JP2018530899A - Silver alloy wire - Google Patents

Abstract

A silver alloy wire comprising or consisting of a wire core, wherein the wire core itself is (a) 0.1 to 3 wt. % Palladium in an amount in the range of 0.1% to 3 wt. % In the amount of gold, and (c) 20 to 700 wt. nickel in an amount in the range of ppm, and (d) 20 to 200 wt. calcium in an amount in the range of ppm, and (e) 93.91 to 99.786 wt. % In the amount of silver, and (f) 0 to 100 wt. ppm of additional components, where wt. % And wt. A silver alloy wire having an average diameter in the range of 8 to 80 μm, wherein all amounts of ppm are based on the total weight of the core. [Selection] Figure 1

Description

  The present invention relates to an 8 to 80 μm thick silver alloy wire comprising a core comprising a specific weight ratio of silver, palladium, gold, nickel and calcium. The invention further relates to a process for producing such a wire.

  The use of bonding wires in electronics and microelectronic applications is a known state of the art. Bonding wires were initially made of gold, but now less expensive materials such as copper, copper alloys, silver and silver alloys are used.

  With regard to wire shape, the most common ones are bonding wires with a circular cross section and bonding ribbons with a somewhat rectangular cross section. Both types of wire shapes have their advantages that make them useful for specific applications.

  The object of the present invention is that, for example, a silver alloy wire has improved corrosion resistance and moisture resistance, but for example of a wide stitch bonding window, an axisymmetric free air ball (FAB) with good reproducibility. A wire that also exhibits a globally balanced spectrum of properties that are suitable for wire bonding applications, including formation, low FAB hardness, high stitch tensile strength, soft wire, low electrical resistivity, low electromigration, etc. It is to provide a silver alloy wire suitable for use in bonding applications.

  The contribution to the solution of the object is provided by the subject matter of the categorization claims. The dependent claims of the category forming claims represent preferred embodiments of the present invention, whose subject matter also contributes to the solution of the above-mentioned object.

2 shows an exemplary annealing curve of a silver-palladium-gold-nickel-calcium alloy 18 μm wire, Sample 1 (see Table 1). The annealing time was selected to a constant value by adjusting the speed of the moving wire. The annealing temperature is a variable parameter on the X axis. The graph shows the measured values of break load (BL, gram) and elongation (EL,%) of the wire. The elongation was determined by a tensile test. Elongation measurements showed a typical maximum of about 19% in the example shown, achieved at an annealing temperature of about 700 ° C. The sample wire 1 was annealed at 480 ° C., which is 220 ° C. below the maximum elongation temperature according to FIG. This resulted in an elongation value of about 8%, which is 40% below the maximum elongation value. 2 shows an exemplary ion milled cross-sectional image of a silver-palladium-gold-nickel-calcium alloy 18 μm wire, Sample 1 (Table 1). The particle morphology of the three differently positioned wires, HAZ and FAB is evident. Wire sample 1 was annealed at 480 ° C. and 7.5% EL. A ball size to wire ratio (BSR) of 1.8 and EFO current of 18 mA and EFO time of 455 μs were applied.

In the first aspect, the present invention provides a wire core (also referred to as “core” for short) in itself,
(A) 0.1 to 3 wt. % (% By weight,% by weight), preferably 0.5 to 1.5 wt. Palladium in an amount in the range of%,
(B) 0.1 to 3 wt. %, Preferably 0.2 to 1.5 wt. % Amount of gold,
(C) 20 to 700 wt. ppm (ppm by weight, ppm by weight), preferably 275 to 325 wt. nickel in amounts in the ppm range;
(D) 20 to 200 wt. ppm, preferably 20 to 50 wt. an amount of calcium in the ppm range;
(E) 93.91 to 99.786 wt. %, Preferably 96.9625 to 99.2595 wt. % Amount of silver and
(F) 0 to 100 wt. consisting of additional components in ppm (components other than palladium, gold, nickel, calcium and silver),
Here, wt. % And wt. All amounts of ppm are based on the total weight of the wick,
It relates to a silver alloy wire comprising or consisting of a wire core, wherein the silver alloy wire has an average diameter in the range of 8 to 80 μm or even in the range of 12 to 55 μm.

  The silver alloy wire is preferably a bonding wire for bonding in microelectronics. The silver alloy wire is preferably a monolithic object. Numerous shapes are known and appear to be useful for the silver alloy wires of the present invention. Preferred shapes are circular, oval and rectangular shapes in the cross-sectional view.

  The average diameter of a wire or wire core, or simply the diameter, can be obtained by a “sizing method”. The physical weight of a defined length of silver alloy wire according to the method 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 average of five measurements of five sections of a particular wire.

