EP2468926A1 - Method for producing a workpiece made of metal or an alloy of a metal with a coating - Google Patents

Abstract

The method of producing a workpiece made of a metal or a metal alloy with a coating of a layer that is made of tin or tin alloy and optionally a further layer arranged between the metal or metal alloy and made of a further metal or an alloy of a further metal and with an intermetallic phase containing the metal and tin and further metal and the further alloy and arranged between the metal or metal alloy and the layer or further layer, comprises sectionally applying the tin or tin alloy or the further metal or alloy of the further metal on a blank, and placing the blank on some sections. The method of producing a workpiece made of a metal or a metal alloy with a coating of a layer that is made of tin or tin alloy and optionally a further layer arranged between the metal or metal alloy and made of a further metal or an alloy of a further metal and with an intermetallic phase containing the metal and tin and further metal and the further alloy and arranged between the metal or metal alloy and the layer or further layer, comprises sectionally applying the tin or tin alloy or the further metal or alloy of the further metal on a blank, and placing the blank on some sections for formation or reinforcement of the intermetallic phase at a temperature of 185-200[deg] C or maintained at a temperature below the melting point of tin or tin alloy for 10 seconds. Each position of the blank is placed at the temperature for 20-25 seconds, where the blank is heated during the placement on the sections. The tin or tin alloy is applied galvanically or by contacting with a melt of tin or tin alloy and/or the further metal or the alloy of the further metal is applied galvanically or by contacting with a melt of the further metal or alloy of the further metal. The tin or tin alloy is applied on the blank or the further layer in a thickness of 2-4 Pm. The further metal or alloy of the further metal is applied on the blank in a thickness of 100-200 nm. The blank is present in the form of a stamped strip, which is dragged through the processing stations. A first roll formed from the strip is unrolled, then passed through the processing stations and is rolled up without a release agent on a second roll formed from the belt. The intermetallic phase has a thickness of 70-100 nm. The surface of the workpiece exhibits an oxide layer that is thinner than 0.2 nm.

Description

The invention relates to a method for producing a workpiece from a metal or an alloy of a metal having a coating of at least one layer of tin or a tin alloy and having a metal-containing intermetallic phase between the metal or the alloy of the metal and the layer. In the method, the tin or tin alloy is applied to a blank made of the metal or alloy of the metal or a further metal layer deposited on the blank, the blank thereafter for forming or strengthening the intermetallic phase at a temperature below the melting point of the tin or the tin alloy is heated.

From the prior art it is known to provide copper or copper alloys by hot tinning or galvanically with a coating of tin. In order to achieve a better adhesion of the tin and / or a greater hardness of the coating, it is favorable if an intermetallic phase is formed or the strength of such a phase is increased between the copper or the copper alloy and the tin. The intermetallic phase contains both copper and tin. Immediately after formation, the intermetallic phase may consist to a lesser extent of Cu ₃ Sn and to a greater extent of Cu ₆ Sn ₅ , with the Cu ₆ Sn ₅ converting to Cu ₃ Sn over time, so that the intermetallic phase then only consists of Cu ₃ Sn. In hot-dip copper or hot-dip copper alloys is such intermetallic phase already exists, while it is missing in galvanically applied tin immediately after the order.

To form or increase the strength of the intermetallic phase, the coated copper or the coated copper alloy may be subjected to a so-called reflow treatment. Such a method is for example from the JP 01159397 A known. In this case, the applied tin or the applied tin alloy is heated to just above the melting point of the tin. A disadvantage is that it comes in the melting of the tin to an uneven distribution of the tin. In particular, the tin flows off the edges of a coated surface of a workpiece as it accumulates in the center of the surface so that the geometry of the coated workpiece deviates from its original geometry. The workpiece can thereby have a deteriorated bendability, solderability and accuracy of fit. If the workpiece is a plug, the uneven distribution of the tin may lead to a deviation from a desired insertion force.

An advantage of the method, however, is that it dissolves in the metal existing tensions and the, especially in electronic components dangerous, whisker formation is reduced.

