JP2001079684A - BRAZING FILLER METAL FOR Al-BASED METAL, AND CERAMIC CIRCUIT BOARD USING THE SAME - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a brazing filler metal to join a ceramic substrate with an alloy plate mainly consisting of Al which can provide a ceramic board durable in repeated heat cycle and high in reliability by setting the quantity of Fe, Cr and Mn as impurities of Al alloy to be less than a predetermined value. SOLUTION: This brazing filler metal consists of Al-based alloy containing 1.5 wt.% or less Fe, Cr and Mn and impurities, and containing Mg and at least one kind of Cu, Si and Ge. In particular, the brazing filler metal contains 0.05-3% Mg and at least 85% Al, and the temperature at which the liquidus is generated is 500 to 630 deg.C. A ceramic circuit board ready for applications requiring high reliability in which a ceramic substrate is excellently with a circuit formed of a metal sheet mainly consisting of Al can be obtained using this brazing filler metal by joining the alloy sheet mainly consisting of Al with the ceramic substrate consisting of at least one kind of aluminum nitride, silicon nitride, silicon carbide and alumina.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brazing material for joining a ceramic substrate and a metal plate used in a power module or the like, and a highly reliable ceramic circuit board using the same.

[0002]

2. Description of the Related Art Conventionally, as a circuit board for a power module or the like for mounting a semiconductor element or the like which generates a large amount of heat, an electrically conductive ceramic substrate such as an alumina (Al ₂ O ₃ ) ceramic is formed on the surface of the substrate. 2. Description of the Related Art A circuit board in which circuit layers having different properties are joined has been widely used.

However, in recent years, the amount of heat generated by these semiconductor elements has tended to increase with the miniaturization and high performance of equipment, and the heat generated by the semiconductor elements has been dissipated in order to obtain reliable and stable operation. Therefore, it has become more important to make the temperature sufficiently lower than the temperature at which the element is not destroyed, and in addition to high electrical insulation properties as the characteristics of the circuit board, higher thermal conductivity has been required. .

[0004] In response to the above demand, a copper circuit board having high heat dissipation has been developed using ceramics such as aluminum nitride (AlN) having high thermal conductivity as a substrate material. However, the copper circuit board has insufficient mechanical properties, and when used as a circuit board, the copper circuit layer of the ceramic portion may be subjected to repeated thermal cycling or temperature changes in the operating environment due to the operation of the semiconductor element. There is a problem that cracks are apt to occur near the joint and reliability is low.

As a solution to this problem, for example, Japanese Unexamined Patent Publication No.
JP-A No. 12554 and JP-A-4-18746 disclose ceramic circuit boards using aluminum (Al) having a lower yield strength than copper as a circuit material.

However, with regard to the heat cycle resistance of repeatedly cooling and heating from -40 ° C. to 125 ° C., which is an index of reliability, even with the above-mentioned circuit board, peeling of aluminum circuit material occurs about 1000 times. As a result, problems such as cracks in the ceramic substrate occur, and it is not possible to sufficiently cope with applications requiring high reliability as described above.

Japanese Patent Application Laid-Open No. 8-208359 discloses a circuit board in which Al is directly bonded to an AlN substrate using a molten metal of Al. According to the present invention, Al
The circuit board alone has achieved heat cycle resistance of more than 3000 times.

[0008] However, the direct bonding using the molten aluminum causes a large variation in the thickness of the Al circuit layer, so that not only a stable and highly reliable circuit board cannot be obtained, but also equipment cost and equipment. There is a problem that maintenance is required and the cost is increased.

On the other hand, the brazing material joining method has almost no variation in the thickness of the Al circuit layer and the equipment cost is low.
Heretofore, the emphasis has been placed on additive components, and little attention has been paid to Al impurities. However, Al is often used as a recycled product, and when producing an alloy by melting, there is contamination from a stirring rod, a jig, or the like, and various impurities may be mixed.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the circumstances of the above-mentioned known technology, and requires high reliability such as a power module applicable to electric vehicles and railways. It is an object of the present invention to provide a ceramic circuit board that can be used for various applications.

