JP6622415B2 - Coated wire - Google Patents

Description

  The present invention relates to a coated wire including a copper-based core and a coating layer overlapping the surface of the core. The invention further relates to a process for producing this coated wire.

  The use of bonding wires in electronic and microelectronic applications is a well-known state of the art. Bonding wires were initially made of gold, but cheaper materials such as copper, copper alloys, silver and silver alloys are now used. Such wires may have a metal coating.

  Regarding wire shape, bonding wires with a circular cross-section and bonding ribbons with a substantially rectangular cross-section are most common. Both types of wire shapes have useful advantages for specific applications.

  It is an object of the present invention to provide a coated copper alloy wire suitable for use in wire bonding applications. This wire especially improves the free air ball (FAB) configuration, corrosion resistance, OCB (eccentric ball), and second bonding window, but the overall balance of the wire and its bonding application, such as the distribution of coating material on the FAB Also shows a range of properties.

  The solution to this object is provided by the subject matter of the category claim. The dependent claims of the category forming claim represent preferred embodiments of the present invention, the subject matter of which also helps to solve the above object.

In a first aspect, the present invention relates to a wire including a wire core having a surface (hereinafter also referred to as “core” for short), the wire core having a coating layer overlapping the surface,
(A) silver in an amount of 0.1 to 0.3 wt% (wt%, weight percent), preferably 0.2 wt%;
(B) copper in an amount ranging from 99.64 to 99.9 wt%, preferably 99.7 to 99.9 wt%, and even more preferably 99.75 to 99.85 wt%;
(C) 0-100 wt ppm (weight ppm, weight parts per million), preferably 50-100 wt ppm, more preferably 70-80 wt ppm, especially 75 wt ppm phosphorus;
(D) further components (components other than silver, copper and phosphorus) in an amount ranging from 0 to 500 wt ppm, preferably 0 to 100 wt ppm,
The individual amount of any further ingredients is less than 30 wt ppm;
All amounts in wt% and wt ppm are based on the total weight of the core,
The covering layer is a double layer composed of an inner layer (base layer) of palladium and an outer layer (top layer) of adjacent gold,
The weight of the inner layer of palladium ranges from 1.5 to 2.5 wt% with respect to the wire core weight,
The weight of the gold outer layer is in the range of 0.09 to 0.18 wt% with respect to the wire core weight.

  The following table summarizes some preferred embodiments of the wire core composition.

The wire of the present invention is preferably a bonding wire for bonding in microelectronics. An integrated object is preferable. Numerous shapes are known and are clearly useful for the wire of the present invention. Preferred shapes are cross-sectional views, which are circles, ellipses and rectangles. For the present invention, the term “bonding wire” includes all cross-sectional shapes and all normal wire diameters, but bonding wires having a circular cross-section and a narrow diameter are preferred. The average cross section is, for example, in the range of 50-5024 μm ² , or preferably 113-2375 μm ² , so for a preferred circular cross section, the average diameter is, for example, in the range of 8-80 μm, or preferably 12-55 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 material weight of a defined length of wire is determined. The diameter of the wire or wire core is calculated using the density of the wire material based on this weight. The diameter is calculated as the arithmetic average of five measurements for five sections of a particular wire.

  In accordance with the above, the wire core includes (a) silver, (b) copper and (c) phosphorus in the relative ratios disclosed above. However, the silver alloy copper core of the coated wire of the present invention may contain (d) additional components in a total amount of 0-500 wt ppm, preferably 0-100 wt ppm. In this situation, this additional component is often referred to as an “unavoidable impurity” and is an impurity present in the raw material used or a small amount of chemical elements and / or compounds resulting from the wire manufacturing process. That is, the presence of additional components of type (d) may result from impurities present in, for example, silver and / or copper. Examples of such further components are Au, Ni, Pd, Pt, Fe, Si, Mn, Cr, Ce, Mg, La, Al, B, Zr, Ti, S and the like. A low total amount of 0 to 500 wt ppm of additional component (d), or even 0 to 100 wt ppm, ensures excellent reproducibility of wire properties. The further component (d) present in the core is usually not added separately. Each individual additional component is included in an amount of less than 30 wt ppm, based on the total weight of the wire core.

