JPH0347749B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application] This invention relates to a method of engaging a lead wire to a thermoelectric element made of a metal silicide, and in particular, the present invention relates to a method of engaging a lead wire to a thermoelectric element made of a metal silicide, and in particular, a method of engaging a lead wire to a thermoelectric element made of a metal silicide, and in particular, a method of engaging a lead wire to a thermoelectric element made of a metal silicide. It relates to a joining method that can connect.

[Prior art and its problems]

A metal silicide thermoelectric element consisting of a PN junction is
Due to its high thermoelectric performance, by adopting a configuration in which multiple pairs are electrically connected, thermoelectric devices such as those placed near the burner of a stove and the generated thermoelectromotive force directly rotate a fan motor can be used. It is expected to have a wide range of applications as a power generator.

However, since the surface of metal silicide is coated with a strong oxide, the soldering technology that uses flux to remove the oxide cannot remove the coating oxide sufficiently. It is not possible to attach electrical connections or output lead wires to the silicide.

In contrast, in the past, for example, Cerasolza (trade name), a lead-tin solder alloy developed by Asahi Glass Co., Ltd. to which several trace elements are added, was used to remove oxides on the surface of metal silicides. A method of directly attaching lead wires has been proposed. According to this method using Cerasolzer, adhesion is achieved through chemical bonding at the adhesion interface, so it has the advantage of not requiring any flux for activation, but it is necessary to eliminate an air layer at the adhesion surface. , for this, the third
A drawback is that a special soldering device is required to combine the ultrasonic vibrator and heater as shown in the figure.

Furthermore, Cerasolzer's main component is basically a composition with a higher content of lead than that of ordinary lead-tin solder alloys, so although it has a melting point of approximately 300°C, which is high for a solder alloy, It still has the disadvantage that its melting point is too low to be used as a thermoelectric element or thermoelectric generator placed nearby.

Furthermore, when attempting to directly solder a metal silicide and a lead wire via a Cerasolzer, there is a problem in that ultrasonic vibration cannot be effectively applied unless the shape of the lead wire is specified. To deal with this, we first form a layer of Cerasolza only on the metal silicide,
After this, attempts were made to attach lead wires on the Cerasolzer layer using ordinary soldering techniques, but this increased the number of man-hours and was strained by the low melting point of ordinary solder alloys, resulting in lead wires being attached to the Cerasolzer layer. This results in the disadvantage that the melting point of the wire connection portion becomes low.

In addition, as a joining technology for connecting lead wires to metal silicides other than soldering technology, there is a method using silver brazing welding using BAg-7 (JIS standard) alloy whose main component is silver; Although bonding was possible by forming another metal film on the surface of the metal silicide, cracking occurred due to the difference in coefficient of thermal expansion between the metal silicide and the alloy, so there was no practical solution.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and includes a metal silicide coated with an oxide.
By providing a bonding method that uses ordinary soldering technology without using special soldering equipment to form a high melting point solder layer with sufficient bonding strength and connect lead wires through this layer, it is possible to The aim is to improve the practicality of thermoelectric elements and thermoelectric generators.

[Structure of the invention]

In order to achieve this object, the present invention coats a boric acid or hydrofluoric acid flux on a metal silicide and heat-fuses a high-temperature solder alloy containing zinc as a main component thereon. A high temperature solder alloy layer is formed directly on the metal silicide oxide film, and a lead wire for electrical connection or output output is connected to the metal silicide through this high temperature solder alloy layer.

Hereinafter, the present invention will be explained in detail based on Examples.

[Embodiments of the invention]

FIG. 1 shows a metal silicide thermoelectric element to which lead wires are connected by the connection method according to the present invention. That is, 1 is, for example, a metal silicide
A metal consisting of a PN junction between FeSi ₂ (iron silicide) doped with Mn to make it P-type Fe _1-X Mn _X Si ₂ and Fe _1-Y Co _Y Si ₂ made N-type by doping Co It is a silicide thermoelectric element. This thermoelectric element 1
A zinc-based solder alloy layer 2 formed by the bonding method according to the present invention is formed on the top surface of both ends of the thermoelectric element 1. or lead wires 3 for mutual electrical connection when a plurality of pairs of thermoelectric elements 1 are connected to form a thermoelectric generator.
One end of the will be buried.

An example of the component ratio of the zinc-based solder alloy used as the zinc-based solder alloy layer of the solder gold layer 2 is shown in FIG. This zinc-based solder alloy containing zinc as a main component is characterized by its melting point of approximately 400°C, which is higher than the approximately 300°C of lead-tin solder alloy.

On the other hand, in soldering technology and brazing technology, removal of surface oxide film of base material and molten metal (solder alloy, brazing material),
It is also necessary to use flux to prevent oxidation during heating, and it is extremely important to select an appropriate flux according to the solder alloy, etc. to be used. The general characteristics that flux should have are: (a) It should have the ability to treat and clean oxides on the surface of the base material.

