KR102595696B1 - coated wire - Google Patents

Abstract

A wire comprising a wire core having a surface, the wire core having a coating layer superimposed on its surface, the wire core itself being a silver wire core or a silver-based wire core, the coating layer being a single layer of gold having a thickness of 1 to 1000 nm. -layer or a bi-layer consisting of an inner layer of palladium having a thickness of 1 to 100 nm and an adjacent outer layer of gold having a thickness of 1 to 250 nm, the gold layer being at least selected from the group consisting of antimony, bismuth, arsenic and tellurium. It is characterized in that it contains one member 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 superimposed on the surface of the wire core. The invention also relates to a method for manufacturing such coated wire.

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

With regard to wire geometry, bonding wires of circular cross-section and bonding ribbons with a more or less rectangular cross-section are the most common. Both types of wire geometry have advantages that make them useful for certain 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 the off-centered ball (OCB) phenomenon during ball bonding.

A contribution to the solution of the above object 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 contributes to solving the above-mentioned objectives.

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 superimposed on its surface, and the wire core itself is a silver wire. core or a silver-based wire core, and 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. The present invention relates to a wire, wherein the gold layer contains at least one member selected from the group consisting of antimony, bismuth, arsenic and tellurium, in an amount of 10 to 10% based on the weight of the wire. It is characterized in that it is contained in a total ratio of 100 ppm by weight (ppm by weight), preferably in the range of 10 to 40 ppm by weight. 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. For the present invention, the term “bonding wire” includes all cross-sectional shapes and all conventional wire diameters, but bonding wires with circular cross-sections and thin diameters are preferred. The average cross-sectional area ranges for example from 50 to 5024 μm ² , or preferably from 110 to 2400 μm ² ; Therefore, in the case of a preferred circular cross-section, the average diameter ranges for example from 8 to 80 μm, or preferably from 12 to 55 μm.

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

The wire core is a silver wire core or is silver-based; That is, the wire core is made of (a) silver, that is, pure silver, or is made of 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 silver" means (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. refers to pure silver composed of (components)

As used herein, the term "doped silver (doped sliver)" means (b1) silver in an amount ranging from >99.49 to 99.997% by weight, (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 means (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) further 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).

As used herein, the term "silver alloy" means silver in an amount ranging from (c1) 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 a total amount ranging from (c3) 0 to 100 ppm by weight of additional components (components other than silver and at least one alloying element) in a total amount ranging from 0 to 100 ppm by weight. In a preferred embodiment, the term "silver alloy" as used herein means (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 ranging from 0.5 to 10% by weight, preferably in the range from 0.5 to 2% by weight, and (c3) a further component (silver) in a total amount from 0 to 100 ppm by weight. , refers to a silver alloy composed of ingredients other than nickel, platinum, palladium, gold, copper, rhodium, and ruthenium).

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

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

The core of the wire of the invention may comprise so-called additional components in a total amount ranging from 0 to 100 ppm by weight, for example from 10 to 100 ppm by weight. In this context, additional components, sometimes also referred to as “inevitable impurities”, are impurities present in the raw materials used or small amounts of chemical elements and/or compounds originating from the wire core manufacturing process. Low total amounts of additional components of 0 to 100 ppm by weight ensure good reproducibility of wire properties. Additional components present in the core are typically not added separately. Each individual additional ingredient 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 surface areas that may exhibit somewhat different properties, the properties of the core of the wire are understood as properties of homogeneous regions of the bulk material. The surfaces of bulk material regions may differ in terms of morphology, composition (eg, sulfur, chlorine, and/or oxygen content), and other characteristics. The surface is the interface area between the wire core and the coating layer superimposed on the wire core. Typically, the coating layer completely overlaps the surface of the wire core. In the area of the wire between the core of the wire and the coating layer superimposed thereon, combinations of materials of both core and coating layers may be present.

The coating layer superimposed 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 internal layer of palladium 1 to 100 nm thick, preferably 1 to 30 nm thick. 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 in an amount of 10 to 100 ppm by weight, preferably 10 to 40 ppm, based on the weight of the wire (wire core + coating layer). Included as a total percentage in the weight ppm range. At the same time, in one embodiment, the total proportion of said at least one member is 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. It may be a range.

