JPH0653624A - High-strength aluminum nitride circuit board and its manufacture - Google Patents

Abstract

PURPOSE:To obtain a high-strength circuit board through brazing by controlling the weight ration of oxygen/yttrium in ceramics, diffraction-resistant strength of a ceramic substrate, remaining quantity of boron nitride on the surface of the ceramic substrate, and roughness on the surface. CONSTITUTION:A ceramic substrate 1 has main composition of aluminum nitride. It has diffraction-resistant strength of more than 30kg/mm<2>, the weight ration of oxygen to yttrium (Owt/Ywt) of more than 0.7, the ratio of substrate surface roughness Ra to average crystal grain diameter D (Ra/D) of less than 11X10<-2>, and the ratio of X-ray diffraction strength of remaining boron nitride on the substrate surface layer to X-ray diffraction strength of aluminum nitride (IBN/ IAIN) of more than 6X10<-2>. On either main side of the substrate 1 is formed a conductive circuit 2 through a single element of at least 1 kind selected from a group composed of Ti, Zr, and Hf, or a wax material 3 containing hydrogen compound.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit board made of a high-strength AlN ceramics / metal composite and a method for manufacturing the same, and more specifically, it has high thermal conductivity and high strength suitable for mounting integrated circuits and semiconductor parts. The present invention relates to an aluminum nitride circuit board and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, a ceramic circuit board having a conductive circuit has been widely used as a mounting board for electronic parts such as hybrid ICs and high-power modules that generate a large amount of heat. Attention has been focused on the application of AlN ceramic circuit boards with high index,
In order to manufacture a high-quality AlN ceramic circuit board, various measures have been taken in manufacturing a ceramic board, forming a conductive circuit, and the like.

In AlN, Al ₂ O ₃ is Al ₂ O ₃ = 2Al + as the aluminum vacancy V _Al is formed.
It is known to exist in the form of 3O + V _Al . Also,
Y ₂ O ₃ reacts with Al ₂ O _{3 in} AlN at a high temperature to form a liquid of a complex oxide of aluminum and yttrium to promote sintering, and the sintered substrate has a grain boundary of AlN ceramic crystal grains. Al ₂ Y ₄ O ₉ (YAM), AlYO ₃ (Y
It is known that aluminum and yttrium complex oxides such as AL) and Al ₅ Y ₃ O ₁₂ (YAG) exist.

Therefore, in the production of AlN ceramic substrates, in order to obtain a dense substrate, rare earth oxides represented by yttria (Y ₂ O ₃ ) and alkaline earth oxides represented by calcia are generally contained in a percentage of several percent. The thing is added as a sintering aid. For example, AlN ceramic substrates with high thermal conductivity currently on the market generally have 2 to
About 8 wt% Y ₂ O ₃ is added.

When mass-producing AlN ceramic substrates, several or several tens of substrates are stacked and sintered at one time. At this time, separation is performed to prevent adhesion between the substrates. Boron nitride (BN) and the like have been widely used as agents.

On the other hand, in forming a conductive circuit on the surface of a ceramic substrate, a conductive paste is printed on the surface of the substrate and the conductive circuit is formed by firing at a high temperature (Japanese Patent Laid-Open No. 2-149485, Japanese Patent Laid-Open No. 2-149485). 2-258686), the AlN ceramic substrate is previously treated in air at a temperature of about 1000 ° C. to generate alumina on the surface of the substrate, and then heated in an inert atmosphere using a copper plate containing oxygen. Alternatively, by heating oxygen-free copper in an oxidizing atmosphere, a eutectic solution of Cu ₂ O and Cu is generated at the interface, and an AlN ceramic substrate and a copper plate on which alumina is formed on the surface. Direct bonding method to form a conductive circuit by joining the wires (Japanese Patent Laid-Open No. 3-93687), and a brazing material is applied in a circuit shape on the substrate surface, and a copper part is placed on this brazing material and heated. By chance A method such as a brazing method for joining a substrate and a copper part to form a conductive circuit has been generally used. In particular, in the case of forming a conductive circuit at the time of manufacturing a high power circuit board, a direct bonding method or a brazing method has been mainly used.

On the surface of the AlN ceramic substrate,
There is a surface layer with a high grain boundary constituent phase component formed by the exudation of the grain boundary constituent phase component, and impurities such as a mold release agent remain on the surface and hinder the bonding between aluminum nitride and the conductive circuit. Therefore, Japanese Patent Laid-Open No. 2-258686 discloses an invention in which a grain boundary constituent phase component needs to be removed by a method such as lapping and honing when a conductive circuit is formed by a metallizing method.

