JPH06263554A - Jointed substrate of ceramics-metal - Google Patents

Abstract

PURPOSE:To provide a joined substrate of ceramics-metal, satisfying a high joining strength and simultaneously having excellent heat-resistant cycle characteristics and high reliability. CONSTITUTION:This joined substrate of ceramics-metal is obtained by joining a metallic plate through a solder layer containing at least one active metal selected from Ti, Zr, Hf and Nb on at least one principal plane of an aluminum nitride-based ceramic substrate thereto. The content of a liquid-phase component in the vicinity of the joining surface of the aluminum nitride-based ceramic substrate to the metallic plate is regulated to <=1wt.%. Otherwise, the area (A) of the joining surface (1a) of the metallic plate 1 to the ceramic substrate 2 is smaller than the area (B) on the side of the surface (1b) and the area (C) of the solder layer 3 containing the active metal is larger than the area (A) of the joining surface (1a) of the metallic plate 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bonded substrate of a ceramic substrate and a metal plate, and more particularly to a ceramic-metal bonded substrate having excellent heat resistance cycle characteristics.

[0002]

2. Description of the Related Art Generally, ceramic materials are characterized by being lightweight and having high hardness, excellent electrical insulation properties, and excellent heat resistance and corrosion resistance. It is used as a material.
In particular, aluminum nitride-based ceramic materials have been attracting attention as substrates for mounting semiconductor elements that emit a large amount of heat because of their high thermal conductivity, and their practical use is being promoted.

By the way, when a ceramic member is used as a mounting board for electronic parts, it is indispensable to join a metal member in order to form a circuit and a part mounting portion. As a method of joining the ceramics substrate and the metal plate,
Conventionally, the method of using refractory metals such as Mo and W, Cu-Cu
A method of directly joining copper plates using a eutectic of ₂ O (DBC
Method), a method using an active metal such as a 4A group element or a 5A group element is known, and among them, the active metal method is widely used because high strength and high sealing property can be obtained. is there.

The above-mentioned active metal method is a bonding method utilizing the fact that metal elements such as Ti, Zr, Hf and Nb easily wet and react with ceramic members, particularly nitride ceramic members such as aluminum nitride. , And is generally used as a brazing method using a brazing material to which an active metal is added. Specifically, it is a method of adding an active metal such as Ti to a eutectic brazing material of Cu and Ag, interposing this between a ceramic substrate and a metal plate, and performing heat treatment at an appropriate temperature to bond them. .

[0005]

By the way, while a high bonding strength is required for the bonded substrate of the ceramic substrate and the metal plate, the coefficient of thermal expansion of the ceramic material is smaller than that of the metal material. There is a strong demand for suppressing the occurrence of defects caused by the difference. That is,
When a ceramic substrate and a metal plate, which differ greatly in thermal expansion coefficient, are joined, residual stress caused by the difference in thermal expansion occurs during the cooling process after joining, and the joint strength is greatly reduced due to the synergistic effect with external stress. Cracks may occur from the maximum stress point due to the subsequent cooling process or the addition of thermal cycles,
Further, it causes problems such as destruction of the ceramic substrate.

On the other hand, the bonding substrate to which the above-mentioned active metal method is applied has high bonding strength and DBC.
Compared with other methods, since the brazing filler metal layer acts as a stress relaxation layer, it has relatively good heat resistance cycle characteristics, but it is not sufficient considering that it is used as a mounting board for semiconductor elements whose heat dissipation increases year by year. Notably, there has been a strong demand for improvement in heat-resistant cycle characteristics. In addition, in the conventional bonded substrate, stress concentration is likely to occur at the edge portion (bonding edge corner portion) of the metal plate in terms of shape, and cracks are likely to occur from such a portion, so that the stress concentration due to shape is reduced. There has been a demand for alleviation to further improve the heat resistance cycle characteristics.

The present invention has been made in order to solve such a problem, and provides a highly reliable ceramic-metal bonded substrate which satisfies high bonding strength and shows excellent heat cycle characteristics. It is an object.

