JPH0521641A - Ceramic circuit board - Google Patents

Abstract

PURPOSE:To provide a ceramic circuit board having little breaking in the bent parts, which are terminal connection parts, of copper circuit boards and having a high strength and a high reliability. CONSTITUTION:In a ceramic circuit board of a structure, wherein copper circuit boards 7a to 7e and 2 are jointed integrally with a ceramic substrate 1 and are formed on the substrate 1 and terminal connection parts 3a to 3e formed in such a way as to float from the substrate 1 by bending the end parts of the boards 7a to 7e for connecting a terminal 4 of a module are provided, the radiuses R1 and R2 of curvature of bent parts P3 and P4 of the end parts 3a to 3e are set in a radius of 0.2mm or longer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramics circuit board, and more particularly to a ceramics circuit board with high strength and high reliability in which a terminal connecting portion for mounting a module is not broken.

[0002]

2. Description of the Related Art In recent years, a copper plate having both high thermal conductivity and high conductivity on a surface of a substrate body formed of a ceramic sintered body as a circuit substrate such as a substrate for a power transistor module or a substrate for a high power switching power supply module. Ceramic circuit boards in which metal plates such as the above are integrally bonded are widely used.

This ceramic circuit board is shown in FIG.
As shown in FIG. _2, a plurality of ceramic substrates 1 each having a thickness of about 0.3 to 3 mm and made of a sintered body of alumina (Al ₂ O ₃ ) or aluminum nitride (AlN) are punched and formed into a predetermined shape. The copper circuit boards 2a, 2b, 2c are placed in contact with each other and heated to generate a eutectic liquid phase composed of Cu—Cu ₂ O at the bonding interface between the two, and the liquid phase wets the surface of the ceramic substrate 1 and then It is manufactured by a so-called DBC (Direct Bond Copper) method in which the ceramic substrate 1 and the copper circuit boards 2a to 2c are directly joined by cooling and solidifying.

A terminal connecting portion 3 for connecting terminals of an LSI circuit element or a module mounted on the ceramics circuit board 1 is formed at an end portion of a part of the copper circuit board 2a. As shown in FIG. 4, the terminal connecting portion 3 is formed in advance so that when the copper circuit board 2a is punched out by a press, its ends are bent at the same time so that the cross section has a substantially U-shape. Then, after the copper circuit board 2a is integrally joined to the surface of the ceramic substrate 1 by the DBC method, the free end side of the terminal connecting portion 3 is held in a state of floating from the surface of the ceramic substrate 1. A terminal 4 of a module (not shown) is joined to the upper surface of the terminal connecting portion 3 with solder 5.

Further, in order to improve the solder wettability with respect to the copper terminal connecting portion 3 and to increase the bonding strength between the terminal 4 and the connecting portion 3, the surfaces of the copper circuit boards 2 to 2c are electroless plated, for example. The Ni plating layer 6 having a thickness of about 2 to 6 μm is formed.

Even when the terminal 4 is displaced in the vertical direction as shown by an arrow in FIG. 4 due to thermal expansion or the like, the displacement is absorbed by the bending around the base end portion of the terminal connecting portion 3. Therefore, the stress due to the thermal expansion is effectively prevented from being concentrated on the ceramic substrate 1.

[0007]

However, in the conventional ceramics circuit board, as described above, the Ni plating layer is formed on the copper circuit board in order to improve the solder wettability. Therefore, there is a problem that the copper circuit board is easily hardened and damaged. That is, the copper material before forming the Ni plating layer is soft and rich in elasticity, but since Ni itself is hard, the copper circuit board is hardened when the Ni plating layer is formed. In FIG. ₁ and P ₂ become brittle, and the repeated bending strength of that portion is reduced.

Further, the radii of curvature R _{1 of} the bent portions P ₁ and P ₂ ,
Since R ₂ is as small as about 0.1 mm, bending stress is concentrated on the bent portions P ₁ and P ₂ , cracks are likely to occur, and the terminal connecting portion 3 is ruptured in a short period of time, resulting in reduced durability. There is a problem to do.

The present invention has been made in order to solve the above problems, and an object of the present invention is to provide a ceramic circuit board which has few breakages of terminal connection portions and has high strength and high reliability.

[0010]

[Means and Actions for Solving the Problems]
Various measures have been examined for improving the durability of the base end portion of the terminal connecting portion without impairing the bonding strength between the terminal and the terminal connecting portion. As a result, it was found that the curvature radius of the bent portion on the base end side of the terminal connecting portion had a great influence on the durability of the portion, and the present invention was completed based on this finding.

That is, the ceramics circuit board according to the present invention is formed by integrally bonding a copper circuit board on the ceramics board, and bending the ends of the copper circuit board to connect the terminals of the module. A ceramic circuit board having a terminal connecting portion formed by floating from the ceramic substrate is characterized in that the bending radius of the bent portion of the terminal connecting portion is 0.2 mm or more.

The radius of curvature of the bent portion has a great influence on the degree of stress concentration on the base end portion of the terminal connecting portion, and is set to 0.2 mm or more. Radius of curvature 0.2
If it is less than mm, stress is likely to be concentrated on the bent portion of the terminal connecting portion, and cracks are likely to occur in a short period of time to break. On the other hand, even if the radius of curvature is set to exceed 0.5 mm, a significant improvement effect on durability cannot be expected, so the radius of curvature is 0.2 to 0.5.
It is set in the range of mm. In particular, when the radius of curvature is 0.3 mm or more, it is possible to obtain bending strength and repeated bending fatigue strength equivalent to those of the copper circuit board at the stage where the Ni plating layer is not formed.

