CN111805040A

CN111805040A - Gold-based brazing filler metal suitable for sealing and brazing ultrahigh vacuum electronic device

Info

Publication number: CN111805040A
Application number: CN202010621024.4A
Authority: CN
Inventors: 曲文卿; 吴永超; 牟国倩; 刘振鑫; 张志强; 赵海云; 庄鸿寿
Original assignee: Beihang University
Current assignee: Beihang University
Priority date: 2020-06-30
Filing date: 2020-06-30
Publication date: 2020-10-23

Abstract

The application provides a gold-based brazing filler metal for packaging and brazing vacuum electronic devices capable of being used for ultrahigh vacuum degree requirements, wherein the brazing filler metal alloy comprises the following metal elements in percentage by mass: au: 55-69 wt%, Cu: 15-25 wt%, Ni: 8-12 wt%, Ga: 5 to 8 wt%. The gold-based solder provided by the invention effectively reduces the content of noble metal Au, has a melting range similar to that of 72Ag-28Cu solder, has a vapor pressure lower than that of 72Ag-28Cu solder by 2 orders of magnitude, has good processability, has good wetting and spreading performance on common vacuum electronic device materials, and is particularly suitable for packaging and soldering of ultrahigh vacuum electronic devices.

Description

Gold-based brazing filler metal suitable for sealing and brazing ultrahigh vacuum electronic device

Technical Field

The invention relates to a gold-based brazing filler metal suitable for sealing and brazing of an ultrahigh vacuum electronic device.

Background

The 72Ag-28Cu brazing filler metal comprises: moderate soldering temperature (about 800-850 ℃), good wettability and fluidity to copper, nickel and other metals, easy processing into various shapes such as sheet/foil/plate/wire and the like, is a packaging solder which is widely applied in the electric vacuum industry, is widely used for welding and sealing vacuum electronic devices such as vacuum switch tubes, transmitting tubes, microwave devices and the like, and accounts for more than 80 percent of the total amount of the solder of the vacuum electronic devices. However, the brazing filler metal takes Ag as a matrix, and the vapor pressure of Ag is high, so that the saturated vapor pressure of the 72Ag-28Cu brazing filler metal is relatively high, Ag in the brazing filler metal is easy to volatilize and deposit on a cathode when the brazing filler metal works in a long-term high-temperature environment, cathode poisoning is caused, an electron gun cannot work normally, and the vacuum electronic device fails. In addition, with the technical development of vacuum electronic devices and the requirement of ultrahigh vacuum degree performance, the Ag72Cu28 brazing filler metal is difficult to realize the performance requirement of ultrahigh vacuum sealing of the vacuum electronic devices. Therefore, the development of ultra-low vapor pressure electronic device sealing solder capable of realizing ultra-high vacuum performance is urgent.

Researches find that the vapor pressure is reduced only by reducing the Ag element content of the solder, for example, by adding In, Sn and other elements, the Ag content is difficult to be greatly reduced, and the vapor pressure of the solder is difficult to be effectively reduced; therefore, only lower vapor pressure elements can be used for replacing Ag to serve as a brazing filler metal matrix, such as Au, Cu, Ni and the like, but the melting temperature of the brazing filler metal taking the elements as the matrix is greatly different from that of 72Ag-28Cu brazing filler metal, and no suitable low vapor pressure brazing filler metal exists.

Patent 201811118277.9 proposes a low vapor pressure low melting point packaging gold-based solder, which comprises the following components (by mass percent): 67-79 wt% of Au, 15-25 wt% of Cu and 6-8 wt% of Ga, has the remarkable advantage of ultralow vapor pressure, has a melting point equivalent to that of Ag72-Cu28 solder and excellent plasticity, and becomes a preferred substitute for 72Ag-28Cu solder; however, the solder contains Au up to 79%, and the cost is extremely high. Therefore, on the basis of maintaining the excellent performance of the brazing filler metal, how to effectively reduce the content of the noble metal element Au has extremely important engineering practical value.