  In the context of the present invention, the term “bonding wire” includes all shapes of cross sections and all normal wire diameters, but bonding wires having a circular cross section and a small diameter are preferred.

  In line with the foregoing, the wire core includes (a) palladium, (b) gold, (c) nickel, (d) calcium, and (e) silver in the previously disclosed proportions. However, the core of the silver alloy wire of the present invention has (f) 0 to 100 wt. Additional components in a total amount of ppm can be included. In this context, further components, often also referred to as “unavoidable impurities”, are small amounts of chemical elements and / or compounds present in the raw materials used or derived from impurities from the wire manufacturing process, ie (f The presence of additional components of type) may be derived from impurities present in one or more of, for example, silver, palladium, gold, nickel and calcium. Examples of such additional components are Cu, Fe, Si, Mn, Cr, Ce, Mg, La, Al, B, Zr, Ti, S, and the like. 0 to 100 wt. A low total amount of ppm ensures good reproducibility of wire properties. The additional component (f) present in the core is usually not added separately.

In one embodiment, the core of the silver alloy wire of the present invention comprises less than the amount of the following additional component (f):
(I) 30 wt. less than ppm Cu,
(Ii) 2 wt. Any one of Cr, Ce, Mg, La, Al, Be, In, Mn, Ti less than ppm,
(Iii) 15 wt. Any one of Si, Fe, and S less than ppm.

  In this context, the core of a silver alloy wire is defined as a uniform region of bulk material. Since any bulk material always has a surface region that can exhibit different properties to some extent, the properties of the core of the wire are understood as the properties of a uniform region of the bulk material. The surface of the bulk material region can vary in terms of morphology, composition (eg, sulfur, chlorine and / or oxygen content) and other characteristics. The surface may be the outer surface of a wire core, and in such embodiments, the silver alloy wire of the present invention comprises a wire core. In other selectable methods, the surface can be the interfacial region between the wire core and the covering layer superimposed on the wire core.

  The term “superposed” in the context of the present invention is used to describe the relative position of a first member, eg a wire core, with respect to a second member, eg a covering layer. “Overlapped” characterizes that additional members, such as an intermediate layer, may (but need not) be placed between the first member and the second member. Preferably, the second member is at least partially overlapped on the first member, eg, at least 30%, 50%, 70% or at least 90%, for example, each with respect to the total surface of the first member. Most preferably, the second member is fully superimposed on the first member.

  The term “intermediate layer” in the context of the present invention refers to the region of the silver alloy wire between its core and the overlying coating layer. In this area, there is a combination of both core and cover layer materials.

  In the context of the present invention, the term “thickness” is used to define the size of a layer in a direction perpendicular to the longitudinal axis of the core, where the layer is at least partially superimposed on the surface of the core. It is done.

  In one embodiment, the core has a surface with a coating layer superimposed on the surface of the core.

  In one embodiment, the weight of the coating layer is 5 wt. % Or less, preferably 2 wt. % Or less. If a coating layer is present, the coating layer is often 0.1 wt. % Or more or 0.5 wt. % Minimum mass. Applying a small amount of material as the covering layer maintains the properties defined by the wire core material. On the other hand, the coating layer imparts certain properties to the wire surface, such as inertness to the environment, resistance to corrosion, improved bondability, and the like. For example, the thickness of the covering layer is in the range of 20 to 120 nm for a 18 μm diameter wire. In the case of a wire having a diameter of 25 μm, the covering layer may have a thickness in the range of 30 to 150 nm, for example.

  In one embodiment, the covering layer may be made of a noble metal element. The covering layer may be a single layer of one of the elements. In another embodiment, the cover layer may be a multilayer composed of several overlapping adjacent sublayers, each sublayer being made of a different noble metal element. Common techniques for the deposition of such noble metal elements on the core include plating such as electroplating and electroless plating, deposition of materials from the gas phase such as sputtering, ion plating, vacuum and physical vapor deposition, and melts. Is the deposition of material from.

