JPH05279140A - Method for joining oxide superconductor - Google Patents

Abstract

PURPOSE:To enable the soldering at a low contact resistivity without being affected by technique of an operator by using a solder having a prescribed value or below of a melting temperature or an Sn-Pb-based solder containing a prescribed amount of silver in joining a conductor composed of an oxide superconductor to other conductors. CONSTITUTION:In the first method, a solder having <=100 deg.C [e.g. Rose's alloy having a composition of Bi(50%)-Pb(28%)-Sn(22%), 76 deg.C melting point and a solidifying range of 77-94 deg.C] is used. In the second method, the first conductor composed of an oxide superconductor is joined through a silver film formed on the surface of the first conductor to the second conductors. An Sn-Pb- based solder containing 2-5wt.% silver is used as a joining material. For example, both ends of a wiry bismuth-based superconductor 1 are sputter coated with the silver to 5mum thickness [parts (2a) and (2b)], then heat-treated (at 840 deg.C for 15hr) and subsequently joined to copper electrodes 4 and 4 with a solder material 5, composed of In-Sn-Cd and having 93 deg.C melting point.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for joining a conductor comprising an oxide superconductor to another conductor, and more particularly,
When disposing oxide superconductors in the fields of electric power, transportation, high energy, medical care and electronics,
TECHNICAL FIELD The present invention relates to a method for suppressing contact resistance to be low and joining with another conductor.

[0002]

2. Description of the Related Art When a conductor made of an oxide superconductor is joined to another conductor (for example, a metal), the surface of the oxide superconductor is first deposited by vapor deposition or sputtering. Metallization with silver or the like is preferable.

With respect to such metallization, for example, metallization with silver or gold is described in Appl. Phy
s. Lett. 52 (21), 23 May 1988.
Has been reported to. By metallization, a metal film having a thickness of several μm is formed on the surface of the oxide superconductor. By metallizing with gold or silver, it is possible to carry out the bonding while keeping the contact resistance relatively low.

After such metallization, the superconductor is
It is soldered to another conductor through a metal film formed by metallization. In this soldering,
Generally, Pb-Sn eutectic solder is used.

However, in the conventional joining method using solder, the contact resistance between the joined oxide superconductor and the metal varies greatly depending on the technique of the soldering worker, particularly the time required for the work. Further, the contact resistivity after joining was relatively high at about 10 ⁻³ Ω · cm ² .

An object of the present invention is to provide a method for joining a conductor made of an oxide superconductor and another conductor at a low contact resistivity without depending on the technique of an operator.

[0007]

[Means and Actions for Solving the Problems] As a result of investigating the cause of the above-mentioned problems, a phenomenon in which metallized metal is melted in molten solder during soldering occurs, and the metallized metal is therefore energized. However, it has been found that the film becomes unfavorably thin or disappears.

If the metallized metal film is too thin, the contact resistance will be high, but if it is too thick, the effect of reducing the contact resistance will be saturated, which is inefficient in terms of working time and cost, and actually It doesn't fit. Therefore, there is an optimum value for the film thickness of the metallized metal, which is 3 to 10 μm in the case of silver metallization, for example. With such a film thickness, it was desirable from the viewpoint of working time and cost to carry out soldering work and keep the contact resistance low.

As a result of the above findings and consideration by the present inventor, the present inventor has studied a method in which the film thickness of the metallized metal is not affected by the soldering work time. As a result of the study, first, it was found that the higher the temperature of the molten solder in contact with the metal film by metallization, the faster the dissolution rate of the metal film in the solder, and the lower the temperature, the lower the dissolution rate. As a result of further studies, the present inventor has found that a solder material having a melting temperature of 100 ° C. or less causes almost no change in the thickness of the metal film even after a long soldering operation, and has completed the first invention. It was

That is, the method for joining an oxide superconductor according to the first invention is a method for joining a first conductor made of an oxide superconductor to a second conductor through a metal film formed on the surface thereof. It is characterized in that solder having a melting point of 100 ° C. or lower is used as the bonding material.

