Production of surface modified copper strips for laser bonding

Abstract

The invention relates to a method for producing a wire, having at least the following steps: (i) providing a wire precursor; (ii) pressing depressions on the wire precursor and optionally molding the wire precursor in the process; and (iii) annealing the wire precursor provided with depressions in order to form the wire; wherein the wire has a content of at least 95 wt.% of copper based on the total weight of the wire. The invention additionally relates to a wire which can be obtained according to the aforementioned method and to the use of a roller in order to produce the wire and / or in order to set the roughness at at least one location of the wire.

Description

[0001] The invention relates to a method for producing a wire, comprising at least the following steps: (i) providing a wire precursor; (ii) impressions of depressions on the wire precursor and optionally forming the wire precursor in the process; and (iii) annealing the wire precursor provided with depressions to form the wire, wherein the wire has a copper content of at least 95 wt.%, based on the total weight of the wire, with further features. The invention further relates to a wire obtainable by said method and to the use of a roller for producing the wire and / or for adjusting the roughness at at least one point on the wire. Background of the invention

[0002] Bond wires are used in semiconductor manufacturing to electrically connect an integrated circuit and a printed circuit board during semiconductor manufacturing. Bond wires are also used in power electronics to electrically connect transistors, diodes, and the like to the contact surfaces of the package, also called pads or pins. While bond wires were once made of gold, more cost-effective materials such as copper are now used. Copper wire exhibits very good electrical and thermal conductivity. However, copper wires are susceptible to oxidation.

[0003] In terms of wire geometry, bonding wires with a circular cross-section and ribbons, which have a more or less rectangular cross-section, are the most common. Both types of wire geometries have their advantages that make them useful for specific applications. Thus, both geometries have their share of the market. Ribbons have a larger contact area for a given cross-sectional area because they can lie flat against an element. However, the bendability of ribbons is limited. Furthermore, the orientation of a ribbon must be taken into account during bonding to achieve sufficient electrical contact between the ribbon and the element to which it is connected. As for bonding wires, these are more flexible.However, bonding involves either welding and / or significant deformation of the wire in the bonding process, which may result in damage or even destruction of the bond pad and the underlying electrical structures of the connected element.

[0004] Of particular interest is laser bonding. This is a process in which the energy required for bonding is transferred to the bonding wire using laser beams. Metal ribbons are often used instead of wires because the ribbon offers a larger surface area for coupling the laser. One advantage of ribbon bonding is that they can be easily positioned and held in place compared to round wires. This significantly increases the reliability of the bond. Due to the larger connection in ribbon bonding, higher currents can be carried through such connections. Nevertheless, there is a constant need for further technological improvements with regard to the bonding wire itself and the bonding processes.

[0005] It is known that roughened surfaces exhibit a higher absorption of electromagnetic radiation due to their larger surface area. Thus, an enlarged surface area of ​​bond wires should also enable a higher absorption of laser radiation in a laser bonding process. Surface roughening can be achieved using mechanical or chemical processes (such as brushing or etching). However, these processes often result in residues on the wire surfaces, which can have a negative impact on the bond. In the case of mechanical processes, these residues can be abrasion from the brushes or particle removal of the wire material, which can be deposited at another location on the wire during the brushing process. These residues can lead to incorrect melting of the wire during the bonding process and thus to less reliable bonds.Furthermore, the alternative processes mentioned above can lead to overlaps in the wire material. During laser bonding, these overlaps can cause the wire material to splash due to the strong heating and sudden expansion of the air volume trapped underneath. This splash of wire material can lead to unreliable bonding results due to material loss and to harmful contamination of other electronic components. Furthermore, chemical processes have the disadvantage that the dimensions of the recesses, both in terms of their depth and location, are more difficult to adjust. For example, single-sided etching of a ribbon can only be achieved with complex masking steps. The introduction of patterns to recesses also requires increased effort.

[0006] The document JP H04 46604 A forms the basis for the preamble of claim 1. Tasks

[0007] An object of the present invention is to at least partially overcome one or more of the disadvantages resulting from the prior art.

[0008] It is a particular object of the invention to provide a method by means of which a wire surface optimized for the laser bonding process can be produced.

