TWI394849B - Ag-based alloy wire and method for manufacturing the same - Google Patents

Description

Silver-based alloy wire and manufacturing method thereof

The present invention relates to silver-based alloy wires, and more particularly to a highly reliable alloy wire for wire bonding of electronic packages.

In general, semiconductors and light-emitting diode (LED) electronic products require good reliability in order to ensure the service life, and automotive electronic products are particularly demanding in terms of reliability. Taking the application of electric vehicles as an example, the inverter of the electric vehicle motor control unit is the most important component for converting the electric energy of the battery into the kinetic energy of the vehicle, and its most important insulated gate bipolar transistor (IGBT). The power module is subjected to voltages and currents much higher than those of general power components and consumer electronics. In addition, high-voltage, high-current power components are also required for high-speed rail, trains, MRT, machine tools, plant equipment, ships, power plants, etc. For these high-voltage, high-current electronic products, the package wire bonding requires a more reliable wire bond material.

In addition to providing signal and power transmission between the wafer and the substrate, the package wire bonding wire can also have a heat dissipation function. Therefore, the wire bonding wire must have excellent electrical conductivity and thermal conductivity, and requires sufficient strength and ductility. However, in order to avoid the wafer from being ruptured by the hot pressing process of the wire bonding, and the wire is in good contact with the pad to ensure good bonding, the hardness of the wire should not be too high. In addition, since the encapsulated polymer seal often contains corrosive chloride ions, and the polymer seal itself has environmental hygroscopicity, the wire must have good oxidation resistance and corrosion resistance.

In addition, the first contact (the solder ball point) of the wire bonding is cooled from the molten state to the room temperature, and high heat is transmitted through the wire, so that the wire near the solder ball point generates a heat affected zone (Heat Affected Zone). That is to say, the wire in this area will grow due to heat accumulation, resulting in local coarse grains, and these local coarse grains have low strength, which causes the wire to be affected by the heat during the Wire Pull Test. The zone breaks and affects the joint strength.

When the semiconductor or LED package is completed, the high current density of the wire may also cause electro-migration of the internal atoms during the use of the product, causing holes at one end of the wire to reduce conductivity and thermal conductivity, even The wire breakage and product failure; the current may also cause the package wire to be partially melted, causing the voltage to rise rapidly, and finally causing wire breakage and product failure. This problem is particularly serious for the packaging of high voltage and high current electronic products, which affects these electrons. The main factor of product reliability.

Commonly used package wires, for example, include the following options:

(1) Gold wire: Gold wire can have low resistivity, but a large amount of brittle intermetallic compound (including Au ₂ Al, AuAl ₄ , Au ₅ Al _{2 ,} etc.) is formed at the bonding interface between the gold wire and the aluminum pad to make conductivity. reduce. In addition, the gold/aluminum interfacial metal intermetallic reaction is accompanied by the generation of many Kirkendall voids, which further increase the joint interface resistivity and lead to a decrease in the reliability of the joint.

(2) Copper wire: In recent years, the packaging industry has begun to use copper wire as a wire for semiconductor and light-emitting diode wire bonding. Although the copper wire has better conductivity, it is easily oxidized. Therefore, the wire storage and transportation process requires sealing protection. The wire bonding process requires expensive nitrogen and hydrogen assist, and the reliability test of the subsequent packaged electronic products is still Will encounter oxidation and corrosive problems. In addition, the copper wire material is too hard, and the wire bonding is likely to cause problems such as cracking of the wafer. Although in some studies a method of plating other metal plating on the surface of the copper wire to improve the problem of oxidative and corrosion problems has been proposed (for example, see US Pat. No. 7,645,522 B2, US 2003/0173659 A1, US Pat. No. 7820913 B2), due to the high hardness of the copper wire itself, The wire bonding step is prone to failure, so the reliability required for high voltage and high current electronic product packaging cannot be achieved.

(3) Silver wire: Silver is the lowest resistivity element among all materials, but pure silver has the problem of sulphide corrosion in a sulfur-containing environment, and a pure silver wire also forms a brittle intermetallic compound when it is wire bonded on an aluminum pad ( Ag ₂ Al or Ag ₄ Al). In addition, the pure silver wire is prone to Ion Migration inside the water-containing encapsulating material. That is, pure silver will hydrolyze and dissolve silver ions in an aqueous gas environment, and then react with oxygen to become unstable silver oxide (AgO), which will deoxidize to form silver atoms and to the positive electrode. The silver whiskers that grow the leaf veins eventually cause a short circuit between the positive and negative electrodes (refer to: 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 plating on the surface of the silver wire to improve the problem 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, an alloy mainly composed of gold and an alloy mainly composed of silver. These alloys include, for example, elements such as copper, platinum, manganese, chromium, calcium, and indium. However, these alloy wires are still not capable of both low impedance and high reliability.

