JPH06216485A - Formation of connecting conductor of ceramic wiring board - Google Patents

Abstract

PURPOSE:To realize a connecting conductor which can connect a component surely by a method wherein a nickel film and a gold film are formed on a ceramic-board sintered conductor and a heat treatment is then executed. CONSTITUTION:A plating pretreatment is executed to a mullite ceramic board 2 composed of a tungsten sintered conductor 1, the board is immersed in an electroless nickel plating liquid, a nickel film 3 is formed on the sintered conductor 1 and immersed in a substituted gold plating liquid, a substituted gold film 4 is formed on it and immersed in an electroless gold plating liquid, and a gold film 5 is formed. Then, a ceramic wiring board is put, for ten minutes, into a belt-type electric furnace, at 750 deg.C, which is provided with a hydrogen-nitrogen reducing atmosphere, the nickel film and the gold film which have been formed on the sintered conductor are diffused thermally, a diffused layer 6 is formed, and a conductor for connection of a component is formed. Consequently, a diffusion concentration grade is produced, the clear boundary of an intermetallic compound layer between a bonding brazing material and the connecting conductor is eliminated, the concentration of a stress can be suppressed in thermal expansion, and the bonding reliability of each component can be increased by leaps and bounds.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a surface conductor of a ceramic wiring board in which components are connected and mounted by various brazing materials, and more particularly, a diffusion layer of nickel and gold is formed on a sintered conductor of the ceramic wiring board. The present invention relates to a method for forming a connecting conductor.

[0002]

2. Description of the Related Art With the increase in the density of ceramic wiring boards, the density of mounting parts and the mounting method have been diversified. For example, there are mounting methods such as mounting semiconductor chips and input / output terminal leads on the surface of a wiring board and wire bonding accompanying wiring changes.The connection method is also solder, gold-tin, gold-germanium, etc. A method using a material or ultrasonic bonding technology is used.

In connecting the above various components, a nickel film and a gold film are usually formed by a plating method (electroless or electroplating method) on the connecting conductor metal on the substrate surface. As the most general method for forming a metal film, for example, a technique described in Japanese Patent Application Laid-Open No. 1-268876, that is, an electroless plating method is known. In this method, a palladium catalyst is selectively formed on a sintered conductor (tungsten or molybdenum) of a sintered ceramic substrate, and then a nickel film is formed to a desired film thickness by electroless plating, followed by ceramic firing. In order to ensure the adhesion between the conductor and the nickel film, heat treatment is performed in a reducing atmosphere at 500 to 900 ° C., and then a gold film is applied on the nickel film by electroplating or electroless plating. hand,
This is a method of forming a connecting conductor.

[0004]

However, since the nickel film is slightly oxidized during the heat treatment of the nickel film, in the formation of the gold film after the heat treatment, the interfacial bonding force between nickel and gold, that is, the adhesion The power is not satisfied enough.

Further, in connection with a brazing material such as solder, gold-tin or gold-germanium to the nickel film surface, diffusion of the brazing material component to the nickel film surface or the nickel film does not proceed sufficiently. Further, although an intermetallic compound layer with the joining brazing material is formed, the interface thereof clearly appears. For these reasons, the connection to the nickel film surface has a problem in reliability of component connection against thermal stress.

An object of the present invention is to provide a connection conductor which has a higher bonding strength than that of the prior art described above and a higher reliability of component connection, and which can reliably perform component connection by semiconductor chips, input / output terminal leads or wire bonding. It is to provide a forming method.

[0007]

According to one aspect of the present invention, in order to achieve the above object, a nickel film and a gold film are formed on a ceramic substrate sintered conductor, and then the nickel film and the gold film are heat-treated. Take the method of spreading and.

In the present invention, electroplating, electroless plating, vapor deposition or sputtering is suitable for forming a nickel film and a gold film on a sintered conductor of a ceramic wiring board, that is, a tungsten or molybdenum conductor. is there.
In particular, for application to a high-density ceramic substrate, the electroless nickel plating method and the electroless gold plating method are more suitable.

Regarding the thickness of the nickel film and the gold film formed on the sintered conductor, nickel is 1.5 to 8 μm, preferably 2.5 to 5 μm, and gold is 1 to 5 μm, preferably 1.5 to
3 μm is good.

