Coated wire

Abstract

The invention relates to a wire comprising a wire core having a surface, which wire core has a coating superimposed on its surface, wherein the wire core itself is a silver-based wire core, wherein the coating is a double layer consisting of a 1 nm to 100 nm thick inner layer of nickel or palladium and an adjacent 1 nm to 250 nm thick outer layer of gold, characterized in that the wire exhibits a total carbon content of ≤ 40 wt.-ppm.

Description

[0001] This invention relates to a coated wire comprising a silver-based wire core and a coating superimposed on the surface of the wire core. The invention also relates to a process for manufacturing such a coated wire.

[0002] The use of bonding wires in electronic and microelectronic applications is a well-known technical practice. Although bonding wires were initially made of gold, cheaper materials such as copper, copper alloys, silver, and silver alloys are now used. These wires may have a metallic coating.

[0003] Regarding wire geometries, the most common are joint lines with a circular cross-section and joint strips with more or less rectangular cross-sections. Both types of wire geometries have their advantages, making them suitable for specific applications.

[0004] The object of the present invention is to provide a coated silver-based wire suitable for wire bonding applications, which has outstanding wire tensile properties and thus allows for high bonding speeds and difficult wire loop shapes.

[0005] The contribution to the solution to the stated objective is provided by the subject matter of the category forming the claims. The dependent claims of the category forming the claims represent preferred embodiments of the invention.

[0006] In a first aspect, the present invention relates to a wire comprising a wire core (hereinafter also simply referred to as "core") having a surface, the wire core having a coating superimposed on its surface, wherein the wire core itself is a silver-based wire core, wherein the coating is a bilayer consisting of a nickel or palladium inner layer of 1 nm to 100 nm thickness and an adjacent gold outer layer of 1 nm to 250 nm thickness, characterized in that the wire exhibits a total carbon (TC) content of ≤40 wt.-ppm (weight-ppm).

[0007] The wire of the present invention is preferably a bonding wire for bonding in microelectronics. The wire is preferably a one-piece object. Many shapes are known and appear to be suitable for the wire of the present invention. Preferred shapes are circular, elliptical, and rectangular in cross-sectional view. For the purposes of this invention, the term "bonding wire" includes all shapes of cross-sections and all common wire diameters, but bonding wires with circular cross-sections and small diameters are preferred. The average cross-section is, for example, 50 μm. 2 Up to 5024μm 2 Or preferably 110μm 2 Up to 2400μm 2 The average diameter is within the range of 8 μm to 80 μm or preferably 12 μm to 55 μm in the case of a preferred circular cross-section.

[0008] The average diameter, or simply the diameter of the wire or wire core, can be obtained through a "sizing method." This method determines the physical weight of a wire of a defined length. Based on this weight, the diameter of the wire or wire core is calculated using the density of the wire material. The diameter is calculated as the arithmetic mean of five measurements taken at five notches on a particular wire.

[0009] The wire core is a silver-based core; that is, the wire core is composed of silver-based material in the form of (a) silver doping, (b) silver alloy or (c) silver alloy doping.

[0010] As used herein, the term “silver doped” means a silver-based material consisting of: (a1) silver in an amount ranging from >99.49 wt.% to 99.997 wt%, (a2) at least one dopant element other than silver in a total amount ranging from 30 wt.% to <5000 wt.% to ppm%, and (a3) ​​additional components (other than silver and at least one dopant element) in a total amount ranging from 0 wt.% to 100 wt.% to ppm. In a preferred embodiment, the term “doped silver” as used herein means doped silver consisting of: (a1) silver in an amount ranging from >99.49% to 99.997% by weight, (a2) at least one doping element selected from the group consisting of calcium, nickel, platinum, palladium, gold, copper, rhodium and ruthenium in a total amount ranging from 30 wt.-ppm to <5000 wt.-ppm, and (a3) ​​additional components (other than silver, calcium, nickel, platinum, palladium, gold, copper, rhodium and ruthenium) in a total amount ranging from 0 wt.-ppm to 100 wt.-ppm.

