JP2001121287A - BRAZING FILLER METAL FOR Al SERIES METAL AND CERAMICS CIRCUIT BOARD USING THE SAME - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ceramics circuit board with high reliability having an Al circuit almost free from the variation of the thickness of a circuit layer and stable in joining. SOLUTION: In this brazing filler metal for joining a ceramics board and a metallic sheet consisting essentially of Al, the content of oxygen is <=0.5 mass %, and, preferably, an Al series brazing filler metal containing Mg of 0.05 to 3 mass % is used.

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 used for a power module or the like to a metal plate forming a circuit or a heat sink, and a highly reliable ceramic using the same. Related to a circuit board.

[0002]

2. Description of the Related Art Conventionally, alumina (A) has been used to mount a semiconductor element or the like which generates a large amount of heat such as a power module.
l ₂ O ₃ ) Ceramic circuit boards formed by bonding a conductive circuit layer to the surface of a ceramic substrate having excellent insulating properties such as ceramics are widely used.

[0003] With respect to ceramic circuit boards, the amount of heat generated tends to increase with the miniaturization and high performance of equipment to be mounted, and semiconductor elements and the like are generated in order to obtain reliable and stable operation. It is becoming more important to dissipate heat and make the temperature sufficiently lower than the temperature at which the element is not destroyed. In addition to high electrical insulation properties, ceramic substrates are required to have even higher thermal conductivity. ing.

In response to the above demand, a copper circuit board has been developed in which ceramics such as aluminum nitride (AlN) having excellent heat dissipation properties are used as a substrate material and a circuit made of conductive copper is provided on the substrate. I have. However, the copper circuit board has insufficient mechanical characteristics, and when used as a circuit board, the copper circuit layer of the ceramic portion may be subjected to repeated thermal cycles or temperature changes in the operating environment due to the operation of the semiconductor element. There is a problem that cracks are likely 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, when a heat cycle test in which cooling and heating are repeated from −40 ° C. to 125 ° C. is performed,
Even with the above circuit board, problems such as peeling of the aluminum circuit material or cracking of the ceramics substrate occur after about 1000 times, and cannot sufficiently cope with applications requiring high reliability.

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

[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, as a method of providing an Al circuit on a ceramic substrate, a method of interposing an Al-based brazing material is known. However, in this brazing material joining method, there is almost no variation in the thickness of the Al circuit layer, and equipment costs are reduced. Is inexpensive, but the bonding may not be stable, and the yield is not always satisfactory.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the circumstances of the above-mentioned known art, and is, for example, extremely reliable and can be applied to power modules for electric vehicles and railways. It is an object of the present invention to provide a ceramic circuit board.

[0011]

Means for Solving the Problems In order to achieve the above object, the present inventor has studied in detail Al-based brazing material, and has found that a ceramic substrate and a circuit metal plate containing Al as a main component are made of Al-based brazing material. When joining with a brazing material, when the oxygen amount in the Al-based brazing material is equal to or less than a specific amount, it is possible to improve the bonding state between the ceramic substrate and the Al-based brazing material, and furthermore, between the Al-based brazing material and the metal plate for a circuit. Was found. As a result, the resulting ceramic circuit board receives heat in actual use,
The present invention has been made based on the finding that the circuit material does not peel off or the ceramic substrate does not crack even by the cooling cycle.
Although the reason for the above is not clear, Al-based brazing filler metal is that, as a raw material, Al is often used as a recycled product, that it is easily oxidized when the alloy is melt-produced, and that the brazing filler metal is Since the metal powder is often used as a metal powder and the surface of the metal powder is easily oxidized by oxygen in the air, the amount of oxygen contained in the metal powder may increase. However, it is considered that most of the oxygen content is present as a metal oxide in the brazing material. Therefore, if the oxygen content in the Al-based brazing material is large, the ceramic substrate, the brazing material, and the metal It is considered that the contact between the circuit board and the brazing material becomes insufficient, and as a result, only a brazing state in which the bonding state is poor can be obtained. The circuit board that appears to be bonded appears to have problems such as peeling of the circuit metal plate from the ceramic substrate in a heat cycle test or the like, and sufficient reliability cannot be ensured.

