TWI778583B - Silver alloy wire - Google Patents

Abstract

An alloy wire is provided. The alloy wire includes a ternary components of Ag-Pt-Ge, wherein the alloy contains 0.1~3wt% of Pt, 1ppm~2wt% of Ge. The alloy may also contains 1ppm~0.1wt% of at least one of the elements of Ca, Cu, In, Mg, Si, Ti and Sc. The alloy wire may also contains surface coating, which includes Au, Pd or Pt, wherein the thickness of the surface coating ranges from 0.01 to 10μm. The shape of the alloy wire may be round or flat ribbon.

Description

Silver alloy wire

The present invention relates to an alloy wire, and in particular to an alloy wire used for wire bonding of electronic packages.

Wire bonding is the primary interconnection method for integrated circuit (IC) and light emitting diode (LED) packaging processes. In addition to providing signal and power transmission between the chip and the substrate, the wire bonding wire can also serve as a heat dissipation function. Therefore, the wire bonding wire must have high electrical conductivity, high thermal conductivity, sufficient strength and ductility. However, in order to avoid chip cracking caused by the hot pressing process of wire bonding, and at the same time to ensure good bonding between the wire and the pad, the hardness of the wire should not be too high. Since the encapsulated polymer sealant often contains corrosive chloride ions, and the polymer sealant itself has environmental moisture absorption, the wire must have good oxidation resistance and corrosion resistance.

In the wire bonding process, the end of the wire is first sintered by high-voltage discharge (Electric Flame Off, EFO), and the surface tension is used to form a ball (Free Air Ball, FAB), and then the ball is pressed down through the porcelain nozzle. The bonding pads form a first bonding point, and the other end of the wire is pulled to another conductive bonding pad, and is bonded to the other conductive bonding pad to form a second bonding point, thereby forming a conduction of a circuit. The shape of the knot ball determines the quality of the subsequent first ball bond. In addition, intermetallic compounds may be formed at the bonding interface between the first ball pad and the semiconductor wafer pad. These intermetallic compounds can ensure interfacial bonding, but excessive intermetallic compounds can cause interfacial embrittlement and Kirkendall voids. In addition, the oxidation resistance and corrosion resistance of the wire itself are the elements that determine the reliability of electronic products.

When the semiconductor or light-emitting diode package is completed and the product is in use, the high current density of the wire may also drive the internal atoms to produce Electron Migration, which makes one end of the wire form a hole, thereby reducing electrical conductivity and thermal conductivity. Causes disconnection and product failure; passing current may also cause partial melting of the packaging wire, causing the voltage to rise rapidly, and finally lead to disconnection and product failure. This problem is particularly serious for the packaging of high-voltage and high-current electronic products, which affects these electronic products. A major factor in product reliability.

At present, the common package conductors include the following options:

(1) Gold wire: The gold wire may have low resistivity, but a large amount of brittle intermetallic compounds (including Au2Al, AuAl4, Au5Al2, etc.) will be formed at the wire bonding interface between the gold wire and the aluminum pad, which will reduce the conductivity. In addition, the intermetallic reaction at the gold/aluminum interface will accompany the formation of many Kirkendall voids, which further increases the resistivity of the bonding interface, resulting in a decrease in the reliability of the contact.

(2) Copper wire: In recent years, the packaging industry has begun to use copper wire as a wire for wire bonding of semiconductors and light-emitting diodes. Although copper wire has better electrical conductivity, it is easy to be oxidized, so the wire storage and transportation process need to be sealed and protected, and the wire bonding process requires expensive nitrogen and hydrogen assistance, and the reliability test of subsequent packaging electronic products is still Oxidation and corrosion problems are encountered. In addition, the material of the copper wire is too hard, and the wire bonding is likely to cause problems such as chip cracking. Although some studies have proposed methods of plating other metal coatings on the surface of copper wires to improve the problems of easy oxidation and corrosion (for example, refer to US Pat. The wire bonding step is prone to failure, so the reliability required for the packaging of high-voltage and high-current electronic products cannot be achieved.

