JPH06310850A - Aluminum nitride substrate having cu circuit - Google Patents

Abstract

PURPOSE:To provide an aluminum nitride substrate having Cu circuit enhancing the endurance to the thermal shock or the heat history, i.e., the heat cycle resistance without notable changes in the aluminum nitride substrate, junction process or circuit structure. CONSTITUTION:As for the ceramic substrate wherein a Cu circuit is formed after a Cu plate and an aluminum nitride substrate are heat-junctioned using a solder paste, the aluminum nitride substrate having the Cu circuit comprising a solder paste containing Ag particles, Cu particles, zirconium particles and/or zirconium(Zr) hydride particles and tungsten(W) particles as the metallic components is to be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum nitride substrate having a copper circuit used for a power module of electronic parts.

In recent years, with the high performance of industrial equipment such as robots and motors, the transition of high power modules such as high power and high efficiency inverters is progressing, and the heat generated from semiconductor elements is also increasing. . In order to efficiently dissipate this heat, various methods have been conventionally used in high power module substrates. In particular, since ceramic substrates with good thermal conductivity have recently become available, after mounting a metal plate such as a copper plate on the substrate and forming a circuit, the semiconductor device is mounted as it is or after plating or other treatment. The structure that does is also being adopted.

There are various methods for joining metal and ceramics, but from the viewpoint of manufacturing circuit boards, the Mo-Mn method,
The active metal brazing method, the copper sulfide method, the DBC method, the copper metallizing method and the like can be mentioned.

Particularly in high power module substrates, attention has been paid to aluminum nitride substrates having high thermal conductivity in place of conventional alumina. As a method for joining copper plates, an active metal may be contained between the copper plates and the aluminum nitride substrate. An active metal brazing method in which a material (hereinafter simply referred to as "brazing material") is interposed and heat-treated to form a joined body (for example, JP-A-60-177).
No. 634), or 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. .

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, it cannot be said that it has sufficient durability against damage caused by heat shock such as heat shock and heat cycle, and heat history, and it is new. A technology proposal was awaited. Therefore, it is proposed to add Mo, W, etc. to the brazing filler metal (Japanese Patent Laid-Open Nos. 4-50186 and 2-36553) or to use metal foil or alloy foil (Japanese Patent Laid-Open No. 4-6174). However, all have problems in mass productivity.

As a result of intensive studies to solve the above problems, the inventors of the present invention have found that the metal of the brazing material paste for forming the joining layer interposed between the copper plate and the aluminum nitride substrate. As ingredients, silver (Ag) powder, copper (C
The present invention has been completed by finding that it is sufficient to include u) powder, zirconium powder (Zr) and / or zirconium hydride powder, and tungsten (W) powder.

[0008]

That is, according to the present invention, in a ceramic substrate in which a copper circuit is formed by heating and joining a copper plate and an aluminum nitride substrate with a brazing material paste, the brazing material paste is used as a metal component. , Silver (Ag) powder, copper (Cu) powder, zirconium (Zr) powder and / or zirconium hydride powder, and tungsten (W) powder, and an aluminum nitride having a copper circuit. The substrate.

The present invention will be described in more detail below. Generally, in the active metal brazing method, a brazing material containing a silver component and a copper component as main components is used. Further, an active metal component is added in order to ensure the wettability of the brazing material and the ceramic during melting. This active metal component reacts with the ceramic substrate to generate an oxide or a nitride, and this reaction layer strengthens the bond between the copper plate and the ceramic substrate.

Also in the present invention, such an active metal component is contained, and specific examples thereof are zirconium and / or zirconium hydride. Since oxides of these active metals are often more stable than oxides of copper, the active metal components reduce the surface of the copper plate to clean it, so that the brazing material and the copper plate become well wetted. As a result, the brazing material and the copper plate diffuse into each other to form a bonding layer.

The joining layer in the case of using such a brazing filler metal is composed of large particles of an alloy formed of a main component of a silver component or a copper component and an active metal component of zirconium and / or zirconium hydride. Therefore, it has a high rigidity, has almost no function of relaxing the thermal stress caused by the difference in thermal expansion between copper and aluminum nitride, and directly transfers the thermal stress of the copper plate to the aluminum nitride substrate, often resulting in damage. .