[0011] As used herein, the term "silver alloy" means a silver-based material consisting of: (b1) silver in an amount ranging from 89.99% to 99.5% by weight, preferably from 97.99% to 99.5% by weight; (b2) at least one alloying element in a total amount ranging from 0.5% to 10% by weight, preferably from 0.5% to 2% by weight; and (b3) other components (other than silver and at least one alloying element) in a total amount ranging from 0 wt.-ppm to 100 wt.-ppm. In a preferred embodiment, the term "silver alloy" as used herein means a silver alloy consisting of: (b1) silver in an amount ranging from 89.99% to 99.5% by weight, preferably from 97.99% to 99.5% by weight; (b2) at least one alloying element selected from the group consisting of nickel, platinum, palladium, gold, copper, rhodium and ruthenium in a total amount ranging from 0.5% to 10% by weight, preferably from 0.5% to 2% by weight; and (b3) additional components (other than silver, nickel, platinum, palladium, gold, copper, rhodium and ruthenium) in a total amount ranging from 0 wt.-ppm to 100 wt.-ppm.

[0012] As used herein, the term "doped silver alloy" means a silver-based material consisting of: (c1) silver in an amount ranging from >89.49 wt% to 99.497 wt%, preferably from 97.49 wt% to 99.497 wt%; (c2) at least one doping element in a total amount ranging from 30 wt.-ppm to <5000 wt.-ppm; (c3) at least one alloying element in a total amount ranging from 0.5 wt% to 10 wt%, preferably from 0.5 wt% to 2 wt%; and (c4) additional components (other than silver, at least one doping element, and at least one alloying element) in a total amount ranging from 0 wt.-ppm to 100 wt.-ppm, wherein the at least one doping element (c2) is different from the at least one alloying element (c3). In a preferred embodiment, the term "silver-doped alloy" as used herein means a silver-doped alloy consisting of: (c1) silver in an amount ranging from >89.49% to 99.497% by weight, preferably from 97.49% to 99.497% by weight; (c2) at least one dopant element selected from the group consisting of calcium, nickel, platinum, palladium, gold, copper, rhodium, and ruthenium in a total amount ranging from 30 wt.-ppm to <5000 wt.-ppm; (c3) at least one alloying element selected from the group consisting of nickel, platinum, palladium, gold, copper, rhodium, and ruthenium in a total amount ranging from 0.5% to 10% by weight, preferably from 0.5% to 2% by weight; and (c4) additional components (other than silver, calcium, nickel, platinum, palladium, gold, copper, rhodium, and ruthenium) in a total amount ranging from 0 wt.-ppm to 100 wt.-ppm, wherein the at least one dopant element (c2) is different from the at least one alloying element (c3).

[0013] This disclosure refers to "additional components" and "doping elements". The individual amount of any additional component is less than 30 wt.-ppm. The individual amount of any doping element is at least 30 wt.-ppm. All amounts, expressed in weight percent and wt.-ppm, are based on the total weight of the core or its precursor article or elongated precursor article.

[0014] The core of the wire of the present invention may contain so-called additional components in total amounts ranging from 0 wt.-ppm to 100 wt.-ppm, for example, from 10 wt.-ppm to 100 wt.-ppm. In the context of the present invention, additional components (also commonly referred to as "unavoidable impurities") are impurities originating from the raw materials used or from trace amounts of chemical elements and / or compounds arising from the wire core manufacturing process. The low total amount of additional components, from 0 wt.-ppm to 100 wt.-ppm, ensures good reproducibility of the wire properties. Additional components present in the core are generally not added individually. Based on the total weight of the wire core, the amount of each individual additional component is less than 30 wt.-ppm.

[0015] The core of a wire is a homogeneous region of bulk material. Since any bulk material always has surface areas that can exhibit different properties to some extent, the properties of the wire core are understood as the properties of the homogeneous region of the bulk material. The surface of the bulk material region can differ in morphology, composition (e.g., sulfur, chlorine, and / or oxygen content), and other characteristics. This surface is the interface region between the wire core and the coating superimposed on it. Typically, the coating is completely superimposed on the surface of the wire core. In the region of the wire between the core and the coating superimposed thereon, a combination of materials from both the core and the coating may exist.

[0016] The coating superimposed on the surface of the wire core is a double layer, consisting of an inner layer of nickel or palladium with a thickness of 1 nm to 100 nm, preferably 1 nm to 30 nm, and an adjacent outer layer of gold with a thickness of 1 nm to 250 nm, preferably 20 nm to 200 nm. In this context, the term "thickness" or "coating thickness" refers to the magnitude of the coating in the direction perpendicular to the longitudinal axis of the core.