That is, the present invention provides a ceramic substrate and Al
Is a brazing material for joining a metal plate whose main component is oxygen, wherein the amount of oxygen is 0.5% by mass or less, and Mg is 0.05% by mass or more and 3% by mass. % Or less. In particular, Cu, S
It is preferable to be Al containing at least one of i and Ge. Also, a metal plate containing Al as a main component is
A ceramic circuit board characterized by being joined to one or more ceramic substrates selected from the group consisting of aluminum nitride, silicon nitride, silicon carbide, and alumina via the brazing material.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The brazing filler metal according to the present invention has an oxygen content of 0.1.
It is a brazing material having a content of 5% by mass or less. If the content exceeds 0.5% by mass, not only is it not possible to obtain a good yield at a relatively low joining temperature at which a brazing defect is not generated when joining a ceramic substrate and a metal plate containing Al as a main component, but also,
When a ceramic circuit board is used, the reliability is significantly reduced. In a heat cycle test (−40 ° C. to 125 ° C.), which is a general reliability evaluation, A is reduced to 1,000 times or less.
One-circuit peeling occurs. Preferably, it is 0.1% by mass or less.

In the brazing material of the present invention, Mg is 0.05
It is preferably from 3% by mass to 3% by mass. If the Mg content is less than 0.05% by mass, the effect of removing oxides at the bonding interface between the ceramic substrate and the brazing material or the metal plate and the brazing material is low, and if it exceeds 3% by mass, the reason is not clear. However, the bondability may be deteriorated. It is considered that Mg not only removes the oxide present at the interface that hinders the joining, but also contributes to lowering the melting point of the brazing material.

On the other hand, when a ceramic substrate and a metal plate containing Al as a main component are joined together, if the joining temperature is high, not only the phenomenon of partial melting is likely to occur, but also a soldering defect is liable to occur. It is important to lower the melting point of the brazing filler metal since the residual stress later increases. Therefore, the brazing material of the present invention is preferably Al containing at least one or more elements of the group consisting of Cu, Si, and Ge. still,
Even if Cu, Si, and Ge are used alone, they contribute to lowering the melting point of the brazing alloy, but a plurality of these can be used in combination. Further, as long as the amount of the impurities in the brazing material of the present invention does not impair the object of the present invention, it may be contained, and typical examples of the impurities include Fe and M.
n, Zn, V, Ti, Cr, Ni and the like.

When a metal plate mainly composed of Al and a ceramic substrate are joined (brazed) using the brazing material, a vertical force of 10 ^{5 to} 5 × 10 ⁶ Pa is applied to the joining surfaces. It is desirable.

The form of the brazing material of the present invention may be any form such as a foil form or a powder form. For example, in the case of a foil shape, only aluminum is melted in a graphite-silicon carbide composite crucible, a predetermined amount of metal is added thereto, and sufficiently stirred and dissolved. When the content of oxygen is large, etc., a flux is added if necessary, and the mixture is sufficiently stirred to remove slag and the like, and then the dissolved brazing material is poured into a mold and solidified by cooling. Then, it may be gradually formed into a foil through a rolling mill.

When the ceramic substrate is joined to a circuit or heat dissipating metal plate mainly composed of Al using the brazing material of the present invention, the foil may be used as it is, or a metal having a desired composition may be used. A method in which the powder is dispersed in an organic solvent to form a slurry paste may be used.

When using the paste method, the metal powder is used by being mixed with an organic binder or an organic solvent. Typical examples of the organic binder include acrylic polymers, and examples of the solvent include isophorone and terpineol.
As for the size of the particles constituting the powder, the finer the better, in consideration of the bondability, but in order to minimize the increase in the amount of oxygen due to oxidation of the powder surface by air or the like, the maximum particle size should be 44 μm or less. It is preferable that the average diameter is about several μm to 20 μm. Further, the powder may be a mixed powder of each metal alone, but Mg alone is very easily oxidized and difficult to handle. Therefore, it is preferable to use Mg as an alloy powder of Al or the like.

As the ceramic substrate used in the present invention, any substrate may be used as long as it is electrically insulating and has high thermal conductivity. For example, a carbonized substrate to which alumina (Al ₂ O ₃ ) or beryllia (BeO) is added is used. Silicon (SiC), silicon nitride (Si ₃ N ₄ ), aluminum nitride (AlN), and the like can be given. Among these, considering that a large power device generates a large amount of heat, an aluminum nitride substrate having a high withstand voltage and a high thermal conductivity, a silicon carbide substrate to which silicon nitride and beryllium are added are preferable. For general-purpose applications, an alumina substrate is inexpensive and 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 by 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.