It is preferred that antimony is present in the gold layer. It is much more desirable for antimony to be present alone in the gold layer, i.e. without bismuth, arsenic and tellurium present simultaneously. In other words, in a preferred embodiment, the gold layer is free of bismuth, arsenic and tellurium and contains 10 to 100 ppm by weight, preferably 10 to 40 ppm, based on the weight of the wire (wire core + coating layer). Contains 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 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. there is.

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, the gradient being oriented toward the wire core, i.e., perpendicular to the longitudinal axis of the wire core. increases in the direction of

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

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

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

(2) stretching the precursor article to form a stretched precursor article until a median cross-sectional area ranging from 706 to 31400 μm ² or a median diameter ranging from 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 stretched precursor article obtained after completion of method step (2),

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

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

Step (2) may include one or more sub-steps of intermediate batch annealing of the precursor article at an oven set temperature of 400 to 800° C. for an exposure time ranging from 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 comprising 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 allows the rapid production of wire with high reproducibility. In the context of the present invention, strand annealing means that the annealing is carried out dynamically while the coated precursor to be annealed is pulled or moved through a conventional annealing oven and, after leaving the annealing oven, spooling onto a reel. do. Here, the annealing oven is typically in the form of a cylindrical tube of a given length. Annealing time/oven temperature parameters can be defined and set according to a defined temperature profile at a given annealing rate, which can for example be selected in the range of 10 to 60 meters/minute.

The term “oven set temperature” is used herein. This refers to the temperature fixed 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).

The present disclosure distinguishes between precursor articles, drawn precursor articles, coated precursor articles, coated precursors, and coated wires. The term “precursor” is used for wire precursors that have not reached the desired final cross-sectional area or final diameter of the wire core, while the term “precursor” is used for wire precursors that have the desired final cross-sectional area or desired final diameter. After completion of method step (5), i.e. after final strand annealing of the coated precursor of the desired final cross-sectional area or desired final diameter, a coated wire in the sense of the 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 is comprised of (a) silver, i.e. 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, for example, 2 to 25 mm and a length, for example, of 2 to 100 m. Such silver rods can be manufactured by continuously casting 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 with the desired amount of the required component. Doped silver or silver alloys or doped silver alloys can be prepared by conventional methods known to those skilled in the art of metal alloys, for example by melting the components together in the desired proportional proportions. In so doing, 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 have a purity rating of, for example, 99.99% by weight or higher. 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 with a diameter of eg 2 to 25 mm and a length of eg 2 to 100 m. Such rods can be manufactured by continuously casting a silver-based melt using a suitable mold followed by cooling and solidification.

In method step (2), the precursor article is stretched until a median cross-sectional area ranging from 706 to 31400 μm ² or a median diameter ranging from 30 to 200 μm is obtained, forming a stretched precursor article. Techniques for stretching precursor articles are known and appear to be useful in the context of the present invention. Preferred techniques include rolling, swaging, die drawing, etc., of which die drawing is particularly preferred. For die drawing, the precursor article is drawn in several process steps until the 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 can be used, and conventional drawing lubricants can be used to assist in drawing.

Step (2) of the method of the present invention may include one or more sub-steps of intermediate batch annealing of the stretched precursor article at an oven set temperature ranging from 400 to 800° C. for an exposure time ranging from 50 to 150 minutes. The above optional intermediate batch annealing can be carried out with rods drawn to a diameter of, for example, 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 atmospheres and reducing atmospheres are known in the art and used to purge annealing ovens. Among known inert atmospheres, nitrogen or argon are 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 90 to 98 volume percent nitrogen and thus 2 to 10 volume percent hydrogen, with the volume percent totaling 100 volume percent. Preferred mixtures of nitrogen/hydrogen are equal to 93/7, 95/5 and 97/3 volume%/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 on the surface of the drawn precursor article obtained after completion of method step (2). is applied to superimpose a coating on 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 embodiment of the wire, i.e. the layer thickness after the coated precursor article has been finally stretched. Those skilled in the art are aware of numerous techniques for forming coating layers of materials according to embodiments on silver or silver-based surfaces. Preferred techniques are plating, such as electroplating and electroless plating, deposition of material from the vapor phase, such as sputtering, ion plating, vacuum deposition and physical vapor deposition, and deposition of material from a melt. When applying the double-layer consisting of an inner palladium layer and an outer gold layer, it is preferred to apply the palladium layer by electroplating.

