JPH1129371A - Brazing material and jointing between aluminum nitride and metal material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a brazing material that does not sag out to not-jointed area, when an aluminum nitride member is jointed to a metallic member, by constituting the brazing material with a powdery mixture of silver, copper, and activated metallic powder in which the proportion of the particles of a specific particle size is set lower than a specific value. SOLUTION: Silver and copper, preferably with average particle sizes of <=45 μm, respectively, an activated metallic powder of an element, preferably in the group IV a of the periodic table and its hydride with an average particle size of 10-45 μm, more preferably titanium (hydride) are mixed so that the proportion of the particles of <=5 μm is made η5 wt.%, preferably <=1 wt.% more preferably <=0.8 wt.%. The amounts of silver and copper are preferably in their eutectic composition, comprising 72 pts.wt. of silver and 28 pts.wt. of copper and the amount of the activated metallic powder is preferably 0.2-10 pts.wt. based on 100 pts.wt. of the whole composition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brazing material suitable for joining an aluminum nitride member and a metal member, and a method for joining an aluminum nitride member and a metal member via the brazing material.

[0002]

2. Description of the Related Art Conventionally, various studies have been made on joining a metal and aluminum nitride. Among them,
The use of copper as a metal is considered to be the most advantageous in terms of electrical characteristics and the like, and is being actively studied at present. Particularly, a thick copper plate is bonded as a circuit, and is used as a large current, large voltage, high frequency semiconductor mounting substrate.

A copper plate and an aluminum nitride substrate are joined by a DBC method utilizing a eutectic reaction between an oxide layer formed on the surface of the aluminum nitride and copper (for example, Japanese Unexamined Patent Publication No.
No. 40404) and an active metal method utilizing a reaction at the interface between a metal active with nitrogen and an aluminum nitride (for example, JP-A-60-32343). The active metal method is different from the DBC method in that (1) the surface oxidation treatment of the aluminum nitride substrate is unnecessary.

(2) The joining temperature is low, and the residual stress due to the difference in thermal expansion coefficient between copper and aluminum nitride is reduced.

(3) There are few bonding defects and the bonding strength is stable.

(4) Deterioration of the bonding layer is small even when heat treatment is performed in a hydrogen stream.

There are the following advantages.

In order to make use of this characteristic, a method has been proposed in which a brazing material paste is printed on an aluminum nitride substrate in a desired pattern, and then a copper plate is joined, and only the copper plate is etched to form a desired pattern.

[0009]

However, in the case of joining after printing a pattern, when the substrate is heated to the melting temperature of the brazing material, a liquid phase is generated and flows in the brazing material to ensure insulation. There has been a problem that the brazing material flows out to a required portion, that is, a non-joined portion, and a short circuit between the patterns or a defect due to the flowing out of the brazing material to the insulating pattern portion has occurred.

In order to solve the above problem, there has been proposed a method of controlling the particle size of copper and silver to suppress the outflow (Japanese Patent Laid-Open No. 4-80407). No mention is made of the particle size of.

The present inventors have confirmed that the liquid phase of only silver-copper has poor wettability with the aluminum nitride member, so that the liquid phase may flow out to the copper plate or metal member side, It was found that it did not flow onto the member. It was also found that when the brazing material flowed out onto the aluminum nitride member, titanium flowed out together with the silver-copper. In other words, the flow of brazing material
There are two forms, the case where the brazing material flows out to the copper plate or metal member side and the case where it flows out onto the aluminum nitride member. Regarding the flow out on the aluminum nitride member, it is an important issue how to suppress the flow of the liquid phase containing titanium. I found it. The invention disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 4-80407 has not been solved in this regard.

[0012]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in order to solve the above problems, and found that by controlling the particle size of the active metal powder, it is possible to prevent the brazing material from flowing out. As a result, the present invention has been completed.

That is, the present invention comprises a mixed powder containing silver, copper and an active metal powder, and has a particle diameter of 5 μm in the active metal powder.
A brazing material characterized in that the ratio of the following particles is 5% by weight or less, and further provides a method for joining an aluminum nitride member and a metal member using the brazing material.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION In a mixed powder composed of silver, copper and an active metal, silver and copper do not need to be single element powders, but may be alloy powder or a mixture of alloy powder and single element powder. It may be. Specifically, silver powder, copper powder mixture, silver-copper alloy powder, silver-copper alloy powder and silver powder mixture, silver-copper alloy powder and copper powder mixture, silver-copper alloy powder A mixture of silver powder and copper powder can be exemplified. In particular, the use of a silver-copper eutectic alloy powder is preferable because the powder is melted at the lowest temperature and the metal member and the aluminum nitride member can be joined at a low temperature.

