TW201718887A - Alloyed silver wire - Google Patents

Abstract

An alloyed silver wire comprising or consisting of a wire core, the wire core itself consisting of: (a) palladium in an amount in the range of from 0.1 to 3 wt.-%, (b) gold in an amount in the range of from 0.1 to 3 wt.-%, (c) nickel in an amount in the range of from 20 to 700 wt.-ppm, (d) calcium in an amount in the range of from 20 to 200 wt.-ppm, (e) silver in an amount in the range of from 93.91 to 99.786 wt.-%, and (f) 0 to 100 wt.-ppm of further components, wherein all amounts in wt.-% and wt.-ppm are based on the total weight of the core, wherein the alloyed silver wire has an average diameter in the range of from 8 to 80 [mu]m.

Description

Alloyed silver wire

The present invention relates to a 8 to 80 μm thick alloyed silver wire comprising a core comprising silver, palladium, gold, nickel and calcium in a specific weight ratio. The invention further relates to a method for making such a wire.

The use of wiring in electronic and microelectronic applications is well known in the state of the art. Although the wiring was initially made of gold, less expensive materials such as copper, copper alloys, silver and silver alloys are now used.

With regard to wire geometry, the most common are circular cross-section wires and bond strips having a nearly rectangular cross-section. Both types of line geometry have the advantage of making them suitable for a particular application.

It is an object of the present invention to provide an alloyed silver wire suitable for use in wire bonding applications, which is improved in particular in terms of corrosion resistance and moisture resistance, and which also exhibits a generally balanced balance with wire bonding applications. Range of features including, for example, wide-pin joint windows, axially symmetric airless solder balls (FAB) with good reproducibility, low FAB hardness, high stitch bond tensile strength, cord, low resistivity, low power Migration, etc.

The contribution of the item solution is provided by the subject matter of the request item forming the category. The dependent sub-items that form the category of claim items represent preferred embodiments of the present invention, the subject matter of which also contributes to solving the above-mentioned objectives.

In a first aspect, the present invention relates to an alloyed silver wire comprising a wire core or consisting of a wire core (hereinafter also referred to simply as "core"), the wire core itself being composed of the following group Form: (a) palladium in an amount ranging from 0.1 to 3 wt.-% (% by weight), preferably in the range of 0.5 to 1.5 wt.-%, and (b) gold in an amount of 0.1 to 3 wt.-% Within the range, preferably in the range of 0.2 to 1.5 wt.-%, (c) nickel, in an amount ranging from 20 to 700 wt.-ppm (parts per million by weight, one part per million by weight), Preferably, in the range of 275 to 325 wt.-ppm, (d) calcium, in an amount ranging from 20 to 200 wt.-ppm, preferably in the range of 20 to 50 wt.-ppm, (e) silver, in an amount of 93.91 to 99.786 wt.-%, preferably in the range of 96.9625 to 99.2595 wt.-%, and (f) 0 to 100 wt.-ppm of other components (components other than palladium, gold, nickel, calcium and silver) Wherein all amounts in wt.-% and wt.-ppm are based on the total weight of the core, wherein the alloyed silver wire has an average diameter in the range of 8 to 80 μm, or even in the range of 12 to 55 μm.

The alloyed silver wire is preferably a wire for bonding in microelectronics. The alloyed silver wire is preferably a one-piece article. Numerous shapes are known and appear to be suitable for use in the alloyed silver wire of the present invention. The preferred shape is (in cross-sectional view) a circular, elliptical, and rectangular shape.

In short, the average diameter or diameter of the wire or core can be obtained by the "quantity size method". The physical weight of the alloyed silver wire of defined length is determined according to this method. Based on this weight, the wire or core diameter is calculated using the line material density. The diameter is calculated as the arithmetic mean of the five measurements on the five cuts of a particular line.

For the purposes of the present invention, the term "wiring" encompasses all cross-sectional shapes and all common wire diameters, but wires having a circular cross-section and a thin diameter are preferred.

Consistent with the foregoing, the proportional ratios previously disclosed in the core include (a) palladium, (b) Gold, (c) nickel, (d) calcium and (e) silver. However, the core of the alloyed silver wire of the present invention may contain (f) other components in a total amount of from 0 to 100 wt.-ppm. In this context, other components often referred to as "inevitable impurities" are derived from impurities present in the raw materials used or from small amounts of chemical elements and/or compounds derived from the wire manufacturing process, ie, type (f) The presence of other components can, for example, be derived from impurities present in one or more of silver, palladium, gold, nickel, and calcium. Examples of such other components are: Cu, Fe, Si, Mn, Cr, Ce, Mg, La, Al, B, Zr, Ti, S, and the like. The low total amount of 0 to 100 wt.-ppm of the other component (f) ensures good reproducibility of the line characteristics. The other component (f) present in the core is usually not added separately.

In one embodiment, the core of the alloyed silver wire of the present invention comprises less than the following components (f): (i) Cu, amount <30 wt.-ppm; (ii) Cr, Ce, Mg, La Any one of Al, Be, In, Mn, and Ti, each of which is <2 wt.-ppm; (iii) any of Si, Fe, and S, each of which is <15 wt.-ppm.

