CLAD WIRE AND METHOD FOR PRODUCING CLAD WIRES

Abstract

The invention relates to a clad wire (1) for producing test needles or sliding contacts having a wire core (2) made of rhodium or a rhodium-based alloy, an inner cladding (3) made of copper or silver or aluminum or a copper-based alloy or a silver-based alloy or an aluminum-based alloy, wherein the inner cladding (3) covers or completely encloses the wire core (2) on at least two opposite sides, an adhesion-promoting layer (5) made of gold or a gold-based alloy, which is arranged between the wire core (2) and the inner cladding (3), and an outer cladding (4) made of a metal or a metal alloy having a greater hardness than the material of the inner cladding (3), wherein the outer cladding (4) encloses the inner cladding (3). The invention also relates to a method for producing a clad wire and to a test needle having at least one clad wire (1) or produced from a clad wire (1) and a test needle array having a plurality of test needles spaced apart from one another and a sliding contact having a plurality of clad wires (1) or produced from a clad wire (1).

Claims

1. A clad wire for producing a test needle or a sliding contact, the clad wire comprising: a wire core made of rhodium or a rhodium-based alloy, an inner cladding made of copper or silver or aluminum or a copper-based alloy or a silver-based alloy or an aluminum-based alloy, wherein the inner cladding covers the wire core on at least two opposite sides or completely encloses the wire core, an adhesion-promoting layer made of gold or a gold-based alloy, which is arranged between the wire core and the inner cladding, and an outer cladding made of a metal or a metal alloy having a greater hardness than the material of the inner cladding, wherein the outer cladding encloses the inner cladding.

2. The clad wire of claim 1, wherein the volume of the wire core is at least as large as the volume of the inner cladding, and/or the wire core and the inner cladding have a thickness or a layer thickness at least twice as large as the adhesion-promoting layer.

3. The clad wire of claim 1, further comprising: a diffusion protection layer arranged as a diffusion barrier between the inner cladding and the outer cladding.

4. The clad wire of claim 3, wherein the inner cladding has a layer thickness at least twice as large as the diffusion protection layer.

5. The clad wire of claim 1, wherein the outer cladding consists of rhodium, a rhodium-based alloy, a copper-tin-zinc alloy, a palladium-nickel alloy or a gold-based alloy.

6. The clad wire of claim 1, wherein the clad wire at room temperature has a modulus of elasticity (mE) of at least 150 GPa, and/or the clad wire at room temperature has a 0.2% offset yield strength Rp.sub.0.2 of at least 1800 MPa, and/or the clad wire at room temperature has an electrical conductivity of at least 40% IACS.

7. The clad wire of claim 1, wherein the clad wire has a diameter or a thickness of at most 200 μm.

8. The clad wire of claim 1, wherein the wire core has a diameter or a thickness of between 9 μm and 100 μm, and/or the inner cladding has a layer thickness of between 1 μm and 20 μm, and/or the outer cladding has a layer thickness of between 0.5 μm and 5 μm, and/or the adhesion-promoting layer has a layer thickness of between 100 nm and 1000 nm.

9. The clad wire of claim 1, wherein the adhesion-promoting layer, the inner cladding, the outer cladding and optionally the diffusion protection layer are galvanic coatings.

10. The clad wire of claim 1, wherein the wire core is work-hardened, and/or the wire core is a coated or uncoated strip.

11. A method for producing a clad wire comprising the following chronological steps: A) providing a wire core made of rhodium or a rhodium-based alloy, B) coating the wire core with an adhesion-promoting layer made of gold or a gold-based alloy, C) coating the wire core, coated with the adhesion-promoting layer, with an inner cladding of copper or silver or aluminum or a copper-based alloy or a silver-based alloy or an aluminum-based alloy, and D) coating the wire core, coated with the adhesion-promoting layer and the inner cladding, with an outer cladding made of a metal or a metal alloy with a greater hardness than the material of the inner cladding.

12. The method of claim 11, wherein the wire core is shaped strip-like and a step C1) takes place between steps C) and D), step C1) comprising: cutting the coated strip-like wire core perpendicular to a longitudinal axis of the strip-like wire core into a plurality of coated wire cores, in which the wire cores are coated on two opposite sides by the adhesion-promoting layer and the inner cladding, wherein in step D) each of the coated wire cores is coated with the outer cladding.

13. The method of claim 11 further comprising a step C2) carried out between steps C) and D), step C2) comprising: coating of the wire core, coated with the adhesion-promoting layer and the inner cladding, with a diffusion protection layer, wherein in step D) the wire core, coated with the adhesion-promoting layer, the inner cladding and the diffusion protection layer, is coated with the outer cladding.

