JP2000226272A - Ceramic-metal conjugate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ceramic-metal conjugate having high reliability of conjugation. SOLUTION: This ceramic-metal conjugate comprises a ceramic substrate 1 having high thermal conductivity, a metal plate 3 having high electroconductivity and a low-melting point metal layer 51 disposed between the substrate 1 and the metal plate 3 and integrally conjugation both components. The low-melting point metal layer 51 is flexible and has at least one strain relaxing layer 52 having <=40 μm thickness and composed of silver solder or a solder. Thermal stress in production of the conjugate is relaxed by the strain relaxing layer 52, and thermal stress by heat and cold cycle in using is relaxed by the flexible low-melting point metal layer 51.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high heat conductive insulating substrate used for a power module or the like.

[0002]

2. Description of the Related Art In recent years, various devices have been required to have higher performance such as higher functionality and smaller size. Such a flow is not an exception in a device such as a power module. Power modules are also required to have large capacity, high speed, small size, and low cost.

In a large-capacity power module, the circuit of the module is a high-current circuit. Therefore, heat is generated in the connection portion such as the Si chip or the Al wire, and it is important to prevent damage to the circuit due to the generated heat.
As a high current circuit board used in such a high current circuit, a ceramic-metal composed of a high thermal conductive insulating substrate and a metal plate joined to the high thermal conductive insulating substrate and formed with a current circuit through which a current flows is formed. A conjugate is used.

As a general ceramic-metal joined body used for an electronic circuit, an alumina ceramic is used as an insulating substrate, and a Cu plate having a specific resistance of 1.7 μΩcm is used as a metal plate on which a current circuit is formed. However, aluminum nitride ceramics having a thermal conductivity of 180 W / mK are used in large-capacity power modules that require high thermal conductivity.

[0005] There are several types of ceramic-metal joints by joining a Cu plate and a ceramic plate. For example, there are a joined body in which a Cu plate is directly joined to an aluminum nitride plate, a joined body in which an Al plate is brazed to an aluminum nitride plate and joined. The joined body directly joined to the Cu plate is
A Cu plate is joined to a ceramic plate at a temperature of about 1070 ° C. using a eutectic liquid phase of Cu and O. In this joined body, the joining between the Cu plate and the ceramic plate is strengthened by the eutectic layer of Cu and O.

As another form of a joined body in which a Cu plate is directly joined, there is a joined body in which a Cu plate is joined to a ceramic plate at a temperature of around 840 ° C. by a Ti—Ag—Cu-based active metal braze. This joined body strengthens the joining by the Ti contained in the brazing penetrating into the ceramic plate. There is also a joined body in which a Cu plate on which a circuit is formed is compromised with Al having relatively large electric resistance, and the Al plate is joined with Al-Si brazing. This joined body is manufactured by vacuum brazing an Al—Si alloy braze and an Al clad material on a ceramic plate. This joined body is a joined body excellent in cold-heat cycle resistance.

[0007]

The ceramic-metal joined body has a thermal history in the joining process of the ceramic plate and the metal plate and a power module manufacturing process, and an intermittent when the joined body is used for a substrate for a high current circuit. It is required to be able to withstand a heat cycle at the time of use, such as when a high current flows through the device or when the device is used even in a cold region such as a power module for an automobile.

[0008] The reliability of bonding between a ceramic plate and a metal plate is such that when the metal plate is peeled off from the ceramic substrate when used as a current circuit, heat can no longer be radiated from the current circuit, and the current circuit is damaged and damaged. This is an important issue that will stop functioning. However, the above-mentioned conventional high-current circuit board has the following problems.

A joined body directly joined to a Cu plate, including a joined body brazed with an active metal brazing, is a ceramic plate and a C plate.
The eutectic layer of Cu and O formed at the joint with the u-plate or the joint layer in which Ti diffused was hard. In cooling after joining, thermal stress is generated due to a difference in thermal contraction due to a difference in thermal expansion coefficient between the ceramic plate and the metal plate. In the case of a conventional bonded body, if the production is to be performed in a continuous furnace for cost reduction, the cooling rate of the bonded body after bonding is about 7 to 35 ° C./min, at which the ceramic plate is cracked by thermal stress. Had a problem.