[0017] In one embodiment, the gold outer layer comprises at least one component selected from the group consisting of antimony, bismuth, arsenic, and tellurium, and the total proportion of the at least one component is in the range of 10 wt.-ppm to 100 wt.-ppm, preferably 10 wt.-ppm to 40 wt.-ppm, based on the weight of the wire (wire core plus double coating). Meanwhile, in another embodiment, the total proportion of the at least one component is in the range of 300 wt.-ppm to 3500 wt.-ppm, preferably 300 wt.-ppm to 2000 wt.-ppm, and most preferably 600 wt.-ppm to 1000 wt.-ppm, based on the weight of gold in the gold layer. In a variation of this embodiment, it is preferred that antimony is present within the gold layer. Even more preferred is that antimony exists solely within the gold layer, i.e., bismuth, arsenic, and tellurium are not present simultaneously. In other words, in a preferred variant of the embodiment, the gold layer comprises antimony in a weight percentage ranging from 10 wt.-ppm to 100 wt.-ppm, preferably from 10 wt.-ppm to 40 wt.-ppm, based on the wire (wire core plus double coating), while bismuth, arsenic, and tellurium are absent from the gold layer; simultaneously, in even more preferred embodiments, the proportion of antimony, based on the weight of gold in the gold layer, can range from 300 wt.-ppm to 3500 wt.-ppm, preferably from 300 wt.-ppm to 2000 wt.-ppm, and most preferably from 600 wt.-ppm to 1000 wt.-ppm. In embodiments, at least one component selected from the group consisting of antimony, bismuth, arsenic, and tellurium can exhibit a concentration gradient within the gold layer, said gradient increasing in the direction toward the wire core (i.e., in the direction perpendicular to the longitudinal axis of the wire core). It is unknown in what chemical form or as what chemical species said at least one component exists in the gold layer, i.e., whether it exists in the gold layer in elemental or compound form.

[0018] Importantly, the wire of the present invention exhibits a total carbon content of ≤40 wt.-ppm; that is, a total carbon content of ≤40 wt.-ppm based on the weight of the wire (wire core plus double coating). In other words, the total carbon content of the wire is in the range of 0 wt.-ppm to 40 wt.-ppm; preferably, in the range of 10 wt.-ppm to 30 wt.-ppm. The total carbon content can be determined according to analytical method A of ASTM E1019 as described below. In a preferred embodiment, the wire of the present invention exhibits a carbon content of ≤3 mg carbon per square meter of wire surface (i.e., the gold coating surface of the wire). In other words, preferably, the carbon content on the wire surface is in the range of 0 mg to 3 mg carbon per square meter of wire surface; 0.5 mg to 2.5 mg carbon per square meter of wire surface is preferred, wherein 0.5 mg to 2 mg carbon per square meter of wire surface is even more preferred. The carbon content on the wire surface can be determined by instrumental gas analysis (analytical method B) as described below.

[0019] Unless otherwise stated, all standards referenced in this document are the current versions as of the submission date.

[0020] Determining the total carbon content and the carbon content on the wire surface are quantitative analytical methods; neither allows for the determination of the chemical properties of carbon. Therefore, it is unknown in what chemical form or as what chemical species carbon exists.

[0021] If the total carbon content of the wire exceeds the upper limit of 40 wt.-ppm, the wire appears to become "sticky," resulting in weakened tensile properties and an inability to unwind freely from the wire spool. This leads to an undesirable and unacceptable stop in the wire bonding process, known as a bonding machine stop. The situation worsens if the carbon content on the wire surface exceeds the upper limit of 3 mg carbon per square meter.

[0022] Assume that the total carbon (if any) may be derived from: (i) additives, such as conventional drawing lubricants used, for example, during the drawing process steps (2) and / or (4) below, and / or in particular (ii) at least one quenching additive that may be used during the quenching sub-step of the process step (5) below.

[0023] This disclosure refers to "at least one quenching additive." This at least one quenching additive comprises carbon and is particularly selected from the group consisting of anionic surfactants and water-soluble organic solvents. The anionic surfactant is characterized by a negatively charged hydrophilic polar group attached to a hydrophobic residue, such as a carboxylate group, sulfate group, or sulfonate group directly attached to a long-chain hydrocarbon residue or attached via a linking group to the long-chain hydrocarbon residue. Examples of such anionic surfactants particularly include corresponding base (sodium or potassium) salts or NH4- salts, such as, for example, ammonium lauryl sulfate, sodium lauryl polyoxyethylene ether sulfate, sodium lauryl sarcosinate, sodium myristyl ether sulfate, sodium alkanol polyether sulfate, sodium stearate, sodium lauryl sulfate, and ammonium lauryl polyoxyethylene ether sulfate. Examples of water-soluble organic solvents particularly include alcohols, such as methanol, ethanol, n-propanol, and isopropanol, as well as water-soluble glycol ethers.

