KR20210133276A - coated wire - Google Patents

Abstract

A wire comprising a wire core having a surface, the wire core having a coating layer superimposed on the surface, the wire core itself being a silver wire core or a silver-based wire core, the coating layer being a single piece of gold 1 to 1000 nm thick - a layer or a double-layer consisting of an inner layer of palladium 1 to 100 nm thick and an adjacent outer layer of gold 1 to 250 nm thick, the gold layer being at least selected from the group consisting of antimony, bismuth, arsenic and tellurium It is characterized in that one member is included in a total proportion ranging from 10 to 100 ppm by weight based on the weight of the wire.

Description

coated wire

The present invention relates to a coated wire comprising a silver or silver-based wire core and a coating layer superposed on the surface of the wire core. The invention also relates to a method for producing such a coated wire.

The use of bonding wires in electronics and microelectronics applications is a well-known and state-of-the-art. Initially, bonding wires were made of gold, but today inexpensive materials such as copper, copper alloys, silver and silver alloys are used. Such wires may have a metallic coating.

Regarding wire geometries, bonding wires of circular cross-section and bonding ribbons of somewhat rectangular cross-section are the most common. Both types of wire geometries have advantages that make them useful for specific applications.

It is an object of the present invention to provide a coated silver or silver based wire suitable for use in wire bonding applications, the wire being particularly excellent for forming spherical free air balls (FABs). The coated silver or silver-based wire to be provided should make it possible to effectively suppress the occurrence of an off-centered ball (OCB) phenomenon during ball bonding.

A contribution to the solution of the above objects is provided by the subject matter of the category-forming claims. The dependent claims of the category-forming claims represent preferred embodiments of the invention, the subject matter of which also serves to solve the above-mentioned objects.

In a first aspect, the present invention provides a wire comprising a wire core (hereinafter, also referred to as "core" for short) having a surface, wherein the wire core has a coating layer superposed on the surface, and the wire core itself is a silver wire a core or a silver-based wire core, wherein the coating layer is a single-layer of gold from 1 to 1000 nm thick or a double-layer consisting of an inner layer of palladium from 1 to 100 nm thick and an adjacent outer layer of gold from 1 to 250 nm thick wherein the gold layer comprises at least one member selected from the group consisting of antimony, bismuth, arsenic and tellurium, from 10 to 10 by weight of the wire. It is characterized in that it contains 100 weight ppm (weight-ppm), preferably in a total proportion in the range of 10 to 40 weight ppm. At the same time, in one embodiment, the total proportion of at least one member selected from the group consisting of antimony, bismuth, arsenic and tellurium is 300 to 3500 ppm by weight, preferably 300 to 2000 ppm by weight, based on the weight of gold in the gold layer. , most preferably in the range of 600 to 1000 ppm by weight.

The wire of the present invention is preferably a bonding wire for bonding in microelectronic devices. The wire is preferably a one-piece object. Numerous shapes are known and appear to be useful for the wire of the present invention. Preferred shapes are (in cross-section) circular, ellipsoidal and rectangular shapes. In the case of the present invention, the term "bonding wire" includes all cross-sectional shapes and all ordinary wire diameters, but bonding wires having circular cross-sections and thin diameters are preferred. The average cross-sectional area is, for example, in the range from 50 to 5024 μm ² , or preferably from 110 to 2400 μm ² ; Thus, in the case of a preferred circular cross-section, the average diameter is, for example, in the range from 8 to 80 μm, or preferably from 12 to 55 μm.

The average diameter, or simply the diameter, of a wire or wire core can be obtained by a “sizing method”. According to this method, the physical weight of the wire for a prescribed length is determined. 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 5 measurements on 5 cuts of a particular wire.

The wire core is a silver wire core or is silver based; That is, the wire core consists of (a) silver, that is, pure silver, or a silver-based material in the form of (b) doped silver, (c) silver alloy or (d) doped silver alloy.

As used herein, the term “pure sliver” refers to (a1) silver in an amount ranging from 99.99 to 100 weight-%, and (a2) additional components (other than silver) in a total amount of 0 to 100 ppm by weight. component) means pure silver.