14. The method of claim 11, wherein the coatings according to steps B), C) and D) are applied using a galvanic method and/or are applied using a physical method.

15. A test needle comprising at least one clad wire according to claim 1.

16. A test needle array having a plurality of test needles according to claim 15 spaced apart from one another.

17. A sliding contact comprising a plurality of clad wires according to claim 1.

18. The sliding contact of claim 17, wherein the plurality of clad wires are in the form of a wire bundle.

19. The test needle of claim 15, wherein the test needle is bent perpendicular to a cylinder axis of the at least one clad wire or perpendicular to a longitudinal axis of the at least one clad wire.

Description

[0083] Exemplary embodiments of the invention are explained below on the basis of twelve figures without, however, limiting the invention. Therein:

[0084] FIG. 1: shows a schematic perspective cross-sectional view of a clad wire according to the invention;

[0085] FIG. 2: shows an image of a cross section through a clad wire according to the invention by a scanning electron microscope (SEM);

[0086] FIG. 3: shows a further image of a cross section through a clad wire according to the invention by an SEM;

[0087] FIG. 4: shows a further image of a cross section through a clad wire according to the invention by an SEM;

[0088] FIG. 5: shows a further image of a cross section through a clad wire according to the invention by an SEM;

[0089] FIG. 6: shows a force-elongation graph of a clad wire according to the invention;

[0090] FIG. 7: shows an image of a cross section through a clad wire according to the invention by an SEM with high magnification;

[0091] FIG. 8: shows a further image of a cross section through a clad wire according to the invention by an SEM with a high magnification;

[0092] FIG. 9: shows an image of a cross section through a clad wire according to the invention by an SEM with high magnification and with a crater from a hardness measurement;

[0093] FIG. 10: shows a schematic perspective cross-sectional view of an intermediate product for manufacturing a strip-like clad wire according to the invention from a coated strip;

[0094] FIG. 11: shows a schematic perspective cross-sectional view of a strip-like clad wire according to the invention produced from the intermediate product according to FIG. 10; and

[0095] FIG. 12: shows the sequence of a method according to the invention in the form of a flow chart.

[0096] FIG. 1 shows a schematic perspective cross-sectional view of a clad wire 1 according to the invention with a cylindrically symmetrical structure. The clad wire 1 consists of a wire core 2 made of rhodium or a rhodium-based alloy, an inner cladding 3 made of copper or silver or aluminum or a copper-based alloy or a silver-based alloy or an aluminum-based alloy, an outer cladding 4 made of a metal or a metal alloy, and an adhesion-promoting layer 5 made of gold or a gold-based alloy. Optionally, a metallic diffusion protection layer 6 may be provided.

[0097] The wire core 2 extends in the innermost part of the clad wire 1. The inner cladding 3 encloses the wire core 2. The outer cladding 4 encloses the inner cladding 3 and consists of a metal or a metal alloy having a greater hardness than the material of the inner cladding 3, such as, for example, rhodium, a rhodium-based alloy, a copper-tin-zinc alloy, a palladium-nickel alloy or a gold-based alloy, wherein the gold-based alloy is preferably a gold-cobalt alloy, a gold-iron alloy or a gold-nickel alloy. The adhesion-promoting layer 5 is arranged between the wire core 2 and the inner cladding 3. The diffusion protection layer 6 can be arranged between the inner cladding 3 and the outer cladding 4 and prevent or impede the migration of atoms and ions from the outer cladding 4 into the inner cladding 3 so that they do not impair the electrical conductivity of the inner cladding 3.

[0098] The wire core 2 may have a diameter of about 40 μm, the inner cladding 3 may have a layer thickness of about 10 μm, and the outer cladding 4 may have a layer thickness of about 2 μm. The adhesion-promoting layer 5 and the diffusion protection layer 6 can be thinner than 1 μm.

[0099] In order to produce the clad wire 1, the wire core 2 can first be obtained from a melt by solidifying and then subsequently drawing the wire core 2 as a wire. The wire core 2 is preferably work-hardened in order to improve the mechanical properties of the wire core 2. The surface of the wire core 2 can then be cleaned before the following coating processes. However, the wire core 2 can also be produced using another method and be provided for further processing.

[0100] Subsequently, the adhesion-promoting layer 5 can be applied galvanically to the wire core 2. The inner cladding 3 can then be applied galvanically to the wire core 2 coated with the adhesion-promoting layer 5. This structure can then be galvanically coated with the diffusion protection layer 6. Finally, the outer cladding 4 can be applied galvanically to the diffusion protection layer 6 or directly to the inner cladding 3.

