JPH0451585A - Aluminum nitride wiring board - Google Patents

Abstract

PURPOSE:To enhance the close contact property of a conductor circuit with an aluminum nitride board without increasing the resistance of a conductive layer by a method wherein, when the conductive layer of nickel or the like is formed on the board via a layer of titanium or the like, a metal layer of tungsten or the like is formed between them. CONSTITUTION:A first layer 2 formed of at least one kind of metal selected from titanium, chromium, silver and niobium is formed on the surface of an aluminum nitride board 1; a second layer 3 of at least one kind of metal selected from trungsten and molybdenum is formed on the first layer 2. A third layer 4 of at least one kind of metal selected from nickel, gold and copper is laminated sequentially on the second layer. Thereby, a conductor circuit is formed. By this constitution, the conductive property of the conductor circuit on the board 1 is secured by the third layer 4, and the closed-contact property of the conductor circuit with the surface of the aluminum nitride board is increased by the first layer 2. The mutual diffusion of the metals is prevented between the first layer 1 and the third layer 4, and it is possible to restrain an electric resistance from being increased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an aluminum nitride wiring board, and particularly to an aluminum nitride wiring board comprising a conductor circuit on the surface of the board.

[Prior Art] Recently, the excellent electrical insulation, thermal conductivity, dimensional stability, and mechanical strength of aluminum nitride sintered bodies have attracted attention, and wiring boards using aluminum nitride have been actively developed.

Here, when forming a conductor circuit with pads and electrodes for brazing external lead terminals on the surface of an aluminum nitride substrate, conventionally, a paste mainly made of tungsten was printed on the surface of the substrate to incorporate tungsten particles. By fixing it, a conductor circuit with a desired pattern is formed.

[Problems to be Solved by the Invention] However, as semiconductor technology progresses, wiring boards used as packages are also required to have higher density and higher precision than ever before, and the circuit formation described above is becoming more difficult. A situation arose that could not be handled by this method.

Therefore, attempts have been made to form a thin film of a conductive material on the surface of an aluminum nitride substrate by sputtering or the like, and then perform etching to form a fine circuit pattern.

For example, a thin film forming method has been proposed in which a titanium (Ti) layer is formed on a substrate surface and a nickel (Ni) layer is formed thereon as a conductive layer. Here, the titanium layer is an intervening layer to enable adhesion between the aluminum nitride surface and the nickel layer, but when sintering is performed to improve the adhesion strength between aluminum nitride and titanium after the above thin film is formed. Since titanium diffuses not only into the aluminum nitride but also into the nickel layer, there is a problem in that as a result, the adhesion strength of the thin film to the aluminum nitride cannot be improved, and the electrical resistance of the nickel layer increases.

Furthermore, a thin film forming method has been proposed in which a titanium (Ti) layer is formed on the surface of a substrate, and a platinum (Pt) layer and a gold (Au) layer are formed thereon. Although this thin film has excellent adhesion strength to aluminum nitride, there is a problem in that it cannot be used for general purposes because it uses expensive noble metals and cannot reduce costs.

The present invention was made to solve the above problems, and its purpose is to provide excellent adhesion strength to aluminum nitride,
It is an object of the present invention to provide an aluminum nitride wiring board which can be brazed and is provided with a high-precision, high-density conductor circuit at a low cost.

[Means and effects for solving the problems] In order to solve the above problems, the present invention provides the following features:
a first layer formed of at least one metal selected from titanium, chromium, silver, and niobium; and a first layer formed on the first layer of at least one metal selected from tungsten and molybdenum. A conductor circuit is provided in which a second layer and a third layer made of at least one metal selected from nickel, gold, and copper are sequentially laminated on the second layer.

According to this configuration, conductivity is ensured by the third layer in the conductor circuit on the substrate, and excellent wettability with the brazing material is achieved. Furthermore, the first layer enhances the adhesion between the conductor circuit and the surface of the aluminum nitride substrate. The second layer firmly adheres the first layer and the third layer, and also prevents mutual diffusion of metal between the first layer and the third layer. The functions of each are fully demonstrated.

That is, the presence of the second layer prevents the metal in the first layer from being diffused into the upper layer. Therefore, the first layer metal is diffused only toward the aluminum nitride side, the anchoring effect of the first layer metal is enhanced, and the adhesion strength between the conductive circuit and the substrate is improved. Further, due to the presence of the second layer, the metal in the third layer is not diffused into layers below it, and is not contaminated by the metal in the first layer. Therefore, the third layer metal effectively exhibits these characteristics for a long period of time without losing its inherent conductivity and wettability with the brazing material.

Examples of the metal of the first layer include titanium (Ti), chromium (C''), silver (Ag), and niobium (Nb), which are metals that easily form a solid solution with aluminum nitride.

Examples of the metal for the second layer include tungsten (W) and molybdenum (Mo), which have very high melting points and do not form solid solutions with other metals even under high temperature conditions. It is a metal with a small diffusion coefficient.

As the metal of the third layer, nickel (Ni), gold (A
u) Copper (Cu) is a metal that has relatively good conductivity and excellent wettability with brazing filler metals (alloys of silver and copper) commonly used for semiconductors. .

Examples of means for forming each of the layers include sputtering, chemical vapor deposition, ion blasting, and plating, and any of these methods can be applied.