As used herein, the term "doped sliver" refers to (b1) silver in an amount in the range of >99.49 to 99.997 wt. %, (b2) at least one doping element other than silver in a total amount of 30 to <5000 ppm by weight. , and (b3) additional components (components other than silver and at least one doping element) in a total amount of 0 to 100 ppm by weight. In a preferred embodiment, the term "doped silver" as used herein refers to (b1) silver in an amount ranging from 99.49 to 99.997% by weight, (b2) calcium, nickel, platinum, palladium, gold, copper, rhodium and ruthenium. at least one doping element selected from the group consisting of and in a total amount of 30 to <5000 ppm by weight, and (b3) additional components (silver, calcium, nickel, platinum, palladium, gold, copper, rhodium) in a total amount of 0 to 100 ppm by weight. and components other than ruthenium).

The term "silver alloy" as used herein refers to (c1) silver in an amount ranging from 89.99 to 99.5% by weight, preferably 97.99 to 99.5% by weight, (c2) 0.5 to 10% by weight, preferably 0.5 to 2% by weight. means a silver-based material consisting of at least one alloying element in the total amount of the range, and (c3) additional components (components other than silver and at least one alloying element) in a total amount of 0 to 100 ppm by weight. In a preferred embodiment, the term “silver alloy” as used herein refers to (c1) silver in an amount ranging from 89.99 to 99.5% by weight, preferably 97.99 to 99.5% by weight, (c2) nickel, platinum, palladium, gold, copper , at least one alloying element selected from the group consisting of rhodium and ruthenium and in a total amount in the range from 0.5 to 10% by weight, preferably from 0.5 to 2% by weight, and (c3) a further component in a total amount from 0 to 100 ppm by weight (silver , nickel, platinum, palladium, gold, copper, components other than rhodium and ruthenium) means a silver alloy.

As used herein, the term “doped silver alloy” means (d1) silver in an amount ranging from >89.49 to 99.497 wt%, preferably 97.49 to 99.497 wt%, (d2) at least one in a total amount of 30 to <5000 wtppm. (d3) at least one alloying element in a total amount in the range from 0.5 to 10% by weight, preferably from 0.5 to 2% by weight, and (d4) a further component in a total amount from 0 to 100% by weight (silver, at least one of a doping element and at least one alloying element), wherein the at least one doping element (d2) is different from the at least one alloying element (d3). In a preferred embodiment, the term "doped silver alloy" as used herein refers to (d1) silver in an amount ranging from >89.49 to 99.497 wt%, preferably 97.49 to 99.497 wt%, (d2) calcium, nickel, platinum, at least one doping element selected from the group consisting of palladium, gold, copper, rhodium and ruthenium and in a total amount of from 30 to <5000 ppm by weight, (d3) from the group consisting of nickel, platinum, palladium, gold, copper, rhodium and ruthenium at least one alloying element selected and in a total amount ranging from 0.5 to 10% by weight, preferably from 0.5 to 2% by weight, and (d4) additional components (silver, calcium, nickel, platinum, palladium) in a total amount of 0 to 100 ppm by weight , gold, copper, elements other than rhodium and ruthenium) means a doped silver alloy, wherein at least one doping element (d2) is different from the at least one alloying element (d3).

This disclosure refers to “additional components” and “doping elements”. The individual amounts of any additional components are less than 30 ppm by weight. The individual amounts of optional doping elements are at least 30 ppm by weight. All amounts in weight percent and ppm by weight are based on the total weight of the core or its precursor article or elongated precursor article.

The core of the wire of the invention may comprise so-called additional components in total amounts ranging from 0 to 100 ppm by weight, for example from 10 to 100 ppm by weight. Additional components, often referred to as "essential impurities" in this context, are impurities present in the raw materials used or small amounts of chemical elements and/or compounds derived from the wire core manufacturing process. A low total amount of 0 to 100 ppm by weight of additional components ensures good reproducibility of the wire properties. Additional components present in the core are usually not added separately. Each individual additional component is included in an amount of less than 30 ppm by weight based on the total weight of the wire core.