The solder used in the first invention is not particularly limited as long as it has a melting point of 100 ° C. or less and is well adhered to a metal and has low resistance. For example, Bi
Rose alloy having a composition of (50%)-Pb (28%)-Sn (22%) (melting point: 76 ° C, solidification range: 77 ° C to 94 ° C)
C) and Bi (50 ± 1%)-Pb (24 ± 1%)-
Wood alloy having a composition of Sn (14 ± 1%)-Cd (12 ± 1%) (melting point 65 ° C, solidification range 66 ° C to 71 ° C)
Has a sufficiently low melting point, can be sufficiently bonded even when hot water is used as a heating source, is inexpensive, and has excellent conductivity, and thus can be used as a preferable solder material.

In the first aspect of the invention, if the melting temperature of the solder is so low, the wettability of the metallized metal or the composite metal with the solder may deteriorate.
The soldering may be performed while applying ultrasonic waves to the bonding surfaces. Further, when the metallization is a composite metal, the wettability may not be improved so much,
In that case, the surface of the composite metal may be thinly coated with Sn-Pb solder before joining.

On the other hand, as a result of further investigation, if the molten solder in contact with the metal film already has a solid solution of silver, for example, if the molten solder contains silver up to the upper limit of the melting degree of silver, It was concluded that the silver film was not dissolved. Sn containing 2% by weight or more and 5% by weight or less of silver
With the use of -Pb-based solder, it was found that the amount of the silver film dissolved in the solder was very small, and that amount was almost negligible within the time required for the soldering work, leading to the completion of the second invention. It was

That is, the method of joining an oxide superconductor according to the second invention is a method of joining a first conductor made of an oxide superconductor to a second conductor through a silver film formed on the surface thereof. The Sn-Pb-based solder containing 2 wt% to 5 wt% of silver is used as the bonding material.

When the amount of silver contained in the solder used in the second invention is less than 2% by weight, the silver film is dissolved during soldering, resulting in a considerably high contact resistance between the superconductor and silver. turn into. Also, the amount of silver added is 5
If the content exceeds 10% by weight, the melting point becomes high, which hinders the soldering work.

The Sn-Pb-based solder containing silver in the above range can adhere well to the silver film and can join the conductor made of a superconductor to another conductor. Further, since the solder according to the present invention has a low resistance, the contact resistance at the time of joining can be kept low.

The Sn-Pb-based solder used in the second invention is not particularly limited, but is, for example, P.
b-Sn, Pb-Sn-Sb, Pb-Sn-Cd, and Pb-Sn-In. According to the present invention, silver may be added to these alloys in an appropriate amount in the range of 2% by weight to 5% by weight.

In the first and second inventions, the oxide superconductor includes an yttrium-based, bismuth-based, thallium-based oxide superconductor, or the like.

In the first and second inventions, the metal film formed on the surface of the oxide superconductor is preferably made of, for example, silver or gold. The thickness of the metal film is preferably 3 to 10 μm as described above,
5 μm is more preferable.

In the first and second inventions, the conductor joined to the oxide superconductor may be, for example, a metal or another oxide superconductor whose surface is metallized. The method of the present invention can be applied not only when bonding a metal and an oxide superconductor but also when bonding a plurality of oxide superconductors in a bundle.

[0021]

【Example】

Example 1 A linear bismuth-based superconductor (Bi ₂ Sr ₂ CaCu ₂ Ox, produced by the unidirectional solidification method, critical current Ic: 200)
Both ends of A) were sputter coated with silver to a thickness of 5 μm. The obtained wire is as shown in FIG. 1 (a), and silver coatings 2a and 2b are formed on both ends of the bismuth-based superconductor 1, respectively.

Next, the wire rod was heated at 840 ° C. for 15 hours,
After heat treatment, In44%, Sn42%, Cd1
Copper electrodes were soldered to both ends of the wire using solder composed of 4% and having a melting point of 93 ° C. At the time of soldering, in order to improve the wettability of the copper electrode with respect to solder, ultrasonic waves were applied to the adhesive surface with an ultrasonic soldering iron.

The wire obtained after soldering is shown in FIG.
Shown in. In the bismuth-based superconductor 1, the portions coated with silver are passed through the holes formed in the copper electrodes 4 and 4 ', and are joined to the respective copper electrodes by the solder material 5.

100 in between the copper electrodes 4, 4'in liquid nitrogen.
When the direct current of A was passed and the voltage between the electrodes was measured to calculate the contact resistivity, it was as low as 10 ⁻⁸ Ω · cm ² . Also, a current of 190 A could be passed between the electrodes without quenching for 100 hours.