(3) Silver wire: Silver is the element with the lowest resistivity among all materials, but pure silver will have the problem of sulfide corrosion in a sulfur-containing environment, and at the same time pure silver wire will also generate brittle intermetallic compounds ( Ag ₂ Al or Ag ₄ Al). In addition, the pure silver wire is prone to electrolytic ion migration phenomenon (Ion Migration) inside the encapsulation material containing moisture. That is, pure silver will hydrolyze and dissolve silver ions through the action of electric current in a water-containing gas environment, and then react with oxygen to become unstable silver oxide (AgO). Leaf vein-like silver whiskers grow and eventually short-circuit the positive and negative electrodes (see: H. Tsutomu, Metal Migration on Electric Circuit Boards, Three Bond Technical News, Dec. 1, 1986.). In addition, in some studies, a method of plating other metal coatings on the surface of the silver wire to improve the problems of sulfide corrosion and silver ion migration has been proposed (for example, refer to US Pat. No. 6,696,756), but the formed wire still cannot achieve the desired reliability and resistivity.

(4) Alloy wire: The alloy wire includes, for example, a gold-based alloy and a silver-based alloy. For example, these alloys further include elements such as copper, platinum, manganese, chromium, calcium, indium, etc. However, these alloy wires still cannot have the properties of low impedance and high reliability at the same time.

To sum up, the existing various pure metal wires, metal-plated composite wires, and alloy wires with added elements cannot meet all the packaging requirements. Therefore, there is still a need for a wire with high reliability.

Some embodiments of the present disclosure provide an alloy wire comprising three elements of Ag-Pt-Ge, including 0.1 to 3 wt % of Pt, 1 ppm to 2 wt % of Ge, and the balance of Ag.

In some embodiments, the alloy wire further includes an additive element selected from at least one of Ca, Cu, In, Mg, Si, Ti or Sc, the total amount of the additive element is 1 ppm to 0.1 wt %, and the additive element is The respective addition amounts of the elements are smaller than the contents of Pt or Ge.

In some embodiments, the alloy wire is a round wire.

In some embodiments, the diameter of the alloy wire is 10 μm to 300 μm.

In some embodiments, the alloy wire is a flat ribbon wire.

In some embodiments, the thickness of the alloy wire is 20 μm to 300 μm.

In some embodiments, the width of the alloy wire is 100 μm to 2000 μm.

In some embodiments, the alloy wire further includes a surface coating, the surface coating contains Au, Pd, Pt, alloys thereof, or a combination thereof, and the thickness of the surface coating is 0.01 to 10 μm.

The following disclosure provides numerous embodiments, or examples, for implementing various elements of the provided subject matter. Specific examples of elements and their configurations are described below to simplify the description of embodiments of the invention. Of course, these are only examples, and are not intended to limit the embodiments of the present invention. For example, if the description mentions that the first element is formed on the second element, it may include embodiments in which the first and second elements are in direct contact, and may also include additional elements formed between the first and second elements , so that they are not in direct contact with the examples. Furthermore, embodiments of the present invention may repeat reference numerals or letters in various examples. This repetition is for the purpose of brevity and clarity and is not intended to represent a relationship between the different embodiments or configurations discussed.

Furthermore, spatially relative terms such as "below", "below", "lower", "above", "higher" and the like may be used for ease of description The relationship between one component or feature(s) and another component(s) or feature(s) in a drawing. Spatially relative terms are used to include different orientations of the device in use or operation, as well as the orientation depicted in the drawings. When the device is turned in a different orientation (rotated 90 degrees or otherwise), the spatially relative adjectives used therein will also be interpreted according to the turned orientation.

When the terms "about," "approximately," and the like are used herein to describe numbers or ranges of numbers, the term is intended to encompass numerical values that are within a reasonable range including the number described, such as within +/- 10 of the number being described. %, or other numerical values understood by those of ordinary skill in the technical field to which the present invention belongs. For example, the term "about 5 nm" covers a size range from 4.5 nm to 5.5 nm.

The terms used herein are used to illustrate particular embodiments only, and are not intended to limit the inventive concept. The use of the expression in the singular also encompasses the expression in the plural unless the expression has a clearly different meaning in the context. In this specification, it should be understood that terms such as "comprising", "having", and "comprising" are intended to indicate the presence of features, numbers, steps, acts, components, parts, or combinations thereof disclosed in this specification, while It is not intended to exclude the possibility that one or more other features, numbers, steps, acts, components, parts, or combinations thereof may be present or added.

The present disclosure provides an alloy wire including three elements of ternary Ag-Pt-Ge, which improves the sulfidation resistance, high temperature creep resistance and balling during the wire bonding process, and improves the wire bonding yield.

