JP2506270B2 - High thermal conductivity circuit board and high thermal conductivity envelope - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit board and an envelope having a high thermal conductivity, and a high thermal conductivity circuit board using a substrate (hereinafter referred to as an AlN substrate) substantially made of aluminum nitride ceramics. The present invention relates to a high thermal conductivity envelope.

[0002]

2. Description of the Related Art As materials conventionally used for circuit boards, there are various materials such as ceramic boards such as Al ₂ O ₃ and resin boards. Among them, the Al ₂ O ₃ ceramic substrate is excellent in mechanical strength and electrical insulation.
Since it can be easily made into a green sheet, it can be used for high-density wiring such as multilayer wiring, and is widely used.

On the other hand, with the recent progress in miniaturization of electronic devices, the mounting density of electric elements (ICs, etc.) on a circuit board is increasing. Furthermore, when considering the mounting of power semiconductors, etc., the amount of heat generated on the circuit board tends to increase,
Effective heat dissipation is required.

However, the thermal conductivity of the Al ₂ O ₃ ceramic substrate is as low as about 20 W / m · K, and when a large amount of heat is generated, heat radiation from the substrate side cannot be expected so much. Therefore, considering heat dissipation from the board side in high-density mounting, power semiconductor mounted modules, etc., the characteristics required for a circuit board such as mechanical strength and electrical insulation are provided, and good thermal conductivity is provided. Development of circuit boards is required.

With the progress of fine ceramics technology in recent years, ceramic materials such as SiC and AlN having excellent mechanical strength have been developed. These materials have excellent thermal conductivity, and their application as structural materials has been studied. Also, Si
There is a movement to use C as a circuit board by utilizing its good thermal conductivity, but it has a high dielectric constant and a low withstand voltage. There is.

The AlN substrate has good electrical insulation and thermal conductivity, and is expected to be applied to a circuit board. However, AlN has poor wettability with respect to metal, and it has been difficult to join the conductor layers, for example, as used as a crucible for melting aluminum metal. Therefore AlN
There is no circuit board in which a conductor path is directly formed on the base body, and at most, a power semiconductor such as a thyristor is fixed with an organic adhesive and used as a heat sink.

Japanese Patent Laid-Open Nos. 52-37914 and 50-
No. 132022 discloses a technique for directly bonding a copper plate to a ceramic, and it is conceivable to form a conductor layer on an AlN substrate by using this technique, but there is a limit to the formation of a fine pattern. Multilayer wiring, which is essential for high-density wiring, was also difficult.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above points, and has a high thermal conductivity circuit board excellent in electrical insulation, mechanical strength and thermal conductivity, and a high thermal conductivity outer substrate. The purpose is to provide an enclosure.

[0009]

To accomplish the above object In order to achieve the above, the aluminum nitride ceramic substrate, and Al ₂ O ₃ layer formed on the substrate on, is formed on the the Al ₂ O ₃ layer on the And a glass layer, the circuit board having a high thermal conductivity is provided.

[0010] The present invention includes an aluminum ceramic substrate nitride, and Al ₂ O ₃ layer formed on this substrate on, the Al is formed on the ₂ O ₃ layer, resistance conductor powder in the glass layer is dispersed The present invention provides a circuit board having high thermal conductivity, which comprises a body layer.

The present invention further provides an aluminum nitride ceramic substrate, an Al ₂ O ₃ layer formed on this substrate,
A high thermal conductivity envelope comprising a glass layer formed on the Al ₂ O ₃ layer and a cap formed on the glass layer.

In the present invention, the glass layer is formed by firing glass paste. Further, in the present invention, the resistor layer is formed by firing a glass paste in which conductor powder is dispersed.

The present invention is based on the application of an AlN substrate having an oxide layer formed thereon to a circuit board.