[0024] It is further assumed that the carbon on the wire surface (if any) may originate from the at least one quenching additive that may be used during the quenching sub-step of process step (5) below.

[0025] It has been found that the use of the additives (such as conventional drawing lubricants) has only a limited effect on the total carbon content and the carbon content on the wire surface; that is, the use of the conventional drawing lubricants is acceptable and does not cause the total carbon content threshold and the carbon content threshold on the wire surface to be exceeded. However, at least one quenching additive that may be used during the quenching sub-step of process step (5) below has a stronger effect, and it has been found that its amount should not exceed a certain threshold in any aqueous quenching solution used during the quenching sub-step of process step (5) below. Therefore, it is important that the quenching sub-step of the following process step (5) is carried out using water as a carbon-free quenching medium or preferably in the form of an aqueous quenching solution, the aqueous quenching solution comprising water and at least one quenching additive or consisting of water and at least one quenching additive present in an amount that results in a total organic carbon (TOC) content of the aqueous quenching solution ≤10 mg / L; a total organic carbon content of the aqueous quenching solution in the range of >0.0001 mg / L to 10 mg / L is preferred, wherein the range of >0.001 mg / L to 10 mg / L is even more preferred.

[0026] The total organic carbon content of the aqueous quenching solution can be determined according to analytical method C of ASTM D7573 as described below.

[0027] In another aspect, the invention also relates to a process for manufacturing the coated wire of the invention in any of the disclosed embodiments above. The process comprises at least steps (1) to (5):

[0028] (1) Provide silver-based precursor items

[0029] (2) Stretch the precursor article to form an elongated precursor article until a value of 706 μm is obtained. 2 Up to 31400μm 2 The intermediate cross-section within the range of 30μm to 200μm, or the intermediate diameter within the range of 30μm to 200μm.

[0030] (3) Apply a double coating of nickel or palladium inner layer and an adjacent gold outer layer to the surface of the elongated precursor article obtained after process step (2).

[0031] (4) Further elongate the coated precursor article obtained after process step (3) until the desired final cross-section or diameter and a bilayer are obtained, the bilayer consisting of an inner layer of nickel or palladium having a desired final thickness in the range of 1 nm to 100 nm and an adjacent outer layer of gold having a desired final thickness in the range of 1 nm to 250 nm, and

[0032] (5) Finally, the coated precursor obtained after process step (4) is subjected to strand annealing at an oven temperature in the range of 200°C to 600°C for an exposure time in the range of 0.4 seconds to 0.8 seconds, and the coated precursor is then quenched to form coated wire.

[0033] Step (2) may include one or more of the following sub-steps: intermediate batch annealing of the precursor article at an oven setting temperature of 400°C to 800°C for an exposure time of 50 to 150 minutes, and wherein the application of the gold layer in step (3) is performed by electroplating the gold layer from a gold plating bath containing gold.

[0034] This document uses the term "stretch annealing." It is a continuous process that allows for the rapid production of materials with high reproducibility. In the context of this invention, stretch annealing means that annealing is performed dynamically as the coated precursor to be annealed is pulled or moved through a conventional annealing oven and wound onto a reel after leaving the annealing oven. Here, the annealing oven is typically in the form of a cylindrical tube of a given length. The annealing time / oven temperature parameters can be defined and set using its defined temperature profile at a given annealing rate selectable, for example, from 10 m / min to 60 m / min.

[0035] The term "oven set temperature" is used in this article. It refers to the temperature fixed in the temperature controller of the annealing oven. The annealing oven can be a chamber furnace type oven (in the case of batch annealing) or a tubular annealing oven (in the case of strand annealing).

[0036] This disclosure distinguishes between precursor articles, elongated precursor articles, coated precursor articles, coated precursors, and coated wires. The term "precursor article" is used for those early stages of wires that have not yet reached the desired final cross-section or final diameter of the wire core, while the term "precursor" is used for the early stages of wires that are at the desired final cross-section or desired final diameter. After process step (5) is completed, i.e., after the final stranding annealing of the coated precursor at the desired final cross-section or desired final diameter, the coated wire in the sense of this invention is obtained.

