JP3460167B2 - Method for manufacturing aluminum nitride circuit board having metal circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an aluminum nitride circuit board having a metal circuit.

[0002]

2. Description of the Related Art In recent years, with the high performance of industrial equipment such as robots and motors, the transition of high power and high efficiency inverters and other high power modules has progressed, and the heat generated from semiconductor elements has also continued to increase. ing. In order to efficiently dissipate this heat, various methods have been conventionally used for high power module substrates. Especially recently, since ceramic substrates with good heat conduction have become available,
A structure is also being adopted in which a metal plate such as a copper plate is bonded onto a ceramic substrate to form a circuit, and then a semiconductor element is mounted as it is or after a treatment such as plating is performed.

Such a module was initially used for a simple machine tool, but has been used for a few years in a welding machine, a train drive part, an electric vehicle, and more stringent requirements such as a current density. In order to increase the thickness, it has been required to increase the circuit copper thickness, improve the durability against thermal shock, and further reduce the size. At present, the only ceramic substrate that can meet these requirements is an aluminum nitride substrate.

There are various methods for joining a metal and a ceramic, but for joining a copper plate and an aluminum nitride substrate,
An active metal brazing method in which a brazing material containing an active metal is interposed between the two and heat-treated to form a joined body (for example, JP-A-60-177).
No. 634), and a DBC method (for example, Japanese Patent Laid-Open No. 56-163093) in which an aluminum nitride substrate whose surface is oxidized and a copper plate are heated and bonded at a temperature lower than the melting point of copper and higher than the eutectic temperature of Cu—O. is there.

The active metal brazing method has the following advantages over the DBC method. (1) Since the processing temperature for obtaining the bonded body is low, the residual stress caused by the difference in thermal expansion between the aluminum nitride substrate and the copper plate is small. (2) Since the brazing material is a ductile metal, it is highly durable against heat shock and heat cycles.

[0006]

However, even if the active metal brazing method is used, the durability against heat shock and heat cycle cannot be said to be sufficient, and the advent of a new technique has been awaited. Therefore, the volume of the metal circuit board (usually provided on the upper surface of the ceramic substrate) is adjusted to be 50 to 90% of the volume of the metal heat dissipation plate on the opposite surface (Japanese Patent Laid-Open No. 63-24815). The thickness of the heat radiation side copper plate should be 50% or less of the thickness of the circuit side copper plate (JP-A-5-1).
No. 70564), but these alone are not sufficient to meet the above strict requirements.

Therefore, improvement of ceramics such as aluminum nitride sintered body is essential. There are an atmospheric pressure sintering method and a hot pressing method for sintering ceramics. Compared with the hot pressing method, the atmospheric pressure sintering method can produce ceramics more easily and mass-produced, but it tends to cause defects such as pores in the sintered body, and the reaction between the sintering aid component and the ceramic component. Since the second and third phases generated by have a relatively high vapor pressure, segregation is likely to occur, and the thermal shock resistance tends to be weaker than that of the sintered body produced by the hot pressing method. In particular, this tendency is remarkable in the aluminum nitride sintered body.

On the other hand, as a means for improving the brittleness of ceramics, so-called "zirconia tahund ceramics", in which pure stable tetragonal zirconia is partially stabilized and dispersed, has already been put into practical use. This is a method of strengthening the toughness by absorbing the fracture energy and inhibiting the progress of cracks by utilizing the volume change accompanying the transformation of tetragonal crystal to stable monoclinic crystal. Since the conductivity is not so good, it is not suitable as an insulating substrate that requires high thermal conductivity.

The object of the present invention is to generate tetragonal zirconia on the surface of an aluminum nitride substrate to the extent that its thermal conductivity is not impaired, and to utilize the toughness of tetragonal zirconia to withstand heat shock and heat cycle. A method of manufacturing an aluminum nitride circuit board having a metal circuit with further improved durability.

