TWI473282B - Wire having active solder coating and using method thereof - Google Patents

Description

Conductor with active solder coating and method of use thereof

The present invention relates to a solar cell electrode and a method of fabricating the same, and more particularly to a wire having an active solder coating and a method of using the same.

In recent years, due to the gradual shortage of fossil fuels, the development of various renewable alternative energy sources (such as solar cells, fuel cells, and wind power) has gradually received attention. Among them, solar power generation has received the most attention.

Referring to FIG. 1, a cross-sectional view of a conventional solar cell element is disclosed. When the conventional solar cell element is fabricated, a p-type germanium semiconductor substrate 11 is first provided for surface acid roughening, and then Phosphorus or the like forms a n-type diffusion layer 12 of one type of reverse conductivity on the light-receiving side of the p-type germanium semiconductor substrate 11 by thermal diffusion, and forms a p-n junction. Then, an anti-reflection layer 13 and a front electrode 14 are formed on the n-type diffusion layer 12, wherein silicon nitride is formed on the n-type diffusion layer 12 by plasma chemical vapor deposition or the like. As the antireflection layer 13, a silver conductive paste containing silver powder is applied to the antireflection layer 13 by screen printing, followed by baking drying and high temperature sintering to form the front electrode 14. In the high-temperature sintering process, the conductive paste for forming the front electrode 14 may be sintered and penetrated through the anti-reflection layer 13 until electrically contacting the n-type diffusion layer 12.

On the other hand, on the back side of the p-type germanium semiconductor substrate 11, one of the aluminum back surface electrode layers 15 is formed by printing using an aluminum conductive paste containing aluminum powder. Subsequently, the drying and baking process is carried out, followed by sintering under the same high temperature sintering as described above. During the sintering process, the aluminum alloy is transformed from the dry state to the aluminum back electrode layer 15; at the same time, aluminum atoms are diffused into the p-type germanium semiconductor substrate 11, so that the back electrode layer 15 and the p-type germanium semiconductor substrate 11 are A p ⁺ layer 16 containing one of a high concentration of aluminum dopant is formed. This layer is commonly referred to as a back surface field (BSF) layer and contributes to improving the light conversion efficiency of solar cells. Since the aluminum back electrode layer 15 is not weldable (poor wettability). In addition, a silver-aluminum conductive paste can be printed on the back electrode layer 15 by screen printing, and after sintering, a good soldering wire 17 is formed, so that a plurality of solar cells are connected in series to form a module. .

However, the conventional solar cell elements still have the following problems in practical manufacturing. For example, the front electrode layer 14, the back electrode layer 15, and the wires 17 are connected to each other using conductive pastes such as silver, aluminum, and silver-aluminum. And wires, but the material cost of the silver, aluminum and silver-aluminum conductive paste is quite high, accounting for about 10 to 20% of the entire module manufacturing cost. In addition, the conductive paste contains a certain proportion of metal powder, glass powder, and an organic vehicle, such as Japanese Kokai Patent Publication No. 2001-127317 and No. 2004-146521, and Japanese Patent Application No. I339400, which is filed by DuPont. The conductive paste contains glass particles which reduce conductivity and are unfavorable for solderability; and further contains components such as an organic solvent, so that contamination of the solar wafer is caused after sintering, and therefore it is necessary to particularly clean. Furthermore, the use of conductive paste to make wires must be sintered at a high temperature of about 450 to 850 ° C, but this high temperature condition may cause deterioration or failure of materials of other material layers, thereby seriously affecting the yield of the battery. The need for precise control of the high-temperature sintering conditions described above also makes the high-temperature sintering step relatively time consuming and complicated, and affects the overall production capacity of the battery produced per unit time.

Therefore, it is necessary to provide a method for manufacturing solar cell electrodes to solve the problems of the conventional technology.

The main object of the present invention is to provide a wire with an active solder coating and a method of using the same, which uses a lower cost active solder to coat the outer surface of the wire to form a wire with an active solder coating. When a wire is used, if the active solder coating of the wire contacts a preheated substrate (such as a solar cell substrate), it can be soldered and bonded to the substrate to form a circuit pattern, thereby reducing material cost, simplifying and accelerating the circuit process, and enhancing Electrical effect.