Further, in Japanese Patent Laid-Open No. 2-149485, the grain boundary constituent phase components deposited on the surface of the AlN ceramic substrate roughen the bonding surface, lower the bonding strength between the ceramic substrate and the conductor, and reduce the thermal conductivity. In order to impair the temperature, a method of removing the surface grain boundary constituent phase component by a liquid solvent is disclosed.

Furthermore, Japanese Patent Laid-Open No. 3-93687 discloses AlN.
Grain boundary constituent phase components deposited on the surface of the ceramic substrate remain on the surface of the AlN ceramic substrate with almost no effect of oxidation treatment, and adhere between the surface coating layer (aluminum oxide layer in the direct bonding method) and the ceramic substrate. It discloses a method of forming a surface coating layer after performing a chemical surface treatment using an acidic solution to remove the grain boundary constituent phase components in order to reduce the force.

[0010]

In a ceramic circuit board for a high power power module, not only semiconductors and integrated circuits but also coarse electrodes are connected on the board, and a large force is applied to the ceramic circuit board. Further, in integrated circuit boards, miniaturization of conductive circuit patterns has been promoted. Therefore, in recent years, although high-strength bonding between the conductive circuit and the ceramic substrate is required, when a circuit board is manufactured by the above-mentioned conventional direct bonding method, the conductive circuit portion of the substrate and the ceramic substrate are Peel strength is 10kg /
I could only get around cm. Further, when the circuit board is manufactured by the brazing method, the average value of the bonding strength is high, but the variation is large, and the peel strength may be 10 kg / cm or less.

Therefore, when such a low-bonding-strength substrate is used as a power module circuit substrate, there is a problem that peeling easily occurs at the joint between the conductive circuit and the ceramic substrate.

Therefore, an object of the present invention is to solve the above-mentioned problems of the conventional techniques and to provide a high-strength aluminum nitride circuit board having a stable and sufficient bonding strength and a method for manufacturing the same.

[0013]

Means for Solving the Problems The present invention has been intensively studied to solve the above problems, and as a result, the bending strength of a ceramic substrate, the weight ratio of oxygen and yttrium in the ceramic substrate, the surface roughness of the ceramic substrate, It has been found that the amount of boron nitride remaining on the surface of the ceramic substrate and the bonding temperature have a strong influence on the bonding strength, and the present invention can be provided.

That is, the present invention has a bending strength of 30 kg / mm.
² or more, the ratio of the oxygen content (Owt) to the yttrium content (Ywt) (Owt / Ywt) is 0.71 or more, the surface roughness (Ra) to the average crystal grain size (D) (Ra / D) Is 11
X10 ^-2 or less, and the ratio of the X-ray diffraction intensity (IBN) of boron nitride remaining in the surface layer to the X-ray diffraction intensity (IAN) of aluminum nitride (IBN / IAN) is 6 x 10 ^-2 or less Is electrically conductive to at least one main surface of the aluminum nitride-based ceramic substrate through a brazing material containing a simple substance of at least one element selected from the group consisting of Ti, Zr and Hf, or a hydrogen compound thereof. A high-strength aluminum nitride circuit board having a circuit formed and a peel strength of 30 kg / cm or more; and a conductive circuit on at least one main surface of a ceramic board containing aluminum nitride as a main component. A method of manufacturing an aluminum nitride circuit board comprising: a bending strength of 30 kg / mm ²
As described above, the ratio (Owt / Ywt) of the oxygen content (Owt) to the yttrium content (Ywt) is 0.71 or more, and the ratio (Ra / D) of the surface roughness (Ra) to the average crystal grain size (D) is 11
X10 ^-2 or less, and the ratio of the X-ray diffraction intensity (IBN) of boron nitride remaining in the surface layer to the X-ray diffraction intensity (IAN) of aluminum nitride (IBN / IAN) is 6 x 10 ^-2 or less A conductive circuit is formed on at least one main surface of the aluminum nitride ceramic substrate, which is a simple substance of at least one element selected from the group consisting of Ti, Zr, and Hf, or a brazing material containing a hydrogen compound thereof. The present invention provides a method for manufacturing a high-strength aluminum nitride circuit board, which comprises bonding the metal constituting the conductive circuit and the ceramic board by heating this in a vacuum and an inert gas atmosphere.

[0015]

When a circuit board is manufactured by the brazing method, a sound bonded body can be obtained by controlling the brazing conditions such as the composition, temperature, time and atmosphere of the brazing material. In the circuit board manufactured by controlling the brazing conditions in this way, the bonding strength between the metal and the brazing material and between the brazing material and the ceramics is greater than the strength of the ceramics themselves.