[0010]

SUMMARY OF THE INVENTION That is, the present invention is, It
The aluminum nitride substrate manufactured by using the rear as a sintering aid was subjected to an oxidation treatment, and α-alumina (10
4) Diffraction line intensity I 104 of surface and yttrium aluminate
The ratio of the diffraction line intensity I400 of (400) (I104 / I4
00) is 0.1 to 2.5 , alumina is formed on the surface, and then it and a metal plate are mixed with 69 to 100 parts by weight of silver.
An active metal brazing material containing 0.5 to 10 parts by weight of zirconium or a compound thereof per 100 parts by weight of copper and 0 to 31 parts by weight of copper in a vacuum of 10 −7 to 10 −5 Torr.
A method of manufacturing an aluminum nitride circuit board having a metal circuit, which comprises forming a circuit by etching the metal of the bonded body after bonding under the condition of a temperature of 700 to 900 ° C. , and yttria as a sintering aid. The manufactured aluminum nitride substrate is subjected to oxidation treatment, and then α
Luminous (104) plane diffraction line intensity I104 and aluminate
Ratio of diffraction line intensity I400 of yttrium (400) (I
104 / I400) is 0.1 to 2.5 and alumina is formed on the surface thereof , and then the metal circuit pattern is added to 69 to 100 parts by weight of silver and 0 to 31 parts by weight of copper.
Zirconium or its compound per 100 parts by weight
Active metal brazing filler metal containing 0.5 to 10 parts by weight , and 10-7 to
In a vacuum of 10-5 Torr, at a temperature of 700 to 900 ° C
A method for manufacturing an aluminum nitride circuit board having a metal circuit, which is characterized in that bonding is performed under certain conditions to form a circuit.

[0011]

The present invention will be described in more detail below.

A feature of the present invention is that, in a circuit board in which an aluminum nitride substrate and a metal circuit are bonded via a bonding layer, the surface of the aluminum nitride substrate, which is the starting point of the breakage, or the sufficient bonding strength is maintained. Tetragonal zirconia was formed in the vicinity by the reaction between the alumina component on the surface of the aluminum nitride substrate and the zirconium component of the active metal brazing material, further improving the durability against heat shock and heat cycle without impairing the thermal conductivity. That is.

Today, the circuit board most desired to be improved in terms of reliability is a copper-thickened circuit board used in power modules and the like, and usually has a thickness of 0.15 to 0.5 m.
Although a copper circuit of m is formed on the aluminum nitride substrate, when a thermal history is applied, stress is generated due to the difference in thermal expansion between copper and aluminum nitride. Small stress is mainly due to the elasticity of the copper plate
Although absorbed by plastic deformation, the stress accumulated during repeated thermal history and the stress generated by large temperature changes are
It is released by breaking the aluminum nitride substrate. That is, when the aluminum nitride substrate is damaged by the thermal stress, the interface where the metal is bonded, that is, the surface of the aluminum nitride substrate substrate and its vicinity becomes the starting point of the destruction. Therefore, the presence of tetragonal zirconia only on or near the surface of the aluminum nitride substrate leads to a large toughness improving effect, and since the amount of tetragonal zirconia can be reduced, the thermal conductivity of the aluminum nitride circuit board can be reduced. Does not have a great adverse effect.

In the present invention, the amount of tetragonal zirconia present can be easily determined by X-ray diffraction. That is, the metal circuit and the bonding layer are dissolved with an acid such as nitric acid or hydrofluoric acid from an aluminum nitride substrate having a metal circuit, and the remaining aluminum nitride substrate is subjected to X-ray diffraction analysis to obtain a diffraction line intensity ratio. You can If the presence of tetragonal zirconia is too small, the effect of improving the toughness will be small, and if it is too large, the thermal resistance will be large. Therefore, in the present invention, 0.02 ≦ I _Z / I _A ≦ 0.3
Is appropriate. Where I _A is (1 of aluminum nitride
The diffraction line intensity of the (01) plane, I _Z, is (1) of tetragonal zirconia.
11) Diffraction line intensity of plane. In X-ray diffraction, tetragonal zirconia on the surface of the aluminum nitride substrate or in the vicinity thereof is measured and is ignored, but in the present invention, the presence of tetragonal zirconia on the surface of the aluminum nitride substrate or in its vicinity is important. This measurement method is adopted because it exists.