A secondary object of the present invention is to provide a wire with an active solder coating and a method of using the same, wherein when applied to a solar cell substrate, the wire can be directly bonded to the solar cell substrate at a relatively low melting point temperature. The aluminum back electrode layer which is not solderable (poor wettability) is connected between the plurality of back electrodes by forming a circuit pattern, so that it is not necessary to make a wire by a screen printing silver-aluminum conductive paste, and The high-temperature sintering process is advantageous in avoiding uneven printing and substrate material degradation due to high-temperature sintering operation, so as to relatively improve the substrate manufacturing yield and enhance the electrical effect.

Another object of the present invention is to provide a wire with an active solder coating and a method of using the same, which has good electrical conductivity in a metal wire material having an active solder coating, can effectively reduce power consumption, and thereby improve solar cell The conversion efficiency is not caused by the problem that the conductive paste contains glass particles which are not electrically conductive and which are not favorable for solderability.

A further object of the present invention is to provide a wire having an active solder coating and a method of using the same, which can be further selected to be thickened by electroless plating or electroplating on a circuit pattern formed by an active solder coating. In addition to increasing the thickness of the circuit pattern, the bonding property, the electrical conductivity, and the ability to prevent oxidation and rust of the circuit pattern combined with the external circuit can also be increased.

For the above purposes, the present invention provides a wire having an active solder coating comprising: a wire having an outer surface; and an active solder coating applied to the outer surface of the wire; wherein the active solder One of the active solders of the coating comprises at least one solder alloy mixed with at least one active ingredient of 6% by weight or less and at least one rare earth element (Re) of from 0.01 to 2% by weight.

Furthermore, the present invention further provides a method of using a wire having an active solder coating, comprising the steps of: providing a substrate; providing a wire having a wire and an active solder coating coated on the wire, Wherein the active solder coating comprises at least one solder alloy mixed with at least one active ingredient of 6% by weight or less and at least one rare earth element (Re) of 0.01 to 2% by weight; firstly preheated at a temperature lower than 450 ° C Heating the wire and the substrate; placing the preheated wire on the preheated substrate, contacting, melting and soldering the active solder coating on the preheated substrate; and cooling and solidifying An active solder of the active solder coating of the wire to form a circuit pattern by the wire.

In an embodiment of the invention, the material of the wire is selected from the group consisting of a silver-based alloy, a copper-based alloy, an aluminum-based alloy, a nickel-based alloy, a gold-based alloy, or a mixed alloy thereof.

In an embodiment of the invention, the solder alloy is selected from the group consisting of a tin based alloy, a bismuth based alloy, or an indium based alloy.

In an embodiment of the present invention, the tin-based alloy, the bismuth-based alloy or the indium-based alloy is blended with at least one active ingredient of 6 wt% or less, for example, selected from titanium (Ti) containing less than 4 wt%, vanadium ( V), magnesium (Mg), lithium (Li), zirconium (Zr), hafnium (Hf) or a mixture thereof.

In an embodiment of the invention, the rare earth element is selected from the group consisting of lanthanum (Sc), lanthanum (Y) or "lanthanide", wherein "lanthanide" comprises: lanthanum (La), lanthanum (Ce) ), 鐠 (Pr), 钕 (Nd), 钜 (Pm), 钐 (Sm), 铕 (Eu), 釓 (Gd), 鋱 (Td), 镝 (Dy), 鈥 (Ho), 铒 (Er ), 銩 (Tm), 镱 (Yb) or 鑥 (Lu).

In one embodiment of the invention, in the step of placing the wire on the substrate, the active solder coating is contacted, melted and solder bonded to the substrate by the aid of ultrasonic waves.

In an embodiment of the invention, after the circuit pattern is formed, the method further comprises: performing electroless plating or electroplating on the circuit pattern selection to increase the thickness of the circuit pattern.

In an embodiment of the invention, the metal used for electroless plating or electroplating is copper, silver, nickel, gold or a composite layer thereof.

In one embodiment of the invention, the active solder coating has a thickness between 10 and 200 microns (um).

In an embodiment of the invention, the substrate is selected from the group consisting of a solar cell, a light emitting diode (LED), a capacitive element, an oscillator element, a semiconductor wafer, a semiconductor substrate of other active or passive components, a metal oxide substrate, and a fuel cell. Electrode plate or ceramic substrate.

In an embodiment of the invention, the substrate selects a substrate of a solar cell, wherein the solar cell substrate has a back surface, and the wire forms the circuit pattern on the back surface to electrically connect the plurality of back electrodes.