The metal powder which does not contain an active metal component such as silver or copper used herein preferably has an average particle size of 45 μm or less in order to prevent printing from flowing to a copper plate to be joined or from 1 to 5. Those having a size of about 45 μm are more preferable.

The composition ratio of silver and copper in the above mixed powder is as follows: when the total weight of silver and copper is 100 parts by weight,
0 to 80 parts by weight and 20 to 60 parts by weight of copper are preferably employed. This composition ratio is the same whether silver and copper are each a single element powder or an alloy powder. This composition ratio is arbitrarily selected depending on the processing temperature and time in the subsequent bonding step, but a so-called eutectic composition of 72 parts by weight of silver and 28 parts by weight of copper is desirable from the viewpoint of lowering the processing temperature and relaxing thermal stress. A single element may be used for each of silver and copper, or a eutectic alloy powder may be used instead of using these elements.

As the active metal, an element belonging to Group IVa of the periodic table and its hydride can be used, and in general, titanium, zirconium and hafnium are used.
Among them, titanium is particularly preferable because it has a high reactivity with the aluminum nitride member and can greatly increase the bonding strength. Further, if a hydride of titanium, that is, titanium hydride is used, the influence of oxygen during the bonding step Oxidation is less likely to occur, and a more favorable bonding state can be obtained. This is because titanium hydride releases hydrogen for the first time by heat treatment in the bonding step to become active titanium metal, which reacts with the aluminum nitride member.

The amount of the active metal powder to be added to 100 parts by weight of the total of silver and copper is 0.2 to maintain the bonding strength between the aluminum nitride member, the brazing material and the copper member by the active metal powder. -10 parts by weight is preferred. More preferably, it is 0.5 to 5.0 parts by weight.

In the present invention, the proportion of particles having a particle size of 5 μm or less in the active metal powder must be 5% by weight or less, preferably 1% by weight or less, and more preferably 0.8% by weight.
It is more preferable that the content be not more than weight%. If the ratio of the particles having a particle size of 5 μm or less in the active metal powder exceeds 5% by weight, the brazing material easily flows out to the non-joined portion, which is not preferable.

The particle size of the active metal powder and 5 μm in the powder
The weight ratio of the powder having a particle size of m or less can be easily measured by using a liquid phase sedimentation method. In the liquid-phase sedimentation method, when the form of the powder is irregular, the major axis and the minor axis cannot be distinguished from each other, and the average value is regarded as the particle diameter.
This average value is regarded as the particle size, and no distinction is made between the major and minor diameters of the particle size. Also, the particle size in the present patent refers to the primary particle size, not the aggregate particle size. This can be easily measured by dispersing the powder in a solvent with ultrasonic waves.

The active metal powder desirably has a uniform particle size distribution, and the average particle size is optimally 10 to 45 μm in order to suppress particles having a particle size of 5 μm or less to 5% by weight or less.
Good adhesion is that the printed film thickness of the brazing material layer is 20 to 50 μm, and the particle size distribution of the active metal powder is that at least 40% by weight of all particles exist between the particle diameters of 20 to 60 μm. It is preferable for developing strength.

As a method for mixing the components constituting these powders, the respective components are mixed in a powder state using a stirrer such as a ball mill or an attritor, or an organic solvent and a binder are mixed, and the powder is mixed with a ball mill, a planetary. It can also be mixed using a mixer, a three-roll mill, etc. to form a paste.

In general, it is difficult to form a pattern on a substrate in the form of a metal powder, so that it is desirable to knead the mixture into a paste. When forming a paste, methylcellosolve, ethylcellosolve, isophorone, toluene, ethyl acetate, terpineol, texanol, etc. are used as an organic solvent, and a high molecular compound such as ethylcellulose, methylcellulose, an acrylic resin is used as a binder. .