[0010] In addition, in a thermal cycle depending on the use environment, a stress is applied such that the film is torn from both sides. As a result, there has been a problem that the ceramic plate is cracked so as to be peeled off at the center in the thickness direction. When the Al plate is joined by brazing, when the Al plate is joined by brazing, irregularities occur on the surface due to shrinkage due to cooling after brazing to the surface of the Al plate. For this reason, the surface of the Al plate needs to be polished. In addition, A also depends on the heat cycle in the usage environment.
1 is deformed, and irregularities occur on the surface. Therefore, in the actual case where the Si chip is mounted,
Is plastically deformed, so that the Al surface rises at the solder joint below the chip, which adversely affects the life of the solder joint. further,
Since Al has a higher specific resistance than Cu, it is not a material that satisfies the demand for higher output, higher speed, and smaller size.

The present invention has been made in view of the above circumstances, and has as its object to provide a ceramic-metal bonded body having high bonding reliability.

[0012]

Means for Solving the Problems In order to solve the above problems, the present inventors have repeatedly studied to improve the bonding reliability and found that a soft low melting point metal layer has a strain relaxation function. Further, they have found that the above problem can be solved by forming the strain relaxation layer thin between the high heat conductive base material and the high conductive metal plate.

That is, the ceramic-metal joined body of the present invention is integrally joined with a high thermal conductive ceramic substrate, a high conductive metal plate, and a high thermal conductive ceramic substrate and a high conductive metal plate interposed therebetween. A low-melting point metal layer, comprising: a low melting point metal layer that is soft and has at least one strain relaxation layer made of silver brazing or solder having a thickness of 40 μm or less. It is characterized by the following.

Here, the term "soft" means a recrystallization temperature of Ag-Cu binary Ag wax, which is a typical Ag wax composition,
In particular, at 170 ° C. or less, which is assumed in a thermal cycle depending on the use environment, it means that the Ag—Cu binary Ag wax exhibits an elongation greater than or equal to the plastic deformation in a tensile test.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION A ceramic-metal joined body of the present invention comprises a highly thermally conductive ceramic base, a highly conductive metal plate,
And a soft low-melting metal layer interposed and integrally joined between the high thermal conductive ceramics base material and the highly conductive metal plate. The ceramic-metal bonded body of the present invention has at least one strain relaxation layer made of a soft silver braze or solder between a high thermal conductive ceramic base material and a highly conductive metal plate. By having this strain relaxation layer between the high thermal conductive ceramics base material and the high conductive metal plate, the ceramic-metal bonded body has a bending moment generated by thermal stress due to cooling after high-temperature bonding and thermal cycling under the usage environment. Can be relaxed.
In the prior art, the eutectic layer of Cu and O or the Ti diffusion layer cannot absorb the thermal stress and peels off the ceramic substrate. In the present invention, however, the thermal stress is absorbed by the plastic deformation of the strain relaxation layer.

The strain relieving layer is made of silver brazing or solder. The strain relaxation layer is to soften the strain generated in the ceramic-metal joined body due to cooling after high-temperature joining or thermal cycling during use by plastic deformation (its own ductility), and must be a soft joining material. Silver solder or solder is used as such a soft material. The strain relaxation layer has a thickness of 40 μm or less between the high thermal conductive ceramics base material and the highly conductive metal plate, and has at least one layer. The strain relaxation layer absorbs the stress generated by cooling after joining the high thermal conductive ceramic base material and the high conductivity metal plate sandwiching the strain relaxation layer by plastic deformation of the strain relaxation layer. When the thickness exceeds 40 μm, the bending moment that deflects the joined body increases due to the thermal stress generated by the difference in the thermal expansion coefficient between the high thermal conductive ceramic base material and the high conductive metal plate, and the concave shape is formed toward the surface side. Warpage is excessively generated in the conjugate. Further, when a joined body in which a high-conductivity metal plate is joined to both sides of a high-thermal-conductivity ceramic base material, which is a general configuration as an actual product, is cooled in a continuous furnace at a cooling rate of 7 to 35 ° C./min, a layer is formed. Is 40μm thick
If the ratio exceeds the above range, cracks occur in the high thermal conductive ceramics base material.