In the present invention, in order to allow tetragonal zirconia to exist on the surface of the aluminum nitride substrate or in the vicinity thereof, the aluminum nitride substrate is oxidized to form an alumina layer on the surface thereof, and a metal plate or a metal circuit pattern is formed thereon. Can be carried out by a reaction during heat bonding with an active metal brazing material containing zirconium or a compound thereof.

If the amount of the alumina layer on the surface of the aluminum nitride substrate is too large, it may peel off partially or entirely from the surface. Therefore, the thickness is preferably 10 μm or less. The lower limit is at least 1 of the required amount
It is / 10. Here, the necessary amount is the amount necessary for all zirconium of the active metal brazing material to become zirconia.

In order to form the alumina layer on the surface of the aluminum nitride substrate, the aluminum nitride substrate is placed in the atmosphere,
It is preferable to perform heat treatment at 950 to 1300 ° C. for about 15 to 90 minutes. If the temperature is lower than 950 ° C., the alumina layer is not formed, and if it exceeds 1300 ° C., the non-uniform reaction layer is formed due to the increase in the formation rate of the alumina layer, and sufficient bonding strength cannot be obtained.

Among them, an aluminum nitride substrate manufactured by using yttria as a sintering aid is subjected to an oxidation treatment under the above conditions,
The ratio (I ₁₀₄ / I _{40 0} ) of the diffraction line intensity I _{10 4 on the} α-alumina (104) plane by X-ray diffraction and the diffraction line intensity I ₄₀₀ of yttrium aluminate (400) was set to 0.1 to 2.5. Aluminum nitride substrates are the most suitable. By using such an aluminum nitride substrate, α-alumina reacts with the zirconia component of the active metal brazing material to form a thermal stress buffer layer, and yttrium aluminate reacts with the active metal brazing material to form a strong bonding layer. . Therefore, it is possible to manufacture an aluminum nitride circuit board having further improved durability against heat shock and heat cycle while maintaining a strong bonding strength.

The metal component of the active metal brazing material used in the present invention is mainly composed of silver, copper, silver-copper, zinc, indium, cadmium, tin, etc., and ensures wettability with the ceramic substrate during melting. Therefore, an active metal is used as a sub ingredient. The active metal reacts with the aluminum nitride substrate to generate an oxide or a nitride, and these products strengthen the bond between the brazing material and the aluminum nitride substrate. Specific examples of the active metal include titanium, zirconium, hafnium, niobium, tantalum, vanadium and compounds thereof. In the present invention, the main component of the metal component is preferably silver or silver-copper, but the active metal component is zirconium or its compound as an essential component. The preferred active metal component is
The use of zirconium or its compounds in combination with other active metal components, especially titanium or its compounds. One example of these ratios is 0.5 to 10 parts by weight, especially 1 to 8 parts by weight of zirconium or its compound per 100 parts by weight of the total amount of 69 to 100 parts by weight of silver and 0 to 31 parts by weight of copper. When the amount of zirconium or its compound is too much, the joining temperature becomes high and the thermal stress generated when cooling to room temperature after joining becomes large, and when it is too little, the amount of tetragonal zirconia produced becomes small and the effect of improving the toughness becomes small.

The active metal brazing material is usually used in a paste, which is prepared by adding an organic solvent and, if necessary, an organic binder to the above metal components and mixing them with a roll, a kneader, a universal mixer, a raider or the like. Can be prepared by.
As the organic solvent, methyl cellosolve, terpineol,
Isophorone, toluene, etc. are used, and as the organic binder, ethyl cellulose, methyl cellulose, polymethacrylate, etc. are used.

