EP0087132A1 - Method for the manufacture of strips coated with noble metal as semiproducts for electrical contacts - Google Patents

Abstract

A process for the production of electroplated selectively with noble metal or a noble metal alloy and with a diffusion-inhibiting intermediate layer, in particular of nickel, of base metal strips for use as a semi-finished product for electrical contacts is described, in which the strips after the galvanic coating of a recrystallization annealing and be subjected to a rolling process, in particular a cold rolling process.

Description

The starting point of the invention is a method with the features specified in the preamble of claim 1.

It is known to make strips of a base metal, e.g. made of copper, brass, bronze, nickel silver or other metal materials suitable for the support of electrical contacts, galvanically coated with a noble metal or with a noble metal alloy, mostly with fine gold or with a high-quality gold alloy. For reasons of precious metal savings, the coating is carried out selectively, namely only on one side of the belt or only in the form of strips or spots on the carrier belt.

It is also known to galvanically coat pre-punched strips; these are strips in which areas which would otherwise be eliminated in the subsequent shaping into individual contact parts were in part removed by stamping before the galvanic coating; Precious metal can no longer precipitate on the areas removed by stamping, but instead may possibly on the cut surfaces produced by stamping, as a result of which the Quality of the precious metal layer can be improved, in particular with regard to its adhesive strength.

As a rule, the strips that carry the precious metal layer contain a lot of copper. Under the influence of heat - also in switching operation - copper tends to migrate through precious metal coatings, in particular through those made of gold or silver or their alloys, to the surface of the precious metal coating and form copper oxide there, which increases the contact resistance. Conversely, the precious metals also tend to diffuse into the carrier. In order to avoid this, it is known for contact bimetals to provide a diffusion barrier between the noble metal layer and the carrier. The diffusion barrier mostly consists of a thin nickel intermediate layer, but other materials for such an intermediate layer have also been investigated, e.g. Chrome and cobalt. Such a diffusion-inhibiting intermediate layer can completely cover the carrier tape, but at least selectively covers it at those points at which the noble metal coating is applied. The intermediate layer can be applied galvanically.

After galvanic coating, individual contact parts are produced from the coated strips by punching and bending processes. The galvanically however, different coatings, especially the diffusion-inhibiting intermediate layers, are relatively brittle. Their lack of ductility means that they tend to tear or even peel off the carrier during the required punching and bending processes. In addition, the abrasion resistance of the electroplated noble metal layer is lower than the abrasion resistance of those noble metal layers which were welded to a base metal base by cold or hot roll cladding. In the case of contact bimetallic strips produced in this way, the plated-on coating is sufficiently ductile and abrasion-resistant, but because of the high degrees of deformation during rolling, it is subject to considerable fluctuations in its thickness and possibly also in its width and position on the carrier strip. These fluctuations must be taken into account in the dimensioning of the precious metal layer and its thickness and width must therefore be chosen to be relatively large, namely significantly larger than would be necessary with a galvanically applied precious metal layer. Roll-clad bimetallic strips therefore require a higher use of precious metals than galvanically coated bimetallic strips.

The invention has for its object to provide a particularly economical process for the production of contact bimetallic strips, the use of which gives firmly adhering ductile and abrasion-resistant precious metal coatings with high constancy of the layer thickness and width.

The method according to the invention is the subject of claim 1. Advantageous further developments of the invention are the subject of the dependent claims.

The use of both a heat treatment and a rolling process ensures that the diffusion-inhibiting intermediate layer and the noble metal layer become so ductile that punching and bending processes, which are usually required for producing finished contact parts from the strip, do not impair the quality of the coating. At the same time, the noble metal layer is solidified and has less wear in switching operation than an equally composed, galvanically deposited noble metal layer, which has not been post-treated by heat treatment and rolling. It is also observed that the adhesive strength of the noble metal layer on the intermediate layer and the intermediate layer on the carrier tape is significantly improved.

When manufacturing contact bimetallic strips, the method according to the invention combines the advantages of roll cladding (well-adhering and ductile coatings) with the advantages of galvanically applying the coating (high dimensional accuracy, uniform layer thicknesses, most economical use of precious metals (it is possible that the thickness of the precious metal coating in the finished semi-finished product is considerably smaller than 1 pm, for example only 0.1 µm or 0.2 µm to keep thick!), practicability lovely overlay pattern on ribbons of any length). The advantageous effects of the method according to the invention are particularly evident in the production of strips with gold or gold alloy overlays over an intermediate layer of nickel.

The process according to the invention is preferably carried out in such a way that, after the plating has been electrodeposited, it is first subjected to a heat treatment and then cold-formed by rolling. However, it is also conceivable to combine these two steps to form a hot rolling process.