The core of the alloyed silver wire in this context is defined as a homogeneous region of the bulk material. Since any bulk material always has a surface area that exhibits different characteristics to some extent, the characteristics of the core are understood to be characteristics of the homogeneous region of the bulk material. The surface of the bulk material region may be different in terms of morphology, composition (e.g., sulfur, chlorine, and/or oxygen content) and other characteristics. The surface may be the outer surface of the core; in this embodiment, the alloyed silver wire of the present invention is composed of a core. In an alternative, the surface can be the interface area between the core and the coating superimposed on the core.

In the context of the present invention, the term "overlay" is used to describe, for example, the relative position of a first item of a core relative to a second item such as a coating. The "overlay" feature is that other items such as the intermediate layer may (but need not) be disposed between the first and second items. Preferably, the second article is at least partially superimposed on the first article relative to the total surface of the first article, for example at least 30%, 50%, 70% or at least 90%. Best, second thing The product is completely superimposed on the first item.

In the context of the present invention, the term "intermediate layer" means the region of the alloyed silver wire between the core of the alloyed silver wire and the coating superimposed thereon. In this region, there is a combination of materials for both the core and the coating.

In the context of the present invention, the term "thickness" is used to define the dimension of a layer in a direction perpendicular to the longitudinal axis of the core which is at least partially superimposed on the surface of the core.

In an embodiment, the core has a surface in which the coating is superimposed on the surface of the core.

In one embodiment, the mass of the coating is no more than 5 wt.-%, preferably no more than 2 wt.-% or less, relative to the total mass of the core. When a coating is present, each has a minimum mass of 0.1 wt.-% or higher, or 0.5 wt.-% or higher, relative to the total mass of the core. Coating a small amount of material as a coating maintains the characteristics defined by the core material. On the other hand, the coating imparts specific characteristics to the surface of the wire, such as inertness with respect to the environment, corrosion resistance, improved adhesion, and the like. For example, for a wire having a diameter of 18 μm, the thickness of the coating is in the range of 20 to 120 nm. For wires having a diameter of 25 μm, the coating can have a thickness, for example, in the range of 30 to 150 nm.

In an embodiment, the coating may be made of a precious metal element. The coating can be a single layer of one of the elements. In another embodiment, the coating can be a plurality of layers comprising a plurality of superposed adjacent sub-layers, wherein each sub-layer is made of a different precious metal element. Common techniques for depositing such precious metal elements on the core are plating such as electroplating and electroless plating, deposition of materials from the vapor phase such as sputtering, ion plating, vacuum evaporation, and physical vapor deposition, and self-melting of materials. Deposition of matter.

In one embodiment, the alloyed silver wire of the present invention or a core thereof is characterized by at least one of the following intrinsic properties (see "Test Method A" as described below): (1) the average wire size (average particle size) is less than 10 μm, for example in the range of 2 to 6 μm, preferably in the range of 2 to 4 μm, (2) the line grain [100] or [101] or [111] orientation plane is less than 7%, for example in the range of 1% to 5% Preferably, in the range of 2% to 3.5%, the (3) line twin boundary fraction is less than 60%, for example, in the range of 30% to 50%, preferably in the range of 40% to 45%, (4) FAB exhibits columnar grains (grain elongation), (5) FAB average particle size 18 μm, for example in the range of 6 to 14 μm, preferably in the range of 8 to 12 μm, (6) FAB grain [101] orientation plane is less than 45%, for example in the range of 30% to 40%, preferably 32% to Within the range of 36%, (7) the FAB twin boundary fraction is less than 70%, for example, in the range of 30% to 65%, preferably in the range of 60% to 65%, and/or at least characterized by the following intrinsic properties. One of: (α) corrosion resistance has a value of no more than 5% of the rising of the ball, for example, in the range of 0 to 5% (see "Test Method B" as described below), (β) has no moisture resistance. More than 5% of the value of the joint ball rise, for example, in the range of 0 to 5% (see "Test Method C" as described below), the hardness of the (γ) core does not exceed 85 HV, for example, in the range of 50 to 85 HV, Preferably in the range of 65 to 75 HV (see "Test Method D" as described below), (δ) has a process window area for stitch bonding with at least 12000 mA. The value of g, for example for a line with a diameter of 18 μm, a value of 13,000 to 14400 mA. g (see the specific disclosure below and "Test Method E"), the resistivity of the (ε) line is less than 2.5μΩ. Cm, for example at 1.7 to 2.4 μΩ. Within the range of cm, preferably between 2.2 and 2.4 μΩ. Within the range of cm (see "Test Method F" below), the yield strength of the (ζ) line does not exceed 170 MPa, for example in the range of 140 to 170 MPa (see "Test Method G" as described below), (η) The silver dendritic growth of the line does not exceed 4 μm/s, for example, in the range of 2 to 4 μm/s, preferably in the range of 2 to 3 μm/s (see "Test Method H" as described below).