The core of the wire is a homogeneous region of bulk material. Since any bulk material always has a surface area that can exhibit some different properties, the property of the core of a wire is understood as a property of a homogeneous area of the bulk material. The surface of the bulk material region may differ in terms of morphology, composition (eg, sulfur, chlorine and/or oxygen content) and other characteristics. The surface is the interface region between the wire core and the coating layer superimposed on the wire core. Typically, the coating layer is completely superimposed on the surface of the wire core. In the region of the wire between the core of the wire and the coating layer superposed thereon, a material combination of both the core and the coating layer may be present.

The coating layer superposed on the surface of the wire core is a single-layer of gold 1 to 1000 nm thick, preferably 20 to 300 nm thick, or an interior of palladium 1 to 100 nm thick, preferably 1 to 30 nm thick. It is a double-layer consisting of a layer and an adjacent outer layer of gold that is 1 to 250 nm thick, preferably 20 to 200 nm thick. In this context, the term “thickness” or “coating layer thickness” means the size of the coating layer in the direction perpendicular to the longitudinal axis of the core.

The single or outer gold layer contains at least one member selected from the group consisting of antimony, bismuth, arsenic and tellurium, 10 to 100 ppm by weight based on the weight of the wire (wire core + coating layer), preferably 10 to 40 Included in total proportions in the range ppm by weight. At the same time, in one embodiment, the total proportion of said at least one member is from 300 to 3500 ppm by weight, preferably from 300 to 2000 ppm by weight, most preferably from 600 to 1000 ppm by weight, based on the weight of gold in the gold layer. can be a range.

It is preferred that antimony is present in the gold layer. It is even more desirable for antimony to be present alone in the gold layer, i.e., bismuth, arsenic and tellurium not present simultaneously. In other words, in a preferred embodiment, the gold layer has no bismuth, arsenic and tellurium present in the gold layer and is 10 to 100 ppm by weight, preferably 10 to 40 ppm by weight based on the weight of the wire (wire core + coating layer) antimony in proportions in the ppm range; At the same time, in an even more preferred embodiment, the proportion of antimony may range from 300 to 3500 ppm by weight, preferably 300 to 2000 ppm by weight, most preferably 600 to 1000 ppm by weight, based on the weight of gold in the gold layer. have.

In one embodiment, at least one member selected from the group consisting of antimony, bismuth, arsenic and tellurium may exhibit a concentration gradient within the gold layer, wherein the gradient is in a direction towards the wire core, ie perpendicular to the longitudinal axis of the wire core. increases in the direction of

Applicants have discovered that the presence in the gold layer of at least one member selected from the group consisting of antimony, bismuth, arsenic and tellurium is accompanied by a number of surprising and beneficial effects. For example, a gold layer is distinguished by exhibiting a bright, shiny yellow gold appearance; Formation of spherical and axisymmetric FABs becomes possible, and when ball bonding the coated wire of the present invention, the occurrence of OCB phenomenon can be suppressed or even prevented. It is not known in what chemical form or in what species the at least one member is present in the gold layer, ie whether it is present in the gold layer in elemental form or in the form of a compound.

In another aspect, the present invention also relates to a method of making the coated wire of the present invention in any of the embodiments disclosed above. The method is

(1) providing a silver precursor article or a silver-based precursor article;

(2) stretching the precursor article to form a stretched precursor article until a median cross-sectional area in the range of 706 to 31400 μm ^{2 or a median diameter in the range of 30 to 200 μm is obtained;}

(3) applying a single-layer of gold, or a double-layer coating of an inner layer of palladium and an adjacent outer layer of gold, on the surface of the elongated precursor article obtained after completion of method step (2);

(4) a single-layer of gold having a desired final cross-sectional area or diameter, and a desired final thickness in the range of 1 to 1000 nm, or an inner layer of palladium having a desired final thickness in the range of 1 to 100 nm and a thickness of 1 to 200 nm. further stretching the coated precursor article obtained after completion of method step (3) until a double-layer consisting of adjacent outer layers of gold having a desired final thickness is obtained, and