FIG. 1 shows a joined body in which a Cu plate is joined to one side of an aluminum nitride substrate having a thickness of 0.635 mm plated with Ni and having a thickness of 3 μm by using an Ag braze; FIG. 10 is a view showing a result of measuring concave warpage of the Cu plate surface when the thickness of the Ag braze is changed in a joined body in which a Cu plate is joined using an Ag braze having a Cu intermediate layer on one surface of the Cu plate. . here,
The concave warpage of the Cu plate surface was measured by measuring the radius of curvature of the Cu plate surface when a 0.25 mm thick Cu plate was joined to one surface of the aluminum nitride substrate with an Ag braze. The thickness of the Ag brazing layer is the thickness of one Ag brazing layer as shown in the lower right circle of FIG. Ag wax-C
As shown in the upper right circle of FIG. 1, the thickness of the u-Ag brazing layer is represented by the total of the Cu layer and the Ag brazing layers on both sides of the Cu layer, and the thickness of each Ag brazing here Is 20 μm
And was fixed.

As can be seen from FIG. 1, the radius of curvature becomes shorter as the thickness of the Ag braze becomes larger, as can be seen from the radius of curvature of the joined body joined with only the Ag braze. The radius of curvature can be reduced by
That is, it shows that the warpage of the Cu plate surface is large. In addition, it can be seen that the joined body joined by the Ag brazing having the Cu intermediate layer has a larger radius of curvature than that of the joined body joined by only the Ag brazing, and the warpage of the Cu plate is smaller.

The ceramic-metal joined body of the present invention preferably has a highly conductive metal plate on both surfaces of a highly thermally conductive ceramic substrate. By having the highly conductive metal plates on both sides of the high thermal conductive ceramic base, the warpage of the metal plate can be suppressed by canceling out the warpage of the metal plates formed on both sides of the high thermal conductive ceramic base. The high thermal conductive ceramic substrate is a substrate formed of one of boron nitride, aluminum nitride, silicon nitride and alumina, and the highly conductive metal plate is formed of at least one metal of copper, aluminum, tungsten and molybdenum or an alloy thereof. Preferably, it is formed. In addition, since the ceramic-metal bonded body of the present invention is used for a high current circuit board, it is preferable that the high thermal conductive ceramic base material has sufficient insulating properties.

The high thermal conductive ceramic substrate is required to have high thermal conductivity. As such a material, boron nitride,
Ceramics formed of one of aluminum nitride, silicon nitride, and alumina are used. The high thermal conductive ceramic substrate preferably has a thermal expansion coefficient close to that of the Si chip.

The highly conductive metal plate is made of a material having a small specific resistance. Such a metal plate includes at least one of copper, aluminum, tungsten and molybdenum.
Kinds of metals or alloys thereof can be mentioned. The highly conductive metal plate preferably has a coefficient of thermal expansion close to the coefficient of thermal expansion of the highly thermally conductive ceramic substrate. By approximating the coefficient of thermal expansion, the bending moment generated between the metal plate and the ceramic substrate can be reduced.

Preferably, the high thermal conductive ceramic substrate is an aluminum nitride substrate, the highly conductive metal plate is a metal plate made of copper or a copper alloy, and the strain relieving layer is formed of silver brazing having good heat conductivity. . This aluminum nitride-Ag braze-Cu joint uses an aluminum nitride base material having high thermal conductivity, a Cu plate having a small specific resistance, and a soft Ag braze as a joining material. This aluminum nitride-A
The g-Cu-joint joins the bending moment generated in the aluminum nitride base material generated during cooling after the joining.
The plate itself and the soft Ag wax plastically deform and absorb and relax.

In the aluminum nitride-Ag braze-Cu joint, the thickness of the strain relaxation layer is preferably 40 μm or less, more preferably 20 μm or less. When the thickness of the Ag brazing layer forming the strain relaxation layer exceeds 40 μm, the bending moment generated during cooling after joining increases, and the effect of strain relaxation becomes insufficient. In the aluminum nitride-Ag braze-Cu joint, the low melting point metal layer includes at least one intermediate layer made of a copper foil or a copper alloy foil and both sides of the intermediate layer and a strain relaxation layer located between the intermediate layers. It is preferable to be formed of a laminated brazing material. That is, by providing an intermediate layer made of copper or a copper alloy foil in the low melting point metal layer, the bending moment generated at the time of cooling after joining can be reduced even if the low melting point metal layer is relatively thick. This is clear from FIG. Therefore, the production of the low melting point metal layer becomes very easy. It is easy to manufacture because the low melting point metal layer is 50 to 1
It is at the time of 00 μm.