As used herein, the terms "intrinsic property" and "non-inherent property" relate to a core or FAB. Inherent characteristics mean the characteristics of the core or FAB itself (independent of other factors), while the intrinsic characteristics depend on the relationship between the line of sight core or FAB and other factors, such as the measurement method used and/or the measurement conditions.

In the case of a preferred embodiment of the invention, the hardness of the core (i.e., the hardness prior to bonding) is less than 85 HV, preferably in the range of 65 to 75 HV. Further, the hardness of the FAB treated using the wire of the present invention prior to joining is less than 80 HV, preferably in the range of 60 to 70 HV. This hardness or (more precisely) softness of the core and FAB helps to prevent damage to the sensitive substrate during the bonding process. Experiments have also shown that such cords of the present invention exhibit extremely soft FAB characteristics. This limitation of FAB hardness is especially useful if the mechanically sensitive structure is arranged below the bond pad. This is especially true if the bond pad consists of a soft material such as aluminum or gold. For example, the sensitive structure may comprise one or several porous ceria layers, which in particular have a dielectric constant of less than 2.5. This porous and therefore weak material has become more common because materials can help to improve device performance. Thus, the mechanical properties of the wiring of the present invention can be optimized to avoid cracking or other damage to such weak layers.

In a particular embodiment, the alloyed silver wire of the present invention exhibits silver dendritic growth at a rate of less than 4 μm/s, such as in the range of 2 to less than 4 μm/s, preferably in the range of 2 to 3 μm/s, It is about 1/10 to 1/7 of the growth rate of about 25 μm/s of the 4N pure silver wire.

In another advantageous embodiment, the resistivity of the wire is less than 3.2 μΩ. Cm, for example at 2.0 to 2.4 μΩ. Within the range of cm, preferably between 2.2 and 2.4 μΩ. Within the scope of cm, it means that it is suitable for many applications.

In another aspect, the invention is also directed to a method for making an alloyed silver wire of any of the embodiments disclosed above. The method comprises at least the following steps: (1) providing a precursor article comprising: (a) palladium in an amount ranging from 0.1 to 3 wt.-%, preferably from 0.5 to 1.5 wt.-%, (b) gold in an amount ranging from 0.1 to 3 wt.-%, preferably in the range of from 0.2 to 1.5 wt.-%, and (c) nickel in an amount ranging from 20 to 700 wt.-ppm, preferably In the range of 275 to 325 wt.-ppm, (d) calcium, in an amount ranging from 20 to 200 wt.-ppm, preferably in the range of 20 to 50 wt.-ppm, (e) silver in an amount of 93.91 to 99.786 wt. In the range of .-%, preferably in the range of 96.9625 to 99.2595 wt.-%, and (f) 0 to 100 wt.-ppm of other components, all in wt.-% and wt.-ppm Based on the total weight of the precursor article, (2) elongating the precursor article to form a wire precursor until the desired final diameter of the core is obtained; and (3) finally, after completing method step (2), at 400 to 600 The obtained wire precursor is subjected to strip annealing for an exposure time in the range of 0.4 to 0.8 seconds at an oven set temperature in the range of ° C to form an alloyed silver wire, wherein the step (2) includes an oven at 400 to 800 ° C. One or more sub-steps of moderately batch annealing the elongated precursor article to an exposure time in the range of 50 to 150 minutes at a set temperature, and/or an elongation precursor at an oven set temperature of 400 to 800 ° C Object One or more sub-steps performed within the exposure time of the annealed strip was moderate from 0.4 to 1.2 seconds range.

The term "strip annealing" is used herein. It is a continuous process that allows rapid production of lines with high reproducibility. Strip annealing means that the annealing is performed dynamically, at which time the elongated wire precursor article or the wire precursor to be annealed is moved through the annealing oven and wound onto the spool after having left the annealing box.

The term "oven set temperature" is used herein. It means the temperature control of the annealing oven The temperature fixed in the controller. The annealing oven can be a chamber furnace (in the case of batch annealing) or a tubular annealing oven (in the case of strip annealing).

The invention distinguishes precursor articles, wire precursors and alloyed silver wires. The term "precursor article" is used in the pre-wire stage, which has not yet reached the desired final diameter of the core, and the term "line precursor" is used in the pre-line phase with the desired final diameter. After completion of method step (3), i.e., after final strip annealing of the line precursor having the desired final diameter, an alloyed silver line in the sense of the present invention is obtained.

The precursor article as provided in method step (1) can be obtained by blending/doping silver with the desired amount of palladium, gold, nickel and calcium. The silver alloy itself can be prepared by conventional methods known to those skilled in the art of metal alloys, for example, by melting together silver, palladium, gold, nickel and calcium in a desired ratio. In this case, 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 is advantageously operated under vacuum or under an inert gas atmosphere. The material used may have a purity level of, for example, 99.99 wt.-% and higher. The melt thus produced can be cooled to form a homogeneous piece based on the silver precursor article. Typically, the precursor article is in the form of a rod having a diameter of, for example, 2 to 25 mm and a length of, for example, 5 to 100 m. The rod can be made by casting the silver alloy melt into a suitable mold at room temperature, followed by cooling and solidification.