(5) at least a final strand annealing of the coated precursor obtained after completion of method step (4) with an oven set temperature in the range of 200 to 600° C. for an exposure time in the range of 0.4 to 0.8 seconds to form a coated wire;

Step (2) may comprise one or more sub-steps of intermediate batch annealing the precursor article to an oven set temperature of 400 to 800° C. for an exposure time in the range of 50 to 150 minutes,

The application of the gold layer in step (3) is carried out by electroplating the gold layer from a gold electroplating bath containing gold and at least one member selected from the group consisting of antimony, bismuth, arsenic and tellurium. do.

The term "strand annealing" is used herein. This is a continuous process that enables the rapid production of wires with high reproducibility. In the context of the present invention, strand annealing means that the annealing is performed dynamically while the coated precursor to be annealed is pulled or moved through a conventional annealing oven and spooled onto a reel after leaving the annealing oven do. Here, the annealing oven is typically in the form of a cylindrical tube of a given length. The annealing time/oven temperature parameter can be defined and set according to a defined temperature profile at a given annealing rate, which can be selected, for example, in the range of 10 to 60 meters/minute.

The term “oven set temperature” is used herein. This means a fixed temperature in the temperature controller of the annealing oven. The annealing oven may be a chamber furnace type oven (for batch annealing) or a tubular annealing oven (for strand annealing).

This disclosure distinguishes between precursor articles, elongated precursor articles, coated precursor articles, coated precursors, and coated wires. The term "precursor" is used for a wire pre-stage that has not reached the desired final cross-sectional area or final diameter of the wire core, while the term "precursor" is used for a wire pre-stage of the desired final cross-sectional area or desired final diameter. After completion of method step (5), ie after final annealing of the coated precursor of the desired final cross-sectional area or desired final diameter, a coated wire in the sense of the present invention is obtained.

The precursor article provided in method step (1) is a silver precursor article or is silver-based; That is, the precursor article consists of (a) silver, ie, pure silver, (b) doped silver, (c) a silver alloy, or (d) a doped silver alloy. With regard to the meaning of the terms “pure silver”, “doped silver”, “silver alloy” and “doped silver alloy”, reference is made to the foregoing disclosure.

In an embodiment of the silver precursor article, the silver precursor article is typically in the form of a rod having a diameter of eg 2 to 25 mm and a length of eg 2 to 100 m. Such silver rods may be made by continuous casting of silver using a suitable mold followed by cooling and solidification.

In embodiments of the silver-based precursor article, the silver-based precursor article may be obtained by alloying, doping, or alloying and doping silver in desired amounts of the required components. The doped silver or silver alloy or doped silver alloy can be prepared by conventional methods known to those skilled in the art of metal alloying, for example by melting the components together in the desired proportions. In doing so, it is possible to use one or more conventional master alloys. The melting process can be carried out, for example, using an induction furnace, and it is convenient to work under vacuum or under an inert gas atmosphere. The materials used may for example have a purity rating of at least 99.99% by weight. The resulting melt can be cooled to form a homogeneous piece of silver-based precursor article. Typically, such precursor articles are in the form of rods having, for example, a diameter of 2 to 25 mm and a length of, for example, 2 to 100 m. Such rods may be made by continuous casting of a silver-based melt using a suitable mold followed by cooling and solidification.

In method step (2), the precursor article is stretched to form a stretched precursor article until a median cross-sectional area in the range of ^{706 to 31400 μm 2 or a median diameter in the range of 30 to 200 μm is obtained.} Techniques for stretching precursor articles are known and appear to be useful in the context of the present invention. Preferred techniques are rolling, swaging, die drawing and the like, of which die drawing is particularly preferred. In die drawing, the precursor article is drawn in several process steps until a desired intermediate cross-sectional area or desired intermediate diameter is reached. Such wire die drawing processes are well known to those skilled in the art. Conventional tungsten carbide and diamond drawing dies may be used, and conventional drawing lubricants may be used to assist drawing.

