JPH0215972B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for bonding a contact made of a silver-based material onto a support whose at least the surface is made of a copper-based material. Silver-based contacts made of materials such as Ag, Ag-CdO, and Ag-Ni are widely used in electrical machine contacts due to their excellent contact performance. However, since silver is expensive, the contacts are usually fixed on a support, and the support is often made of copper or its alloy, which has good conductivity. For fixing the contacts, for example, refer to "Electric Materials Manual" (New Technology Development Center Co., Ltd., 1973).
As described on pages 635 to 638 (published in October 2016), this is done by caulking, welding, or brazing, which are the usual joining methods between metal members. Caulking is easy to perform at high speed automatically, but large-sized contacts require a large force, and the contact material may be wasted, or the silver-based contacts, which have been hardened during processing, may soften over time at room temperature. This has disadvantages such as weakening of adhesion to the support. Since welding utilizes heat generated by energizing the contact and support, it is not often applied to silver-based contacts, which have low electrical resistance. Silver brazing is the most common;
This is done by sandwiching a silver solder foil between the support and the contact, and melting the silver solder using a gas burner, resistance heating, high frequency induction heating, or the like. However, it is difficult to automate because it requires expensive silver solder and the work of inserting the silver solder foil into the specified position.
Requires skilled workers, use of flux tends to contaminate the working environment, and gas generated from flux may cause contacts to move during brazing work or defects such as bubbles to occur in the joint. There are drawbacks such as: Therefore, it is also known to use diffusion bonding instead of these methods. However, in this case as well,
As stated in Publication No. 78060, the bonding side of the contact must be made of only silver, or
As described in Publication No. 61456, there are restrictions such as the fact that the process must be carried out in a vacuum chamber, so it is difficult to apply it easily in general. As a bonding method that eliminates these drawbacks, the present applicant has developed a bonding method in which a silver-based contact is brought into contact with a support whose at least the surface is made of a silver-based material under a pressure of 1 Kgf/cm ² or less, and heated at 700°C in a non-oxidizing atmosphere. An application has already been filed for a method of heating at temperatures above. To explain this method with reference to the drawings, when joining the silver-based contact 1 shown in FIG. Alternatively, after cleaning with pickling, place the contact 1 on the base metal 2 as indicated by the arrow in the figure, and place it in a furnace with non-oxidizing atmosphere at 700℃.
Heat at above temperature. As the surrounding atmosphere, an inert gas such as nitrogen or argon at normal pressure or a reducing gas such as hydrogen or ammonia decomposition gas can be used, but a vacuum may also be used. As a result of this heating, the Ag atoms in the contact and the Cu atoms in the alloy diffuse into each other to form an intermediate bonding phase, so if the contact is cooled by slow or rapid cooling, the contact 1 will become a base as shown in Figure 2. Fixed to gold 2. Figures 3A to 3C show each stage of fixation.As shown in Figure 3A, the silver-based contact 1 is placed on the base metal 2 made of tough pitch copper, and the center is heated in a nitrogen atmosphere. , Figure 3B
As shown in FIG. 3, a liquid phase alloy layer 3 is formed at the contact portion between the contact point 1 and the base metal 2 due to the eutectic reaction between the two, and as the diffusion progresses, a fillet portion 31 is formed as shown in FIG. 3C. At the same time, the surface of the contact point 1 sinks by a dimension s. The heating temperature is in the range of 780 to 850°C, especially preferably 820°C, for Ag contacts, and in the range of 700 to 850°C, particularly preferably 780°C, for Ag-Cd contacts. For contact, the temperature is in the range of 780 to 870°C, particularly preferably 850°C. If the heating temperature is lower than this range, an alloy layer will be formed locally on the contact surface, resulting in a gap between the contact and the support after cooling, resulting in a decrease in bonding strength, which is undesirable. When the heating temperature is within the above range, wetting by the alloy liquid phase occurs over the entire contact surface, a uniform bonding layer is formed over the entire surface, and a high bonding force is obtained, which is preferable. Furthermore, if the heating temperature is higher than the above range, the alloy liquid phase will increase and the amount of sinking of the contact point, which will be explained next, will increase, which is not preferable. Table 1 shows the amount of sinking and high-temperature shear strength of the joint when contacts made of these materials are joined using the above-mentioned diffusion bonding method, and for comparison, the high-temperature shear strength when silver brazing is used. show.