[0009] It is a further object of the invention to provide a method by means of which a wire can be produced whose at least one surface has a defined roughness.

[0010] It is a further object of the invention to provide a wire with a roughness that is free from impurities, residues and voids.

[0011] A further object of the invention is a method for producing a wire whose wire surface absorbs the proportion of incident laser radiation during laser bonding as extensively as possible.

[0012] Another object of the invention is a method for producing a wire, wherein the wire heats up more at the same intensity of the incident laser light compared to other bonding wires.

[0013] Another object of the invention is a method for producing a wire, wherein no impurities or residues are formed during laser bonding.

[0014] A further object is to simplify the production process for manufacturing the bonding wires according to the invention, e.g., by reducing the required steps. Thus, in addition to the technical advantages, the method according to the invention can achieve cost and time savings in the production of the wires according to the invention.

[0015] It is known to use bond wires for laser bonding that are roughened on one side, away from the electrical contact surface. It has been observed that, for the same amount of laser radiation emitted, a higher energy transfer to the bond wire occurs with roughened bond wires than with smooth bond wires. Without being bound by any theory, it is assumed that the roughened side results in a higher degree of absorption of the incoming laser radiation by the bond wire, or that less laser radiation is reflected. Nevertheless, there is still room for improvement to further increase the quality and reliability of the bond connection.

[0016] It has now been found that the quality of the bond connection can be increased in terms of contamination / yield if the roughening of the bond wire is not done by removing material, i.e. by brushing or milling, but by creating depressions, for example by embossing. Preferred embodiments of the invention

[0017] A contribution to at least partially fulfilling at least one of the aforementioned objects is made by independent claim 1. The dependent claims provide preferred embodiments that contribute to at least partially fulfilling at least one of the objects. General

[0018] In this description, range specifications also include the values ​​referred to as limits. A specification such as "in the range from X to Y" with respect to a quantity A therefore means that A can assume the values ​​X, Y, and values ​​between X and Y. Unilaterally limited ranges such as "up to Y" for a quantity A correspondingly mean values ​​Y and less than Y. Detailed description of the invention

[0019] A first aspect of the present invention relates to a method for producing a wire according to the subject matter specified in claim 1.

[0020] In principle, all wires and raw wires known to a person skilled in the art that appear suitable for bonding in microelectronics and power electronics can be considered as wire precursors. The wire precursor, like the formed wire, is usually a one-piece article. Numerous shapes are known and suitable. Preferred shapes—in cross-sectional view—are round, ellipsoidal, and rectangular. A bonding wire with an approximately rectangular cross-section is also referred to as a ribbon wire.

[0021] According to the invention, the wire has a proportion of at least 95 wt.% copper, preferably at least 99.95 or at least 99.9 wt.%, or at least 99.99 wt.% copper, wherein the wt.% is based on the total weight of the wire.

[0022] The wire therefore contains up to 5 wt.%, e.g. 4 wt.%, or 3 wt.% of further constituents. Suitable further constituents are all elements familiar to the person skilled in the art and which appear suitable in this case, in particular metals which can be alloyed with copper, as well as metals, semimetals and non-metals which can form intermetallic phases with copper. The following metals are preferably considered as further constituents: tin (Sn), iron (Fe), nickel (Ni). The following semimetals are preferably considered as further constituents: Si. The following non-metals are preferably considered as further constituents: phosphorus (P). Combinations of two or more metals, semimetals and non-metals are also possible, both within one class (metals, semimetals, non-metals) and components from different classes. In addition to the deliberate addition of further constituents, the wire may also contain impurities.

[0023] Typically, the wire precursor has the same proportion of copper as the wire formed from the wire precursor by the process according to the invention.

[0024] In a preferred embodiment, the wire precursor is a flat ribbon. This can then be cut lengthwise into several ribbon wires after step (ii) or after step (iii). According to another preferred embodiment, the wire produced according to the invention is a ribbon.

[0025] The provision in step (i) can, in principle, be carried out in a manner known to any person skilled in the art and deemed suitable. Preferably, the provision takes place by straightening the wire precursor in a device.