Step (2) of the method of the present invention may comprise one or more sub-steps of intermediate batch annealing of the stretched precursor article to an oven set temperature in the range of 400 to 800° C. for an exposure time in the range of 50 to 150 minutes. Said optional intermediate batch annealing can be carried out in which the rod is drawn to a diameter of eg 2 mm and wound on a drum.

The optional intermediate batch annealing of method step (2) may be performed under an inert or reducing atmosphere. Numerous types of inert and reducing atmospheres are known in the art and are used to purge annealing ovens. 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 mixture of hydrogen and nitrogen is from 90 to 98% by volume of nitrogen and thus from 2 to 10% by volume of hydrogen, for a total of 100% by volume. Preferred mixtures of nitrogen/hydrogen are equal to 93/7, 95/5 and 97/3 vol %/vol %, respectively, based on the total volume of the mixture.

In method step (3), a coating in the form of a single-layer of gold or a double-layer coating of an inner layer of palladium and an adjacent outer layer of gold is applied onto the surface of the stretched precursor article obtained after completion of method step (2). applied to superimpose the coating over the surface.

A person skilled in the art knows how to calculate the thickness of such a coating on the stretched precursor article to finally obtain a coating of the layer thickness disclosed for the example of the wire, ie the layer thickness after the final stretch of the coated precursor article. A person skilled in the art is aware of numerous techniques for forming a coating layer of a material according to an embodiment on a silver or silver-based surface. Preferred techniques are plating, such as electroplating and electroless plating, deposition of material from a vapor phase, such as sputtering, ion plating, vacuum deposition and physical vapor deposition, and deposition of material from a melt. When applying the above double-layer consisting of an inner palladium layer and an outer gold layer, it is preferable to apply the palladium layer by electroplating.

The gold layer is applied by electroplating. Gold electroplating is performed using a gold electroplating bath, ie, an electroplating bath that allows the surface of a silver or silver-based or palladium cathode to be electroplated with gold. In other words, a gold electroplating bath is a composition that allows the direct application of gold in elemental metal form onto a silver or silver-based or palladium surface wired as a cathode. the gold electroplating bath comprises gold and at least one member selected from the group consisting of antimony, bismuth, arsenic and tellurium; Accordingly, the gold electroplating bath is a composition that allows not only to deposit elemental gold, but also to deposit in the gold layer said at least one member selected from the group consisting of antimony, bismuth, arsenic and tellurium. It is not known what species the at least one member is, ie whether it is present in elemental form or as a compound in the gold layer. A gold electroplating bath may be prepared by adding said at least one member in a suitable chemical form to an aqueous composition containing gold as a dissolved salt or dissolved salts. Examples of such aqueous compositions to which at least one member may be added are Aurocor® K 24 HF manufactured by Atotech and Auruna® 558 and Auruna® 559 manufactured by Umicore. Alternatively, a gold electroplating bath which already contains at least one member selected from the group consisting of antimony, bismuth, arsenic and tellurium, for example MetGold Pure ATF manufactured by Metalor can be used. The concentration of gold in the gold electroplating bath may be, for example, in the range from 8 to 40 g/l (grams/liter), preferably from 10 to 20 g/l. The concentration of at least one member selected from the group consisting of antimony, bismuth, arsenic and tellurium in the gold electroplating bath may be, for example, in the range of 15 to 50 ppm by weight, preferably 15 to 35 ppm by weight.

Electroplating application of the gold layer is performed by directing an uncoated stretched precursor article or a palladium-coated stretched precursor article wired as a cathode through a gold electroplating bath. The gold-coated precursor article thus obtained exiting the gold electroplating bath may be rinsed and dried before method step (4) is performed. It is convenient to use water as the rinsing medium, alcohols and alcohol/water mixtures are other examples of rinsing media. Gold electroplating of an uncoated stretched precursor article or a palladium-coated stretched precursor article through a gold electroplating bath, for example at a direct voltage in the range of 0.2 to 20 V, for example 0.001 to 5 A, in particular It can occur with currents ranging from 0.001 to 1 A or from 0.001 to 0.2 A. Typical contact times may range, for example, from 0.1 to 30 seconds, preferably from 2 to 8 seconds. The current densities used in this context may for example be in the range of ^{0.01 to 150 A/dm 2 .} The gold electroplating bath may for example have a temperature in the range from 45 to 75 °C, preferably from 55 to 65 °C.