In one embodiment, the silver alloy wire of the present invention or the core thereof is
(1) The average wire particle 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 wire particle [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%.
(3) The wire twin boundary ratio is less than 60%, for example in the range of 30 to 50%, preferably in the range of 40% to 45%.
(4) FAB shows columnar particles (particles are stretched),
(5) FAB average particle size is 18 μm or less, for example, in the range of 6 to 14 μm, preferably in the range of 8 to 12 μm.
(6) The surface of the FAB particle [101] orientation is less than 45%, for example in the range of 30 to 40%, preferably in the range of 32 to 36%.
(7) FAB twin boundary ratio is less than 70%, for example in the range of 30 to 65%, preferably in the range of 60% to 65%.
By at least one of the intrinsic properties (see “Test Method A” as described below),
And / or (α) the corrosion resistance has a value of bonded ball lift in the range of 5% or less, for example in the range of 0 to 5% (see “Test Method B” as described below),
(Β) Moisture resistance has a bonded ball lift value of 5% or less, for example in the range of 0 to 5% (see “Test Method C” as described below),
(Γ) The hardness of the wire core is 85 HV or less, 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) The process window area for stitch bonding has a value of at least 12000 mA · g, eg 13000 to 14400 mA · g for a wire with a diameter of 18 μm (detailed disclosure and “Test Method E” as described below) reference),
(Ε) The resistivity of the wire is less than 2.5 μΩ · cm, for example in the range of 1.7 to 2.4 μΩ · cm, preferably in the range of 2.2 to 2.4 μΩ · cm (as described below See Test Method F),
(Ζ) The yield strength of the wire is 170 MPa or less, for example in the range of 140 to 170 MPa (see “Test Method G” as described below),
(Η) Silver dendritic growth of the wire is 4 μm / s or less, 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) ,
Characterized by at least one of the extrinsic characteristics.

  The terms “inherent property” and “exogenous property” are used herein with respect to a wire core or FAB. Intrinsic properties mean the properties that the wire core or FAB has (independently of other factors) themselves, while extrinsic properties are like the measurement method and / or measurement conditions used for the wire core or FAB. Depends on the relationship with other factors.

  In the preferred embodiment of the present invention, the hardness of the wire core (ie, the hardness before bonding) is less than 85 HV, preferably in the range of 65 to 75 HV. Furthermore, the hardness of the FAB treated with the wire of the present invention prior to bonding is less than 80 HV, preferably in the range of 60 to 70 HV. Such hardness, or more precisely, the softness of the wire core and FAB helps to prevent damage to delicate substrates during the bonding process. Experiments have also shown that such flexible wires according to the present invention exhibit very flexible FAB characteristics. Such FAB hardness limitations are particularly useful when mechanically delicate structures are lined under the bond pad. This is particularly true when the bond pad is made of a soft material such as aluminum or gold. The delicate structure may include, for example, one or several layers of porous silicon dioxide, specifically having a dielectric constant of less than 2.5. Such porous and therefore soft materials are becoming increasingly popular as they can help to increase device performance. Thus, the mechanical properties of the bonding wire of the present invention can be optimized to prevent such soft layer cracking or other damage.

  In certain embodiments, the silver alloy 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 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 4N pure silver wire.

  In another advantageous embodiment, the resistivity of the wire is less than 3.2 μΩ · cm, for example in the range of 2.0 to 2.4 μΩ · cm, preferably in the range of 2.2 to 2.4 μΩ · cm, That means adaptability to many applications.

In another aspect, the present invention also relates to a process for the production of a silver alloy wire in any of its embodiments disclosed above. The process,
(1) wt. % And wt. All amounts of ppm are based on the total weight of the precursor component,
(A) 0.1 to 3 wt. %, Preferably 0.5 to 1.5 wt. Palladium in an amount in the range of%,
(B) 0.1 to 3 wt. %, Preferably 0.2 to 1.5 wt. % Amount of gold,
(C) 20 to 700 wt. ppm, preferably 275 to 325 wt. nickel in amounts in the ppm range,
(D) 20 to 200 wt. ppm, preferably 20 to 50 wt. calcium in amounts in the ppm range,
(E) 93.91 to 99.786 wt. %, Preferably 96.9625 to 99.2595 wt. % In the amount of silver, and (f) 0 to 100 wt. providing a precursor component comprising additional components of ppm;
(2) stretching the precursor member to form a wire precursor until a desired final diameter of the wire core is obtained;
(3) Finally obtained after completion of process step (2) at a furnace set temperature ranging from 400 to 600 ° C. for an exposure time ranging from 0.4 to 0.8 seconds to form a silver alloy wire. Strand annealing the resulting wire precursor, wherein step (2) is a stretched precursor member at a furnace set temperature of 400 to 800 ° C. for an exposure time in the range of 50 to 150 minutes One or more sub-steps of intermediate batch annealing and / or an extended precursor member at a furnace set temperature of 400 to 800 ° C. for an exposure time in the range of 0.4 to 1.2 seconds One or more sub-steps of intermediate strand annealing.

  The term “strand annealing” is used herein. This is a continuous process that allows the initial production of wires with high reproducibility. Strand annealing is done dynamically while the stretched wire precursor member or wire precursor to be annealed is moved through the annealing furnace and wound on the reel after leaving the annealing furnace. Means that.

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

  The present disclosure distinguishes between precursor members, wire precursors and silver alloy wires. The term “precursor member” is used for the pre-stage of those wires that have not reached the desired final diameter of the wire core, while the term “wire precursor” is the pre-stage of the wire of the desired final diameter. Used for. After the completion of process step (3), i.e. after final strand annealing of the desired final diameter wire precursor, a silver alloy wire in the sense of the present invention is obtained.