If, as disclosed in some embodiments of the first aspect of the present invention, a coating in the form of a single layer or multiple layers is present on the core of the alloyed silver wire, it is preferred to apply the coating to the wire precursor article. The article may not have been stretched without final elongation or even sufficient elongation to the desired final diameter. The skilled person knows how to calculate the thickness of this coating on the precursor article to obtain a coating having the thickness disclosed in the embodiment of the wire, i.e., after elongating the body article prior to coating to form a wire precursor. As has been disclosed above, numerous techniques for forming a coating of a material on a surface of a silver alloy in accordance with an embodiment are known. Preferred techniques are plating such as electroplating and electroless plating, deposition of materials from the vapor phase such as sputtering, ion plating, vacuum evaporation, and physical vapor deposition, and deposition of materials from the melt.

In order to superimpose a single or multiple layer metal coating onto the core disclosed in some embodiments of the first aspect of the invention, it is advantageous to interrupt method step (2) once the desired diameter of the precursor article is reached. This diameter can be, for example, in the range of 80 to 200 μm. The single or multiple layer metal coating can then be applied, for example, by one or more plating process steps. Thereafter, method step (2) is continued until the desired final diameter of the core is obtained.

In method step (2), the precursor article is elongated to form a wire precursor until the desired final diameter of the core is obtained. In the context of the present invention, the technique of elongating a precursor article to form a wire precursor is known and practical. The preferred technique is roll, swage, die drawing or the like, with die stretching being preferred. In the latter case, the precursor article is stretched in several method steps until the desired and final diameter of the core is reached.

The desired and final diameter of the core may range from 8 to 80 μm, or preferably from 12 to 55 μm. This wire drawing stretching method is well known to those skilled in the art. Conventional tungsten carbide and diamond tensile dies can be used, and conventional stretching lubricants can be used to support stretching.

Step (2) of the method of the present invention comprises one or more sub-steps of moderately batch annealing the elongated precursor article to an exposure time in the range of 50 to 150 minutes at an oven set temperature of 400 to 800 ° C, and / or one or more sub-steps of moderately strip annealing the elongated precursor article to an exposure time in the range of 0.4 seconds to 1.2 seconds at an oven set temperature of 400 to 800 °C. One or more intermediate annealing steps of the elongated precursor article may be performed between two or more than two multiple elongation or stretching steps. To illustrate this step by way of example, three moderate annealing steps can be performed at three different stages during stretching, for example, a first moderate batch annealing: in a oven set temperature range of 400 to 800 ° C, the rod is The product is stretched to a diameter of 2 mm and wound on a roll for an exposure time of 50 to 150 minutes, and the second medium strip is annealed: the precursor article is stretched to 47 μm in an oven set temperature range of 400 to 800 °C. The exposure time of 0.4 to 1.2 seconds in diameter and the third moderate strip annealing: further stretching the precursor article to a diameter of 27 μm for 0.4 to 1.2 seconds in an oven set temperature range of 400 to 800 ° C time.

In method step (3), the strand precursor obtained after the completion of method step (2) is finally subjected to strip annealing. The final strip annealing is performed at an oven set temperature range of, for example, 400 to 600 ° C for an exposure time of 0.4 to 0.8 seconds, or in a preferred embodiment, between 0.5 and 0.7 seconds in the range of 400 to 500 °C.

The final strip annealing is typically performed by stretching the elongated wire precursor through a conventional annealing oven at a specified annealing rate, typically in the form of a cylindrical tube having a specified length and a defined temperature profile selected at a rate For example, in the range of 10 to 60 meters per minute. This can define and set the annealing time/oven temperature parameters.

In a preferred embodiment, the final strip annealed alloyed silver wire is quenched in water. In one embodiment, the water may contain one or more additives, such as from 0.01 to 0.07 volume percent of the additive. Quenching in water means, for example, by impregnation or dripping, the alloyed silver wire which is finally annealed by the strip, either immediately or rapidly (ie within 0.2 to 0.6 seconds), from which it undergoes in method step (3) The temperature was cooled to room temperature.

With respect to an embodiment of the present invention, it has been found that performing final strip annealing at temperatures below the maximum elongation can result in beneficial line characteristics, since the line morphology can be affected in a positive manner. By this adjustment, other characteristics such as, for example, line hardness, ball joint performance, and the like can be positively affected.