In order to achieve the formation or reinforcement of the intermetallic phase, but to avoid the uneven distribution of the tin on the workpiece and to obtain the original geometry of the workpiece as much as possible, the workpieces after coating with tin instead of a reflow treatment of several hours Be subjected to treatment at 150 ° C to 180 ° C. In the case of a copper strip or copper stamping tape, the tape is rolled up on a roll after coating and, if necessary, cleaning. To prevent damage to the still soft coating, rolling up can take place with an intermediate layer of a special heat-resistant and therefore expensive paper serving as release agent. The roll is then placed in an oven for about 15 hours at 150 ° C to 180 ° C tempered. This method is called a postbake method. As a result of this treatment, the intermetallic phase is formed or reinforced and the coating is thereby hardened. The thickness of the intermetallic phase is usually about 1 μm after the treatment. After carrying out the postbake process, the roll for inserting an intermediate layer of paper serving to protect the surface during transport and possibly removing the paper inserted before tempering is unrolled and rolled up again. A disadvantage of this method is that it is very time-consuming and labor-intensive and the material is subjected to the required winding and unwinding bending loads. This can lead to fatigue and the formation of cracks. If the tape is rolled up after coating without the release paper, further handling of the roll in the soft tin will easily result in scratches and plastic deformation due to contact with overlying and underlying layers of the tape and upon heating to cake each other contacting band sections.

The object of the present invention is to provide a less time-consuming and labor-intensive method for forming or reinforcing the intermetallic phase. This object is solved by the features of claim 1. Advantageous embodiments emerge from the features of claims 2 to 17.

According to the invention, a method for producing a workpiece made of metal or an alloy of a metal with a coating of at least one layer of tin or a tin alloy and optionally a further layer of a further metal or a metal arranged between the metal or the alloy of the metal and the layer Alloy of a further metal, and provided with a metal and tin or in the presence of the further layer containing the metal and the further metal-containing intermetallic phase. The intermetallic phase is located between the metal or the alloy of the metal and the layer or the further layer. The Tin or the tin alloy or the further metal or the alloy of the further metal and thereon the tin or the tin alloy is / are applied in sections to a blank consisting of the metal or the alloy of the metal. Thereafter, the blank, optionally after a partial cleaning carried out to form or reinforce the intermetallic phase in sections to a temperature above 100 ° C and below the melting point of the tin or the tin alloy or kept at such a temperature.

"Sectionally" is to be understood in the sense of the invention that in each case a portion of the blank and not the blank as a whole is brought to the temperature or kept at the temperature. It can be covered by the sections of each site of the workpiece or a large area of the workpiece or it can only be covered by sections of individual parts of the workpiece. When carrying out the method according to the invention, the section on the workpiece can also "walk along".

The tin or the tin alloy can be applied to the blank or the further layer in a thickness of 1.5 to 20 .mu.m, in particular 2 to 7 .mu.m, in particular 2 to 4 .mu.m.

In the method according to the invention, the thickness and geometry of the coating produced by applying the tin or the tin alloy and optionally further layers remains largely unchanged. Thus, the original workpiece geometry remains almost unchanged.

Compared with the conventional multi-hour postbake process, in which a coated with the very soft tin band-shaped workpiece must be rolled and rolled again, the risk of damage to such a workpiece in the inventive method is significantly reduced. The intermetallic phase is formed or reinforced immediately after coating, thereby resulting in a higher hardness of the coating shortly after application of the coating.

The method according to the invention has the significant advantage in manufacturing that the setting or holding of the temperature can be carried out in the otherwise usual processing steps of the workpiece. For example, at the end of a series of processing steps or between individual processing steps, e.g. B. be carried out using a continuous furnace. As a result, the total production time is only slightly increased and it can be kept significantly shorter cycle times than when using the usual post-bake method. In addition, eliminating the conventional post-bake process before tempering to protect the surface of a band-shaped workpiece possibly taking place an intermediate layer of paper and removing this paper after tempering and the unwinding and rewinding of the workpiece for inserting an intermediate layer of paper and the mechanical loads caused thereby. The insertion of the paper liner can be omitted because between the coating and tempering there is no risk that the surface of the workpiece is scratched or plastically deformed and because there is no risk of caking due to the non-contact with other locations of the tape during tempering. In the case of a roll-up of the band-shaped workpiece which takes place after tempering anyway, the insertion of a paper to protect the surface of the workpiece can take place without additional mechanical stress.

The metal may be copper. The other metal may be nickel or copper. The alloy of the further metal may be an alloy containing copper and nickel. Both the metal and the further metal may be copper. By the additional metal, in particular in the form of copper, the surface of the workpiece can be smoothed. As a result, a better adhesion of the tin can be achieved. The crystallographic orientation of the metal and the further metal may differ.

The further layer may be, for example, a barrier layer which at least largely prevents the formation of an intermetallic phase from the metal and the tin. Such a barrier layer may for example consist of nickel or a copper-nickel alloy. If the metal is copper and the other metal is nickel, an intermetallic phase of nickel and copper is formed upon heating. The diffusion of tin atoms into copper and interactions between tin and copper are inhibited or prevented. As a result, the formation of whiskers can be greatly inhibited. The further layer can be applied galvanically. It can be applied, for example, in a thickness of up to 3 microns.

