JP2001062588A - Brazing material for aluminum circuit board, and ceramic circuit substrate using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a brazing material for a high reliability substrate of a ceramic substrate and an aluminum metal plate by including Mg, at least one or more kinds of elements out of Cu, Si and Ge, and the balance of Al. SOLUTION: Temperature, where at least one part is formed into a liquid phase, is 500 deg.C-630 deg.C, and it is preferable that Mg is 0.05-3 wt.%. It is preferable that a ceramic substrate is any of aluminum nitride, silicon nitride, silicon carbide, or alumina. However, in consideration of a power device with large power and large heat generation, aluminum nitride and silicon nitride with high insulation resistance and high heat conductivity are suitable. In consideration of reliability after jointing, it is desired that purity of the aluminum plate is 99.0 wt.% or more. By lowering the jointing temperature of the Al circuit material and the like ceramic substrate, a thermal stress generated at the manufacturing time can be reduced, so as to endure the thermal stress caused by a heat cycle. Thereby, such a substrate for a power module is obtained, which can be applied for the uses of electric vehicles, railways or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brazing filler metal between a ceramic substrate and a metal plate used for a power module or the like, and a highly reliable ceramic circuit substrate 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 accordance with the above demand, a copper circuit board having high heat dissipation using ceramics such as aluminum nitride (AlN) having high heat conductivity as a substrate material has been developed. 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.
No. 12554 and Japanese Patent Application Laid-Open No. 4-18746 disclose aluminum (A) having a lower yield strength than copper as a circuit material.
A ceramic circuit board using 1) is disclosed.

However, with regard to the heat cycle resistance of repeatedly cooling and heating from -40.degree. C. to 125.degree. C., which is an index of reliability, even if the circuit board is used, the aluminum circuit material may peel off after about 1500 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.

[0009]

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.

[0010]

Means for Solving the Problems As a result of the inventor's intensive studies to achieve the above object, the present inventors have found that a reduction in the joining temperature between an aluminum (Al) material, which is a circuit material, and a ceramic substrate causes a problem during manufacturing. The present inventors have found that the thermal stress can be reduced and the thermal stress due to the heat cycle can be withheld, and the present invention has been achieved.

That is, the present invention relates to a brazing material for joining a ceramic substrate and a metal plate containing aluminum as a main component, wherein Mg and at least one element selected from the group consisting of Cu, Si and Ge are used. A brazing filler metal containing at least a part of which is Al, and a temperature at which at least a part thereof becomes a liquid phase is 500 ° C. to 630 ° C., and particularly, 0.05% by weight of Mg -3% by weight.

Further, the present invention is a ceramic circuit board characterized in that a ceramic substrate and a metal plate mainly composed of aluminum are joined via the brazing material. Further, the ceramic substrate is any one of aluminum nitride, silicon nitride, silicon carbide, and alumina.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The metal plate containing aluminum as a main component used in the present invention is made of aluminum in consideration of reliability after joining.
The purity of the plate is preferably 99.0% by weight or more. When the purity is lower than 99.0% by weight, the yield strength is large, and when a circuit board is used, a heat cycle test (-40 ° C ← → 1
(25 ° C.) 1000 times or less
One-circuit peeling may occur.

The components of the brazing material include Mg, Cu, S
It is important that at least one element of the group consisting of i and Ge is included, and the balance is Al. 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,
Although Si and Ge each alone contribute to lowering the melting point of the brazing alloy, a plurality of these can also be used.

The brazing material preferably 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. If the temperature exceeds 630 ° C., the thermal stress remaining on the aluminum plate or the ceramic substrate increases, and the melting point of the aluminum material becomes close to the melting point of the aluminum material. Is likely to occur.

In the present invention, Mg is preferably 0.05% by weight to 3% by weight. 0.05% by weight
If the amount is less than the above, the effect of removing oxides is low. When the aluminum plate and the ceramic substrate are joined (brazed) using the alloy, it is desirable to apply a normal force of 1 to 50 kgf / cm ² to the joining surface.

Regarding the method of producing the brazing material of the present invention, for example, only Al 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. Thereafter, the foil is gradually formed into a foil through a rolling mill, and if necessary, annealed to form a foil having a thickness of 20 μm. Further, a mixture of metal powders having a desired composition may be dispersed in an organic solvent.

Further, ceramics as a base material include:
Any material may be used as long as it is electrically insulating and has high thermal conductivity. For example, silicon carbide (SiC) to which alumina (Al ₂ O ₃ ) or beryllia (BeO) is added, silicon nitride,
Among them, aluminum nitride (AlN) substrate and aluminum nitride (AlN) substrate can be used because of their high withstand voltage and high thermal conductivity, considering that a large power device generates a large amount of heat. Silicon (S
i ₃ N ₄ ) are preferred.

The circuit board of the present invention can be formed by a method in which a metal plate containing aluminum as a main component and a ceramic substrate such as an aluminum nitride substrate are joined by heating using a joining material and then etched, or a method of punching from the metal plate. Thus, a circuit pattern can be formed in advance by using a brazing material according to the present invention, and a circuit pattern can be manufactured by using a brazing material according to the present invention.