To screen print a good brazing material pattern, the viscosity of the paste should be 20 to 200 kcps.
Is preferably controlled. By blending the organic solvent in the paste in the range of 5 to 15% by weight of the total paste and the binder in the range of 1 to 5% by weight, a paste having excellent printability can be obtained. In addition, by blending the binder in the above range, the binder can be promptly removed in the degreasing step after printing, which is preferable. When a paste is used, a dispersant can be added to improve the dispersibility of each component.

The metal member to be joined to aluminum nitride is not particularly limited as long as the brazing material can be joined and the melting point of the metal member is higher than the melting point of the brazing material. In general, copper, copper alloy, silver, silver alloy, nickel, nickel alloy, nickel-plated molybdenum, nickel-plated tungsten, nickel-plated iron alloy, and the like can be used. Among them, it is most preferable to use copper as the metal member from the viewpoints of electrical resistance, stretchability, and low migration. It is also preferable to use silver if electrical resistance is important,
When reliability after bonding is considered rather than electrical characteristics, it is preferable to use molybdenum or tungsten, because the thermal expansion coefficient of the metal is close to that of aluminum nitride, so that thermal stress during bonding can be reduced. .

When joining the aluminum nitride member and the metal member, it is preferable to apply the paste uniformly, and the coating method may be any method such as screen printing, metal mask printing, roll coating, spraying, and transfer. The method is adopted. Generally, the screen printing method is the simplest method. However, if there are coarse particles of the active metal powder in the paste, the screen may be clogged or the like, and printing may not be performed in a desired pattern. Is preferably not contained.

When printing a finer wiring pattern, a screen having a fine mesh must be used, and clogging is more likely to occur. Therefore, it is preferable to control the maximum particle size of the active metal powder to 85 μm or less. It is. However, there is no limitation on the form of application such as application on an aluminum nitride member, application on a metal member, application on both an aluminum nitride member and a metal member.

After applying the paste, it is generally desirable to perform degreasing to remove the binder component. The processing conditions such as heating temperature and time during degreasing vary depending on the binder component.However, if the processing is performed in a non-oxidizing atmosphere such as in nitrogen or argon or in a vacuum, the active metal will be reduced. It is suitable without being oxidized. Even in an oxidizing atmosphere, if the active metal is not oxidized more than necessary by limiting the amount of oxygen, a suitable bonding state can be obtained even if degreasing is performed in a trace oxygen concentration or in a wet atmosphere. Here, the wet atmosphere is an atmosphere formed by passing a non-oxidizing atmosphere gas through water or hot water and then feeding the gas into a processing chamber.

Then, the brazing members having been degreased are overlapped so that the brazing members are disposed between the metal member and the aluminum nitride member, and the joining is performed at a temperature at which the brazing material is melted.

In order that the brazing material sufficiently wets the aluminum nitride member and the metal member, and that the thermal shock resistance of the aluminum nitride member and the metal member is prevented from lowering due to residual stress due to the difference in thermal expansion between the aluminum nitride member and the metal member, the joining temperature is set to 800 to 800 ° C. 950 ° C. is preferred.

[0031] Also, it is possible to obtain it is the active metal powder and copper powder to perform the process in a vacuum, without any good bonding state that the metal member is oxidized for atmosphere, especially ^10-4
It is desirable that the bonding be performed at a degree of vacuum of Torr or less.

Further, by applying a load at the time of joining, the metal member and the brazing material and the aluminum nitride member and the brazing material can more reliably come into contact with each other, and a good joining state can be obtained. As the weight, a load of 1 to 50 g / cm ² can be adopted.

Further, by using the active metal powder as in the present invention, the active metal plays the role of a filler to prevent the brazing material from flowing out even when a high load that normally causes the brazing material to flow out is applied. be able to.

In the joined body obtained in this manner, a joint pattern similar to the form in which the pattern was applied in the paste application step was formed, and the subsequent resist coating and etching treatments did not cause the brazing material to flow out. Further, an aluminum nitride bonding member having a metal circuit having a good bonding state can be obtained. In the case where the metal circuit is easily oxidized, a plating film such as electroless nickel may be formed on the surface of the metal circuit after the etching process in order to prevent the metal from being oxidized.

[0035]

According to the present invention, if a metal member and an aluminum nitride member are joined after forming a pattern with a brazing material paste according to the present invention, a suitable metal-aluminum nitride joining member can be obtained without flowing of the brazing material during joining. Can be.

