. Insulated circuit board. The insulation according to claim 1, wherein in the aluminum plate, the Cu concentration B at a position 100 μm in the thickness direction from the bonding interface is within the range of 0.04 mass% or more and 0.96 mass% or less. Circuit board. After performing 2000 cold and thermal cycles with holding at −65 ° C. for 5 minutes and holding at 150 ° C. for 5 minutes as one cycle, the aluminum plate was placed in a region up to 100 μm in the thickness direction from the bonding interface of the aluminum plate. The insulating circuit substrate according to claim 1 or 2, wherein Al—Cu compound particles containing Al and Cu are precipitated at the grain boundaries and in the crystal grains. The Al-precipitated after 2000 cold cycles of holding at −65 ° C. for 5 minutes and holding at 150 ° C. for 5 minutes as one cycle within a range of 50 μm from the bonding interface to the aluminum plate side in the thickness direction. The insulating circuit substrate according to claim 3, wherein the number density of Cu compound particles is in the range of 0.50 / μm ² or more and 8.50 / μm ^{2 or less.} Within the range where the average circle-equivalent diameter of the Al-Cu compound particles precipitated after 2000 cold cycles of holding at −65 ° C. for 5 minutes and holding at 150 ° C. for 5 minutes is 30 nm or more and 130 nm or less. The insulated circuit board according to claim 3 or 4, wherein the insulating circuit board is provided. At the bonding interface between the aluminum plate and the ceramic substrate, the area ratio of the Al—Cu eutectic phase within a range of 1 mm from the end in the width direction of the bonding interface toward the center is 30% or less. The insulated circuit board according to any one of claims 1 to 5.

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