Preferably, no point of the blank is for more than three minutes, in particular more than two minutes, in particular more than one minute, in particular more than 40 seconds, in particular more than 30 seconds, in particular more than 25 seconds, in particular more than 20 seconds, in particular more than 15 seconds, in particular more than 10 seconds, brought to the temperature or kept at the temperature. It is particularly preferred if each point of the blank is brought to the temperature or held at the temperature for 10 to 40 seconds, in particular 15 to 30 seconds, in particular 20 to 25 seconds. An advantage of this method over the post-bake method is that the workpiece may have higher strength and hardness after the method has been performed. To increase the strength and the hardness of the workpiece before applying the layer or the further layer, especially if it consists of pure copper or copper with a low foreign metal content, often cold formed, ie compacted, for example by cold rolling. The resulting increased hardness and strength is often lost in a long tempering associated with the postbake process by recrystallization and recovery processes. Due to the relatively short temperature in the process according to the invention, however, the strength and hardness of the blank hardly or not at all reduced.

Furthermore, the relatively short tempering has the advantage that only a thin intermetallic phase is formed, on which the layer of tin or the tin alloy can rest in one or more layers and fine-grained. Fine-grained layers of tin or of the tin alloy are formed by electroplating, the number of individual layers corresponding to the number of galvanic coatings. By virtue of the abovementioned structure, the workpiece has improved further processing properties and / or service properties. In particular, the bending behavior is improved by the thin intermetallic phase compared to workpieces with a thicker intermetallic phase, as formed in the conventional multi-hour postbake process. In bending, the occurrence of surface cracks and consequent corrosion of the metal thus exposed or the alloy of the metal thereby exposed is largely prevented. Cracks in the surface of the workpiece often also provide a starting point for further cracking of the metal or alloy of the metal. The cracks then continue in the metal or alloy of the metal.

Furthermore, the strength of the intermetallic phase increases at the expense of the thickness of the layer or the further layer during storage of the workpiece over time, regardless of how the intermetallic phase was generated. This can even go so far that the layer or the further layer completely transforms into the intermetallic phase. A surface formed by the intermetallic phase can only be soldered with the aid of solder and a flux for removing oxides on the surface. The formation of an only thin intermetallic phase in the process according to the invention leaves more material than the tin applied to the blank or the tin alloy applied to the blank, in particular after prolonged storage, than in the formation of a thicker intermetallic phase. This material is available for subsequent soldering processes or at least forms a protective layer that prevents oxides from being removed from the surface during soldering by a flux. The solderability of the workpiece is characterized, especially after a long time Storage of the workpiece, significantly improved and the shelf life of the workpiece is increased.

In addition, formed by the short tempering on the surface of the workpiece only a very thin oxide layer. Preferably, the oxide layer is thinner than 3 .mu.m, in particular thinner than 1 .mu.m, in particular thinner than 0.5 .mu.m, in particular thinner than 0.2 .mu.m, in particular thinner than 0.2 nm. From the very small thickness of the oxide layer results in a significantly improved Solderability to a surface with a thicker oxide layer, as z. B. arises in the conventional multi-hour postbake process. This is probably due to the fact that the surface of a workpiece with a thin oxide layer can be better wetted with solder material than the surface of a workpiece with a thicker oxide layer. Due to the matte surface and the associated low surface reflection and laser welding of the workpiece is easily possible.

The tempering, which lasts for a maximum of three minutes, significantly reduces the processing time compared with the processing time when carrying out the conventional multi-hour postbake process. For a workpiece that passes through several stations during processing, shortening the tempering time can either increase the speed of the cycle or reduce the cycle time and / or reduce the distance required to hold or adjust the temperature. The plants provided for the implementation of the method in a continuous process can thereby be shorter and less expensive.

It has proved to be particularly favorable when the temperature is brought to the blank in sections or on which it is held in sections 150 ° C to 210 ° C, in particular 175 ° C to 205 ° C, in particular 180 ° C to 200 ° C, especially 185 ° C to 200 ° C, is.

Preferably, the blank is brought to the temperature by heating. It is not absolutely necessary to control the temperature of the blank. The process is characterized procedurally simple and therefore inexpensive to perform. For example, a continuous furnace can be used for this purpose.