[0008]

In order to achieve the above-mentioned object, the present inventor has conducted various studies on conventional ceramics-metal bonded substrates. As a result, when an aluminum nitride-based substrate is used, Found that fragile liquid-phase components such as Al ₅ Y ₃ O ₁₂ (YAG) and AlYO ₃ (YAL) present on the surface of the steel are factors that reduce reliability. That is, when a metal plate is joined to a surface of aluminum nitride having a relatively large amount of fragile liquid phase component by a brazing material containing an active metal, even if high joining strength is obtained, it becomes fragile due to the addition of heat cycle. A crack is generated from the portion where the liquid phase component is present, and the joint strength and the like are reduced accordingly.

The first invention of the ceramic-metal bonded substrate relating to the present invention was made on the basis of the above-mentioned findings, and comprises an aluminum nitride ceramic substrate, Ti, and Z.
Ceramic-metal bonding comprising a metal plate bonded to at least one main surface of the aluminum nitride ceramic substrate through a brazing material layer containing at least one active metal selected from r, Hf and Nb On the board,
The aluminum nitride ceramic substrate is characterized in that the amount of liquid phase component in the vicinity of the bonding surface with the metal plate is 1% by weight or less.

The second invention of the ceramic-metal bonded substrate according to the present invention focuses on the shape on the metal plate side, and improves the shape near the interface on the metal plate side after heat bonding so that the bonding end is improved. It was made by finding that the stress concentration of
A ceramic-metal bonded substrate comprising a metal plate bonded to at least one main surface of the ceramic substrate via a brazing material layer containing at least one active metal selected from Ti, Zr, Hf and Nb In, the metal plate is
The area of the joint surface with the ceramic substrate is smaller than the area on the front surface side, and the area of the brazing material layer containing the active metal is larger than the area of the joint surface of the metal plate.

The ceramic-metal bonded substrate of the present invention is
A ceramic substrate and a metal plate are joined together using a brazing material containing at least one active metal selected from Ti, Zr, Hf and Nb (hereinafter referred to as active metal brazing material). The brazing filler metal used here is, for example, a eutectic composition of Ag-Cu (72 wt% Ag-28 wt% Cu) or a composition near Ag-C.
Examples include u-based brazing materials and Cu-based brazing materials. Then, the above active metal is added to these brazing filler metals with respect to the total amount of the brazing filler metal.
Add about 10% by weight to 10% by weight to use as an active metal brazing material. The composition of the Ag-Cu brazing filler metal is preferably such that the amount of Cu is about 15% by weight to 35% by weight with respect to the total amount of the brazing filler metal.

In addition, the above active metal brazing material is practically used by being mixed and dispersed in a resin binder to form a paste. At this time, the amount of oxygen contained in the paste is 30 ppm
The following is preferable. For example, considering the joining form between the nitride ceramics substrate and the active metal brazing material, the active metal (for example, Ti) in the brazing material reacts with nitrogen in the ceramic, and a compound of the active metal and nitrogen is formed at the joining interface. By forming the layer (for example, TiN layer), the ceramic substrate and the active metal brazing material, and by extension, the metal plate are firmly bonded. Here, an active metal such as Ti is more likely to react with oxygen than nitrogen in terms of free energy of formation. Therefore,
If the brazing paste contains a large amount of oxygen, it reacts with oxygen before it reacts with nitrogen in the ceramics, making it impossible to uniformly form a compound layer of the active metal and nitrogen. On the other hand, by setting the oxygen content in the brazing paste to 30 ppm or less in advance, the reaction between the active metal and nitrogen in the ceramics can be promoted, thus reproducing a high-strength ceramic-metal bonded substrate. It is possible to obtain it with good performance.

The ceramic substrate used in the above-mentioned first invention is composed of a sintered body containing aluminum nitride as a main component and yttrium oxide, aluminum oxide or the like as a sintering aid component (liquid phase forming component). is there. here,
The aluminum nitride ceramic substrate used in the first invention has a liquid phase component content of 1% by weight or less in the vicinity of the bonding surface with the metal plate. The liquid phase component here is
Al ₅ Y ₃ O ₁₂ (YAG) formed by the above sintering aid component
AlYO ₃ (YAL) and the like, which are basically present at the grain boundaries, have the property of leaching in the surface direction during firing (sintering). Therefore, in the stage after sintering,
A relatively large amount of liquid phase component is present on the surface of the sintered body.