  The core of the wire is a uniform area of the bulk material. Since every bulk material always has a surface area that exhibits some different properties, the core nature of the wire is understood as the nature of the uniform 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. This surface is the interface region between the wire core and the coating layer that overlaps the wire core. Usually, the coating layer completely overlaps the surface of the wire core. In the region of the core of the wire and the overlying coating layer, there may be a combination of both materials, the core and the coating layer.

The coating layer overlying the wire surface is a double layer composed of an inner palladium layer and an adjacent outer gold layer. The weight of the inner layer of palladium ranges from 1.5 to 2.5 wt% with respect to the weight of the wire core, and the weight of the outer layer of gold ranges from 0.09 to 0.18 wt% with respect to the weight of the wire core. is there. Both the inner palladium layer and the outer gold layer are thin layers. In this context, the terms “thin”, “thick” or “coating layer thickness” mean the dimension of the coating layer in the direction perpendicular to the longitudinal axis of the core. For the exemplary wire having an average cross-section in the range of 50-5024 μm ² or the circular wire having the average diameter in the range of 8-80 μm typical, the inner layer of palladium is, for example, 20-350 nm, preferably 30-340 nm. The thickness of the gold outer layer may be, for example, 1 to 25 nm, preferably 2 to 20 nm. In an exemplary embodiment of a round wire having a diameter of 18 μm, the inner palladium layer may have a thickness in the range of 60-90 nm, for example, and the outer gold layer has a thickness in the range of, for example, 1-10 nm, preferably 2-6 nm. Good.

  For the composition of the bilayer, the palladium content of the inner layer is, for example, at least 50 wt%, preferably at least 95 wt%, based on the total weight of the inner coating layer. Particularly preferably, the inner coating layer consists of pure palladium. Pure palladium usually has less than 1 wt% of additional components (components other than palladium) based on the total weight of the inner coating layer. The gold content of the adjacent outer gold layer is, for example, at least 50 wt%, preferably at least 95 wt%, based on the total weight of the outer coating layer. Particularly preferably, the outer covering layer consists of pure gold. Pure gold usually has less than 1 wt% of additional components (other than gold) based on the total weight of the outer coating layer.

In one embodiment, the core of the wire of the invention is characterized by at least one of the following intrinsic properties (i) to (iii) (see “Test Method A” below):
(I) Average wire particle size (average particle size) is measured in the vertical direction (longitudinal direction of the wire core) and is in the range of 3-6 μm.
(Ii) The ratio of the average particle size measured in the longitudinal direction to the diameter of the wire core is in the range of 0.05 to 0.25, preferably 0.1 to 0.20.
(Iii) The ratio of the standard deviation (RSD) of the average particle size to the average particle size of the core measured in the longitudinal direction is in the range of 0.1 to 0.4.

  The term “inherent property” is used herein with respect to a wire core. The inherent property means the property that the wire core itself has (regardless of other factors). The extrinsic properties as opposed to the intrinsic properties depend on the relationship between the wire core and other factors such as the measurement method used and / or the measurement conditions.