[0011]

Means for Solving the Problems The present inventors have made intensive studies to achieve the above object, and as a result, have found that the impurities, especially F
When a large amount of e, Cr, Mn is contained in the brazing filler metal, they form an intermetallic compound with Al or the main component,
For this reason, the inventors have found that not only the bonding state between the ceramic substrate and the circuit board may be defective, but also that the reliability of the obtained circuit board cannot be sufficiently secured. By reducing the amount of the impurities and lowering the bonding temperature between the aluminum (Al) material as the circuit material and the ceramic substrate, the thermal stress generated at the time of bonding can be reduced, and bonding defects due to the generation of intermetallic compounds can be reduced. The present invention has been found to be able to suppress the heat cycle and to significantly improve the reliability such as heat cycle resistance, and the present invention has been accomplished.

That is, the present invention provides a ceramic substrate and Al
Is a brazing material for joining to a metal plate whose main component is Fe, Cr, and Mn as impurities, each of which is 1.5% by weight or less, and at least one of Mg, Cu, Si, and Ge. Al alloy containing one or more kinds. In a particularly preferred embodiment, Mg is contained in an amount of 0.05% by weight or more and 3% by weight or less, Al is contained in an amount of 85% by weight or more, and the temperature at which a liquid phase is formed is 500 ° C to 630 ° C. It is brazing material. The present invention also provides a metal plate containing Al as a main component using the brazing material, aluminum nitride,
A ceramic circuit board characterized by being bonded to a ceramic substrate made of at least one selected from the group consisting of silicon nitride, silicon carbide, and alumina.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, it is essential that Fe, Cr and Mn as impurity elements are all 1.5% by weight or less. In the brazing material, when there are many Fe, Cr, and Mn as impurity elements, an intermetallic compound is generated, and when the ceramic substrate and the metal plate containing aluminum as a main component are brazed, the bonding state is deteriorated.
The reliability of the obtained ceramic circuit board also decreases. The formation of the intermetallic compound depends on the temperature rising rate and the temperature decreasing rate during the bonding, but any one of the above-mentioned elements is 1.
If it exceeds 5% by weight, it becomes remarkable. As a result, the reliability of a ceramic circuit board is significantly reduced, and a heat cycle test (−40 ° C.) which is a general reliability evaluation is performed.
(← → 125 ° C.), cracks, Al circuit peeling, etc. occur on the substrate after 1000 times or less. The preferable amount of each of the impurity elements is 0.5% by weight or less.

When a ceramic substrate and a metal plate containing Al as a main component are joined together, if the joining temperature is high, the residual stress after joining increases, so it is important to lower the melting point of the brazing material. . For that purpose, Mg, Cu, Si,
It is preferable to include at least one element in the group consisting of Ge. It is considered that Mg not only removes oxides present at the interface that hinders joining, but also contributes to lowering the melting point of the brazing material. When used in combination with Mg, Cu, Si, and Ge alone can contribute to lowering the melting point of the brazing alloy even if used alone, but a plurality of these can also be used.

On the other hand, Mg is preferably 0.05% by weight to 3% by weight. When the content of Mg is less than 0.05% by weight, the effect of removing oxides is low. On the contrary, when the content exceeds 3% by weight, the reason is not clear, but the joining property may be deteriorated. Further, the aluminum (Al) in the brazing material is preferably at least 85% by weight. When the content is less than 85% by weight, even if the alloy containing Al as the main component can be joined, the difference in the coefficient of thermal expansion between the alloy containing Al as the main component and the brazing material becomes large, or the yield strength of the brazing material decreases. For reasons such as an increase in size, the heat cycle resistance may be reduced when a circuit board is used. More preferably, the Al content in the brazing material is 90% by weight or more. For the above-mentioned reasons, Mg is not more than 0.
An Al alloy comprising at least one element selected from the group consisting of Cu, Si, and Ge, in which the content of Al is at least 85% by weight, and the balance is at least one of a ceramic substrate and Al. It is suitable for joining with a metal plate to be formed.