However, when the first layer is formed by sputtering or the like, the sputtered metal layer is generally amorphous and does not necessarily have sufficient adhesion strength to aluminum nitride. Therefore, it is preferable to sinter the first layer of metal onto the aluminum nitride substrate by heating the entire substrate after forming the three-layer thin film, thereby improving the adhesion strength between the two.

Incidentally, the thickness of the first layer is preferably in the range of 0.05 to 2.0 μm.

If the film thickness is less than 0.05 μm, most of the metal in the first layer will diffuse into the substrate, and there will be virtually no remaining film thickness, resulting in a decrease in adhesive strength with the second layer. On the other hand, 2
．． If it exceeds 0 μm, the residual stress in the first layer becomes large and cracks are likely to occur, which is not preferable.

The thickness of the second layer is preferably in the range of 1.0 to 5.0 μm.

If the film thickness is less than 1.0 μm, it will not be able to fully exhibit its function as a diffusion prevention layer. - side, 5.0μ
If it exceeds m, the residual stress in the second layer becomes large and cracks are likely to occur, which is not preferable.

The thickness of the third layer is 0. It is preferably in the range of 2 to 5.0 μm.

If the film thickness is less than 0.2 μm, the effect of improving wettability with the brazing material decreases. On the other hand, if it exceeds 5.0 μm,
Residual stress in the third layer becomes large and cracks are likely to occur, which is undesirable.

Generally, after forming the three-layer thin film on an aluminum nitride substrate, a mask of photoresist or the like is formed and etching is performed to form a desired circuit pattern on the substrate. Alternatively, a conductor circuit with a desired pattern can be formed by forming a mask in advance on the surface of the aluminum nitride substrate to cover areas where no circuit will be formed, and then forming the thin film on the exposed areas of the surface. Form and may.

Examples and comparative examples embodying the present invention will be described below.

[Example] An aluminum nitride substrate formed by laminating a plurality of aluminum nitride green sheets and firing them simultaneously was immersed in aqua regia for 1 minute, and then thoroughly washed with water and dried to clean the substrate surface.

While this aluminum nitride substrate was heated to 100° C., reverse sputtering was performed on its surface using an IKW output for 10 minutes, and then sputtering was performed using titanium as a target. Then, as shown in FIG. 1, a titanium layer 2 (thickness: 0.1 μm) was formed as a first layer on the surface of the aluminum nitride substrate 1.

Thereafter, in the same manner, molybdenum and nickel are sequentially sputtered using molybdenum and nickel as targets, thereby forming a molybdenum layer 3 (thickness 29 mm) as a second layer on the titanium layer 2.
0 μm), nickel layer 4 as the third layer (thickness 1.0
μm), respectively, to form a thin film 5 having a three-layer structure.

Subsequently, the aluminum nitride substrate 1 on which the thin film 5 was formed
A negative photoresist was uniformly applied to the surface of the substrate, and the circuit forming portion was irradiated with ultraviolet rays to photocure the portion.

This substrate 1 was immersed in an alkaline solution to dissolve and remove the uncured photoresist, thereby exposing a portion of the thin film 5. Then, the surface of the substrate 1 is etched using a mixed solution of hydrofluoric acid (HF) and nitric acid (HNO3),
The exposed portion of the thin film 5 was removed. Thereafter, the cured photoresist was treated with an organic solvent and removed, thereby exposing the thin film 5 on the surface of the substrate 1 and forming a conductor circuit in a desired pattern.

Pins were soldered to the thus obtained substrate using silver solder at 800°C. The fixation strength of the pin at this time showed an excellent value of 3.0 kgf/mm2.

[Comparative Example] A thin film was formed on an aluminum nitride substrate by sputtering in the same manner as in the above example.

However, this thin film did not have a molybdenum layer corresponding to the second layer of the above example, that is, it had a two-layer structure of a titanium layer and a nickel layer.

Pins were soldered to the thus obtained substrate using silver solder at 800°C. At this time, the fixing strength of the pin was 1,0 kgf/mm''.

[Effects of the Invention] As detailed above, the present invention provides an aluminum nitride wiring board that has excellent adhesion strength to aluminum nitride, can be brazed, and has high-precision, high-density conductor circuits. It has the excellent effect of being able to be provided at a low cost.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a laminated structure of thin films in an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Aluminum nitride substrate, 2... Titanium layer as a first layer, 3... Molybdenum layer as a second layer, 4
...Nickel layer as the third layer. Patent applicant: IBIDEN Co., Ltd. Agent: Patent attorney: Hironobu Onda (and one other person)
4

Claims (1)

[Scope of Claims] 1. A first layer (2) formed of at least one metal selected from titanium, chromium, silver, and niobium on the surface of an aluminum nitride substrate (1); and the first layer. (2) a second layer (3) formed of at least one metal selected from tungsten and molybdenum; and a second layer (3) formed of at least one metal selected from nickel, gold, and copper. A third formed of at least one kind of metal.
An aluminum nitride wiring board comprising a conductor circuit formed by sequentially laminating layers (4). 2. The thickness of the first layer (2) is 0.05 to 2.0 μm, the thickness of the second layer (3) is 1.0 to 5.0 μm, and the thickness of the third layer (4) is 0.05 to 2.0 μm. The aluminum nitride wiring board according to claim 1, wherein the aluminum nitride wiring board has a thickness of 0.2 to 5.0 μm.