In the aluminum nitride-Ag braze-Cu joint, the high thermal conductive ceramic substrate is plate-shaped, and the high-conductivity metal plates are integrally joined to both surfaces thereof via a low-melting metal layer. preferable. In other words, by forming a highly conductive metal plate on both sides of the plate-shaped high thermal conductive ceramic base material, a bending moment due to thermal stress is uniformly applied to both sides of the plate-shaped base material, thereby suppressing warpage.

(Method of Manufacturing Aluminum Nitride-Cu Joint) Of the ceramic-metal joints of the present invention, an aluminum nitride-Cu joint can be manufactured by the following method. First, Pd plating is performed on an aluminum nitride substrate to form a Pd plating layer on the surface of the substrate. Thereafter, the surface of this Pd layer is plated with Ni to form an aluminum nitride substrate, P
A laminated substrate obtained by laminating a d plating layer and a Ni plating layer in this order is obtained.

Thereafter, Ag wax, C
u board or Ag brazing, copper foil, Ag brazing, Cu board are laminated and H2-
It is manufactured by heating under an N2 mixed atmosphere to melt-bond Ag braze. At this time, the Ag brazing, the copper foil, and the Ag brazing may be clad in advance. This ceramic-metal bonded body is made by bonding a ceramic base and a metal plate to a soft Ag brazing or a softer Ag brazing-copper foil-Ag.
It is a joined body joined by using a brazing material, and the Ag brazing or the Ag brazing-copper foil-Ag brazing absorbs and relieves thermal stress in cooling after high-temperature bonding or in a thermal cycle in a use environment.

[0027]

The present invention will be described below with reference to examples. (Example 1) As Example 1, aluminum nitride-Ag
A wax-Cu joint was manufactured. Fig. 2 shows a cross section of this joined body.
It was shown to.

In this embodiment, the substrate 1, the metal plate 3, the bonding layers 51 and 55 formed between the substrate 1 and the metal plate 3,
Consists of Here, an AlN ceramic plate having a length of 17 mm, a width of 30 mm, and a thickness of 0.635 mm is used for the substrate 1, and a 0.25 mm thick CN is used for the metal plate 3.
A u-plate was used. Further, between the ceramic substrate 10 and the bonding layer 51, the ceramic substrate 10, the Pd layer 1
3. The Ni plating layer 15 was laminated in this order.

Surface bonding layer 51 formed on the surface of the bonded body
Are an intermediate layer 53 made of copper foil, and Ag solder layers 52, 52 made of Ag solder formed on both surfaces of the intermediate layer 53.
And are laminated. The back surface bonding layer 55 formed on the back surface of the bonded body is formed only of the Ag brazing having no intermediate layer. (Manufacturing method of Embodiment 1) AlN-Ag solder of this embodiment
The method for producing the Cu joined body is described below.

First, aluminum nitride was fired by a usual method for producing ceramics to produce an aluminum nitride plate having a break line of 17 × 30 mm and a thickness of 0.635 mm. Subsequently, the surface of the aluminum nitride plate was subjected to a degreasing treatment using a commercially available alkaline degreasing solution. Then, at 60 ° C., 5 mol / l NaOH
The surface of the aluminum nitride plate was roughened by etching with an aqueous solution. At this time, the surface roughness Rz was 6 μm. After drying the roughened aluminum nitride plate, a resist film was printed on the surface and dried at 120 ° C.

Thereafter, after the Sn ions were adsorbed on the surface, the Sn ions were replaced in a Pd chloride solution to precipitate metal Pd on the surface, thereby forming a plating nucleus for plating. Subsequently, a Pd layer having a thickness of 0.3 μm was formed on the precipitation nucleus using a commercially available electroless Pd plating solution. After forming the Pd layer, the resist was removed and a vacuum heat treatment was performed at 1200 ° C. for 2 hours.