As a result of the present inventors' research on the application of an AlN substrate to a circuit board, they have found that the formation of an oxide layer on the surface of an AlN substrate provides a very excellent circuit board. That is, by forming the oxide layer, not only the conductor layer can be bonded, but also the glass layer can be bonded. Especially good adhesion of the glass layer has various advantages.

AlN ceramics are known to have poor wettability with metals and the like, but also have poor wettability with glass. However, by forming the oxide layer, the wettability with respect to the metal is improved, and the conductor layer can be formed. Further, when the glass layer is directly formed on the AlN substrate having no oxide layer, bubbles are generated in the glass layer and a strong bond cannot be obtained. It is considered that this is because when the AlN substrate is exposed to a high temperature in the atmosphere, a gas such as ammonia gas is generated. On the other hand, A having an oxide layer
Such a wrinkle does not occur in the glass layer formed on the 1N substrate, and good bonding with the substrate can be obtained.

It is very important for a circuit board that good glass layer bonding can be obtained. For example, when sealing is performed, it is necessary to bond the cap and the substrate, but at this time, sealing with glass can be performed. Glass bonding can also be used in consideration of adhesion between the lead frame and the substrate. Further, when printed multilayer wiring is performed, a dielectric layer for interlayer insulation is required, but a glass layer can be used as the dielectric layer.

Further, it is particularly advantageous when the resistor is formed on the substrate. In general, the resistor paste has conductor powder dispersed in glass, so that good glass bonding must be performed. In the case of a resistor, reproducibility of its resistance value is important from the viewpoint of circuit design. When an AlN substrate on which no oxide layer is formed is used, bubbles are generated in the resistor, which is a glass layer, as described above, and therefore the resistance value is greatly varied, but according to the present invention, bubbles are generated. Since a good junction can be obtained without any deterioration, the reproducibility of the resistance value is very good and the variation is small.

As for the oxide layer, the glass layer and AlN
Considering the bonding strength with the substrate, the effect is not exhibited if the oxide layer is too thin, so about 0.5 μm or more is preferable. On the other hand, if it is too thick, peeling of the oxide layer may occur due to the difference in the coefficient of thermal expansion between the oxide layer and the AlN substrate.
It is preferably about 0 μm or less. This oxide layer is made of alumina, boehmite, or the like, but it is inferior in thermal conductivity to AlN, so that it is better to be as thin as possible within the range where a similar bonding strength can be obtained, and it is preferably about 2 to 20 μm.

As a method for forming the oxide layer on the AlN substrate, for example, high temperature treatment in the atmosphere can be mentioned.
The thickness of the oxide layer formed changes depending on the heat treatment temperature and the treatment time. Although the processing time becomes shorter as the processing temperature of this high-temperature processing becomes higher, 1000 to 1300
It is preferable to carry out at a temperature of about 3 to 0.5 hr. In addition, heat treatment in an oxidizing atmosphere such as water vapor (comparatively lower temperature than in air, may be 100 to 140 ° C. 2 to
It is preferable to carry out under high pressure such as 3 atm. ), Various methods such as immersion in an acidic liquid.

The AlN substrate used in the present invention is an AlN raw material to which additives such as Y, a rare earth element and an alkaline earth element are added (about 0.01 to 15 wt% in terms of metal element) under normal pressure sintering and hot pressing. Method, a method of using an AlN raw material containing oxygen of about 7 wt% or less at normal pressure for sintering and hot pressing, and a method of hot-pressing the AlN raw material alone without substantially adding the additive. It is manufactured by a method such as pressing. The present invention is based on Al with or without additives.
As long as it is an N substrate, it can be applied to any one manufactured by any method.

The thermal conductivity of the AlN substrate is 40 W / m · K.
For example, 2 of 100 W / mK and alumina ceramic
Remarkably superior to 0W / m ・ K and has a mechanical strength of 4
0 to 50 kg / mm ² (alumina 25 kg / mm ² ),
Electrical dielectric strength 140-170 kV / cm (alumina 1
00 kV / cm) and the characteristics required as a circuit board are alumina or higher. By utilizing such good characteristics of AlN ceramics, it is possible to obtain a high thermal conductivity circuit board and a high thermal conductivity envelope.