In summary, the existing various pure metal wires, metal-plated composite wires, and alloy wires with added elements cannot meet the requirements of high-voltage and high-current electronic product packaging. Therefore, there is a need for a highly reliable wire. .

In an embodiment of the present invention, a silver-based alloy wire is provided, which is an alloy wire formed of at least silver, palladium, rhodium, and platinum, wherein a weight ratio of silver:palladium in the alloy wire is 90-99.99: 0.01-10. And the content of bismuth is below 1500 ppm, the content of platinum is below 350 ppm, and the alloy wire comprises a central portion and a peripheral portion, and the central portion has elongated grains or equiaxed grains, and the peripheral portion has an equiaxed portion The crystal grains, and the number of crystal grains having an annealing twins structure in the alloy wire, account for more than 20% of the total number of crystal grains of the alloy wire.

In another embodiment of the present invention, there is provided a method of manufacturing a silver-based alloy wire, comprising: providing a thick wire, the alloy wire formed of at least silver, palladium, rhodium, and platinum, wherein the alloy wire is silver: The weight ratio of palladium is 90~99.99: 0.01~10, and the content of bismuth is below 1500ppm, the content of platinum is below 350ppm; and the multiple cold forming step and the multiple annealing step are alternately performed to successively reduce the line of the thick wire Forming a thin wire, wherein the cold forming step and the annealing step comprise at least the following steps: performing a penultimate cold forming step; thereafter, performing a penultimate annealing step, the penultimate annealing step The annealing temperature is 0.5Tm~0.7Tm, and the annealing time is 1~5 seconds, wherein Tm is the melting point of the absolute temperature standard of the material of the thick wire; then, the last cold forming step is performed, so that the last cold forming step is The amount of deformation between the formed wire and the wire formed by the penultimate cold forming step is 1% or more and not more than 15%; and thereafter A final annealing step, the annealing step is a final annealing temperature is higher than the annealing temperature of the annealing step of the penultimate channel 20 ℃ ~ 100 ℃, annealing for 2 to 30 seconds.

The above and other objects, features and advantages of the present invention will become more <RTIgt;

Several different embodiments are set forth below in accordance with various features of the invention. The specific elements and arrangements of the present invention are intended to be simplified, but the invention is not limited to these embodiments. For example, a description of forming a first element on a second element can include an embodiment in which the first element is in direct contact with the second element, and also includes having additional elements formed between the first element and the second element such that An embodiment in which one element is not in direct contact with the second element. In addition, the present invention is represented by the repeated reference numerals and/or letters in the different examples for the sake of brevity, but does not represent a particular relationship between the various embodiments and/or structures.

The invention provides a silver-based alloy wire and a forming method thereof, which are improved by the wire structure of the wire, and the reliability of the wire can be greatly improved, in addition to the control of the alloy composition.

In an embodiment of the invention, the silver-based alloy wire is an alloy wire formed by adding at least palladium, rhodium and platinum to the main component silver, the alloy wire comprising a central portion and a peripheral portion, and the central portion has a long strip shape a grain or equiaxed grain, the peripheral portion having equiaxed grains, and the number of grains having an annealing twins structure in the alloy wire accounts for more than 20% of the total number of grains of the alloy wire .

At present, most of the conventional alloy wires still contain a certain amount of gold elements, which form a metal intermetallic compound with the aluminum pad during the bonding of the package wires, causing the joint interface to be brittle, accompanied by the generation of many Kirkend holes (Kirkendall holes). ), resulting in reduced reliability of the packaged product contacts. Therefore, in a preferred embodiment of the present invention, the alloy wire is mainly composed of silver (Ag), and the addition of gold (Au) element is completely avoided, so that the formation of the brittle gold-aluminum intermetallic compound can be avoided and the reliability of the alloy wire can be improved. degree. In addition, a large number of annealed twin structures can increase the strength of the material, thereby improving reliability.

Fig. 1 is a flow chart showing a method of forming a silver-based alloy wire in an embodiment of the present invention. Referring to Fig. 1, in step 102, a thick wire is provided, the thick wire being an alloy wire formed of at least silver, palladium, rhodium, and platinum. In step 104, a plurality of cold working forming steps and a plurality of annealing steps are alternately performed to successively reduce the wire diameter of the thick wire to form a thin wire. The detailed method of the above steps is described below.

Referring to step 102, a thick wire is provided, the thick wire being an alloy wire formed of at least silver, palladium, rhodium, and platinum. The choice of silver, palladium, rhodium and platinum is because these four elements can completely dissolve each other on the phase equilibrium diagram, and do not produce any brittle intermetallic phase precipitates, so the formed alloy wire can have The preferred ductility and the addition of palladium, rhodium and platinum do not have a large effect on the electrical resistivity.