  The precursor member as provided in process step (1) can be obtained by alloying / doping silver with the desired amount of palladium, gold, nickel and calcium. The silver alloy itself can be prepared by conventional processes known to those skilled in the art of metal alloys, for example, by melting together silver, palladium, gold, nickel and calcium in the desired ratio. In doing so, it is possible to utilize one or more conventional master alloys. The melting process may be performed, for example, using an induction furnace and it is appropriate to work under vacuum or in an inert gas atmosphere. The material used is, for example, 99.99 wt. % Or more purity grade. The melt so produced may be cooled to form a uniform portion of the silver based precursor member. Typically, such precursor members are in the form of rods having a diameter of, for example, 2 to 25 mm and a length of, for example, 5 to 100 m. Such rods can be made by casting the silver alloy melt in a suitable mold at room temperature, followed by cooling and solidification.

  If a coating layer in the form of a single layer or multiple layers is present on the core of a silver alloy wire as disclosed for some of the embodiments of the first aspect of the invention, this coating layer is preferably still drawn. Applies to wire precursor members that may not be stretched and ultimately stretched or even fully stretched to the desired final diameter. Those skilled in the art will be able to obtain a coating layer of the thickness disclosed for the wire embodiment, ie after stretching the precursor member having the coating layer to form a wire precursor, such on the precursor member. Know how to calculate the thickness of the coating layer. As already disclosed above, numerous techniques are known for forming a coating layer of a material according to embodiments on a silver 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 and physical vapor deposition, and deposition of materials from the melt.

  Process steps (once the desired diameter of the precursor member has been achieved to overlay the metallization as a single layer or multiple layers onto a wire core as disclosed for some of the embodiments of the first aspect of the invention) It is appropriate to interrupt 2). Such a diameter may be in the range of 80 to 200 μm, for example. The single layer or multi-layer metallization can then be applied, for example, by one or more electroplating process steps. Process step (2) is then continued until the desired final diameter of the wire core is obtained.

  In process step (2), the precursor member is stretched to form a wire precursor until the desired final diameter of the wire core is obtained. Techniques for stretching a precursor member to form a wire precursor are known and deemed useful in the context of the present invention. Preferred techniques are rolling, swaging, die drawing, etc., among which die drawing is particularly preferred. In the latter, the precursor member is stretched in several process steps until the desired and final diameter of the wire core is achieved.

  The desired and final diameter of the wire core may be in the range of 8 to 80 μm, or preferably in the range of 12 to 55 μm. Such wire die drawing processes are well known to those skilled in the art. Conventional tungsten carbide and diamond stretching dies may be employed and conventional stretching lubricants may be employed to aid stretching.

  Step (2) of the process of the present invention comprises one or more sub-stages of intermediate batch annealing of the extended precursor member at a furnace set temperature of 400 to 800 ° C. with an exposure time ranging from 50 to 150 minutes. One or more sub-steps of intermediate strand annealing of the step and / or extended precursor member at a furnace set temperature of 400 to 800 ° C. with an exposure time in the range of 0.4 to 1.2 seconds Including. One or more steps of intermediate annealing of the stretched precursor member may be performed during two or more of the plurality of stretching or stretching steps. To illustrate this by way of example, three intermediate annealing steps at three different stages during stretching, for example a diameter of 2 mm at a furnace set temperature ranging from 400 to 800 ° C. with an exposure time of 50 to 150 minutes. First intermediate batch annealing of the rod stretched to and wound on a drum, stretched to a diameter of 47 μm at a furnace set temperature ranging from 400 to 800 ° C. with an exposure time of 0.4 to 1.2 seconds A second intermediate strand anneal of the precursor member and a third of the precursor member further stretched to a diameter of 27 μm at a furnace set temperature in the range of 400 to 800 ° C. with an exposure time of 0.4 to 1.2 seconds. Intermediate strand annealing can be performed.

  In process step (3), the stretched wire precursor obtained after completion of process step (2) is finally strand annealed. The final strand anneal is for example an exposure time of 0.4 to 0.8 seconds at a furnace set temperature in the range of 400 to 600 ° C., or in a preferred embodiment, 0.5 to 0.7 at 400 to 500 ° C. Run for seconds.

  Final strand annealing typically involves drawing the drawn wire precursor into a conventional annealing furnace, typically in the form of a cylindrical tube of a given length, and for example 10 to 60 meters / This is done by pulling on a defined temperature profile for a given annealing rate that can be selected in the range of minutes. The annealing time / furnace temperature parameter may then be determined and set.