It is preferable that the brazing material forms a liquid phase at least partially in a temperature range of 500 ° C. to 630 ° C. That is, if the temperature is lower than 500 ° C., the bonding property may not be sufficient, and if the temperature exceeds 630 ° C., the thermal stress remaining on the aluminum plate or the ceramic substrate increases,
This is because the temperature is close to the melting point of the aluminum material, so that a brazing defect is likely to occur. When joining (brazing) a metal plate containing aluminum as a main component and a ceramic substrate using the brazing material, 1 to 50 kgf /
It is desirable to apply a normal force of cm ² .

With regard to the method of producing the brazing material of the present invention, for example, only aluminum is melted in a crucible of a graphite-silicon carbide composite material, a predetermined amount of metal is added thereto, and sufficiently stirred and dissolved. Subsequently, after adding a flux and sufficiently stirring to remove slag and the like, the molten brazing alloy is poured into a mold and solidified by cooling. Then, gradually rolled through a rolling mill,
What is necessary is just to pulverize. Alternatively, a method in which a metal powder is weighed so as to have a desired composition and dispersed in an organic solvent to form a slurry may be used.

As the ceramic substrate, any substrate may be used as long as it is electrically insulating and has high thermal conductivity. For example, alumina (Al ₂ O ₃ ) or beryllia (Be)
Silicon carbide (SiC) to which O) is added, silicon nitride, aluminum nitride, and the like can be given. Of these,
Considering that a large power device generates a large amount of heat and has high withstand voltage and high thermal conductivity, an aluminum nitride (AlN) substrate, silicon nitride (Si ₃ N ₄ )
Is preferred.

The circuit board of the present invention may be formed by heating a metal plate containing aluminum as a main component and a ceramic substrate such as an aluminum nitride substrate using the brazing material and then etching the metal plate, or by punching the metal plate. For example, a circuit pattern can be formed in advance by, for example, a method in which the circuit pattern is joined to a ceramic substrate using the brazing material.

[0020]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

[Examples 1 to 11 and Comparative Examples 1 to 3] A ceramic substrate was 50 mm × 50 mm × 0.6.
A 35 mm aluminum nitride substrate and a silicon nitride substrate each have a thermal conductivity of 1
Those having 75 W / mK and 75 W / mK and average values of the three-point bending strengths of 420 MPa and 560 MPa were prepared. In addition, as a metal plate containing aluminum as a main component, a JIS designation 1085 material having a thickness of 0.4 mm was used.

As for the method of producing the brazing material, 5% by weight of Cu-1.5% by weight of Mg-1.5% by weight of Fe-remaining Al
The case of the foil described above is exemplified below. Only Al is melted at 750 ° C. in a graphite-silicon carbide composite crucible, 5% by weight of Cu is added thereto, and 1.5% by weight of Fe is further added. did. Next, the molten metal was heated to 750 ° C., a flux for alloy (for example, N406 manufactured by Nippon Metal Chemical Co., Ltd.) was added, and the mixture was sufficiently stirred to remove slag and the like. Was poured into a mold and cooled and solidified. Thereafter, thinning and annealing at 350 ° C. were repeated through a rolling mill to finally form a foil having a thickness of 20 μm. Alloy foils were prepared for other brazing materials in accordance with the above. The prepared alloy foil was analyzed by a fluorescent X-ray method (calibrated by chemical analysis), and it was confirmed that the alloy had a desired composition.

On both sides of the ceramic substrate, Table 1
Through 20μm braze alloy foils having various compositions shown in overlaid the aluminum plate, 35 kgf / cm ² in the vertical direction
And pressurized. Then, at a temperature of 5 in a vacuum of 10 ^-4 Torr.
The aluminum plate and the aluminum nitride substrate were soldered while pressing under the conditions of 00 ° C to 650 ° C to obtain a joined body. Table 2 shows the joining conditions of the examples and the comparative examples.