Here, when Ti is used as an active metal, the interface between the aluminum nitride-based substrate and the metal plate after bonding is
TiN formed at the interface between aluminum nitride and brazing material layer
And a brazing material layer that does not contain much active metal. It is considered that the stress caused by the difference in linear expansion coefficient between the aluminum nitride-based substrate and the metal plate after heat bonding or when a heat cycle is applied is alleviated particularly by the former TiN layer. However, when a metal plate is bonded to the surface of an aluminum nitride-based substrate having a relatively large amount of the liquid phase component as described above with an active metal brazing material, the reaction between aluminum nitride and the active metal is inhibited, and the optimum The TiN layer is not formed to the thickness, and as a result, the stress applied to the aluminum nitride-based substrate increases. Further, since the liquid phase component is composed of a brittle compound, the portion where the liquid phase component exists becomes a starting point of cracking due to the addition of the heat cycle. Due to these, the heat resistance cycle characteristic is significantly deteriorated.

Therefore, in the first invention, the amount of the liquid phase component in the vicinity of the bonding surface of the aluminum nitride ceramics substrate with the metal plate is set to 1% by weight or less. In this way, by reducing the amount of liquid phase component on the bonding surface, the thickness of the reaction layer (for example, TiN layer) at the bonding interface can be optimized, so that the stress applied to the aluminum nitride-based substrate can be relaxed, Therefore, a bonded substrate having excellent bonding strength and heat cycle characteristics can be obtained. In addition,
In the present invention, the liquid phase component amount in the vicinity of the surface refers to a value measured by, for example, X-ray diffraction, and refers to a weight ratio of the liquid phase component in the range of 10 μm from the surface in the depth direction.

The above-mentioned aluminum nitride ceramics substrate in which the amount of liquid phase component in the vicinity of the bonding surface is 1% by weight or less is an appropriate range in the depth direction from the surface after sintering.
It is obtained by grinding by honing or the like. The amount of grinding from the sintered surface shall be set so that the amount of liquid phase component in the vicinity of the surface is 1% by weight. Specifically, grinding in the depth direction (plate thickness direction) is about 3 to 5 μm. Preferably.

The ceramic substrate used in the second invention is not particularly limited to its material, and it may be an aluminum oxide sintered substrate or a mullite sintered body (3Al ₂ O 3).
From ₃ -2SiO ₂₎ based oxide based substrate, such as a substrate, sintered aluminum system board nitride, to non-oxide substrates such as silicon carbide sintered system board, it is possible to apply various ceramic materials, applications Ya It is possible to appropriately select and use it according to required characteristics. However, it is particularly effective for an aluminum nitride-based substrate which has relatively low mechanical strength and is susceptible to cracks and the like due to the addition of heat cycles.

The metal plate used in the present invention may be appropriately selected from various metal materials according to the application, for example, Cu plate, Cu
Examples include alloy plates, Ni plates, Ni alloy plates, single plates such as W and Mo, and alloy plates. Further, regarding the first invention, the shape thereof is not particularly limited, and may be set according to the application or the like. The metal plate may be bonded to at least one main surface of the ceramic substrate, but from the viewpoint of stress relaxation,
It is preferable to bond to both main surfaces of the ceramic substrate.

The metal plate used for the ceramic-metal bonded substrate of the second invention has an area slightly smaller than the required surface area of the metal plate. That is, when the ceramic substrate and the metal plate are heat-bonded, the metal plate expands according to the bonding temperature due to the difference in linear expansion coefficient between the two.
Here, in the cooling process after joining, the joining surface side of the metal plate is fixed to the brazing material layer, but there is no particular limitation on the surface side, so that the metal sheet expands according to the difference in linear expansion coefficient. The initial metal plate shape is set so that the surface area of the metal plate after the heating and joining is the required surface area of the metal plate.