It has been found through experiments that an appropriate amount of palladium can effectively improve the oxidation resistance and sulfidation resistance of silver wire, and at the same time, due to its extremely low diffusion rate and barrier properties of surface products, the ion migration of silver can be avoided. In addition, it also has an inhibitory effect on the interfacial metal transition of silver and aluminum pads. However, when the content of palladium is too high, the electrical resistance of the alloy wire is increased. In addition, an appropriate amount of germanium (Ge) can effectively improve the oxidation resistance and vulcanization properties of the wire, and at the same time, the joint strength of the solder joint can be improved, but when the content of germanium is too high, the ductility of the wire is lowered. In addition, an appropriate amount of platinum (Pt) can enhance the oxidation resistance, sulfidability and chloride ion corrosion of the wire, and also has a significant inhibitory effect on the ion migration phenomenon of silver, and also reduces the formation of a metal intermetallic compound between the silver alloy wire and the aluminum pad. However, when the content of platinum is too high, the electrical resistivity of the wire is remarkably improved.

In one embodiment, silver is the main component of the thick wire, and palladium, rhodium, and platinum are added, wherein the content of palladium is about 0.01 to 10 wt%; the content of antimony is below 1500 ppm, preferably between 10 ppm and 1500 ppm; It is below 350 ppm, preferably between 5 ppm and 350 ppm; and the content of silver, palladium, rhodium, and platinum is 100% by weight (for example, the content of silver is about 90 to 99.99% by weight). In another embodiment, the alloy wire further comprises boron and the boron content is below 20 ppm, preferably between 1 ppm and 20 ppm. In this embodiment, the content of silver, palladium, rhodium, platinum, and boron is 100% by weight. Appropriate amount of boron can cause grain boundary segregation in silver alloy. Generally, the segregation of impurity elements at the grain boundary of the material will cause the material to break along the crystal. However, the grain boundary segregation of boron will not cause the grain boundary embrittlement, but instead It plays a beneficial role in strengthening the grain boundary and can significantly improve the ductility and fatigue resistance of the wire. However, when the content of boron is too high, embrittlement inside the crystal grains is still caused. In other embodiments, the above-mentioned thick wire may include other elements, but the precipitation of the element to form a metal phase with silver may be avoided, resulting in problems such as embrittlement of the material, improvement of corrosivity, or decrease in conductivity. Therefore, it is preferred that the added elements be completely miscible with silver atoms without the formation of precipitates to ensure the ductility of the wires.

It should be noted that in other examples, the alloy wire may further include other metals, non-metal elements, or other impurity components, and the invention is not limited to a silver-palladium-ruthenium-platinum quaternary alloy or silver-palladium-ruthenium. - a five-element alloy of platinum-boron. Therefore, as long as the weight ratio of silver:palladium in the thick wire is controlled to be 90~99.99:0.01~10, and silver is the main component of the thick wire, and the content of palladium, iridium, platinum, boron or other components is not more than the content of silver. Within the scope of the invention. In addition, since it is difficult to completely remove all impurities in the process of actual smelting, refining, cold forming, etc., and accurately achieve a mathematical or theoretical specific concentration, when the above impurity content falls within the corresponding standard or specification Within the scope of the acceptance, it is still considered to be within the scope of the present invention. Those having ordinary skill in the art to which the present invention pertains should understand that the above-mentioned corresponding standards or specifications may vary depending on different properties, conditions, requirements, etc., and thus specific standards or specifications are not listed below.

In one embodiment, the method of forming the thick wire is to heat-melt silver, palladium, rhodium, and platinum, and then cast into an ingot. Thereafter, the ingot is cold worked to form the above-mentioned thick wire formed of at least silver, palladium, rhodium, and platinum. In another embodiment, after the silver, palladium, rhodium, and platinum are heated and melted, the above-mentioned thick wire is formed by continuous casting. In one embodiment, the thick wire has a wire diameter of about 5 to 10 mm.