In one embodiment, the final strip annealing may be performed at a temperature at least 150 ° C lower than the temperature at which the maximum elongation value is obtained by annealing, for example, 210 to 240 ° C lower; this may result in an elongation value of the wire after annealing. Exceeding 70% of the maximum elongation value, such as 30% to 60% of the maximum elongation value. For example, method step (3) can be carried out at a temperature at least 150 ° C lower than the maximum elongation temperature T _{ΔL (max)} , preferably at least 180 ° C lower, or at least 200 ° C lower. The temperature of method step (3) is often not lower than T _{ΔL(max) by} more than 250 °C. The maximum elongation temperature T _ΔL(max) is determined by testing the elongation at break of the sample (line) at different temperatures. Data points were collected in the graph showing elongation (in %) as a function of temperature (°C). The resulting graph is often referred to as the "annealing curve." In the case of a silver based line, the temperature is observed when the elongation (in %) is reached to the maximum. This is the temperature T _ΔL(max) of the maximum elongation. An example is shown in Figure 1, which shows an exemplary annealing profile for the 18 [mu]m alloyed silver wire of Sample 1 (Table 1). The annealing temperature is a variable parameter of the x-axis. The graph shows the measured values of the breaking load (BL, in grams) and elongation (EL, in %) of the wire. The elongation was measured by a tensile test. The elongation measurements show a typical local maximum of about 19% in the example shown, which is obtained at an annealing temperature of about 700 °C. If the final strip annealing is performed on the line of sample 1 at a temperature lower than the maximum elongation of 420 ° C at a temperature lower than the maximum elongation, the result is an elongation value of about 8%, which is The maximum elongation value is less than 40%.

The intermediate annealing of method step (2) and the final strip annealing of method step (3) can be carried out in an inert or reducing atmosphere. Numerous types of inert atmospheres and reducing atmospheres are known in the art and are used in purge annealing ovens. Nitrogen or argon is preferred in known inert atmospheres. Hydrogen is preferred in known reducing atmospheres. Another preferred reducing atmosphere is a mixture of hydrogen and nitrogen. Preferably, the mixture of hydrogen and nitrogen is from 90 to 98 vol.-% nitrogen and correspondingly from 2 to 10 vol.-% hydrogen, wherein the total vol.-% is 100 vol.-%. Preferably, the nitrogen/hydrogen mixture is equal to 93/7, 95/5 and 97/3 vol.-%/vol.-%, each based on the total volume of the mixture. If some portion of the surface of the alloyed silver wire is sensitive to oxidation by air, it is preferred to apply a reducing atmosphere during annealing. Such a type of inert or reducing gas purge is preferably in the range of 10 to 125min ^-1, more preferably in the range of 15 to 90min ^-1, optimal gas exchange rate at the range 20 to 50min ^-1 (= Gas flow rate [liters per minute]: volume in the oven [liters]).

A unique combination of the composition of the precursor material material (which is identical to the other of the finished alloyed silver wire core) and the primary annealing parameters during method steps (2) and (3) provides at least one of the above disclosed The line of the invention of inherent and/or extrinsic properties is important. The temperature/time conditions of the moderate and final strip annealing steps allow for the intrinsic and extrinsic properties of the alloyed silver core to be obtained or adjusted.

Upon completion of method step (3), the alloyed silver wire of the present invention is completed. In order to fully benefit from its characteristics, it is advantageous or immediately (ie, without delay) to use it for wire bonding applications, such as no more than 10 days after completing method step (3). Alternatively, in order to maintain the characteristics of the wide wire bonding process window of the alloyed silver wire and to prevent oxidation or other chemical attack, the finished wire is usually wound and vacuum sealed immediately after the completion of the method step (3) (ie without delay). , for example, within <1 to 5 hours after completion of method step (3), and then stored for further use as a wire. Store under vacuum tight conditions should not exceed 6 months. After opening the vacuum seal, the alloyed silver wire should be used for wire bonding in less than 10 days.

Preferably, all process steps (1) through (3) and winding and vacuum sealing are carried out in clean room conditions (US FED STD 209E clean room standard, 1k standard).

A third aspect of the invention is that the alloyed silver wire is obtainable by the method of the second aspect of the invention disclosed above or an embodiment thereof. This alloyed silver wire has been found to be more suitable for use in wire bonding applications. Wire bonding techniques are well known to the skilled person. In the wire bonding process, ball bonding (first bonding) and stitch bonding (second bonding, wedge bonding) are typically formed. A force is applied (usually in grams) during the formation of the joint, which is supported by the application of ultrasonic energy (usually in milliamps). 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 in the wire bonding method defines the wire bonding process window: (the upper limit of the applied force - the lower limit of the applied force) . (Upper limit of applied ultrasonic energy - lower limit of applied ultrasonic energy) = wire bonding process window.

The wire bonding process window defines the area of the force/ultrasonic energy combination that allows for the formation of a wire bond that conforms to the specification, that is, the wire is joined by, for example, a conventional tensile test, a ball shear test, and a ball. A well-known test for tensile testing.

In other words, the first bonding (ball bonding) process window region is the product of the difference between the upper and lower limits of the force used in the bonding and the difference between the upper and lower limits of the applied ultrasonic energy, wherein the resulting bonding must conform to certain ball shear test specifications. For example, a ball of 0.0085 g/m 2 is sheared, adhered to the bonding pad, etc., and a second bonding (pin bonding) process window area is used for bonding The difference between the upper and lower limits of the force and the difference between the upper and lower limits of the applied ultrasonic energy, wherein the resulting joint must meet certain tensile test specifications, such as a tensile force of 2.5 grams, adhered to lead, and the like.