  In a preferred embodiment, the final strand annealed silver alloy wire is in one embodiment one or more additives, such as 0.01 to 0.07 vol% additive (s). Quench in water. Quenching in water immediately or rapidly, i.e. within 0.2 to 0.6 seconds, it was experienced in process step (3) in the final strand annealed silver alloy wire, for example by dipping or dripping. It means cooling from temperature to room temperature.

  With respect to embodiments of the present invention, it has been found that final strand annealing at temperatures below the maximum elongation temperature can provide beneficial wire properties since the wire morphology can be positively affected. With this adjustment, other characteristics such as wire hardness, ball bonding behavior, etc. can be influenced in a good direction.

In one embodiment, the final strand annealing may be performed at a temperature that is at least 150 ° C., eg, 210 to 240 ° C. lower than the temperature at which the maximum elongation value is achieved by annealing, which is 70% of the maximum elongation value. In the following, it can lead to an elongation value of the wire after annealing which is for example 30 to 60% of the maximum elongation value. For example, process step (3) may be performed at a temperature that is at least 150 ° C., preferably at least 180 ° C., or at least 200 ° C. lower than the temperature of maximum elongation T _{ΔL (max)} . Often, the temperature in process step (3) is 250 ° C. or more below T _{ΔL (max)} . The temperature of the maximum elongation T _{ΔL (max)} is determined by testing the breaking elongation of the test piece (wire) at different temperatures. Data points are summarized in a graph showing percent elongation as a function of temperature (° C.). The resulting graph is often referred to as an “annealing curve”. In the case of a silver-based wire, a temperature at which the elongation (%) reaches the maximum is observed. This is the temperature of the maximum elongation T _{ΔL (max)} . An example is shown in FIG. 1, which shows an exemplary annealing curve of an 18 μm silver alloy wire from Sample 1 (Table 1). The annealing temperature is a variable parameter on the X axis. The graph shows the measured values of wire breaking load (BL, grams) and elongation (EL,%). The elongation was determined by a tensile test. Elongation measurements showed a typical maximum of about 19% in the example shown, achieved at an annealing temperature of about 700 ° C. If the wire from Sample 1 was not annealed at this maximum elongation temperature, but was annealed at 480 ° C., which was 220 ° C. below the maximum elongation temperature, the result was about 40% below the maximum elongation value. The elongation value is 8%.

The intermediate annealing of process step (2) as well as the final strand annealing of process step (3) can be carried out in an inert or reducing atmosphere. Numerous types 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 to 98% by volume nitrogen, and thus 2 to 10% by volume hydrogen, with a total volume% of 100% by volume. Preferred mixtures of nitrogen / hydrogen are equal to 93/7, 95/5 and 97/3% by volume / volume%, each based on the total volume of the mixture. Applying a reducing atmosphere in annealing is particularly preferred when some portion of the surface of the silver alloy wire is sensitive to oxidation by oxygen in the air. Purging with the type of inert or reducing gas, preferably 125Min ^-1, more 90min ^-1 preferably from 15, most preferably gas exchange rate ranging from 20 to 50min ^-1 (= gas flow rate from 10 [L / min]: Internal furnace volume [L].

  The composition of the precursor component material (same as the material of the finished silver alloy wire core) and the unique combination of annealing parameters widely used during process steps (2) and (3) are the specific features disclosed above. And / or considered to be essential for obtaining a wire of the present invention exhibiting at least one of the extrinsic properties. The temperature / time conditions of the intermediate and final strand annealing steps make it possible to achieve or adjust the intrinsic and extrinsic properties of the silver alloy wire core.

  After the completion of the process step (3), the silver alloy wire of the present invention is completed. In order to fully benefit from its properties, it is also suitable to use it immediately for wire bonding applications, ie without delay, for example within 10 days after completion of process step (3). Alternatively, to maintain the wide wire bonding process window characteristics of the silver alloy wire and to prevent it from oxidative or other chemical attacks, the finished wire is typically immediately after completion of process step (3). That is, without delay, for example, wound in less than 1 to 5 hours after completion of process step (3) and vacuum sealed and then stored for further use as a bonding wire. Storage in vacuum sealed conditions should not exceed 6 months. After opening of the vacuum seal, the silver alloy wire should be used for wire bonding within 10 days.

  All process steps (1) to (3) and wrapping and vacuum sealing are preferably performed under clean room conditions (US FED STD 209E clean room standard, 1k standard).

A third aspect of the present invention is a silver alloy wire obtainable by the previously disclosed process according to the second aspect of the present invention or an embodiment thereof. The silver alloy wire has been found to be 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 certain force (typically measured in grams) is applied, supported by the application of ultrasonic energy (typically measured in mA). The product of the difference between the upper and lower limits of the applied force and the difference between the upper and lower limits of ultrasonic energy applied in the wire bonding process establishes 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 is a force that allows the formation of wire bonds that meet standards, ie pass conventional tests such as conventional tensile tests, ball shear tests and ball tensile tests to name a few. / Determine the region of the ultrasonic energy combination.