Referring to step 104, a plurality of cold forming steps and a plurality of annealing steps are alternately performed to successively reduce the wire diameter of the thick wire. Figure 2 shows the more detailed steps of the plurality of cold forming steps and annealing steps described in step 104. In FIG. 2, the plurality of cold forming steps and annealing steps described in step 104 include at least the following steps: in step 104-1, performing a first cold forming step, the wire formed by the first cold forming step The amount of deformation between them is 10% or more and not more than 90%. . In step 104-2, a first annealing step is performed. The annealing temperature of the first annealing step is 0.5Tm~0.7Tm, and the annealing time is 1~10 seconds, wherein Tm is the absolute temperature scale of the material of the thick wire. The melting point. The cold forming step and the annealing step of steps 104-1 and 104-2 may be repeated alternately as needed. Then, in step 104-3, the penultimate cold forming step is performed. In step 104-4, performing a penultimate annealing step, the annealing temperature of the penultimate annealing step is 0.5Tm~0.7Tm, and the annealing time is 1~5 seconds, wherein Tm is the material of the thick wire. The melting point of the absolute temperature scale. In step 104-5, a final cold forming step is performed such that the amount of deformation between the wire formed by the last cold forming step and the wire formed by the penultimate cold forming step is 1% or more and does not exceed 15%. The amount of deformation described above refers to the reduction in the cross-sectional area of the material to be cold worked due to the cold working forming step. In step 104-6, a final annealing step is performed. The annealing temperature of the last annealing step is 20 ° C to 100 ° C higher than the annealing temperature of the penultimate annealing step, and the annealing time is 2 to 30 seconds. It should be noted that in an embodiment, step 104 may also perform only two cold forming steps (steps 104-3, 104-5) and two annealing steps (steps 104-4, 104-6).

In one embodiment, the cold forming step includes wire drawing, extrusion, or a combination of the foregoing. Alternatively, the cold forming step and the annealing step described above may be any known or future developed cold working/annealing mode.

The thin wire formed after the cold forming and annealing step is an alloy wire formed of at least silver, palladium, rhodium, and platinum, wherein the alloy wire includes a central portion and a peripheral portion, and the central portion has a strip a shaped grain or an equiaxed grain having an equiaxed grain, and the number of grains having an annealing twins structure in the thin wire accounts for 20% of the total number of grains of the thin wire the above. In one embodiment, the wire diameter of the thin wire is 10 to 50 μm. The above thin wire can have better reliability than conventional metal wires.

The reason for the formation of the above annealed twin structure can be inferred according to the principle of physical metallurgy (refer to George E. Dieter, Mechanical Metallurgy, McGRAW-HILL Book Company, 1976, P. 135-141. and RW Cahn, Physical Metallurgy, 1970, P .1184-1185). The formation of the annealed twin structure is due to the accumulation of strain strain inside the material during the cold working process, which will drive the atomic uniform shear (Shear) of the partial region to the inside of the grain where it is not sheared during the subsequent annealing heat treatment. The moving atoms form a mirror-symmetric lattice position, which is an Annealing Twin, and the mutually symmetrical interface is the Twin Boundary. The annealed twins mainly occur in the crystal lattice material with the closest lattice arrangement (Face Centered Cubic; FCC), and the twin boundary is a low energy Σ3 special grain boundary, and the crystal orientation is {111} plane. Compared to the high angle grain Boundary formed by general annealing recrystallization, the interfacial energy of the twin boundary is only about 5% of the high angle grain boundary. In addition, in general, the smaller the stacking fault energy, the more easily the material is annealed, and the stacking energy of the main components of the alloy wire, silver and palladium, is about 50 erg/cm ² or less. Annealed twins are formed. That is, not all metals can easily form a twin structure. For example, although aluminum is a face-centered cubic crystal structural material, its stacking energy is about 200 erg/cm ² , so annealing twins rarely occur.

In addition, the cold forming step described in FIG. 2 is also one of the factors for annealing the twin structure. Sufficient cold work deformation cumulative strain energy can provide atomic driving force to produce annealed twins, but if the cold work deformation is too large, most grain nucleation will occur during the initial recrystallization stage of the annealing heat treatment (Nuclei of Recrystallized Grains), thus forming a large number of fine grains, reducing the chance of annealing twins. It should be noted that the method of forming the alloy wire described in FIG. 2 is only a preferred embodiment of the present invention, but the method of forming the alloy wire of the present invention is not limited thereto.

3A and 3B are views showing a silver-based alloy wire 300 formed in an embodiment of the present invention. FIG. 3A shows a schematic view of a line segment of a portion of the silver-based alloy wire 300. Fig. 3B shows a longitudinal sectional view along the longitudinal direction parallel to the alloy wire 300 shown in Fig. 3A.

Referring to Fig. 3A, the silver-based alloy wire 300 is an alloy wire formed by adding at least palladium, rhodium, or platinum as a main component silver. Referring to FIG. 3B, the longitudinal section of the alloy wire 300 is a polycrystalline structure of a face-centered cubic phase, and the entirety is an equiaxed grain 302. In addition, each of the crystal grains is bounded by a high-angle grain boundary 304, wherein the number of crystal grains having an annealing twins structure 306 is 20 of the total number of crystal grains of the silver-based alloy wire 300. %the above. In a preferred embodiment, the number of grains of the annealed twin structure accounts for 30% to 60% of the total number of grains of the alloy wire, wherein the size of the equiaxed grains 302 is, for example, between 0.1 μm and 6 μm. The aspect ratio is between 1 and 2. In Fig. 3C, although the alloy wire is still substantially equiaxed grain 302, its central portion further includes elongated grains 308. Among them, the long-diameter ratio of the elongated grains is greater than 2. The center portion refers to a portion within a range of a wire radius value of 30% in the radial direction of the wire from the axial center of the wire.