In another aspect, the present invention also relates to a process for producing a coated wire of the present invention in any of the embodiments disclosed above. This process includes at least steps (1) to (5):
(1) providing a precursor of the desired composition, (a) silver in an amount of 0.1-0.3 wt%, preferably 0.2 wt%;
(B) copper in an amount ranging from 99.64 to 99.9 wt%, preferably 99.7 to 99.9 wt%, or even more preferably 99.75 to 99.85 wt%;
(C) phosphorus in the range of 0-100 wt ppm, preferably 50-100 wt ppm, more preferably 70-80 wt ppm, especially 75 wt ppm;
(D) further components (components other than silver, copper and phosphorus) in an amount ranging from 0 to 500 wt ppm, preferably 0 to 100 wt ppm,
The individual amount of any further ingredients is less than 30 wt ppm;
All amounts of wt% and wt ppm are based on the total weight of the precursor,
Providing a precursor; and
(2) stretching the precursor to obtain an elongated precursor until an intermediate cross section in the range of 5024 to 70650 μm ² or an intermediate diameter in the range of 80 to 300 μm, preferably 130 to 230 μm, is obtained;
(3) depositing a double layer coating of an inner layer of palladium (base layer) and an adjacent outer layer of gold (top layer) on the surface of the elongated precursor obtained after completion of process step (2);
(4) further stretching the coating precursor obtained after completion of process step (3) until the desired final cross-section or diameter is obtained;
(5) Finally, the coating precursor obtained after the end of the process step (4) is subjected to strand annealing at a furnace set temperature in the range of 450 to 650 ° C. and an exposure time in the range of 0.1 to 3 seconds to coat Forming a wire.

  The term “strand annealing” is used herein. In contrast to “batch annealing”, strand annealing is a continuous process that can produce wires quickly with high reproducibility. In the context of the present invention, strand annealing means that annealing is performed dynamically while the coating precursor to be annealed passes or moves through a conventional annealing furnace, exits the annealing furnace and is then wound around a rotating part. Here, the annealing furnace is usually a cylindrical tube having a predetermined length. The annealing time / furnace temperature parameters can be defined and set using the defined temperature profile at a predetermined annealing speed that can be selected, for example, in the range of 10-60 meters / minute.

  The term “furnace set temperature” is used herein to mean the temperature fixed by the temperature controller of the annealing furnace.

  The annealing furnace may be a chamber furnace (in the case of batch annealing) or a tubular annealing furnace (in the case of strand annealing).

  The present disclosure distinguishes between precursors, stretch precursors, coating precursors, coating precursors and coated wires. The term “precursor” is used in the previous stage of the wire that does not reach the desired final cross-section or wire core final diameter, and the term “precursor” is used in the previous stage of the desired final cross-section or wire of the desired final diameter Used. After the end of process step (5), i.e. after final strand annealing of the coating precursor with the desired final cross-section or the desired final diameter, a coated wire in the meaning of the invention is obtained.

  The precursor as provided in process step (1) can be obtained by alloying / doping copper with the desired amount of silver, and optionally also with an appropriate amount of phosphorus. . The copper alloy itself can be prepared by conventional processes known to those skilled in the metal alloy art, such as melting copper, silver and any phosphorus together in the desired ratio. By doing so, a master alloy can be used. The melting process can be carried out, for example, by using an induction furnace, and it is appropriate to operate under a vacuum or an inert gas atmosphere. The material used may have a purity of, for example, 99.99 wt% and above. The melt thus produced can be cooled to form a uniform piece of copper-based precursor. Usually, such precursors are rod-shaped with a diameter of, for example, 2 to 25 mm and a length of, for example, 2 to 100 m. Such a rod can be produced by casting the copper alloy melt with an appropriate mold and then cooling and solidifying it.

In process step (2), the precursor is stretched to form an elongated precursor until an intermediate cross section in the range of 5024 to 70650 μm ² or an intermediate diameter in the range of 80 to 300 μm, preferably 130 to 230 μm is obtained. Techniques for stretching the precursor are known and are clearly useful in the present invention. Preferred techniques are rolling, swaging, die drawing, etc., and die drawing is particularly preferred.

  In the latter case, the precursor is stretched in several process steps until the desired intermediate cross section or the 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 oils can be used to support the drawing.

  Step (2) of the inventive process may comprise one or more sub-steps relating to the intermediate annealing of the stretch precursor. Such intermediate annealing can be performed at a furnace set temperature in the range of 200 to 650 ° C., for example, at an exposure time of 0.5 to 1 second. Such intermediate annealing is usually performed by a strand annealing method.