The temperature for diffusing the nickel film and the gold film formed on the above-mentioned sintered conductor is 500 to 900 ° C., preferably 650 to 750 ° C. As the heat treatment atmosphere, a mixed gas of hydrogen and nitrogen is suitable. By setting the thickness of the diffusion layer (interdiffusion layer) of nickel and gold by the above-mentioned means to be at least 0.5 μm or more, preferably 1 μm or more, the adhesion between the nickel and gold interface is good, and the component A strong joint strength with the connecting brazing material is achieved.

The bondability between the sintered conductor and the nickel film can be simultaneously achieved by the above heat treatment.

[0012]

By heat-treating the nickel film and the gold film formed on the sintered conductor, the interdiffusion of gold and nickel makes the adhesion of the interface very strong. In addition, mutual diffusion causes a diffusion concentration gradient of gold and nickel, and there is little exposure of nickel on the gold surface. For example, from the viewpoint of gold wire bonding (ultrasonic bonding) accompanying wiring change or wettability with brazing material, Is suitable as

Further, in connection with a brazing material such as solder, gold-germanium or gold-tin, the brazing material component rapidly penetrates through the gold diffused in the nickel film, and the nickel, gold and brazing material are introduced. It forms an intermetallic compound with the material components.
Further, due to the concentration gradient of the compound layer, no clear interface of the intermetallic compound layer appears. As a result, stress concentration due to thermal expansion or the like in the film is unlikely to occur, and the joining reliability of each component can be dramatically improved.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for forming a connecting conductor for a ceramic wiring board according to the present invention will be described below in detail with reference to the drawings.

Example 1 A sectional view of a metal film formed by a plating process is shown in FIG. 1, and the plating process will be described with reference to this figure.

A mullite ceramic substrate 2 made of a sintered tungsten conductor 1 is used at 90 ° C. as a pretreatment for plating.
After immersing in a 10 wt% sodium hydroxide solution for 10 minutes, washing with water, palladium activation treatment (60 ° C., 5 minutes, Nippon Kanigen activation solution No3) was performed, and then 60 ° C. electroless nickel plating solution (Japan SB-55-1 made by Kanigen)
And a nickel film 3 having a thickness of 2.5 μm was formed on the tungsten sintered conductor. After that, it is immersed in a displacement gold plating solution (lectroless prep made by Tanaka Kikinzoku) for 10 minutes to form a substitution gold film 4 of about 0.08 μm on the nickel film, and further immersed in an electroless gold plating solution to a thickness of 2.5 μm. Gold film 5 was formed. The composition and conditions of the electroless gold plating solution used are as follows.

(Composition) Sodium chloroaurate: 2.5 g / l Sodium hydroxide: 4 g / l Sodium thiosulfate: 10 g / l Sodium sulfite: 25 g / l Sodium tetraborate: 30 g / l Thiourea: 2 g / l (Conditions) pH: 10.0 Temperature: 80 ° C. Then, the above ceramic wiring board was treated with hydrogen-nitrogen (1:
1) For 750 ° C belt type electric furnace with reducing atmosphere
It was put in for 0 minutes, and nickel and gold formed on the sintered conductor were thermally diffused to form a conductor for connecting components.

A cross-sectional view of the connecting conductor formed by this process is shown in FIG. Reference numeral 6 in FIG. 2 indicates a diffusion layer formed by thermal diffusion of nickel and gold. Since the boundaries between the layers are not clear, they are schematically represented by straight lines.

The above-mentioned connecting conductor is a solder brazing material (eutectic solder) of 37Sn composition, Au-12Ge brazing material, Au-
In the bonding of the 20Sn brazing material and the gold wire, all showed good connectivity. In addition, thermal shock test (-25 to 15
Even after 1000 cycles (0 ° C.), good bondability was exhibited. As an example of joining, a lead pin joining method using an Au-12Ge brazing material will be described below.

The Au-12Ge brazing material was previously fused to the lead pin, placed in a carbon jig, aligned with the bonding pad, and then heated in a reducing atmosphere furnace at 400 ° C. for 10 minutes, Lead pins were attached by melting the brazing material and wetting the connecting conductor. FIG. 3 shows the structure of the joint after the lead pin joint. Since the boundaries between the layers are not clear, they are schematically shown by straight lines.

(Embodiment 2) In the same manner as in Embodiment 1, a nickel plating film 2.5 μm and a gold plating film 2.5 μm are formed as shown in FIG. 1, and the wiring board is hydrogen-nitrogen. In a (1: 1) atmosphere, heat treatment was performed for 10 minutes at a temperature of either 600 ° C. or 900 ° C. to form a conductor for connecting parts as shown in FIG. 2 as in Example 1. . With respect to both of the conductors treated by the two temperatures, the solder brazing material (eutectic solder) of 37Sn composition, the Au-12Ge brazing material, and the ultrasonic bonding of the gold wire were respectively bonded by the same bonding method as in Example 1. As a result of the tests, all of them showed good bondability.