In an embodiment of the invention, the substrate and the circuit pattern form a stacked structure with a copper cladding layer, and the stacked structure may be further stacked on each other with another identical stacked structure.

The above and other objects, features and advantages of the present invention will become more <RTIgt; Furthermore, the directional terms mentioned in the present invention, such as "upper", "lower", "before", "after", "left", "right", "inside", "outside" or "side", etc. Just refer to the direction of the additional schema. Therefore, the directional terminology used is for the purpose of illustration and understanding of the invention.

Referring to FIGS. 2A-2D, there is shown a schematic flow chart of a method for using a conductive solder coated wire according to a preferred embodiment of the present invention, wherein the method mainly comprises the steps of: providing a substrate 2; providing a wire 3, It has a wire 31 and an active solder coating 32 coated on the wire 31, wherein the active solder coating 32 comprises at least one solder alloy and is blended with at least one active ingredient of 6% by weight or less and 0.01 to 2% by weight of at least one rare earth element (Re); preheating the substrate 2 at a temperature lower than 450 ° C; and then placing the preheated wire 3 on the preheated substrate 2 to make the activity The solder coating 32 is contacted, melted and soldered to the preheated substrate 2; and the active solder of the active solder coating 32 of the wire 3 is cooled to form a circuit pattern 3 by the wire 3.

Referring to FIG. 2A, a preferred embodiment of the present invention uses a reactive solder to form a solar cell electrode. First, a substrate 2 is provided. In this step, the substrate 2 can be selected from a solar cell, a light emitting diode (LED), a capacitive element, an oscillator element, a semiconductor wafer, a semiconductor substrate of other active or passive components, a metal oxide substrate, and a fuel cell electrode. Plate or ceramic substrate. In this embodiment, the substrate 2 is exemplified by a solar cell substrate, for example, a solar cell (for example, polycrystalline germanium, single crystal germanium or amorphous germanium) or a compound solar cell (for example, III-V arsenic). a wafer type or film type substrate of a gallium, a II-VI group of cadmium telluride CdTe, a cadmium sulfide CdS and a multicomponent compound of copper indium selenide CuInSe2 or a copper indium gallium selenide CIGS, or an organic solar cell, wherein the substrate 2 is selected from the group consisting of In the case of a wafer-type substrate of a solar cell, the substrate 2 may optionally include a p-type germanium semiconductor substrate 21, but the invention is not limited thereto.

As shown in FIG. 2A, in an embodiment, when the substrate 2 includes the p-type germanium semiconductor substrate 21, the front side of the p-type germanium semiconductor substrate 21 may be pre-formed in an n-type from the inside to the outside. The diffusion layer 22, an anti-reflection layer 23 and a plurality of front electrodes 24. Further, on the back side of the p-type germanium semiconductor substrate 21, an aluminum back electrode layer 25 and a p ⁺ layer 26 are sequentially formed from the outside. The structure of the above-mentioned substrate 2 is similar to that of the conventional solar cell element of Fig. 1, and is only one embodiment of the present invention, so that the same portions as the prior art will not be described in detail herein.

Referring to FIG. 2B, a preferred embodiment of the present invention is a method for manufacturing a solar cell electrode by using an active solder. Next, a wire 3 having a wire 31 and an active solder coating coated on the wire 31 is provided. Layer 32, wherein the active solder coating 32 comprises at least one solder alloy mixed with at least one active ingredient of 6% by weight or less and at least one rare earth element (Re) of from 0.01 to 2% by weight. In this step, the active solder of the active solder coating 32 may initially be in the form of a linear solid electrode, a powdered solder powder or a cream solder, and the active solder is melted at a melting point lower than 450 ° C during coating. Melting, the wire 31 is immersed in the molten active solder, or may be applied to the outer surface of the wire 31 by brushing; or the active solder may be coated on the outer surface of the wire 31 by extrusion. Or the active solder is electroplated on the outer surface of the wire 31, or the active solder may be plated on the outer surface of the wire 31 by a physical vapor deposition (PVD) method, wherein the active solder coating The coating thickness of 32 and the diameter or cross-sectional shape of the wire 31 are designed according to actual substrate requirements. For example, in the present embodiment, the wire 31 is a wire-shaped body having a flat strip shape, and the thickness of the active solder coating layer 32 is between 10 and 200 micrometers (um), and the diameter of the wire 31 is at least larger than the diameter. The thickness of the active solder coating 32.