[0022]

[Examples 1 to 9 and Comparative Examples 1 and 2] As a ceramic substrate, an aluminum nitride substrate of 50 mm × 50 mm × 0.635 mm was prepared. As for the characteristics, the thermal conductivity by the laser flash method was 175 W / mK, and the average value of the three-point bending strength was 420 MPa. A 0.4 mm thick J
IS designation 1085 material was used.

Further, the brazing material shown in Table 1 was melted by melting only aluminum in a crucible of a graphite-silicon carbide composite material, a predetermined amount of metal was added thereto, sufficiently stirred and dissolved, and a flux was added as necessary. After sufficiently stirring to remove slag and the like, the melted brazing material was poured into a mold and cooled and solidified to form an alloy. The alloy foil was gradually formed into a desired thickness by repeating rolling and annealing in a roll rolling mill, and the alloy powder was adjusted using an atomizing device. The composition of the produced brazing material was evaluated by an X-ray fluorescence method (calibrated by chemical analysis), and the amount of oxygen in the brazing material was quantitatively evaluated by an O / N simultaneous analyzer of LECO.

On both sides of the ceramic substrate, Table 1
The aluminum plates were stacked via a brazing filler metal having various compositions shown in (1) and pressure was applied at 3.5 × 10 ⁶ Pa in the vertical direction. Then, the aluminum plate and the aluminum nitride substrate were soldered to each other under pressure of 600 ° C. in a vacuum of 1.33 × 10 ⁻² Pa to obtain 50 bonded bodies.

[0025]

[Table 1]

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 applied to a thickness of 3 μm to obtain a ceramic circuit board. The reliability of the obtained ceramic circuit board was evaluated as shown below.

<Reliability Evaluation Test> A heat cycle of -40 ° C. × 20 minutes to room temperature × 10 minutes to 125 ° C. × 20 minutes to room temperature × 10 minutes was applied to the ceramic circuit board for three cycles.
Loaded 000 times. Thereafter, the ceramic circuit board was visually and visually inspected for abnormalities such as peeling of the circuit by ultrasonic flaw detection and occurrence of cracks in the ceramic board. Table 2 shows the results.

[0028]

[Table 2]

From Table 2, it can be seen that the ceramic circuit board of the present invention has a good bonding state between the circuit material and the ceramic substrate, peeling of the circuit material and cracking of the ceramic substrate even after a heat cycle of 3000 times. No abnormalities such as the above are recognized, and it is clear that the circuit board has high reliability.

[0030]

According to the brazing material of the present invention, since the oxygen content is controlled to 0.5% by mass or less, there are few substances which hinder the joining at the time of brazing. And a metal plate mainly composed of: Further, since the brazing material of the present invention further contains Mg and at least one of Cu, Si, and Ge, the ceramic substrate and the metal plate containing aluminum as a main component are more preferably formed at a relatively low temperature. It has the characteristic that it can be bonded to a ceramic circuit board, so that the thermal stress remaining on the resulting ceramic circuit board can be reduced, and as a result, a highly reliable ceramic circuit board that is durable to thermal cycling can be easily obtained. it can.

In the ceramic circuit board of the present invention, the ceramic board and the circuit composed of a metal plate containing aluminum as a main component are satisfactorily joined via 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.

 ────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Masahiro Ibukiyama 3-5-1 Asahimachi, Machida-shi, Tokyo Denki Kagaku Kogyo Co., Ltd. F-term (reference) 4E351 AA08 AA09 AA10 AA11 AA12 BB01 BB30 CC18 CC19 DD04 DD10 DD21 DD52 EE01 EE13 EE24 GG03 GG04 5E338 AA18 BB71 CC04 CC08 EE02 EE27 EE28 EE33

Claims (4)

[Claims] 1. A brazing material for joining a ceramic substrate and a metal plate containing Al as a main component, wherein the amount of oxygen is 0.5% by mass or less. 2. The brazing material according to claim 1, wherein said brazing material contains 0.05% by mass or more and 3% by mass or less of Mg. 3. The brazing material according to claim 1, wherein said brazing material is Al containing at least one of Cu, Si, and Ge. 4. A metal plate containing Al as a main component,
A ceramic circuit board which is bonded to at least one ceramic substrate selected from the group consisting of aluminum nitride, silicon nitride, silicon carbide, and alumina via the brazing material according to claim 2 or 3. .