(Embodiment 3) A nickel plating film of 2.5 μm was formed in the same manner as in Embodiment 1, and then an electric gold plating solution (Temperex 401 made by Tanaka Kikinzoku Co., Ltd.) was used at a liquid temperature of 50 ° C. and a current density. Film thickness 25 μm under the condition of 1 A / dm ^2.
Of gold was formed. Then, the belt-type electric furnace at 750 ° C. having a reducing atmosphere of hydrogen-nitrogen (1: 1) was charged with the ceramic wiring board subjected to the above treatment and held for 10 minutes to thermally diffuse nickel and gold. To form a connecting conductor.

By the same joining method as in Example 1, the above-mentioned connecting conductors exhibited good joining properties with respect to the 37Sn composition solder, 3.5Ag solder and Au-12Ge brazing material.

(Embodiment 4) By the following processing, a metal film structure shown in FIG. 1 was obtained similarly to Embodiment 1. That is, the tungsten sintered conductor 1 obtained by sintering the tungsten film 2 was formed on the ceramic substrate simultaneously with the sintering of the substrate. The tungsten film is subjected to surface treatment by mechanical polishing and liquid honing, chemical etching of tungsten as a pretreatment for plating and palladium activation treatment are performed, and then tungsten is subjected to electroless plating using dimethylaminoborane as a reducing agent. A nickel film 3 having a thickness of 1 to 5 μm was formed on the sintered conductor. After that, a substitution gold film 4 having a thickness of about 0.1 μm was formed on the nickel film 3 by displacement gold plating, and further immersed in an electroless gold plating solution to form a gold film 5 having a thickness of 0.5 μm or more.

Then, the above-mentioned ceramic wiring board is hydrogenated.
For 10 minutes in a 750 ° C belt type electric furnace having a reducing atmosphere of nitrogen (1: 1), the nickel and gold formed on the sintered conductor are thermally diffused to connect components as shown in FIG. Of the conductor.

The Au-13Ge brazing material was previously fused to the lead pin, placed in a carbon jig, aligned with the bonding pad, and then heated at 400 ° C. in a reducing atmosphere furnace to obtain the brazing material. Was melted and wetted with the connection conductor to carry out lead pinning, a joint having a structure as shown in FIG. 3 was obtained, and good joint strength was exhibited.

[0027]

According to the present invention, since a diffusion concentration gradient is generated, there is no clear boundary between the joining brazing material and the connecting conductor in the intermetallic compound layer, and stress concentration during thermal expansion can be suppressed. As a result, the joint reliability of each component can be dramatically improved.

Further, the nickel is exposed to the gold surface very little, and the ultrasonic bonding property of the gold wire or the wettability with the brazing material can be sufficiently ensured. Furthermore, since heat treatment is not performed with the nickel film exposed,
No oxidation of nickel occurs during heat treatment, and the interfacial bonding force between nickel and gold is not impaired.

[Brief description of drawings]

FIG. 1 is a sectional view of a metal film formed on a ceramic wiring board.

FIG. 2 is a sectional view of a connecting conductor of a ceramic wiring board after a diffusion process.

FIG. 3 is a sectional view of a lead pin joint portion.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ceramic substrate 2 Sintered conductor 3 Ni plating film 4 Substitution Au plating film 5 Electroless Au plating film 6 Au, Ni diffusion layer 7 Ni, W diffusion layer 8 Au, Ge brazing material 9 Lead pin 10 Au, Ge, Ni Diffusion layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Ryohei Sato Inventor Ryohei Sato 292 Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa Inside the Hitachi, Ltd. Institute of Industrial Science (72) Inventor Hiroyuki Mizukoshi 1 Horiyamashita, Hadano-shi, Kanagawa Stock Company General Computer Division, Hiritsu Factory (72) Inventor Tetsuya Watanabe 1 Horiyamashita Horiyamashita, Hadano City, Kanagawa Prefecture

Claims (1)

[Claims] 1. A method of forming a surface conductor for connecting components with a brazing material on a conductor of a ceramic wiring board, wherein a nickel film and a gold film are formed in this order on a sintered ceramic substrate conductor, A method for forming a conductor for connecting a ceramic wiring board, which comprises forming a diffusion layer of the nickel film and the gold film by heat treatment at 900 ° C.