Therefore, when the present inventors further added tungsten (W) to the brazing filler metal paste, surprisingly, the size of the alloy particles generated in the bonding layer became small and the thermal stress of the copper plate was reduced. It was found to be alleviated. It is considered that the principle is that the addition of tungsten enhances the action of particle dispersion and makes it possible to control the growth of crystal grains when the alloy is solidified from the molten state.

The brazing paste used in the present invention is composed mainly of a silver component and a copper component, and contains a specific amount of zirconium and / or
Or, to a metal component consisting of an active metal component of zirconium hydride, an organic solvent and optionally an organic binder,
It is adjusted by mixing using a mixing machine such as a roll, a kneader, a Banbury mixer, a universal mixing machine, and a ladle mixer. In this case, the metallic components of silver, copper and active metal are mixed in powder form. In that case, as the organic solvent, methyl cellosolve, ethyl cellosolve, terpineol, isophorone, toluene, etc., and as the organic binder, ethyl cellulose, methyl cellulose, polymethyl methacrylate, etc. are used.

The ratio of the metal components constituting the brazing material paste is 69 to 75 parts by weight of silver and 25 to 31 parts by weight of copper, which is a total amount of 10 parts.
It is preferred that the amount of zirconium and / or zirconium hydride is 3 to 35 parts by weight, especially 20 to 30 parts by weight, and tungsten 1 to 10 parts by weight, especially 2 to 5 parts by weight, per 0 parts by weight. If the amount of tungsten is less than 1 part by weight, the effect of particle dispersion becomes insufficient, and if the amount of tungsten is more than 10 parts by weight, the reaction of zirconium and / or zirconium hydride with the active metal becomes too active, resulting in an aluminum nitride substrate. The reactivity is weakened, sufficient bonding strength cannot be obtained, and the heat cycle resistance deteriorates.

[0015]

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples. Examples 1 to 5 Comparative Examples 1 to 3 The proportions of the metal components of the brazing material were compounded as shown in Table 1, and 15 parts by weight of terpineol and a toluene solution of polyisobutyl methacrylate as an organic binder were used in a solid content of 1.
5 parts by weight were added and mixed well to prepare a brazing material paste. This brazing paste was applied to the entire surface of a 60 mm × 30 mm × 0.65 mm aluminum nitride substrate by screen printing. The coating amount (after drying) at that time was 6 to 8 mg / cm ² .

Next, a 60 mm × 30 mm × 0.25 mm copper plate is placed in contact with both sides of the aluminum nitride substrate coated with the brazing material paste, and then placed in a furnace at a temperature of 900 ° C. in a high vacuum.
After heating for 30 minutes, the bonded body was manufactured by cooling at a temperature decrease rate of 2 ° C./min.

Next, a UV-curing type etching resist is applied to the circuit pattern by screen printing on the copper plate of this bonded body, and then an etching treatment is performed using a cupric chloride solution to dissolve and remove unnecessary portions of the copper plate. The etching resist was stripped with a 5% caustic soda solution. In the joined body after this etching treatment, there is a residual unnecessary brazing material between the copper circuit patterns and a reaction product of the active metal component and the aluminum nitride substrate. Immerse in the solution for 10 minutes.

A heat cycle (thermal shock) test was conducted on an aluminum nitride substrate having a copper circuit manufactured through these series of treatments. For heat cycle test, hold in air at -40 ℃ for 30 minutes, then leave at 25 ℃ for 10 minutes.
After holding at 25 ° C. for 30 minutes, standing at 25 ° C. for 10 minutes was performed as one cycle, and the number of heat cycles at which the copper plate started peeling was measured. The results are shown in Table 1.

[0019]

[Table 1]

[0020]

According to the present invention, the durability against heat shock and heat history of the copper plate and the aluminum nitride substrate, that is, the heat cycle resistance is improved without significantly changing the aluminum nitride substrate, the bonding method, or the circuit structure. Can be made.

Claims (1)

[Claims] 1. A ceramics substrate obtained by heating a copper plate and an aluminum nitride substrate with a brazing paste to form a copper circuit and then forming a copper circuit, wherein the brazing paste contains silver (Ag) powder, copper (Cu) as a metal component. ) Powder, zirconium (Zr) powder and / or zirconium hydride powder, and tungsten (W) powder, and an aluminum nitride substrate having a copper circuit.