Alloys or metallic compositions – Containing over 50 per cent metal but no base metal – Copper containing
Patent
1982-07-30
1983-10-25
Skiff, Peter K.
Alloys or metallic compositions
Containing over 50 per cent metal but no base metal
Copper containing
420502, C22C 3002
Patent
active
044118643
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an inexpensive Cu-Ag base alloy brazing filler material that has a relatively low silver content and yet achieves satisfactory cold workability, brazability and low vapor pressure.
BACKGROUND ART
The technique of vacuum brazing is used to fabricate electron tubes and vacuum tubes. If a brazing filler material having high vapor pressure is exposed to the vacuum brazing atmosphere, the vapor fouls the area to be brazed as well as the inner wall of the vacuum furnace. The brazed part is also exposed to high temperatures during the service of the tubes, and the filler material is evaporated to give a vapor that not only reduces the degree of vacuum in the tubes but also fouls their interior. For these reasons, an alloy having low vapor pressure is used as the brazing filler material. Typical filler materials having low vapor pressure include an Ag-Cu alloy filler material (silver brazing filler material BAg-8 of JIS Z 3261) consisting of 27-29% Cu with the balance being Ag and incidental impurities and an Ag-Cu-Sn alloy brazing filler material consisting of 59-61% Ag, 9.5-10.5% Sn, with the balance being Cu and incidental impurities (all percents used herein are by weight). One example of each type is listed in Table 26.1 on page 297 of "Brazing Manual" published by Kogaku Tosho Shuppan, October 1980 which is a translation of "Brazing Manual", 3rd ed., edited by American Welding Society, 1976. These conventional Ag-Cu base alloy brazing filler materials have good brazability, but their silver content is so high that with the rapid increase and considerable fluctuation in the price of silver in recent years, economic considerations put rigid limits on expanding the applications of these filler materials. Attempts have been made to reduce the silver content, but this results in reduced wettability and increased brazing temperatures, which in turn impair the brazability, the cold workability in particular, of the filler materials, and the filler materials cannot be worked into a foil or very fine wire that is required in electronics to fabricate ICs and LSIs.
DISCLOSURE OF THE INVENTION
Therefore, the present inventors made studies to produce a brazing filler material that has a relatively low silver content, and also achieves good brazability and satisfactory cold workability and has low vapor pressure. As a result, they successfully obtained an alloy that meets all of these requirements. The alloy filler material according to the present invention comprises more than 35 to 50% of Ag, 2.2 to 6% of Si, 1 to 4% of at least one optional element selected from among Sn and In, 0.001 to 0.5% of at least one optional element selected from among B and Li, and 1 to 5% of at least one element selected from among Fe, Ni and Co, with the balance being Cu and incidental impurities. This Cu-Ag base alloy, having a relatively low Ag content, has cold workability acceptable for practical purposes. More than that, it has better brazability than the conventional Ag-Cu base alloy filler material of high Ag content, as well as reduced vapor pressure.
The present invention has been accomplished on the basis of these findings. The criticality of the amounts of the respective components defined above is described below.
(a) Ag
Silver is effective not only in improving the cold workability of filler materials but also in lowering their melting point and improving their wettability. If the silver content is 35% or less, these effects are not achieved. On the other hand, even if the content is more than 50%, no corresponding improvement is obtained. Therefore, by economic considerations, the silver content is limited to the range of from more than 35% to not more than 50%.
(b) Si
Silicon is capable of improving the wettability of the filler material without increasing its vapor pressure. Silicon is also capable of reducing the melting point of the filler material by forming a Cu-Ag-Si ternary eutectic system. If the silicon content is less than 2.2%, these effects are not achi
REFERENCES:
patent: 2196303 (1940-04-01), Hensel et al.
patent: 2279282 (1942-04-01), Wassermann
patent: 2953844 (1960-09-01), Gelb et al.
Kishida Kunio
Morikawa Masaki
Tanaka Chuji
Yoshida Hideaki
Mitsubishi Kinzoku Kabushiki Kaisha
Skiff Peter K.
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