[0026] In step (ii), indentations are pressed into the wire precursor. The wire precursor can be formed simultaneously or subsequently. Preferably, the forming takes place simultaneously with the indentations.

[0027] Indentation refers to wire processing that occurs essentially without material removal. This differs from abrasive processing, where material removal is caused by the abrasive process itself. Examples of abrasive processing include brushing and grinding. As a result, a wire is lighter after abrasive processing than before.

[0028] In principle, indentation can be performed by any method known and deemed suitable to any person skilled in the art. Preferably, indentation is performed by a method selected from the group consisting of punching, notching, embossing, stamping, countersinking, and grooving. Indentation is particularly preferably performed by embossing.

[0029] According to a further preferred embodiment, the indentation is carried out by rolling. Rolling is understood to be a processing method in which a material, in this case a wire precursor, is processed between two or more rotating tools. According to the invention, a relief is transferred into the wire precursor by rolling. Preferably, the wire precursor is formed simultaneously during rolling. In this case, a ribbon wire can be obtained. Rolling can be carried out as either hot rolling or cold rolling. Rolling is preferably carried out as cold rolling. Particularly preferably, indentation is carried out by embossing rolling. This means that forming and embossing take place simultaneously and in one step.

[0030] According to a further preferred embodiment, the rolling is carried out by at least one roller. The roller often has a cylindrical surface, although other roller geometries are also known to those skilled in the art and may be considered suitable. According to a further preferred embodiment, the roller is provided with a relief, wherein the relief is formed by height differences of the cylindrical surface. According to a further preferred embodiment, the relief has a pattern.

[0031] According to a further preferred embodiment, the height difference (D) of the relief of the roller is in a range from 3 to 9 µm, for example from 4 to 8 µm, or 5 to 7 µm, or 4 to 9 µm, or 5 to 9 µm.

[0032] According to a further preferred embodiment, the depressions form a pattern. A pattern in the present context means a recurring image or design. The pattern formed by the relief on the roller corresponds to the pattern of depressions on a wire processed by rolling with the roller.

[0033] According to the invention, the wire has multiple locations, with the recesses being introduced only at a first location. Preferably, the wire, particularly if it is a ribbon wire, has multiple sides, with the recesses being introduced only at a first side.

[0034] According to the invention, the wire has a roughness R z in a range from 3 to 9 µm, for example from 4 to 8 µm, or 5 to 7 µm, or 4 to 9 µm, or 5 to 9 µm, at least at one point. Preferably, if the wire is a ribbon wire, the wire has a roughness R z on a first side in a range from 3 to 9 µm, for example from 4 to 8 µm, or 5 to 7 µm, or 4 to 9 µm, or 5 to 9 µm. The roughness is determined according to DIN EN ISO 4287 (2010-07) and DIN EN ISO 4288 (1998-04).

[0035] According to the invention, at least one further point of the wire is smooth, wherein the at least one further point is located on a point of the wire facing away from the first point of the wire.

[0036] In the present context, smooth means a spot or a surface, or a part thereof, if it has a roughness R z in a range from 0.1 to 1 µm, for example from 0.2 to 0.6 µm, or from 0.2 to 0.4 µm.

[0037] If the wire is a ribbon, instead of a first point and a further point of the ribbon, a part of a first side, or an entire first side, and instead of the further point, a part of another side of the ribbon, or an entire other side, can have the properties described here.

[0038] According to a further preferred embodiment, in the case of a ribbon, at least one further side of the wire is smooth, wherein the at least one further side is located on a side of the wire facing away from the first side of the wire.

[0039] According to a further preferred embodiment, an element selected from the group consisting of the wire and the wire precursor has a cross-sectional area QA in a range from 25,000 to 900,000 µm 2 , wherein the cross-sectional area QA is arranged perpendicular to a longitudinal direction L of the element. If the cross-sectional area of ​​the element is not the same at all locations, the cross-sectional area QA is calculated as the arithmetic mean of several measurements of the cross-sectional area at at least seven different locations on the element.