Further, the wire 31 alloy used in the present invention is selected from the group consisting of a silver-based alloy, a copper-based alloy, an aluminum-based alloy, a nickel-based alloy, a gold-based alloy, or a mixed alloy thereof.

Further, the solder alloy used in the present invention is selected from the group consisting of a tin-based alloy, an indium-based alloy, a bismuth-based alloy, other solder alloys, or a mixture thereof. The tin-based alloy, bismuth-based alloy or indium-based alloy is blended with at least one active ingredient of 6% by weight or less, for example, selected from titanium (Ti), vanadium containing 0.1 to 6.0, 0.1 to 5.0 or 0.1 to 4.0% by weight. (V), magnesium (Mg), lithium (Li), zirconium (Zr), hydrazine (Hf) or a mixture thereof. Meanwhile, the tin-based alloy, the niobium-based alloy or the indium-based alloy is also blended with 0.01 to 2.0, 0.01 to 1.0 or 0.01 to 0.5% by weight of at least one rare earth element (Re). For example, the rare earth element is selected from the group consisting of lanthanum (Sc), lanthanum (Y) or "lanthanide", wherein "lanthanide" further comprises: lanthanum (La), cerium (Ce), strontium (Pr) , Nd, Pm, Sm, Eu, Gd, Td, Dy, Ho, Er, Tm , Yb or Lu, in the use of the industry, the rare earth elements usually exist in the form of a mixture, and the common rare earth element mixture is, for example,: lanthanum (La), cerium (Ce), lanthanum ( Pr), niobium (Nd) or niobium (Sm) and a very small amount of iron (Fe), phosphorus (P), sulfur (S) or antimony (Si).

Referring to FIG. 2C, a preferred embodiment of the present invention uses a reactive solder to form a solar cell electrode. The method further comprises: preheating the substrate 2 at a temperature below 450 °C. In this step, according to the actual composition ratio of the active solder, the predetermined melting point temperature range of the active solder can be maintained substantially at a relatively low heating temperature lower than 450 ° C, for example, between 100 ° C and 450 ° C, Between 150 ° C and 400 ° C or between 200 ° C and 350 ° C, but is not limited thereto. In the present invention, before the wire 3 is solder bonded to the substrate 2, the substrate 2 is preheated so that the back surface (or front surface) of the substrate 2 has a melting point lower than or equal to or higher than that of the active solder. It is worth noting that the heating temperature is much lower than the conventional conventional screen printing sintering method, such as the high temperature sintering temperature of the front electrode 24 and/or the wire 3' and/or the back electrode 25 of the substrate 2 (about 450 to 850 ° C). Therefore, the present embodiment is a relatively low heating temperature, so that no deterioration of any material of the substrate is caused. In addition, the problem of lowering the conductivity does not occur. For example, in the conductive paste of silver, aluminum and silver-aluminum which are generally screen printed, the conversion efficiency of the solar cell is lowered due to the absence of conductive glass particles.

Referring to FIG. 2C, in a preferred embodiment of the present invention, a method for manufacturing a solar cell electrode by using an active solder is followed by: placing the preheated wire 3 on the preheated substrate 2 to make the activity. The solder coating 32 is contacted, melted and soldered to the preheated substrate 2 to form a back conductor 3'. In this step, the present invention places the wire 3 on the back surface of the substrate 2 and between the plurality of back electrodes 25. In more detail, the wire 3 is pressed onto the back surface of the substrate 2 by using a tool 4 (for example, a pressing bar), so that the active solder coating 32 is contacted, melted and soldered to the back surface of the substrate 2, Thus, it becomes a back conductor 3', wherein the back conductor 3' comprises a wire 31' and an active solder coating 32', and the active solder coating 32' is melted and soldered to the substrate 2. This combination process can also be referred to simply as a wire bonding operation. The front electrode 24 is implemented in the same manner as described above, and thus the same portions as the prior art will not be described in detail herein. In addition, during the above-mentioned wire bonding operation, the present invention preferably also selects an active solder applied to the active solder coating 32 of the wire 3 via the tool 4 to activate a reaction between the active solder and the substrate 2. The bonding layer (not shown), wherein the frequency of the ultrasonic wave and the processing time are adjusted according to the type of the active solder and the required blade thickness, and the present invention does not limit parameters such as frequency and processing time. When the energy of the ultrasonic wave is applied to the active solder, the wave energy of the ultrasonic wave enters the active solder, and the surface oxide film of the molten active solder can be broken by the agitation of the ultrasonic wave to expose the metal solder of the active solder and The active ingredient promotes the reaction between the active component of the molten active solder and the substrate 2 to form a reactive bonding layer; in addition, the ultrasonic wave can also impart solidity to the substrate 2 of the high hardness intermetallic compound particles in the active solder. The surface provides a frictional cleaning effect that facilitates removal of surface contamination of the substrate 2 from the passivation layer. Furthermore, the ultrasonic wave can also impart additional kinetic energy to the active solder so as to penetrate into the dead holes of the micro-holes of the substrate 2, so that the active solder can be directly and firmly bonded to the cleaned substrate 2 after subsequent cooling and solidification. Solid surface. In the ultrasonic assisted bonding process of the present embodiment, the substrate 2 and the preheating temperature of the lead 3 may be soldered to the substrate 2 by ultrasonic energy below the melting point of the active solder.