For industrial applications, it is desirable to have a wide wire bonding process window (force (in g) versus ultrasonic energy (in mA) for reasons of wire bonding method robustness. The wire of the present invention exhibits an extremely wide wire bonding process window.

The following non-limiting examples illustrate the invention. The examples are intended to be illustrative of the invention and are not intended to limit the scope of the invention or the scope of the invention.

Instance

Prepare FAB:

The procedure is described in accordance with the procedure described in the KNS Process User Guide for Free Air Ball (Kulicke & Soffa Industries, Fort Washington, PA, USA, 2002, May 31, 2009). FAB was prepared by conventional roasting (EFO) roasting by standard calcination (single step, 18 mA EFO current, 455 μs EFO time).

Test method A. to J.

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

A. Line and FAB electronic backscatter diffraction (EBSD) map analysis:

The main steps used in the measurement line and FAB structure are sample preparation to obtain a good Kikuchi diagram and component calculations: firstly, epoxy resin cans are sealed with or without FAB and polished according to standard metallographic techniques. . Ion milling is applied during the final sample preparation step to remove any mechanical deformation, contamination, and oxide layers from the wire surface. The surface of the ion-milled cross-section sample was sputtered with gold. Two additional rounds of ion milling and gold sputtering were then performed. No chemical etching or ion etching is performed.

The sample was loaded into a FESEM with a holder at a 70[deg.] angle to the surface of the normal FESEM (field emission scanning electron microscope) sample holder. FESEM is additionally equipped with EBSD Detector. An electron backscatter pattern (EBSP) containing linear crystal information is obtained.

The grain orientation fraction, average particle size, etc. of these patterns were further analyzed (using a software called QUANTAX EBSD program, developed by Bruker). Points similar to orientation are grouped together to form structural components.

In order to distinguish between different structural components, a maximum tolerance angle of 15° is used. Set the line stretch direction to the reference orientation. The [100], [101], and [111] structure percentages were calculated by measuring the percentage of crystals having planes of [100], [101], and [111] oriented parallel to the reference orientation.

The average particle size of the crystal orientation between adjacent lattice points greater than the minimum (here, 10°) is defined to determine the grain boundary position. The EBSD software calculates the area of each grain and converts it into an equivalent circle diameter, which is defined as the "average grain size". All grains in the longitudinal direction of the line along the length in the range of ~100 μm were calculated to determine the average and standard deviation of the average grain size.

The twin boundaries (also known as the Σ3 CSL twin boundaries) are not included in the average particle size calculation. The intertwined boundary is described by a 60° rotation around the <111> orientation plane between adjacent crystalline domains. The number of dots depends on the step size, which is less than 1/5 of the average grain size.

B. Bonding ball salt solution soaking test:

The ball was bonded to an Al-0.5 wt.-% Cu bond pad. The test device with the wire thus joined was immersed in the salt solution for 10 minutes at 25 ° C, washed with deionized (DI) water, and then washed with acetone. The salt solution contained 20 wt.-ppm NaCl in deionized water. The number of ascending spheres was measured at a magnification of 100X under a low power microscope (Nikon MM-40). Observations of the number of higher rising balls indicate severe interface current corrosion.

C. Wet resistance test of the joint ball:

The ball was bonded to an Al-0.5 wt.-% Cu bond pad. The test device with such a bond wire was stored in a high accelerated stress test (HAST) chamber at 130 ° C temperature, 85% relative humidity (RH) for 8 hours, and then under a low power microscope (Nikon MM-40) at 100X. amplification Rate to detect the number of rising balls. Observations of the number of higher rising balls indicate severe interface current corrosion.

D. Vickers Micro-hardness:

Hardness was measured using a Mitutoyo HM-200 test apparatus with a Vickers indenter. A force of 10 mN indentation load was applied to the test sample of the line for a residence time of 12 seconds. Test on the center of the wire core and on the FAB.

E. Pin-joining process window area:

The measurement of the bonding process window area is performed by a standard procedure. Test lines were joined using a KNS-iConn bonding machine tool (Kulicke & Soffa Industries, Fort Washington, PA, USA). The process window value is based on a line having an average diameter of 18 μm, wherein the wire fingers bonded to the wire are composed of silver.

The four corners of the process window are derived by overcoming two major failure modes: (1) supply of low force and ultrasonic energy can cause the wire to adhere to the lead finger (NSOL, non-stick on lead finger), and (2) The supply of high force and ultrasonic energy can lead to short tail (SHTL).

F. Resistivity:

Connect both ends of the test sample (that is, a line length of 1.0 meters) to a power source that supplies a constant current/voltage. The device is used to record the resistance to the supply voltage. The measurement device is the HIOKI model 3280-10 and the test is repeated with at least 10 test samples. The arithmetic mean of the measured values is used for the calculations given below.

The resistance R is calculated from R=V/I.

The specific resistance ρ is calculated from ρ = (R x A) / L, where A is the average cross-sectional area of the line, and L is the line length between the two measurement points of the means for measuring the voltage.