[0037] The precursor article provided in process step (1) is a silver-based precursor article; that is, the precursor article consists of (a) silver doping, (b) a silver alloy, or (c) a silver-doped alloy. For the meaning of the terms “silver doping,” “silver alloy,” and “silver-doped alloy,” refer to the aforementioned disclosure.

[0038] Silver-based precursor articles can be obtained by alloying, doping, or alloying and doping with silver in desired amounts of the required components. Doped silver or silver alloys or silver-doped alloys can be prepared using conventional processes known to those skilled in the art of metal alloys, for example, by melting the components together in a desired proportional ratio. In doing so, one or more conventional master alloys can be used. The melting process can be performed, for example, using an induction furnace, and advantageously, under a vacuum or in an inert gas atmosphere. The materials used can have a purity grade of, for example, 99.99% by weight or higher. The resulting melt can be cooled to form a homogeneous sheet of the silver-based precursor article. Typically, such precursor articles are in the form of rods having a diameter of, for example, 2 mm to 25 mm and a length of, for example, 2 m to 100 m. Such rods can be produced by continuously casting a silver-based melt using a suitable mold, followed by cooling and solidification.

[0039] In process step (2), the precursor article is elongated to form an elongated precursor article until a value of 706 μm is obtained. 2 Up to 31400μm 2 The intermediate cross-section or intermediate diameter is within the range of 30 μm to 200 μm. Techniques for drawing precursor articles are known and appear useful in the context of this invention. Preferred techniques are rolling, forging, die drawing, etc., with die drawing being particularly preferred. In the latter case, the precursor article is drawn in several process steps until the desired intermediate cross-section or desired intermediate diameter is achieved. Such wire drawing processes are well known to those skilled in the art. Conventional tungsten carbide and diamond dies can be used, and additives (such as conventional drawing lubricants) can be used to support the drawing process.

[0040] Step (2) of the process of the present invention may include one or more of the following sub-steps: intermediate batch annealing of the elongated precursor article at an oven set temperature in the range of 400°C to 800°C for an exposure time in the range of 50 minutes to 150 minutes. For example, the optional intermediate batch annealing may be performed on a bar that has been drawn to a diameter of 2 mm and wound on a roller.

[0041] Optional intermediate batch annealing of process step (2) can be performed under an inert or reducing atmosphere. Many types of inert atmospheres and reducing atmospheres are known in the art and are used to purge the annealing oven. Among known inert atmospheres, nitrogen or argon is preferred. Among known reducing atmospheres, hydrogen is preferred. Another preferred reducing atmosphere is a mixture of hydrogen and nitrogen. A preferred hydrogen and nitrogen mixture is 90 vol% to 98 vol% nitrogen and correspondingly 2 vol% to 10 vol% hydrogen, wherein the total vol% is 100 vol%. Preferred nitrogen / hydrogen mixtures are equal to 93 / 7 vol% / vol%, 95 / 5 vol% / vol%, and 97 / 3 vol% / vol%, each based on the total volume of the mixture.

[0042] In process step (3), a coating in the form of a double coating of nickel or palladium inner layer and an adjacent gold outer layer is applied to the surface of the elongated precursor article obtained after process step (2) is completed, so as to superimpose the coating on the surface.

[0043] Those skilled in the art know how to calculate the thickness of such a coating on an elongated precursor article to ultimately (i.e., after the coated precursor article has been ultimately elongated) obtain a coating at the layer thickness disclosed in the embodiment for wire. Those skilled in the art are familiar with various techniques for forming a coating of the material according to the embodiment on a silver-based surface. Preferred techniques include material deposition from vapor deposition (such as electroplating and electroless plating), such as sputtering, ion plating, vacuum evaporation, and physical vapor deposition, as well as material deposition from melt. In the case of applying the bilayer consisting of a nickel or palladium inner layer and a gold outer layer, it is preferred to apply the nickel or palladium layer by electroplating.