In one embodiment, the weight ratio of silver:palladium in the alloy wire 300 is 90-99.99:0.01-10, and the strontium content is below 1500 ppm, preferably between 10 ppm and 1500 ppm. The platinum content is below 350 ppm, preferably between 5 ppm and 350 ppm. Among them, silver is the main component of the alloy wire 300, and the content of palladium, rhodium, platinum or other components is not more than the content of silver. In another embodiment, the alloy wire further comprises boron and the boron content is below 20 ppm, preferably between 1 ppm and 20 ppm. The advantages of the above alloys include, for example: 1. No gold is added, so that the metal-aluminum interfacial metal embrittlement can be avoided; 2. Palladium is added to improve the corrosion resistance and ion migration damage of the silver alloy wire, and the silver alloy wire and the aluminum pad are inhibited. Interface intermetallic reaction; 3. Adding antimony to enhance the oxidation resistance and vulcanization of silver alloy wire, and improve the joint strength of the solder joint; 4. Adding platinum to enhance the oxidation resistance, vulcanization and chloride ion corrosion of the wire, while suppressing Silver ion migration phenomenon and silver/aluminum interfacial metal transition; 5. Boron is added to strengthen the grain boundary of the alloy to improve the ductility and fatigue resistance of the wire.

However, it should be noted that the above-mentioned silver-based alloy wire has silver as a main component and contains palladium, rhodium, platinum, and boron in a specific ratio, but the scope of the present invention is not limited thereto. In other examples, the silver-based alloy wire may further include other metals, non-metallic elements, or other unavoidable impurity components. It should be noted that the addition of other metal elements needs to 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, a material strengthening effect is generated, but the copper element causes a significant decrease in the oxidation resistance and sulfidation corrosion resistance of the alloy wire, and since the silver-copper alloy generates discontinuous precipitates at the grain boundary. , causing a disconnection. In addition, copper also increases the hardness of the alloy to become brittle, making the drawing process difficult, and at the same time, it is easy to cause wafer breakdown during the wire bonding process.

In addition, although the addition of rare earth elements can make the grain refinement of the alloy, but for the application of the wire bonding of the wire bonding, the fine grains have more grain boundaries, and these grain boundaries hinder the electron transport, so that the resistivity of the alloy is improved, so Suitable for high-speed operation and packaging requirements of high-frequency integrated circuit electronic products. In addition, the chemical activity of rare earths will increase their oxidation and corrosion damage, making the package wire easier to fuse when passing current, which is not conducive to the reliability of electronic products. Furthermore, the addition of calcium to the alloy deteriorates the ductility of the material; the addition of a low melting point of indium or tin to the alloy forms a low temperature phase, which deteriorates the temperature resistance of the wire, and the continuous current is likely to cause the wire to be melted; (Be) is a toxic flammable solid, dry dust or smoke is toxic; when adding ruthenium (Ru), rhodium (Rh), osmium (Os), iridium (Ir), its melting point (2310 ° C , 1965 ° C, 3045 ° C and 2410 ° C) are much higher than the boiling point of silver (2212 ° C), so its melting is extremely difficult, and will greatly increase the resistivity. In addition, some of the added elements form a precipitate of the intermetallic phase with silver on the phase equilibrium diagram, which causes embrittlement and high corrosivity of the material, and further reduces the conductivity of the wire.

The alloy wire of the various embodiments of the present invention may have the following advantages, for example, compared to conventional wire materials, including:

(1) Low resistance:

Although silver has a low electrical resistivity, the crystal grains of the silver wire in the conventional process are fine crystal grains (average particle diameter of about 0.5 to 2 μm), so that a large number of high-angle grain boundaries are formed, resulting in an increase in electrical resistivity. In addition, when the silver wire is wire bonded on the aluminum pad, a brittle intermetallic compound (Ag ₂ Al or Ag ₄ Al) is formed, which causes a decrease in conductivity.

The alloy wire of the present invention includes a large number of Annealing Twins, and the Twin Boundary of the annealed twin structure is a Coherent crystal structure, belonging to a low energy Σ3 special grain boundary, and its interface energy It is only 5% of the general high angle grain boundary. Therefore, the symmetric lattice arrangement of these annealed twins has minimal resistance to electron transport and exhibits lower resistivity.

(2) Good mechanical strength:

The alloy wire in each embodiment of the present invention includes at least 20% of the crystal grains containing an Annealing Twin structure, thereby maintaining the preferred mechanical strength of the wire. It is further explained that since the twin structure has a different crystal orientation with respect to the crystal grains in which it is located, the movement of the dislocation can be blocked, and a material strengthening effect is produced. Thereby, the tensile strength close to that of the general fine grain structure wire can be maintained, but since the difference row and the atom can cross the crucible, the ductility is higher than that of the general fine grain.

