JPH03295871A - Method for joining alumina ceramic to metal - Google Patents

Abstract

PURPOSE:To prevent the swelling of plating layers formed on the surfaces of alumina ceramic and a metal to be joined due to brazing and to improve the reliability of joining by plating the surfaces with Ni in a prescribed thickness. CONSTITUTION:The surface of alumina ceramic to be joined is plated with Ni in 2-15mum thickness. The surface of a metal (e.g., 'Kovar(R)') to be joined is plated with Ni in 2-10mum thickness. The alumina ceramic having a metallizing layer is joined to the metal having a metallizing layer by brazing.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a method of joining alumina ceramic and metal by brazing.

[Conventional technology]

Bonding of alumina ceramics and metals is used in various fields, but in particular in the cases of power flat thyristors and vacuum pulp for vacuum circuit breakers, not only the bond strength but also the airtightness of the joint are important characteristics. It becomes. Such joining is generally done by silver brazing, but since alumina ceramic cannot be brazed directly to metal, Mo (molybdenum), Mo-Mn (molybdenum-manganese) is used on the joint surface of alumina ceramic. ), W(
Baking of high melting point metal powder such as tungsten), so-called metallization, is performed, and Ni plating is further applied to prevent oxidation. On the other hand, although sealing alloys such as Kovar alloy and Fe-42 alloy that are brazed to alumina ceramics have a certain degree of wettability to the brazing material, even when brazed in a vacuum atmosphere, the surface is oxidized, resulting in a decrease in wettability, and preventing oxidation requires an ultra-high vacuum atmosphere, which is not economically viable. In addition, during the brazing process, if silver solder enters the grain boundaries of the sealing alloy, the sealing alloy becomes brittle, and the coefficient of thermal expansion of the sealing alloy is slightly larger than that of the alumina ceramic and the sealing alloy. Solidification causes tensile stress to act on the sealing alloy, and this stress may cause cracks to occur. For these reasons, the joint surfaces of the sealing alloy are also plated with Ni in advance. [Problems to be Solved by the Invention] However, when conventional alumina ceramics plated with Ni are exposed to high temperatures of 800 to 900°C during brazing, the plating layer bulges, which impairs airtightness. There was a problem that Also, with regard to sealing alloys, if the plating layer is too thin, the plating layer will sometimes be eroded by the silver solder and the original purpose will not be achieved, while on the other hand, if the plating layer is too thick, the adhesion between the plating layer and the sealing alloy will deteriorate. The problem was that the brazing would cause blisters due to the heat generated over time. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a method for joining alumina ceramic and metal in which the alumina ceramic and sealing alloy are coated with optimal Ni plating to prevent the above phenomenon from occurring. [l! ! ! [Means for Solving the Problems] In the case of joining an alumina ceramic having a metallized layer and a metal, the present invention applies Ni plating to a thickness of 2 to 15 μm on the joint surface of the alumina ceramic, and coats the joint surface of the metal with Ni plating with a thickness of 2 to 15 μm. Ni plating with a thickness of ~10 μm shall be applied.

[For use]

We experimented with various plating thicknesses and found that for alumina ceramics with metallized layers, 2-15 μm of Ni
It was confirmed that blistering can be prevented by plating. Similarly, it was confirmed that applying Ni plating of 2 to 10 μm to the sealing alloy improves its wettability with the brazing metal, effectively preventing the intrusion of the brazing metal, and preventing blistering. .

【Example】

First, Table 1 shows the relationship between the thickness of the Ni plating layer of alumina ceramic and the swelling of the plating layer after heating. According to this, no blistering occurs when the thickness is between 2 and 15 μm, and when the thickness exceeds 15 μm, the blisters become large.
It can be seen that the number also increases and tends to decrease slightly when the thickness becomes 25 μm or more. It does not reach Table 1. Therefore, it is thought that blistering occurs most when the plating layer has an intermediate thickness. Next, Table 2 shows the adhesion between the sealing alloy and the plating layer after Ni plating of various thicknesses was applied to the sealing alloy (Kovar alloy), and the condition of the plating layer after brazing. It is something. Table 2 This can be explained as follows. Gases stored inside the plating layer or metallized layer are released by heating during brazing, but if the plating layer is relatively thin, this gas will permeate through the plating layer, causing blistering. There is no stress that would cause it to occur. On the other hand, if the plating layer becomes considerably thick, the plating layer will have a strength greater than the stress of the emitted gas, so blistering will occur.
After heating in a vacuum at °C for 30 minutes, the samples were taken out and judged based on the presence or absence of blistering of the plating layer. In addition, the state of the plating layer was determined by combining the plated sealing alloy and the metallized alumina ceramic in a vacuum at 850°C.
After heating and brazing for several minutes, the cross section was observed using an optical microscope and an electron microscope. Regarding the adhesion between the sealing alloy and the Ni plating layer, no abnormality was observed when the thickness of the plating layer was 10 μm or less, and good adhesion was exhibited. However, when the thickness exceeded 10 μm, blistering was observed in some cases. It was particularly noticeable at around 15 μm, and tended to decrease as the thickness increased further. On the other hand, later cross-sectional observations of brazing showed that when the thickness of the plating layer was less than 2 μm, it did not exist as a plating layer but was diffused into the solder layer, and was alloyed with Cu (copper) contained in the silver solder. . Further detailed observation using an electron microscope revealed that
Ag (silver) was detected from the grain boundaries of the sealing alloy. This Ag
Since this is a component of silver solder and is not included in the sealing alloy, it can be said that the silver solder has entered the grain boundaries of the sealing alloy during brazing.

【Effect of the invention】

According to the present invention, it is possible to effectively prevent the occurrence of blistering caused by brazing the Ni plating layer applied to the joint surface of the alumina ceramic and the sealing alloy, and to improve the reliability of the joint between the alumina ceramic and the metal in airtight applications. can improve sex. Procedural amendment (voluntary) Name of the invention Person amending the joining method of alumina ceramic and metal Contents of amendment 1, “rFe-42 alloy” on page 2, line 10 of the specification”
Corrected as "Fe42Ni alloy". 2. On page 2 of the specification, line 11, "to some extent" is amended to "to some extent." Relationship to the case Patent applicant

Claims (1)

[Claims] 1) When joining an alumina ceramic having a metallized layer and a metal, apply Ni plating with a thickness of 2 to 15 μm on the joint surface of the alumina ceramic, and apply Ni plating with a thickness of 2 to 10 μm on the joint surface of the metal. A method for joining alumina ceramic and metal, characterized by applying