The specific conductivity is calculated from σ = 1 / ρ.

G. Elongation (EL):

The tensile properties of the test line were tested using an Instron-5564 instrument. Needle at 2.54cm/min For the 254mm gauge (L) test line. The load and elongation on the fracture or break were obtained in accordance with ASTM Standard F219-96. Elongation is the difference between the gauge length (ΔL) of the line between the start and end of the tensile test, which is usually reported as (100.ΔL/L) (in percent), using the recorded load ratio elongation Stretch the graph to calculate. The tensile strength and yield strength are calculated by dividing the fracture and yield load by the line area. The actual diameter of the wire is measured by the size method, the line of the standard length is weighed, and the density is used.

H. Line electromigration test:

The two wires were kept parallel on the PTFE plate at a distance of within a centimeter at a low magnification microscope of Nikon MM40 at 50X magnification. Water droplets are formed between the two wires to be electrically connected by a micropipette. One wire is connected to the positive electrode and the other is connected to the negative electrode, and 5V is applied to the wire. Apply a 5V bias to the two wires in a closed circuit and connect them in series to a 10kΩ resistor. The circuit is closed by wetting the two wires with a few drops of deionized water as an electrolyte. Silver electromigrates from the cathode to the anode in the electrolyte to form silver dendrites, sometimes the two wires are bridged together. The rate at which silver dendrites grow strongly depends on alloy addition. The diameter of the tested line was 75 μm.

Example 1

In each case, a certain amount of silver (Ag), palladium (Pd), and gold (Au) having a purity of at least 99.99% ("4N") is melted in the crucible. A small amount of silver-nickel and silver-calcium master alloy was added to the melt, and the uniform distribution of the added components was determined by stirring. Use the following silver-nickel and silver-platinum master alloys:

For the alloy of Table 1, a corresponding combination of the master alloys Ag-0.5 wt.-% Ni and Ag-0.5 wt.-% Ca was added.

The core precursor article in the form of a 8 mm rod was then continuously cast from the melt. The core precursor article is then stretched in several stretching steps to form 18±0.5 μm A core precursor with a specified diameter. The cross section of the core is substantially circular in shape.

The rods stretched to a diameter of 2 mm and wound onto a roll were subjected to a moderate batch annealing at an oven set temperature of 500 ° C for an exposure time of 60 minutes. The second intermediate strip annealing was performed on the precursor article having a diameter of 47 μm at an oven set temperature of 600 ° C for an exposure time of 0.8 seconds, and was stretched to a diameter of 27 μm at an oven set temperature of 600 ° C. The precursor article was subjected to a third moderate strip annealing for an exposure time of 0.6 seconds. The 18 μm core precursor was subjected to final strip annealing at an oven set temperature of 480 ° C for an exposure time of 0.6 seconds, followed by quenching the line thus obtained in water containing 0.05 vol.-% of surfactant. A moderate batch annealing was performed using an argon purge gas, and strip annealing was performed using a 95 vol.-% nitrogen: 5 vol.-% nitrogen purge mixed gas.

By this procedure, comparative silver lines of 1 to 5 and 4N purity of several different samples of the alloyed silver wire of the present invention were produced (reference).

Table 1 shows the composition of the different lines (samples 1 to 5) of the present invention. The palladium content is in the range of 1 to 3 wt.-%. The gold content is in the range of 1 to 1.5 wt.-%. The amount of nickel added varies from 30 to 300 wt.-ppm. The calcium content was each maintained at 30 and 50 wt.-ppm.

The particle size of the sample 1 to 5 was measured and the average particle size was reported. In each case, the results were in the range of 2 to 5 μm. For Sample 1, the average particle size was 2.91 μm.

Table 2 below shows the evaluation results of the corrosion resistance and moisture resistance of the bonding wires, the performance of the second bonding process window, and the performance of FAB formation. Wire samples 1 to 5 and 4N pure silver comparative wires as defined above were bonded to an Al-0.5 wt.-% Cu bond pad and tested according to the above disclosure Method to test. Except for electromigration testing for 75 μm lines, all tests were performed on 18 μm nickel.

All line samples produce a program window that is more suitable for industrial applications. A significant improvement in the corrosion resistance and moisture resistance of the joined balls was observed. In particular, line sample 1 shows a value close to zero (i.e., 2 balls rise), which is a particularly improved compared to the 4N pure silver line (reference).

In addition, the silver dendritic growth of line samples 1 to 5 was much lower than the silver dendritic growth of the 4N pure silver line.

Table 3 shows the average particle size and structural components of Line Sample 1 (line, FAB, and heat affected zone (HAZ)).