  In process step (3), a double layer coating composed of an inner layer of palladium and an adjacent outer layer of gold is deposited on the surface of the elongated precursor obtained after the end of process step (2) and overlays the coating on the surface . Those skilled in the art will appreciate that the weight of the inner layer of palladium is in the range of 1.5 to 2.5 wt% with respect to the weight of the extension precursor, and the weight of the outer layer of gold is 0.09 to 0.000 with respect to the weight of the extension precursor. It will be understood that an inner layer of palladium and an outer layer of gold are deposited so as to be in the range of 18 wt%.

  Those skilled in the art are aware of how to calculate the thickness of such coatings on the stretch precursor, and the layer thickness disclosed in the wire embodiments, i.e., the layer thickness after the coating precursor has been finally stretched. The final coating is obtained. Those skilled in the art are aware of numerous techniques for forming a coating layer of a material according to embodiments on a copper alloy surface. Preferred techniques are plating such as electroplating and electroless plating, deposition of materials from the gas phase such as sputtering, ion plating, vacuum deposition and physical vapor deposition, and deposition of materials from the melt. In the context of the present invention, electroplating is a preferred technique.

  In process step (4), the coating precursor obtained after completion of process step (3) is further stretched until the final cross section or diameter of the desired wire is obtained. The technique for stretching the coating precursor is the same as the stretching technique described above in the disclosure of process step (2).

  In process step (5), the coating precursor finally obtained after completion of process step (4) is preferably a furnace set temperature in the range of 450-650 ° C., an exposure time of 0.1-3 seconds, or preferred, for example. In the embodiment, strand annealing is performed at 500 to 600 ° C. for 0.3 to 1 second. In an exemplary embodiment, particularly an exemplary embodiment relating to a wire having a diameter of about 18 μm, the final strand annealing can be performed at a furnace set temperature of 530 ° C. and an exposure time of 0.8 seconds.

  In preferred embodiments, the final strand annealed coating precursor, i.e., still hot coated wire, in certain embodiments, is water that may contain one or more additives, such as 0 to 1000 wt ppm additive. It is cooled rapidly. Quenching with water is immediate or rapid, i.e. within 0.2 to 0.6 seconds, e.g. by dipping or dripping, from the temperature at which the final strand annealed coating precursor was received in process step (5) to room temperature. Means cooling.

  Intermediate annealing, which is an optional sub-step of process step (2), and final strand annealing of process step (5) may be performed under an inert or reducing atmosphere. A number of inert and reducing atmospheres are known in the art and are used to purge the annealing furnace. Of the known inert atmospheres, nitrogen or argon is preferred. Of the 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 90-98 vol% nitrogen and thus 2-10 vol% hydrogen. Vol% is 100 vol% in total. Preferred nitrogen / hydrogen mixtures are equal to 93/7, 95/5 and 97/3 vol% / vol%, respectively, based on the total volume of the mixture.

The purge using this kind of inert or reducing gas is a gas exchange rate (= gas flow rate [liter] in the range of 10 to 125 min ⁻¹ , more preferably 15 to 90 min ⁻¹ , most preferably 20 to 50 min ^−1. / Min]: It is preferable to carry out at a furnace volume [liter].

  After process step (5) and optional quenching, the coated wire of the present invention is finished. In order to fully take advantage of its properties, it is appropriate to use it for wire bonding applications immediately, ie without delay, for example within the 60-day downtime after the end of process step (5). Alternatively, to maintain the wide wire bonding process window characteristics of the wire and to prevent oxidation or other chemical attack, the finished wire is usually immediately after the end of the process step (5), i.e. without delay, e.g. process step (5) Wrapped within 1-5 hours after completion, vacuum sealed and stored for further use as a bonding wire. Storage in a vacuum-sealed state should not exceed 6 months. After opening the vacuum seal, the wire is used for wire bonding within 60 days.