At this time, the application area of the paste containing the active metal brazing material is set to be an area slightly smaller than the required surface area of the metal plate, like the initial shape of the metal plate. When the above-mentioned metal plate having a slightly smaller area is placed on the coating layer of the brazing material paste and heat-bonded, the brazing material paste wets the ceramics substrate after liquefaction and begins to flow a little, Spreads on the substrate slightly larger than the junction end of.
On the other hand, since the joining surface side of the metal plate is fixed to the brazing material layer as described above, the joining area is formed by substantially maintaining the area. Moreover, since the surface side of the metal plate expands, it becomes slightly larger than the joint end. This state is shown in FIGS. 1 and 2.

That is, the metal plate 1 is the ceramic substrate 2
The area (A) of the joint surface 1a with and the area (B) on the surface 1b side
The area (C) of the brazing material layer 3 which is smaller and which contains the active metal is larger than the area (A) of the joining surface 1a of the metal plate. Here, the area (B) on the surface 1b side of the metal plate 1 is
It is the required metal plate area. The shape of the vicinity of the interface on the side of the metal plate 1 and the shape of the brazing material layer 3 after heat bonding are
Shapes as described above (B> A, C> A, and brazing material layer 3)
Is spread in the plane direction on the ceramic substrate 2), the stress concentration at the joint end is relaxed, and the residual stress can be reduced. This makes it possible to improve the bonding strength and the heat resistance cycle characteristics.

As described above, the shapes of the vicinity of the interface on the side of the metal plate 1 and the shape of the brazing material layer 3 after the above-mentioned heat bonding satisfy the areas A, B, and C satisfying B> A and C> A, respectively. However, the ratio is not particularly limited.

The ceramic-metal bonded substrate of the present invention is
For example, it can be manufactured as follows.

First, a ceramics substrate and a metal plate are prepared, and a brazing material containing an active metal as described above is made into a paste and applied to, for example, the ceramics substrate side. Here, regarding the second invention, the brazing material layer is applied so that the application area thereof is slightly smaller than the required metal plate area. In addition, the coating thickness of the brazing material layer is preferably such that the layer thickness of the brazing material layer after heating and joining is 40 μm in order to improve the heat resistance cycle characteristics. The thickness is preferably 30 μm or less, though depending on the case. If the layer thickness of the brazing filler metal layer after heat bonding exceeds 40 μm, the thickness of the reaction layer will become too thick for the addition of heat cycle.
On the contrary, the stress applied to the ceramics may increase, and the heat cycle characteristics may be deteriorated.

Next, a metal plate is laminated on the ceramic substrate coated with the brazing material paste, and the temperature corresponding to the brazing material used, such as Ag, is set in vacuum or in an inert atmosphere such as an argon atmosphere. -Cu-based brazing material is Ag-Cu
Heat treatment is performed at a temperature at which a eutectic is formed, and the ceramic substrate and the metal plate are joined together by utilizing the liquid phase of the brazing material and the reaction between the active metal and the ceramic. Further, as described above, it is preferable that the bonding atmosphere is a vacuum or an inert atmosphere also in order to inhibit the reaction between the active metal in the brazing paste and oxygen.

When the circuit is formed on the metal plate, the circuit may be formed by etching after the metal plates are joined together, or the circuit-formed metal plates may be joined together. However, regarding the second invention, the latter method is adopted.

[0027]

EXAMPLES Next, examples of the present invention will be described.

Example 1 First, a sintered body (shape: 63 mm × 29 mm × thickness: about 0.635 mm: thermal conductivity = 170 W / m K) for an AlN substrate was prepared. This AlN
The sintered body contains AlN as the main component and 3% by weight as a sintering aid.
It contains Y ₂ O ₃ . At the stage after this sintering, the surface of the sintered body was subjected to X-ray diffraction and the amount of liquid phase components on the surface was measured. As a result, the amount of YAG was 2.3% by weight and the amount of YAL was 4.5% by weight.

Next, honing was performed twice on both main surfaces of the AlN sintered body, and grinding was performed in the depth direction by about 3.8 μm. The honing conditions are # 220WA, pressure 3.5kgf / cm.
^2. Belt speed was 1.8m / min. After this honing process, the amount of liquid phase components on the surface of the AlN sintered body was measured in the same manner.YAG amount was 0.2% by weight, YAL amount was 0.3% by weight (total
0.5% by weight).