The bonding conditions of the aluminum nitride substrate having the alumina layer formed on the surface thereof and the metal plate or the pattern of the metal circuit are in a vacuum of about 10 ^-7 to 10 ^-5 Torr and at a temperature of 70.
It is about 0 to 900 ° C, preferably about 750 to 850 ° C.

The thickness of the aluminum nitride substrate is preferably about 0.3 to 0.8 mm because if it is too thick, the thermal resistance will increase, and if it is too thin, the durability will decrease.

The surface condition of the aluminum nitride substrate is important, and since minute defects and dents have a great adverse effect on the contact area with the metal plate or the metal circuit pattern, it is desirable that the surface is smooth. Alternatively, it is desirable that the honing treatment is performed after the oxidation treatment.

Copper, aluminum, tungsten, molybdenum, etc. are used as the material of the metal circuit, but copper is generally used. The thickness of the metal circuit is preferably thicker than 0.3 mm because the current density tends to increase in recent years. Further, in the present invention, a circuit board having a structure in which a metal circuit is formed on the surface of the aluminum nitride substrate and a metal heat dissipation plate is formed on the back surface thereof may be used, and the material of the metal heat dissipation plate is as described above. Is used, and its thickness is preferably 0.2 mm or less.

As a method of forming a metal circuit on one surface of the aluminum nitride substrate and a metal heat dissipation plate on the other surface, a method of etching a bonded body of the aluminum nitride substrate and the metal plate, and a metal stamped from the metal plate are used. It can be performed by a method of joining the circuit pattern and / or the metal heat sink plate pattern to the aluminum nitride substrate.

[0026]

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples.

Examples 1 to 4 Comparative Example 1 96 parts by weight of aluminum nitride powder, 4 parts by weight of yttria powder and 2 parts by weight of oleic acid were premixed in a vibration mill, and then 8 parts by weight of ethyl cellulose and 3 parts by weight of glycerin trioleate. And 12 parts by weight of water were mixed and mixed with a mixer. This mixture is molded at a molding speed of 1.0 m / min and a molding pressure of 55.
Extrusion molding at ~ 70kg / cm ² and 1 in far infrared
After drying at 20 ° C. for 5 minutes, it was degreased in air at 480 ° C. for 10 hours, and baked at a temperature of 1950 ° C. for 30 minutes.

From the obtained aluminum nitride sintered body, an aluminum nitride substrate (60 mm × 36 mm × 0.65 m
m) is machined and honed, then in air 110
Heat treatment was performed at 0 ° C. for 30 minutes to form an alumina layer on the surface of the aluminum nitride substrate. When the subjected to X-ray diffraction analysis to determine the ratio of the diffraction intensity I ₄₀₀ of the α-alumina (104) plane diffraction intensity I ₁₀₄ and yttrium aluminate of _{(400) (I 104 / I} 400), 1.0 Met.

Metal powders were mixed in the proportions shown in Table 1,
To 100 parts by weight of this metal component, 14 parts by weight of terpineol and 7 parts by weight of a solid solution of a toluene solution of polyisobutylmethacrylate were added, and the mixture was kneaded by a raker machine to prepare an active metal brazing material paste. This brazing paste was applied to the circuit surface (front surface) of the aluminum nitride substrate manufactured above by screen printing to form an L-shaped pattern having a pattern ratio of 0.20, and the entire surface of the heat dissipation surface (back surface) was applied.
The coating amount (after drying) at that time was 9 mg / cm ² .

Next, on the surface, 60 mm × 36 mm × 0.
A copper plate with a thickness of 3 mm and a back surface of 60 mm x 3
After placing a copper plate having a thickness of 6 mm × 0.15 mm in contact with the copper plate, heat treatment was performed for 30 minutes at a temperature shown in Table 1 under a vacuum of 1 × 10 ⁻⁶ Torr or less, and then at a temperature decrease rate of 2 ° C./minute. After cooling, a joined body of the aluminum nitride substrate and the copper plate was manufactured.