(3) With resistance to oxidation and corrosion:

In general, silver often has the problem of sulphide corrosion in a sulfur-containing environment, so other precious metals are plated on the silver to avoid vulcanization. However, the noble metal will be completely dissolved into the molten silver solder ball substrate during the wire bonding process, so that the wire bonding component of the wire bonding is only a silver alloy containing a trace amount of protective precious metal, so the ball bonding point of the wire bonding is still Vulcanization corrosion occurs, so it is still impossible to effectively avoid the short circuit of the ball joint caused by the migration of silver electrolysis ions, and the Kirkenda hole effect when the aluminum pad is wire-bonded.

However, in the alloy wire of each embodiment of the present invention, at least 20% of the crystal grains contain an Annealing Twin structure, which can avoid oxidation, sulfurization and chloride ions due to the lower interfacial energy of the twin boundary. Corrosion path, it can show better oxidation resistance and corrosion resistance.

(4) Grain growth during packaging is not easy:

After the fine grain structure of the conventional wire material is joined by wire bonding, the heat of solidification of the solder ball point accumulates in the vicinity of the wire, which causes the grain to rapidly grow to form a heat-affected zone, thereby reducing the tensile test strength. However, at least 20% of the grain of the alloy wire of each embodiment of the present invention contains Annealing Twin structure, and the Annealing Twin structure has a lower interfacial energy, and the structure is higher than the general high angle grain boundary. stable. Therefore, not only in the high temperature state, the twin boundary itself is not easy to move, but also the high-angle grain boundary around the crystal grain is locked, so that the high-angle grain boundaries cannot move, and the overall grain structure does not There is obvious grain growth. Therefore, even if the first contact (bump point) is cooled from the molten state to the room temperature during the wire bonding process, the original grain size can be maintained. In addition, when the packaged product undergoes various high-temperature reliability tests, it is less likely to cause unstable growth of the crystal grains.

(5) Low electron mobility:

In the traditional process, the pure silver wire is prone to Ion migration inside the water-containing encapsulating material, and finally causes a short circuit between the positive and negative electrodes. In addition, when the pure silver wire is bonded to the aluminum pad, since the diffusion coefficient of silver in the aluminum atom base is about 10 ² to 10 ³ times faster than the aluminum atom in the silver base, the huge difference in the diffusion speed of the interface causes the so-called The Kirkenda hole causes an increase in resistivity and failure of the wire bond ball.

On the other hand, in the alloy wire of the present invention, since the diffusion rate of atoms through the low-energy twin boundary or across the twin boundary is extremely low, when applied to an electronic product, the internal atoms of the wire are not easily moved even at a high density current.

In view of the above advantages, the alloy wire of the present invention can be used for a high-voltage, high-current electronic product requiring high reliability, particularly a wire for packaging wire bonding of a power component. Of course, depending on the needs of the user, the alloy wire of the present invention can also be applied to other technical fields and applications, such as: audio lines, signal or power transmission lines, transformer lines, etc., and the wire diameter of the alloy wire can also be changed according to requirements. It is not limited to the scope of the above exemplification.

In addition, it has been found experimentally that at least 20% of the grains in the alloy wire contain an annealed twin structure to achieve the above advantages. Therefore, although in the process of conventional metal wire for wire bonding, there may be occasions when an annealed twin structure occurs, but the number of crystal grains containing an annealed twin structure is usually less than 10% of all the crystal grains of the wire or even It does not contain an annealed twin structure at all, so it still cannot have the above advantages.

The invention has been studied by the inventors for a long time and meticulously, and the alloying elements with specific composition and the control of the cold working deformation amount and the annealing temperature time can form a material structure containing a large amount of annealed twin crystals, and obtain a low resistivity, Packaged wire with high thermal conductivity, high strength, high ductility and excellent oxidation resistance. In more detail, the alloy composition provides the best coordination of electrical conductivity and mechanical properties, and the twin boundary has characteristics such as effectively suppressing electromigration, improving material strength and ductility, and therefore, in the case of wire bonding, not only Very low resistivity and excellent performance in reliability testing. For example, in the most severe Pressure Cooker Test (PCT), it can withstand temperatures of more than 128 hours at temperatures (Ta) = 121 ° C, relative humidity (RH) = 100%, and 2 atm. It is required for 96 hours of general electronic product reliability testing. In another embodiment, in the High Accelerated Stress Test (HAST), it can be achieved under the conditions of temperature (Ta)=148° C., relative humidity (RH)=90%, and 3.6 volts. More than 128 hours, it is also much higher than the 96 hours required by the general electronic product reliability test specification. Therefore, the alloy wire in the embodiments of the present invention can be applied to various high-speed power exchange integrated circuits, for example, a voltage drop type DC voltage exchange integrated circuit with an input voltage range of 4.5V to 17V and an operating frequency of 1200KHZ (Buck) DC/DC Converter), not limited to the voltage drop type DC voltage switching integrated circuit applied below the generally slower speed of 500KHZ.