The layer may be applied galvanically or by contacting it with a melt of the tin or the tin alloy. The further layer can also be applied galvanically or by bringing it into contact with a melt of the further metal or the alloy of the further metal. Immediately after the electroplating, no intermetallic phase is present, while during the application of the layer or the further layer by contacting with the melt, an intermetallic phase is formed which is intensified by the method according to the invention. The contacting with the melt can, for. B. done by a so-called hot tinning. The blank can be driven through a tank with liquid tin. Thereafter, the liquid tin, z. B. far removed by means of air nozzles that the tin remains in the desired thickness on the workpiece.

The further metal or the alloy of the further metal are preferably applied to the blank in a thickness of 50 to 500 nm, in particular 100 to 200 nm.

Preferably, the blank is in the form of a belt, in particular a punching belt, which passes longitudinally through a plurality of processing stations, so that at the same time, except for processing the beginning and the end of the belt, different processing steps are performed. Thereby, a portion of the belt traveling along the belt, after the application of the layer when passing through one of the processing stations, e.g. B. in a continuous furnace, brought to the temperature or kept at the temperature. The layer can also be formed by multiple electroplating, which usually takes place at the temperature or at the temperature hold only after the last galvanic application. In the presence of the blank in the form of a band, the advantages of the method according to the invention come particularly to advantage, because the total processing time of a different processing stations continuous band increases only by the time of tempering the band. A multi-hour "baking" in an oven and the associated steps are eliminated.

In terms of process technology, it is particularly advantageous if the strip is pulled through the processing stations. This prevents compression and thus caused kinks of the tape and is possible without great technical effort and thus cost.

Preferably, the tape is unrolled from a first roll, then passes through the processing stations and is then rolled up, in particular without a release agent, on a second roll. Both the first and second rolls can be formed by the tape itself. Alternatively, the rollers may each be formed by rolling the tape on a carrier.

The intermetallic phase preferably has a thickness of at most 500 nm, in particular a thickness of 30 to 300 nm, in particular a thickness of 50 to 150 nm, in particular a thickness of 70 to 100 nm. Such a thin intermetallic phase improves, especially in combination with a fine-grained layer of tin, the further processing and in particular the bending properties of the workpiece. When bending the workpiece, the formation of cracks in the layer is largely avoided.

The alloy of the metal may be CuFe, in particular CuFe2P, or CuNiSn, CuNiSi, brass (CUZn), CuBe or CuSnZn or a bronze, in particular CuSn ₄ , CuSn ₆ or CuSn ₈ .

The workpiece can be a stamped grid, a punched strip, a component or a composite of components. The component / components is preferably a component / components for the electrical industry, in particular a contact / contacts. The punching tape is a stamped tape. For example, can be punched out of the tape material have been that the remaining material, apart from remaining on both sides remaining continuous metal strip, contacts for the electrical industry, which are punched out of the tape at the end or after performing the method.

The invention will be explained in more detail with reference to an embodiment.

• In der ersten Station erfolgt eine gründliche Entfettung in einem Bad eines fettlösenden Lösungsmittels und ein anschließendes Abblasen noch anhaftenden Lösungsmittels vom Stanzband. Dann erfolgt eine Aktivierung, bei der das Stanzband durch eine saure Lösung geführt wird, gefolgt von einem gründlichen Spülen zum Entfernen der noch anhaftenden sauren Lösung. Daraufhin wird das Band durch ein galvanisches Bad gezogen, in dem elektrochemisch Zinn auf dem Stanzband abgeschieden wird. Nach erneutem Spülen oder auch ohne weiteres Spülen können noch weitere galvanische Verzinnungsschritte erfolgen, an die sich vor einem weiteren Verzinnungsschritt ggf. jeweils ein gründliches Spülen anschließt. Nach dem Verzinnen wird das Band gespült und getrocknet und durch einen Durchlaufofen gezogen. Die Geschwindigkeit, mit der das Band bewegt wird, und die Länge des Durchlaufofens sind dabei so aufeinander abgestimmt, dass jede Stelle des Stanzbandes für 20 Sekunden auf eine Temperatur von 180°C gebracht wird. Im weiteren Verlauf des Verfahrens kühlt das Stanzband ab und wird auf der zweiten Rolle aufgerollt.