Example 2 A linear bismuth-based superconductor (Bi ₂ Sr ₂ CaCu ₂ Ox, produced by the unidirectional solidification method, critical current Ic: 200)
Both ends of A) were sputter coated with silver to a thickness of 5 μm. The obtained wire rod is as shown in FIG.

Next, the wire rod was heated at 840 ° C. for 15 hours,
After heat treatment, Bi (50 ± 1%)-Pb (24
Copper electrodes were soldered to both ends of the wire using a wood alloy having a melting point of 65 ° C. made of ± 1%)-Sn (14 ± 1%)-Cd (12 ± 1%). At the time of soldering, in order to improve the wettability of the silver coating with solder, ultrasonic waves were applied to the joint surface with an ultrasonic soldering iron. After soldering, the obtained wire is as shown in FIG. 1 (b).

A direct current of 100 A was passed between the copper electrodes in liquid nitrogen, the voltage between the electrodes was measured, and the contact resistivity was calculated to be as low as 10 ⁻⁹ Ω · cm ² . Also, a current of 190 A could be passed between the electrodes without quenching for 100 hours.

Example 3 A bismuth-based superconducting wire (Bi ₂ Sr ₂ CaCu ₂ O) having a length of 1.5 mm and a length of 100 mm manufactured by the unidirectional solidification method.
x, critical current Ic: 200 A) 5 μm of silver on the entire surface
After sputter coating with a thickness of 15
Heat treated for hours.

Ten wire rods thus obtained were bundled and fixed with two silver tapes, and the distance between the wire rods was set to Bi (50 ± 1).
%)-Pb (24 ± 1%)-Sn (14 ± 1%)-Cd
A wood alloy having a melting point of 65 ° C. (12 ± 1%) was used for adhesion. At the time of soldering, in order to improve the wettability with the silver-coated solder, ultrasonic waves were applied to the adhesive surface with an ultrasonic soldering iron.

Immerse the entire bonded wire in liquid nitrogen 1
When a direct current of 95 A was passed, it could be passed without quenching for 100 hours while maintaining the superconducting state.

Comparative Example 1 A linear bismuth-based superconductor (Bi ₂ Sr ₂ CaCu ₂ Ox, produced by the unidirectional solidification method, critical current Ic: 200).
Both ends of (A) were sputter coated with silver to a thickness of 5 μm to obtain a wire as shown in FIG.

Next, the wire rod was heated at 840 ° C. for 15 hours,
After the heat treatment, a solder composed of In52% and Sn48% and having a melting point of 118 ° C. was used to bond the ends of the wire to FIG.
Copper electrodes were soldered as shown in FIG. At the time of soldering, ultrasonic waves were applied to the joint surface in the same manner as described above in order to improve the wettability of the silver coating to the solder.

A direct current of 10 A was passed between the copper electrodes in liquid nitrogen, the voltage between the electrodes was measured, and the contact resistivity was calculated to be as high as 10 ⁻³ Ω · cm ² . When a current of 30 A was applied between the electrodes, the superconductor melted due to Joule heat generation.

Comparative Example 2 A bismuth-based superconducting wire (Bi ₂ Sr ₂ CaCu ₂ O) having a length of 1.5 mmφ × 100 mm manufactured by the unidirectional solidification method.
x, critical current Ic: 200 A) 5 μm of silver on the entire surface
After sputter coating with a thickness of 15
Heat treated for hours.

Ten wire rods thus obtained were bundled and fixed with two silver tapes.
Bonding was performed with solder having a melting point of 118 ° C. composed of 48%.
Upon soldering, ultrasonic waves were applied to the joint surface in the same manner as above in order to improve the wettability of the silver coating solder.

When the entire bonded wire was immersed in liquid nitrogen and a direct current of 1 A was applied, a voltage was generated in the wire. This is because the contact resistance between the combined silver tape and the superconducting wire was high, so that the current did not flow from the silver tape to the superconducting wire, and the generated voltage was due to the resistance of silver.

Example 4 A linear bismuth-based superconductor (Bi ₂ Sr ₂ CaCu ₂ Ox, produced by the unidirectional solidification method, critical current Ic: 200)
Both ends of A) were sputter coated with silver to a thickness of 5 μm. The obtained wire is as shown in FIG. 1A, and silver coatings 2a and 2b are formed on both ends of the bismuth-based superconductor 1, respectively.