The degree of deformation caused by rolling depends on the composition and structure of the noble metal layer and the type of intermediate layer, as well as on the desired solidification of the noble metal layer, the intermediate layer and the carrier material. The degree of deformation (indicated as the decrease in thickness of the strip based on its thickness before the start of the deformation) should be between 10% and 50%. vorzugswei _'s are between 20% and 40%. This degree of deformation can possibly be achieved by a one-step rolling process, but should preferably be achieved by a three- or four-step rolling process, preferably cold and without intermediate annealing.

In the process of heat treatment, the treatment temperatures and the treatment time are not chosen independently of one another, but coordinated with one another in such a way that the desired increase in ductility occurs within a reasonable period of time (approx. 5 minutes to 15 minutes). The higher the temperature, the shorter the treatment time. The upper limit of the temperature is determined so that the temperature effect in the surrounding medium: neither the carrier tape nor the precious metal layer adversely changes.

Unless the material selection for the base carrier tape requires a lower treatment temperature, treatment temperatures between 400 ° C and 750 ° C, in particular between 550 ° C and 650 ° C, are preferred when using the most common precious metal coatings (fine gold, gold alloys, silver, palladium alloys).

The galvanically applied intermediate layer is preferably aftertreated together with the noble metal coating by the action of heat and a rolling process, in particular a cold rolling process. However, it is also possible to subject the intermediate layer to a heat treatment and possibly also a rolling process before the noble metal coating is applied (claims 8 to 10). If the carrier material permits this, the nickel layer can be exposed to a higher temperature than the noble metal coating during the separate heat treatment and therefore achieve a higher degree of ductility than if it were only subjected to a heat treatment together with the precious metal layer.

The process according to the invention can also advantageously be applied to the production in a corresponding application: of strips which are selectively galvanically coated with precious metal and which either do not have a diffusion-inhibiting intermediate layer of nickel or the like. need or in which the diffusion-inhibiting intermediate layer, in particular made of nickel, has already been applied to the strip by cold or hot roll cladding and only the noble metal layer has to be electrodeposited. In these cases, the process brings about strengthening and an increase in ductility, combined with an improvement in the adhesive and abrasion resistance of the precious metal layer and a considerable saving in precious metal.

A particular advantage of the invention is that it can also be used to produce precious metal coatings from alloys that are difficult or impossible to separate from a galvanic alloy bath; this applies especially to low-carat. Gold alloys. According to a development of the invention, the constituents of the alloy are deposited in layers one above the other and are left in the course of the subsequent heat treatment the metals deposited in layers diffuse into each other to form alloys. In order to keep the time required for alloy formation short, it can be advantageous not to separate the constituents of the alloy to be formed in only one layer, but in several layers, which alternate with layers of the other alloy constituents. In this way the diffusion paths are shortened.

The method according to the invention for the aftertreatment of electroplated precious metal coatings for the production of contact bimetallic strips can also be applied to the aftertreatment of precious metal coatings which have been deposited, in particular vapor-deposited, from the gas phase.