US 8101123B2 patent discloses a silver alloy wire composed of Ag-Au-Pd, although adding Au and Pd in the Ag alloy composition can improve the mechanical properties and oxidation resistance of pure silver wire, and adding Pd can further reduce the ion migration problem of silver, However, abnormal phenomena such as eccentric balls or nib balls often occur in the EFO balling process of alloy wires with this composition, resulting in a decrease in the yield of the wire. In addition, the wire has poor high temperature creep resistance, and its gloss and sulfidation resistance are also poor. The US20130171470 patent discloses a silver alloy wire composed of Ag-Au-Pd and its grain structure exhibits a large number of annealing twins. Although the twin structure can improve the electromigration life of the wire, it is not good in spheroidization, high temperature latent resistance, and gloss. and sulfidation resistance are also insufficient. Patents such as JP1997275120, US20080240975A1, CN10215454A, US20130126934, TWI 408787 and US10840208B2 add Pt and other trace elements into the Ag alloy. However, these conventional silver alloy wires also have poor nodularity in the wire bonding process and are resistant to high temperature latent degeneration. Insufficient, and its gloss and vulcanization resistance are also poor.

The addition of Ge to the silver alloy wire in this case can effectively improve the sulfidation resistance of the wire, and at the same time can improve the bonding strength of the solder joint, but when the content of germanium is too high, the ductility of the wire will be reduced. In addition, an appropriate amount of platinum (Pt) can enhance the oxidation resistance, sulfidation and chloride ion corrosion resistance of the wire, and also has a significant inhibitory effect on the ion migration of silver, and also reduces the formation of intermetallic compounds between the silver alloy wire and the aluminum pad. However, when the content of platinum is too high, the resistivity of the wire will be significantly increased. The example also proves that the ternary Ag-Pt-Ge silver alloy wire only needs to add a small amount of Ge, and the high temperature latent resistance of the ternary Ag-Pt-Ge silver alloy wire is greatly improved compared with the binary Ag-Pt silver alloy wire. In addition, in the EFO process, the ternary Ag-Pt -The FAB of the Ge silver alloy wire is very perfect, which is better than that of any silver alloy wire currently known, so the shape and quality of the first ball solder joint formed by the wire bonding are also excellent. In addition, the examples prove that the interfacial intermetallic growth of the ternary Ag-Pt-Ge silver alloy wire bonding and subsequent reliability tests is slower than that of the traditional gold wire, and the interfacial intermetallic is less likely to occur than the copper wire or the palladium-coated copper wire. Insufficient metal, unable to pass the metal residue test, the ball shear strength and wire pull strength after joining are also excellent, and a trace amount of quaternary element is added. Elements can further enhance the aforementioned beneficial effects.

According to some embodiments, FIG. 1 is a circular alloy wire 10 according to a first aspect of the disclosure. Fig. 1 is a part of the wire segment of the round alloy wire 10. The material of the round alloy wire 10 is Ag-Pt-Ge ternary alloy formed by adding Pt and Ge to the silver base material at the same time, wherein the silver base material is substantially Sterling silver on and the round alloy wire 10 includes about 0.1 to about 3 wt % Pt, such as about 1 to about 2 wt % or about 0.5 to about 1.5 wt %, about 1 ppm to 2 wt % Ge, such as about 100 ppm to about 1 wt % % or about 500 ppm to about 1.5 wt%, and the balance Ag. The diameter of the round alloy wire 10 is about 10 μm to about 300 μm, eg, about 100 μm to 200 μm or about 50 μm to 250 μm. In other embodiments, the round alloy wire 10 may also include other elements, but it should be avoided that the added elements and silver form intermetallic phase precipitates, which may cause problems such as material embrittlement, increased corrosion, or reduced electrical conductivity. Therefore, it is preferable that the added elements can completely dissolve the silver atoms into each other without the formation of precipitates, so as to ensure the ductility of the wire. For example, in some embodiments, the round alloy wire 10 may include an additive element selected from at least one of Ca, Cu, In, Mg, Si, Ti, or Sc, and the total additive amount of the aforementioned additive element is about 1 ppm to about 0.1 wt %, for example, about 10 ppm to about 0.05 wt % or about 5 ppm to about 0.01 wt %, the respective added amounts of the above-mentioned additional elements are less than Pt or Ge. In some embodiments, the round alloy wire 10 does not contain additional elements, that is, the round alloy wire 10 only has Pt and Ge added to the silver base material. It should be noted that, in some embodiments, the above-mentioned round alloy wire can also be uniformly coated with a surface plating layer on the outer layer, as shown in FIGS. 2A to 2B, and FIG. 2B is the longitudinal direction of FIG. 2A. Cutaway. The surface coating 22 may comprise substantially pure gold, substantially pure palladium, substantially pure platinum, alloys thereof, or combinations thereof. The surface coating 22 can be formed by a suitable coating method (eg, electroplating, sputtering and vacuum evaporation). Due to the chemical inertness of the material of the surface plating layer 22, the round alloy wire 20 in it can be protected from being corroded, and at the same time, a lubricating effect can be exerted during wire drawing. The thickness of the surface plating layer 22 is about 0.01 to about 10 μm, for example About 0.1 μm to about 5 μm or about 1 μm to about 8 μm.