Referring to FIG. 2D, a method for fabricating a solar cell electrode with active solder according to a preferred embodiment of the present invention is followed by: cooling and curing the active solder of the active solder coating 32 of the backside conductor 3' to 3' forms a circuit pattern. After the wire bonding operation is completed, the substrate 2 is subsequently cooled to cure the active solder, and the back surface wire 3' is firmly bonded to the back surface of the substrate 2 to form a circuit pattern, which may be vertically or horizontally arranged or Other arrangements. Furthermore, after forming the circuit pattern, the present invention optionally further includes the following processing steps: electroless plating or electroplating is selected to form a protective layer (not shown) for increasing the thickness of the circuit pattern. . The metal used in the electroless plating or electroplating process is preferably copper, nickel, gold, silver, tin or a composite layer thereof, and the electroless plating or electroplating process can form a metal plating layer as a protective layer, and the protective layer is beneficial to increase the circuit. The bonding property of the pattern combined with the external wires, the electrical conductivity and the ability to prevent oxidation and rust. Preferably, the thickness of the circuit pattern is finally between 10 and 200 micrometers (um) after the thickness is increased by the electroless plating or electroplating process.

In another embodiment of the present invention, the substrate 2 may be a multi-layer circuit substrate, wherein the wire 3 is soldered and bonded to the outside of the substrate 2 to form a circuit pattern substrate, and is formed by stacking another circuit pattern substrate. A stacked structure (not shown), wherein the stacked structure is further stacked on top of another stacked structure, and two or more stacked structures are stacked in the same manner to form the multilayer circuit substrate.

As described above, the use of silver, aluminum, and silver-aluminum conductive pastes for the preparation of the front electrode, the back electrode layer, and the wire must be performed at a temperature of about 450 to 850 ° C in comparison with the conventional solar cell element of FIG. 1 . Sintering may cause material deterioration, failure, and the conductive paste contains non-conductive glass particles, resulting in high resistance, low conversion efficiency, etc. The invention of FIGS. 2A to 2D uses a lower cost active solder. Coating the outer surface of the wire 31 to form the wire 3 having the active solder coating 32. When the wire 3 is used, if the active solder coating 32 of the wire 3 contacts the preheated substrate 2 (such as a solar cell substrate), The circuit pattern can be formed by soldering on the substrate 2, thereby reducing the material cost, simplifying and accelerating the circuit process, and reducing the resistance coefficient of the wire, thereby increasing the conversion efficiency.

Furthermore, when the present invention is applied to a solar cell substrate, the wire 3 can be soldered to the back electrode layer of the solar cell substrate at a relatively low melting point temperature to form a circuit pattern to be connected between the plurality of back electrodes 25. Therefore, it is not necessary to form the wire by sintering the silver-aluminum conductive paste at a high temperature, thereby facilitating the deterioration of the substrate material due to the high-temperature sintering operation, so as to relatively improve the substrate manufacturing yield.

In addition, the present invention can further selectively perform thickening treatment such as electroless plating or electroplating on the circuit pattern formed by the wire 3 having the active solder coating 32, which can increase the circuit pattern in addition to the thickness of the circuit pattern. Bonding properties, electrical conductivity, and ability to prevent oxidation and rust combined with external circuits.