On the other hand, an active metal-containing brazing material having a weight ratio of Ag: Cu: Ti = 67.7: 26.3: 6.0 was prepared, a resin binder and a dispersion medium were added to the brazing material in appropriate amounts, and the brazing material paste was thoroughly mixed. Was produced. This brazing paste was screen-printed on the surface of the AlN sintered body after the honing so that the coating thickness was 30 μm.

Then, as shown in FIG. 3, a patterned Cu plate 11 having a thickness of 0.3 mm is used as a semiconductor element mounting side metal plate (front pattern), and a heat radiation side metal plate (back pattern).
As a result, a Cu plate 12 with a thickness of 0.25 mm is placed on each coating layer of the brazing filler metal paste, and is placed in a vacuum of 1 × 10 ⁻⁴ Torr.
Bonding was performed under the condition of 50 ° C. × 10 minutes. In this way, Al
An AlN—Cu bonded substrate 15 was obtained in which the Cu plates 11 and 12 were bonded to both main surfaces of the N-based substrate 13 via the active metal-containing brazing material layer 14, respectively. The active metal brazing material layer 14 had a thickness of about 35 μm.

As a comparison with the present invention, A after sintering
lN substrate (YAG amount = 2.3% by weight, YAL amount = 4.5% by weight, total
6.8% by weight) except that the Cu plates were joined in the same manner as in the above example (Comparative Example 1), and an AlN-based substrate with only one honing process (YAG amount = 1.2% by weight, YAL amount = 2.1 Weight
%, A total of 3.3% by weight) was used, and a Cu plate was joined (Comparative Example 2) in the same manner as in the above-mentioned Examples.

The characteristics of each AlN-Cu bonded substrate produced in Example 1 and Comparative Examples 1 and 2 were evaluated as follows. First, the peel strength was measured as the bonding strength of each AlN-Cu bonded substrate. In addition, as the heat resistance cycle characteristic η, the presence or absence of cracks after the heat cycle test (TCT) is determined by fluorescence penetration testing (P
T) Evaluated by inspection. The TCT conditions were -40 ° C × 30 minutes + RT × 10 minutes + 125 ° C × 30 minutes + RT × 10 minutes as one cycle. After 30 cycles of this, the presence or absence of cracks was evaluated. The results are shown in Table 1 together with the amount of liquid phase components on the surface. The evaluation results of the heat resistance cycle characteristic η were shown as 100% "no crack by TCT" and 0% "total crack generation by TCT".

[0034]

[Table 1] As is clear from Table 1, the AlN-Cu bonded substrate according to Example 1 using the aluminum nitride-based substrate in which the liquid phase component amount in the vicinity of the surface is 1% by weight or less has sufficient bonding strength and thermal cycling. It can be seen that even after the test, almost no cracks were generated and the heat cycle characteristics were excellent.
On the other hand, the AlN-Cu bonded substrates according to Comparative Example 1 and Comparative Example 2 each have high initial bonding strength, but many cracks have occurred after the thermal cycle test, resulting in a decrease in bonding strength. It is clear.

Example 2 First, 98% by weight of Ag-Cu eutectic alloy powder (72 wt% Ag-28 wt% Cu) was added.
To 100 parts by weight of powder mixed with 2% by weight of Ti powder, 10 parts by weight of carboxyl group-polymerized acrylic resin, 20 parts of terpineol and 0.1 cc of oleic acid were added, and sufficiently mixed to prepare a brazing paste. .

Two brazing pastes were prepared, one of which was
(a) Stored in a nitrogen box under conditions of temperature of 20 ° C and humidity of 40%, and the other one was stored in (b) atmosphere for 3 months. When the contents of oxygen in these brazing pastes were analyzed, the results were 25 ppm for (a) and 300 ppm for (b).

Using these two brazing filler metal pastes, AlN-Cu bonded substrates were prepared in the same manner as in Example 1. However, phosphorus deoxidized copper was used as the copper plate. The peel strength and heat cycle characteristics (TCT 100 cycles) of each AlN-Cu bonded substrate thus obtained were measured and evaluated. The results are shown in Table 2.