[0040] According to a further preferred embodiment, an element selected from the group consisting of the wire precursor and the wire has a cross-sectional plane QE passing through the element, wherein the cross-sectional plane QE is arranged perpendicular to a longitudinal direction L of the element, wherein the cross-sectional plane QE forms a cross-sectional area QA with the element, wherein the cross-sectional area QA includes two perpendicularly intersecting lines L1 and L2, wherein a shortest possible section A L1 of the line L1 is defined by an intersection with the edge of QA, and wherein a longest possible section A L2 of the line L2 is defined by an intersection with the edge of QA, wherein the quotient of A L2 and A L1 is a number of 2 or more, for example in a range from 2 to 30, or from 5 to 20, or from 5 to 10. The determination of the cross-sectional plane QE and the further features mentioned in this paragraph is carried out as in the Figures 1 and 2If the geometry of the element, its cross-sectional plane QE and its other characteristics are to be determined, from the Figures 1 and 2 If the wire precursor deviates from the schematically shown shape, the skilled person will recognize and select a determination method that most closely approximates the diagram shown, taking into account the different geometry. It is entirely possible for a wire precursor to have a different geometry, e.g., the quotient of A L2 and A L1 is a number of 1. In this case, the wire precursor is round. It is then formed by the process such that the wire has the aforementioned quotient of 2 or more.

[0041] If the wire is a ribbon, it can optionally be divided into several ribbons after stamping by suitable cutting processes, so that the longest possible section of the ribbon, A L2, is shortened while maintaining the shortest possible section, A L1. The cutting process can optionally be performed before or after annealing the ribbon.

[0042] A tool is used for the pressing process. In principle, any device known to a person skilled in the art and deemed suitable is suitable.

[0043] A preferred tool is a roller. A roller is generally understood to be an essentially cylindrical body. The roller can, in principle, have any diameter. Rollers with a diameter of 50–150 mm are preferred for the intended application. Furthermore, the roller should be made of a material that, under operating conditions, is harder than the object being formed. Rollers are often made of forged steel, hard metal, or cast steel.

[0044] In a preferred embodiment, the tool is designed as an arrangement comprising at least one roller. Arrangements with multiple rollers, for example, two or more rollers, are also possible. For example, an arrangement in which at least two rollers rotate in opposite directions and the object to be formed is passed between the two counter-rotating rollers is suitable. The two counter-rotating rollers are arranged such that a gap is provided between the two rollers. This gap is preferably equal to the thickness of the formed wire.

[0045] In the present case, at least one first roller has a relief on its surface. The height differences of the relief on the first roller can, in one embodiment, form a pattern. The relief (also in the form of a pattern) is introduced into the object to be formed as it passes through the tool. The depth of the indentations introduced into the wire depends on the penetration depth of the relief of the first roller into the object. It is quite possible that the height difference (D) of the relief is greater than the indentations introduced into the object. With regard to the indentations in the formed object, the introduced height difference (D) of the transferred relief is referred to as roughness Rz or embossing depth. The forming of an object with rollers, wherein at least one first roller has a relief that is transferred to the object during forming, is also referred to as "embossing rolling."The (first) roller is called the "embossing roller".

[0046] In another embodiment, the impression is made by stamping. A stamp is a surface provided with a relief. The relief has a height difference (D). In principle, all materials known to a person skilled in the art and deemed suitable are suitable for a stamp, but in particular the same materials as for the rollers. During stamping, a stamp is lowered onto an object to be processed. The relief is pressed into the object until the desired depth of the indentations is formed. This often corresponds to the height difference (D) of the relief, but sometimes the depth of the indentations is less than the height difference (D) of the relief. With regard to the indentations in the formed object, the introduced height difference (D) of the transferred pattern is referred to as roughness R z or stamp depth.Typically, when stamping an object, an additional tool, plate, or similar device is provided on the side of the object facing away from the stamp. This tool is designed so that the object to be formed cannot deflect from the stamp. Rather, the object to be formed is held in position relative to the stamping direction by the additional tool.