In other words, the resulting bond must meet certain ball shear test standards such as 0.0085 grams / μm ² ball shear, no non-stick on bond pad, etc. The first bond (ball bond) process window region is the product of the difference between the upper and lower limits of the force used in bonding and the difference between the upper and lower limits of applied ultrasonic energy, while Second bond (stitch bond) process window area where the bond must meet certain tensile test standards such as 2.5 grams tensile force, no non-stick on lead, etc. Is the difference between the upper and lower limits of the force used in bonding. And the product of the difference between the upper and lower limits of the applied ultrasonic energy.

  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 process robustness. The wire of the present invention exhibits a fairly wide 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.

Preparation of FAB:
Worked according to the procedure described in KNS Process User Guide for Free Air Ball (Kulike & Soffa Industries Inc, Fort Washington, PA, USA, May 31, 2009). The FAB was prepared by performing a conventional electric torch (EFO) ignition with standard ignition (single step, 18 mA EFO current, EFO time 455 μs).

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

A. Electron backscatter diffraction (EBSD) pattern analysis of wire and FAB:
The main steps employed to measure wire and FAB tissue were sample preparation, acquisition of a good Kikuchi pattern and component calculation.

  Wires with or without FAB were first embedded with epoxy resin and polished by standard metallographic techniques. Ion milling was applied in the final sample preparation step to remove any mechanical deformation of the wire surface, contaminants and oxide layers. The ion milled sample cross section was sputtered with gold. Ion milling and gold sputtering were then performed twice more. No chemical or ion etching was performed.

  The sample was loaded into a FESEM (Field Emission Scanning Electron Microscope) equipped with a holder at an angle of 70 ° to the surface of a normal FESEM sample holding table. The FESEM was further equipped with an EBSD detector. An electron backscatter pattern (EBSP) containing wire crystallographic information was acquired.

  These patterns were further analyzed (using software called the QUANTAX EBSD program developed by Bruker) for particle orientation, average particle size, and the like. Points of similar orientation were grouped together to form a tissue component.

  A maximum tolerance angle of 15 ° was used to distinguish different tissue components. The wire drawing direction was set as the reference orientation. [100], [101] and [111] texture proportions were calculated by measuring the proportion of crystals having [100], [101] and [111] oriented faces parallel to the reference orientation.

  In order to determine the position of the grain boundaries, the average grain size was analyzed by determining the crystallographic orientation between adjacent lattice points larger than the minimum, 10 ° herein. The EBSD software calculated the area of each particle and converted it to the corresponding circle diameter, defined as the “average grain size”. All particles along the length of the wire within about 100 μm in length were counted to determine the average and standard deviation of the average crystal grain size.

  Twin boundaries (also referred to as Σ3 CSL twin boundaries) were excluded from the average particle size calculation. Twin boundaries were delineated by a 60 ° rotation around the plane of <111> orientation between adjacent crystallographic domains. The number of points depended on the step size and was less than 1/5 of the average grain size.

B. Bonded ball salt solution immersion test:
The wire was Al-0.5 wt. Ball bonded to a% Cu bond pad. The test device with the wire so bonded was immersed in a salt solution for 10 minutes at 25 ° C. and washed with deionized (DI) water and later with acetone. The salt solution is 20 wt. Contains ppm NaCl. The number of lifted balls was examined at 100X magnification under a low magnification microscope (Nikonmm-40). An observation of a larger number of lifted balls indicated severe interfacial galvanic corrosion.

C. Moisture resistance test for bonded balls:
The wire was Al-0.5 wt. Ball bonded to a% Cu bond pad. A test device with such bonded wires is stored in a highly accelerated stress test (HAST) chamber at a temperature of 130 ° C. and a relative humidity (RH) of 85% for 8 hours, and the number of balls subsequently lifted is reduced. Inspection was performed at 100X magnification under a microscope (Nikonmm-40). An observation of a larger number of lifted balls indicated severe interfacial galvanic corrosion.

D. Vickers microhardness:
Hardness was measured using a Mitutoyo HM-200 tester equipped with a Vickers indenter. A force of 10 mN indentation load was applied to the wire specimen for a residence time of 12 seconds. The test was performed at the center of the wire core and FAB.

E. Stitch bonding process window area:
Measurement of the bonding process window area was performed according to standard procedures. Test wires were bonded using a KNS-iConn bonding tool (Kullike & Soffa Industries Inc., Fort Washington, PA, USA). The process window value was based on a wire having an average diameter of 18 μm, where the lead finger to which the wire was bonded was made of silver.