[0038]

[Table 2] From Table 2, it can be seen that the oxygen content of the brazing paste has an effect on the bonding strength and heat cycle characteristics.

Example 3 Ag: Cu: Ti = 67.7: 26.3: 6.0 by weight on an AlN-based substrate (thermal conductivity = 170 W / m K) similar to the AlN sintered body used in Example 1.
A brazing material paste obtained by adding an appropriate amount of a resin binder and a dispersion medium to the active metal-containing brazing material of was screen-printed so as to have a size of 1 / 1.01 of a desired metal plate pattern (surface pattern of the metal plate after joining). The coating thickness of the brazing paste was 30 μm.

Next, on the printed pattern of the above-mentioned brazing filler metal paste, in a similar manner, 1 / 1.01 of the desired metal plate pattern is formed.
Place a Cu plate, and in a vacuum of 1 × 10 ^-4 Torr, 850 ℃ × 10
The desired pattern size is obtained by joining under the condition of min.
An AlN-Cu bonded substrate was obtained.

When the shape of the joint interface of the AlN-Cu jointed substrate thus obtained was examined, as shown in FIG. 2, the area (A) of the joint surface 1a of the Cu plate 1 with the AlN-based substrate 2 was examined. On the surface 1
The area was smaller than the area (B) on the b side, and the bonding surface 1a of the Cu plate 1 with the AlN-based substrate 2 was sufficiently covered with the active metal brazing material layer 3. The thickness of the active metal brazing material layer 3 is about
It was 35 μm.

Next, the heat resistance cycle characteristics of the AlN-Cu bonded substrate were evaluated in the following manner. First, the same TCT as in Example 1 was performed for 20 cycles, 30 cycles, and 50 cycles, respectively, to measure the peel strength of the bonded substrate after each test and to evaluate the presence or absence of cracks. As a result, the peel strength was 10% for all AlN-Cu bonded substrates after TCT.
A good value of about 12 kgf / mm was shown, and no crack was observed.

[0043]

As described above, according to the ceramic-metal bonded substrate of the present invention, it is possible to stably obtain a high bonding strength and suppress cracks on the ceramic substrate side due to the addition of a heat cycle. it can. Therefore, it is possible to provide a highly reliable ceramic-metal bonded substrate having high bonding strength and excellent thermal cycle characteristics with good reproducibility.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing one structural example of a ceramics-metal bonded substrate of the present invention.

FIG. 2 is an enlarged view showing a main part of the ceramic-metal bonded substrate shown in FIG.

FIG. 3 is a cross-sectional view showing a ceramic-metal bonded substrate according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Metal plate 1a ... Bonding surface with ceramic substrate 1b ... Surface 2 ... Ceramic substrate 3 ... Brazing material layer containing active metal 11 ... Patterned Cu plate on semiconductor element mounting side 12 ... Heat radiation side Cu plate 13 ... AlN-based substrate 14 ... Active metal-containing brazing material layer 15 ... AlN-Cu bonding substrate A ... Area of bonding surface of metal plate with ceramics substrate B ... Area of front surface side of metal plate C ... Brazing material layer area

Claims (3)

[Claims] 1. An aluminum nitride ceramic substrate,
A ceramic comprising a metal plate bonded to at least one main surface of the aluminum nitride ceramic substrate through a brazing material layer containing at least one active metal selected from Ti, Zr, Hf and Nb. In the metal-bonded substrate, the aluminum-nitride-based ceramic substrate has a liquid phase component content of 1% by weight or less in the vicinity of the bonding surface with the metal plate. 2. The ceramic-metal bonded substrate according to claim 1, wherein the brazing material layer containing the active metal has a thickness of 40 μm or less. 3. A ceramic substrate and Ti, Zr, Hf and Nb
In a ceramic-metal bonded substrate comprising a metal plate bonded to at least one main surface of the ceramic substrate via a brazing material layer containing at least one active metal selected from The area of the bonding surface with the ceramics substrate is smaller than the area on the surface side, and the area of the brazing material layer containing the active metal is larger than the area of the bonding surface of the metal plate. .