[0047] In step (iii), the dimpled wire precursor is annealed to form a wire. Annealing takes place below the melting temperature of copper, preferably at temperatures TG in a range of 500 to 900 °C, for example, in a range of 550 to 650 °C or 750 to 850 °C. The specified annealing temperature TG is the temperature at which a workpiece, in this case the wire, is heated over a specified time. Annealing the wire takes approximately 10 seconds to 6 minutes.

[0048] Annealing can be carried out discontinuously or continuously. Continuous annealing is preferred. A continuous furnace is suitable for this. A passage section in the continuous furnace and a temperature TO of the continuous furnace are selected such that a wire passing through the passage section has the temperature TG for the duration specified above. In all cases, the furnace temperature, for example of the continuous furnace TO, can be higher than the annealing temperature TG. The passage section of the continuous furnace can also be longer and have a temperature gradient at the inlets and outlets. It is also possible to use a continuous furnace with multi-zone heating. This allows specific temperature profiles to be applied to a passing wire.

[0049] The continuous furnace can be heated and maintained conventionally using a heating device located in the furnace wall or acting externally on the furnace wall. An electric heater is suitable for this purpose. In another embodiment, the annealing temperature TG in the continuous furnace can be generated by a plasma. A nitrogen plasma can be used for this purpose, e.g., at a typical power of 750 W and a process gas pressure (N 2 ) of 25 mbar.

[0050] Annealing the wire is preferably carried out in an atmosphere such as nitrogen (N 2 ). This is also referred to as a protective gas atmosphere. The presence of oxygen (O 2 ) is excluded wherever possible to prevent surface oxidation of the wire.

[0051] In a further embodiment of the present invention, the atmosphere contains up to 10 vol.%, for example, in a range of 2 to 8 vol.%, or approximately 5 vol.%, of hydrogen (H2). The hydrogen has a reducing effect in the protective gas atmosphere. This causes any copper oxidized to copper oxides (CuO or Cu2O) on the surface of the wire to be reduced to elemental copper.

[0052] The wire may be characterized by at least the following features: (a) A first point of the wire, in the case of a ribbon a first side, has a roughness R z of 3 to 9 µm, for example of 4 to 8 µm, or 5 to 7 µm, or 4 to 9 µm, or 5 to 9 µm; (b) A quotient of AL2 and AL1 of 2 or more, determined by the method described in connection with the first aspect of the invention; (c) A proportion of at least 95 wt.% copper, the proportion based on the total weight of the wire (2).

[0053] Preferably, the wire is characterized by at least one of the following additional features: (d) at least one further part of the wire is smooth; in the case of a ribbon, at least one further side of the ribbon is smooth; (e) the wire has a cross-sectional area QA in a range from 25000 to 900000 µm 2<.

[0054] Further preferably, the wire has the features (a) to (c), and additionally at least one of the further features (d) or (e), further preferably both features.

[0055] A second subject matter is a method for producing a device comprising at least one electrically conductive connection, the method comprising the following steps: (I) producing a wire by a method according to the first aspect of the invention or one of its embodiments; (II) providing a substrate having at least a first contact surface and the wire; (III) positioning the wire in a mechanical connection with the first contact surface; (IV) heating a first point of the wire by means of electromagnetic radiation in a wavelength range from 700 to 1100 nm, thereby obtaining an electrically conductive connection between the first contact surface and the wire, wherein the first point of the wire has a roughness R z in a range from 3 to 9 µm, for example from 4 to 8 µm, or 5 to 7 µm, or 4 to 9 µm, or 5 to 9 µm, wherein a further point of the wire facing away from the first point of the wire and facing the contact surface has a roughness R z in a range from 0.1 to 1 µm.

[0056] Laser beams are preferably selected as the electromagnetic radiation. Laser beams are electromagnetic waves, often within a very narrow frequency range and exhibiting high radiation intensity. Laser beams with a wavelength in the range of 700 to 1100 nm are particularly preferred. For heating a wire as in step (IV), for example, a 400 W fiber laser with a focus diameter of 25 µm is used.

[0057] According to a further preferred embodiment, the wire is a ribbon. The first and further points of the ribbon are then each part of a first or further side, or a first or further side as a whole.

[0058] In the present context, an electrically conductive connection is understood to mean a contact between two electrically conductive elements, for example a wire with a contact surface (for example a power semiconductor or a substrate surface (for example DCB or leadframe).