[0044] Gold is applied by electroplating. Gold plating is performed using a gold plating bath (i.e., a plating bath that allows gold to be plated onto the cathode surface of nickel or palladium). In other words, a gold plating bath is a composition that allows the direct application of elemental, metallic gold onto the surface of nickel or palladium, where the wiring serves as the cathode. The gold plating bath contains gold and preferably also contains at least one component selected from the group consisting of antimony, bismuth, arsenic, and tellurium; therefore, the gold plating bath is preferably a composition that not only allows the deposition of elemental gold but also preferably allows the deposition of at least one component selected from the group consisting of antimony, bismuth, arsenic, and tellurium within the gold layer. It is unknown what chemical species the at least one component is, i.e., whether it exists in the gold layer in elemental form or as a compound. Preferred gold plating baths can be prepared by adding the at least one component in a suitable chemical form to an aqueous composition containing gold as a dissolving salt or a class of dissolving salts. An example of such an aqueous composition to which at least one component can be added is produced by Atotech. K 24HF and manufactured by Umicore 558 and 559. Alternatively, a gold plating bath already containing at least one component selected from the group consisting of antimony, bismuth, arsenic, and tellurium, such as MetGold Pure ATF manufactured by Metalor, may be used. The concentration of gold in the gold plating bath may be, for example, in the range of 8 g / L to 40 g / L, preferably 10 g / L to 20 g / L. In a preferred gold plating bath, the concentration of at least one component selected from the group consisting of antimony, bismuth, arsenic, and tellurium may be, for example, in the range of 15 wt.-ppm to 50 wt.-ppm, preferably 15 wt.-ppm to 35 wt.-ppm.

[0045] The electroplating of a gold layer is performed by guiding an elongated precursor article coated with nickel or palladium, with wiring serving as the cathode, through a gold plating bath. Before performing process step (4), the thus-obtained gold-coated precursor article leaving the gold plating bath can be rinsed and dried. Water is advantageous as the rinsing medium, with alcohols and alcohol / water mixtures being further examples. Gold plating of the elongated precursor article coated with nickel or palladium through the gold plating bath can be performed at a DC voltage, for example, in the range of 0.2V to 20V, and at a current, for example, in the range of 0.001A to 5A, particularly 0.001A to 1A or 0.001A to 0.2A. The contact time is typically in the range of, for example, 0.1 seconds to 30 seconds, preferably 2 seconds to 8 seconds. The current density used in this context can be, for example, 0.01A / dm³. 2 Up to 150A / dm 2 Within a certain range. The gold plating bath may have a temperature in the range of, for example, 45°C to 75°C, preferably 55°C to 65°C.

[0046] The thickness of the gold coating can be adjusted as needed, primarily by the following parameters: the chemical composition of the gold plating bath, the contact time between the elongated precursor article and the gold plating bath, and the current density. In this context, the thickness of the gold layer can typically be increased by increasing the gold concentration in the gold plating bath, by increasing the contact time between the elongated precursor article, which is used as a cathode, and the gold plating bath, and by increasing the current density.

[0047] In process step (4), the coated precursor article obtained after process step (3) is further stretched until (4) a desired final cross-section or diameter of a double-layered wire is obtained, the double layer consisting of an inner layer of nickel or palladium having a desired final thickness in the range of 1 nm to 100 nm, preferably 1 nm to 30 nm, and an adjacent outer layer of gold having a desired final thickness in the range of 1 nm to 250 nm, preferably 20 nm to 200 nm. The technique used to stretch the coated precursor article is the same stretching technique mentioned above in the disclosure of process step (2).

[0048] Process step (5) includes a stranding annealing sub-step and a quenching sub-step. In process step (5), the coated precursor obtained after process step (4) is finally subjected to stranding annealing at an oven set temperature in the range of 200°C to 600°C, preferably 350°C to 500°C, for an exposure time in the range of 0.4 seconds to 0.8 seconds, and quenched to form a coated wire. The finally stranded annealed coated precursor (i.e., the still hot coated wire) is quenched in water, or preferably in an aqueous quenching solution containing water and at least one quenching additive, or water and at least one quenching additive, wherein the at least one quenching additive is present in an amount resulting in a total organic carbon content of ≤10 mg / L in the aqueous quenching solution. A total organic carbon content of the aqueous quenching solution in the range of >0.0001 mg / L to 10 mg / L is preferred, wherein the range of >0.001 mg / L to 10 mg / L is even more preferred. Quenching means cooling the coated precursor, which is to be finalized and annealed, from the temperature it experienced in process step (5) to room temperature immediately or rapidly (i.e., within 0.2 to 0.6 seconds), for example by immersion or dripping.

[0049] After the stranding annealing and quenching of process step (5) are completed, the coated wire of the present invention is finished. To fully benefit from its properties, it is advantageous to use it immediately (i.e., without delay, for example, within 28 days after the completion of process step (5)) for wire bonding applications. Alternatively, in order to maintain the wire's wide wire bonding process window properties and to prevent its oxidation or other chemical corrosion, the finished wire is typically wound and vacuum-sealed immediately after the completion of process step (5) (i.e., without delay, for example, within <1 hour to 5 hours after the completion of process step (5)) and then stored for further use as bonding wire. Storage under vacuum-sealed conditions should not exceed 12 months. After the vacuum seal is opened, the wire should be used for wire bonding within 28 days.