[Comparative Example 1] Alloy wire with a small amount of twinned structure

The high-cycle electrothermal vacuum melting alloy is used, and the alloy composition thereof is Ag-8wt%Au-3wt%Pd-0.005wt.%La. The above alloy was obtained in a continuous casting manner to obtain a thick wire having a wire diameter of 6 mm. The cold working and the annealing heat treatment were performed 8 times in the cold working forming step to form a thin wire having a wire diameter of 25.4 μm. Then, the second last cold working forming step was carried out by drawing to form a thin wire having a wire diameter of 22.6 μm, and then annealing at 600 ° C for 5 seconds. Finally, the final cold forming step is performed to form a thin wire of 17.5 μm, and a final annealing step is performed, which has an annealing temperature of 700 ° C and an annealing time of 10 seconds. After the final annealing step is completed, the coil wire completes the alloy wire product required for wire bonding.

Fig. 4 is a cross-sectional view showing the alloy wire of Comparative Example 1, the center portion having elongated crystal grains and a few very coarse equiaxed grains, and the periphery having fine equiaxed grains having a grain size of about 1 μm. The annealed twin structure accounts for only about 10% of the total number of grains.

The above-mentioned alloy wire having a small amount of annealed twin structure was tested by passing a current of 0.2 A for 1200 hours, and the results are shown in Fig. 5. Referring to Fig. 5, after the current is passed through the alloy wire of Comparative Example 1, the elongated crystal grains at the center portion disappear, and the overall grain size is greatly increased by about 8 μm, and the wire is melted.

[Example 1] Alloy wire with a large number of twin structures

The composition of the alloy containing silver as the main component by high-frequency electrothermal melting can be referred to Table 1. Table 1 shows the contents of palladium, rhodium, platinum, and boron in the alloy, while the other components in the alloy are silver. That is, the content of silver and the total content of palladium, rhodium, platinum, and boron in Table 1 reached 100% by weight. The above alloy was obtained in a continuous casting manner to obtain a thick wire having a wire diameter of 6 mm. The cold working forming step was performed by wire drawing extension and annealing heat treatment to form a thin wire having a wire diameter of 22.6 μm. Then, the second last cold working forming step was carried out by drawing to form a thin wire having a wire diameter of 20 μm, and then annealing at 530 ° C for 2 seconds. Finally, the final cold forming step was taken to form a thin wire of 17.5 μm, and a final annealing step was performed, which was performed at an annealing temperature of 600 ° C and an annealing time of 15 seconds. After the final annealing step is completed, the coil wire completes the alloy wire product required for wire bonding.

Figure 6 is a cross-sectional view showing an Ag-3.2 wt.% Pd-50 ppm Ge-50 ppm Pt alloy wire of composition 10 in various compositions of the silver-based alloy wire of the list 1 of Example 1, the center portion having elongated crystal grains, and the periphery The equiaxed grain size is about 4 μm, which is larger than the peripheral equiaxed grains of the alloy wire of Comparative Example 1. As shown in Fig. 6, the alloy wire of Example 1 having an excess of 30% of the total grain number has an annealed twin structure.

The above alloy wire was tested by passing a current of 0.2 A for 1200 hours, and the results are shown in Fig. 7. Referring to Fig. 7, after the current is passed through the alloy wire of the composition 10 in the first embodiment, the elongated crystal grains at the center portion disappear, the outer equiaxed grains grow only slightly, and the wire does not melt (the comparative example) Figure 5 of 1).

Reliability test:

In addition, the alloy wire of the composition 10 in the first embodiment is used for wire bonding to form a high-speed power exchanger product, and a series of reliability tests are performed on the high-speed power exchanger product, and the results are shown in Table 2, among which the most severe. The Pressure Cooker Test (PCT) can withstand more than 128 hours, which is much higher than the 96 hours required for the reliability test of general electronic products. Another equally severe High Accelerated Stress Test (HAST) test. Actually it can reach more than 128 hours, which is also much higher than the 96 hours required by the general electronic product reliability test specification.

Table 3 shows the test results of the properties and reliability of the alloy wire formed by the ratio of different metal components in each of the examples.

While the invention has been described above in terms of several preferred embodiments, it is not intended to limit the scope of the present invention, and any one of ordinary skill in the art can make any changes without departing from the spirit and scope of the invention. And the scope of the present invention is defined by the scope of the appended claims.