The thickness of the gold coating layer can be adjusted as desired via essentially the following parameters: chemical composition of the gold electroplating bath, contact time of the gold electroplating bath with the stretched precursor article, current density. In this context, the thickness of the gold layer can generally be increased by increasing the concentration of gold in the gold electroplating bath, increasing the contact time of the gold electroplating bath with the stretched precursor article wired as a cathode, and increasing the current density. can

Applicants do not know whether the aforementioned beneficial effect is due to the presence of said at least one member in the gold electroplating bath, or whether its mere presence in the gold layer is key.

In method step (4), the coated precursor article obtained after completion of method step (3) is a mono-layer of gold having a desired final thickness in the range from 1 to 1000 nm, preferably from 20 to 300 nm, or from 1 to double-composed of an inner layer of palladium having a desired final thickness in the range of 100 nm, preferably 1 to 30 nm and an adjacent outer layer of gold having a desired final thickness in the range of 1 to 250 nm, preferably 20 to 200 nm It is further stretched until the desired final cross-sectional area or diameter of the wire with the layer is obtained. The technique for stretching the coated precursor article is the same stretching technique as mentioned above at the start of method step (2).

In method step (5), the coated precursor obtained after completion of method step (4) is subjected to final strand annealing with an oven set temperature ranging from 200 to 600° C., preferably from 350 to 500° C., for an exposure time ranging from 0.4 to 0.8 seconds. to form a coated wire.

In a preferred embodiment, the final strand annealed coated precursor, i.e. the still hot coated wire, is quenched in water which in one embodiment may contain one or more additives, for example 0.01 to 0.2% by volume of additive(s). . In-water quenching is, for example, via dipping or dripping, the final strand annealed coated precursor immediately or rapidly from the temperature encountered in method step (5) to room temperature, i.e. within 0.2 to 0.6 seconds. means cooling.

After completion of method step (5) and optional quenching, the coated wire of the present invention is completed. In order to fully enjoy the benefits of its properties, it is convenient to use the coated wire immediately for wire bonding applications, ie without delay, for example within 28 days after completion of method step (5). Alternatively, in order to maintain the wide wire bonding process window properties of the wire and to prevent oxidation or other chemical attack, the finished wire is typically immediately after completion of process step (5), i.e. without delay, e.g. Spooled, vacuum sealed, for example within < 1 to 5 hours after completion of method step (5), then stored for further use as bonding wire. Storage in a vacuum sealed state should not exceed 12 months. After opening the vacuum seal, the wire should be used for wire bonding within 28 days.

All method steps (1) to (5), as well as spooling and vacuum sealing, are preferably performed under cleanroom conditions (US FED STD 209E cleanroom standard, 1k standard).

A third aspect of the present invention is a coated wire obtainable by the method disclosed above according to any embodiment. 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. Wire bonding techniques are well known to those skilled in the art. In the wire bonding process, it is typical that a ball bond portion (a first bond portion) and a stitch bond portion (a second bond portion, a wedge bond portion) are formed. During bond formation, a specific force (typically measured in grams) is applied, supported by the application of ultrasonic energy (typically measured in mA). The mathematical product of the difference between the upper and lower limits of the applied force in the wire bonding process and the difference between the upper and lower limits of the applied ultrasonic energy defines the wire bonding process window:

(Upper limit of applied force - Lower limit of applied force)·(Upper limit of applied ultrasonic energy - Lower limit of applied ultrasonic energy) = Wire bonding process window .