[0031]

[Table 1]

Then, a UV curing type etching resist is applied by screen printing on the copper plate of this joined body,
An etching treatment was performed using a cupric chloride solution to dissolve and remove unnecessary portions of the copper plate, and the etching resist was peeled off with a 5% caustic soda solution. In the bonded body after this etching treatment, there is a residual unnecessary brazing material or a reaction product of the active metal component and the aluminum nitride substrate between the copper circuit patterns.
It was immersed for a minute and removed. Then, Ni plating having a thickness of 2 μm was performed to manufacture an aluminum nitride circuit board having a copper circuit.

Comparative Examples 2 to 6 Aluminum nitride having a copper circuit was prepared in the same manner as in Examples 1 to 4 or Comparative Example 1 except that an aluminum nitride substrate which was not heat-treated at 1100 ° C. for 30 minutes in the atmosphere was used. A circuit board was manufactured.

The peel strength of the aluminum nitride circuit board having the copper circuit thus manufactured was measured by a push-pull measuring device (pulling speed: 50 mm / min). In addition, after holding at -40 ° C for 30 minutes in air, 25 ° C
× 10 minutes, 125 ° C × 30 minutes, 25 ° C
A heat cycle resistance test was conducted on Sample 10 by leaving it for 1 cycle for 10 minutes as a cycle, and the number of heat cycles at which the heat dissipation copper plate or the copper circuit started to peel was measured. Furthermore, the heat dissipation copper plate of the circuit board and the copper circuit and the bonding layer are removed with the above chemical solution,
The remaining aluminum nitride substrate was subjected to X-ray diffraction analysis to measure the amount of tetragonal zirconia (I _Z / I _A ). The results are shown in Table 2.

[0035]

[Table 2]

[0036]

According to the present invention, it is possible to manufacture an aluminum nitride circuit board having a metal circuit with further improved durability against heat cycles.

Continuation of the front page (56) Reference JP-A-5-102629 (JP, A) JP-A-4-149075 (JP, A) JP-A-6-53357 (JP, A) JP-A-7-101774 (JP , A) JP-A-7-305162 (JP, A) JP-A-2-306653 (JP, A) JP-A-5-63110 (JP, A) JP-A-7-170041 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H05K 1/03 630

Claims (2)

(57) [Claims] An aluminum nitride substrate manufactured by using yttria as a sintering aid is subjected to an oxidation treatment, and then subjected to X-ray diffraction.
Diffraction line intensity I104 of α-alumina (104) plane
Diffraction line intensity I400 of yttrium mynate (400)
After forming alumina on the surface so that the ratio (I104 / I400) is 0.1 to 2.5 , the alumina and the metal plate are mixed with silver.
Total amount of 69-100 parts by weight and copper 0-31 parts by weight 100
0.5 to 0.5 parts by weight of zirconium or its compound per part by weight.
Active metal brazing material containing 10 parts by weight , 10-7 to 10-5
A method for manufacturing an aluminum nitride circuit board having a metal circuit, comprising: forming a circuit by bonding the metal of the bonded body in a Torr vacuum at a temperature of 700 to 900 ° C. and then etching the metal. 2. An aluminum nitride substrate manufactured by using yttria as a sintering aid is subjected to an oxidation treatment and then subjected to X-ray diffraction.
Diffraction line intensity I104 of α-alumina (104) plane
Diffraction line intensity I400 of yttrium mynate (400)
After forming alumina on the surface so that the ratio (I104 / I400) is 0.1 to 2.5, 69 to 100 parts by weight of silver and 0 to 31 parts by weight of copper are added to the alumina and the metal circuit pattern. Of
Active metal brazing filler metal containing 0.5 to 10 parts by weight of zirconium or a compound thereof per 100 parts by weight of the metal is 10-7.
10 to 5 Torr vacuum, 700 to 900 ℃ temperature
A method for manufacturing an aluminum nitride circuit board having a metal circuit, which comprises bonding under the conditions to form a circuit.