Thereafter, electroless Ni-B for depositing Ni
Plating was performed to form a Ni layer having a thickness of 3 μm. Further, the aluminum nitride substrate was divided along the break lines to produce a 17 × 30 mm aluminum nitride substrate. 0.25mm Cu plate / 20μmA for carbon jig
g-row / aluminum nitride substrate / (20 μm Ag-row /
50 μm Cu foil / 20 μm Ag wax) /0.25 mmC
u-plates are sequentially laminated, a weight of 200 g is placed, and H2
The mixture was heated to 840 ° C. in an atmosphere of a mixture of —N2 and the Ag braze was melt-bonded to produce an aluminum nitride—Ag braze—Cu joint.

Finally, aluminum nitride-Ag wax-C
electroless Ni-P on the surface of the Cu plate forming the u-joint surface
Plating was applied to a thickness of 4 μm. In the obtained aluminum nitride-Ag braze-Cu joint, the concave warpage on the surface was 6 μm / 30 mm. (Embodiment 2) In this embodiment, an aluminum nitride substrate and C
aluminum nitride-Ag comprising a u-plate and an Ag braze
It is a wax-Cu joined body. The joined body of Example 2 was manufactured in the same manner as in Example 1 except that the joined body of Example 1 did not have the intermediate layer made of copper foil.

At the time of manufacturing the joined body of Example 2, each thickness when laminated on a carbon jig is as follows:
It was manufactured by laminating in the order of 0.25 mm Cu plate / 20 μm Ag braze / aluminum nitride substrate / 20 μm Ag braze / 0.25 mm Cu plate. In addition, in the obtained aluminum nitride-Ag brazing-Cu joined body, the concave or convex warpage of the surface was 5 μm / 30 mm.

(Evaluation) As an evaluation of the joined bodies of Examples 1 and 2, a thermal cycle test was performed. The thermal cycle test is a test for measuring the bonding strength of a substrate when the thermal cycle is applied up to 5000 cycles, with one cycle of 125 ° C. for 3 minutes and −40 ° C. for 3 minutes.

The method of measuring the joining strength is as follows. A sample was prepared by joining an M5 size nut to the surface of the joined body of Example 1 and Example 2 by soldering, and the nut portion of the sample was pulled upward. The measurement was performed by measuring the strength at the time of breaking. The state of destruction was also observed. The state of this test is shown in FIG. Then, a stainless steel hook was passed through the nut of the test sample, and a tensile test was performed in this state. That is, by pulling the hook upward, the nut is pulled by the hook, and eventually comes off from the surface of the joined body. The joining strength was determined based on the breaking strength at this time. In addition, fracture sites were observed by classifying into fracture in the aluminum nitride base material and fracture in the solder joint.

(Results) The joined body of Example 1 had a joint strength value of 198 kgf when the number of cooling / heating cycles was 0, and at this time, the solder joint of the nut was broken. The joined body of Example 1 has a cooling / heating cycle number of 1,000,
At any cycle number of 2000, 3000, and 5000, the joint strength was 180 kgf or more, and the appearance of both fractures was at the nut solder joints.

In the joined body of Example 2, the value of the joining strength when the number of cooling / heating cycles was 0 was 201 kgf. At this time, the solder joint of the nut was broken.
Further, similarly to the joined body of Example 1, when the number of cycles is 1,000, 2000, and 3000, the joined strength of the joined body of Example 2 is 180 kgf or more. It was a destruction in the part, but 5
At 000 cycles, the bonding strength was 90 kgf, and the state of destruction was such that the aluminum nitride substrate was cracked.

As a comparative example, a conventional joined body directly joined to a Cu plate, aluminum nitride-A having a thick active metal brazing layer
The joining strength of the joined body composed of the g-Cu-plate was determined. The joined body in which the Cu plate was joined to the aluminum nitride plate as a conventional example using the eutectic liquid phase of Cu and O had a breaking strength of 140 kgf in 0 cycles of the same cooling and heating cycle as in the example, and the number of cycles Exceeds 100, the bonding strength is 50
kgf or less. In addition, the state of destruction was also caused by the cracking of the aluminum nitride substrate.

Further, a conventional bonded body in which a Cu plate is bonded with a Ti-Ag-Cu-based active metal braze of 30 μm has a bonding strength of 140 cycles at 0 cycle in the same cooling / heating cycle as in the embodiment.
kgf, and when the number of cycles exceeded 200, the bonding strength was 50 kgf or less. In addition, the state of destruction was also caused by the cracking of the aluminum nitride substrate.