Therefore, physical stress is applied to the substrate to try to separate the metal and the ceramic, or the difference in the thermal expansion coefficient between the ceramic and the metal is used to repeatedly heat and cool the substrate, thereby physically When stress is generated at the interface of the substrate to try to separate the metal and the ceramic, the separation occurs due to the destruction of the ceramic substrate itself. Therefore, in order to obtain high bonding strength, it is better that the strength of the substrate is large.

According to the research conducted by the present inventors, AlN
A correlation was observed between the bending strength and the peel strength of the ceramic substrate up to a bending strength of 30 kg / mm ^2, and it was confirmed that the peel strength increases with an increase in the bending strength.
Therefore, the bending strength of the AlN ceramic substrate is 30
It must be at least kg / mm ² .

The fracture mode when the bending strength exceeds 30 kg / mm ² is mainly divided into two types shown in FIGS. 3 and 4 depending on the crack development. That is, in the AlN ceramic substrate 1 having the copper parts 2 formed on both main surfaces thereof, the one having high peel strength has cracks deeply penetrating into the AlN ceramic substrate 1 to cause peeling (FIG. 3), and the peel strength is low. In the case of the material, peeling occurs at the surface layer (about 10 μm from the surface) of the AlN ceramic substrate 1 (FIG. 4).

When the average crystal grain size and grain size distribution in the AlN ceramic substrate are constant, the rougher the surface of the ceramic substrate is, the smaller the peel strength is, and the surface layer often peels off. This is because as the surface becomes rougher, the contact area between the crystal particles on the surface of the substrate and the surrounding and internal particles becomes smaller, and the crystal particles on the surface of the substrate are more likely to peel off.

Further, as shown in FIG. 2, since the brazing filler metal 3 cannot necessarily sufficiently wet the surface of the AlN ceramic substrate, the brazing filler metal cannot penetrate into the concave portion of the surface of the ceramic substrate and only the convex portion is present. A non-contact portion 7 is formed between the brazing material 3 and the substrate by joining with the metal conductor. Therefore, in order to obtain sufficient bonding strength, it is necessary to make the substrate surface smooth, and specifically, the ratio (Ra) of the surface roughness Ra measured according to JIS standard and the average crystal grain size D of the ceramic substrate (Ra / D) is preferably 11 × 10 ^-2 or less.

Further, as shown in FIG. 2, the boron nitride 6 used as a separating agent when firing the AlN ceramic substrate often remains at the grain boundaries of the AlN crystal grains 5 in the surface layer of the AlN ceramic substrate. However, if the amount of remaining boron nitride is large, sufficient bonding strength cannot be obtained even if the above surface roughness conditions are satisfied.

This is because aluminum nitride and boron nitride have poor reactivity with each other due to poor reactivity, and boron nitride itself is a substance having a strong cleavage property, and therefore boron nitride itself has low strength. Therefore, in order to obtain high bonding strength, it is better to reduce the remaining amount of boron nitride on the substrate surface. For the specific remaining amount of boron nitride, use a Rigaku Denki X-ray diffractometer. Cu, acceleration voltage and acceleration current of 50 kV and
When the surface of the ceramic substrate was diffracted under the condition of 30 mA, the diffraction strength IBN of the (002) plane of boron nitride and the average diffraction strength IAlN of the (100), (002), (101) planes of aluminum nitride Ratio (IBN / IAlN) is 6 × 10 ^-2
It must be:

The surface roughness of the ceramic substrate and the residual amount of boron nitride differ depending on the manufacturing process of the substrate. If the above conditions are satisfied at the time of sintering, the surface of the ceramic substrate is further increased. If it is not necessary to perform processing and the above conditions are not met, honing,
The surface treatment may be performed by a mechanical or chemical method such as lapping, grinding, etching with a chemical.

When Y ₂ O ₃ is used as a sintering aid, Al ₂ Y ₄ O ₉ (YA
M), AlYO ₃ (YAL), Al ₅ Y ₃ O ₁₂ (YA
It is confirmed that the AlN ceramic substrate having the YAG phase at the grain boundary has a higher bonding strength than the substrate having the grain boundary phase composed of YAL and YAM, though the composite oxide of aluminum and yttrium as in G) exists. ing. That is, the grain boundary phase of the AlN ceramic substrate varies depending on the amount of oxygen in the AlN raw material powder, the amount of Y ₂ O ₃ added, the amount of residual carbon in the green body before sintering, the atmosphere, etc., but YAG, YAL, Y
The weight ratio O / Y of oxygen and yttrium in AM is respectively
Since they are 0.71, 0.54 and 0.41, if the O / Y of the AlN ceramic substrate is 0.71 or more, the grain boundary phase YAG can be formed.