Figure 1 shows an exemplary annealing curve for a 18 μm silver-palladium-gold-nickel-calcium alloy wire (Sample 1, see Table 1). The annealing time is selected to be a constant value by adjusting the speed of the moving line. The annealing temperature is a variable parameter of the x-axis. The graph shows the measured values of the breaking load (BL, in grams) and elongation (EL, in %) of the wire. The elongation was measured by a tensile test. The elongation measurements show a typical local maximum of about 19% in the example shown, which is obtained at an annealing temperature of about 700 °C. Annealing of sample line 1 was carried out at 480 ° C, which according to Figure 1 was 220 ° C lower than the temperature of the maximum elongation. This produces an elongation value of about 8% which is more than 40% lower than the maximum elongation value.

Figure 2 shows an exemplary ion mill cross-sectional image of a 18 μm silver-palladium-gold-nickel-calcium alloy wire (Sample 1, Table 1). The grain morphology, HAZ and FAB of the three different position lines are obvious. Line sample 1 was annealed at 480 ° C, 7.5% EL. The ball-to-wire size ratio (BSR) of 1.8 and the EFO current of 18 mA and the EFO time of 455 μs were applied.

Claims (16)

An alloyed silver wire comprising a core or consisting of a core, the core itself consisting of (a) palladium in an amount ranging from 0.1 to 3 wt.-%, and (b) gold in an amount from 0.1 to In the range of 3 wt.-%, (c) nickel, in an amount ranging from 20 to 700 wt.-ppm, (d) calcium, in an amount ranging from 20 to 200 wt.-ppm, (e) silver, in an amount of 93.91 And other components in the range of 99.786 wt.-%, and (f) 0 to 100 wt.-ppm, wherein all amounts in wt.-% and wt.-ppm are based on the total weight of the core, wherein The alloyed silver wire has an average diameter in the range of 8 to 80 μm. The alloyed silver wire of claim 1 having an average diameter in the range of 12 to 55 μm. The alloyed silver wire of claim 1, wherein the amount of palladium is in the range of 0.5 to 1.5 wt.-%. The alloyed silver wire of claim 1, wherein the amount of gold is in the range of 0.2 to 1.5 wt.-%. The alloyed silver wire of claim 1, wherein the amount of nickel is in the range of 275 to 325 wt.-ppm. The alloyed silver wire of claim 1, wherein the amount of calcium is in the range of 20 to 50 wt.-ppm. The alloyed silver wire of claim 1, wherein the amount of silver is in the range of 96.9625 to 99.2595 wt.-%. The alloyed silver wire of claim 1, which has a circular, elliptical or rectangular shape in cross-sectional view. The alloyed silver wire of claim 1, wherein the core has a surface, wherein the surface is an outer surface or an interface region between the core and a coating superposed on the core area. An alloyed silver wire according to claim 9, which has a coating layer superimposed on the core, wherein the coating is a single layer made of a precious metal element or a plurality of layers including a plurality of adjacent sub-layers, wherein each of the sub-layers The layers are made of different precious metal elements. The alloyed silver wire of claim 1, wherein the core is characterized by at least one of the following intrinsic characteristics: (1) an average line size of less than 10 μm, (2) a line grain [100] or [101] or [111 ] The orientation plane is less than 7%, the (3) line twin boundary fraction is less than 60%, (4) FAB exhibits columnar grains, and (5) FAB average grain size 18μm, (6) FAB grain [101] orientation plane is less than 45%, (7) FAB twin boundary fraction is less than 70%, and / or at least one of the following non-inherent characteristics: (α) corrosion resistance The property has a value of not more than 5% of the rising of the bonding ball, (β) the moisture resistance has a value of not more than 5% of the rising of the bonding ball, (γ) the hardness of the core does not exceed 85 HV, and (δ) is used for the stitching. The process window area has at least 12000 mA. The value of g, (ε) the resistivity of the line is less than 2.5μΩ. Cm, (ζ) The yield strength of the line does not exceed 170 MPa, and (η) the silver dendritic growth of the line does not exceed 4 μm/s. A method for producing an alloyed silver wire according to any of the preceding claims, wherein the method comprises at least the steps of: (1) providing a precursor article having a core composition as claimed in claim 1, (2) elongating The precursor article to form a wire precursor until the desired final diameter of the core is obtained; (3) after the method step (2) is completed, the obtained wire precursor is subjected to final strip annealing at an oven set temperature in the range of 400 to 600 ° C for an exposure time in the range of 0.4 to 0.8 seconds to form the An alloyed silver wire, wherein step (2) comprises one or more sub-steps of moderately batch annealing the elongated precursor article to an exposure time in the range of 50 to 150 minutes at an oven set temperature of 400 to 800 °C. And/or one or more sub-steps of moderately strip annealing the elongated precursor article to an exposure time in the range of 0.4 seconds to 1.2 seconds at an oven set temperature of 400 to 800 °C. The method of claim 12, wherein the final strip annealing is performed at an oven set temperature in the range of 400 to 500 ° C for an exposure time in the range of 0.5 to 0.7 seconds. The method of claim 12, wherein the final strip annealed alloyed silver wire is quenched in water that may contain one or more additives. The method of claim 12, wherein the moderate annealing of method step (2) and the final strip annealing of method step (3) are carried out in an inert or reducing atmosphere. An alloyed silver wire which is obtainable by the method of claim 12.