  All process steps (1) to (5), winding and vacuum sealing are preferably performed under clean room conditions (USA FED STD 209E clean room standard, 1000 standards).

A third aspect of the present invention is a coated wire obtained by the process disclosed above according to any embodiment. The coated wire of the present invention has been found to be excellent 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, usually a ball bond (first bond) and a stitch bond (second bond, wedge bond) are formed. During bond formation, a specific power (usually measured in grams) is applied, supported by the application of a scrub stroke (usually measured in μm), or by the application of ultrasonic energy (usually measured in mA) Supported. Mathematical product of difference between upper and lower limits of applied power and applied scrub stroke in wire bonding process, or difference of upper and lower limits of applied power, and applied ultrasound The mathematical product of the difference between the energy limits defines the wire bonding process window:
(Applied power upper limit value-applied power lower limit value)-(applied scrub stroke upper limit value-applied scrub stroke lower limit value) = wire bonding process window,
Or (upper limit value of applied power−lower limit value of applied power) · (upper limit value of applied ultrasonic energy−lower limit value of applied ultrasonic energy) = wire bonding process window.

  The wire bonding process window defines a range of power / scrubbing stroke combinations or power / ultrasonic energy combinations, and conventional tests such as conventional pull tests, ball shear tests and ball pull-out tests, to name a few. A wire bond that meets the specifications is formed.

In other words, the first bond (ball bond) process window range is the product of the difference between the upper and lower limits of the power used for bonding and the upper and lower limits of the applied scrub stroke, or the upper and lower limits of the power used for bonding. It is the product of the difference between the values and the difference between the upper and lower limits of the applied ultrasonic energy. The resulting bond must meet certain ball share test specifications, for example, ball share 0.0085 grams / μm ² , no pad non-stick failure. The second bond (stitch bond) process window range is the product of the upper and lower limits of the power used for bonding and the difference of the upper and lower limits of the applied scrub stroke, or the difference of the upper and lower limits of the power used for bonding. And the product of the upper and lower limits of the applied ultrasonic energy. The resulting bond must meet certain pull test specifications, for example, a pulling force of 2.5 grams, no lead failure.

  For industrial applications, it is desirable to have a wide wire bonding process window (power g vs. scrub stroke μm, or power g vs. ultrasonic energy mA) because of the robustness of the wire bonding process. The wire of the present invention exhibits a significantly wider wire bonding process window.

  The following non-limiting examples illustrate the invention. These examples serve to illustrate the invention and are not intended to limit the scope of the invention or the claims in any way.

Free air ball (FAB) preparation:
It was prepared according to the procedure described in the KNS Process User Guide for FAB (Curic and Sofa, Fort Washington, PA, USA, May 31, 2009). A FAB was prepared by performing a conventional electric torch (EFO) discharge with a standard discharge (single step, 17.8 μm wire, EFO current 50 mA, EFO time 200 μsec, 95 vol% nitrogen / 5 vol% hydrogen atmosphere).

Test methods A to F
All tests and measurements were performed at T = 20 ° C. and relative humidity RH = 50%.

A. Sectioning method First, a wire was embedded using a cold-embedded epoxy resin and then polished (cut horizontally) by a standard metallographic technique. A sample having a minimum deformation strain on the sample surface was ground and polished using a multi-prep semi-automatic polishing machine at a low force and at an optimum speed. Finally, the polished sample was chemically etched with ferric chloride to reveal grain boundaries. According to the ASTM E112-12 standard, the average particle size was measured using an intercept method under a 1000 times optical microscope.

B. FAB morphology The formed FAB was examined by a 1000x scanning electron microscope (SEM).
Rating:
++, very good (round ball)
+, Good (round ball);
0, pass (not completely round, but no obvious plateau on FAB surface);
-Peach-shaped ball--Extreme peach-shaped ball As used herein, the term "peach-shaped ball" means that two plateaus with a clear hemisphere at the FAB tip are formed.