According to some embodiments, FIG. 3 is a flat ribbon-shaped alloy wire 30 according to the second aspect of the disclosure. FIG. 3 shows a portion of the flat strip-shaped alloy wire 30 . The material of the flat strip-shaped alloy wire 30 and its added elements can be referred to the round alloy wire 10 shown in FIG. 1 , which will not be repeated here. According to some embodiments, the thickness of the ribbon-shaped alloy wire 30 is about 20 μm to about 300 μm, eg, about 50 μm to about 125 μm or about 100 μm to about 250 μm. According to some embodiments, the ribbon-shaped alloy wire 30 has a width of about 100 μm to about 2000 μm, such as about 500 μm to about 1400 μm or about 1000 μm to about 1800 μm. It is worth noting that, in some embodiments, the flat ribbon-shaped alloy wire can also be uniformly coated with a surface coating on the outer layer, as shown in FIGS. 4A to 4B , wherein FIG. 4B is a longitudinal direction of FIG. 4A Longitudinal section view. The surface coating 42 may comprise substantially pure gold, substantially pure palladium, substantially pure platinum, alloys thereof, or combinations thereof. The surface coating layer 42 can be formed by a suitable coating method (eg, electroplating, sputtering and vacuum evaporation), and the thickness of the surface coating layer 42 is about 0.01 to about 10 μm, such as about 0.1 μm to about 5 μm or about 1 μm to about 8.5 μm.

Regarding the substantially pure metal described in the specification, taking pure silver as an example, it refers to pure silver that is expected to be completely free of impurities such as other elements, compounds, etc. Removing the above impurities to achieve mathematically or theoretically 100% pure silver is regarded as "substantially pure silver". Therefore, in other embodiments, the alloy wire and/or its coating may further include other metals and non-metal elements , or other impurity components, and when the range of the above impurity content falls within the acceptable range specified by the corresponding standard or specification. Those with ordinary knowledge in the technical field to which the present invention pertains should understand that the above-mentioned corresponding standards or specifications will be different according to different properties, conditions, requirements, etc., so no specific standards or specifications are listed in the text.

In addition, the addition of other metal elements should be adjusted according to the needs of the application to avoid affecting the properties of the alloy wire. For example, when copper is added to the above alloy wire, although the material strengthening effect will be produced, the copper element will greatly reduce the oxidation resistance and sulfidation corrosion resistance of the alloy wire. In addition, copper will also increase the hardness and brittleness of the alloy, making the wire drawing process difficult, and at the same time, it is easy to cause chip breakdown during the wire bonding process.

In addition, although the addition of rare earth elements can refine the grains of the alloy, for the wire application requirements of package wire bonding, the fine grains have more grain boundaries, which will hinder the electron transmission and increase the resistivity of the alloy. It is suitable for the packaging requirements of high-speed operation and high-frequency integrated circuit electronic products. In addition, the chemical activity of rare earth will increase its oxidation and corrosion damage, making the packaging wire easier to fuse when the current is passed, which is not conducive to the reliability of electronic products. Furthermore, adding calcium to the alloy will make the ductility of the material worse; adding indium or tin with a low melting point to the alloy will form a low-temperature phase, which will make the temperature resistance of the wire worse, and continuous current flow will easily cause the wire to melt; adding beryllium (Be) is a toxic flammable solid, and dry dust or smoke is toxic; when ruthenium (Ru), rhodium (Rh), osmium (Os), and iridium (Ir) are added, its melting point (respectively 2310° C, 1965°C, 3045°C, and 2410°C) are all well above the boiling point of silver (2212°C), making it extremely difficult to smelt and greatly increases resistivity. In addition, some of the added elements will form intermetallic phase precipitation with silver on the phase equilibrium diagram, which will cause embrittlement and higher corrosion of the material, and will also reduce the electrical conductivity of the wire.