In the present invention, since the surface of the AlN substrate is oxidized, it cannot be said strictly that it is AlN. However, since the oxide layer is extremely thin, the high thermal conductivity circuit board and high thermal conductivity obtained by the present invention are obtained. The characteristics of the envelope are almost the same as the case of using the AlN substrate having no oxide layer.

As the glass layer of the present invention, those generally used for alumina substrates can be used. For example, P
bO-SiO ₂ -B ₂ O ₃ system and the BaO-SiO ₂ -B ₂
Glass such as O ₃ system can be used. Considering the effects of changes in the oxidation state of the AlN substrate, the softening point is 350-
It is preferable to bond glass at 950 ° C. at a temperature of about 400 to 1000 ° C. In the present invention, the elements constituting the glass layer may diffuse to the oxide layer to some extent at this time,
In the high thermal conductivity circuit board and high thermal conductivity envelope obtained by the present invention, there is no problem even if a small amount of such a diffusion component is contained in the oxide layer.

Further, by using the AlN substrate having an oxide layer in this manner, no bubbles are generated in the thick film pattern formed on the substrate. Therefore, when the thick film resistance pattern is formed, the resistance value thereof can be increased. It has the advantage that it can be formed with good reproducibility. The thick film resistance paste may be a commonly used one for alumina, for example, RuO ₂ paste, LaF ₆ paste, or the like. Also, as a conductor paste, normal Ag,
Au, Cu, Ni, Al paste or the like can be used.

[0025]

According to the present invention, the glass layer is formed on the AlN substrate, and the glass paste is fired through the glass layer to form the glass layer. Therefore, even if the AlN substrate is heat-treated at a high temperature, no gas is generated. Therefore, it is possible to prevent the formation of bubbles in the glass.

[0026]

EXAMPLES Examples of the present invention will be described below. (Example 1) An AlN substrate containing ₃ wt% of Y ₂ O ₃ was subjected to an oxidation treatment in the atmosphere at 1250 ° C for 1 hr.
An Al ₂ O ₃ layer of 6 μm was formed on the surface of the obtained AlN substrate.

Next, a glass paste (Nippon Electric Glass LS0120M) was applied to a predetermined part, and after removing the binder, 3
It was calcined under the conditions of 50 ° C. and 5 minutes. After that, a 42 alloy lead frame was placed and main firing was performed at 420 ° C. for 10 minutes. Next, after mounting and bonding the IC, an alumina cap was fired and bonded using the glass under the conditions of 420 ° C. and 10 min to obtain the envelope of the present invention.

In the envelope of the present invention, no wrinkles were observed in the glass layer, and it was confirmed that good bonding was realized. The bonding strength of both the lead frame and the cap was 500 g or more in the vertical load against breakage, which was a value that was sufficiently satisfactory for practical use. Thermal resistance is similar to that of alumina CERDIP28
This was a 15% reduction compared to the pin package. Therefore, in the case of alumina, 1.2W was the only one that could be input.
You can enter up to. (Example 2) An AlN substrate was immersed in a 10% phosphoric acid solution for oxidation treatment. An oxide film of 3 μm was formed on the surface of the substrate. On this AlN substrate, Au paste (dupo
nt9791) is printed with a 325 mesh pattern at room temperature for 10
After being left for min, it was dried under the conditions of 120 ° C. and 10 min, and subsequently baked under the conditions of 850 ° C. and 10 min. A glass paste (dupont9950) was formed by printing so as to have through holes for conducting the upper and lower conductor layers as a dielectric layer, and was fired in the same process as the above conditions. This glass layer formed a good bond with the AlN substrate. This process was repeated three times to realize three-layer wiring. The circuit board of the present invention thus obtained was free from short-circuits between layers, had sufficient bonding strength, and was highly reliable. (Example 3) An AlN substrate containing 5 wt% of Y ₂ O ₃ was placed in steam at 121 ° C. and 2 atm for 168 hours to be subjected to oxidation treatment. A boehmite film (Al ₂ O ₃ like) having a thickness of 3 to 5 μm was formed on the surface of the substrate. Next, after printing Ag-Pd paste (ESL9601) in a predetermined pattern and drying at 125 ° C. for 10 minutes, 93
A conductor path was formed by firing at 0 ° C. for 10 minutes.
Next, the resistance paste (dupont16 series as a glass layer)
100 kΩ / □, 1 kΩ / □, 10 kΩ / □, 1000
kΩ / □) was printed using a 250 mesh screen. When fired under conditions of 850 ° C. and 10 minutes in air, no bubbles were formed in the resistor and good adhesion was obtained. The circuit boards of the present invention thus obtained all had resistance values within ± 15%. (Comparative Example) As a comparative example, when a resistor was similarly formed on an AlN substrate without oxidation treatment, a very large variation of about ± 30% was exhibited. This tendency was the same in the AlN substrate by hot pressing containing no sintered material.