The radius of curvature of the bent portion of the terminal connecting portion is
It can be arbitrarily set by adjusting the radii of the edge portions of the male and female dies for press punching.

As described above, according to the ceramics circuit board of the present invention, the radius of curvature of the bent portion of the terminal connecting portion is set to 0.
Since the size is set to 2 mm or more, stress concentration on the bent portion can be effectively prevented, and a high-strength ceramic circuit board with few cracks or breaks can be provided.

[0015]

Embodiments of the present invention will now be described with reference to the accompanying drawings. FIG. 1 is a partial cross-sectional view showing an embodiment of a ceramics circuit board according to the present invention, and the same elements as those in the conventional example shown in FIG.

As Examples 1 to 5, a large number of ceramic circuit boards shown in FIG. 1 were prepared as follows. That is, 5% by weight of yttrium oxide and 5% of alumina are added to aluminum nitride.
Weight%, silicon dioxide 5 weight% containing thickness 0.6
The temperature of the ceramic substrate 1 of 35 mm is 1100 in the air.
It was heated at 1250 ° C. for 1 to 5 hours to form an oxide layer on the surface.

On the other hand, a tough-pitch electrolytic copper plate having a thickness of 0.3 mm is punched out by using a punching press forming machine, and the radii of curvature R ₁ , R ₂ of the bent portions P ₃ , P ₄ of the terminal connecting portions 3a to 3e.
Are 0.2mm, 0.3mm, 0.4mm, 0.5mm,
A large number of copper circuit boards 7a to 7e having a width of 3 mm were prepared to have a thickness of 0.6 mm.

Next, the copper circuit boards 7a to 7e were brought into contact with the oxide layer of the ceramic substrate 1 and joined by the DBC method. That is, the copper circuit boards 7a to 7e on which the terminal connecting portions 3a to 3e are formed are brought into contact with the ceramics substrate 1 and heated in a nitrogen gas atmosphere at a temperature at which a eutectic of Cu and O can be obtained for 10 minutes to integrate them. Joined.

Next, the copper circuit board 7a is formed by electroless plating.
To 7e, 2 are formed with a Ni plating layer 6 having a thickness of 3 μm, and the terminals 4 of the module are connected to the respective terminal connecting portions 3a to 3
Examples 1 to 5 shown in FIG.
The ceramic circuit board of

On the other hand, as Comparative Example 1, a ceramic circuit board was processed in the same manner as in Example 1 except that the radius of curvature R ₁ , R ₂ of the bent portion of the terminal connecting portion was set to 0.1 mm as in the conventional case. Obtained.

Further, as Comparative Example 2, a ceramic circuit board was prepared in the same manner as in Example 1 except that the Ni plating layer was not formed.

A vibration test was conducted to evaluate the durability of the ceramic circuit boards of Examples 1 to 5 and Comparative Examples 1 and 2 thus obtained. That is, the terminal 4 joined to each terminal connecting portion is vibrated in the direction of the arrow shown in FIG. 1 at an amplitude of 1 mm at a rate of once per second, and the number of bendings until either of the bent portions P ₃ and P ₄ is broken is determined. The measurement was performed and the results shown in FIG. 2 were obtained.

As is apparent from the results shown in FIG. 2, the ceramic circuit boards of Examples 1 to 5 in which the radius of curvature R of the bent portions P ₃ and P ₄ is set to 0.2 mm or more, the radius of curvature R is 0. Compared with the circuit board of Comparative Example 1 having a size of 0.1 mm,
It was found that the number of bends until breakage was significantly increased, and that it had high durability.

In particular, by setting the radius of curvature R to 0.3 mm or more, it was possible to secure the number of bends equal to or more than that of the circuit board of Comparative Example 2 in which the Ni plating layer was not formed.

That is, since the Ni plating layer is formed,
Although the terminal connection portion was hardened, the bending strength and fatigue strength equivalent to those of the copper circuit board, in which the Ni plating layer was not formed, were obtained, and a highly reliable ceramic circuit board was obtained.

[0026]

As described above, according to the ceramics circuit board of the present invention, since the radius of curvature of the bent portion of the terminal connecting portion is set to be 0.2 mm or more, stress concentration on the bent portion can be prevented. It is possible to provide a high-strength ceramic circuit board that can be effectively prevented and has few cracks or breaks.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view showing an embodiment of a ceramics circuit board according to the present invention.

FIG. 2 is a graph showing the relationship between the radius of curvature of a terminal connecting portion and the number of bends before breaking.

FIG. 3 is a perspective view showing the structure of a conventional general ceramics circuit board.

FIG. 4 is a partial sectional view taken along the line IV-IV in FIG.

[Explanation of symbols]

1 Ceramics Substrate 2,2a, 2b, 2c Copper Circuit Board 3,3a, 3b, 3c, 3d, 3e Terminal Connection Part 4 Terminal 5 Solder 6 Ni Plating Layer 7a, 7b, 7c, 7d, 7e Copper Circuit Board P ₁ , P ₂ , P ₃ , P ₄ Bent part R, R ₁ , R ₂ , radius of curvature

Claims (1)

Claim: What is claimed is: 1. A ceramic circuit board formed by integrally bonding a copper circuit board on a ceramic board, and bending the ends of the copper circuit board to connect the terminals of the module. A ceramic circuit board having a terminal connecting portion formed by floating from above, wherein the radius of curvature of the bent portion of the terminal connecting portion is 0.2 mm or more.