The wire bonding process window allows the formation of wire bonds that meet specifications, i.e., passing conventional tests such as conventional tensile tests, ball shear tests, and ball tensile tests to name a few. Define the area.

Yes

Preparation of FAB:

Work was performed under ambient atmosphere following the procedure described in the KNS Process User Guide for FAB (Kulicke & Soffa Industries Inc, Fort Washington, PA, USA, 2002, 31 May 2009). FABs were prepared by performing conventional electric flame-off (EFO) firing by standard firing (single step, 17.5 μm wire, EFO current of 50 mA, EFO time 125 μs).

Test Methods A and B:

All tests and measurements were performed at T = 20 °C and relative humidity RH = 50%.

A. FAB form

The formed FAB was examined by scanning electron microscopy (SEM) at 1000×.

evaluation:

++++ = good (spherical axisymmetric ball)

+++ = good (spherical axisymmetric ball)

++ = Satisfied (ball is not perfectly round, but no apparent inclination (< 2 degrees) to wire axis)

+ = Inferior (ball is not perfectly round, but there is no distinct plateau on the FAB surface, tilted 5 to 10 degrees relative to the wire axis)

B. OCB Occurrence

The formed FAB descended from a predefined height (tip of 203.2 μm) and velocity (contact speed of 6.4 μm/sec) to an Al-0.5 wt% Cu bond pad. Upon contact with the bond pad, a defined set of bonding parameters (bonding force of 100 g, ultrasonic energy of 95 mA, and bonding time of 15 ms) was executed to deform the FAB and form a bonded ball. After forming the ball, the capillary was raised to a predefined height (kink height of 152.4 μm and loop height of 254 μm) to form a loop. After forming the loop, the capillary was lowered to the lead to form a stitch. After forming the stitch, the capillary is raised and the wire clamp is closed to cut the wire to form a predefined tail length (a tail length extension of 254 μm). For each sample, a significant number of 2500 bonded wires were optically inspected using a microscope at 1000x magnification. The percentage of defects was determined.

wire example

An amount of silver (Ag), in each case at least 99.99% pure (“4N”), and optionally palladium (Pd) or palladium (Pd) and gold (Au) were melted in a crucible. Next, a wire core precursor article in the form of an 8 mm rod was continuously cast from the melt. Next, the rod was drawn in several drawing steps to form a wire core precursor having a circular cross section with a diameter of 2 mm. The wire core precursor was intermediate batch annealed with an oven set temperature of 500 °C for an exposure time of 60 min. The rod was further drawn in several drawing steps to form a wire core precursor having a circular cross-section with a diameter of 46 μm. The wire core precursor was then electroplated with a single-layer of gold or with a double-layer coating of an inner layer of palladium and an adjacent outer layer of gold. For this purpose, the wire core precursor is transferred through a warm gold electroplating bath at 61 °C, or a warm palladium electroplating bath at 53 °C, and then through a warm gold electroplating bath at 61 °C while being routed as a cathode. became

The palladium electroplating bath (based on [Pd(NH ₃ ) ₄ ]Cl ₂ , with a buffer of pH 7) had a palladium content of 1.45 g/l (grams/liter).

Four different gold electroplating baths containing antimony, bismuth, arsenic or tellurium were prepared.

A gold electroplating bath containing antimony (Sb) (based on MetGold Pure ATF from Metalor) had a gold content of 13.2 g/l and an antimony content of 20 ppm by weight.

A gold electroplating bath containing bismuth (Bi) ( _{based on KAu(CN) 2} , with a buffer of pH ₅ ; addition of BiPO 4 ) had a gold content of 13.2 g/l and a bismuth content of 25 ppm by weight.

A gold electroplating bath containing arsenic (As) ( _{based on KAu(CN) 2} , with a buffer of pH 5; addition of As ₂ O ₃ ) had a gold content of 13.2 g/l and an arsenic content of 25 ppm by weight.

A gold electroplating bath comprising tellurium (Te) ( _{based on KAu(CN) 2} , with a buffer of pH 5; _{addition of TeO 2} ) had a gold content of 13.2 g/l and a tellurium content of 25 ppm by weight.