In any of the above joining methods, it is important that the joining can be performed at a lower temperature in order to keep the thermal stress during joining as low as possible. However, the present inventors have proposed that the joining between a metal plate and a ceramic substrate such as an aluminum nitride substrate can be performed. As a result of various experimental studies on the joining, a ceramic circuit board obtained when joining using a brazing material having a liquid phase generating temperature of 500 ° C. to 630 ° C., and a module manufactured using the same. It has been found that the reliability of the present invention can be improved, and the present invention has been achieved.

[0021]

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 10 and Comparative Examples 1 to 3 As ceramic substrates, 50 mm × 50 mm × 0.63
5 mm aluminum nitride substrate and silicon nitride substrate,
Thermal conductivity by laser flash method is 175 each
W / mK and 75 W / mK, and the three-point bending strength average values of 420 MPa and 560 MPa were prepared.
Also, a JIS-named 1085 material having a thickness of 0.4 mm was prepared as a metal plate containing aluminum as a main component.

As an example of the production of the brazing alloy foil, a case of a composition having a composition of 4% by weight of Cu, 1% by weight of Mg and the remaining Al will be exemplified. Only Al was melted in a graphite-silicon carbide composite crucible at 750 ° C, and 4 wt% of Cu was added thereto, and the mixture was sufficiently stirred and dissolved at 900 ° C. Subsequently, a flux (for example, N406 manufactured by Nippon Metal Chemical Co., Ltd.) is added, and after sufficiently stirring to remove slag and the like, 1 wt% of Mg is added.
The melted brazing alloy was poured into a mold and solidified by cooling. Thereafter, thinning and annealing at 350 ° C. were repeated through a rolling mill to finally form a foil having a thickness of 20 μm. Other brazing alloy foils were also prepared according to the above.

On both the front and back surfaces of the aluminum nitride substrate,
They were overlaid with 20 μm brazing alloy foils of various compositions shown in Table 1 and pressed vertically at 35 kgf / cm ² . Then, in a vacuum of 10 ^-4 Torr, a temperature of 500 ° C. to 650 ° C.
The aluminum plate and the aluminum nitride substrate were joined while pressing under the conditions described above. Table 2 shows the joining conditions of the examples and the comparative examples.

[0025]

[Table 1]

[0026]

[Table 2]

After bonding, an etching resist was screen-printed on a desired portion of the aluminum plate surface, and was etched with a ferric chloride solution to form a circuit pattern. Next, after the resist was removed, 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: -50 ° C. × 30 minutes → room temperature × 10 minutes → 150 ° C. × 30 minutes → room temperature × 10 minutes
The heat cycle was performed 1000 times.
Thereafter, the presence or absence of abnormalities such as peeling of the circuit board by visual inspection and ultrasonic flaw detection and the occurrence of cracks in the ceramic substrate was observed. Table 3 shows the results.

[0029]

[Table 3]

As can be seen from Table 3, all of the examples of the present invention have a heat cycle of 10 in the reliability evaluation.
No abnormalities such as circuit peeling and solder cracks were observed even after the 00th operation, which was sufficient for a highly reliable substrate.

[0031]

According to the present invention, in a brazing material for joining a ceramic substrate and a metal plate containing aluminum as a main component, Mg and at least one element of the group consisting of Cu, Si and Ge are used. Including, the rest is made of Al, so that the joining temperature can be reduced compared to the conventional brazing material,
The residual thermal stress can be reduced, and a highly reliable circuit board can be provided with good reproducibility and at low cost.

Further, the ceramic circuit board of the present invention comprises:
Since the brazing material is used, it has a feature of low residual thermal stress and therefore high reliability, and is extremely useful in industry.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H05K 3/38 H05K 3/38 E // B23K 101: 42 (72) Inventor Masahiro Ibukiyama Machida, Tokyo 3-5-1 Asahicho, Central Research Laboratory, Denka Kagaku Kogyo Co., Ltd. (72) Inventor Isao 3-5-1 Asahimachi, Machida City, Tokyo F-term, Central Research Laboratory, Denki Kagaku Kogyo Co., Ltd. 4E351 AA07 AA08 AA09 AA14 DD04 DD08 DD11 EE03 GG01 GG03 GG04 5E343 AA02 AA22 DD52 ER39 GG02

Claims (5)

[Claims] 1. A brazing material for joining a ceramic substrate and a metal plate containing aluminum as a main component, comprising:
A brazing material comprising at least one element selected from the group consisting of u, Si, and Ge, with the balance being Al. 2. The temperature at which at least a part of the liquid phase becomes 500.
The brazing material according to claim 1, wherein the temperature is from ℃ to 630 ° C. 3. The brazing material according to claim 1, wherein Mg is 0.05% by weight to 3% by weight. 4. A ceramic circuit board comprising a ceramic substrate and a metal plate containing aluminum as a main component, joined via the brazing material according to claim 1. 5. A ceramic substrate comprising: aluminum nitride;
The ceramic circuit board according to claim 4, wherein the ceramic circuit board is any one of silicon nitride, silicon carbide, and alumina.