A copper stamping tape is unrolled from a first roll and rolled up on a second roll. The tape is pulled by a drive from the first roll to the second roll out. Between the first and second rollers, the belt continuously passes through various processing stations at a constant speed:

• In the first station, a thorough degreasing is carried out in a bath of a fat-dissolving solvent and then blowing off solvent still adhering to the punched strip. Then, an activation is performed in which the punching tape is passed through an acidic solution, followed by thorough rinsing to remove the adhering acidic solution. The strip is then pulled through a galvanic bath in which tin is electrochemically deposited on the punching tape. After rinsing again or without further rinsing, further galvanic tinplating steps can be carried out, followed by a thorough rinsing, if necessary, before a further tin-plating step. After tinning, the tape is rinsed and dried and pulled through a continuous oven. The speed with which the belt is moved, and the length of the continuous furnace are coordinated so that each point of the punching belt is brought to a temperature of 180 ° C for 20 seconds. In the further course of the process, the punching tape cools and is rolled up on the second roll.

Claims (17)

A method of making a workpiece of metal or an alloy of a metal having a coating of at least one layer of tin or a tin alloy and optionally another layer of another metal or alloy of another between the metal or alloy of the metal and the layer Metal, and with a metal and tin or in the presence of the further layer containing the metal and the further metal intermetallic phase between the metal or the alloy of the metal and the layer or the further layer, wherein the tin or the tin alloy or the further metal or the alloy of the further metal and then the tin or the tin alloy is / are applied in sections to a blank consisting of the metal or the alloy of the metal, the blank then being sectioned to a temperature above that for forming or reinforcing the intermetallic phase of 100 ° C and below the melting point of the tin or tin alloy or maintained at such a temperature. The method of claim 1, wherein the metal is copper. The method of claim 1 or 2, wherein the further metal is copper or nickel or the alloy of the further metal is a copper and nickel-containing alloy. Method according to one of the preceding claims, wherein no position of the blank for more than three minutes, in particular more than two minutes, in particular more than one minute, in particular more than 40 seconds, in particular more than 30 seconds, in particular more than 25 seconds, in particular more than 20 seconds, in particular more than 15 seconds, in particular more than 10 seconds, brought to the temperature or kept at the temperature. Method according to one of the preceding claims, wherein each point of the blank for 10 to 40 seconds, in particular 15 to 30 seconds, in particular 20 to 25 seconds, brought to the temperature or maintained at the temperature. Method according to one of the preceding claims, wherein the temperature of 150 ° C to 210 ° C, in particular 175 ° C to 205 ° C, in particular 180 ° C to 200 ° C, in particular 185 ° C to 200 ° C, is. Method according to one of the preceding claims, wherein the blank is brought to the temperature by heating. Method according to one of the preceding claims, wherein the tin or the tin alloy galvanic or by contacting with a melt of the tin or the tin alloy and / or the further metal or the alloy of the further metal galvanically or by bringing into contact with a melt of the further metal or alloy the further metal is applied. Method according to one of the preceding claims, wherein the tin or tin alloy in a thickness of 1.5 to 20 .mu.m, in particular 2 to 7 .mu.m, in particular 2 to 4 .mu.m, is applied to the blank or the further layer. Method according to one of the preceding claims, wherein the further metal or the alloy of the further metal in a thickness of 50 to 500 nm, in particular 100 to 200 nm, is applied to the blank. Method according to one of the preceding claims, wherein the blank is in the form of a band, in particular a punching tape, which passes longitudinally through a plurality of processing stations, so that at the same time, except for a processing of the beginning and the end of the tape, different processing steps are performed wherein a portion of the belt traveling along the belt is raised to or maintained at temperature after application of the layer as it passes through one of the processing stations. The method of claim 11, wherein the tape is pulled by the processing stations. A method according to claim 11 or 12, wherein the tape is unrolled from a first, in particular formed by the tape roll, then passes through the processing stations and then, in particular without a release agent, on a second, in particular formed by the tape roll is rolled up. Method according to one of the preceding claims, wherein the intermetallic phase has a thickness of at most 500 nm, in particular a thickness of 30 to 300 nm, in particular a thickness of 50 to 150 nm, in particular a thickness of 70 to 100 nm. Method according to one of the preceding claims, wherein the surface of the workpiece has an oxide layer thinner than 3 .mu.m, in particular thinner than 1 .mu.m, in particular thinner than 0.5 .mu.m, in particular thinner than 0.2 .mu.m, in particular thinner than 0.2 nm , is. Method according to one of the preceding claims, wherein the alloy of the metal is CuFe, in particular CuFe2P, or CuNiSn, CuNiSi, brass (CuZn), CuBe or CuSnZn or a bronze, in particular CuSn ₄ , CuSn ₆ or CuSn ₈ . Method according to one of the preceding claims, wherein the workpiece is a stamped grid, a punched strip, a component or a composite of components.