The reason why such effects can be obtained by the present invention has not been elucidated yet, but the present inventors presume as follows. Fine particles in the active metal powder adversely affect the joining between the metal member and the aluminum nitride member.
In the present invention, since the amount of the fine particles in the active metal powder is small, the amount of the active metal powder for achieving the required bonding strength can be reduced. As a result, it is considered that the outflow due to the excess active metal powder could be prevented.

[0037]

The present invention will be specifically described below with reference to examples and comparative examples.

Example 1 A mixed powder obtained by adding 1.5 parts by weight of titanium powder to 72 parts by weight of silver powder and 28 parts by weight of copper powder, for a total of 100 parts by weight,
After blending 8% by weight of terpineol, 3% by weight of an acrylic resin, and 0.1% by weight of a dispersant based on the total paste, the mixture was mixed using a planetary mixer to obtain 120k.
A cps paste was created. The average particle size of the powder used was 1.8 μm for silver, 11.6 μm for copper, and 37 for titanium.
μm, powder of 5 μm or less in all powders of titanium is 0.0
It was 1% by weight. In addition, the particle diameter of all titanium powder is 20.
The proportion of particles of ６０60 μm was 44% by weight.

This paste was screen-printed on a 54 mm × 36 mm aluminum nitride member substrate as shown in FIG.
(Pattern surface) and a pattern as shown in FIG. 2 (heat sink surface) with a thickness shown in Table 1.

Thereafter, it was dried and degreased in a nitrogen atmosphere at 320 ° C. for 5 minutes. Further, after the copper member, the aluminum nitride member, and the copper member are stacked, the copper member and the aluminum nitride member are subjected to a heat treatment at 850 ° C. for 15 minutes in a vacuum (10 ⁻⁵ Torr) while applying a load of 10 g / cm ^2. Was joined. Thereafter, the same resist pattern as that of the pattern in FIG. 1 was printed, and unnecessary portions of the copper member were removed to produce a desired copper-aluminum nitride bonding member. The material of the produced joining member has a cross-sectional shape as shown in FIG.

The flow of the brazing material into the non-printing area was 0 out of 40 sheets. In addition, when the bonding state was observed with an ultrasonic flaw detector, a favorable bonding state was observed.

Further, the joined copper plate was pulled in a direction of 90 ° with respect to the aluminum nitride substrate, and the peel strength was measured to determine the joining strength. The bonding strength was 19 kgf / cm.

Examples 2 to 10 Using the materials shown in Table 1, brazing filler metal pastes were prepared, and copper-aluminum nitride bonding members were prepared in the same manner as in Example 1. The loads at the time of joining are as shown in Table 1. The joining member thus obtained did not cause the brazing material to flow out to the non-printed portion, and the joining state was good even when observed by an ultrasonic flaw detector.

Comparative Examples 1 to 4 A brazing filler metal paste was prepared using a titanium-containing material having a proportion of 5 μm or less of 8.0% by weight shown in Table 1, and a copper-aluminum nitride joint was performed in the same manner as in Example 1. A member was manufactured.
The load at the time of joining is as shown in Table 1. In the joining member obtained in this way, it was found that the brazing material flowed out to the non-printing portion.

[0045]

[Table 1]

[Brief description of the drawings]

FIG. 1 is a plan view (pattern surface) of an aluminum nitride substrate coated with a brazing material manufactured in Example 1.

FIG. 2 is a bottom view (heat sink surface) of the aluminum nitride substrate coated with the brazing material manufactured in Example 1.

FIG. 3 is a cross-sectional view of the aluminum nitride substrate coated with the brazing material manufactured in Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Aluminum nitride member 2, 2 '... Metal member 3 ... Brazing material

Claims (2)

[Claims] 1. A brazing material comprising a mixed powder containing silver, copper and an active metal powder, wherein the proportion of particles having a particle size of 5 μm or less in the active metal powder is 5% by weight or less. 2. A method of joining an aluminum nitride member and a metal member, wherein the brazing material according to claim 1 is applied to at least one of the joining surfaces of the aluminum nitride member and the metal member, and then the two members are bonded together. A method of joining an aluminum nitride member and a metal member, characterized by heating.