[0101] The clad wire 1 thus produced can optionally be aftertreated with a heat treatment. It is possible to wind the clad wire 1 as a long endless wire (at least 10 m) on a spool (not shown) to simplify later processing. Short pieces can be cut from the clad wire 1, which are then joined together as bundles in order to provide a wire bundle as a sliding contact. Alternatively, a plurality of wire pieces of the clad wire 1 can also be arranged in a manner spaced apart from one another as arrays in order to form test needle arrays.

[0102] FIGS. 2 to 5 and 7 to 9 show images of cross sections of clad wires 11 according to the invention which were taken by a scanning electron microscope (SEM). The contrast arises in FIGS. 2 to 5 by backscattered electrons and in FIGS. 7 to 9 by secondary electrons.

[0103] The clad wires 11 have a wire core 12 made of a rhodium-zirconium alloy comprising 20 wt % of zirconium and 80 wt % of rhodium including common impurities. This alloy is also referred to as RhZr0.2. The rhodium-zirconium alloy is work-hardened by repeated forming. Because of the zirconium in the rhodium, the wire core 12 can be drawn particularly finely. The high tensile strength allows relatively thick copper layers to be applied to the wire core 12. Pure rhodium becomes brittle and can break at a diameter of between 80 μm and 100 μm or less.

[0104] An inner cladding 13 therefore consists of copper and an outer cladding 14 consists of a palladium-nickel alloy. The inner cladding 13 made of copper increases the electrical conductivity of the clad wire and, at the same time, improves the resilient properties of the clad wire 11. The outer cladding 14 is used to protect the copper of the inner cladding 13 from mechanical loads and wear effects. For this purpose, the outer cladding 14 is harder than the inner cladding 13. An adhesion-promoting layer 15 of gold is arranged between the wire core 12 and the inner cladding 13 in order to improve the mechanical connection of the inner cladding 13 to the wire core 12. The adhesion-promoting layer 15 thus improves the service life of the clad wire 11. Detachment of the copper from the rhodium-zirconium alloy of the wire core 12 can thus be prevented by the adhesion-promoting layer 15. A diffusion protection layer 16, which prevents palladium from diffusing into the copper of the inner cladding 13, can be provided between the inner cladding 13 and the outer cladding 14. This increases the service life of the clad wire 11 and the electrical conductivity of the clad wire 11 remains more constant over time. The diffusion protection layer 16 may also consist of a plurality of different diffusion barriers.

[0105] The wire cores 12 have a diameter of between 44 μm and 47 μm. The inner claddings 13 have a layer thickness of between 2.5 μm and 10 μm. The outer claddings 14 have a layer thickness of between 1.4 μm and 2 μm. The adhesion-promoting layers 15 have a layer thickness of between 420 nm and 470 nm. The relatively thick copper layer as an inner cladding 13 results in a strong increase in the electrical conductivity of the clad wire 11.

[0106] FIG. 6 shows a force-elongation graph of such a clad wire 11. The clad wire 11 withstands a force of about 1700 N per mm.sup.2. The clad wire 11 had a diameter of 55 μm. A biasing force of 30 N/mm.sup.2 was used. The speed in the flow region is 0.00025 s.sup.−1.

[0107] The modulus of elasticity m.sub.E, the 0.2% offset yield strength Rp.sub.0.2 and the tensile strength R.sub.m are determined by means of a Zwick Z250 tensile testing machine. The tensile test was carried out on a clad wire with a wire diameter of 55 μm and relates thereto. The test speed with respect to the modulus of elasticity m.sub.E and the yield strength Rp.sub.0.2 was 1 mm/min, while the test speed for the tensile strength R.sub.m was 10 mm/min.

[0108] The electrical conductivity was determined with a 4-pole measurement of the voltage drop across the test specimen for a defined length with a Burster Resistomat 2316.

[0109] The measurement is carried out using a clad wire with a wire length of between 0.06 m and 0.07 m, a diameter of 52 μm and a measurement current of 10 mA.

[0110] The following mechanical properties for the clad wire 11 according to the invention arise from the experiments: m.sub.E 215.0 kN/mm.sup.2, Rei 2240 MPa, Rp.sub.0.2 2171.8 N/mm.sup.2, R.sub.m 2368.3 N/mm.sup.2, F.sub.m 5.6 N, A 100 mm 0.53%. For the clad wire, 2171.8 MPa/215 GPa arises for the quotient Rp.sub.0.2/m.sub.E, which corresponds to a ratio of 0.0101. In comparison, the quotient Rp.sub.0.2/m.sub.E for pure rhodium is 2300 MPa/370 GPa, which corresponds to a ratio of only 0.0062.