However, when the grain boundary phase contains a large amount of YAG, sufficient thermal conductivity cannot be achieved, and therefore the amount of YAG must be controlled appropriately. Therefore, in the present invention, as the amount of YAG phase in the AlN ceramic substrate, X
Diffraction intensity of (640) crystal plane of YAG by line diffraction and A
The ratio of the diffraction intensity of the (100) crystal plane of 1N (IYAG / I
AlN) in the range of 0.001 to 0.030, preferably 0.005 to
It was set to 0.025. By setting IYAG / IAlN in the above range, it is possible to provide an AlN ceramic substrate having a peel strength of 30 kg / cm or more and a thermal conductivity of 150 W / m · k or more.

It has also been confirmed that the bonding temperature affects the quality of the circuit board. If the bonding temperature is low, the reaction at the bonding interface becomes insufficient, and high bonding strength cannot be obtained. Conversely, if the joining temperature is high, the brazing filler metal and the metal conductor react violently, so the brazing filler metal wraps around the metal conductor surface,
Color unevenness will occur. Therefore, it is necessary to join at a joining temperature suitable for the brazing material. For example, when using an Ag-Cu-Ti based brazing material, a joining temperature of 780 to 900 ° C for 1 minute or more, preferably 790 to 850 ° C. By maintaining the bonding temperature for 5 to 60 minutes, it is possible to manufacture a circuit board having high bonding strength and no color unevenness.

Incidentally, Japanese Patent Laid-Open No. 2-25 shown in the prior art mentioned above.
According to the inventions disclosed in 8686, JP-A-2-149485 and JP-A-3-93687, the grain boundary constituent phase components precipitated on the surface of the AlN ceramic substrate are the metallizing paste and Cu ₂ generated at the grain boundaries. Since it is difficult to react with the O-Cu eutectic liquid (in the case of the direct bonding method), the bonding strength between the conductive circuit and the ceramic substrate is adversely affected.

However, for a high-purity AlN ceramic substrate having a high thermal conductivity of 200 W / mK or more, the adverse effect of the grain boundary constituent phase components deposited on the surface is particularly strong, but As described above, in the case of a substrate having a thermal conductivity of 200 W / mK or less, since the amount of the grain boundary constituent phase component exuding on the surface of the sintered body is small, its influence is extremely small. Also, since the brazing filler metal containing the active metal used when forming a conductive circuit by the brazing method can react with the grain boundary constituent phase components, the grain boundary constituent phase components deposited on the surface should not adversely affect the bonding. Has been confirmed.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited by the following examples.

[0030]

Examples 1 to 5 Using the separating agent boron nitride (BN) as shown in Table 1 and honing conditions, IBN
Five types of substrates having / IAln of 6 × 10 ^-2 or less and Ra / D of 11 × 10 ^-2 or less were prepared. In addition, these substrates have a weight ratio O / Y of oxygen and yttrium of 1.29,
The grain boundary phase is composed of YAG.

[0031]

[Table 1] First, at a predetermined position on both main surfaces of the AlN ceramic substrate 1 prepared above, a brazing material 3 which is made into a paste by adding various additives to a mixed powder of titanium, silver and copper is printed by a printing method, and the printed paste Place the copper part 2 on the
^{In a} vacuum of ^-5 torr, heating was performed at 810 ° C for 20 minutes to bond the copper parts and the ceramic substrate to produce a circuit substrate as shown in Fig. 1.

Next, the peel strength of each circuit board obtained as described above was measured (the peel strength was measured at the peel strength measuring point 4 in FIG. 1), and the results are shown in Table 1. It was As can be seen from Table 1, the peel strength was 30 kg / cm or more in any circuit board.

[0033]

Examples 6 to 12 A circuit board was manufactured and peel strength was measured in the same manner as in Example 2 except that the joining temperature was changed within the range of 780 to 910 ° C. The results are shown in Table 1 and Table 1. Shown in 2.

[0034]

[Table 2] As can be seen from Tables 1 and 2, the peel strength was 30 kg / cm or more in any of the circuit board substrates.

[0035]

Example 13 Weight ratio of oxygen and yttrium (O /
Y) is 0.77 and the grain boundary phase consists of YAG and YAL,
IBN / IAlN on the surface is 0.7 × 10 ^-2 or less and Ra /
Manufacturing of a circuit board in the same manner as in Examples 1 to 5 except that an AlN ceramic substrate having D of 8.4 × 10 ^-2 was used.
Also, the peel strength was measured, and the results are also shown in Table 2. As can be seen from Table 2, the peel strength is 40 kg / cm.
That was all.