The gold layer is applied by electroplating. Gold electroplating is performed using a gold electroplating bath, that is, an electroplating bath that allows a silver or silver-based or palladium cathode surface to be electroplated with gold. In other words, a gold electroplating bath is a composition that allows direct application of gold in elemental metallic form onto a silver or silver-based or palladium surface wired as a cathode. The gold electroplating bath includes 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 said at least one member selected from the group consisting of antimony, bismuth, arsenic and tellurium within a gold layer. It is not known what chemical species the at least one member is, i.e. whether it exists in elemental form or as a compound in the gold layer. A gold electroplating bath can be prepared by adding the 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 may be used, for example MetGold Pure ATF manufactured by Metalor, which already contains at least one member selected from the group consisting of antimony, bismuth, arsenic and tellurium. The concentration of gold in the gold electroplating bath may range, for example, from 8 to 40 g/l (grams per 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 for example range from 15 to 50 ppm by weight, preferably from 15 to 35 ppm by weight.

Electroplating application of the gold layer is performed by guiding an uncoated or 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; alcohol 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 passing through a gold electroplating bath can be carried out at a direct current voltage in the range of for example 0.2 to 20 V, for example from 0.001 to 5 A, especially This can occur with currents ranging from 0.001 to 1 A or 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 density used in this context may for example range from 0.01 to 150 A/dm ² . The gold electroplating bath may have a temperature ranging for example from 45 to 75°C, preferably from 55 to 65°C.

The thickness of the gold coating layer can be adjusted as desired essentially through the following parameters: chemical composition of the gold electroplating bath, contact time of the stretched precursor article with the gold electroplating bath, and 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 the cathode, and increasing the current density. You can.

The applicant does not know whether the beneficial effects described above are 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 single-layer of gold having a desired final thickness ranging from 1 to 1000 nm, preferably from 20 to 300 nm, or from 1 to 300 nm. Bi-layer consisting of an inner layer of palladium having a desired final thickness ranging from 100 nm, preferably 1 to 30 nm, and an adjacent outer layer of gold having a desired final thickness ranging from 1 to 250 nm, preferably 20 to 200 nm. It is further drawn until the desired final cross-sectional area or diameter of the layered wire 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 at 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. This forms 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 the additive(s). . Submerged quenching immediately or rapidly, i.e., within 0.2 to 0.6 seconds, brings the final strand annealed coated precursor from the temperature encountered in method step (5) to room temperature, for example by dipping or dripping. It means cooling.

After completion of method step (5) and optional quenching, the coated wire of the present invention is complete. In order to fully enjoy the benefits of its properties, it is convenient to use the coated wire in wire bonding applications immediately, i.e. 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 prevent oxidation or other chemical attack, the finished wire is typically produced immediately after completion of process step (5), i.e. without delay, e.g. For example, within <1 to 5 hours after completing method step (5), it is spooled and vacuum sealed, and then stored for further use as a bonding wire. Storage under vacuum seal should not exceed 12 months. After opening the vacuum seal, the wire must 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 invention is a coated wire obtainable by the method disclosed above according to any of the embodiments. 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, a ball bond (first bond) and a stitch bond (second bond, wedge bond) are typically formed. During bond formation, a specific force (typically measured in grams) is applied supported by the application of ultrasonic energy (typically measured in mA). In a wire bonding process, the mathematical product of the difference between the upper and lower limits of the applied force 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 determines the force/ultrasonic energy combination that allows the formation of a wire bond that meets specifications, i.e., passes conventional tests such as conventional tensile testing, ball shear testing, and ball tensile testing, to name a few. Define the area.

yes

Preparation of FAB:

It was operated under ambient conditions according to the procedures described in the KNS Process User Guide for FAB (Kulicke & Soffa Industries Inc, Fort Washington, PA, USA, 2002, 31 May 2009). FAB was 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× magnification.

evaluation:

++++ = Excellent (spherical, axisymmetric ball)