The choice of Ag, Pt, and Ge is because these three elements can be completely dissolved in each other on the phase equilibrium diagram (Solid Solution), and will not produce any brittle intermetallic phase precipitates, so the formed alloy wire can have better performance. ductility, and the addition of Pt and Ge will not have much influence on the resistivity of Ag.

In some embodiments, the method for forming the alloy wire is to form a thick alloy wire first, and then alternately perform a plurality of cold working forming steps and a plurality of annealing steps to reduce the wire diameter of the thick wire successively. The method of forming the thick wire is to heat and melt Ag, Pt, and Ge, and then cast them to obtain an ingot. Then, the ingot is cold-worked to form the above-mentioned thick wire rod formed of at least Ag, Pt and Ge. In another embodiment, after heating and melting Ag, Pt and Ge, the thick wire rod is formed by continuous casting. In some embodiments, the cold forming step described above includes drawing, extrusion, or a combination thereof. Alternatively, the cold forming and annealing steps described above may be any known or future developed cold working/annealing means.

The features of several embodiments are summarized above, so that those with ordinary knowledge in the technical field to which the present invention pertains can more easily understand the viewpoints of the embodiments of the present invention. It should be understood by those skilled in the art to which the present invention pertains that other processes and structures can be easily designed or modified based on the embodiments of the present invention to achieve the same objectives and/or advantages of the embodiments described herein. Those with ordinary knowledge in the technical field to which the present invention pertains should also understand that such equivalent processes and structures do not depart from the spirit and scope of the present invention, and can be made in various ways without departing from the spirit and scope of the present invention. Various changes, substitutions and substitutions.

10: Round alloy wire

20: Round alloy wire

22: Surface coating

30: Flat ribbon-shaped alloy wire

40: Flat ribbon alloy wire

42: Surface coating

Various aspects of the present disclosure will be described in detail below with reference to the accompanying drawings. It should be noted that, in accordance with standard practice in the industry, the various features are not drawn to scale and are illustrative only. In fact, the dimensions of elements may be arbitrarily enlarged or reduced to clearly represent the features of the present disclosure. FIG. 1 depicts a portion of a segment of a circular alloy wire, according to some embodiments. FIG. 2A depicts a portion of a segment of a round alloy wire coated with a surface coating, according to some embodiments. FIG. 2B is a longitudinal section view along the length of the round alloy wire parallel to the surface coating shown in FIG. 2A, according to some embodiments. FIG. 3 depicts a portion of a wire segment of a ribbon-shaped alloy wire, according to some embodiments. FIG. 4A depicts a portion of a wire segment of a ribbon-shaped alloy wire coated with a surface coating, according to some embodiments. FIG. 4B is a longitudinal section view along the length of the ribbon-shaped alloy wire parallel to the surface coating shown in FIG. 4A , according to some embodiments.

20: Round alloy wire

22: Surface coating

Claims (8)

An alloy wire includes three elements of Ag-Pt-Ge, including 0.1 to 3wt% of Pt, 500ppm to 2wt% of Ge and the balance of Ag, wherein the core material of the alloy wire does not include Pd. The alloy wire rod as described in item 1 of the claimed scope further comprises an additive element selected from at least one of Ca, Cu, In, Mg, Si, Ti and Sc, and the total additive amount of the additive element is 1 ppm to 0.1 wt%, and the respective addition amount of the additive element is less than the content of Pt or Ge. The alloy wire as described in claim 1, wherein the alloy wire is a round wire. The alloy wire according to claim 3, wherein the diameter of the alloy wire is 10 μm to 300 μm. The alloy wire as described in claim 1, wherein the alloy wire is a flat ribbon-shaped wire. The alloy wire as described in claim 5, wherein the alloy wire has a thickness of 20 μm to 300 μm. The alloy wire as described in claim 5, wherein the alloy wire has a width of 100 μm to 2000 μm. The alloy wire as described in any one of items 1 to 7 of the scope of the application, further comprising a surface coating, the surface coating contains Au, Pd, Pt, alloys or combinations thereof, and the thickness of the surface coating is 0.01 to 10μm.

Images