[0050] Preferably, all process steps (1) to (5), as well as winding and vacuum sealing, are performed under cleanroom conditions (US FEDSTD 209E Cleanroom Standard, 1k Standard).

[0051] A third aspect of the invention is a coated wire that can be obtained by the process disclosed above according to any embodiment thereof. It has been found that the coated wire of the present invention is well-suited for use as a bonding wire in wire bonding applications. Example

[0052] Analytical methods A through C.

[0053] A. Determination of the total carbon content of the wire

[0054] The total carbon (TC) content of the wire was determined using a CS 844 analyzer from LECO based on ASTM E 1019. For each analysis, 0.5 g of the corresponding wire and 1.5 g of Leco Cu accelerator were placed in an alumina crucible. The crucible was heated to 1500 °C for 45 s in an oxygen flow (3 L / min) to oxidize the carbon in the wire. The oxidized carbon was detected by infrared absorption.

[0055] B. Determination of carbon content on wire surface

[0056] The carbon content on the wire surface was determined using an RC 612 multiphase determinant from LECO. It will show 0.22 dm. 2 A section of wire with a surface area of ​​[missing information] was placed in a nickel crucible and heated at 600°C for 120 s in an oxygen flow (0.5 L / min). The oxidized carbon was detected by infrared absorption.

[0057] C. Determination of the total organic carbon (TOC) content of aqueous quenching solutions

[0058] TOC is determined by ASTM D7573.

[0059] Evaluation of the ball-wedge bonding process and the stopping of the bonding machine

[0060] Ball-wedge bonding involves multiple steps: first EFO firing, wire tip melting, free air ball (FAB) formation, first bonding to bonding pads (ball bonding), looping, second bonding on substrate or plated fingers (wedge bonding or pin bonding), and wire tail cutting.

[0061] Here, the FAB descends from a predefined height (203.2 μm tip) and speed (6.4 μm / s contact speed) to the Al-0.5 wt% Cu bonding pad. Upon contact with the bonding pad, a set of defined bonding parameters (100 g bonding force, 95 mA ultrasonic energy, and 15 ms bonding time) come into play to deform the FAB and form a bonding ball. After the bonding ball is formed, a capillary rises to a predefined height (152.4 μm junction height and 254 μm loop height) to form a loop. After the loop is formed, the capillary descends to the lead to form a pin. After the pin is formed, the capillary rises, and the wire clamp closes to cut the wire to form a predefined tail length (254 μm tail length extension). For each sample, a considerable number of 1250 wires are bonded.

[0062] Evaluation of the stopping of the coupling machine :

[0063] Poor: ≥1 splicing machine stops during the formation of 1250 wire splices. Unwinding the wire from the spool is difficult, or the tail cut is of inconsistent length, resulting in a short tail. This means there is not enough wire remaining for EFO burning and the splicing machine stops. This is disadvantageous because lead wire needs to be threaded to restart the splicing cycle.

[0064] Good: Zero splicing machines stopped during the formation of 1250 wire splices.

[0065] Wire Examples 1 to 8

[0066] 98.5% silver (Ag) and 1.5% palladium (Pd), each exhibiting a purity of at least 99.99% by weight (“4N”), were melted in a crucible. The melt was then continuously cast into wire core precursor articles in the form of 8mm rods. The rods were then drawn in several drawing steps to form wire core precursors with a circular cross-section having a diameter of 2mm. The wire core precursors were then subjected to intermediate batch annealing at an oven setting temperature of 500°C for 60 minutes. The rods were further drawn in several drawing steps to form wire core precursors with a circular cross-section having a diameter of 46μm. The wire core precursors were then electroplated with a double-layer coating of a nickel inner layer and an adjacent gold outer layer. For this purpose, the wire core precursors were moved through a 60°C nickel plating bath while the wiring acted as the cathode, and subsequently through a 61°C gold plating bath. The nickel plating bath contains 90 g / L Ni(SO3NH2)2, 6 g / L NiCl2 and 35 g / L H3BO3, while the gold plating bath (based on Metalor's MetGold Pure ATF) has a gold content of 13.2 g / L and an antimony content of 20 wt.-ppm.