As described in the above embodiments, by forming an oxide layer on the AlN substrate regardless of whether or not the additive is included, the resistor layer and the glass layer can be joined to each other, and the AlN substrate can be joined. A high thermal conductivity circuit board or a high thermal conductivity envelope can be obtained by fully utilizing the high thermal conductivity, high pressure resistance and mechanical strength of the substrate.

[0030]

As described above, according to the present invention, A
It is possible to provide a highly heat-conductive circuit board and an envelope in which a glass layer and a resistor layer can be firmly connected on an IN substrate and variation in the resistance value of the resistor can be suppressed.

Claims (12)

(57) [Claims] 1. A high thermal conductivity comprising an aluminum nitride ceramic substrate, an Al ₂ O ₃ layer formed on the substrate, and a glass layer formed on the Al ₂ O ₃ layer. Circuit board. 2. The high thermal conductivity circuit board according to claim 1, wherein the film thickness of the Al ₂ O ₃ layer is 0.5 μm or more and 100 μm or less. _{3. The} thickness of the Al ₂ O ₃ layer is 2 μm or more 20
The high thermal conductivity circuit board according to claim 1, having a thickness of not more than μm. 4. The high thermal conductivity circuit board according to claim 1, 2 or 3, wherein the glass layer is formed by firing a glass paste. 5. An aluminum nitride ceramic substrate, an Al ₂ O ₃ layer formed on this substrate, and a resistor layer formed on this Al ₂ O ₃ layer and containing conductive powder dispersed in a glass layer. A circuit board having high thermal conductivity, comprising: 6. The high thermal conductivity circuit board according to claim 5, wherein the film thickness of the Al ₂ O ₃ layer is 0.5 μm or more and 100 μm or less. 7. The thickness of the Al ₂ O ₃ layer is 2 μm or more 20
The high thermal conductivity circuit board according to claim 5, which has a thickness of not more than μm. 8. The high thermal conductivity circuit board according to claim 5, wherein the resistor layer is formed by firing a glass paste in which conductor powder is dispersed. . 9. An aluminum nitride ceramic substrate, an Al ₂ O ₃ layer formed on this substrate, a glass layer formed on this Al ₂ O ₃ layer, and a cap formed on this glass layer. An envelope having high thermal conductivity, comprising: 10. The high thermal conductivity envelope according to claim 9, wherein the film thickness of the Al ₂ O ₃ layer is 0.5 μm or more and 100 μm or less. 11. The film thickness of the Al ₂ O ₃ layer is 2 μm or more 2
The high thermal conductivity envelope according to claim 9, which has a thickness of 0 μm or less. 12. The glass layer according to claim 9, wherein the glass layer is formed by firing glass paste.
0 or the high thermal conductivity envelope according to claim 11.