C. Bonded ball shape The formed FAB descended to an Al-0.5 wt% Cu bond pad at a predetermined height (tip 203.2 μm) and speed (contact speed 6.4 μm / sec). Upon contact with the bond pad, a series of defined bonding parameters (bonding force 100 g, ultrasonic energy 95 mA, bonding time 15 ms) caused FAB deformation to form bonded balls. After forming the ball, the capillary was raised to a predetermined height (kink height 152.4 μm, loop height 254 μm) to form a loop. After the loop formation, the capillary was lowered to the lead to form a stitch. After the stitch formation, the capillary was raised, the wire clamp was closed, and the wire was cut to obtain a predetermined tail length (tail length extension 254 μm). For each sample, five bonded wires were optically inspected using a 1000 × microscope.
Rating:
+, Round;
0, pass;
-Flower shape.

D. Eccentric ball (OCB)
The same method as described in Method C was applied, but instead of examining the roundness of the ball, the centrality of the ball was measured. For each sample, five bonded wires were optically inspected.
Rating:
++, perfectly centered +, centered;
0, off center with tolerance;
-Off-center;
--- Very off-center.

E. FAB Pd distribution First, the wire was embedded using cold embedded epoxy and cut laterally by standard metallographic techniques. A sample having a minimum deformation strain on the sample surface was ground and polished using a multi-prep semi-automatic polishing machine at a low force and at an optimum speed. Finally, the polished samples were examined with a 1000 × high magnification microscope. Five FABs were optically examined for each sample.
Visual evaluation:
++ Pd covers the FAB shell very uniformly with a Pd coverage of 80% or more of the FAB height;
+, Pd uniformly covers the FAB shell with a Pd coverage of 70% or more of the FAB height;
0, Pd partially covers the FAB shell and partially diffuses into the ball with a Pd coverage of 50-70% of the FAB height;
-Pd greatly diffuses into the ball while forming a Cu-Pd alloy with a Pd coverage of 50% or more of the FAB height;
---------------------------------------------------------------------------------------------------------------------------------------- Pd is diffused to the balls.

F. Corrosion resistance:
The wire was ball bonded to an Al-0.5 wt% Cu bond pad. The test device with the wires thus bonded is stored in a highly accelerated stress test (HAST) chamber for 96 hours at a temperature of 130 ° C. and a relative humidity (RH) of 85%, followed by a 100 × low magnification microscope (Nikon MM-40). ) Below, the number of balls that have risen was investigated. More rising balls were observed, indicating severe interfacial galvanic corrosion. Rated by ranking:
++, least raised balls +, few raised balls;
0, the raised ball is in the middle;
-More balls lifted;
-The highest number of raised balls.

Example 1: Wire samples 1-8
Large quantities of copper, silver and phosphorus, each at least 99.99% pure (“4N”), were melted in a crucible in a vacuum furnace at about 1200 ° C. Thereafter, an 8 mm rod-shaped wire core precursor was continuously cast from the melt. Thereafter, the rod was stretched in several stretching steps to form a wire core precursor having a circular cross section with a diameter of 200 μm. The wire core precursor was electroplated with a double layer coating consisting of an inner layer of 840 nm thick palladium and an outer layer of 45 nm thick gold. Thereafter, the film was further stretched to a final diameter of 17.8 μm having a final palladium coating layer having a thickness of 75 nm and a final gold coating layer having a thickness of 4 nm, followed by final strand annealing at a furnace setting temperature of 530 ° C. and an exposure time of 0.8 seconds. The coated wire thus obtained was immediately cooled in water containing 500 wt ppm of a surfactant.

  This procedure produced several different palladium and gold coated copper-based inventions and comparative samples 1-9. Table 1 shows the composition of the wire core.

Example 2: Wire samples 9-10
Produced in the same way as Example 1, Sample 5, but the layer thicknesses of the inner palladium and outer gold coatings were changed as recorded in Table 2.

