JPH06283844A - Insulating circuit board - Google Patents

Abstract

PURPOSE:To prevent deterioration of reliability by preventing formation of intermetallic compounds due to solder on an insulating circuit board having a conductor pattern applied with an Au film thereby preventing the soldering strength from lowering due to the intermetallic compounds. CONSTITUTION:A conductor pattern applied, at least on the surface thereof, with an Au film 23 is formed on an insulating substrate 1 of alumina ceramic, for example, and an electronic component 4 is mounted on the conductor pattern through a tin solder 5. In such insulating circuit board, a second conductor pattern 3 laminating an Ni film 31 and a thin Au film 32 is formed on the surface of the conductor pattern where the Au film 23 is soldered. Even if an Au-Sn intermetallic compound 6 is produced when a component is soldered to the thin Au film 32, the Ni film 31 functions as a barrier for blocking spread of the intermetallics 6 up to the Au film 23 of the conductor pattern 2 thus preventing deterioration of bonding strength or reliability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit board in which a conductor pattern is formed on an insulating substrate, for example, an alumina ceramic substrate, and more particularly to an insulating circuit board which prevents deterioration of joint strength due to tin solder and improves reliability. .

[0002]

2. Description of the Related Art Conventional alumina ceramic substrates (hereinafter referred to as
FIG. 3 shows an example of a circuit board having a conductor thin film pattern formed on the surface of an insulating substrate). In the figure, 1 is an insulating substrate, on the surface of which a Ta ₂ N film 21 and Ni are sequentially formed.
A conductor film having a multi-layer structure in which the -Cr film 22 and the Au film 23 are sequentially formed is formed, and this conductor film is formed into a desired pattern by the photolithography technique to form the conductor pattern 2. The Ni-Cr film 22 is also formed on the back surface of the insulating substrate 1.
And the conductor pattern 2 composed of the Au film 23 is formed.
Then, in order to mount the chip-shaped electronic component 4 on the conductor pattern 2, the electrode thereof is bonded to the Au film 23 of the conductor pattern 2 by using Sn63 eutectic solder 5.

[0003]

In such a conventional circuit board, an Au film 23 having a good wettability with solder is provided on the uppermost layer of the conductor pattern.
Since the electronic component 4 is bonded using the n63 eutectic solder 5, as shown in the figure, the solder 5 is diffused in the Au film 23 and the Au-Sn based intermetallic compound is spread over a wide range of the soldering portion. 6 is generated. When such an intermetallic compound is generated, the bonding force between the Au film 23 and the underlying Ni—Cr film 22 is reduced in this portion, the component bonding strength of the electronic component 4 is degraded, and the reliability is reduced. May occur. Therefore, in the past, this has been dealt with by managing severe construction conditions and skill management of workers, but it is extremely difficult to manage and it is difficult to obtain the desired effect. It is an object of the present invention to provide an insulated circuit board which prevents generation of intermetallic compounds by solder and prevents deterioration of solder joint strength and deterioration of reliability due to the intermetallic compounds.

[0004]

According to the present invention, in an insulated circuit board in which an upper layer of a conductor pattern formed on an insulating substrate is composed of an Au film, at least a surface of a tin soldering portion of the conductor pattern has a Ni film and a thin film. A second conductor pattern in which an Au film is laminated is formed. For example, a conductor pattern in which a Ta ₂ N film, a Ni—Cu film, and an Au film are laminated is formed on an alumina ceramic substrate, and a Ni film and a thin Au film are laminated at least on a soldering portion on the surface of the conductor pattern. A second conductor pattern is formed. Further, a preliminary solder layer may be formed on the surface of the tin soldering portion of the Au film of the second conductor pattern.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of an embodiment of the circuit board of the present invention. Ta ₂ N film 2 is formed on the surface of alumina ceramic substrate 1.
1, the Ni—Cr film 22 and the Au film 23 are sequentially formed, and the conductor pattern 2 is formed by forming the laminated film into a desired pattern by a photolithography technique or the like.
Here, the Ta ₂ N film 21 is 1000 Å, Ni-Cr
The film 22 is formed to a thickness of 2000 Å, and the Au film 23 is formed to a thickness of 4 to 7 μm. Further, here, the Ni-Cr film 22 and the Au film 23 are laminated on the back surface of the alumina ceramic substrate 1 to form the conductor pattern 2 as a grounding conductor pattern.
Each film on the back surface side is formed at the same time as the corresponding film on the front surface side, so that the film thickness of each film is the same as the film thickness on the surface.

Then, a Ni film 31 and an Au film 32 are formed so as to overlap each other on at least a portion of the conductor pattern 2 where the electronic component is mounted, that is, a portion where the electrode of the electronic component is joined by soldering. The second conductor pattern 3 is formed. The Ni film 31 is formed to have a film thickness of 2.5 to 5 μm.
The u film 32 is formed to a very thin thickness of 0.1 to 0.3 μm. The Ni film 31 has good adhesiveness to the uppermost Au film 23 of the conductor pattern 2 and the Au film 32 of the upper layer of itself, but does not form an intermetallic compound with tin solder. In this embodiment, on the back surface of the alumina ceramic substrate 1,
The second conductor pattern 3 is formed on the entire surface of the conductor pattern 2.