Disclosure of Invention

The invention is mainly provided aiming at the defect that the low-vapor-pressure low-melting-point packaging gold-based solder provided by the patent 201811118277.9 is high in cost, so that the invention aims to effectively reduce the dosage of Au element by adding low-cost low-vapor-pressure element on the basis of ensuring that the performance (especially the melting temperature) of the solder provided by the patent 201811118277.9 is not changed, thereby achieving the purpose of reducing the cost. The invention provides a gold-based solder suitable for sealing and brazing of ultrahigh vacuum electronic devices, which effectively reduces the using amount of Au in the solder by adding a low-cost low-vapor-pressure element Ni into an Au-Cu-Ga system, wherein the minimum mass percentage of Au is only 55 wt%, so that the cost of the solder is greatly reduced by nearly 30%, and meanwhile, the advantages of ultralow vapor pressure, equivalent melting temperature of the solder to 72Ag-28Cu solder, excellent processing performance and the like are maintained. The invention relates to a gold-based brazing filler metal suitable for sealing and brazing of ultrahigh vacuum electronic devices, which consists of 55-69 wt% of Au, 15-25 wt% of Cu, 8-12 wt% of Ni and 5-8 wt% of Ga, wherein the brazing filler metal is prepared by a vacuum melting method, and the content ratio of Ga to Ni elements in the brazing filler metal is approximately 2: 3, or a salt thereof.

The gold-based brazing filler metal suitable for sealing and brazing of the ultra-high vacuum electronic device has the advantages that: 1. compared with the gold-based solder disclosed in patent 201811118277.9, the performances of a series of solders such as vapor pressure, melting range and the like are equivalent, and the cost is reduced by nearly 30%; 2. compared with the existing 72Ag-28Cu solder, the saturated vapor pressure of the solder can be reduced by at least 2 orders of magnitude; 3. the melting temperature of the brazing filler metal is equivalent to that of 72Ag-28Cu brazing filler metal, the brazing filler metal meets the requirement of brazing in the range of 820-850 ℃, and the difficulty of replacing equipment and technology is avoided; 4. the plastic processing performance is equivalent to 72Ag-28Cu brazing filler metal; 5. the wetting spreading performance of the solder is equivalent to that of 72Ag-28Cu solder; 6. the method is particularly suitable for the packaging and soldering of the vacuum electronic device with ultrahigh vacuum requirement.

Detailed Description

The following examples are further illustrative of the present invention, but the scope of the present invention is not limited to the embodiments set forth herein. In the following description, all percentages relating to the composition of the solder alloy are percentages by mass.

The brazing filler metal smelting comprises the following steps:

weighing Au, Cu, Ni and Ga with the purity of 99.99% according to the component ratio, and putting the metals into a vacuum induction melting furnace; the vacuum degree reaches 4 multiplied by 10^-1～4×10^-2Then heating at 1100-1200 ℃; filling argon after the alloy is completely melted, preserving the heat for 20-30 min, and cooling and solidifying to obtain the alloyAnd obtaining the brazing filler metal cast ingot. Removing oxide skin on the surface of the cast ingot, then cold rolling to the thickness of 1-2 mm; then annealed at 600 c until cold rolled into a 0.1mm thick foil.

Examples the metal element ratios are shown in table 1.

TABLE 1 elemental composition (unit: wt%) of solder alloy examples

Examples	Au	Cu	Ni	Ga
					1	69	18	8	5
2	55	25	12	8
					3	60	24	10	6
4	67	15	11	7

For comparison with solders of other alloy composition, the following comparative examples are provided, the compositions of which are shown in table 2.

TABLE 2 elemental composition (unit: wt%) of comparative brazing filler metal alloy examples

Comparative example	Ag	Au	Cu	Ga
					1	72	—	28	—
2	—	72	20	8
					3	—	79	15	6

The performance of each of the solder alloys of the examples and comparative examples was tested and the saturated vapor pressure of the solder was calculated according to the formula. The melting temperatures (liquidus temperature and solidus temperature) of the solder were obtained by differential thermal analysis testing. The hardness of the brazing filler metal is tested by a Vickers hardness tester. The wetting test was carried out by placing the same volume of spherical solder on a copper plate and a nickel plate, heating to 825 deg.C in a vacuum furnace, holding for 10 minutes, and then calculating the spreading factor. Formula for calculating spreading coefficient (K): k ═ D-H)/H × 100%; wherein D is the diameter (mm) of the spherical brazing filler metal; h is the residual height (mm) of the spread brazing filler metal. The results of the various performance calculations and tests are shown in tables 3 and 4 below.

TABLE 3 vapor pressure comparison table for solder

TABLE 4 solder Performance comparison Table

Claims

1. A gold-based brazing filler metal suitable for sealing and brazing of ultrahigh vacuum electronic devices is characterized in that: the brazing filler metal consists of the following metal elements in percentage by mass: au: 55-69 wt%, Cu: 15-25 wt%, Ni: 8-12 wt%, Ga: 5 to 8 wt%.

2. The gold-based solder suitable for sealing and soldering of ultra-high vacuum electronic devices as claimed in claim 1, wherein: the content ratio of Ga to Ni elements in the brazing filler metal is approximately 2: 3, or a salt thereof.