[Table] As is clear from Table 1, the shear strength at 500°C is much higher when using the diffusion bonding method than when using silver brazing, and has desirable properties for practical use as a contact. On the other hand, the sinking amount s usually increases in the case of an alloy contact because the amount of liquid phase generated increases, but in the case of Ag-CdO, the sinking amount is smaller than that of the Ag contact, as shown in Table 1. This seems to be because the oxide (CdO) is interposed between the contact layer and the support layer and suppresses mutual diffusion. In such diffusion bonding, contact 1 is connected to base metal 2.
If the contact point is simply placed on the support body, there is a risk that the position of the contact point relative to the support body may shift when a liquid phase is generated at the contact portion of the contact point with the support body due to heating. For this purpose, a protrusion 21 is formed on the support (base metal) 2 as shown in FIG. As shown, a recess 22 is formed in the base metal 2 and the contact 1 is inserted therein.
The method is to insert the bottom of the Furthermore, in the case of Fig. 5A, the surface of the contact 1 is lowered and the opening distance increases, so lift a part of the base metal as shown in Fig. 5B to reduce the opening distance by a predetermined dimension. is also taken into consideration. However, all of these require troublesome processing on the base metal. In view of this, it is an object of the present invention to provide a method for joining contact materials that does not cause positional shift during heating by simple processing on a base metal. This objective is achieved by providing through holes in part of the area of the support in which the contacts are placed. Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG. 6A, the base metal 2 has a through hole 23.
When the contact 1 is placed on it and heated, a liquid phase 3 is generated at the contact area between the contact 1 and the base metal 2 as shown in FIG. 6B. The penetration portion 32 is formed. This penetration part 32, together with the viscosity of the liquid phase, prevents the liquid phase 3 from moving along the surface of the base metal 2, so that no displacement of the contact point 1 occurs during heating. The size d of the through hole 23 is desirably selected to be 1/3 to 1/5 of the lateral dimension L of the contact 1. The cross-sectional shape of the through hole 23 may be circular or rectangular, but is preferably circular in view of workability when forming the through hole by press working. This through hole 23 also serves as a vent hole for gas generated from the alloy liquid phase during the bonding process, and is therefore effective in producing a healthier bond. In addition to pure copper such as tough pitch copper and oxygen-free copper, the support may also be copper alloy such as brass or Cu-Fe alloy (Fe2%), or bonding copper foil onto an easily available iron support. A through hole may be easily formed by pressing or the like. Further, a support made of two layers of copper and iron made by sintering may be used, and in this case, through holes can be formed at the same time in the sintering process. As explained above, the present invention involves bringing a silver-based contact and the surface of a support made of a copper-based material into contact with each other with almost no processing, heating the surface, and forming a liquid phase at the contact portion when performing diffusion bonding. By providing a through hole in the joint portion of the support, displacement of the contact point relative to the support due to this is cleverly prevented. Since the through holes can be easily formed by press working, the present invention can be easily carried out and the effects obtained are extremely large.

[Brief explanation of drawings]

Figures 1 and 2 are perspective views explaining the diffusion bonding method of contacts, Figures 3 A to C are cross-sectional views explaining each stage of the bonding process, and Figures 4 and 5 A and B are during the bonding process. Cross-sectional views showing various methods for preventing misalignment of the 6th
Figures A and B are cross-sectional views illustrating each step of the bonding process in an embodiment of the diffusion bonding method in which positional displacement is prevented according to the present invention. 1...Contact, 2...Support (base metal), 23...
Through hole, 3... bonding layer.

Claims (1)

[Claims] 1 A silver-based contact is placed on a support whose surface is made of a copper-based material, and then placed in a non-oxidizing atmosphere.
A method for bonding silver-based contacts, characterized in that, when the contact and the support are bonded by heating to 700 to 870° C., a through hole is provided in a part of the area of the support where the contact is placed.