The four corners of the process window are the two major failure modes,
(1) Overcoming too low force and ultrasonic energy supply leading to lead finger non-stickiness (NSOL) of the wire, and (2) too high force and ultrasonic energy supply leading to short wire tail (SHTL). Led by.

F. Electrical resistivity:
The ends of the specimen, i.e., a 1.0 meter long wire, were connected to a power supply providing a constant current / voltage. Resistance was recorded on the device for supply voltage. The measuring device was a HIOKI model 3280-10 and the test was repeated with at least 10 specimens. The arithmetic mean of the measurements was used for the calculations shown below.

  The resistance R was calculated according to R = V / I.

  The specific resistivity ρ was calculated according to ρ = (R × A) / L, where A is the average cross-sectional area of the wire and L is the length of the wire between the two measurement points of the device for measuring voltage. Is).

  The specific conductivity σ was calculated according to σ = 1 / ρ.

G. Elongation rate (EL):
The tensile properties of the wire were tested using an Instron-5564 instrument. The wire was tested for 254 mm gauge length (L) at a rate of 2.54 cm / min. The breaking (breaking) load and elongation were obtained according to ASTM standard F219-96. Elongation is the difference in the gauge length (ΔL) of the wire between the beginning and end of the tensile test, reported as a percentage (usually (100 · ΔL / L)) calculated from the recorded load versus tensile elongation plot. Met. Tensile strength and yield strength were calculated from break and yield load divided by wire area. The actual diameter of the wire was measured by using the sizing method, a standard length of wire weigh and its density.

H. Wire electromigration testing:
The two wires were kept parallel to a distance of 1 millimeter or less on the PTFE plate under the objective lens of the low magnification microscope Nikon MM40 model at 50 × magnification. Water droplets were formed by a micropipette between two electrically connected wires. One wire was connected to the anode and the other to the cathode, and 5 V was applied to the wire. Two wires were connected in series with a 10Ω resistor and biased with 5V DC in a closed circuit. The circuit was closed by wetting the two wires with a few drops of deionized water as the electrolyte. Silver electromigrationd from the cathode to the anode in the electrolyte to form silver dendrites and sometimes two wires formed a bridge. The rate of silver dendrite growth is strongly dependent on alloy addition. The diameter of the tested wire was 75 μm.

Example 1
In each case, quantities of silver (Ag), palladium (Pd) and gold (Au) of at least 99.99% purity (“4N”) were melted in the crucible. A small amount of silver-nickel and silver-calcium master alloy was added to the melt and agitated to ensure uniform distribution of the added ingredients. The following silver-nickel and silver-platinum master alloys were used.

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

  A wire core precursor member in the form of an 8 mm rod was then continuously cast from the melt. The wire core precursor member was then stretched in several stretching steps to form a wire core precursor having a specific diameter of 18 ± 0.5 μm. The cross section of the wire core was substantially circular.

  The rod, drawn to a diameter of 2 mm and wound on a drum, was subjected to an intermediate batch annealing at an oven set temperature of 500 ° C. for an exposure time of 60 minutes. Second intermediate strand annealing of the precursor member stretched to a diameter of 47 μm with an exposure time of 0.8 seconds at a furnace set temperature of 600 ° C. and 27 μm with an exposure time of 0.6 seconds at a furnace set temperature of 600 ° C. A third intermediate strand anneal of the precursor member stretched to the diameter of was performed. After performing a final strand annealing of 18 μm wire core precursor with an exposure time of 0.6 seconds at a furnace set temperature of 480 ° C., the wire thus obtained contains 0.05% by volume of surfactant. Quenched in water. Intermediate batch annealing was performed using an argon purging gas, while strand annealing was performed using a 95 vol% nitrogen: 5 vol% nitrogen purging gas mixture.

  By this procedure, several different samples of silver alloy wires according to the invention 1 to 5 and 4N purity comparative silver wires (reference) were produced.

  Table 1 shows the composition of the different wires according to the invention, samples 1 to 5. The palladium content is 1 to 3 wt. % Range. The gold content is 1 to 1.5 wt. % Range. Nickel addition is 30 to 300 wt. Different up to ppm. The calcium content was 30 and 50 wt. Maintained at ppm.

  The particle size of wire samples 1-5 was measured and the average particle size was reported. Results were in the range of 2 to 5 μm in all cases. For sample 1, the average particle size was 2.91 μm.

  Table 2 below shows the results of evaluating the corrosion resistance and moisture resistance of the bonded wires, the behavior of the second bond process window and the performance of FAB formation. Wire samples 1 to 5 as defined above and 4N pure silver comparative wires were Al-0.5 wt. Bonded to a% Cu bond pad and tested according to the test method disclosed above. All tests were performed on 18 μm wire except for electromigration tests performed on 75 μm wire.