• 1. Auf ein 0,55 mm dickes Trägerband aus der Bronze CuSn6 wird zunächst ein 3 mm breiter, in Längsrichtung verlaufender Streifen aus Nickel in einer Schichtdicke von 3 um galvanisch abgeschieden. Anschließend wird auf den Nickelstreifen ein ebenfalls 3 mm breiter Streifen aus Feingold mit einer Schichtdicke von 2 um galvanisch abgeschieden. Anschließend wird das Band einer Wärmebehandlung unterzogen und dabei ca. 5 min. lang bei einer Temperatur von ca. 600°C geglüht. Nach der Wärmebehandlung wird das Band in vier Walzstichen auf eine Enddicke von 0,4 mm kalt herabgewalzt, wobei der vierte Walzstich die geringste Dickenabnahme des Bandes bewirkt.
• 2. Auf ein 0,7 mm dickes Trägerband aus CuNi 9 Sn2 wird zunächst einseitig eine 4 mm breite streifenförmige Nickelschicht mit'einer Dicke von 5 um galvanisch abgeschieden. Anschließend wird das vernickelte Band einer Wärmebehandlung unterzogen und dabei für die Dauer von ca. 5 min. bei einer Temperatur von ca. 650°C geglüht. Danach wird das Band in 3 Walzstichen kalt auf eine Dicke von 0,55 mm herabgewalzt. Auf das derart vorbereitete Band wird nun aus einem Legierungsbad eine 3 um dicke Schicht aus der Legierung Au 80 Ag 20 in Form eines 3 mm.breiten Streifens auf die Nickelschicht abgeschieden. Anschließend wird das Band einer Wärmebehandlung unterzogen und dabei für die Dauer von ca. 8 min. bei einer Temperatur von ca. 630°C geglüht. Danach wird das Band wie im 1. Beispiel kalt auf eine Enddicke von 0,4 mm herabgewalzt.
• 3'. Auf ein 0,4 mm dickes Trägerband aus Neusilber Cu Ni 12 Zn 24 wird zunächst eine 3 um dicke Nickelschicht in Form eines 3 mm breiten Streifens galvanisch abgeschieden. Zur Erzeugung einer Edelmetallauflage aus 70 Gew.-% Gold, 25 Gew.-% Silber und 5 Gew.-% Kupfer werden über der Nickelschicht in Form von 2 mm breiten Streifen die entsprechenden Mengen an Gold, Silber und Kupfer in Schichten übereinander gesondert galvanisch abgeschieden, und zwar in der Schichtenfolge beginnend mit Silber auf der Nickelschicht gefolgt von Gold, Kupfer, Silber, Gold, Kupfer und zuoberst noch einmal Gold. Diese sandwichartige Edelmetallauflage wird durch eine nachfolgende Glühbehandlung, bei der das Band für die Dauer von etwa 8 min. einer Temperatur von ungefähr 630°C ausgesetzt wird, unter Bildung einer Au-Ag-Cu-Legierung durch Diffusion der Legierungskomponenten ineinander homogenisiert. Anschließend wird das Band in 3 Walzstichen kalt auf eine Enddicke von 0,3 mm herabgewalzt.
• 4. Zur Herstellung eines vernickelten Trägerbandes geht man aus von einer schmalen, langgestreckten, 30 mm dicken Platte aus Silberbronze CuAg2, in welche eine 0,5 mm tiefe Nut eingefräst wird. In die Nut wird ein 0,5 mm dicker Nickelstreifen eingelegt und anschließend wird die Platte durch Warmwalzplattieren in ein 0,55 mm dickes Band umgeformt. Dieses Band kann nach einem jeden der Beispiele 1 bis 4 mit einer Edelmetallauflage versehen und weiterverarbeitet werden.
• 5. Anstelle einer Zwischenschicht aus Nickel kann-irr-den Beispielen 1 bis 4 auch eine solche aus Kobalt oder Chrom verwendet werden.
• 6. Auf ein 0,7 mm dickes Band aus SE-Kupfer mit einer 3 mm breiten und 225 µm dicken, durch Walzplattieren hergestellten Einlageplattierung au.s Silber wird galvanisch eine 8 um dicke Feingoldschicht. auf die Silbereinlage abgeschieden. Artschließend. wird das Band 5 min. lang bei einer Temperatur von ca. 560.°C geglüht und danach in drei oder vier Walzstichen kalt und ohne Zwischenglühdngen um 30 %.(Dickenabnahme- bezogen auf die Ausgangsdicke des Bandes) auf Endmaß herabgewalzt.

Some exemplary embodiments of the method according to the invention are given below.