[0111] The greater the quotient Rp.sub.0.2/m.sub.E, the better the resilient properties in the elastic region.

[0112] Further experiments have shown that the resilient properties (quantifiable by the quotient Rp.sub.0.2/m.sub.E) of the clad wire 11 could be drastically improved (68% improvement compared to a wire of rhodium). Furthermore, the electrical conductivity (EC) could be increased by 79% in comparison with a wire made of rhodium.

TABLE-US-00001 Rhodium Clad wire Modulus of elasticity m.sub.E 370 GPa 215 GPa EC 32% IACS 57.5% IACS Rp.sub.0.2 2300 MPa 2171.8 MPa Rp.sub.0.2/m.sub.E 0.006 0.010

[0113] Table 1: Comparison of physical properties of the clad wire according to the invention in comparison with a wire made of rhodium

[0114] The electrical conductivity (EC) is measured by means of 4-pole measurement for measuring the voltage drop across a test body of the rhodium wire or clad wire for a defined length. A BURSTER® Resistomat 2316 was used for measurement. The measurement is carried out at room temperature (22° C.).

[0115] A resistance of 1.00 ohm resulted for a length of 70 mm, a diameter of 52 μm and a cross-sectional area of 0.0021 mm.sup.2 of a clad wire according to FIGS. 2 to 5 and 7 to 9. This results in a specific electrical resistance R.sub.spec of 0.030 ohm mm.sup.2/m and an electrical conductivity of 32.90 m/(ohm mm.sup.2) or 56.7% IACS. A resistance of 0.70 ohms resulted for a length of 50 mm, a diameter of 52 μm and a cross-sectional area of 0.0021 mm.sup.2 of a clad wire according to FIGS. 2 to 5 and 7 to 9. This results in a specific electrical resistance R.sub.spec of 0.030 ohm mm.sup.2/m and an electrical conductivity of 33.73 m/(ohm mm.sup.2) or 58.2% IACS. 100% IACS corresponds to 58 m/(ohm mm.sup.2).

[0116] Alternatively to the clad wire 1 shown in FIG. 1, a strip-like wire core 22 can also be used to produce a clad wire 21, as shown in FIG. 11.

[0117] FIG. 10 shows a schematic perspective cross-sectional view of an intermediate product 20 for producing a strip-like clad wire 21 according to the invention. FIGS. 10 and 11 show the manufacture of a strip-like clad wire 21 via the intermediate product 20 shown in FIG. 10. FIG. 11 shows a schematic perspective cross-sectional view of the clad wire 21 according to the invention. The clad wire 21 consists of a wire core 22 made of rhodium or a rhodium-based alloy, an inner cladding 23 made of copper or silver or aluminum or a copper-based alloy or a silver-based alloy or an aluminum-based alloy, an outer cladding 24 made of a metal or a metal alloy, and an adhesion-promoting layer 25 made of gold or a gold-based alloy. Optionally, a metallic diffusion protection layer 26 may be provided between the inner cladding 23 and the outer cladding 24.

[0118] The strip-like wire core 22 initially has a rectangular cross section, as shown in FIG. 10. This strip-like wire core 22 is coated with the adhesion-promoting layer 25 and the inner cladding 23. Subsequently, the thus coated wire core 22, i.e. the intermediate product 20, is cut perpendicular to a longitudinal direction of the strip-like wire core 22 (into the image plane in FIG. 10) into many pieces. One of the sectional planes is indicated in FIG. 10 by a dashed line as a sectional plane 28. The cut pieces of the coated wire core 22 are coated on two opposite sides with the adhesion-promoting layer 25 and the inner cladding 23. These pieces are then galvanically coated with the diffusion protection layer 26 and then with the outer cladding 24 or coated only with the outer cladding 24. As a result, the clad wire 21 is obtained as shown in FIG. 11.

[0119] The wire core 22 extends in the innermost part of the clad wire 21. The inner cladding 23 covers the wire core 22 on two opposite sides. The outer cladding 24 encloses the inner cladding 23 and the wire core 22 and consists of a metal or a metal alloy having a greater hardness than the material of the inner cladding 23, such as, for example, rhodium, a rhodium-based alloy, a copper-tin-zinc alloy, a palladium-nickel alloy or a gold-based alloy, wherein the gold-based alloy preferably is a gold-cobalt alloy, a gold-iron alloy or a gold-nickel alloy. The adhesion-promoting layer 25 is arranged between the wire core 22 and the inner cladding 23. The diffusion protection layer 26 may be arranged between the outer cladding 24 and the inner cladding 23 and also between the outer cladding 24 and the wire core 22 and prevent or impede the migration of atoms and ions from the outer cladding 24 into the inner cladding 23 so as not to impair the electrical conductivity of the inner cladding 23.

