JPH06350215A - Aluminium nitride board having copper circuit - Google Patents

Abstract

PURPOSE:To enhance resistance against thermal impact or thermal hysteresis without requiring significant modification of the aluminium nitride board, the bonding method, or the circuit structure by setting the Vickers hardness at the part of a copper circuit at a specified value or below. CONSTITUTION:A copper circuit is formed using a copper plate having Vickers hardness of 55 or less. The copper board is obtained by annealing and preferably held in an nonoxidative atmosphere of nitrogen, argon, vacuum, etc., for 2-4 hours, especially for 2-3 hours, at 300-600 deg.C, especially at 400-500 deg.C. Annealing effect can be achieved when the treating temperature is too low or the holding time is too short and the mechanical strength becomes unsuitably strong when the treating time is too high or the holding time is too long. An oxygen-free copper plate is generally employed but a tough pitch copper plate including some impurities may also be employed.

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.

[0002]

2. Description of the Related Art 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 has progressed, and the heat generated from semiconductor elements has also continued to increase. ing. In order to efficiently dissipate this heat, various methods have been conventionally used in high power module substrates. Especially in recent years, since it has become possible to use a ceramic substrate having good heat conduction, after joining a metal plate such as a copper plate on the substrate and forming a circuit, as it is or after performing a plating treatment or the like. A structure for mounting a semiconductor element 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 focused on aluminum nitride substrates having high thermal conductivity in place of conventional alumina. As a method for joining copper plates, a brazing filler metal containing an active metal (hereinafter , Simply called "wax material")
An active metal brazing method (for example, Japanese Patent Application Laid-Open No. 60-177634) in which heat treatment is performed to form a joined body, or an aluminum nitride substrate and a copper plate whose surfaces are oxidized are provided at a temperature lower than the melting point of copper and higher than the eutectic temperature of Cu-O DBC method of heat bonding (for example, JP-A-56-163093)
No. gazette) is used.

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.

However, even if the active metal brazing method is used, it cannot be said that the durability against heat shock and heat history such as heat shock and heat cycle is sufficient, and the proposal of a new technique has been awaited. Therefore, in order to reduce the difference in the coefficient of thermal expansion between copper and ceramics, which is the cause of thermal stress due to thermal shock, there is a study to use a clad material instead of a copper plate with a large coefficient of thermal expansion, but the electrical conductivity decreases. However, it has not been put to practical use.

As a result of further studies to solve the above problems, the present inventors have found that the copper plate is 400 to 600 ° C. before being joined to the aluminum nitride substrate.
If the mechanical property of the copper plate, that is, the Vickers hardness (Hv) is changed to 55 or less by heat treatment at a moderate temperature, an aluminum nitride substrate having a copper circuit with sufficient durability against thermal shock and thermal history is manufactured. The inventors have completed the present invention by finding out what can be done.

[0007]

That is, the present invention is an aluminum nitride substrate having a copper circuit, characterized in that the Vickers hardness (Hv) of the copper circuit portion is 55 or less.

The present invention will be described in more detail below. It is sufficient that the aluminum nitride aluminum nitride substrate used in the present invention is manufactured by a conventional method such as a hot pressing method and an atmospheric pressure sintering method. The aluminum nitride powder used at this time does not have to be special, and those produced by the metal Al direct nitriding method, the alumina reduction nitriding method, the vapor phase method or the like are used. The sintered density of the aluminum nitride substrate is preferably 95% or more in relative density from the viewpoint of mechanical strength and electrical characteristics.

As a method of forming a copper circuit on an aluminum nitride substrate, a method of etching a bonded body of an aluminum nitride substrate and a copper plate to form a copper circuit, or a copper circuit pattern punched from a copper plate is bonded to an aluminum nitride substrate. And the like. As the method for joining the copper plate or the copper circuit pattern to the aluminum nitride substrate, the active metal brazing method or DB
C method etc. can be adopted.

The metal component of the brazing filler metal in the active metal brazing method contains silver and copper as main components in accordance with a conventional method, and the active metal as a sub component for ensuring wettability with the aluminum nitride substrate during melting. . This active metal component reacts with the aluminum nitride substrate to generate an oxide or a nitride, and these products strengthen the bond between the brazing material and the aluminum nitride substrate. Specific examples of the active metal include titanium, zirconium, hafnium, niobium, tantalum, vanadium and compounds thereof. Since these active metal oxides are often more stable than copper oxides,
The active metal component reduces the surface of the copper plate to clean it, so that the brazing material and the copper plate are well wetted. As a result, the brazing material and the copper plate diffuse into each other and a strong bonding layer is formed.