+++ = Good (spherical, axisymmetric ball)

++ = Satisfactory (ball is not perfectly round, but has no significant inclination (< 2 degrees) about the wire axis)

+ = Inferior (ball is not perfectly circular, but has no apparent plateau on the FAB surface and is inclined at 5 to 10 degrees to the wire axis)

B. Occurrence of OCB

The formed FAB was lowered from a predefined height (tip of 203.2 μm) and speed (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 (bond force of 100 g, ultrasonic energy of 95 mA and bond time of 15 ms) were implemented 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 (tail length extension of 254 μm). For each sample, a significant number of 2500 bonded wires were optically inspected using a microscope at 1000× magnification. The percentage of defects was determined.

wire example

A quantity 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, wire core precursor articles in the form of 8 mm rods were continuously cast from the melt. Next, the rod was drawn in several drawing steps to form a wire core precursor with a circular cross-section with a diameter of 2 mm. The wire core precursor was medium 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 with a circular cross-section with a diameter of 46 μm. Next, the wire core precursor was electroplated with a single-layer of gold or a double-layer coating of an inner layer of palladium and an adjacent outer layer of gold. For this purpose, the wire core precursor, while wired as a cathode, is moved 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. It has been done.

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

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

The gold electroplating bath with 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.

The gold electroplating bath with bismuth (Bi) (based on KAu(CN) ₂ with buffer at pH 5; BiPO ₄ added) had a gold content of 13.2 g/l and a bismuth content of 25 ppm by weight.

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

The gold electroplating bath containing tellurium (Te) (based on KAu(CN) ₂ , with buffer at pH 5; added TeO ₂ ) had a gold content of 13.2 g/l and a tellurium content of 25 ppm by weight.

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

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

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

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

Table 2 below shows specific test results.

“Formed under gas purge” means that the FAB was purged with 95/5 vol%/vol% nitrogen/hydrogen during its formation, while “under atmospheric air” means that the FAB formation was carried out under an air atmosphere.

Claims (9)

A wire comprising a wire core having a surface, the wire core having a coating layer superimposed on its surface, the wire core itself being a silver wire core or a silver-based wire core, the coating layer having a thickness of 1 to 1000 nm. A wire, which is either a single-layer of gold 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,
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, and the at least one member Wire, characterized in that the total ratio ranges from 300 to 3500 ppm by weight based on the weight of gold in the gold layer. According to paragraph 1,
A wire with an average cross-sectional area ranging from 50 to 5024 μm ² . According to paragraph 1,
A wire having a circular cross-section with an average diameter ranging from 8 to 80 μm. According to paragraph 1,
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, the concentration gradient increasing in a direction perpendicular to the longitudinal axis of the wire core. According to paragraph 1,
A wire wherein antimony is present in the gold layer. According to clause 5,
A wire wherein bismuth, arsenic and tellurium are not present simultaneously in the gold layer. In the method of manufacturing the coated wire of claim 1,
(1) providing a silver precursor article or silver-based precursor article,
(2) forming a stretched precursor article by stretching the precursor article until a median cross-sectional area ranging from 706 to 31400 μm ² or a median diameter ranging from 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 stretched precursor article obtained after completion of method step (2),
(4) a single-layer of gold having the desired final cross-sectional area or diameter and a desired final thickness ranging from 1 to 1000 nm, or an inner layer of palladium having a desired final thickness ranging from 1 to 100 nm and a desired final thickness ranging from 1 to 200 nm. further stretching the coated precursor article obtained after completion of method step (3) until a bi-layer consisting of adjacent outer layers of gold having the desired final thickness is obtained, and
(5) final strand annealing of the coated precursor obtained after completion of method step (4) at an oven setting temperature ranging from 200 to 600° C. for an exposure time ranging from 0.4 to 0.8 seconds to form the coated wire.
Includes at least
Step (2) may include one or more sub-steps of batch annealing the precursor article at an oven set temperature of 400 to 800° C. for an exposure time ranging from 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 comprising gold and at least one member selected from the group consisting of antimony, bismuth, arsenic and tellurium. method. In clause 7,
The method of claim 1, wherein the palladium layer is applied by electroplating. delete