As described above, the joined body of the embodiment has a sufficient joining strength even when the number of cooling / heating cycles is increased. Since the aluminum nitride substrate has high thermal conductivity, the aluminum nitride-Ag braze-Cu bonded body of this example is useful as a substrate for a high current circuit such as a power module. In addition, it is resistant to cooling and heating cycles and can be used in harsh environments such as automobiles. As an example of use, an inverter having a fin formed of aluminum on the back surface side can be cited.

(Embodiment 3) First Embodiment and Second Embodiment
With regard to the bonded body of Example 1, evaluation was performed up to 5000 cycles, with the target value of the durability being 3000 cycles of cooling and heating. The target value of the durability is based on the assumption that the engine room will be further mounted in a vehicle. However, in the evaluation of Example 1 and Example 2, the bonding strength of Example 1 did not decrease even after 5000 cycles of cooling and heating. Also in Example 2, the bonding strength was halved in 5000 cycles, but 3000
There was no strength reduction until the cycle.

Therefore, a more severe test was performed to try to determine the limit value of the cooling / heating cycle. The means include conducting a thermal test up to a longer cycle and joining Cu
We chose to make the board thicker. When the Cu plate becomes thicker, thermal stress applied to the aluminum nitride substrate during cooling after joining increases. Further, the configuration of the Ag row is slightly different between the first embodiment and the second embodiment. In Example 2, 20 μm Ag brazing was arranged on both sides of the aluminum nitride substrate, whereas in Example 1, one side was 20 μm Ag brazing and the other side was 2 μm.
A laminated material having a 50 μm Cu foil sandwiched between two 0 μm Ag brazing foils is used. Therefore, as Example 3, in order to compare and evaluate the Ag brazing single-layer bonding and the laminated Ag brazing with the Cu foil interposed therebetween, a Cu plate was bonded to both surfaces of the aluminum nitride substrate with the laminated Ag brazing material with the Cu foil interposed therebetween.

(Manufacturing Method of Embodiment 3) A manufacturing method of an aluminum nitride-Ag braze-Cu joint in this embodiment will be described below. First, an aluminum nitride substrate was manufactured in the same manner as in Example 1. Here, the break line and the plate thickness of the aluminum nitride plate, the Pd plating thickness, and the Ni of the outermost surface
The plating thickness is the same as in Example 1. Next, a Cu plate / (20 μm Ag wax / 50 μm Cu foil / 2
0 μm Ag wax) / aluminum nitride substrate / (20 μm
Ag wax / 50 μm Cu foil / 20 μm Ag wax) / Cu
The boards are sequentially laminated and put on a weight of 200 g.
The mixture was heated to 840 ° C. in a mixed atmosphere to melt-bond the Ag braze. Here, the thicknesses of the two Cu plates are the same, and the thicknesses of the Cu plates are 0.25 mm, 0.3 mm, 0.5
Aluminum nitride-Ag braze-Cu
A joined body was manufactured. Finally, electroless Ni-P plating was applied to the surface of the Cu plate of the three types of aluminum nitride-Ag braze-Cu joints to a thickness of 4 µm.

(Evaluation) Similarly to the evaluations of Examples 1 and 2, a cooling / heating cycle test was also performed on Example 3.
For comparison, a cooling / heating cycle test was performed again on Example 2.

(Results) In Example 3, the thickness of the Cu plate was 0.2
The 5 mm bonded body exceeded 5,000 cycles of cold and heat, and was 180 kgf or more even in 10,000 cycles of cold and hot. Further, the joined body of the comparative example of Example 2 has
The load was 180 kgf or more up to the 00 cycle, and the state of destruction was that the solder joint of the nut was broken.
In the 0 cycle retest, the load was 160 kgf and in the 10000 cycle it was 80 kgf, and the state of destruction was such that the aluminum nitride substrate cracked.