A major feature of the present invention is that in an aluminum nitride substrate having such a copper circuit, the copper circuit is formed using a copper plate having a Vickers hardness (Hv) of 55 or less. Annealing is a specific means for obtaining a copper plate having a Vickers hardness (Hv) of 55 or less under the conditions of non-oxidizing atmosphere such as nitrogen, argon and vacuum.
2 to 0 to 600 ° C., especially 400 to 500 ° C.
It is desirable to hold for 4 hours, especially for 2 to 3 hours. If the treatment temperature is too low or the holding time is too short, the effect of annealing cannot be obtained, and if the treatment temperature is too high or the holding time is too long, the mechanical properties become too strong, which is unsuitable. . As the copper plate to be annealed, an oxygen-free copper plate is generally used, but a copper plate containing a certain amount of impurities such as a tough pitch copper plate may be used.

[0012]

In the active metal brazing method, the joining temperature between the copper plate or the copper circuit pattern and the aluminum nitride substrate is 80.
Although the temperature is about 0 to 1000 ° C., since the above reaction occurs in a relatively short time, the copper crystal particles react with the metal component of the brazing material faster than they grow by annealing. Copper is not given the effect of improving mechanical properties by annealing, and the Vickers hardness (Hv) remains considerably large. When the copper plate or copper circuit pattern in such a state is bonded to the aluminum nitride substrate, the heat generated by the difference in the coefficient of thermal expansion between the copper plate or copper circuit pattern and the aluminum nitride substrate during cooling to room temperature or a thermal shock test. Since the stress increases, the aluminum nitride substrate having low ductility is greatly damaged.

On the other hand, in the case of the DBC method, the joining temperature is 1000 ° C. or higher, which is higher than that of the active metal brazing method, so that the crystal grains of copper grow excessively, which causes Vickers hardness (Hv). Cannot be expected, that is, the effect of relaxing the thermal stress due to the difference in thermal expansion coefficient from the aluminum nitride substrate cannot be expected. This tendency is more often seen in the tough pitch copper plate containing a large amount of oxygen and the like, which has been used preferably in recent years, than the oxygen-free copper plate.

On the other hand, as in the present invention, the copper circuit is subjected to a treatment such as annealing in advance and the Vickers hardness (H
If the copper plate with v) of 55 or less is used, the above thermal stress can be relaxed.

[0015]

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples.

Examples 1-4 Comparative Examples 1-4 Silver powder 72 parts by weight, copper powder 28 parts by weight, zirconium powder 30
1 part by weight and 15 parts by weight of terpineol and 1.5 parts by weight of solid content of a toluene solution of polyisobutyl methacrylate as an organic binder were kneaded to prepare a brazing paste.
This brazing paste was applied over the entire surface of a 60 mm × 30 mm × 0.65 mmt aluminum nitride substrate by screen printing. The coating amount (after drying) at that time is 6 to 8 mg / cm ² .

Both sides of the aluminum nitride substrate coated with the brazing material paste were previously heat-treated at various temperatures and holding times to change the Vickers hardness (Hv).
After placing 60mm x 30mm x 0.25mmt copper plate in contact, put it into the furnace, heat it in a high vacuum of 1 x 10 ^-5 Torr at 900 ℃ for 30 minutes, and then cool it at a cooling rate of 2 ℃ / min. A bonded body of a copper plate and an aluminum nitride substrate was manufactured.

Next, a UV-curing type etching resist is applied on the circuit board 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. Further, the etching resist was stripped with a 5% caustic soda solution. In the bonded body after this etching treatment, there are residual unnecessary brazing filler metal and the reaction product of the active metal component and the aluminum nitride substrate between the copper circuit patterns, so soak them in 60% at 10% ammonium fluoride solution for 10 minutes Removed.

A heat cycle (thermal shock) test was conducted on an aluminum nitride substrate having a copper circuit obtained through the series of treatments. The heat cycle test conditions are
Hold in air at -40 ° C for 30 minutes, then leave at 25 ° C for 10 minutes.
After holding at 125 ℃ for 30 minutes, it was left at 25 ℃ for 10 minutes as one cycle. Then, the state was observed every 50 cycles, and the number of times the copper circuit was peeled off was measured. The results are shown in Table 1.

[0020]

[Table 1]

[0021]

According to the present invention, an aluminum nitride substrate having a copper circuit having sufficiently improved durability against thermal shock and thermal history without making a great change in the aluminum nitride substrate, the bonding method, or the circuit structure. Can be manufactured.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koichi Uchino 1 Shinkai-cho, Omuta-shi, Fukuoka Prefecture Electro-chemical industry company Omuta factory

Claims (1)

[Claims] 1. An aluminum nitride substrate having a copper circuit, wherein the Vickers hardness (Hv) of the copper circuit portion is 55 or less.