  All of the wire samples produced process windows well suited for industrial applications. Significant improvements in corrosion resistance and moisture resistance of the bonded balls were observed. Specifically, wire sample 1 showed a value close to zero, ie a 2-ball lift, which is a specific improvement compared to 4N pure silver wire (reference).

  Furthermore, the silver dendritic growth of wire samples 1 to 5 was much lower than that of 4N pure silver wire.

Table 3 shows the average particle diameter and the tissue component of the wire sample 1 (wire, FAB and heat affected zone (HAZ)).

Claims (16)

A silver alloy wire comprising or consisting of a wire core, the wire core itself,
(A) 0.1 to 3 wt. Palladium in an amount in the range of%,
(B) 0.1 to 3 wt. % Amount of gold,
(C) 20 to 700 wt. nickel in amounts in the ppm range;
(D) 20 to 200 wt. an amount of calcium in the ppm range;
(E) 93.91 to 99.786 wt. % Amount of silver and
(F) 0 to 100 wt. consisting of additional components in ppm,
Here, wt. % And wt. All amounts of ppm are based on the total weight of the core,
A silver alloy wire, wherein the silver alloy wire has an average diameter in the range of 8 to 80 μm.   2. A silver alloy wire according to claim 1 having an average diameter in the range of 12 to 55 [mu] m.   The amount of palladium is 0.5 to 1.5 wt. The silver alloy wire according to claim 1 or 2, wherein the silver alloy wire is in the range of%.   The amount of gold is 0.2 to 1.5 wt. The silver alloy wire according to any one of claims 1 to 3, which is in a range of%.   The amount of nickel is 275 to 325 wt. The silver alloy wire according to any one of claims 1 to 4, which is in a ppm range.   The amount of calcium is 20 to 50 wt. The silver alloy wire according to any one of claims 1 to 5, which is in a range of ppm.   The amount of silver is 96.9625 to 99.2595 wt. The silver alloy wire according to any one of claims 1 to 6, which is in a range of%.   The silver alloy wire according to any one of claims 1 to 7, which has a circle, an ellipse, or a rectangular shape in a cross-sectional view.   The wire core has a surface, and the surface is an outer surface or an interface region between the wire core and a coating layer superimposed on the wire core. Silver alloy wire as described.   The silver alloy wire has a coating layer superimposed on the wire core, and the coating layer is a single layer made of a noble metal element or a multilayer composed of a plurality of adjacent sublayers that are overlapped The silver alloy wire according to claim 9, wherein each sublayer is made of a different noble metal element. The wire core is
(1) The average wire particle size is less than 10 μm.
(2) The wire particle [100] or [101] or [111] orientation plane is less than 7%.
(3) The wire twin boundary ratio is less than 60%.
(4) FAB shows columnar particles,
(5) The FAB average particle size is 18 μm or less.
(6) The plane of FAB particle [101] orientation is less than 45%.
(7) FAB twin boundary ratio is less than 70%,
By at least one of the intrinsic properties,
And / or (α) the corrosion resistance has a value of bonded ball lift of 5% or less,
(Β) Moisture resistance has a bonded ball lift value of 5% or less,
(Γ) The wire core has a hardness of 85 HV or less.
(Δ) the process window region of stitch bonding has a value of at least 12000 mA · g;
(Ε) The resistivity of the wire is less than 2.5 μΩ · cm,
(Ζ) The yield strength of the wire is 170 MPa or less,
(Η) The silver dendritic growth of the wire is 4 μm / s or less,
A silver alloy wire according to any one of the preceding claims, characterized by at least one of the extrinsic properties. A process for producing a silver alloy wire according to any one of claims 1 to 11, wherein the process comprises:
(1) providing a precursor member comprising the composition of the wire core according to any one of claims 1 to 7;
(2) stretching the precursor member to form a wire precursor until a desired final diameter of the wire core is obtained;
(3) obtained after completion of process step (2) at a furnace 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 silver alloy wire. And finally strand annealing the wire precursor,
Step (2) includes one or more sub-steps of intermediate batch annealing of the stretched precursor member at a furnace set temperature of 400 to 800 ° C. for an exposure time ranging from 50 to 150 minutes; One or more sub-steps of intermediate strand annealing of the stretched precursor member at a furnace set temperature of 400 to 800 ° C. for an exposure time in the range of 0.4 to 1.2 seconds Including processes.   The process of claim 12, wherein the final strand 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.   14. A process according to claim 12 or 13 wherein the finally strand annealed silver alloy wire is quenched in water which may contain one or more additives.   Process according to any one of claims 12 to 14, wherein the intermediate annealing of process step (2) and the final strand annealing of process step (3) are carried out in an inert or reducing atmosphere.   A silver alloy wire obtainable by the process according to any one of claims 12 to 15.