[0036]

Comparative Examples 1 and 2 Weight ratio of oxygen and yttrium (O /
Y) was 0.59 and 0.52, and the circuit board was manufactured and the peel strength was measured in the same manner as in Example 13 except that the AlN ceramic substrate in which the grain boundary phase was YAL and YAM was used. It is also shown in Table 2. As can be seen from Table 2, the peel strength was less than 30 kg / cm for any circuit board.

[0037]

[Comparative Examples 3 to 5] Manufacturing of circuit boards and peeling were carried out in the same manner as in Examples 1 to 5, except that the method of using the separating agent (BN) was liquid coating and the ceramic substrates manufactured with a small honing pressure were used. The strength was measured, and the results are also shown in Table 2. As can be seen from Table 2, the peel strength was 20 kg / cm or less in any circuit board.

From these results, IBN / IAInN was 6
Sufficient bonding strength, not only when × 10 ^-2 or more and Ra / D is 11 × 10 ^-2 or more, but also when either one of IBN / IAln and Ra / D has the above value. Couldn't get

[0039]

As described above, by controlling the weight ratio of oxygen and yttrium in the ceramic, the bending strength of the ceramic substrate, the amount of boron nitride remaining on the surface of the ceramic substrate, and the surface roughness, brazing can be performed. It has become possible to manufacture high-strength aluminum nitride circuit boards by the method. Therefore, it has become possible to provide a high-strength circuit board with a peel strength of 30 kg / cm or more to the market. Further, the present invention can be widely applied not only to the production of high-strength aluminum nitride circuit boards, but also to the production of composites of AlN ceramics and metals that require high bonding strength.

[Brief description of drawings]

FIG. 1 is a perspective view showing an example of a high-strength aluminum nitride circuit board of the present invention.

FIG. 2 is a schematic cross-sectional view showing a state of a surface layer of an AlN ceramic substrate and a bonding interface between a brazing material and an AlN ceramic substrate.

FIG. 3 is a diagram showing an example of a fracture pattern of a peel strength measurement sample, which is a cross-sectional view of a fractured ceramic circuit board.

FIG. 4 is a diagram showing another example of the fracture pattern of the peel strength measurement sample, which is a cross-sectional view of the ceramic circuit board in which the fracture has occurred.

[Explanation of symbols]

 1 ... AlN ceramic substrate 2 ... copper parts 3 ... brazing material 4 ... peel strength measurement point 5 ... AlN crystal grains 6 ... boron nitride 7 ... uncontacted part

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Yu Namura 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd. (72) Masami Kimura 1-2-8 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd.

Claims (2)

[Claims] 1. A flexural strength of 30 kg / mm ² or more, a ratio (O) of a weight content of oxygen (Owt) to a weight content of yttrium (Ywt).
wt / Ywt) is 0.71 or more, the ratio (Ra / D) of the surface roughness (Ra) to the average crystal grain size (D) is 11 × 10 ^-2 or less, and the X-ray diffraction of boron nitride remaining in the surface layer. On at least one main surface of a ceramic substrate containing aluminum nitride as a main component, the ratio (IBN / IAIn) of the diffraction strength (IBN) to the X-ray diffraction strength (IAN) of aluminum nitride is 6 × 10 ^-2 or less. That a conductive circuit is formed through at least one element selected from the group consisting of Ti, Zr, and Hf, or a brazing material containing a hydrogen compound thereof, and a peel strength of 30 kg / cm or more. Characteristic high-strength aluminum nitride circuit board. 2. A method for manufacturing an aluminum nitride circuit board having a conductive circuit on at least one main surface of a ceramic substrate containing aluminum nitride as a main component, which has a bending strength of 30 kg / mm ² or more. The ratio (Owt / Ywt) of the oxygen weight (Owt) to the contained yttrium weight (Ywt) is 0.71 or more, and the ratio of the surface roughness (Ra) to the average crystal grain size (D) (R
a / D) is 11 × 10 ⁻² or less, and the ratio of the X-ray diffraction strength (IBN) of boron nitride remaining in the surface layer to the X-ray diffraction strength (IAN) of aluminum nitride (IBN / IAN)
A brazing material containing at least one element selected from the group consisting of Ti, Zr, and Hf, or a brazing material containing a hydrogen compound thereof is provided on at least one main surface of the aluminum nitride ceramic substrate having a value of 6 × 10 ^-2 or less. To form a conductive circuit, and by heating the conductive circuit in a vacuum and an inert gas atmosphere, the metal constituting the conductive circuit and the ceramic substrate are bonded to each other. .