• 1. A 3 mm wide, longitudinally extending strip of nickel is first electrodeposited onto a 0.55 mm thick carrier tape made of bronze CuSn6 in a layer thickness of 3 μm. Then a strip of fine gold, likewise 3 mm wide, with a layer thickness of 2 μm is electrodeposited on the nickel strips. The strip is then subjected to a heat treatment and in the process about 5 minutes. long annealed at a temperature of approx. 600 ° C. After the heat treatment it will The strip was cold rolled down to a final thickness of 0.4 mm in four pass passes, the fourth pass causing the strip to have the smallest decrease in thickness.
• 2. A 4 mm wide strip-shaped nickel layer with a thickness of 5 μm is first electroplated onto a 0.7 mm thick carrier tape made of CuNi 9 Sn2. The nickel-plated strip is then subjected to a heat treatment and for a period of about 5 minutes. annealed at a temperature of approx. 650 ° C. The strip is then cold rolled in 3 pass passes to a thickness of 0.55 mm. A 3 µm thick layer of Au 80 Ag 20 alloy in the form of a 3 mm wide strip is then deposited on the nickel layer on the strip prepared in this way from an alloy bath. The strip is then subjected to a heat treatment and for a period of about 8 minutes. annealed at a temperature of approx. 630 ° C. The strip is then cold rolled down to a final thickness of 0.4 mm as in the first example.
• 3 '. A 3 μm thick nickel layer in the form of a 3 mm wide strip is first electrodeposited onto a 0.4 mm thick carrier tape made from nickel silver Cu Ni 12 Zn 24. To produce a precious metal coating from 70% by weight gold, 25% by weight silver and 5% by weight of copper, the corresponding amounts of gold, silver and copper are electrodeposited in layers one above the other in the form of strips 2 mm wide, in the layer sequence starting with silver on the nickel layer followed by gold, copper , Silver, gold, copper and gold again. This sandwich-like precious metal layer is subjected to a subsequent annealing treatment in which the strip is held for about 8 minutes. is subjected to a temperature of about 630 ° C, homogenized to form an Au-Ag-Cu alloy by diffusion of the alloy components into one another. The strip is then cold rolled down to 3 mm in a final pass of 0.3 mm.
• 4. To produce a nickel-plated carrier tape, one starts from a narrow, elongated, 30 mm thick plate made of silver bronze CuAg2, into which a 0.5 mm deep groove is milled. A 0.5 mm thick nickel strip is inserted into the groove and then the plate is formed into a 0.55 mm thick band by hot roll cladding. According to each of Examples 1 to 4, this strip can be provided with a precious metal coating and further processed.
• 5. Instead of an intermediate layer made of nickel, examples 1 to 4 can also be used made of cobalt or chrome.
• 6. An 8 µm thick fine gold layer is electroplated onto a 0.7 mm thick strip of SE copper with a 3 mm wide and 225 µm thick inlay plating made of silver, which is produced by roll cladding. deposited on the silver inlay. Style closing. the tape is 5 min. annealed for a long time at a temperature of approx. 560 ° C and then cold rolled in three or four pass passes and without intermediate annealing by 30% (reduction in thickness based on the initial thickness of the strip) to the final dimension.

Claims (14)

1. A process for the production of electroplated selectively with noble metal or a noble metal alloy and with a diffusion-inhibiting intermediate layer, in particular made of nickel, strips of base metal for use as semi-finished products for electrical contacts, characterized in that the strips after the galvanic coating of a heat treatment, which enables a recrystallization of the electroplated layers and the base material and, at the same time or subsequently, is subjected to a rolling process in the course of which the electroplated band is deformed to a final dimension with a thickness reduction of between 10% and 50% of its original thickness. 2. The method according to claim 1, characterized in that the heat treatment at temperatures between 400 ° C and 750 ° C, preferably between 550 ° C and 65d ° C, over a residence time between 5 min. and 15 min. he follows. 3. The method according to claim 1 or 2, characterized in that the rolling process is a hot rolling process. 4. The method according to claim 1 or 2, characterized in that the rolling process is a cold rolling process, which follows the heat treatment. 5. The method according to any one of the preceding claims,
characterized in that the rolling process takes place in three to four passes, in particular by cold rolling without intermediate annealing. 6. The method according to any one of the preceding claims, characterized in that the decrease in thickness of the strip due to rolling is between 20% and 40%, preferably about 30%. 7. The method according to any one of the preceding claims, characterized in that the heat treatment for the intermediate layer and for the noble metal coating is carried out together. 8. The method according to any one of claims 1 to 6, characterized in that the galvanically applied intermediate layer is subjected to a separate heat treatment before the application of the noble metal coating. 9. The method according to claim 8, characterized in that the intermediate layer is hot-rolled at the same time with its separate heat treatment, but preferably cold-rolled after this separate heat treatment, the strip provided with the intermediate layer having a thickness reduction of between 10%. and 50%, preferably about 30% based on its original thickness. 10. The method according to claim 8 or 9, characterized in that the intermediate layer consists of nickel or cobalt and the heat treatment is carried out before the application of the noble metal coating at temperatures between 550 ° C and 650 ° C. 11. Use of a method according to one of claims 1 to 6 for the production of selectively electroplated with precious metal or with a noble metal alloy metal strips for use as a semi-finished product for electrical contacts with the proviso that no galvanic between the carrier and the electroplated precious metal layer applied, diffusion-inhibiting intermediate layer is provided. 12. Application of a method according to any one of claims 1 to 6 to the production of selectively galvanically coated with precious metal or with a precious metal alloy strips of metal for use as semi-finished products for electrical contacts with the proviso that the precious metal or the precious metal alloy a band previously provided by roll cladding with a diffusion-inhibiting coating, in particular made of nickel, is galvanically deposited. 13. Application of a method according to one of the preceding claims to the treatment of precious metal deposits deposited from the gas phase. 14. The method according to any one of the preceding claims, characterized in that for the production of a tape with a coating of a noble metal alloy, the components of which cannot be electrodeposited from a bath, the various metals of this noble metal alloy are successively electrodeposited and then jointly subjected to heat treatment undergo, in the course of which the deposited metals diffuse into one another.