  Table 3 below shows the specific test results.

Claims (14)

A wire including a wire core having a surface, the wire core having a coating layer overlapping the surface, the wire core itself,
(A) silver in an amount of 0.1 to 0.3 wt%;
(B) copper in an amount ranging from 99.64 to 99.8825 wt%;
(C) phosphorus in an amount ranging from 0 to 100 wt ppm;
(D) further components (components other than silver, copper and phosphorus) in an amount ranging from 0 to 500 wt ppm,
The individual amount of any further ingredients is less than 30 wt ppm;
All amounts of wt% and wt ppm are based on the total weight of the core,
The coating layer is a double layer composed of an inner layer of palladium and an outer layer of adjacent gold,
The weight of the inner layer of palladium ranges from 1.5 to 2.5 wt% with respect to the weight of the wire core,
The weight of the gold outer layer is in the range of 0.09 to 0.18 wt% with respect to the weight of the wire core.   The wire of claim 1, wherein the amount of silver is 0.2 wt%.   The wire according to claim 1 or 2, wherein the amount of phosphorus is 50 to 100 or 70 to 80 wt ppm.   4. A wire according to any one of claims 1 to 3, wherein the amount of further components is 0 to 100 wt ppm. 5. A wire according to any one of claims 1 to 4 having an average cross section in the range of 50-5024 [mu] m < ² >.   6. A wire according to any one of the preceding claims having a circular cross section with an average diameter in the range of 8 to 80 [mu] m. The wire according to any one of claims 1 to 6, wherein the wire core has at least the following intrinsic properties:
(I) the average wire particle size is in the range of 3-6 μm as measured in the longitudinal direction;
(Ii) The ratio of the average particle size measured in the longitudinal direction to the diameter of the wire core is in the range of 0.05 to 0.25, preferably 0.1 to 0.20.
(Iii) The ratio of the standard deviation (RSD) of the average particle size to the average particle size of the core measured in the longitudinal direction is in the range of 0.1 to 0.4.
A wire characterized by one of the following: A coated wire manufacturing process according to any one of claims 1 to 7, wherein said process is at least steps (1) to (5):
(1) providing a precursor of the desired composition;
(2) stretching the precursor to form an elongated precursor until an intermediate cross section in the range of 5024 to 70650 μm ² or an intermediate diameter in the range of 80 to 300 μm is obtained;
(3) A double layer coating of an inner layer of palladium and an adjacent outer layer of gold on the surface of the elongated precursor obtained after completion of the process step (2), and the weight of the inner layer of palladium is the weight of the elongated precursor. Depositing such that the weight of the gold outer layer is in the range of 0.09 to 0.18 wt% relative to the weight of the stretched precursor;
(4) further stretching the coating precursor obtained after completion of process step (3) until the desired final cross-section or diameter is obtained;
(5) Finally, the coated precursor obtained after the completion of the process step (4) is subjected to strand annealing at a furnace set temperature in the range of 450 to 650 ° C. and an exposure time in the range of 0.1 to 3 seconds, and the coated wire Forming a process.   The process of claim 8, wherein step (2) comprises one or more sub-steps of intermediate annealing of the stretch precursor.   The process according to claim 8 or 9, wherein the final strand annealing is performed at a furnace set temperature of 500 to 600 ° C and an exposure time of 0.3 to 1 second.   11. A process according to any one of claims 8 to 10, wherein the finally strand annealed coating precursor is quenched with water which may contain one or more additives.   12. Process according to any one of claims 8 to 11, wherein the final strand annealing of process step (5) is carried out under an inert or reducing atmosphere. Used as the bonding wire in wire bonding applications, coated wire Ya according to any one of claims 1 to 7.   A method of using a coated wire obtained by the process according to any one of claims 8 to 12,
  A method of using the coated wire as a bonding wire in wire bonding applications.