Thereafter, after the coated wire precursor was further drawn to a final diameter of 17.5 μm, immediately after final strand annealing at an oven set temperature of 220° C. for an exposure time of 0.6 seconds, the so obtained coated wire was treated with 0.07 volume % surfactant quenched in water containing

By this procedure, several different samples 1-26 were prepared of palladium and gold coated silver and silver based wires, and uncoated reference silver wires of 4N purity (Reference).

Table 1 below shows the composition of the uncoated wire and the coated wire.

The presence of Sb, Bi, As, Te, Au, and Pd was determined by ICP (Inductively Coupled Plasma). The layer thickness was measured on the cross section by Scanning Transmission Electron Microscopy (STEM).

Table 2 below shows specific test results.

"Formed under a gas purge" means that the FAB was purged with 95/5 vol%/vol% nitrogen/hydrogen during its formation, whereas "under atmosphere" means that the FAB formation was performed under an air atmosphere.

Claims (9)

A wire comprising a wire core having a surface, the wire core having a coating layer superimposed on the surface, the wire core itself being a silver wire core or a silver-based wire core, the coating layer being 1 to 1000 nm thick A wire comprising a single-layer of gold or a double-layer consisting of an inner layer of palladium 1 to 100 nm thick and an adjacent outer layer of gold 1 to 250 nm thick,
The gold layer comprises at least one member selected from the group consisting of antimony, bismuth, arsenic and tellurium in a total proportion ranging from 10 to 100 ppm by weight based on the weight of the wire. According to claim 1,
wherein the total proportion of said at least one member selected from the group consisting of antimony, bismuth, arsenic and tellurium is in the range of 300 to 3500 ppm by weight based on the weight of gold in said gold layer. 3. The method of claim 1 or 2,
A wire having an average cross-sectional area in the range from 50 to 5024 μm ^{2 .} 3. The method of claim 1 or 2,
A wire having a circular cross section with an average diameter in the range from 8 to 80 μm. 5. The method according to any one of claims 1 to 4,
wherein the at least one member selected from the group consisting of antimony, bismuth, arsenic and tellurium exhibits a concentration gradient within the gold layer, wherein the concentration gradient increases in a direction perpendicular to the longitudinal axis of the wire core. 6. The method according to any one of claims 1 to 5,
wherein antimony is present in the gold layer. 7. The method of claim 6,
wherein bismuth, arsenic and tellurium are not present simultaneously in said gold layer. In the manufacturing method of any one of claims 1 to 7, the coated wire,
(1) providing a silver precursor article or a silver-based precursor article;
(2) stretching the precursor article to form a stretched precursor article until a median cross-sectional area in the range of 706 to 31400 μm ^{2 or a median diameter in the range of 30 to 200 μm is obtained;}
(3) applying a single-layer of gold, or a double-layer coating of an inner layer of palladium and an adjacent outer layer of gold, on the surface of the elongated precursor article obtained after completion of method step (2);
(4) a single-layer of gold having a desired final cross-sectional area or diameter, and a desired final thickness in the range of 1 to 1000 nm, or an inner layer of palladium having a desired final thickness in the range of 1 to 100 nm and a thickness of 1 to 200 nm. further stretching the coated precursor article obtained after completion of method step (3) until a double-layer consisting of adjacent outer layers of gold having a desired final thickness is obtained, and
(5) final strand annealing of the coated precursor obtained after completion of method step (4) with an oven set temperature ranging from 200 to 600° C. for an exposure time ranging from 0.4 to 0.8 seconds to form the coated wire;
at least comprising
Step (2) may comprise one or more sub-steps of intermediate batch annealing the precursor article to an oven set temperature of 400 to 800° C. for an exposure time in the range of 50 to 150 minutes,
The application of the gold layer in step (3) is performed by electroplating the gold layer from a gold electroplating bath comprising gold and at least one member selected from the group consisting of antimony, bismuth, arsenic and tellurium. Way. 9. The method of claim 8,
wherein the palladium layer is applied by electroplating.