[0067] The coated wire precursor was then further stretched to a final diameter of 20 μm, followed by a final strand annealing at a set temperature of 430 °C for 0.6 seconds. The resulting coated wire was then quenched in water (Type II deionized water from Bestchem) or in an aqueous quenching solution (Type II deionized water from Bestchem with isopropanol and / or anionic surfactant (sodium stearate)) as shown in Table 1. Each wire was in contact with the aqueous quenching solution for 0.3 s. After quenching, the wire was wound into 300 m lengths.

[0068] The 20μm thick wire has a 9nm thick nickel inner layer and an adjacent 90nm thick gold outer layer.

[0069] Table 1

[0070]

[0071] Examples 1 to 5: According to the present invention

[0072] Examples 6 to 8: Comparative Examples

Claims

1. A wire comprising a wire core having a surface, the wire core having a coating superimposed on its surface, wherein the wire core itself is a silver-based wire core, wherein the coating is a bilayer consisting of a nickel or palladium inner layer of 1 nm to 100 nm thickness and an adjacent gold outer layer of 1 nm to 250 nm thickness, characterized in that, The wire exhibits a total carbon content of ≤40wt.-ppm and a carbon content of 0.5mg to 2mg per square meter of the wire surface.

2. The wire according to claim 1, wherein the wire has a diameter of 50µm. 2 Up to 5024µm 2 The average cross-section within the range.

3. The wire according to claim 1, wherein the wire has a circular cross-section with an average diameter in the range of 8µm to 80µm.

4. The wire according to any one of claims 1-3, wherein the nickel or palladium inner layer is 1 nm to 30 nm thick.

5. The wire according to any one of claims 1-3, wherein the gold outer layer is 20 nm to 200 nm thick.

6. The wire according to any one of claims 1-3, wherein the gold outer layer comprises at least one component selected from the group consisting of antimony, bismuth, arsenic and tellurium, and the total proportion of the at least one component is in the range of 10 wt.-ppm to 100 wt.-ppm based on the weight of the wire.

7. The wire according to claim 6, wherein the total proportion of the at least one component is in the range of 300 wt.-ppm to 3500 wt.-ppm based on the weight of gold in the gold outer layer.

8. The wire according to any one of claims 1-3, wherein the total carbon content of the wire is in the range of 10 wt.-ppm to 30 wt.-ppm.

9. A process for manufacturing a wire according to any one of claims 1-8, wherein the process comprises at least steps (1) to (5): (1) Provide silver-based precursor items (2) Stretch the precursor article to form an elongated precursor article until a value of 706µm is obtained. 2 Up to 31400µm 2 The intermediate cross-section within the range of 30µm to 200µm, or the intermediate diameter within the range of 30µm to 200µm. (3) Apply a double coating of nickel or palladium inner layer and an adjacent gold outer layer to the surface of the elongated precursor article obtained after process step (2). (4) Further elongate the coated precursor article obtained after process step (3) until a desired final cross-section or diameter and a bilayer are obtained, the bilayer consisting of an inner layer of nickel or palladium having a desired final thickness in the range of 1 nm to 100 nm and an adjacent outer layer of gold having a desired final thickness in the range of 1 nm to 250 nm, and (5) Finally, the coated precursor obtained after process step (4) is subjected to strand annealing at an oven temperature ranging from 200°C to 600°C for an exposure time ranging from 0.4 seconds to 0.8 seconds, and the coated precursor is quenched to form the coated wire. Step (2) includes one or more of the following sub-steps: intermediate batch annealing of the precursor article at an oven set temperature of 400°C to 800°C for an exposure time ranging from 50 minutes to 150 minutes, and The application of the gold outer layer in step (3) is performed by electroplating the gold outer layer from a gold plating bath containing gold.

10. The process of claim 9, wherein the nickel or palladium layer is applied by electroplating.

11. The process according to claim 9 or 10, wherein the quenching is performed in water.

12. The process according to claim 9 or 10, wherein the quenching is carried out in an aqueous quenching solution comprising water and at least one quenching additive or water and at least one quenching additive, wherein the at least one quenching additive is present in an amount such that the total organic carbon content of the aqueous quenching solution is ≤10 mg / L.

13. The process according to claim 12, wherein the total organic carbon content of the aqueous quenching solution is in the range of >0.0001 mg / L to 10 mg / L.

14. The process according to claim 12, wherein at least one quenching additive is selected from the group consisting of anionic surfactants and water-soluble organic solvents.

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