300. . . Alloy wire

302. . . Equiaxed grain

304. . . High angle grain boundary

306. . . Annealed twin structure

308. . . Long grain

Fig. 1 is a flow chart showing a method of forming a silver-based alloy wire according to an embodiment of the present invention.

Figure 2 shows the more detailed steps of the plurality of cold forming steps and annealing steps described in step 104.

3A-3C show a silver-based alloy wire formed in an embodiment of the present invention. Fig. 3A shows the appearance of the alloy wire, and Fig. 3B shows that the entire wire is an equiaxed grain, and Fig. 3C shows that the center of the wire has elongated grains and the outer periphery has equiaxed grains.

Fig. 4-5 shows an alloy wire of a comparative example of the present invention. Figure 4 shows the original alloy wire, and Figure 5 shows the alloy wire after the current test.

6-7 show an alloy wire according to an embodiment of the present invention. Figure 6 shows the original alloy wire, and Figure 7 shows the alloy wire after the current test.

300. . . Alloy wire

302. . . Equiaxed grain

304. . . High angle grain boundary

306. . . Annealed twin structure

308. . . Long grain

Claims (15)

A silver-based alloy wire, which is an alloy wire formed of at least silver, palladium, rhodium and platinum, wherein the weight ratio of silver:palladium in the alloy wire is 90~99.99:0.01~10, and the content of bismuth is below 1500ppm, The content of platinum is below 350 ppm, and the alloy wire comprises a central portion and an outer portion, the central portion having elongated grains or equiaxed grains, the peripheral portion having equiaxed grains, and in the alloy wire The number of crystal grains having an annealed twin structure accounts for more than 20% of the total number of crystal grains of the alloy wire. The silver-based alloy wire according to claim 1, wherein the equiaxed grains have an aspect ratio of 1 to 2. The silver-based alloy wire according to claim 1, wherein the elongated grain has an aspect ratio of more than 2. The silver-based alloy wire according to claim 1, wherein the alloy wire has a grain size of 0.1 to 6 μm. The silver-based alloy wire according to claim 1, wherein the wire diameter of the alloy wire is between 10 and 50 μm. The silver-based alloy wire according to claim 1, wherein the alloy wire further comprises boron. The silver-based alloy wire according to claim 5, wherein the alloy wire has a boron content of 20 ppm or less. A method for manufacturing a silver-based alloy wire, comprising: providing a thick wire material, wherein the thick wire material is an alloy wire formed of at least silver, palladium, rhodium, and platinum, wherein a weight ratio of silver:palladium in the alloy wire is 90 to 99.99: 0.01~10, and the content of bismuth is below 1500ppm, and the content of platinum is below 350ppm; and the plurality of cold working forming steps and the plurality of annealing steps are alternately performed to successively reduce the wire diameter of the thick wire to form a thin wire, wherein The cold forming step and the annealing step include at least the following steps: performing a penultimate cold forming step; thereafter, performing a penultimate annealing step, wherein the penultimate annealing step has an annealing temperature of 0.5 Tm to 0.7 Tm, annealing time is 1~5 seconds, wherein Tm is the melting point of the absolute temperature standard of the material of the thick wire; then, the last cold forming step is performed, so that the wire formed by the last cold forming step and the penultimate The amount of deformation between the wires formed by the cold forming step is 1% or more and not more than 15%; and thereafter, the final annealing step is performed The final annealing step annealing temperature is higher than the annealing temperature of the annealing step of the penultimate channel 20 ℃ ~ 100 ℃, annealing for 2 to 30 seconds. The method for manufacturing a silver-based alloy wire according to claim 8, wherein the thin wire comprises a central portion and a peripheral portion, and the central portion has elongated grains or equiaxed grains, the periphery The portion has equiaxed grains, and the number of crystal grains having an annealed twin structure in the thin wire accounts for more than 20% of the total number of crystal grains of the thin wire. The method for producing a silver-based alloy wire according to the invention of claim 8, wherein the cold forming step comprises drawing, extruding or a combination of the foregoing. The method for producing a silver-based alloy wire according to claim 8, wherein the providing of the thick wire comprises the steps of: heating and melting silver, palladium, rhodium and platinum, and casting into an ingot; The ingot is cold worked to form the thick wire. The method for producing a silver-based alloy wire according to claim 8, wherein the providing of the thick wire comprises the steps of: heating and melting silver, palladium, rhodium and platinum, and forming the thick wire by continuous casting. . The method for producing a silver-based alloy wire according to the eighth aspect of the invention, wherein the wire diameter of the thick wire is 5 to 10 mm, and the wire diameter of the wire is 10 to 50 μm. The method for producing a silver-based alloy wire according to claim 8, wherein the thick wire further comprises boron. The method for producing a silver-based alloy wire according to claim 14, wherein the thick wire has a boron content of 20 ppm or less.