[0024]

[Table 1]

[0025]

[Table 2]

With respect to the joined body, the joined state was confirmed visually and by ultrasonic flaw detection. Further, with respect to the joined body in which no abnormality was observed, an etching resist was screen-printed on a desired portion of the aluminum plate surface and etched with a ferric chloride solution to form a circuit pattern. Next, after removing the resist, the electroless Ni-
P plating was performed at 3 μm to obtain a circuit board. The reliability of the obtained circuit board was evaluated as described below.

Reliability evaluation: -40 ° C. × 30 minutes → room temperature × 10 minutes → 125 ° C. × 30 minutes → room temperature × 10 minutes
The heat cycle was applied 3000 times.
Thereafter, the circuit board was visually and visually inspected for abnormalities such as peeling of the circuit by ultrasonic flaw detection and crack occurrence on the ceramic substrate. Table 3 shows the results.

[0028]

[Table 3]

From Table 3, all the circuit boards of the present invention are in a good bonding state between the circuit and the ceramic substrate, and abnormalities such as peeling of the circuit and solder cracks are recognized even after the heat cycle of 3000 times. Therefore, it is clear that the circuit board has high reliability.

[0030]

According to the brazing material of the present invention, Fe, Cr and Mn as impurity metal elements are all controlled to 1.5% by weight or less, so that an intermetallic compound is formed during brazing. Therefore, the ceramic substrate and the metal plate containing aluminum as a main component can be satisfactorily joined. In the brazing material of the present invention, Al is 85% by weight or more, and Mg, Cu, S
from at least one of i and Ge,
It is characterized in that a ceramic substrate and a metal plate containing aluminum as a main component can be more preferably bonded. In addition, the brazing material of the present invention has a temperature at which a liquid phase is generated at 500 ° C.
Since the ceramic circuit board can be manufactured at a low joining temperature since the temperature is up to 630 ° C., the thermal stress remaining on the obtained ceramic circuit board can be reduced, and as a result, a highly reliable ceramic circuit that is durable to thermal cycles. A substrate can be easily obtained.

In the ceramic circuit board of the present invention, the ceramic substrate and the circuit composed of a metal plate containing aluminum as a main component are satisfactorily joined using the brazing material.
Since the residual thermal stress is low, it is a highly reliable ceramic circuit board that is durable to repeated thermal cycles, and is very useful in industry.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masahiro Ibukiyama 3-5-1 Asahicho, Machida-shi, Tokyo Denka Kagaku Kogyo Co., Ltd. (72) Inventor Shigeo Hiyama 3 Asahicho, Machida-shi, Tokyo No.5-1, Denka Kagaku Kogyo Co., Ltd., Central Research Laboratory

Claims (5)

[Claims] A brazing material for joining a ceramic substrate and a metal plate containing Al as a main component, wherein the brazing material is Fe,
A brazing material comprising an Al-based alloy in which Cr and Mn are each 1.5% by weight or less. 2. An Al-based alloy comprising Mg, Cu, Si, Ge
The brazing material according to claim 1, wherein the brazing material is an Al alloy containing at least one of the following. (3) Mg is contained in an amount of 0.05 to 3% by weight;
The brazing material according to claim 2, wherein Al is contained in an amount of 85% by weight or more. 4. The method according to claim 1, wherein the temperature at which the liquid phase is formed is 500 ° C. to 630 ° C.
The brazing material described. 5. A metal plate containing Al as a main component,
Claims 1. A semiconductor device comprising a brazing material according to claim 2, 3, or 4, which is joined to a ceramic substrate made of at least one selected from the group consisting of aluminum nitride, silicon nitride, silicon carbide, and alumina. Characteristic ceramic circuit board.