[0059] The wire according to the second aspect of the invention is preferably obtainable by the process according to the first aspect of the invention or one of its embodiments.

[0060] The roughness R z according to the second aspect of the invention was preferably created at least at the first point of the wire by indentation. The indentation was preferably selected from the group consisting of graining, notching, embossing, stamping, countersinking, and furrowing, or a combination of two or more thereof.

[0061] For example, the roughness R z was induced at least at the first point of the wire by rolling, for example embossing rolling.

[0062] For rolling, for example, a roller could incorporate a relief for producing a wire. The relief preferably had a height difference (D) in a range of 3 to 9 µm. This allowed the roller to create depressions at at least one point on the wire.

[0063] A device comprising at least the following components can also be formed: (1) A first contact surface, (2) A wire according to the second or third aspect of the invention, or a wire obtainable by a method according to the first aspect of the invention, or according to one or more of the respective embodiments described therein; wherein the wire is electrically conductively connected to the first contact surface.

[0064] Optionally, the wire can be electrically connected to one or more additional contact surfaces.

[0065] Also contemplated is the use of a roller comprising a relief for producing a wire, wherein the roller has a—preferably cylindrical—surface, and the relief is characterized by a height difference (D) of the surface in a range from 3 to 9 µm—for example, from 4 to 8 µm, or 5 to 7 µm, or 4 to 9 µm, or 5 to 9 µm—wherein depressions are introduced by the roller at at least one location on the wire. Preferably, the depressions are introduced on one side of the wire if the wire is a ribbon.

[0066] Also contemplated is the use of a roller comprising a relief for adjusting the roughness R z at at least one point on a wire in a range from 3 to 9 µm - for example from 4 to 8 µm, or 5 to 7 µm, or 4 to 9 µm, or 5 to 9 µm -, wherein the roller has a - preferably cylindrical - surface, and the relief is characterized by a height difference (D) of the surface. Preferably, the roughness R z is introduced on one side of the wire when the wire is a ribbon. Preferred embodiments of the first subject matter of the invention are also preferred here, insofar as they relate to the roller, the adjustment of the roughness R z , the roughness R z and the height difference (D). Figures

[0067] The present invention is further illustrated below with reference to figures and examples.

[0068] Neither the figures nor the examples imply a limitation of the claimed subject matter. Fig. 1 shows a schematic view of a wire or wire precursor. Fig. 2 shows a view of a cross-sectional area QA of the in Figure 1 shown object. Fig. 3 shows schematically a method for introducing recesses into a wire. Fig. 4 shows a ribbon a) with relief, b) with brushing. Fig. 5 shows schematically a device with a wire and a contact surface. Description of the characters

[0069] Figure 1 shows a schematic view of a wire 2 or a wire precursor 1 characterized by its length L and a cross-sectional plane QE .

[0070] Figure 2 shows a view of a cross-sectional area QA, as part of the Figure 1 shown cross-sectional plane QE .Due to the cross-sectional area QA are two perpendicular lines L1, L2, These intersect the cross-sectional area QA in the edges of the wire 2 or the wire precursor 1. This will make the sections AL1 and AL2 the lines L1 and L2 formed.

[0071] Figure 3 shows schematically a method for introducing depressions 3 into a wire 2 using a roller with a relief (upper roller, no reference symbol). The lower roller is optional and can be replaced with a different counter surface.

[0072] Figure 4 shows the surface topography a) of a ribbon 2 with inserted pattern 6 from depressions 3; b) a brushed ribbon.