[0120] The wire core 22 may have a width of about 100 μm and a thickness of about 30 μm, the inner cladding 23 may have a layer thickness of about 10 μm, and the outer cladding 24 may have a layer thickness of about 2 μm. The adhesion-promoting layer 25 and the diffusion protection layer 26 may be thinner than 1 μm.

[0121] In order to produce the clad wire 21, the strip-like wire core 22 can first be obtained from a melt by solidifying and subsequently drawing and rolling of the wire core 22 as a strip. The wire core 22 is preferably work-hardened in order to improve the mechanical properties of the wire core 22. The surface of the wire core 22 can then be cleaned before the following coating processes. However, the wire core 22 can also be produced by another method and be provided for further processing.

[0122] Subsequently, the adhesion-promoting layer 25 can be applied galvanically to the strip-like wire core 22. Thereafter, the inner cladding 23 can be galvanically applied to the wire core 22 coated with the adhesion-promoting layer 25 in order to obtain the intermediate product 20. After cutting the intermediate product 20, the cut pieces may be galvanically coated with the diffusion protection layer 26. Finally, the outer cladding 24 can be applied galvanically to the diffusion protection layer 26 or directly to the inner cladding 23 or the wire core 22.

[0123] The strip-like clad wire 21 produced in this way can optionally be aftertreated with a heat treatment. From the clad wire 21, a plurality of strip-like wire pieces of the clad wire 21 can also be arranged as arrays in a manner spaced apart from one another in order to form test needle arrays.

[0124] The sequence of a method according to the invention is depicted below by means of FIG. 12 together with FIGS. 10, 11 and FIG. 1.

[0125] In a first work step 100, the wire core 2, 22 can be produced from the melt and by drawing. An RhZr0.2 alloy can be used as the material for the wire core. The wire core 2, 22 can be work-hardened in order to improve the mechanical properties, in particular the resilient properties of the clad wire to be produced. The surface of the wire core 2, 22 can be cleaned before the further processing.

[0126] In a second work step 101, the wire core 2, 22 can be galvanically coated with a thin gold layer as an adhesion-promoting layer 5, 25.

[0127] In a third work step 102, a copper layer or a silver layer or an aluminum layer can be applied galvanically to the wire core 2, 22 coated with the adhesion-promoting layer 5, 25 as an inner cladding 3, 23.

[0128] In an optional fourth work step 103, the intermediate product 20, i.e. the coated strip-like wire core 22, can be cut perpendicular to the longitudinal axis of the strip-like wire core into pieces, as indicated by the dashed line in FIG. 10 as the sectional plane 28.

[0129] In an optional fifth work step 104, a diffusion protection layer 6, 26 of nickel can be applied to the inner cladding 3, 23 and optionally also to open surfaces of the wire core 22.

[0130] In a sixth work step 105, a layer of rhodium, a rhodium-based alloy, a gold-based alloy, a gold-cobalt alloy, a gold-iron alloy, a gold-nickel alloy, a copper-tin-zinc alloy or a palladium-nickel alloy as an outer cladding 4, 24 can be galvanically applied to the inner cladding 3, 23 and optionally also to open surfaces of the wire core 22 or to the diffusion protection layer 6, 26.

[0131] Subsequently, a heat treatment of the clad wire 1, 21 produced in this way can optionally be carried out in a seventh work step 106.

[0132] The features of the invention disclosed in the preceding description, as well as in the claims, figures and exemplary embodiments can be essential both individually and in any combination for realizing the invention in its various embodiments.

LIST OF REFERENCE NUMERALS

[0133] 1, 11, 21 Clad wire [0134] 2, 12, 22 Wire core [0135] 3, 13, 23 Inner cladding [0136] 4, 14, 24 Outer cladding [0137] 5, 15, 25 Adhesion-promoting layer [0138] 6, 16, 26 Diffusion protection layer [0139] 20 Intermediate product [0140] 28 Sectional plane [0141] 100 First work step [0142] 101 Second work step [0143] 102 Third work step [0144] 103 Fourth work step [0145] 104 Fifth work step [0146] 105 Sixth work step [0147] 106 Seventh work step