FIG. 2 shows an example in which chip-shaped electronic components are mounted on the alumina ceramic circuit board having such a structure. As shown in the figure, a chip-shaped electronic component 4 is mounted on the second conductor pattern 3, and its electrode is tin solder, that is, Sn63.
The eutectic solder 5 connects to the Au film 32 of the second conductor pattern 3. At this time, the solder 5 forms Au-Sn together with the Au film 32.
Although the intermetallic compound 6 is generated, since the Au film 32 is formed extremely thin, the generation of the intermetallic compound 6 is limited to an extremely small film thickness. Further, since the Ni film 31 that does not form an intermetallic compound with Sn is formed below the Au film 32, this Ni film 31 serves as a barrier.
The u-Sn intermetallic compound 6 does not extend to the Ni film 31 and the Au film 23 of the conductor pattern 2 below the Ni film 31. As a result, the electronic component 4 is bonded to the Au film 32 and the Ni film 31 by the Sn63 eutectic solder 5, while the intermetallic compound is not generated in the Au film 23 of the conductor pattern 2, so that the Ni film 31 is not formed. On the lower surface thereof, a combined state integrated with the conductor pattern 2 is secured, and as a result, deterioration of the component bonding strength of the electronic component 4 and deterioration of reliability do not occur.

Here, in the above-described embodiment, the conductor pattern 2 is an example in which it is composed of a Ta ₂ N film, a Ni—Cr film, and an Au film, but it is a conductor pattern in which an Au film is formed on the uppermost layer. If so, the lower Ta ₂ N film and the Ni—Cr film may be formed of other metals. Further, the film thickness dimension of each film described above is merely an example, and can be appropriately changed according to the dimension of the component to be soldered and the type of solder used. However, it is preferable that the Au film 32 of the second conductor pattern 3 is formed as thin as possible within a range that does not hinder soldering.

In order to suppress the intermetallic compound between the Au film 32 of the second conductor pattern 3 and the solder, a preliminary solder layer may be formed on the surface of the Au film 32. If this preliminary solder layer is formed, when soldering electronic components,
Since the preliminary solder and the component connecting solder are immediately wet and are connected, Au is suppressed from diffusing into the solder.
Generation of an Au—Sn intermetallic compound with the u film is suppressed. The present invention can be similarly applied to a circuit board in which a conductor pattern is formed on an insulating substrate other than the alumina ceramic substrate.

[0010]

As described above, according to the present invention, the Ni film and the thin A film are formed on the Au film of the conductor pattern formed on the insulating substrate.
Since the second conductor pattern is formed by laminating the u film, even if an Au-Sn intermetallic compound is generated when soldering is performed on the thin Au film, the Au film is extremely thin and The formation of the intermetallic compound was slight, and this intermetallic compound was formed on the lower conductive pattern A by the Ni film.
It is possible to prevent the strength deterioration of the soldered portion and improve the reliability without reaching the u film. Further, by forming the preliminary solder layer on the surface of the tin soldering portion of the Au film of the second conductor pattern, it is possible to prevent the solder and the preliminary solder from immediately getting wet and Au from diffusing into the solder. Are prevented from being generated.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an example of an insulated circuit board of the present invention.

FIG. 2 is a cross-sectional view of a state in which components are mounted on the insulated circuit board of the present invention and soldered.

FIG. 3 is a cross-sectional view of a state in which components are soldered to a conventional insulated circuit board.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Alumina ceramic substrate 2 Conductor pattern 21 Ta ₂ N film, 22 Ni—Cr film, 23 Au
Film 3 Second conductor pattern 31 Ni film, 32 Thin Au film 4 Electronic component 5 Sn63 Eutectic solder 6 Au-Sn based intermetallic compound

Claims (3)

[Claims] 1. An insulated circuit board comprising a conductor pattern formed on an insulating substrate, and an upper layer of the conductor pattern comprising an Au film, wherein a Ni film and a thin Au film are formed on at least a surface of a tin soldering portion of the conductor pattern. An insulated circuit board, characterized in that a second conductor pattern is formed by laminating and. 2. Ta ₂ N on an alumina ceramic substrate
A conductive pattern is formed by stacking a film, a Ni-Cu film, and an Au film, and a second conductive pattern is formed by stacking a Ni film and a thin Au film on at least a tin soldering portion on the surface of the conductive pattern. Item 1. The insulated circuit board of item 1. 3. A preliminary solder layer is formed on the surface of the tin soldering portion of the Au film of the second conductor pattern.
Isolated circuit board.