[0073] Figure 5 shows schematically a device 10 containing a wire 2,which has a first contact surface 12 with a second contact surface 13. Test methods a. Determination of relief height and roughness

[0074] The relief height D and the roughness R z of the wire were determined in accordance with the standards DIN EN ISO 4287 (2010-07) (definition and parameters) and DIN EN ISO 4288 (1998-04) (rules and procedures). The relief height of the roll and the roughness of the wire were determined transverse to the rolling direction. In deviation from the DIN EN ISO 4288 standard, due to the geometric conditions of the ribbons, measurements were taken over a short individual and overall measuring section. A sufficiently long individual measuring section was defined as at least one-third of the ribbon width or the effectively used roll width. A Mahr Perthometer PCV with a 2 µm diamond tip was used. The determination was carried out at at least two different points on the wire or roll. The measured data was evaluated in accordance with DIN EN ISO 4287 using the program MahrSurface XCR20 V1.20-4. b. Determination of the cross-sectional area of ​​a wire or ribbon

[0075] To determine the cross-sectional area, a metallographic section was made and measured using an optical microscope. Examples

[0076] The invention is further illustrated below by examples. The invention is not limited to the examples or the combinations of features or parameters shown therein. 1. Manufacturing copper ribbons

[0077] Copper round wires with a diameter of 0.78 mm and a purity of 99.98 wt.% Cu were used as starting material. The wires were passed through a forming machine with two hard metal rollers in the Figure 3outlined arrangement. Roll No. 1 (in the figure below) was a smooth cylinder with a diameter of 96 mm. Roll No. 2 (in the figure above) also had a cylindrical basic shape with a diameter of 96 mm. In the case of the formed wires (1) - (3), the surface of roll No. 2 had a relief with a relief height D (D max ). In the case of the formed wires (A) and (B), the surface of roll No. 2 was smooth and had no relief structure whatsoever. The wires were passed between rolls No. 1 and No. 2, which rotated in opposite directions but in the transport direction of the wires. Rolls No. 1 and No. 2 had a roll gap S between them. This was set and determined as the shortest distance between the surface of roll No. 1 and the surface of the cylindrical basic shape of roll No. 2, i.e. at a point without relief.The exit speed of the wires in the transport direction was identical to the rotational speed v of the rolls at the contact surface with the wire. A rapidly evaporating rolling oil B-Clean 62S was used as the rolling oil. After the rolling step, the formed wires (1) - (3) and (A) and (B) were annealed in a 2.5 m long continuous furnace at a throughput speed of 10 m / min and an annealing temperature TG of 650°C in a hydrogen atmosphere. After annealing, the formed wires were cooled to ambient temperature. The formed comparison wires (A) and (B) were brushed after the annealing process according to the characteristics in Table 2. The characteristics of the formed wires (1) - (3) are given in Table 1. Table 1 Example No. (1) (2) (3) Relief height D (µm) 4,88 8,63 20,85 D max -roller (µm) 5,99 11,41 22,38 Roll gap size S 0,2 Rotational speed v 45 m / min Dimensions of the ribbon / cross-sectional area of ​​the ribbon after forming 0,20 x 2,05 Rmax (µm) 3,88 9,15 19,19 Roughness R z (µm) 3,32 6,824 18,612 Table 2 Example No. (A) (B) Dimensions of the ribbon / cross-sectional area of ​​the ribbon after forming 0,20 x 2,05 Roughness R max before brushing (µm) 0,87 Roughness R z before brushing (µm) 0,679 Brush material Roller brushes made of high-strength steel Brush wire diameter [µm] 1x 200 + 1x 100 1x 200 Brush rotation speed [rpm] 900 Ribbon speed [m / min] 3 1 Roughness R max after brushing (µm) 4,55 10,96 Roughness R z after brushing (µm) 3,16 6,24 2. Assessment of the quality of the formed wires

[0078] Example No. (1) (2) (3) (A) (B) Residues on the formed wire surface + + + - - - Spatter occurring during the laser bonding process + + - - - - -

[0079] The quality of the formed wires was assessed visually with regard to unwanted residues on the surface using scanning electron microscope images: +: no residues, -: little residues, - - : a lot of residues

[0080] In the next step, the behavior of the formed wires during laser bonding was investigated with regard to any spattering that might occur. For this purpose, the formed wires were bonded into identically constructed electronic components using the same laser bonder settings. The spatter that occurred was counted using an optical microscope: +: no spatter, -: few spatter, - -: many spatter.

[0081] It was observed that the brushed, formed wires (A) and (B) exhibited residues on their surfaces. More residues were identified on the surface in the case of the larger indentations. These residues led to spattering behavior of the brushed, formed wires (A) and (B) during the laser bonding process. In contrast, no residues were detected on the surfaces of the formed wires (1) - (3).