When the test of the joined body of the Cu plate having a thickness of 0.25 mm in the third embodiment and the comparative example 2 was further continued until 20,000 cycles of cooling and heating, the Cu plate having a Cu plate thickness of 0.25 mm was obtained in the third embodiment.
In 25 mm, the solder joint was broken at 180 kgf or more, and in Example 2, at the time of removal from the thermal test machine, the aluminum nitride substrate had already been torn at the center in the thickness direction, and the bonding strength could not be measured. . From the above,
In Example 3, the joined body having a Cu plate thickness of 0.25 mm is 20
It has sufficient bonding strength even in a severe deterioration test of 000 cycles, and is inferior to this, but the bonded body of Example 2 also has sufficient bonding strength even when the number of cooling and heating cycles is large. Was reproduced.

On the other hand, in Example 3, the thickness of the Cu plate was 0.3 m.
Both the joined body of m and the joined body of 0.5 mm were evaluated up to 10,000 cycles of cooling and heating. In Example 3, the joined body having a Cu plate thickness of 0.3 mm was broken at 180 kgf or more up to 10,000 cycles of cooling and heating. Also,
The joined body having a Cu plate thickness of 0.5 mm had a solder joint failure at 180 kgf or more up to 3000 cycles of cooling and heating, but the aluminum nitride substrate broke at 50 kgf at 5000 cycles and was taken out of the cooling test machine at 10000 cycles. At this point, it had already been torn at the center of the aluminum nitride substrate. Therefore, Example 3 is based on Cu
Even under the extremely severe condition of a plate thickness of 0.5 mm, the target value of the durability assuming that it is mounted on an engine room for in-vehicle use and satisfies 3000 cycles of cooling and heating.

[0049]

The ceramic-metal joined body of the present invention is
There is a soft low melting point metal layer between the high thermal conductive ceramic base material and the high conductive metal plate, and at least one thin strain relaxation layer. With this strain relaxation layer, the thermal stress at the time of manufacturing the joined body is relaxed, and the thermal stress due to heat such as a thermal cycle during use is relaxed by the soft low melting point metal layer.

Even if the number of thermal cycles increases, the distortion of the joined body itself can be reduced, so that it is suitable for a substrate for a high current circuit through which a high current flows.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the thickness of an Ag brazing layer and the radius of curvature of a Cu plate.

FIG. 2 shows the aluminum nitride-Ag wax-C of Example 1.
It is sectional drawing of a u junction.

FIG. 3 is a view showing a method of measuring a bonding strength.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate 10 ... Ceramic substrate 1
DESCRIPTION OF SYMBOLS 3 ... Pd layer 15 ... Ni plating layer 3 ... Metal plate 51 ... Surface bonding layer 52 ... Ag brazing layer
53 ... Intermediate layer 55 ... Back joining layer 71 ... Nut 73 ... Soldering joint
75 ... hook

Claims (6)

[Claims] 1. A ceramic comprising a high thermal conductive ceramic substrate, a high conductive metal plate, and a low melting point metal layer interposed between the high thermal conductive ceramic substrate and the high conductive metal plate and integrally joined. A ceramic-metal joined body, wherein the low melting point metal layer is soft and has at least one strain relaxation layer made of silver brazing or solder having a thickness of 40 μm or less. . 2. The high thermal conductive ceramic substrate is a substrate formed of one of boron nitride, aluminum nitride, silicon nitride, and alumina, and the highly conductive metal plate is at least one of copper, aluminum, tungsten, and molybdenum. 2. The ceramic-metal joint according to claim 1, wherein the ceramic-metal joint is formed of a kind of metal or an alloy thereof. 3. The high thermal conductive ceramic substrate is an aluminum nitride substrate, the highly conductive metal plate is a copper or copper alloy metal plate, and the strain relief layer is formed of silver brazing. 2. The ceramic-metal joined body according to 1. 4. The ceramic-metal joined body according to claim 3, wherein said strain relaxation layer has a thickness of 20 μm or less. 5. The laminated brazing material according to claim 1, wherein the low-melting-point metal layer includes at least one intermediate layer made of a copper foil or a copper alloy foil, and the strain relief layer located on both surfaces of the intermediate layer and between the intermediate layers. The ceramic according to claim 3, which is formed of
Metal joint. 6. The ceramic according to claim 3, wherein said high thermal conductive ceramic substrate is plate-shaped, and said highly conductive metal plates are integrally joined to both surfaces thereof via said low melting point metal layer. -Metal joints.