Next, the wire rod was heated at 840 ° C. for 15 hours,
After the heat treatment, each of the solders shown in Table 1 was used to solder copper electrodes to both ends of the wire.

[0039]

[Table 1]

The wire soldered to the copper electrode is shown in FIG.
It is as shown in (b). The silver-coated portions of the bismuth-based superconductor 1 are copper electrodes 4, 4 '.
Through the holes formed in each and are joined to the conductive electrodes by the solder material 5.

With respect to the superconductors joined with solder having the compositions shown in Table 1, a DC current of 100 A was passed between the conductive electrodes in liquid nitrogen, the voltage between the electrodes was measured, and the contact resistivity was calculated. The contact resistivity calculated is shown in the right column of Table 1.

As shown in Table 1, the amount of silver added is 2% by weight.
Examples A to D joined with solder in the range of ~ 5 wt%
Had a low contact resistivity. On the other hand, in Comparative Example A in which the amount of silver alloy added was outside the range of the present invention, the contact resistivity was about 10 ⁵ times that in Examples A to D.

In the wire rods of Examples A to D, a current of 190 A could be passed between the electrodes without quenching for 100 hours, but in Comparative Example A, a current of 30 A was passed between the electrodes. The superconductor melted due to Joule heat generation.

After heat treating the bismuth superconductor shown in FIG. 1 (a) at 840 ° C. for 15 hours, Sn--Pb solder containing 6% by weight of silver was used to form a copper electrode as shown in FIG. 1 (b). When the temperature was raised to 300 ° C., the solder material did not melt and the electrode could not be joined to the superconductor.

Example 5 1.5 mmφ × 100 mm produced by the unidirectional solidification method
Long Bismuth Superconducting Wire (Bi ₂ Sr ₂ CaCu ₂ O
x, critical current Ic: 200 A) 5 μm of silver on the entire surface
After sputter coating with a thickness of 15
Heat treated for hours. Ten wire rods thus obtained were bundled and fixed with two silver tapes, and the wire rods were bonded together with solder having the composition shown in Table 2.

[0046]

[Table 2]

The entire wires joined by the solders of Examples E to H were each immersed in liquid nitrogen, and a direct current of 195 A was applied to the wires.
I was able to flush it without quenching for hours.

On the other hand, when the entire wire material joined by the solder of Comparative Example C was immersed in liquid nitrogen and a direct current of 1 A was applied, a voltage was generated in the wire material. This is because the contact resistance between the bonded silver tape and the superconducting wire was high, so that the current did not flow from the silver tape to the superconducting wire, and the generated voltage was due to the resistance of silver.

As shown above, Sn-Pb contains 2% by weight.
By using the solder to which silver was added in the range of up to 5% by weight, the contact resistance was suppressed to be low and the superconductor and the metal or the superconductors could be joined.

[0050]

As described above, according to the first aspect of the present invention, a solder material having a melting point of 100 ° C. or less is used to join an oxide superconductor having a metal coating formed thereon to another conductor. Thus, the metal coating can be prevented from melting into the solder material, and the joining can be performed at a low contact resistivity without being influenced by the skill of the operator.

According to the second invention, the silver content is 2% by weight.
By using Sn-Pb-based solder containing up to 5% by weight for joining oxide superconductors, conductors composed of oxide superconductors and other conductors with low contact resistivity can be obtained without being influenced by the technique of the operator. Can be joined.

Therefore, the method according to the invention is
It is useful for the placement of oxide superconductors in fields such as transportation, high energy, medical and electronics.

[Brief description of drawings]

FIG. 1 is a perspective view showing a process of providing electrodes on an oxide superconductor having silver coating on both ends in an example.

[Explanation of symbols]

 1 Bismuth-based superconductor 2a, 2b Silver coating 4, 4'Copper electrode 5 Solder material

Claims (2)

[Claims] 1. A method of joining a first conductor made of an oxide superconductor to a second conductor through a metal film formed on the surface thereof, wherein a solder having a melting point of 100 ° C. or less is used as a joining material. A method for joining oxide superconductors, which is characterized by being used. 2. A method of joining a first conductor made of an oxide superconductor to a second conductor through a silver coating formed on the surface thereof, wherein the joining material is 2 wt% to 5 wt% of silver. Sn-Pb containing wt%
A method for joining oxide superconductors, characterized in that a system solder is used.