[0082] The formed wires (1) and (2) with a roughness of R z less than 9 µm showed no spatter behavior during the laser bonding process. In contrast, the formed wire (3) with an increased roughness of R z of 18.6 µm showed significant spatter behavior during the laser bonding process. List of reference symbols

[0083] 1Wire precursor 2Wire 3Depression 4Roller 5Roller surface 6Relief 7First side 8Next side 10Device 11Substrate 12First contact surface DHeight difference QE Cross-sectional plane QA Cross-sectional area LLength L1, L2Line A L1 , A L2 Section

Claims

1. A method for producing a wire (2), comprising at least the following steps: (i) providing a wire precursor (1); (ii) pressing indentations (3) into the wire precursor (1); and (iii) annealing the wire precursor (1) provided with indentations (3) to obtain the wire (2); wherein the wire (2) has a proportion of at least 95 wt.% copper, the proportion being based on the total weight of the wire (2); characterized in that the indentations (3) are made only in a first location (7), wherein the wire (2) has a roughness Rz in a range of 3 to 9 µm in at least the first location; wherein at least one additional location (8) on the wire (2) is smooth and has a roughness Rz in a range of 0.1 to 1 µm, wherein the at least one additional location (8) is in the location on the wire (2) facing away from the first location (7).

2. The method according to claim 1, wherein the pressing-in process is selected from the group consisting of graining, notching, embossing, stamping, recessing, furrowing.

3. The method according to either of the preceding claims, wherein the pressing-in process is carried out by rolling.

4. The method according to claim 3, wherein the rolling is carried out by at least one roller (4), wherein the roller (4) has a cylindrical surface (5) with a relief (6), wherein the relief (6) is formed by height differences (D) of the cylindrical surface (5).

5. The method according to claim 4, wherein the height difference (D) is in a range of 3 to 9 µm.

6. The method according to any of the preceding claims, wherein the indentations (3) form a pattern.

7. The method according to any of the preceding claims, wherein the wire (2) is a bonding wire, preferably a ribbon.

8. The method according to any of the preceding claims, wherein an element selected from the group consisting of the wire (2) and the wire precursor (1) has a cross-sectional area QA in a range of 25,000 to 900,000 µm2, wherein the cross-sectional area QA is arranged perpendicularly to a longitudinal direction L of the element.

9. The method according to any of the preceding claims, wherein a cross-sectional plane QE is laid through an element selected from the group consisting of the wire precursor (1b) and the wire (2), wherein the cross-sectional plane QE is arranged perpendicularly to a longitudinal direction L of the element, wherein the cross-sectional plane QE forms a cross-sectional area QA with the element, wherein the cross-sectional area QA contains two perpendicularly intersecting lines L1 and L2, wherein a shortest possible portion AL1 of the line L1 is defined by a section with the edge of QA, and wherein a longest possible portion AL2 of the line L2 is defined by a section with the edge of QA, wherein the quotient of AL2 and AL1 is a number of 2 or more.

10. A method for producing a device comprising at least one electrically conductive connection, wherein the method comprises the following steps: (I) producing a wire in accordance with a method according to at least one of claims 1 to 9; (II) providing a substrate having at least a first contact surface and the wire; (III) positioning the wire in a mechanical connection with the first contact surface; (IV) heating the first location on the wire by means of electromagnetic radiation in a wavelength range of 700 to 1100 nm while maintaining an electrically conductive connection between the first contact surface of the substrate and the wire, wherein the additional location on the wire facing away from the first location on the wire faces the contact surface.

11. The method according to claim 10, wherein the first location on the wire or the first side of the wire is arranged on the side of the wire facing away from the first contact surface of the substrate.

12. The method according to claim 10 or 11, wherein the roughness Rz in at least the first location on the wire was brought about by rolling, wherein preferably a roller comprising a relief for producing a wire was used for rolling, by means of which indentations were introduced in at least one location on the wire, wherein the relief is characterized by a height difference (D) in a range of 3 to 9 µm.

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