(b) Be activated within the operating temperature range.

(c) It has the effect of promoting fluidity and spreadability of molten metal.

It is. In order to satisfy these conditions, the optimum base material and flux combinations used in conventional soldering and brazing techniques are listed and shown in FIG. For example, if the base material is copper, a chloride-based flux is suitable for soldering technology, and a boric acid-based or hydrofluoric acid-based flux is suitable for brazing technology. Become.

The lead wires used in thermoelectric elements and thermoelectric generators are generally made of copper, which has good electrical conductivity. In soldering techniques using solder alloys, chloride-based fluxes are selected as the flux. However, the inventor's repeated experiments have shown that soldering techniques using chloride fluxes cannot remove the metal silicide oxide film that is tightly coated on the metal silicide surface. It has not been possible to form a based solder alloy layer on the metal silicide surface, and therefore it has not been possible to attach the lead wire to the metal silicide using soldering techniques.

However, as the inventors repeated experiments, they discovered that using boric acid-based or hydrofluoric acid-based fluxes, which are the fluxes used in silver brazing when the base material is copper, is not as good as normal. We have discovered that it is possible to form a zinc-based solder alloy layer directly on the oxide film on the metal silicide surface using soldering technology. Moreover,
It has also been found that even with these boric acid-based and hydrofluoric acid-based fluxes, the solder connection between the zinc-based solder alloy layer and the lead wire made of copper exhibits sufficient strength and can withstand practical use.

Therefore, the present inventor first coated a boric acid-based or hydrofluoric acid-based flux on the thermoelectric element 1 shown in FIG. The formation of the solder alloy layer 2 and the soldering of the lead wire 3 were achieved by placing one end of the wire and heating it until the flux and high-temperature solder melted.

In other words, if a completely different type of flux is used instead of the combination of base material and flux that is generally known in the field of conventional soldering technology, a special type of flux can be formed on the metal silicide oxide film. They discovered that a zinc-based solder alloy layer with a high melting point can be formed using normal soldering techniques that do not require the use of soldering equipment, and that lead wires can be directly connected to metal silicides through this solder alloy layer. .

FIG. 2 shows another embodiment. This is done on a ceramic substrate 4 which is metallized with monbudden-manganese or tungsten, and then plated with nickel or copper, or on a ceramic substrate 4 with silver paste or silver paste.
The above-mentioned zinc-based high-temperature solder is used on the metallized layer 5 made of fired poradiun paste, nickel paste, or copper paste.
Each end of the set of thermoelectric elements 1 and three ends of the lead wires are separately soldered. In addition, 2
is an alloy layer of high temperature solder.

The procedure for forming the solder alloy layer 2 is as follows: First, a boric acid-based or hydrofluoric acid-based flux is applied to one end of the metal silicide thermoelectric element, three ends of the lead wire, and the metallized layer 5, and then the above-mentioned zinc-based flux is applied. Soldering is performed by heating flux together with high-temperature solder in a burner or heating furnace to a temperature above the melting point of the high-temperature solder. In addition, the solder whose main component is zinc is softer and less prone to cracking than the silver solder type BAg-7 alloy mentioned above, and can withstand high temperatures of over 400°C compared to other solder alloys. Application to thermoelectric elements that receive high heat is extremely preferable.

〔Effect of the invention〕

As described above, according to the present invention, since high-temperature solder containing zinc as the main component is used as the solder alloy,
The thermoelectric element can be heated to a high temperature and a high electromotive force can be efficiently obtained, and the soldering using the above-mentioned high-temperature soldering involves the use of a boric acid-based or hydrofluoric acid-based flux that activates the oxide film of the metal silicide. Since the soldering process is carried out in a single step, it is possible to form a solder layer and attach lead wires of any shape firmly and reliably. is obtained

[Brief explanation of drawings]

FIG. 1 is a perspective view of a thermoelectric element showing one embodiment of the thermoelectric element joining method according to the present invention, and FIG. 2 is a perspective view of a thermoelectric element showing another embodiment. FIG. 3 is a diagram showing a soldering device used in the prior art. FIG. 4 is a diagram showing an example of the component ratio of the zinc-based solder alloy used in the present invention, and FIG.
1 is a diagram showing a combination of a base material and flux used in conventional soldering technology. 1 is a thermoelectric element, 2 is a solder alloy layer, and 3 is a lead wire.

Claims (1)

[Claims] 1. In a method for forming a solder layer on a thermoelectric element in which a solder layer for forming an electrode is formed on a metal silicide thermoelectric element, a boric acid-based or hydrofluoric acid-based flux and zinc as the main components are added to the thermoelectric element. A method for joining thermoelectric elements, characterized in that the solder layer is formed by heating and fusing high-temperature solder.