The present invention has been disclosed in its preferred embodiments, and is not intended to limit the invention, and the present invention may be modified and modified without departing from the spirit and scope of the invention. The scope of protection is subject to the definition of the scope of the patent application.

11. . . P-type germanium semiconductor substrate

12. . . N-type diffusion layer

13. . . Antireflection layer

14. . . Front electrode

15. . . Back electrode layer

16. . . Aluminum-bismuth alloy layer

17. . . p ⁺ layer 17

18. . . wire

2. . . Solar cell substrate

twenty one. . . P-type germanium semiconductor substrate

twenty two. . . N-type diffusion layer

twenty three. . . Antireflection layer

twenty four. . . Front electrode

25. . . Back electrode

26. . . p ⁺ layer

3. . . wire

3’. . . Back wire

31. . . Wire

31’. . . Wire

32. . . Active solder coating

32. . . Active solder coating

4. . . tool

Figure 1: A cross-sectional view of a conventional solar cell element.

2A, 2B, 2C, and 2D: A schematic flow diagram of a method of using a wire having an active solder coating in accordance with a preferred embodiment of the present invention.

twenty one. . . P-type germanium semiconductor substrate

25. . . Back electrode

26. . . p ⁺ layer

3. . . wire

3’. . . Back wire

31’. . . Wire

32. . . Active solder coating

4. . . tool

Claims (9)

A method of using a wire with an active solder coating, comprising: providing a substrate; providing a wire having a wire and an active solder coating coated on the wire, wherein the active solder coating comprises at least one a solder alloy mixed with at least one active ingredient of 4% by weight or less and at least one rare earth element of 0.01 to 2% by weight, wherein the solder alloy is selected from a tin-based alloy, a bismuth-based alloy or an indium-based alloy, the active component Selecting from titanium, vanadium, magnesium, lithium, zirconium, hafnium or a mixture thereof; preheating the substrate at a temperature lower than 450 ° C; and placing the preheated wire on the preheated substrate, An active solder coating is contacted, melted and soldered to the preheated substrate; and the active solder of the active solder coating that cures the wire is cooled to form a circuit pattern by the wire. The method of using a wire having an active solder coating according to claim 1, wherein in the step of placing the wire on the substrate, the active solder coating is contacted and melted by the aid of ultrasonic waves. And soldering is bonded to the substrate. The method of using the active solder coating wire according to claim 1, wherein after forming the circuit pattern, the method further comprises: electroless plating or plating to increase the thickness of the circuit pattern. . An active solder coating as described in claim 1 The method for using a wire, wherein the rare earth element is selected from the group consisting of a lanthanum element, a lanthanum element or a lanthanoid element, wherein the lanthanoid element comprises: lanthanum, cerium, lanthanum, cerium, lanthanum, cerium, lanthanum, cerium, lanthanum, cerium,鈥, 铒, 銩, 镱 or 鑥. The wire material of claim 1, wherein the wire alloy is selected from the group consisting of a silver-based alloy, a copper-based alloy, an aluminum-based alloy, a nickel-based alloy, a gold-based alloy, or a mixed alloy thereof. The method of using a wire with an active solder coating according to claim 1, wherein the substrate is selected from the group consisting of a solar cell, a light emitting diode, a capacitor element, an oscillator element, or a semiconductor substrate of a semiconductor wafer, and a fuel cell electrode. A plate, a metal oxide substrate or a ceramic substrate. The method of using a conductive solder coated wire according to claim 6, wherein the substrate selects a substrate of a solar cell, wherein the solar cell substrate has a back surface, the wire forms the circuit pattern on the back surface , electrically connected to several back electrodes. The method for using a conductive solder coated wire according to claim 1, wherein the substrate and the circuit pattern form a stacked structure with another substrate having a circuit pattern, and the stacked structure can be identical to another The stacked structures are further stacked on each other. A wire having an active solder coating, comprising: a wire having an outer surface; and an active solder coating coated on an outer surface of the wire; wherein one of the active solder coatings comprises at least one active solder weld a tin alloy mixed with at least one active ingredient of 4% by weight or less and at least one rare earth element of 0.01 to 2% by weight, wherein the solder alloy is selected from the group consisting of a tin-based alloy, a bismuth-based alloy or an indium-based alloy, the active ingredient It is selected from titanium, vanadium, magnesium, lithium, zirconium, hafnium or a mixture thereof.